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BPSK
milstar: Missions not requiring a residual carrier and having modest data rates (20 ks/s - 200 ks/s) should consider BPSK/NRZ modulation first. ######################## nonreturn-to-zero (NRZ) to binary phase-shift keying It provides a good compromise between spectrum efficiency and simplicity of design. While data imbalance does not result in system losses as in the case of PCM/PM/NRZ modulation, the statistics of each application should be reviewed. Agencies employing a DTTL architecture in their symbol synchronizers, must ensure a sufficient transition density to acquire and maintain synchronization. Manchester encoding prior to BPSK modulation can ensure sufficient transitions. As with PCM/PM/Bi-N modulation, there is a 100% penalty in spectrum efficiency over the NRZ equivalent https://deepspace.jpl.nasa.gov/files/phase3.pdf https://deepspace.jpl.nasa.gov/dsndocs/810-005/208/208B.pdf
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milstar: The relative telemetry performance of residual-carrier operation and suppressedcarrier operation depends strongly on the bit rate. One scheme is said to have better telemetry performance than the other when it has a smaller required PT/N0 for the support of a given bit rate at a given threshold FER. In general, residual carrier has the better telemetry performance for the very low bit rates and especially for low bit rates coupled with larger carrier loop bandwidths (as would be necessary in the presence of significant phase noise or uncompensated Doppler dynamics). For intermediate bit rates, suppressed carrier offers a significant telemetry performance advantage over residual carrier. For high bit rates, suppressed carrier offers a telemetry performance advantage, but it is only about 0.1 dB. Of course, there will be times in which the decision between residual carrier and suppressed carrier is made on grounds having nothing to do with telemetry performance. For example, a residual carrier is sometimes needed for a radio science experiment. Also, in some applications it will important to minimize acquisition time. Then, the choice of residual carrier or suppressed carrier will be based on whichever scheme offers the quicker acquisition https://deepspace.jpl.nasa.gov/dsndocs/810-005/207/207A.pdf
milstar: s. First, the carrier loop signal-to-noise ratio (rL, see paragraph 5.3) must be at least 10 dB if tracking a residual carrier or at least 17 dB if tracking a suppressed carrier. Second, the squarewave subcarrier loop signal-to-noise ratio (rSUB, see paragraph 5.4) must be at least 20 dB. Third, the symbol loop signal-to-noise ratio (rSYM, see paragraph 5.5) must be at least 15 dB. Fourth, the product hSYS ◊Eb/N0 must be at least 0.8 dB, where hSYS is system loss. For each residual-carrier performance curve, it is assumed that at each point on the curve the optimum modulation index is used. The subcarrier loop bandwidth and window factor are assumed to be 50 mHz and 0.25, respectively. The symbol loop bandwidth and window factor are assumed to be 50 mHz and 0.25, respectively. For the case represented in Figure 8 with BL = 0.5 Hz, residual carrier offers better telemetry performance than suppressed carrier for bit rates less than 20 bps, and suppressed carrier is better for bit rates greater than 20 bps. With BL = 1 Hz, the performances of residual carrier and suppressed carrier cross at 50 bps. With BL = 2 Hz, they cross at 100 bps
milstar: The reason residual carrier performs better than suppressed carrier at the low bit rates is because a residual-carrier loop is not subject to half-cycle slips. A suppressed-carrier loop, on the other hand, can slip a half-cycle and therefore requires a higher carrier loop signalto-noise ratio in order to guard against these damaging slips. (A residual-carrier loop can slip a whole cycle, but this is both less likely and less damaging than a half-cycle slip.) In order to get the best performance from residual-carrier operation, it is necessary that the modulation index be optimal or, at least, near optimal. Each residual-carrier performance curve of Figure 8 is based on the assumption that the modulation index is optimized at each point on the curve. Figure 9 shows what happens if this is not the case. In Figure 9, the lower curve (with the better telemetry performance) is the same as the residual-carrier curve with BL = 1 Hz of Figure 8, with an optimized modulation index at each point on the curve. The upper curve of Figure 9 represents residual-carrier performance with BL = 1 Hz under all the same circumstances except that the modulation index is not optimized at each point on the curve; instead, a single modulation index of 54° (the optimum modulation index for a bit rate of 10 bps) is used for the entire curve. The two curves of Figure 9 coalesce at RBIT = 10 bps but, for RBIT greater than 10 bps, a penalty is paid for not using the appropriate optimum modulation index. At RBIT = 1000 bps, the penalty is about 2 decibels.
