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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
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
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