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ППРЧ/FHSS -псевдослучайная перестройка рабочей частоты
milstar: The Milstar satellite provides enhanced communication security by frequency hopping -- *************************************************************************** a first for communication satellites. ***************************** http://www.spaceflightnow.com/titan/b35/030401milstar.html Programma Milstar -verojatno samaja dorogaja programma sputnikowoj swjazi Tolko w 1981 -1991 bolee 5mlrd $ , w segodnjaschnix cenax po otn VVP eto okolo 15 mlrd $ http://archive.gao.gov/d32t10/146911.pdf The first Milstar satellite was launched Feb. 7, 1994 aboard a Titan IV expendable launch vehicle. The second was launched Nov. 5, 1995. The third launch on April 30, 1999, placed the satellite in a non-usable orbit. The fourth through six satellites have a greatly increased capacity because of an additional medium data rate payload and were launched on Feb. 27, 2001, Jan. 15, 2002, and April 8, 2003 The Milstar system is composed of three segments: space (the satellites), terminal (the users) and mission control. Air Force Space Command's Space and Missile Systems Center at Los Angeles Air Force Base, Calif., developed the Milstar space and mission control segments. The Electronics Systems Center at Hanscom AFB, Mass., developed the Air Force portion of the terminal segment. The 4th Space Operations Squadron at Schriever AFB, Colo., is the front-line organization providing real-time satellite platform control and communications payload management. Inventory: 5 Unit Cost: $800 million http://www.af.mil/information/factsheets/factsheet.asp?fsID=118 Milstar/AEHF -zapuschen 14 awgusta 2010 goda http://www.youtube.com/watch?v=lWvr4mfP6A0 http://www.as.northropgrumman.com/products/aehf/assets/AEHF_datasheet_2010_.pdf uplink 44 ghz s polosoj signala 2000 mgz downlink 20 ghz s polosoj signala 1000 mgz Frequency Hopping Systems ( ispolzuetsja w Milstar) ********************************************* Frequency Hoppers (FH) are a more sophisticated and arguably better family of spread spectrum techniques than the simpler DS systems. However, performance comes with a price tag here, and FH systems are significantly more complex than DS systems. The central idea behind a FH system is to retune the transmitter RF carrier frequency to a pseudorandomly determined frequency value. In this fashion the carrier keeps popping up a different frequencies, in a pseudorandom pattern. The carrier itself amy be modulated directly with the data using one of many possible schemes. The available radio spectrum is thus split up into a discrete number of frequency channels, which are occupied by the RF carrier pseudorandomly in time. Unless you know the PN code used, you have no idea where the carrier wave is likely to pop up next, therefore eavesdropping will be quite difficult. Frequency hoppers are typically divided into fast and slow hoppers. A slow frequency hopper will change carrier frequency pseudorandomly at a frequency which is much slower than the data bit rate on the carrier. A fast frequency hopper will do so at a frequency which is faster than that of the data message. http://www.ausairpower.net/OSR-0597.html
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milstar: W Rossii odno iz izwestenjschix razrabotchikow i polzowatelej sistem s FSS -FGUP Impuls ****************************************************************************** ABSU Perimetr - start raket RWSN pri attake protiwnikom i otsutstwii signala na pusk ot Glawkoma,MO,nach.genstaba http://npoimpuls.ru/ http://npoimpuls.ru/index.php?option=atl2&atl=4 ФГУП «НПО «Импульс» является одной из основных организаций Российской Федерации по созданию новейших автоматизированных систем боевого управления (АСБУ) для ВС РФ и РВСН. Основными заказчиками объединения являются Министерство обороны РФ и предприятия «Федерального космического агентства». Общая численность основного персонала объединения на 1 августа 2009 года составляет 1712 человек. (dlja srawnenija Institut Mintza -razrabotchik Don-2N tolko 880 chel ) МОСКВА, 4 августа. (Корр.АРМС-ТАСС). Санкт-Петербургское НПО "Импульс" завершает поставки инозаказчику не имеющей мировых аналогов адаптивной цифровой системы КВ-радиосвязи с псевдослучайной перестройкой рабочей частоты (система КВ с ППРЧ), которая демонстрируется на выставке МВСВ 2006. Как сообщил начальник отдела конверсии и маркетинга предприятия Александр Запретилин, уникальная система разработана в интересах инозаказчика в одной из азиатских стран. Контрактом предусматривается выполнение НИР и поставка макетов аппаратуры. К настоящему времени выполнены все лабораторные испытания системы и близки к завершению трассовые испытания Система КВ с ППРЧ, по словам А.Запретилина, не была востребована на внутреннем рынке по причине сомнения в возможности обеспечения заявленных уникальных характеристик. Однако завершаемый зарубежный контракт вызвал интерес к КВ с ППРЧ со стороны российских организаций, которые начали переговоры с НПО "Импульс" о дальнейшем развитии системы под новые требования. По словам А.Запретилина, адаптивная цифровая система КВ-радиосвязи с псевдослучайной перестройкой рабочей частоты имеет ряд преимуществ перед традиционными системами связи. Адаптивность, в частности, обеспечивает устойчивую работу коротковолновой связи, остро реагирующей на различные природные явления. Система непрерывно ведет поиск частот, на которых обеспечивается идеальная связь со всеми объектами и адаптирует под эту частоту их работу. Псевдослучайная перестройка рабочей частоты, в свою очередь, предотвращает возможность пеленга или подавления связи между объектами. С этой целью алгоритмом системы предусматривается беспрерывный перевод работы объектов с одной найденной идеальной частоты на другую. В зависимости от трех (по желанию заказчика) разных режимов работы время пребывания системы на одной частоте составляет 50, 100 или 200 мс. При этом обеспечивается скорость передачи информации до 19,2 кбит/с. Как пояснил А.Запретилин, в случае, если система все же попала в невыгодные помеховые условия, что является маловероятным при том алгоритме работы, который обеспечивает НПО "Импульс", она способна перейти с максимальной на более низкие скорости передачи информации, т.е. является адаптивной не только по частоте, но и по скорости. В этом состоит уникальность системы КВ с ППРЧ. По словам А.Запретилина, поставки адаптивной системы - первый и пока единственный зарубежный контракт НПО "Импульс". Очевидно, что для предприятия, занятого в сфере создания средств управления военными объектами страны, в том числе РВСН, существуют определенные ограничения на ведение бизнеса с инозаказчиками. Его деятельность более чем на 90 проц. определяется гособоронзаказом. Помимо РВСН, АСУ "Импульса" эксплуатируются в других родах и видах войск. Тем не менее, петербуржские специалисты непрерывно диверсифицируют свою продукцию и активизируют работу по ее продвижению на внутренний и мировой рынки. На выставке "МВСВ-2006" "Импульс" представил также цифровую аппаратуру обмена закрытой речевой информацией по открытым телефонным каналам связи, устройство для ввода и транспортировки информации и информационную бесконтактную карту для жестких условий эксплуатации. ФГУП "НПО "Импульс" создано на базе Проблемной лаборатории Ленинградского политехнического института. В 1961-1987 гг. оно функционировало как ОКБ ЛПИ, а затем было преобразовано в научно-производственное объединение "Импульс". В конце 60-х годов тогда еще ОКБ ЛПИ выиграло конкурс на создание автоматизированной системы управления РВСН. С тех пор самая надежная в мире АСУ безупречно работает более 30 лет. На смену первому поколению уже приняты на вооружение системы второго, третьего и четвертого поколения. Не имеющие аналогов в мире системы разработки "Импульса" обеспечивают беспрерывное сверхнадежное гарантированное управление, а созданная им аппаратура работает безупречно. По словам А.Запретилина, надежность систем и аппаратуры, созданных предприятием, на порядок выше, чем у конкурентов. Все параметры надежности нарабатываются "Импульсом" до запредельно высоких показателей. В частности, вероятность ошибки одного из уникальных приборов, составила 10 в минус 18-й степени, тогда как приемлемым является показатель минус 8. Такими же сверхнадежными являются и созданные предприятием каналы передачи управляющих команд. Для оружия, рассредоточенного по многим регионам страны, эта проблема особенно актуальна.