milstar: MRO communications has operated in three different frequency bands: 1) Most telecom in both directions has been with the Deep Space Network (DSN) at X-band (~8 GHz), and this band will continue to provide operational commanding, telemetry transmission, and radiometric tracking. 2) During cruise, the functional characteristics of a separate Ka-band (~32 GHz) downlink system were verified in preparation for an operational demonstration during orbit operations. After a Ka-band hardware anomaly in cruise, the project has elected not to initiate the originally planned operational demonstration (with yet-to-beused redundant Ka-band hardware). https://descanso.jpl.nasa.gov/monograph/series13/DeepCommo_Chapter6--141029.pdf
milstar: 6.3.1 X-Band: Cruise and Orbital Operations Uplinks to MRO and downlinks from MRO at X-band are the primary means of communication between the MRO and the DSN antennas in California, Spain, and Australia. The X-band communication system on the orbiter uses a 3-meter-diameter (10-foot) HGA and a 100-watt (W) X-band TWTA to transmit signals to Earth. Each of these devices is more than twice as capable as those used by previous Mars missions. As a result, MRO has been sending data back to Earth more than 10 times faster than previous missions. At a maximum distance from Earth (400 million km [250 million miles]), the orbiter is designed to send data at a rate of at least 500 kbps. At closer ranges, the signal strength can be greater, so higher data rates are possible. When the orbiter is at its closest ranges (about 100 million km [60 million miles]), for several months the orbiter will be able to send data to Earth at 3 to 4 megabits per second (Mbps). https://descanso.jpl.nasa.gov/monograph/series13/DeepCommo_Chapter6--141029.pdf
milstar: 2.2 Carrier Recovery For optimum reception of the transmitted data in a BPSK modulated signal, both the carrier as well as data clock signals must be available at the receiver. The extraction or regeneration of these signals from the noisy digitally modulated received waveform, is the task of the carrier recovery and clock and data recovery systems. This section focuses on the operating principles of the former. As previously discussed, to improve the power efficiency of the transmitter, most modern modulation techniques choose to fully suppress the carrier in the transmitted signal. This has the added benefit that now all the transmitted energy resides in the information carrying side-bands. Unfortunately, without the presence of a carrier, ordinary Phase Locked Loops (PLL) cannot be used for carrier recovery. This means that complex carrier recovery techniques are required. Many factors have to be considered during the selection and development of a carrier recovery system. Here, only the basic operating principles of these systems are surveyed. For the sake of simplicity, only BPSK modulation is considered. The task of carrier recovery in most telecommunication applications can be accomplished by one of the following three types of carrier recovery methods: multiplication loop (such as a squaring loop for BPSK), remodulator loop and Costas loop. Other types of carrier recovery schemes are extensions or modifications of these techniques [12]
milstar: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.472.8206&rep=rep1&type=pdf https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1367923&tag=1
milstar: https://gdmissionsystems.com/satcom-technologies/antennas/small-deployable-antennas
milstar: . Unfortunately, this is not completely possible since, for example, a squaring loop (or equivalently a binary phase-shift keying (BPSK) Costas loop) cannot track a quadrature phase-shift keying (QPSK) modulation and likewise a 4th power loop (or equivalently a QPSK Costas loop, sometimes referred to as an in-phase– quadrature (I-Q) loop) cannot properly track a BPSK signal.1 https://pdfs.semanticscholar.org/044d/e86040cbf778d2b4e2e2ecdeefd28e6f12f9.pdf
milstar: Telecommunications teams make use of separate (but coupled) link budgets for carrier, telemetry channel, and ranging channel, each having their own set of assumptions. In order to simplify the discussion, we will assume the case of no-ranging. The carrier channel threshold involves maintaining a minimum carrier tracking loop signal-to-noise ratio (SNR) required to maintain lock. The DSN Telecommunications Link Design Handbook, DSN No. 810- 005 [2] provides recommendations for minimum SNR for different link configurations. For residual carrier tracking involving binary phase-shift keying (BPSK) telemetry, a minimum loop-SNR of 10 dB is required, whereas for suppressed-carrier BPSK, it is 17 dB [2]. There are higher threshold carrier loop-SNR values required for quadrature phase-shift keying (QPSK) telemetry. The carrier link also takes into account transmitter phase noise and solar phase noise (significant at small solar elongation angles). Usually projects maintain a carrier link with 3 dB or higher margin above the SNR threshold. https://ipnpr.jpl.nasa.gov/progress_report/42-208/208B.pdf
milstar: https://deepspace.jpl.nasa.gov/dsndocs/810-005/207/207A.pdf Residual Carrier A residual-carrier signal can be tracked whether or not there is a subcarrier (squarewave or sinewave) present and whether the symbols are non-return-to-zero or Bi-phase.
milstar: 3.3.3 Radio Frequency Subsystem 3.3.3.1 Receivers. The receiver is a narrow-band, double-conversion, superheterodyne, automatic-phase-control design. The receiver has a coherent Voyager Telecommunication 53 amplitude detector that detects and measures received-signal strength and provides the receiver with an automatic gain control (AGC) function. Receiver AGC is telemetered as a primary uplink performance parameter. https://voyager.gsfc.nasa.gov/Library/DeepCommo_Chapter3--141029.pdf
milstar: s. In the residual carrier mode, the X-band carrier Voyager Telecommunication 61 modulation index settings vary from 51 deg for the lowest data rate (10 bps) to 80 deg for the highest (115.2 kbps).1 ##################### 7 A modulation index of 90 deg puts all of the power in the sidebands and therefore produces a suppressed carrier mode. Suppressed carrier mode is used during VIM to extend Voyager 2 playback data rate capability. See Section 3.6, New Telecom Technology.
milstar: lation index be optimal or, at least, near optimal. Each residual-carrier performance curve of Figure 8 is based on the assumption that the modulation index is optimized at each point on the curve. Figure 9 shows what happens if this is not the case. In Figure 9, the lower curve (with the better telemetry performance) is the same as the residual-carrier curve with BL = 1 Hz of Figure 8, with an optimized modulation index at each point on the curve. The upper curve of Figure 9 represents residual-carrier performance with BL = 1 Hz under all the same circumstances except that the modulation index is not optimized at each point on the curve; instead, a single modulation index of 54° (the optimum modulation index for a bit rate of 10 bps) ################### is used for the entire curve. The two curves of Figure 9 coalesce at RBIT = 10 bps but, for RBIT greater than 10 bps, a penalty is paid for not using the appropriate optimum modulation index. At RBIT = 1000 bps, the penalty is about 2 decibels. https://deepspace.jpl.nasa.gov/dsndocs/810-005/207/207A.pdf
milstar: The curves of Figures 20 through 23 are defined by two constraints: rL should be greater than or equal to 10 dB and the product hRADIO ◊Eb/N0 should be greater than the threshold effective energy per bit to noise spectral density ratio. Moreover, for effective residual-carrier tracking the modulation index must be no larger than 80 degrees. ############ https://deepspace.jpl.nasa.gov/dsndocs/810-005/207/207A.pdf
milstar: Still further, if the modulation is known to be other than suppressed carrier, i.e., a modulation index less than π/2 rad, then it is still possible to exploit the power in both the data and residual carrier components for carrier-tracking purposes provided one has knowledge of the modulation index itself. Such knowledge could be derived noncoherently, i.e., in the absence of carrier synchronization, from a suitable modulation index estimator (to be discussed elsewhere in the monograph). Loops of this type have been referred to in the literature as hybrid carrier tracking loops and like their suppressed-carrier counterparts are motivated by the same MAP considerations.
