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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: 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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