milstar: Processing Gain ############ The second major antijamming strategy involves processing gain improvement. The GPS spread-spectrum signal derives some inherent jam protection from the "despreading" process, which converts it from a 20-megahertz bandwidth to a narrower bandwidth. Signal power grows stronger as bandwidth is reduced, so for maximum antijam performance, the narrowest possible bandwidth should be used in the despreading process. ##################################### Just how narrow the bandwidth can be depends in part on the design of the code and carrier tracking loops used by the GPS receiver and the dynamic operating environment. Recall that a GPS receiver gets a signal from a satellite, generates a local copy, and compares the two to derive range and range-rate measurements. The tracking loops try to maintain a "lock" on the satellite signal by driving the difference in the signals (as measured by the signal correlator) to zero. In general, greater antijam performance can be achieved by narrowing the bandwidth of these code and carrier tracking loops. Unfortunately, narrow tracking-loop bandwidths imply sluggish response time, and if a vehicle is undergoing high ######################################################################### acceleration, the narrow-bandwidth tracking loop cannot keep pace. ############################################# If the tracking-loop bandwidth were widened, it would be more responsive to high acceleration, but it would not filter the noise as effectively. In a power-inversion array antenna, the individual elements are geometrically arranged with an interelement spacing of one-half a GPS carrier wavelength. This arrangement is useful for applications where the desired signal is weak and the interference is strong. One solution is to aid the tracking loops by supplying information about the vehicle's acceleration and the motion of the satellite to be tracked. This information could be supplied, for example, by an inertial navigation system and the GPS satellite almanac. With this supplemental information, the receiver's tracking loops can anticipate the dynamics along the line-of-sight to the satellite and use a narrow- bandwidth filter to process the fresh outputs from the signal ############################################################################# correlators. If the aiding information is reasonably accurate, the bandwidth of the tracking loop can be narrowed because it will ########################################################################## only need to track the errors in the aiding information (which vary slowly over time), rather than the absolute motion ########################################################################### of the antenna. ########## The aided tracking loop, with its narrower bandwidth, provides more processing gain and more protection against ######################################################################## jamming; however, it's still not enough to thwart a very strong jammer that may be close to the GPS navigation set. The limitations of aided tracking loops are more practical than theoretical: In actual implementation, the aiding information will contain numerous errors. The most notable errors arise from two sources: imperfect implementation of the aiding data interface, and the inconsistency of the motion between the aiding sensor and the GPS antenna or "lever arm." (In most vehicles, the antenna and the aiding sensors are in different locations, and "lever-arm" compensation must be provided because the GPS antenna is not sensing the same motion as the aiding sensors.) The first error source, the data interface, exists because traditional receivers are designed to use whatever inertial measurement unit is present on the host vehicle. (An inertial measurement unit—or IMU—is a set of gyros and accelerometers that feed the inertial navigation system in an aircraft or missile.) The GPS receiver and the host vehicle communicate over an asynchronous serial bus, and the designer of the GPS receiver usually does not accept the IMU data without "deweighting" it in some manner. This deweighting process can limit the achieved bandwidth reduction below theoretical levels and hence limit the antijam performance. The second error source, lever-arm compensation, is unavoidable if the GPS antenna is not located with the IMU. Unfortunately, many factors—such as vehicle attitude, vehicle rotation, and body flexure—prevent perfect lever-arm compensation, even when the IMU is situated in the same box as the receiver. Hence, the bandwidth of the tracking loops must be wide enough to maintain GPS signal lock despite these factors—and this limits the antijam performance. In some applications, such as small weapons, the antenna is naturally close to the IMU and the body is rigid, so the lever-arm compensation is not as significant an error source as it is in avionics applications. http://www.aero.org/publications/crosslink/summer2002/06.html New Approaches To meet the future challenge of GPS applications that must operate in projected jamming environments, the GPS Joint Program Office is pursuing several promising technologies and a future GPS set architecture that will yield further improvements in antijam performance. Aerospace is actively involved in defining advanced architectures and technologies that will economically provide better antijam performance. Two approaches in particular are generating considerable interest in the field. Microelectromechanics With the recent advances in microelectromechanical systems, new architecture concepts that were unimaginable five years ago have now come within reach. One such technology, the microelectromechanical IMU, will have a significant impact on the future design of user navigation sets. As noted, the best way to reduce the bandwidth of the tracking loops (and thus improve antijam performance) is to keep the GPS antenna and the IMU together, thereby forcing the lever arm to zero. This placement eliminates the need for the lever-arm correction and its associated errors. Of course, when IMUs were first invented, they were very large, and although they've become smaller over the years, they remain large enough to require special attention concerning their placement in a host vehicle or missile. The ability to place an IMU in the same box with the GPS receiver was viewed as a significant step forward. But until recently, no one considered the possibility of embedding the IMU in the antenna itself. A jam-resistant GPS antenna undergoes testing at the Air Force Research Laboratory. That is precisely the thinking now being pursued under the leadership of Aerospace. The cost, size, and performance of microelectromechanical IMUs are improving to the point where they'll soon be good enough to embed in a GPS antenna. This new architecture overcomes many of the factors that prevented the narrowing of tracking-loop bandwidths in older systems. For example, because the IMU would be dedicated to the GPS set, a synchronous interface between the two could be designed with proper attention to interface errors and data latency. In addition, the placement of the IMU with the GPS antenna would make both sensors experience the same motion, so there would be no need for lever-arm compensation with its associated errors. Although the accuracy of microelectromechanical IMUs cannot compete with more traditional technologies (such as those that use ring-laser gyros), accuracy is reaching a level that is adequate for aiding GPS. Extremely high accuracy is not required if the IMU error sources are reasonably stable because the navigation processing algorithm constantly estimates these low-bandwidth error sources and compensates accordingly. In other words, it's the short-term stability of these instrument error sources that's important for aiding GPS. And although short-term stability errors can be sensitive to temperature and acceleration, compensation models whose coefficients are calibrated prior to operation can usually mitigate their effects. So, for short periods of time, errors in the microelectromechanical IMU approach acceptable levels for aiding GPS. It should be noted that the microelectromechanical IMU is not meant to replace the IMU that may be present in the host vehicle. If there is a need for inertial navigation accuracy without GPS, then the microelectromechanical IMU would probably not satisfy that requirement. The microelectromechanical IMU is intended as part of the GPS navigation set (notice that the word "receiver" has not been used), and is present in the GPS antenna regardless of whether there is a need for an IMU by the host vehicle. Ultratight GPS/Inertial Coupling Another technology has recently emerged to address the need for antijam performance. This new technique, called ultratight GPS/inertial coupling, is a different method to jointly process GPS and IMU data (see sidebar, GPS/Inertial Coupling). Several organizations throughout the United States have been performing research in this area, either through independent research and development funds or DOD research contracts. Although each approach is unique in its implementation, they all share certain common traits. For example, they all eliminate the code and carrier tracking operations, which are susceptible to jamming even when aided. All use estimated navigation parameters to generate the local replica signal needed to track the satellite signal. All directly use the correlator outputs (i.e., comparisons of the local and satellite signals) to compute the range and range-rate errors for the navigation processing algorithm. This graph shows the effects of jamming on unprotected GPS performance. For example, at a jammer-to-signal ratio of about 55 decibels, a jammer located about 100 nautical miles from the receiver could jam the GPS signal through a 1-kilowatt signal. At 1000 nautical miles, 100 kilowatts would be required. (View larger image.) Aerospace is an industry leader in ultratight coupling. Four years ago, Aerospace began to develop its formulation of ultratight coupling and filed for a U.S. patent. About the same time, Aerospace became aware of similar research being conducted at other companies and other patents that were pending. When the antijam potential of this processing approach was determined, Aerospace was instrumental in obtaining interest at the various DOD research laboratories to fund development programs. Today, virtually all GPS vendors to DOD have contracts to pursue some sort of ultratight coupling. A milestone was reached in November 2001 when the first official government-sponsored test of an ultratight coupling formulation was conducted at Eglin Air Force Base. The antijam performance was slightly better than predicted. The test results essentially confirmed the performance that had been predicted at Aerospace using simulations. Currently, the Aerospace formulation is being implemented in a real-time computer. One GPS vendor has asked to license the Aerospace formulation, and many other companies are using it for studies. Summary Future GPS systems—particularly for weapon delivery—will benefit from the optimal integration of GPS receivers with inertial measurement units and the use of adaptive processing algorithms and antennas that reject unwanted signal interference while maximizing the power of the desired satellite signal. The combination of all these technologies and the associated system architecture will be the blueprint for DOD GPS sets for the next several decades. Many of the GPS antijam techniques and architectures that will be used in future equipment have roots at Aerospace, which has been the technical conscience of the program since its inception.
milstar: Processing Gain Processing gain is realized at the output of bandpass filter of the sliding carrier based correlator when code alignment is achieved. Here‟s why; When the receiver replica C/A code is not aligned with the transmitted C/A code the received GPS signal power at the output of the bandpass filter is spread over approximately 2mhz of bandwidth ( center lobe of C/A BPSK spectrum is approx 2 Mhz) . When the receiver C/A code is aligned with transmitted code the signal power at the bandpass output is now squished into approximately 100hz of bandwidth ( Center lobe of 50hz random data spectrum). A rule of thumb is to use the ratio of these two bandwidths as the processing gain. Processing gain is remarkable, it is as if the signal is amplified without also amplifying the noise at the same time! Processing Gain = Bandwidth of Uncorrelated Signal / Bandwidth Correlated Signal For a GPS receiver this works out to (in db) Processing Gain GPS Rec.(db ) = 10 log [ 2Mhz / 100Hz] +43dB This number is an estimate of processing gain. A more accurate estimate is the ratio of the SNR before and after correlation. In addition various imperfections in the correlator may also degrade this gain. Regardless the processing gain is large in a GPS receiver and enables the negative SNR environment before correlation to be turned into a positive SNR condition after correlation assuming typical bandwidths before and after. 14 Recovery of signal with Negative SNR The spreading of GPS signal power by the C/A code can lead to the condition where the signal is below the noise floor in one part of the receiver and above it in other sections after processing. When the signal is below the noise floor at a given point in the receiver it has a negative SNR. For a user at the earth‟s surface the received power from the GPS signal is very low. The specified minimum power at the earth‟s surface is approximately – 130dBm. This power is the unmodulated carrier power in one hertz of bandwidth. When the signal is modulated with the C/A code and 50HZ data this power is spread over a larger bandwidth. Once the signal power is spread over 2Mhz the crest of C/A code spectrum is well below the – 130dBm unmodulated carrier power. Ignoring the 50Hz data modulation (data mod off) the carrier power is spread over approximately 2mhz of bandwidth as 1khz equal spaced tones. The power level of these tones in the main lobe is fairly flat at about – 30dB down from the pure carrier level. This puts these lines at approximately – 160dbm. A typical post correlation bandwidth for a analog GPS receiver is 1khz. For a perfect receiver this would put the noise floor at approx. – 143dBm. If we do not have correlation (C/A codes not aligned) the 1khz tones will be well below the noise floor at this point in the receiver resulting in a negative SNR condition. Once we have correlation the signal power is restored to nearly the unmodulated power level and for 1khz bandwidth we would see a SNR of about +13db. So just because a negative SNR condition is present does not mean the GPS signal is “gone”. It is just hiding under the receiver noise floor waiting for the power of the correlation operation to “resurrect” the signal. The exact SNR after correlation will depend on where in the receiver one is talking about and the effective noise bandwidth at that point. In the data demodulator where the data is stripped off the carrier the noise bandwidth can be quite narrow and higher SNR‟s are achieved, typically 20db to 30db. The phenomenon of retrieving a negative SNR signal is hard to swallow. It is the authors feeling that this difficulty can be overcome by understanding what noise is and how it interacts with discrete signals. Noise from a spectral point of view is a density. It is not discrete. Therefore you cannot talk about noise levels or powers quantitatively without specifying the bandwidth that is related to the noise being measured (ie the circuit bandwidth). Noise power goes up as bandwidth widens. A discrete signal is completely different. Discrete signals, such as pure sine waves, have a power (or level) that is independent of the bandwidth of the circuit. Theoretically if one measures the power of a pure sinewave through a bandpass filter whose center frequency equals the sinewave frequency the power measured is independent of filter bandwidth. As we just stated this NOT the case with noise. As stated above the power spectrum of the GPS C/A spectrum is made up of discrete spectral lines spaced at the code repeat rate of 1khz for the case where we have only C/A code modulation (Data =1 or 0 forever). These lines trace out the [sin(x)/x] 2 spectrum. Therefore the spectrum of the C/A modulated signal is not a density but really a collection of discrete signal lines. What would happen if looked at the received signal (before correlation) with an ideal spectrum analyzer that could use extremely narrow bandwidths? Figure A11 shows an ideal spectrum analyzer display of the GPS carrier @1575.42mhz both unmodulated and with C/A code modulation on it (No 50Hz Data Mod). The power levels shown reflect those at the earth‟s surface using a 0db -gain antenna. The unmodulated carrier is shown shaded. Note that once C/A code modulates the carrier, the carrier is suppressed and there would be no signal at that position (in an ideal modulator). Our ideal analyzer does not contribute to the received noise power and has some very narrow Resolution Bandwidths (RBW‟S). For each RBW the theoretical noise floor of the instrument is shown. Note that at a 1khz RBW the C/A tones are well below the noise floor of the instrument. As the RBW is narrowed the noise floor drops by 10Log RBW but the discrete C/A modulation tones remain constant in power/amplitude. At a RBW of 0.1hz we would be able to see the spectral lines of the C/A modulated carrier above the noise floor. So in theory it is possible to see the GPS signal before correlation. It is hoped that this example makes it clear the signal is still there with negative SNR conditions. It is all related to the circuit bandwidth and its effect on noise power. The processing gain of correlation makes it possible to recover the signal and its data by compressing the received signal power into a smaller bandwidth (allowing a reduction in the circuit bandwidth) thereby creating a positive SNR condition.