milstar: https://apps.dtic.mil/dtic/tr/fulltext/u2/a286018.pdf A Costas loop may be used as a suppressed carrier receiver. In Eq. (70), the first term is the carrier while the second term is the data channel. Hence, the modulation index 13i has allocated the total power PT in the transmitted signal VT(t) to the carrier and to the data channel, w' >•re the carrier power and the data power are given respectively as, PC = PT cos^ 2 beta , PD = PT sin^ 2 beta .beta = angle of modulation 45° nositel i dannie mopschnost odinakowa
milstar: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19900010954.pdf RF 20 ghz 1 IF 3.373 ghz
milstar: https://pdfs.semanticscholar.org/f032/bc3474cc45d2e4cb7612549916b9caa99ec8.pdf
milstar: https://deepspace.jpl.nasa.gov/dsndocs/810-005/205/205C.pdf carrier modulation for high gain antenna 1.2 radian 68.75 °
milstar: http://www.nitehawk.com/w3sz/W3SZ-PackRatsConference2014.pdf troposcatter loss examples 302 km 3670 mhz 233 db ====================== Free Space Loss Between Mars and Earth x band 400 mln km -284 db 55 mln km -267 db For the worst case, which occurs about 0.001% of the time, rain attenuation can be as large as 40–50 dB http://www.ka9q.net/mpf_budget.html link bjudzet Required power density at 4740 bps Pr/N0 38.1 dB-Hz Required bit SNR Eb/No 1.2 dB Modulation is binary phase shift keying (BPSK) with residual carrier; low data rates use a greater carrier power fraction, resulting in a higher Eb/No requirement (about 4 dB higher at 5bps).
milstar: Moskwa Spb 650 km 8.5 ghz troposcatter loss approx 250 db
milstar: Knowledge of the transmitted signal parameters greatly simplifies the design and implementation of the receiver. For example, if a residual carrier is present, then the carrier phase-tracking loop may be a simple phase-locked loop (PLL); hence, a Costas loop need not be implemented. ################################## Or, if the modulation type is known to be BPSK, then the receiver need not include any processing of the quadrature component of the signal. ############################## https://descanso.jpl.nasa.gov/monograph/series9/Descanso9_Full_rev2.pdf
milstar: When this is done, the fraction of power allocated to the discrete carrier becomes Pc = Pt cos2 β with the remaining fractional power Pd = Pt sin2 β available for data detection. When using this signaling mode, one must assure oneself that the power spectrum of the data modulation is such that it does not interfere with the extraction of the discrete carrier by an appropriate carrier-tracking loop such as a phase-locked loop (PLL). In other words, the discrete carrier should be inserted at a point where the power spectrum of the data modulation is minimum, preferably equal to zero. In the case of digital data, this rules out direct modulation of the carrier with a non-return-to-zero (NRZ) data stream whose spectrum is maximum at zero frequency, which at radio frequency (RF) would correspond to the carrier frequency. Instead one can first modulate the data onto a subcarrier whose frequency is selected significantly higher than the data rate so that the sidebands of the data modulation are sufficiently reduced by the time they reach the carrier frequency. Alternatively, one can use a data format such as biphase-L (Manchester coding), whose power spectrum is identically equal to zero at zero frequency, and directly modulate the carrier https://descanso.jpl.nasa.gov/monograph/series9/Descanso9_Full_rev2.pdf Although a Costas loop operates with a less efficient performance (e.g., larger mean-squared phase-tracking error) than a PLL, it offers the advantage of not requiring a discrete carrier to lock onto, and thus all of the transmitted power can be used for the purpose of data detection
milstar: If the modulation index estimator has determined that there is a residual carrier, then a phase-locked loop (PLL) may be used to lock onto the residual carrier signal. The residual carrier itself is the output of a low-pass filter of the received signal, which suppresses the data modulation (except for the portion of the spectrum at zero frequency). When a residual carrier is present, the PLL may be the best choice for carrier synchronization in the fine estimation mode ############################################## as well, but this depends on the SNR and the value of the modulation index. In cases when the residual carrier is weak, a hybrid loop may outperform the PLL alone in the fine estimation phase. https://descanso.jpl.nasa.gov/monograph/series9/Descanso9_Full_rev2.pdf
milstar: https://www.fritz.dellsperger.net/downloads/V7a_3-Digital%20Modulation_en.pdf Biphase Simple clock recovery No DC-component Double bandwidth compared to NRZ
milstar: 1 Bi-φ modulation typically is referred to in the literature as Manchester code. because the modulation index is less than 90 degrees, there exists a residual carrier component that can be tracked by the phase-locked loop (PLL) to provide a coherent phase reference. This is particularly useful when the received signal level is weak and/or contains high Doppler dynamics, since it is well known that a PLL can operate at much lower loop signal-to-noise ratios (SNRs) than can a Costas loop. https://ipnpr.jpl.nasa.gov/progress_report/42-128/128B.pdf
milstar: 3.2.1 Direct Modulation, Residual Carrier, Bi-f From a spectrum bandwidth perspective, direct modulation with a Bi-f format is a compromise between direct modulation with an NRZ format and a conventional subcarrier telemetry system. It places the modulated data sidebands closer to the RF carrier while providing a null in the data's frequency spectrum at the RF carrier's frequency. Figure 3-1 (c) shows the PCM/PM/ Bi-f spectrum, which ensures that the carrier will be easily distinguishable from the surrounding data sidebands. The bandwidth advantage of direct modulation schemes is readily apparent in this figure. https://deepspace.jpl.nasa.gov/files/phase1.pdf Sometimes called Manchester modulation, a Bi-f format is formed by the modulo-2 addition of each data symbol with a squarewave clock whose period is equal to that of a data symbol. In addition to moving the data's spectrum away from the RF carrier's frequency, Bi-f modulation also ensures RF carrier phase transitions during each data symbol. With random data, this modulation scheme produces a spectrum with a clearly discernable RF carrier component and a [(sin4 x)/(x)2 ] distribution with peaks at about ± 0.75 Rs (Rs = symbol frequency, fs) due to the modulation. A null in the data's spectrum will lie at the RF carrier's frequency, fc. Additional nulls, on either side of fc will lie at ± 2 fs, ± 4 fs, ± 6 fs, etc. Figure 3-4 shows the spectrum bandwidth at various levels of power containment. For a modulation index, m, of 1.2 radians, Required Bandwidths of 2.5 Rs and 5 Rs are needed for 90% and 95% power containment respectively. A summary of the findings will be found in Table 3-2, columns 2 and 3. Direct Bi-f modulation is useful when bandwidth conservation is important and the modulated symbol rate is sufficient to ensure that the level of data sideband power, falling in the phase locked loop's bandwidth, is sufficiently low. This modulation scheme should find broad application in future missions having low or moderate data rates or where a stable carrier reference frequency is required. Despite this lack of information, some simple observations can be made. Generally, the larger the frequency spectrum's width, the less the susceptibility to in-band interference. This results from the logical assumption that individual interference bursts tend to be concentrated in narrow frequency ranges. Therefore, the larger the width of the transmitted data's frequency spectrum, the less susceptible it is to interference in a portion of that band. This "rule" is one reason why squarewave subcarriers have a distinct advantage over some of the other modulation techniques. Of course, other methods such as high rate convolutional coding and spread spectrum modulation can be used to achieve the same result with any of the direct modulation methods. However, the important point is that restricting the frequency spectrum's width increases the susceptibility to in-band interference.
