ППРЧ/FHSS -псевдослучайная перестройка рабочей частоты

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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

Ответов - 60, стр: 1 2 3 All

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

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