milstar: processing gain sootw. ( smotri nize adaptivnoe izm .polosi do 10 gerz i nize pri tracking) ywelichiwaetsja To reduce the effects of wideband noise contaminating receiver functions, process base bandwidths should be minimized in receiver designs or be allowed to adaptively reduce in response to detected jamming. Such adaptive bandwidth filtering in the predetection bandwidth and carrier/code tracking loops will minimize the jamming power that is able to influence these receiver processes. The minimum predetection bandwidth is 50 Hz to accommodate the satellite ################################################ ephemeris data carried on the GPS signal. ########################### The tracking loops can be reduced in bandwidth to 10 Hz or less to maintain carrier/code lock ############################################# and maximize the accuracy of satellite range measurements via optimum SIR in the presence of wideband jamming. ############################# Adaptive bandwidth filtering is effective particularly for the signal tracking loops where it can provide on the order of 10 dB of jamming resistance. The down side of narrow tracking loop bandwidths, however, is that they do not accommodate platform dynamics very well, and most PGMs are fairly dynamic platforms. ######################### Accordingly, the narrow bandwidths of AJ GPS receivers require inertial measurement units (IMUs) to rate aid the tracking loops. In this process, velocity measurements from the IMU are provided to the tracking loops, enabling them to follow rapidly time varying Doppler shifts (that are the result of platform dynamics) with their narrow tracking filters. ################################ Without velocity aiding from the IMU, these Doppler effects would shift the GPS signal out of the narrow pass band of the tracking loops, resulting in loss of carrier/ code lock. http://wstiac.alionscience.com/pdf/Vol3Num3.pdf
milstar: Performance Study of Hybrid Spread Spectrum Techniques https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes 19 1.7.1 Types of SS Communication Systems Three important types of spread spectrum techniques are direct sequence spread spectrum (DSSS), frequency hopping spread spectrum (FHSS) and time hopping spread spectrum (THSS). In direct sequence spread spectrum, baseband data is spread by directly multiplying the data pulses with a pseudo noise (PN) sequence that is produced by a pseudo noise code generator. In case of spread spectrum (SS) systems, the pseudo noise sequence is known to the transmitter and intended receiver but appears random, with noise like properties, to other receivers in the system. In frequency hopping spread spectrum, the frequency of the carrier is periodically modified (hopped) following a specific sequence of frequencies obtained using a PN sequence generator. Frequency hopping may be slow frequency hopping (SFH) or fast frequency hopping (FFH).
milstar: Figure 2.11 : Concept of Hybrid Slow and Fast Hopping: (a) BPSK data signal (b) Hybrid DS/SFH with 2 bits/hop and one code sequence per symbol (c) Hybrid DS/SFH with 2 bits/hop and two code sequences per symbol (d) Hybrid DS/FFH with 2 hops/bit and one code sequence per symbol (e) Hybrid DS/FFH with 2 hops/bit and two code sequences per symbol rejection. The DS component of a hybrid signal provides LPI characteristics and helps to suppress the interference, and at the same time the signal is hopping from one frequency to another and the FH part is at work to avoid interference. In a hybrid DS/FH system, a saboteur must know both the hopping sequence and the code used by the signal to accurately jam it. Hence, the probability of a saboteur to block or degrade the desired signal is reduced. The spreading factor for a hybrid DS/FH system is a function of the number of chips per bit, and the hopping frequencies used in the system. In the present thesis, the spreading factor for hybrid systems will be defined by the term “total spreading factor” (TSF) which is equal to the product of the DS spreading factor (SF) and , the number of hopping frequencies used. For example, a TSF of 64 might imply that eight hopping frequencies and a code sequence with SF 8 have been used to generate the hybrid signal. Another combination that will provide a TSF of 64 can be of 4 hopping frequencies and a code with SF equal to 16 and so on. Several of these combinations will be analyzed in this work for both hybrid slow and fast hopping system https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes
milstar: Many papers were published on spread spectrum systems in the early 1980’s by Pursley and Geraniotis ([32]-[35]). An important work on coherent hybrid systems was published by M. K. Simon and Andreas Polydoros [37]. Their work investigated the performance of coherent FH and hybrid DS/FH systems with QPSK and QASK modulations. They derived expressions for error probability under partial band noise jamming and partial band multitone jamming. An important consequence of using hybrid spread spectrum was the conversion of a FH multitone jammer to an equivalent AWGN jammer (under certain assumptions); due to spectrum spreading associated with the DS modulation part of hybrid DS/FH systems. In other words, the effect of a spread multitone jammer on bit error probability was found to be equivalent to the effect of AWGN interference. The performance of coherent hybrid DS/FH was further examined by Geraniotis in 1985 [34]. Analysis of synchronous and asynchronous hybrid direct sequence/slow-frequency hopped spread spectrum was carried out over an additive white Gaussian noise channel for both deterministic and random signature sequences. Hopping rates much slower than the data rate (i.e. slow frequency hopping) were used in order to implement coherent demodulation with contemporary receivers. Two types of modulation schemes viz. BPSK and QPSK were considered. Expressions for average probability of error were evaluated for both asynchronous and synchronous DS/SFH systems and for quaternary and binary modulation schemes. Two different techniques were developed for the evaluation of the error probability. The first technique, based on the characteristic function method evaluated error probability by integrating the characteristic function of multiple access interference. Another method was based on evaluating the conditional error probability for a given number of hits from other users and then averaging these over the distribution of hits. A summary of pertinent numerical results from [34] is provided below: Nature of code sequences: For binary hybrid systems, synchronous systems with deterministic code sequences performed considerably better than synchronous systems with random signature sequences. This may be attributed to the lower cross correlation functions of well chosen deterministic sequences. However, as the number of active users increases with length of the sequence (which cannot be increased indefinitely due to code acquisition and synchronization requirements) remaining constant, it is difficult to find distinct code sequences with very good cross correlation properties for all users. Thus for hybrid SSMA systems employing random code sequences, asynchronous systems performed better than the corresponding synchronous systems. This improved performance of asynchronous systems is due to the extra averaging with respect to the time delays which takes place in the asynchronous systems. For deterministic code sequences, the synchronous systems outperform the corresponding asynchronous systems Chip waveform: sinusoidal or rectangular Performance of asynchronous binary and quaternary systems was analyzed for rectangular and sine chip waveforms using random code sequences. Results in [34] indicated that hybrid systems with sine chip waveform perform slightly better than rectangular chip waveform for both the binary and quaternary modulation schemes. Overall, results from [34] suggest that hybrid DS/SFH systems compare favorably to the DS and SFH systems which employ identical modulation and demodulation schemes and have the same bandwidth spread. Synchronous hybrid SS systems supported fewer users than asynchronous hybrid SS systems when random code sequences and hopping patterns were used. Also, hybrid systems with QPSK supported fewer users than the corresponding systems employing BPSK modulation. This accounted for the fact that QPSK can support two different data streams (in phase and quadrature) for each user i.e. it has twice the data rate of a BPSK system with the same bandwidth expansion. Since both in phase and quadrature data signals in QPSK employ the same frequency carrier and hopping pattern, whenever a hit occurs due to another user’s signal, both of these interfere with that signal or vice versa. So, all hits from other signals are double hits. Contrary to this, in BPSK system, all the data signals employ different hopping patterns and only single hits occur from the other signals. Another work by E. A. Geraniotis [28], published in 1986, evaluated performance of non-coherent hybrid DS/SFH spread spectrum systems. Both asynchronous and synchronous systems operating through AWGN channels were investigated. Modulation types studied were M-ary FSK and DPSK (Differential Phase Shift Keying). This work extended that of [34], and the main conclusion drawn was that the multiple access capability of non-coherent hybrid spread spectrum was superior to that of non-coherent pure frequency hopped spread spectrum, and inferior to that of non-coherent pure DSSS with the same bandwidth expansion.