milstar: https://arxiv.org/ftp/arxiv/papers/0709/0709.4288.pdf 100 kilobit sec 750 mln km figure 8
milstar: The X-band uplink signal (Figure 1) to be received is generated by an earth station in the Deep Space Network (DSN) and nominally consists of several components; 1) a phase-modulated residual carrier, 2) a 16 KHz sinusoidal subcarrier that is binary phase-shift-key (BPSK) modulated with uplink command data, and 3) sequential or pseudorandom noise (PN) modulated ranging tones. The residual carrier is used by Uplink Receiver to lock onto the composite signal and track out Doppler effects, while also providing navigation data critical to the noncoherent navigation system. The data modulated subcarrier is used by the command detection unit to lock onto and demodulate uplink command data while tracking out Doppler effects. The ranging tones are demodulated or regenerated and provided to the Downlink Card for use in the turnaround ranging system. https://ieeexplore.ieee.org/document/1367923 The carrier tracking loop is a long loop, type I phase-locked loop (PLL) designed to track Doppler-induced changes in frequency of the X-band uplink carrier received at the spacecraft. The loop filter, which is based on an active imperfect integrator and resides in the digital subsystem, causes the carrier tracking loop to approximate type II PLL behavior
milstar: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=931697
milstar: Convolutional Codes BPSK Modulation with Viterbi Decoder https://link.springer.com/chapter/10.1007/978-3-319-64719-7_23
milstar: https://deepspace.jpl.nasa.gov/dsndocs/810-005/208/208B.pdf
milstar: https://descanso.jpl.nasa.gov/monograph/series3/complete1.pdf
milstar: http://the-eye.eu/public/Books/Electronic%20Archive/mar2000pg100.pdf
milstar: https://pdfs.semanticscholar.org/f032/bc3474cc45d2e4cb7612549916b9caa99ec8.pdf
milstar: https://ipnpr.jpl.nasa.gov/progress_report/42-151/151J.pdf
milstar: Из рисунка 13 наглядно следует, что при перепутывании всех бит информации на выходе дифференциального декодера информация не искажается (за исключением первого бита, показанного красным), и в этом несомненное преимущество DBPSK, которое позволяет существенно упростить передающие и приемные устройства. Но нужно также сказать и о недостатках дифференциального кодирования. Главным недостатком DBPSK по сравнению с BPSK является более низкая помехоустойчивость, поскольку ошибки приема размножаются на этапе декодирования. Рассмотрим пример. Пусть исходный поток равен 011100101, закодированный поток равен 010111001. Пусть при приеме четвертый бит закодированного потока был принят с ошибкой, тогда на входе декодера будет 010101001. И в результате декодирования целых два бита будут декодированы с ошибкой (смотри рисунок 14). http://ru.dsplib.org/content/signal_bpsk/signal_bpsk.html
milstar: Coded RS+(7,1/2) convolutional code (c.c.) BPSKf NRZ rectangular 0.26 0.021 2.6 No 0.0 0.021 2.6 https://ipnpr.jpl.nasa.gov/progress_report/42-151/151J.pdf ############### http://jeffareid.net/misc/msc-21834.pdf What is the purpose of error correction coding? The purpose of error correction coding might be expressed in a multitude of ways such as (1) increasing the reliability of data communications or data storage over a noisy channel, (2) controlling errors so reliable reproduction of data can be obtained, (3) increasing the overall systemts signal-to-noise energy ratio (SNR), (4) reducing noise effects within a system and/or (5) meeting the demand for efficient, reliable, high perfo~ance, and economically practical digital data transmission and storage systems. All of these subjective terms can be defined for a particular application. The Reed-Solomon (RS) codes have been finding widespread applications ever since the 1977 Voyagerls deep space communications system. At the time of Voyager*s launch, efficient encoders existed, but accurate decoding methods were not even available! The Jet Propulsion Laboratory (JPL) scientists and engineers gambled that by the time Voyager II would reach Ura:nusin 1986, decoding algorithms and equipment would be both available and perfected. They were correct! Voyager’s communications systlemwas able to obtain a data rate of 21,600 bits per second from 2 billion miles away with a received signal energy 100 billion times weaker than a common wrist watch battery!