milstar: to analyze the performance of a pure phase coherent slow frequency hopped (SFH) receiver with 1 bit/hop in the presence of AWGN and partial band interference and compared the BER performance with non-coherent FSK systems. When the phase distortion in the channels was not excessive, improved performance compared to a coherent system was observed. The importance of fast frequency hopping (FFH) in mitigating follower jamming was emphasized due to its inherent frequency diversity. Moreover, the frequency hops occurring during each symbol could be combined to achieve a reliable decision state. Considering the scenario when a smart receiver is able to track the hopped frequencies, a hybrid system was proposed in which each hopped frequency is spread with a PN sequence. FFH was found to combat both frequency selective fading (because of frequency diversity) and non-selective fading (when hopped frequencies are combined properly). Under severe fading conditions, follower jamming was found to be less effective against a hybrid spread spectrum system. https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes
milstar: In general, coherent systems (with slow frequency hopping) provided better performance against PBN, Ricean fading, multiple access interference and AWGN. Under severe Rayleigh fading, coherent reception became difficult. Muammar [40] studied the effects of frequency selective Rayleigh fading and log normal shadowing on a DS/FH system with differential phase shift keying (DPSK) modulation. Error probabilities were examined for a Rayleigh fading channel with and without the effects of log normal shadowing. System degradation with log normal shadowing was much smaller than that caused by Rayleigh fading. Byun et al. [42] analyzed a hybrid DS/SFH system subject to a Nakagami fading channel. The bit error probability over a Nakagami fading channel was calculated as a function of the number of jamming tones used by the jammer. Various combinations of number of hopping frequencies and spreading code sequences that satisfied an equal bandwidth constraint were employed. For a low jamming to signal power ratio (JSR) of about 10dB, a pure DSSS system was found to achieve a lower BER than a hybrid DS/SFH system. However, for higher JSR values (20 or 30dB), the hybrid DS/SFH system exhibited superior performance. Also, the worst case performance of a hybrid DS/SFH system was found to be almost equal to the nominal performance of a pure DSSS system. https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes
milstar: . The proposed transceiver is a slow frequency hopping (SFH) system, meaning the hop rate is slower than the symbol rate. It should be noted, though, that our system still requires a high hop rate. There are many fundamental differences in the transceiver design and implementation between a very low hop rate SFH-TDMA system, which hops to a new frequency every frame (i.e., hop rate 50 Hz), and the proposed SFH-CDMA transceiver. It hops every eight symbols, which results in a hop rate of 20 kHz at a symbol rate of 80 kHz. https://pdfs.semanticscholar.org/c2f9/e8284cbaa43eff5ee97c9fe1d89d38e636bb.pdf
milstar: The effect of the hopping rate was also observed for asynchronous systems. Asynchronous systems with a large number of bits/hop outperformed systems with dwell time equal to symbol period https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes Thus jammed and unjammed frequency lots in a hybrid DS/SFH system differ in their spreading gain requirements and a tradeoff must be devised in order to effectively synchronize both of these. https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes
milstar: Figure 5.2 : Performance of a Single User System in an AWGN and Rayleigh Fading Environment for Selected SFs. page 79 The BER performance curves for a varying number of users in a Rayleigh fading environment are presented in Figure 5.3 for SF=64. It is clear that the performance degrades gradually as the number of users is increased from 10 to 30. Even in the presence of 30 users, the system is able to provide an acceptable voice BER of 3 10− at a Eb No / value of just 10 dB. Thus the system can accommodate many users even without error correction coding. It can be inferred from Figures 5.2 and 5.3 that a lower spreading factor than 64 will provide a BER greater than 3 10− at 10 dB, while a higher SF than 64 will reduce the BER and thus many more users than 30 will be accommodated at 10 dB for a BER of 10−3 . https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes
milstar: 5.2 Slow Frequency Hopping: Performance Results For slow frequency hopping systems, 3 sets of simulations were carried out. First, the SFH system was simulated in a Rayleigh fading environment for a single user using 64 hopping frequencies. Following the equal bandwidth constraint, this is equivalent to a SF of 64 in DSSS system. BER performance of a SFH system with 64 hopping frequencies is compared with DSSS system of SF=64 in Figure 5.5. It is evident that the performance of the DSSS system under Rayleigh fading is far better than the SFH system for the same processing gain in a single user system. A second set of SFH system performance results are based on multi-user interference analysis. All the users use two frequencies from a total of 64 frequencies used by the desired user. The SFH system was simulated for a hopping rate equal to 8 bits/hop and 64 hopping frequencies with a varying number of users. Performance results are shown in Figure 5.6 https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes
milstar: Performance of the FFH system for different numbers of users in a Rayleigh fading environment is plotted in Figure 5.11. A hopping rate of 8 hops/bit and 64 hopping frequencies were used. As with Rayleigh fading performance, FFH multiuser performance is better than SFH but inferior to DSSS performance. A second difference between SFH and FFH performance curves is that FFH performance Figure 5.10 : Comparison of SFH, FFH and DSSS Systems under Rayleigh Fading https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.de/&httpsredir=1&article=3781&context=utk_gradthes
milstar: The benefits of frequency hopping spread spectrum (FHSS) are potentially neutralized by a repeater jammer (also known as a follower jammer), which has been investigated for more than ten years. The repeater jamming technique for FHSS has been used in both military communications and commercial communications [1]-[3]. In contrast to this, any power-effective jamming technique used in direct sequence spread spectrum (DSSS) has not been proposed in public literatures. Meanwhile, the current jamming types are ineffective at the current jamming power level when the processing gain is large enough. So it’s necessary to investigate a new power-effective jamming technique for the purpose of both commercial frequency surveillance and military countermeasures. The principal types of jamming on DSSS signals include broadband noise (BBN) jamming, partial-band noise (PBN) jamming, pulsed jamming and tone jamming. The last of these includes both single tone jamming and multiple tones (MT) jamming. The effectiveness of these jamming types is not good, because they are non-correlative jamming types which can not synchronize PN sequences. In order to achieve desired jamming effectiveness, the jammer has to increase power level of jamming signals. Unfortunately the victim receiver will countermine the strong jamming signals with adaptive notch filters, repeat coding and so on [4], [5]. https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4224679&tag=1
milstar: https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=140456 BER 10 -6 SNR 56 db fading SNR 74 db shadowing with jamming worster SNR 11.5 db quasi ideal only Gaussian noise
milstar: IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 23, NO. 5, MAY 2005 1113Wireless Field Trial Results of a High Hopping RateFHSS-FSK TestbedDanijela ˇCabric´, Student Member, IEEE, Ahmed M. Eltawil, Member, IEEE, Hanli Zou, Member, IEEE,Sumit Mohan, and Babak Daneshrad, Member, IEEEAbstract—This paper presents a complete study and charac-terization of a real-time frequency-hopped, frequency shift-keyedtestbed capable of transmitting data at 160 kb/s, with hoppingrates of up to 80 Khops/s operating in the 900 MHz band. Thesystem provides the highest hopping rate reported to date and setsa new trend for FHSS communications with superior low proba-bility of interception/detection and anti-jamming (LPI/LPD/AJ)capabilities. https://www.researchgate.net/publication/3236095_Wireless_field_trial_results_of_a_high_hopping_rate_FHSS-FSK_testbed
milstar: https://epdf.pub/spread-spectrum-communications-handbook.html
milstar: https://pdfs.semanticscholar.org/b6fe/00c0a09c08efcb38f39ab01fc7acf86203c8.pdf ORNL Hybrid SS
milstar: https://www.researchgate.net/publication/261119180_Hybrid_DSFFH_spread-spectrum_A_robust_secure_transmission_technique_for_communication_in_harsh_environments Performance Study of Hybrid DS/FFH Spread-Spectrum Systems in the Presence of Multipath Fading and MultipleAccess Interference Mohammed M. Olama Teja P. Kuruganti Steven F. Smith Computational Sciences & Engineering Division Oak Ridge National Laboratory http://cqr2012.ieee-cqr.org/May15/Technical%20Papers/8-Mohammed_Olama.pdf
milstar: https://www.semtech.com/uploads/documents/an1200.22.pdf
milstar: https://pdfs.semanticscholar.org/5324/a538e19eca9843a27c7966e9d1830a010cb0.pdf
milstar: https://www.rand.org/content/dam/rand/pubs/monograph_reports/2007/MR672.pdf RAND FHSS Interference
milstar: https://b-ok.org/book/3270410/06e3eb Помехозащищенность систем связи с псевдослучайной перестройкой рабочей частоты Макаренко С.И., Иванов М.С., Попов С.А. Монография. – СПб.: Свое издательство, 2013. – 166 с.Данная монография является результатом научной работы авторов по обобщению исследований и опыта применения систем радиосвязи военного и специального назначения с псевдослучайной перестройкой частоты в условиях воздействия средств радиоэлектронной борьбы и подавления. В работе затронуты различные аспекты проблем оценки помехозащищенности систем радиосвязи с псевдослучайной перестройкой частоты, с учетом последних достижений в области средств связи и средств радиоподавления, а так же актуальных исследований в области моделирования радиоэлектронного конфликта. Материал монографии адресован аспирантам и научным работниками ведущим прикладные исследования в области повышения помехозащищенности систем радиосвязи и оценки эффективности воздействия преднамеренных помех в динамике радиоэлектронного конфликта.Оглавление. Использование метода ППРЧ для повышения помехозащищенности систем радиосвязи в условиях радиоэлектронного противоборства.
milstar: Модернизированный Су-30СМ получил элементы системы связи и обмена данными от Су-57 https://tass.ru/armiya-i-opk/6930489 Самая последняя версия технических средств была разработана под Су-57, рассказал начальник научно-технического центра НПП "Полет" Алексей Ратнер МОСКВА, 26 сентября. /ТАСС/. Истребитель Су-30СМ в ходе модернизации получил дополнительные технические средства многоканальной системы связи и передачи данных ОСНОД (объединенная система связи, обмена данными, навигации и опознавания) от истребителя пятого поколения Су-57. Об этом ТАСС рассказал начальник научно-технического центра НПП "Полет" (входит в холдинг "Росэлектроника" госкорпорации "Ростех") Алексей Ратнер. "На Су-57 стоит, конечно же, самая новая модификация технических средств этой системы [ОСНОД]. Они также использованы для Су-30СМ в рамках модернизации самолета", - сказал Ратнер. Он отметил, что сама система уже прожила несколько поколений. Самая последняя версия технических средств была разработана под Су-57. "Модификация на Су-57 разрабатывалась именно под этот самолет", - пояснил собеседник агентства. Система ОСНОД создавалась в интересах оперативно-тактического звена и предназначена для обеспечения управления в реальном масштабе времени различными видами воздушных судов в ходе наземно-водно-воздушных операций. Терминалы ОСНОД могут быть установлены на самолеты, вертолеты, боевые корабли, наземные мобильные и стационарные объекты. Система отличается многофункциональностью, высокой помехозащищенностью и пропускной способностью каналов, гибкой архитектурой. В настоящее время серийно выпускаются терминалы АТМ-2, МТ-2 ОСНОД, которые устанавливаются на летательные аппараты различного класса и наземные пункты управления (узлы связи).
milstar: Target Discrimination Target discrimination is a critical capability for the ASM seeker, especially in the presence of jamming and other EA (Electronic Attack). For this analysis, it is only indicated that the coherent seeker presents more information at, perhaps higher resolution, to the postprocessor for discrimination purposes https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.928.3912&rep=rep1&type=pdf
milstar: to: https://guraran.ru/prezidiym_raran.html copy for information to - .... re:Прыгающий спектр DHSS, FHSS ,Hybrid ... На Су-57 стоит, конечно же, самая новая модификация [ОСНОД] / При более высокой скрытности терминал ОСНОД и значительно более помехоустойчив: на его входе допустимо превышение мощности помехи над мощностью сигнала почти в сто раз (20 дБ).ВОЕННАЯ МЫСЛЬ · No 2 — 2023 На Су-57 стоит, конечно же, самая новая модификация технических средств этой системы [ОСНОД]. Они также использованы для Су-30СМ в рамках модернизации самолета", - сказал Ратнер начальник научно-технического центра НПП "Полет" (входит в холдинг "Росэлектроника" госкорпорации "Ростех") ---------------- При более высокой скрытности терминал ОСНОД и значительно более помехоустойчив: на его входе допустимо превышение мощности помехи над мощностью сигнала почти в сто раз (20 дБ). РЕАЛИЗАЦИЯ КОМПЛЕКСНОГО ОПОЗНАВАНИЯ ЛЕТАТЕЛЬНЫХ АППАРАТОВ ВС РФ В НАЗЕМНЫХ СИСТЕМАХ ПРОТИВОВОЗДУШНОЙ ОБОРОНЫ 67ВОЕННАЯ МЫСЛЬ · No 2 — 2023 https://vm.ric.mil.ru/upload/site178/KTKcn4mdSu.pdf Подполковник запаса С.Б. ЖИРОНКИН, доктор технических наук ----------------------------------------------- (Scanning methods can break the code, however, if the key is short.) Even better, signal levels can be below the noise floor, because the spreading operation reduces the spectral density. See Figure 6. (Total energy is the same, but it is widely spread in frequency.) The message is thus made invisible, an effect that is particularly strong with the direct-sequence spread-spectrum (DSSS) technique. (DSSS is discussed in greater detail below.) Other receivers cannot "see" the transmission; they only register a slight increase in the overall noise level! https://www.analog.com/en/technical-articles/introduction-to-spreadspectrum-communications--maxim-integrated.html Figure 6. Spread-spectrum signal is buried under the noise level. The receiver cannot "see" the transmission without the right spread-spectrum keys. -------------------------------------------------------------- https://people.computing.clemson.edu/~westall/851/fhss_dsss.pdf DSSS is typically chipped using BPSK modulation. Since BPSK modulation has both phase and amplitude information, linear amplification is necessary. That means only Class A or Class AB amplifiers can be used. These are relatively low efficiency amplifiers. A lot of the DC power is turned into thermal energy, which has to dissipate. FHSS typically uses GFSK modulation. This is constant-envelope modulation, so a non-linear, high efficiency Class C amplifier is adequate for its use. These characteristics mean that DSSS is more power hungry and harder to build in a smaller enclosure than FHSS systems. In an indoor radio propagation environment, the measured delay spread statistics have shown that a 100 nSec delay is fairly common. Since this is close to the DSSS chipping rate, there is a potential for inter-chip interference - or in other words, a penalty for performance that may be as much as 10 dB over corresponding Gaussian Channel. Good diversity antennas must be used to overcome some of these problems. FHSS would not see the effects of the 100-nSec delay. For a strong narrow-band jammer environment, FHSS also has a marked advantage if it can avoid the jammed channel by its frequency hopping nature. ¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤¤ If it can not avoid narrow band interference, FHSS systems will still degrade its performance gracefully. On the other hand, DSSS systems will immediately loose a connection with narrow band interference The principal types of jamming on DSSS signals include ------------------------------------------------------------------------------------ broadband noise (BBN) jamming, partial-band noise (PBN) jamming, pulsed jamming and tone jamming. The last of these includes both single tone jamming and multiple tones (MT) jamming. The effectiveness of these jamming types is not good, because they are non-correlative jamming types which can not synchronize PN sequences. In order to achieve desired jamming effectiveness, the jammer has to increase power level of jamming signals. ============================== Frequency Hopping Systems ********************************************* Frequency Hoppers (FH) are a more sophisticated and arguably better family of spread spectrum techniques than the simpler DS systems. However, performance comes with a price tag here, and FH systems are significantly more complex than DS systems. The central idea behind a FH system is to retune the transmitter RF carrier frequency to a pseudorandomly determined frequency value. In this fashion the carrier keeps popping up a different frequencies, in a pseudorandom pattern. The carrier itself amy be modulated directly with the data using one of many possible schemes. The available radio spectrum is thus split up into a discrete number of frequency channels, which are occupied by the RF carrier pseudorandomly in time. Unless you know the PN code used, you have no idea where the carrier wave is likely to pop up next, therefore eavesdropping will be quite difficult. Frequency hoppers are typically divided into fast and slow hoppers. A slow frequency hopper will change carrier frequency pseudorandomly at a frequency which is much slower than the data bit rate on the carrier. A fast frequency hopper will do so at a frequency which is faster than that of the data message. http://www.ausairpower.net/OSR-0597.html Hybrid (FH/DS) Systems =================== If we are really paranoid about being eavesdropped, we can take further steps to make our signal difficult to find. A commonly used example is that of a hybrid spread spectrum system using both FH and DS techniques. Such schemes will typically employ frequency hopping of the carrier wave, while concurrently using a DS modulation technique to modulate the data upon the carrier. In this fashion an essentially DS modulated message is hopped about the spectrum. To successfully intercept such a signal you must first crack the FH code, and then crack the DS code. If you want to be further secure, you encrypt your data stream with a very secure crypto code before you feed it into your DS modulator, and employ cryptographically secure PN codes for the DS and FH operations. Your eavesdropper then has to chew his way through three levels of encoding. Such a scheme is used in the military JTIDS/Link 16 datalink. ---------------- Performance Study of Hybrid DS/FFH Spread-Spectrum Systems in the Presence of Multipath Fading and Multiple- Access Interference Computational Sciences & Engineering Division Oak Ridge National Laboratory https://cqr2012.ieee-cqr.org/May15/Technical%20Papers/8-Mohammed_Olama.pdf https://worldcomp-proceedings.com/proc/p2013/ICW3340.pdf ========================== система спутниковой связи milstar-1 ,milstar-2,AEHF https://www.mitre.org/sites/default/files/pdf/airborne_demo.pdf Receive Frequency 19.2 – 21.2 GHz Transmit Frequency 44.5 – 45.5 GHz FHSS -Frequency Hoping Spread Spectrum ,no DSSS ==================================== AEHF incorporates the existing Milstar low data-rate and medium data-rate signals, providing 75–2400 bit/s and 4.8 kbit/s–1.544 Mbit/s respectively. It also incorporates a new signal, allowing data rates of up to 8.192 Mbit/s =================== 2019 JPL NASA Deep Space https://tda.jpl.nasa.gov/progress_report/42-212/42-212B.pdf VCM is a digital communication methodology that allows for the change of coding and modulation in the course of a communication session in order to adapt the underlying information data rate to dynamic link conditions. In contrast to a conventional communication system that uses a fixed coding and modulation scheme designed to accommodate the worst-case link conditions, VCM can signif- icantly increase overall effective data throughput when the radio is configured adaptively to fully utilize link capacity. rocessing results from one of the tests indicate an overall improvement of ∼ 2 dB in data throughput over standard waveforms. The demonstrated technologies are build- ing blocks of a future cognitive radio system Several classes of channel codes and modulations have been recommended by the Con- sultative Committee for Space Data Systems (CCSDS) for use in space-to-Earth links. The first of these standards [1] includes convolutional codes, Reed-Solomon codes, turbo codes, and low-density parity-check (LDPC) codes to be used with binary phase shift keying (BPSK), quadrature phase shift keying (QPSK) or offset QPSK (OQPSK), and Gaussian minimum shift keying (GMSK) modulations as recommended in [2];
milstar: https://www.eejournal.com/article/fpgas-made-in-china/ FPGAs: Made in China
milstar: https://efir.sfu-kras.ru/downloads/sbornik-spr-2022.pdf
milstar: - - 380 - МОДЕРНИЗАЦИЯ СТАНЦИИ СПУТНИКОВОЙ СВЯЗИ МИЛЛИМЕТРОВОГО ДИАПАЗОНА ВОЛН А.М. Григоренко, Ф.Г. Зограф Институт инженерной физики и радиоэлектроники СФУ 660074, Красноярск, ул. Киренского, 28 E-mail: grigorenkoal906220@gmail.com https://efir.sfu-kras.ru/downloads/sbornik-spr-2022.pdf 380 На территории Российской Федерации серийное производство таких СтСС как коммерческого, так и военного назначения на данный момент отсутствует. С целью организации широкополосной сети спутниковой связи в диапазоне частот Ka/Q (20/44 ГГц) на орбиту выведена группировка космических аппаратов «Благовест» -------------------------------------------------------------------------------- 381 - В настоящее время на «АО НПП «Радиосвязь» разработаны и прошли государственные испытания три абонентских СтСС (перевозимая, автомобильная и носимая) для работы в широкополосной сети спутниковой связи в диапазоне Ka/Q, но они имеют некоторые недостатки. Рассмотрим автомобильную СтСС. В данной СтСС в качестве системы управления используется импортный планшетный ноутбук со специальным программным обеспечением. С его помощью оператор задает долготу КА, символьную скорость приема и передачи информации, тип модуляции, тип синхронизации, частоту приема и передачи для работы с центральной станцией. Данные параметры оператор определяет самостоятельно исходя из частотного плана и зон обслуживания многолучевых антенн космического аппарата, в зависимости от местоположения станции. Структурная схема, иллюстрирующая работу данной СтСС, представлена на рис. 1. Ноутбук имеет избыточную функциональность и большое количество не использующихся при эксплуатации клавиш, которые могут ввести оператора в заблуждение. К тому же он имеет достаточно узкий для РФ диапазон рабочих температур (от минус 20 °С до 50 °С), а в настоящее время ноутбуки подобного класса в РФ не поставляются.
milstar: to : https://krtz.su/node/158 Е-mail: info@krtz.su АО «НПП «Радиосвязь» Галеев Ринат Гайсеевич copy to https://guraran.ru/prezidiym_raran.html copy to GUS_1@mil.ru copy for information to ... Р-444-НМ показано на Международном военно-техническом форуме «Армия-2020». https://3dnews.ru/1019386/sdelano-v-rossii-predstavlena-samaya-kompaktnaya-stantsiya-sputnikovoy-svyazi Satcom on the move video https://gdmissionsystems.com/communications/satcom-on-the-move-antennas re: терминалы для систем спутниковой связи связи Благовест 20/44 gigagerz, конструкция ,система управления ,программное обеспечение ,обучение https://efir.sfu-kras.ru/downloads/sbornik-spr-2022.pdf страница 380-381 - 380 - МОДЕРНИЗАЦИЯ СТАНЦИИ СПУТНИКОВОЙ СВЯЗИ МИЛЛИМЕТРОВОГО ДИАПАЗОНА ВОЛН copy ...Ноутбук имеет избыточную функциональность и большое количество не использующихся при эксплуатации клавиш, которые могут ввести оператора в заблуждение ? ------------------------------- 1. Astra Linux используется национальным центром обороны ========================================== https://astralinux.ru/ у них есть версия с работоспособная с флешки аналогичная Kali Linux life https://www.kali.org/get-kali/#kali-live ллюстративный пример ! AstraLinux допишут необходимое для связи со спутником и БПЛА ==================== 2. nmcli dev wifi con my wifi nmcli dev wifi con Благовест1 nmcli dev wifi con БПЛА1 :~# wpa_cli scan_result Selected interface 'wlan0' bssid / frequency / signal level / flags / ssid ec:bd:1d:81:dc:6c 5260 -56 [WPA2-EAP-CCMP][ESS] sat1 example ec:bd:1d:81:dc:63 2462 -56 [WPA2-EAP-CCMP][ESS] sat1 example a8:9d:21:74:49:ed 5320 -76 [WPA2-EAP-CCMP][ESS] БПЛА1 example a8:9d:21:74:49:ec 5320 -76 [WPA2-EAP-CCMP][ESS] БПЛА2 example a8:9d:21:74:49:e3 2462 -79 [WPA2-EAP-CCMP][ESS] БПЛА3 example обновление всех данных через 1 секунду :~# watch -n1 'iw dev wlan0 link ' Connected to ec:bd:1d:81:dc:6c (on wlan0) SSID: myfifiexample freq: 5260 RX: 500279872 bytes (724060 packets) TX: 12508402 bytes (77938 packets) signal: -55 dBm rx bitrate: 400.0 MBit/s VHT-MCS 9 40MHz short GI VHT-NSS 2 tx bitrate: 400.0 MBit/s VHT-MCS 9 40MHz short GI VHT-NSS 2 bss flags: short-slot-time dtim period: 1 beacon int: 102 система ввода команд должна быть гибкой =============================== оператор должен уметь работать с текстом ,alias function ( nmcli dev wifi con Благовест1 = alias b1) программировать функциональные клавиши виа xmodmap ,печатать 10 пальцами это программа advanced user для школьников 8 класса виа факультатив на 3-6 месяцев =========================================================== директор лицея 1580 при МГТУ Баумана полковник https://www.youtube.com/watch?v=EvtT4VjSoRY ..у нас группа из 15 человек .и ни одной девочки ...они существуют в этом здании 3. есть много фото Российской армии с панасоник CF-33 ,CF-19 4. инструктор мирового уровня для связи через луну в диапазоне 1-77 gigagerz https://www.youtube.com/watch?v=2En_W2EaJFw затрагиваемые темы -РЛС ,связь, баллистика ,модуляция ,конструкция приемника, Doppler ,Kepler 5. для обучения школьников с 14 лет связь через Луну Москва -Пекин receiver until 3 ghz approx 2600 $ https://icomamerica.com/en/products/amateur/receivers/r8600/Icom-R8600-QST-product-Review.pdf https://www.youtube.com/watch?v=VEHqcs8GZvM
milstar: FREQUENCY HOPPING SPREAD SPECTRUM VS. DIRECT SEQUENCE SPREAD SPECTRUM FREQUENCY HOPPING VS. DIRECT SEQUENCE Frequency Hopping vs. Direct Sequence Spread Spectrum Techniques https://people.computing.clemson.edu/~westall/851/fhss_dsss.pdf DSSS is typically chipped using BPSK modulation. Since BPSK modulation has both phase and amplitude information, linear amplification is necessary. That means only Class A or Class AB amplifiers can be used. These are relatively low efficiency amplifiers. A lot of the DC power is turned into thermal energy, which has to dissipate. FHSS typically uses GFSK FREQUENCY HOPPING VS. DIRECT SEQUENCE modulation. This is constant-envelope modulation, so a non-linear, high efficiency Class C amplifier is adequate for its use. These characteristics mean that DSSS is more power hungry and harder to build in a smaller enclosure than FHSS systems. In an indoor radio propagation environment, the measured delay spread statistics have shown that a 100 nSec delay is fairly common. Since this is close to the DSSS chipping rate, there is a potential for inter-chip interference - or in other words, a penalty for performance that may be as much as 10 dB over corresponding Gaussian Channel. Good diversity antennas must be used to overcome some of these problems. FHSS would not see the effects of the 100-nSec delay. For a strong narrow-band jammer environment, FHSS also has a marked advantage if it can avoid the jammed channel by its frequency hopping nature. If it can not avoid narrow band interference, FHSS systems will still degrade its performance gracefully. On the other hand, DSSS systems will immediately loose a connection with narrow band interference.