milstar: When I generally think of communications systems, I usually think of them as a function of only two parameters: signal-to-noise ratio and bandwidth. If we compare an uncoded system with a coded system for the same information rate (i.e., bits per second), the coded system will have a higher symbol rate at the output of the encoder (i.e., s@ols per second) than the uncoded system. In other words, the coded system spreads its signal energy over more transmitted symbols within the same bandwidth. The energy associated with each coded symbol is less than the uncoded symbol. Therefore, the symbol error rate of a coded system will be greater than an uncoded system. If the decoding of an error correction code has a better ..——.. ———-— ______ --? l-- 3jS(~-21XS.$ performance than an uncoded system (i.e., the coded system having redundancy overcomes the higher s@ol error rate better than the uncoded system with its lower symbol error rate without having redundancy) at fairly high-to-low bit error rate regions, then we obtain a coding gain in signal-to-noise energy. If the resultant code has a worse performance, then it is a bad error correction code. An error correction coding system will have worse performance at very high bit error rates than an uncoded system. However, in an error correction system we can fairly easily adjust the coding gain to whatever we need for the operating regions. 1 In summary, error correction coding may not require any additional antenna power or bandwidth; a coding gain can be obtained over the same bandwidth by either decreasing the information rate or by modulation techniques (which are usually more complicated and are designed to spread the available signal energy over more symbols). Error correction coding can even cause the overall power and bandwidth considerations to be relaxed. Referring back to our case of the ~Ion~~and http://jeffareid.net/misc/msc-21834.pdf
milstar: Typically, there were three situations in which the tradition ruled a mandatory usage of noncoherent or differentially coherent techniques ######################################################################################## in order to obtain high performance communications: 1) in the presence of jamming, ########################## 2) with short packets, ##################### and 3) in land mobile wireless communications. ############################# https://ieeexplore.ieee.org/document/6618624
milstar: From the communication channel and implementation aspects of communications, the transmission environment may be sufficiently degraded that introduces practical difficulties in acquiring and tracking a coherent demodulation reference signal. Coherent receivers require exact knowledge of the channel phase for optimum performance. Due to the difficult task of estimating the channel phase, non-coherent as well as differential detection is an attractive alternative to coherent detection. ################################################################################################# A conventional differential detector uses the signal received in the previous symbol interval as a phase reference for the received signal in the current interval. As long as the phase distortion introduced by channel varies slowly relative to the symbol rate, conventional differential detection will work quite well. ############################################################################################# This assumption is not always true, ########################### and, in addition, differentially coherent detection is based on the premise that there is no intersymbol interference (ISI) in the received signal. ################################################################## https://ieeexplore.ieee.org/document/6618624/figures#figures
milstar: https://www.nhk.or.jp/strl/publica/bt/bt14/pdf/le0014.pdf
milstar: Incoherent detection is frequently used in terrestrial mobile transmissions since large fluctuations in amplitude due to fading effects make it difficult to recover the carrier. #################################### Here, however, because the signal itself, which includes noise and distortion, is used as the reference phase in incoherent detection, the bit error characteristics are worse than those of coherent detection. https://www.nhk.or.jp/strl/publica/bt/bt14/pdf/le0014.pdf
milstar: https://pdfs.semanticscholar.org/f5f9/23a42826ef493e88ff6cd13d21ce28644bdc.pdf 18.3 Mobile-Radio Propagation: Large-Scale Fading and SmallScale Fading
milstar: https://www.gaussianwaves.com/2011/05/ebn0-vs-ber-for-bpsk-over-rayleigh-channel-and-awgn-channel-2/ https://www.gaussianwaves.com/2010/04/performance-comparison-of-digital-modulation-techniques-2/
milstar: https://cyberleninka.ru/article/v/modelnoe-issledovanie-pomehoustoychivosti-priema-radiosignalov-s-qpsk-bpsk-8psk-i-dbpsk
milstar: «Самое главное – это создание системы управления и системы неубиваемой связи», – цитирует вице-премьера Дмитрия Рогозина ТАСС.
milstar: https://megapredmet.ru/1-20464.html Методы манипуляции Цифровой радиосвязи Учебное пособие для студентов радиотехнических специальностей Разработчик: заведующий кафедрой СРС, профессор Мелихов С.В. Томск ‑ 2014 Содержание Содержание 1. Дифференциальная (относительная) бинарная (двоичная) фазовая манипуляция – Differential Binary Phase Shift Keying (DBPSK)............................................................................................. 3 1.1.Передатчик DBPSK‑радиосигнала................................................................................ 3 1.2. Когерентная демодуляция DBPSK–радиосигнала..................................................... 7 1.3. Блок восстановления несущей частоты (БВНЧ). Фазовая неоднозначность при формировании опорного колебания............................................................................................................... 9 1.4. Блок восстановления тактовой частоты (БВТЧ)....................................................... 10 1.5. Схема Костаса для квазикогерентной демодуляции DBPSK-радиосигнала........ 12 1.6. Некогерентная демодуляция DBPSK–радиосигнала............................................... 13 При невозможности формирования когерентного опорного колебания, например из‑за значительных фазовых возмущений, вносимых средой распространения радиоволн или аппаратурой приемо-передающего тракта, применяется некогерентная демодуляция. Как уже отмечалось, применение некогерентной демодуляции возможно только при дифференциальном кодировании информационной последовательности в передатчике.
milstar: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=3383&context=smallsat
milstar: https://pdfs.semanticscholar.org/5873/693c56d04cd0a0a44ae6c5f3a15f214790ed.pdf Convolution coding, BPSK, QPSK, QAM-16, DS-CDMA, maximal ratio combining
milstar: Non-coherent modulations can be used by a communication system that does not maintain a phase lock between transmitter and receiver, or have knowledge of the amplitude change of the transmitted symbol caused by the channel. This means that the received symbols are rotated and scaled arbitrarily compared to the transmitted symbol. Therefore the ASK, PSK, or QAM modulations cannot be used because they require the received symbol phase and amplitude to be very close to that transmitted phase and amplitude. The solution is to use differential PSK (DPSK) or differential APSK (DAPSK) modulation. Differential modulations encode the transmitted information to a phase, or phase and amplitude change from one transmitted symbol to the next. This encoding introduces memory to the signal, because transmitted symbols depend on previous symbols. As a consequence, the demodulator has to consider two consecutive symbols when making decisions. The next two sections describe these two modulation methods. http://vig.pearsoned.com/samplechapter/0672321572.pdf The performance loss of DPSK compared to coherent modulation varies with the size of the modulation [11], for DBPSK it is between 1-2dB ############################# the system that does not use channel coding has to spend 5.5dB more energy for each FIGURE 3.11 transmitted bit than the system that uses channel coding
milstar: http://vig.pearsoned.com/samplechapter/0672321572.pdf The performance of channel codes is ultimately limited by the channel capacity formula, Equation 3.1. After about 50 years of research, Turbo-codes [7] have finally emerged as a class of codes that can approach the ultimate limit in performance. Another innovation, and a very active research area, are Low Density Parity Check (LDPC) codes, which also have performance very close to the capacity.
milstar: it uses Recursive codes and iterative soft decoders. Recursive codes for making short constraint length in convolution codes and iterative soft decoder is for improving estimated received message by reapplying the decoded words to the outer and repeats it many times until all reduce below the threshold point. It’s performance depends upon S/N ratio written below: If S/N ratio is low the iterative decoding is worse. If S/N ratio is in between low-medium then iterative decoding is very effective. If S/N ratio is high then iterative decoding converses in few iterations. Overall its performance increases as S/N ratio increases. In Turbo Codes bit error rate (BER) is achieved even for low S/N ratio as errors flow moderate. In Turbo codes high value of Eb / No is achieved. Actually Turbo Codes are Shannon limit error correction 2.2 DBPSK Differential Binary Phase Shift Keying is a signaling technique that conveys data by changing the phase of the carrier wave. It eliminates the need for phase synchronization of the coherent receiver with PSK. In this present value is depending upon past value so it determines the difference between ‘0’ and ‘1’. In DBPSK, input must be a discrete time binary valued signal https://www.researchgate.net/publication/281373596_TURBO_CODES_DBPSK_versus_QPSK
milstar: Turbo codes were recently proposed by Berrou, Glavieux, and Thitimajshima [2] as a remarkable step forward in high-gain, low-complexity coding. It has been claimed these codes achieve near-Shannon-limit error correction performance with relatively simple component codes and large interleavers. A required Eb/N0 of 0.7 dB was reported for a bit error rate (BER) of 10−5, using a rate 1/2 turbo code https://klevas.mif.vu.lt/~skersys/vsd/turbo/120D.pdf
milstar: Deep space exploration requires the use of powerful error correction codes, such as turbo codes [3], lower rate low-density-parity-check (LDPC) codes [4] and concatenated Reed-Solomon (RS) and convolutional codes. Since turbo codes have better performance than LDPC at low SNR [19], they have been chosen as IC. On the contrary, receiving the updated information from the inner decoder, the OC decoder, that is an LDPC code, can fully exploit its deep waterfall region and low error floor spacomm_2013_1_10_30012.pdf Concatenated Turbo/LDPC Codes for Deep Space Communications: Performance and Implementation Carlo Condo Department of Electronics and Telecommunications Politecnico di Torino Torino, Italy carlo.condo@polito.it
milstar: The DSN provides support for the turbo code specified in CCSDS Recommendation 131.0-B-1 for information block lengths (k) of 1784, 3568, 7136, 8920 bits and nominal code rates (r) of 1/2, 1/3, 1/4, and 1/6. The recommendation also permits an information block length of 16,384 bits however the encoder for this block length has not been completely specified and it is not supported by the DSN, The four supported block lengths are the same as would be required for Reed-Solomon encoding using an interleave factor (I) of 1, 2, 4, or 5. https://deepspace.jpl.nasa.gov/dsndocs/810-005/208/208B.pdf
milstar: Low-Density Parity-check (LDPC) Codes Low-Density Parity-Check (LDPC) codes have been developed that provide neartheoretical limit performance at high code rates to complement the similar performance provided by Turbo codes at low code rates. They promise to be especially useful in applications where the bandwidth required to use a Turbo code is not available or would complicate spacecraft equipment design https://deepspace.jpl.nasa.gov/dsndocs/810-005/208/208B.pdf
milstar: http://www.comtechefdata.com/files/appnotes-pdf/The%20Case%20for%20Turbo%20Product%20Coding%20in%20Satellite%20Communications.pdf
milstar: BPSK Rate 21/44 and Rate 5/16 (Flux density reduction modes) Two further code rates - Rate 21/44 BPSK (very close to Rate 1/2) and Rate 5/16 BPSK (very close to Rate 1/3) were then added for a military customer ================================================== and delivered in June 2000. These two rates were developed to address an entirely different case, namely that of transmission from very small antennas, with limited transmitter power. For a dish antenna, the gain is directly proportional to its area, and the lower the gain, the less directional the antenna becomes. Thus, in satellite transmission, even though the dish may be perfectly pointed at the desired satellite, if the beamwidth is wide enough, adjacent satellites will also be illuminated. This is a potential source of interference, and for this reason the ITU (International Telecommunications Union) place strict limits on the power spectral density (also referred to as flux density) of signals arriving at adjacent satellites. One obvious method to reduce the level is to spread the transmitted signal over as wide a bandwidth as possible. In the past, this has sometimes been achieved using Spread Spectrum modulation, but at the expense of demodulator complexity. However, by using BPSK modulation, and low FEC code rates (down to Rate 1/3, for example) the power spectral density may be reduced. Taking Rate 1/2 QPSK as a baseline, moving to Rate 5/16 BPSK Turbo Product Coding gives a reduction in power spectral density of 5 dB. Furthermore, the increased coding gain of this FEC method allows a further reduction in transmitter power. Using Rate 1/2 Viterbi with concatenated Reed-Solomon as a baseline example, Rate 5/16 provides 1.5 - 2.0 dB improvement in coding gain. Putting these two factors together yields an overall reduction in power spectral density of approximately 7 dB. This simultaneously permits a smaller antenna, and reduced transmitter power. The disadvantage is the increased spectral occupancy of the carrier, and it will depend on the particular satellite operator to determine if this poses a severe economic problem. http://www.comtechefdata.com/files/appnotes-pdf/The%20Case%20for%20Turbo%20Product%20Coding%20in%20Satellite%20Communications.pdf
milstar: https://pdfs.semanticscholar.org/eb38/48e2ba091a7445ef11acc084154062cf6d94.pdf shown. DPSK was shown to be an attractive robust alternative to coherent BPSK since only 1.5-4 dB energy penalties are incurred. For FSK, the energy penalty versus coherent BPSK was much larger as predicted by capacity analysis. The use of DPSK and noncoherent FSK is more strongly motivated on fading channels where coherent phase tracking is problematic. This application remains under s
milstar: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660001034.pdf
milstar: C / N dB = 10 log (Eb/No) + 10 log (R / B) R information rate in bits per second; B channel bandwidth in Hertz; C total carrier power N total noise power in the bandwidth.
milstar: https://klevas.mif.vu.lt/~skersys/vsd/turbo/turbo-codec-qpsk-modem.pdf This proof–of–concept modem achieves a BER of 10–10 at an SNR of 2 dB (Rate 1/2 FEC) for data rates from 64 kbit/s up to 2,048 kbit/s using serial concatenated convolutional codes. Rate 1/2 and Rate 3/4 coding can be selected.