milstar: https://www.qsl.net/n9zia/wireless/fhss_vs_dsss.html Processing Gain Frequency hop systems generally possess a large processing gain which allows the systems to operate with a low signal-to-noise ratio at the input of the receiver. The processing gain for frequency hop signals is: Processing Gain = RF Bandwidth / Information Bandwidth For example, a frequency hop signal that has a 10 MHz RF bandwidth and an information bandwidth of 1 kHz has a processing gain of 40 dB. Processing Gain = 10 MHz / 1,000 = 10,000 10 * log10 10,1000 = 40 dB Thus, the output signal-to-noise ratio of the frequency hopping demodulator will be 40 dB higher than the receiver input signal-to-noise ratio. This assumes no loss in the demodulator. Jamming Resistance Since a frequency hop signal generally has numerous frequency slots, the only time a narrow band jammer affects signal reception is when the signal hops to a frequency slot that is occupied by the jammer. If the frequency hopper has 500 frequency slots and a narrow band jammer interfers with the signal reception from one of the 500 slots, the only 1/500th of the signal might be jammed. Therefore. the low average power density combined with the pseudorandom frequency hopping make these signals difficult to intercept. Multiple Access Capability Frequency hop systems can be used for multiple access systems; time division, frequency division and code division multiple access systems can all employ frequency hop signals. Frequency division multiple access systems assign a frequency band for each user. While most frequency division multiple access systems employ narrowband signals, wideband signals could also be used. Short Synchronization Time Frequency hop systems generally require a significantly shorter time to acquire synchronization that other types of systems having the same bandwidth. In frequency hop systems the receiver can usually synchronize with the transmitted signal within a small fraction of a second. Direct sequence systems, for instance, require about a second to achieve synchronization. For some applications like voice communications, the shorter acquisition time is highly desirable. If one or two seconds is required to synchronize, the transmitter has to be keyed at least two seconds before the voice will be received at the receiver. Therefore, a voice reply would be delayed by at least two seconds. By using frequency hop signals, the receiver can synchronize within a fraction of a second and no noticable delay is encountered for voice. Multipath Rejection When the transmitted signal is propagated towards the receiver, several paths may exist which may cause interference due to phase cancellation at the receiver. This is called multipath propagation. If the signal is propagated via the ionosphere, the path delays can range from tens of microseconds to several milliseconds. Similar multipath delays can exist at VHF and UHF frequencies due to reflections from buildings, towers, and other reflective materials. If the hopping rate is adequately high, then the receiver listens on a new frequency slot before the interfering paths have a chance to interfer with the direct path. For slow frequency hoppers, the path propagation times are too fast to allow the receiver to reject the interference. Thus, to be effective, the hopping rate must be kept higher than the inverse of any interfering path delay time. Frequency Diversity Frequency hopping systems provide frequency diversity since many frequencies are used in the system. If proper data coding is used, a severe fade at any one particular frequency will have little effect on the data transmission. At HF frequencies, signals fade independently of one another if the frequency separation is several kilohertz. For frequency hop systems to provide frequency diversity, the minimum separation between frequency slots should be greater than several kilohertz. Typically, the separation used is much larger than a few kilohertz, ranging from 20 kHz minimum separation for voice or data communications. Thus, frequency diversity is easily provided for. Near-Far Performance Frequency hop systems provide better near-far performance that direct sequence systems. Near-far performance describes the behavior of the spread spectrum system with other users both near and far away from the intended users. Traffic Privacy Frequency hop systems provide a great degree of traffic privacy. The low probability of intercept combined with pseudorandom frequency hopping make these signals difficult to demodulate for unintended receivers. If additional security is desired the intelligence may be further encrypted using additional techniques. Low Probability of Intercept Frequency hop signals have a low average power density which can make these signals difficult to intercept. While the instantaneous power level of the frequency that is transmitted is high, the average power of that frequency is equal to the instantaneous power divided by the number of frequency slots. For example, a frequency hop system with 500 frequency slots transmits a specific frequency only a small fraction of the time (1/500th). If the instantaneous power from the transmitter is 100 watts, the average power in any one frequency slot is: Average power per frequency slot = 100 watts / 500 slots = 0.2 watts A frequency hop systems jumps to many different carrier frequencies in a time interval and filters the carrier frequency with the intermediate frequency filter. Users outside the filter's bandwidth are rejected and only the proper signal is demodulated. Since the I.F. filter passes only a narrow bandwidth, potential interferers are more easily rejected. If the other users of the frequency band are near the frequency hop receiver and a frequency hop transmitter is far away, a frequency hop system can more easily reject the nearby interference than a direct sequence system can.
milstar: FHSS vs. DSSS page 3 of 16 sorin m. schwartz seminars sorin m. schwartz seminars And for those interested just in the conclusions, here they are: DSSS has the advantage of providing higher capacities than FHSS, but it is a very sensitive technology, influenced by many environment factors (mainly reflections). The best way to minimize such influences is to use the technology in either (i) point to multipoint, short distances applications or (ii) long distance applications, but point to point topologies. In both cases the systems can take advantage of the high capacity offered by DSSS technology, without paying the price of being disturbed by the effect of reflections. As so, typical DSSS applications include indoor wireless LAN in offices (i), building to building links (ii), Point of Presence (PoP) to Base Station links (in cellular deployment systems) (ii), etc. On the other hand, FHSS is a very robust technology, with little influence from noises, reflections, other radio stations or other environment factors. In addition, the number of simultaneously active systems in the same geographic area (collocated systems) is significantly higher than the equivalent number for DSSS systems. All these features make the FHSS technology the one to be selected for installations designed to cover big areas where a big number of collocated systems is required and where the use of directional antennas in order to minimize environment factors influence is impossible. Typical applications for FHSS include cellular deployments for fixed Broadband Wireless Access (BWA), where the use of DSSS is virtually impossible because of its limitations. http://sorin-schwartz.com/white_papers/fhvsds.pdf FHSS vs. DSSS page 15 of 16 sorin m. schwartz seminars sorin m. schwartz seminars We shall also conclude that for long distances, point-to-multipoint topologies in reflective environments such as cellular deployments in a city, DSSS has no chance to survive, leaving FHSS the absolute winner, based on its famous multipath resistance. 6.- Time and frequency diversity Both DSSS and FHSS retransmit lost packets, until the receiving part acknowledges correct reception. A packet could be lost because of noises or multipath effects. This capability of a system to repeat unsuccessful transmissions at later moments in time is known as “time diversity”. DSSS systems use time diversity, but the problem is that they retransmit on the same 22 MHz sub- band! If the noise is still there or if the topography of the site did not change, and as a result the multipath effects will be again present, the transmission could be again unsuccessful! The multipath effects are a function of frequency. For same topography, some frequencies encounter multipath effects, while others do not. FHSS systems use “time diversity” (they retransmit lost packets at later moments in time) but they also use “frequency diversity” (packets may be retransmitted on different frequencies / hops). Even if some hops (frequencies) encounter multipath effects or noises, others will not, and the FHSS system will succeed in executing its transmission. 7.- Security The issue: Protecting the transmission against eavesdropping IEEE 802.11 compliant DSSS systems use one well known spreading sequence of 11 chips, and can modulate one of the 14 channel defined in the standard. As the sequence used is apriori known, the carrier frequency is fixed for a given system, and the number of possible frequencies is limited, it would be quite easy for a listener to “tune in” on the DSSS transmission. Message protection should be achieved by encrypting the data. This option increases the price of the product, while lowering its performance, because of the processing power needed for the encryption process. In FHSS, the frequencies to be used in the hopping sequence may be selected by the user. In the unlicensed band, any group of 26 frequencies or more (out of the 79 available) is legal. To “tune in”, a listener should know the number of frequencies selected in the system, the actual frequencies, the hopping sequence, as well as the dwell time! The FHSS modulation acts as a layer 1 encryption process. There could be no need for application level encryption
milstar: https://scask.ru/a_book_nd.php?id=29
milstar: https://www.arrl.org/files/file/Technology/tis/info/pdf/0101033.pdf The Signal What does this new mode consist of? Well, there are 16 tones—sent one at a time—at 15.625 baud and spaced 15.625-Hz apart. Each tone represents four binary data bits. The transmission is 316-Hz wide and has a ITU-R specifica- tion of 316HJ2B.13 It’s exactly like RTTY, but with 16 closely spaced tones instead of two wider-spaced tones. With a bandwidth of 316 Hz, the signal easily fits through a narrow CW filter. The tones are continuous phase keyed, which eliminates keying noise, and the phase information can be used to deter- mine tuning and symbol phase. Figure 1 shows an MFSK16 spectrogram (the hori- zontal lines are 300-Hz apart).
milstar: Symbol Rate The basic element of transmission in any data mode is the Symbol. In most modes, each symbol implies a "0" or "1", but in MFSK systems, each symbol carries information according to how many tones there are - three bits of information for 8 tones, four bits for 16 tones, and so on. Each MFSK tone burst is one symbol. The symbol rate is always measured in baud (symbols/second), the reciprocal of the duration of the symbol. Channel Data Rate The data carried by the MFSK tones is inevitably coded in some way so that the "raw data" rate may not be the same as the user input or output data rate. However, the Channel Data Rate is always the number of bits per symbol x the Symbol Rate. The channel data rate is measured in bits/second (bps). For example, for a 10 baud 8FSK mode (8 tone FSK) there are three data bits per symbol, so the raw Channel Data Rate is 3 bits x 10 baud = 30 bps. User Data Rate Very often data is coded using an FEC system Forward Error Correction designed to reduce errors that occur due to the transmission path. For MFSK systems the most appropriate type of FEC is the sequential type, where every user data bit is represented in the transmission by two or more coded data bits. This ratio is the Coding Rate of the coder. For example, if there are two coded bits for every one data bit, the Coding Rate = 1/2. Thus the User Data Rate is the Channel Data Rate x Coding Rate. Alphabet Coding There are many ways to encode the alphabet from the keyboard for transmission. Perhaps the most common now is ASCII (ITA-5), but ITA-2 (as used by teleprinters) is also widely used. MFSK16, like Morse and PSK31, is based on a Varicode, which, unlike most alphabets, assigns a different number of bits to different characters, so that more frequently used characters have fewer bits and are therefore sent faste https://nonstopsystems.com/radio/pdf-radio/zl1bpu_MFSK.pdf
milstar: Worked Example Say we are using an MFSK system with 16 tones (16FSK), operating at 15.625 baud with FEC Rate = 1/2, and an ASCII alphabet using 10 bits/character. Then: Symbol Rate = 15.625 baud Channel Data Rate = 15.625 x log216 = 15.625 x 4 = 62.5 bps User Data Rate = 62.5 x 1/2 (FEC RATE) = 31.25 bps Text Throughput (CPS) = 31.25 / 10 CPS = 3.125 CPS Text Throughput (WPM) = 31.25 x 60 / (10 x 6) = 31.25 WPM This will take place in a bandwidth little more than 16 x 15.625 = 250 Hz. https://nonstopsystems.com/radio/pdf-radio/zl1bpu_MFSK.pdf
milstar: https://www.l3harris.com/sites/default/files/2022-03/cs-gcs-panther-II-man-portable-vsat-spec-sheet-147a.pdf 12 kg The Panther II is a Tri-Band, man-portable VSAT system, available in 60 and 96 centimeter (cm) apertures. Capable of both auto and manual acquisition, this system provides high-speed data communications for Internet, VPN connectivity and video transmission. This highly rugged VSAT system is lightweight, able to be carried in a rucksack or airline-checkable hard case, and offers high data rates over commercial and military satellites. A single interface connection between transceiver and modem significantly reduces critical setup time
milstar: https://www.l3harris.com/sites/default/files/2020-11/cs-tcom-rf-7850s-spr-wideband-secure-personal-radio-datasheet.pdf The L3Harris Falcon III RF-7850S SPR provides the ultimate integration of radio, edge device, GPS and application software in a single, compact and lightweight platform. -116 dBm @ 12 dB SINAD Frequency hopping (ECCM) operation
milstar: Mars Exploration Rover https://ipnpr.jpl.nasa.gov/progress_report/42-153/153A.pdf The X-band DTE link will use a special multiple-frequency-shift-keyed (MFSK) signal format. This has been chosen because the signal conditions of high dynamics and low signal-to-noise ratio (SNR) will not reliably support phase-coherent communications. The X-band DTE link will use a special multiple-frequency-shift-keyed (MFSK) signal format. This has been chosen because the signal conditions of high dynamics and low signal-to-noise ratio (SNR) will not reliably support phase-coherent communications. There will be 256 different signal frequencies, modulated one at a time onto a subcarrier, using the spacecraft capability to switch the subcarrier frequency. During hypersonic entry, the signal frequency can be switched every 10 s, resulting in the communication of 8 bits of information each 10 s. When the lander is suspended from the bridle, and the UHF link is prime, the duration of the modulation frequencies may be extended to 20 s to better facilitate detection during this period of highly varying SNR. This would result in fewer messages of higher reliability than would the use of the 10-s duration
milstar: During periods of highest dynamics, the combination of low SNR and high dynamics makes reliable phase-coherent communications impossible. For example, use of a type III phase-locked loop (PLL) to track the dynamics would require a loop bandwidth on the order of 13 Hz [3]. The required loop SNR should be approximately 11 dB, which is slightly higher than the 10-dB minimum for coherent communications when there is negligible dynamic phase-lag error. With the 13-Hz loop bandwidth, this results in a required carrier power-to-noise density SNR of 22 dB-Hz. For the lowest SNR profile in Fig. 3, the total power SNR is typically 22 dB-Hz. With half of the total power in the carrier, the carrier SNR would be 3 dB less than the nominal requirement. Furthermore, a PLL system would have virtually no chance to maintain lock during parachute deploy- ment, and there would not be sufficient time to reacquire lock after deployment in order to receive the important information sent then. There also would be no margin for lower SNR conditions, which are statistically possible. Thus, coherent communication is not feasible and a special form of MFSK will be used, as described in Section III. https://ipnpr.jpl.nasa.gov/progress_report/42-153/153A.pdf
milstar: https://www.thalesgroup.com/en/markets/defence-and-security/radio-communications/land-communications/land-satcom-terminals
milstar: 4.5 Gbps high-speed real-time physical random bit generator https://opg.optica.org/oe/fulltext.cfm?uri=oe-21-17-20452&id=260648
milstar: Single Tone Jammer The single tone jammer transmits an unmodulated carrier with power PJ some- where in the spread spectrum signal bandwidth. The single tone jammer is easily to generate and is rather effective against direct sequence spread spectrum systems. To achieve the maximum effectiveness of this jammer, the jamming tone should be placed at the center of the spread spectrum signal bandwidth. The single tone jammer is less effective against frequency hopping, since the frequency hopping instantaneous bandwidth is small and, for large processing gains the probability of any hop being jammed is small [33] https://curve.carleton.ca/system/files/etd/3ca5b480-565a-4721-8199-2339ad2af5df/etd_pdf/a661b46493258918a040b402f54e24e5/atta-improvedjammingresistantfrequencyhoppingspread.pdf
milstar: .4 Multiple Tone Jammer A better tone jamming strategy against frequency hopping systems is to use several tones instead of a single tone. However, the power of the single tone jammer will be shared by these multiple jamming tones. The jammer selects a number of tones so that the optimum degradation occurs when the spread spectrum signal hops to a jamming tone frequency. The optimum number of tones is a function of the received ratio of signal power to jammer power (PS /PJ ). Multiple tone jamming is also effective against hybrid systems [33].
milstar: In CAFHSS, which is also named adaptive frequency hopping, the channel char- acteristics are monitored first and then the receiver detects the best available sub- channels and assigns these sub-channels to the transmitter for usage. CAFHSS is also used in single user scenarios to mitigate channel fading by as- signing sub-channels with highest signal-to-noise ratio (SNR) or sub-channels with highest gains to the user’s transmitter and the transmitter use these sub-channels to modulate the transmitted signal in a random fashion. However all of these CAFHSS schemes do not consider the presence of jamming. A new dynamic adaptive frequency hopping (DAFH) scheme is proposed in [67], [68]. The main idea behind this scheme is to assign all the hopping tones to the user and measure the packet error rate (PER). If the PER is higher than a specific threshold the hopping set is divided into two halves and the user randomly select one half of the hopping set to modulate the transmitted signal and the PER is again measured. If the PER is still higher than the threshold the system continue dividing the hopping set until the PER becomes lower than the threshold. Set doubling (joining two hopping sets together) is used if the threshold of the PER is lower than the threshold. This scheme has better through- put performance than adaptive frequency hopping. Instead of using a conventional adaptive frequency hopping scheme, the authors in [69] proposed to divide the to- tal frequency band into many hopping sets and measure the PER of each hopping set and classify them as either good or bad hopping sets based on a predetermined threshold. Then they applied the moving average (MA) technique to the tones in bad sets to detect the tones that are not interfered. This scheme has better PER than conventional adaptive frequency hopping https://curve.carleton.ca/system/files/etd/3ca5b480-565a-4721-8199-2339ad2af5df/etd_pdf/a661b46493258918a040b402f54e24e5/atta-improvedjammingresistantfrequencyhoppingspread.pdf
milstar: All frequency hopping schemes that are used to mitigate interference and fad- ing usually use uncoded communication, and the BER metric is used to compare the performance of these systems. When it comes to comparing frequency hopping systems in the presence of jamming, all uncoded systems have unreasonably high bit error rates if any of the tones in the hopping set are jammed. It is therefore typically necessary to use some form of error control coding to recover data bits that are lost due to jamming. The more important and relevant measure in this case is to consider how much coding we need (i.e. what code rate we should use) to have a robust frequency hopping system to mitigate jamming in a specific channel model. We therefore measure the system performance in terms of the average throughput that can be realized with a rate-adaptive coded system. A type-II hybrid automatic repeat request (ARQ) scheme with incremental re- dundancy is used in this frequency hopping system to achieve reliable data transmis- sion. In this ARQ scheme the receiver sends an acknowledgement to the transmitter if the data is received correctly and this acknowledgement should be received by the transmitter within a specific period of time. If the transmitter does not receive the acknowledgement from the receiver, it will transmit additional parity bits until the receiver sends the acknowledgement back. We assume that a capacity-achieving code is used for error correction, which can be approximated by either a family of rate-compatible fixed-rate codes or, more practically, a rate-adaptive code such as a Raptor code [74], used in conjunction with an incremental redundancy ARQ scheme. We attempt in this thesis to improve battlefield signal transmission using new adaptive frequency hopping spread spectrum schemes that are desired to mitigate interference and jamming in frequency selective fading channels. Different existing frequency hopping schemes such as random frequency hopping (RFH), matched fre- quency hopping (MFH), clipped matched frequency hopping (CMFH), and advanced frequency hopping (AFH) will be presented and compared. We propose to use the MFH, CMFH and AFH as anti-jamming techniques and we also propose to optimize their control parameters to enhance their performance in jammed frequency selective fading channels. We also propose new random frequency hopping techniques that combine the advantages of randomness and adaptivity of frequency hopping and op- timize their parameters to enhance their performance. https://curve.carleton.ca/system/files/etd/3ca5b480-565a-4721-8199-2339ad2af5df/etd_pdf/a661b46493258918a040b402f54e24e5/atta-improvedjammingresistantfrequencyhoppingspread.pdf