milstar: http://www.advantechwireless.com/wp-content/uploads/WP-Turbo-FEC-132191.pdf
milstar: LDR Payload: The LDR payload offers nearly 200 user channels and relays coded teletype and voice messages at data rates of 75 to 2400 bits per second. https://space.skyrocket.de/doc_sdat/milstar-1.htm To perform these complex functions, the MDR digital processing subsystem relies on 14 custom application-specific integrated circuits and 397 large-scale integrated (LSI) circuits, all fabricated in CMOS technology. This figure represents a decrease of 37 percent from the 630 custom LSI circuits required for each LDR payload. https://www.northropgrumman.com/Capabilities/MilstarPayloads/Pages/default.aspx the Milstar MDR payload can push data rates to 1.544 megabits per second. Or, by switching to lower data rates, it can receive signals from small, low-power ground terminals. Or it can operate at some intermediate combination of data rate and terminal power — all without sacrificing anti-jam performance.
milstar: The DSCS III satellite has six independent transponders (one per channel), three uplink antennas to receive signals from earth terminals, and five downlink antennas which retransmit the signals back to earth. The signal transmitted by the ground terminal is received at the satellite in the 7.9 to 8.4 GHz frequency range where it is amplified, down converted, and retransmitted in the 7.25 to 7.75 GHz frequency range. The DSCS III will replace the DSCS II satellites over a period of time. At this time, both are in orbit. The DSCS IIIs have some improvements over the DSCS IIs such as increased hardening, a nulling capability (antijam function), and more transponders. However, the DSCS III only has one NC gimballed dish antenna (GDA) http://www.bits.de/NRANEU/others/amd-us-archive/FM24-11%2890%29.pdf
milstar: 2 MARK RICE, TIM GILES, VOON WONG, ISMAIL SHAKEEL AND DOUG MEIN GROUND MOBILE WGS SATCOM FOR DISADVANTAGED TERMINALS operate at 7.9−8.4 GHz uplinks and 7.25−7.75 GHz downlinks, while the Ka-band beams operate at 30−31 GHz uplinks and 20.2−21.2 GHz downlinks, all in government allocated spectrum. Cross-banding is possible with WGS: X-band users can communicate with Ka-band users. https://www.researchgate.net/publication/228680490_Ground_Mobile_WGS_Satcom_for_Disadvantaged_Terminals MILCIS2009, CANBERRA, 10-12 NOVEMBER 2009 3 locations, 0.1% rain attenuation at Ka band has been found to vary from 20 dB to more than 50 dB, compared to only 0.4 dB to 4 dB at X band [4]
milstar: Defense officials have said DoD does not intent to replace most of its 17,000 satellite terminals. https://spacenews.com/commercial-satellite-roaming-possible-with-existing-military-terminals-experiment-shows/
milstar: https://www.rockwellcollins.com/~/media/Files/Unsecure/Products/Product%20Brochures/Communcation%20and%20Networks/SATCOM/Dket/DKET%20data%20sheet.aspx IF frequency X 950-1450 mhz Ku 950-1700 mhz Ka 1000-2000 mhz Applications FDMA, TDMA voice, video, data Modulation BPSK, QPSK, O QPSK, 8 PSK, 16 QAM Downlink frequency 7.25 - 7.75 GHz 10.95 - 12.75 GHz 20.20 - 21.20 GHz
milstar: На большинстве исследованных трасс имели место условия распространения, описываемые моделью тропосферного канала с релеевскими замираниями #################### https://pandia.ru/text/77/132/788.php
milstar: https://rit.informost.ru/rit/1-2007/rit-1-2007-50-56.pdf
milstar: https://army.informost.ru/2010/sbornik/3-70.pdf Предназначена для замены выработавших свой ресурс станций Р-410 и Р-412, для использования в разрабатываемых перспективных системах связи МО РФ на интервалах связи между объектами 100– 200 км и более https://army.informost.ru/2010/sbornik/3-70.pdf
milstar: https://pdfs.semanticscholar.org/cc7d/4930804a07b1cbf52d47e7d083eec9eee0ea.pdf
milstar: http://dsp7.ee.uct.ac.za/~nicolls/lectures/eee482f/04_chancap_2up.pdf
milstar: Unconstrained Shannon Limit for AWGN channel https://www.gaussianwaves.com/2008/04/channel-capacity/ https://www.ingenu.com/2016/07/back-to-basics-the-shannon-hartley-theorem/ Letting C/B=η (the spectral efficiency in (bits/seconds/Hz)), Here C is the maximum capacity of the channel in bits/second otherwise called Shannon’s capacity limit for the given channel, B is the bandwidth of the channel ##################### 0 bit/sek Eb/No = ln 2 =0.693147 ...= -1.6 db
milstar: BER Performance of OFDM-BPSK and -QPSK Over Generalized Gamma Fading Channel https://pdfs.semanticscholar.org/60f4/afa821965f0db67b78fddbbca34543979d1b.pdf
milstar: https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1053703
milstar: http://www.et.byu.edu/~beard/classes/ece682rweb/www-randy/files/goodpaper4-DivsalarSimon.pdf
milstar: . For general time-varying Rayleigh fading, however, ML-MSDD with low complexity is still an unsolved problem http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.83.3496&rep=rep1&type=pdf
milstar: Fast fading is the case when any or both of the transmitting or receiving ############## nd is moving with some relative speed to the other. As the signal is transmitted rough multipath characteristic, the movement in the surrounding objects of the transitter/receiver also causes fast fading https://core.ac.uk/download/pdf/61799926.pdf The inter symbol interference is independent of the signal to noise ratio, because as the power of the signal is increased the ISI also gets increased The error floor starts to dominate for values of fdTb > 0.001, where Tb is the time interval for one bit t fd Dopller shift
milstar: https://trs.jpl.nasa.gov/bitstream/handle/2014/43454/11-1691_A1b.pdf?sequence=1
milstar: https://pdfs.semanticscholar.org/929b/74ef14d842ca8be7d63fe88282c7f4d9e54d.pdf The BER performance for BPSK in the average channel is still the best among the three, and a/4 DQPSK performs better than FSK. Specifically, at BER = 0.01, BPSK requires an E, /No = 12.1 dB, whereas for the same error performance, a/4 DQPSK requires 15.2 dB, and FSK requires 18.3 dB. The theoretical BER performance of BPSK in a Rayleigh fading channel is also shown in the figure for comparison The theoretical E, /No required for BPSK in a Rayleigh fading channel is 34.1 dB.
milstar: s. For example, in a narrowband 30-kHz channel (such as that used in the North American TDMA cellular standard IS-136) with a Doppler spread of 100 Hz, the coherence time Tc is roughly 80 symbols and in this case the channel can be estimated with minimal overhead expended in the pilot https://web.stanford.edu/~dntse/Chapters_PDF/Fundamentals_Wireless_Communication_chapter3.pdf
milstar: While the coherent approach to signal detection based on the separation of the detection problem into explicit channel estimation and signal detection is most commonly deployed in digital transmission systems, the noncoherent approach appears to be more natural, since the receiver is usually primarily interested in the transmitted information, but not in information about the current state of the channel. Furthermore, noncoherent detection schemes are more robust in rapidly varying transmission scenarios than their coherent counterparts, which rely on the accuracy of the externally obtained channel estimates [3]. They are therefore particularly apt for 1. discontinuous transmission, where coherent transmission would require a relatively large portion of pilot symbols for accurate channel estimation, 2. systems with low cost, high frequency components, where e.g. strong fluctuations of phase and frequency of local oscillators may occur, and 3. systems with time–variant interferences https://pdfs.semanticscholar.org/f9ab/7951ae721b3937032e998d2814810d86e03a.pdf
milstar: Values of JvT ranging from 0.001 to 0.1 are understood to mean very slow to very fast fading respectively. Figures 1.2 and 1.3 show simulated fading envelopes u(t) for values of JvT of 0.01 and 0.1 respectively. The typical behaviour of the amplitude of the Rayleigh fading process is an oscillatory motion with sudden rapid deep fades occurring at almost regular intervals. The depth of the fades can easily be as much as 20 dB and these are the cause of most error events in a communication system. https://core.ac.uk/download/pdf/35466351.pdf
milstar: Conventional differential detection is known to perform poorly on the Rayleigh fading channel due to the fluctuation of the channel state with time. The worles by Ho and Fung [32] and Divsalar and Simon introduce the method of multiple symbol differential detection (MSDD), a technique where a decision is made on a sequence of symbols, rather than on a per symbol basis. MSDD vastly improves performance over conventional differential detection even when decoding over just a few symbols) by exploiting knowledge of the correlation of the fading process. MSDD works best when the channel fading is highly correlated - a contradicting requirement to diversity. We circumvent this problem by interleaving blocks of symbols over which the MSDD is computed, and constructing a multi-level code over these blocks of symbols. The resulting multi-level codes achieve high coding gains and can perform very well in relatively fast fading environments, that is, values of iDT as high as 0.1. ############ https://core.ac.uk/download/pdf/35466351.pdf
milstar: CDMA outperforms FDMA and TDMA as regards to combating fading, capacity and frequency https://www.ee.iitb.ac.in/~comlab/seminar/ashwini1.pdf • Low mobility Users move at walking speeds (3 km/hr, Rayleigh). • High mobility Users move at 30 km/hr, Rayleigh. https://web.stanford.edu/~dntse/Chapters_PDF/Fundamentals_Wireless_Communication_chapter6.pdf
milstar: . When one examines the numerical results in [1], one observes that as the ratio of data rate (R = 1/T) to loop bandwidth (BL) increases, the optimum fractional allocation of power to the carrier, i.e., m2 4 = Pc/Pt, diminishes. In fact, defining this ratio by δ 4 = R/BL = 1/BLT, then for values of δ on the order of a few hundred (which is typical of most system designs), the fraction of total power allocated to the carrier that yields the minimum average error probability is on the order of m2 = 0.1 or less over a large range of total signal-tonoise ratio (SNR), Rt = PtT /N0. This trend suggests the possibility of using a suppressed-carrier system, i.e., m2 = 0, which itself requires replacing the PLL with a loop capable of tracking a fully suppressed carrier, e.g., a Costas loop https://pdfs.semanticscholar.org/26cc/24d7be6fdf82b87fc22316371b5e590d536c.pdf
milstar: . Indeed, since as mentioned above, the Costas loop requires a larger loop SNR than does the PLL to yield a given tracking accuracy, the same is true in terms of the loop SNR required to maintain lock (herein referred to as the threshold value of loop SNR.) Thus, depending on the threshold SNR values decided upon for the two loops (to be discussed later on), there will exist a region of system parameters where one would be forced to employ a residual rather than a suppressed-carrier system, since in this region the loop SNR of the latter is below its threshold value whereas the loop SNR of the former is still above its threshold value. The purpose of this article is to define these regions, which will then clearly spell out for the system designer when to choose the suppressed-carrier option over the residual carrier one or vice versa. In the next section, we present the theoretical background necessary to establish these regions.
milstar: https://ieeexplore.ieee.org/document/950321 When the order of diversity L increases, we can notice a great improvement of the performance but this comes at the expense of a more complicated system and a slower transmission rate (for a fixed transmission bandwidth).
milstar: http://www.ijsrp.org/research_paper_jun2012/ijsrp-June-2012-100.pdf
milstar: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=483276 https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1292540
milstar: Direct modulation schemes are inherently more bandwidth efficient than those employing subcarriers. This is due, in part, to the way that the ITU defined Occupied Bandwidth to be that span of frequencies, covered by the modulated signal, which excludes only the lower 0.5% and the upper 0.5% of the transmitted power. Thus, large frequency gaps between the RF carrier and the subcarrier are included in the Occupied Bandwidth calculation despite the fact that there is no significant modulation sideband energy in large portions of these frequency gaps. https://deepspace.jpl.nasa.gov/files/phase1.pdf
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: 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: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=544468 we obtained simulated estimates for the symbol error probabilities of synchronous and asynchronous FHSS-MA networks using MFSK modulation with noncoherent detection for M = 2,4,8,16,32, and 64 with and without independent Rayleigh fading. An appropriately normalized throughput measure was defined in order to make a fair comparison between the performance of systems employing different modulation orders. Modeling the channel as an Mary symmetric memoryless channel, it was found that there exists an optimum value of M that should be used to obtain the largest possible throughput. It was also observed that the anomalies caused by the (M - 1)/M-bound noticed in [l] for M = 2 are also present for the cases for M larger than two.
milstar: https://www.researchgate.net/publication/3161194_Maximum_throughput_of_FHSS_multiple-access_networks_using_MFSK_modulation
milstar: https://www.wirelessinnovation.org/assets/Proceedings/2011/2011-6a-harris%20chen.pdf
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