milstar: 7.4.5. Futaba Advanced Spread Spectrum Technology Futaba Advanced Spread Spectrum Technology (FASST) is the Tx protocol of the Japanese company Futaba and is used not only in the RF products of Futaba, but also as a part of products made by other manufacturers, such as the DJI Phantom 2. It uses the 2.4-2.485 GHz frequency band with the minimum bandwidth of the channels as 1.1 MHz and sidebands of up to 2 MHz. FASST implements frequency hopping, Gaussian frequency-shift keying, and sometimes a combination with DSSS which significantly increases resistance against interference or jamming. It also has different modes of usage providing 7, 8 or 14 transmit control channels. It’s successor FASSTEST also employs duplex communication [92]. https://www.sciencedirect.com/science/article/pii/S1570870520306788
milstar: https://ieeexplore.ieee.org/abstract/document/4540261 FPGA implementation of FHSS-FSK modulator
milstar: The most difficult area is the receiver path, especially at the despreading level for DSSS, because the receiver must be able to recognize the message and synchronize with it in real time. The operation of code recognition is also called correlation. Because correlation is performed at the digital-format level, the tasks are mainly complex arithmetic calculations including fast, highly parallel, binary additions and multiplications. https://www.analog.com/en/technical-articles/introduction-to-spreadspectrum-communications--maxim-integrated.html
milstar: Одноразовые блокноты являются "теоретически безопасными с точки зрения информации" в том смысле, что зашифрованное сообщение (т.Е. зашифрованный текст) не предоставляет криптоаналитику никакой информации об исходном сообщении (за исключением максимально возможной длины [примечание 1] сообщения). Это очень сильное понятие безопасности, впервые разработанное во время Второй мировой войны Клодом Шенноном и математически доказанное для одноразового блока Шеннона примерно в то же время. Его результат был опубликован в техническом журнале Bell System в 1949 году.[18] При правильном использовании одноразовые пэды безопасны в этом смысле даже против противников с бесконечной вычислительной мощностью. =========================================================
milstar: https://www.gps.gov/governance/advisory/meetings/2014-12/mcgraw.pdf Toughening GPS Receivers Against Interference Ensuring Signal Reception in Spectrally Busy Environments Dr. Gary A. McGraw Manager & Fellow, Navigation & Control Rockwell Collins Advanced Technology
milstar: http://site.iugaza.edu.ps/wp-content/uploads/file/ayash/DC/Data%20Com%20Chapter9.pdf 4. (Q9.2) An FHSS system employs a total bandwidth of Ws = 400 MHz and an individual channel bandwidth of 100 Hz. What is the minimum number of PN bits required for each frequency hop? Solution: # of hops = (400*106) / 100 = 4*106 The minimum number of PN bits = log2 (4 × 106) = 22 bits
milstar: https://archive.org/details/DTIC_ADA172929/page/n34/mode/1up page 1-22 OPTIMUM PARTIAL-BAND NOISE JAMMING PERFORMANCE OF FH/MFSK (M= 8) SQUARE-LAW COMBINING RECEIVERS FOR L = 2 HOPS/SYMBOL WHEN Eb/NQ= 9.09 dB (FOR IDEAL MFSK (M - 8) CURVE THE ABSCISSA READS Eb/NQ FIGURE 1.2-4 OPTIMUM JAMMING PERFORMANCE OF THE AGC FH/MF3K (MM) RECEIVER WHEN E^/N^ = 13.16 dB WITH THE NUMBER OF HOPS/SYMBOL (L) A3 A PARAMETER (FOR IDEAL MFSK (MM) CURVE THE ABSCISSA READS Eb/NQ
milstar: https://cdn.intechopen.com/pdfs/24319/InTech-Frequency_hopping_spread_spectrum_an_effective_way_to_improve_wireless_communication_performance.pdf The design of frequency hopping spreader is shown in Figure 8. The spreader part consists of M-FSK modulator base (with M equal to 64), a From block (Hop index that is created in previous step), a To Frame block and a Multiplication block. The block parameter of FSK modulator is 64 in M-FSK number and it means that there are 64 hopping sections. These sub-bands are selected by the hop indexes. The design of frequency hopping despreader, is the same as spreader section but the output of M-FSK modulator block is complex conjugated as shown Figure 9. This frequency hopping model is used for evaluation of three different modulations: QAM, QPSK, GFSK, and compares the performance with the situation without frequency hopping. Performance evaluation is based on BER values under two situations (with and without FH) versus normalized signal-to-noise ratio (SNR) measured by Eb/N0 values of the channel, as shown in Figure 10, 11, 12.
milstar: PROTECTED SATELLITE COMMAND AND CONTROL (C2) WAVEFORMS AND ENHANCED SATELLITE RESILIENCY https://www.spacefoundation.org/wp-content/uploads/2019/07/Butler-Bryan_Protected-Satellite-C2.pdf from https://www.kratosdefense.com/ lnterference may collide with some hops, as shown in the lower-left corner, but the combination of hopping and forward error correction recover the data from the lost hops. By combining FEC with other techniques, such as interleaving and spreading, non-Gaussian channels (including interference) can often be transformed to have a Gaussian-like effect on the end result. Thus, the FEC performance is a key ingredient in achieving the highest level of robustness in a protected C2 link Since the processing gain, and thus the interference rejection, of spread spectrum is dependent on the spreading bandwidth, it may be desirable to use a higher frequency band, at least for some types of C2 links. command and control (C2) primary concern is the security of the C2 waveform. Although the data stream is usually encrypted, providing secrecy and some degree of authentication, the waveforms themselves do not in any way hide the traffic flow. It is readily apparent when commands are being transmitted, and the telemetry often has different modes depending on the operational state of the satellite (e.g. different data rates or modulation types) that are easily identified when examining the signal externals. The implication is that an external observer can infer things (for example, traffic patterns) about what is happening on our systems, with the possibility of either passive or active exploitation Spread Spectrum This section describes spread-spectrum techniques that are used to provide a number of useful features: - Multi-user access. Although technically a spread-spectrum waveform is not “bandwidth efficient”, it does allow multiple users to share a portion of spectrum. The total capacity of the channel, when the number of user bits per Hz is considered, is often nearly the same when compared to a conventional FDMA channel. - Anti-interference. Spread-spectrum is sometimes touted as “jam-proof”, which is an unfortunate (and unrealizable) characterization of an actual feature, in that narrowband interference occurring on the spread waveform becomes wideband interference (at the same power level) when the received waveform is de- spread, thus reducing the net effect of the jamming or interference. Nothing is ever “jam-proof”, but the advantage of a spread waveform can be easily characterized by the processing gain, which is roughly the ratio of the bandwidth of the spread waveform to the net bit rate. - Covertness. If the waveform is spread with a secure spreading function, the signal will be hard to detect. Signal features, such as symbol rate or frame markers, can often be obscured by the spreading function. Furthermore, a non-repeating secure spreading function will be robust against problems such as replay attacks and cyclostationary detection
milstar: DSSS has the advantage of providing higher capacities than FHSS, but it is a very sensitive technology, influenced by many environment factors (mainly reflections). The best way to minimize such influences is to use the technology in either (i) point to multipoint, short distances applications or (ii) long distance applications, but point to point topologies. In both cases the systems can take advantage of the high capacity offered by DSSS technology, without paying the price of being disturbed by the effect of reflections. As so, typical DSSS applications include indoor wireless LAN in offices (i), building to building links (ii), Point of Presence (PoP) to Base Station links (in cellular deployment systems) (ii), etc. On the other hand, FHSS is a very robust technology, with little influence from noises, reflections, other radio stations or other environment factors. In addition, the number of simultaneously active systems in the same geographic area (collocated systems) is significantly higher than the equivalent number for DSSS systems. All these features make the FHSS technology the one to be selected for installations designed to cover big areas where a big number of collocated systems is required and where the use of directional antennas in order to minimize environment factors influence is impossible. Typical applications for FHSS include cellular deployments for fixed Broadband Wireless Access (BWA), where the use of DSSS is virtually impossible because of its limitations. http://sorin-schwartz.com/white_papers/fhvsds.pdf
milstar: RTO-MP-IST-054 P12 - 1 UNCLASSIFIED/UNLIMITED UNCLASSIFIED/UNLIMITED Robust Frequency Hopping for High Data Rate Tactical Communications https://apps.dtic.mil/sti/pdfs/ADA521139.pdf In Figures 4 and 5, the BER performance is shown for a 1x5MHz system and a 5x1MHz system, respectively, subject to multi-tone (MT) jamming. The jammer waveform consists of 175 jamming tones evenly distributed over the UHF operating band. It is clear that as the signal to jammer ratio (SJR) is decreased, the 5x1MHz scheme in Figure 5 is more robust to this particular form of jamming compared to the 1x5MHz scheme, with the limiting case on performance for the latter scheme being for SJR=-30dB. In other words, the multiple subband system demonstrates a considerable gain in BER performance compared to the single subband scheme in jamming scenarios with relatively high SJRs
milstar: Frequencies above 2 GHz are less densely populated, and wider bandwidths are available. Operating at those high frequencies solves the problem of bandwidth availability and limits the adverse effects of thermal noise: it is a well known fact that sky noise temperature is minimum at frequencies between 1 and 10 GHz, in the so-called microwave window , as shown in figure 1.1 https://apps.dtic.mil/sti/tr/pdf/AD1113822.pdf FHSS spreading In frequency-hopping (FH) systems, the frequency synthesizer is driven by a pseudo- random sequence to hop from one frequency to another, withln a pre-determined frequency range. Most commonly, FH is used in association to an M-ary frequency shift keying (MFSK) modulation. Instead of modulating a fixed frequency carrier, the data symbol modulates a carrier whose frequency is determined by a pseudo-random code. For a given hop, the bandwidth that is occupied during the transmission is identical to the bandwidth of conventional MFSK: however, averaging over several hops, the spectrum spreads to use all the available bandwidth. Current technology permits a spreading over a bandwidth of several GHz, allowing larger processing gains in comparison to DS system . Let us assume that the hopping ratefc is larger than the inverse of the delay difference between the reflected path and the direct path, that is The result is that the FHSS system has switched to another frequency before the arrival of the delayed signal. For this reason FHSS is capable of presenting excellent performance against multipath interference, provided the hopping rate is sufficiently high and that receiver synchronization is not disturbed by the interference. For this reason, fast frequency-hopping systems perform better than slow frequency-hopping system
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