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Results for “PHASE-SHIFT KEYING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1985

Shuttle S-band communications technical concepts

Using the S-band communications system, shuttle orbiter can communicate directly with the Earth via the Ground Spaceflight Tracking and Data Network (GSTDN) or via the Tracking and Data Relay Satellite System (TDRSS). The S-band frequencies provide the primary links for direct Earth and TDRSS communications during all launch and entry/landing phases of shuttle missions. On orbit, S-band links are used when TDRSS Ku-band is not available, when conditions require orbiter attitudes unfavorable to Ku-band communications, or when the payload bay doors are closed. the S-band communications functional requirements, the orbiter hardware configuration, and the NASA S-band communications network are described. The requirements and implementation concepts which resulted in techniques for shuttle S-band hardware development discussed include: (1) digital voice delta modulation; (2) convolutional coding/Viterbi decoding; (3) critical modulation index for phase modulation using a Costas loop (phase-shift keying) receiver; (4) optimum digital data modulation parameters for continuous-wave frequency modulation; (5) intermodulation effects of subcarrier ranging and time-division multiplexing data channels; (6) radiofrequency coverage; and (7) despreading techniques under poor signal-to-noise conditions. Channel performance is reviewed.

Seyl, J. W.↗
NASA NTRS1988

An 8-DPSK TCM modem for MSAT-X

This paper describes the real-time digital implementation of an 8-differentiated phase-shift keying (DPSK) trellis-coded modulation (TCM) modem for operation on an L-band, 5 kHz wide, land mobile satellite (LMS) channel. The modem architecture as well as some of the signal processing techniques employed in the modem to combat the LMS channel impairments are described, and the modem performance over the fading channel is presented.

Jedrey, Thomas C.↗
NASA NTRS1987

False lock performance in polarity-type Costas receivers in the presence of periodic data patterns

The authors address the false-lock performance of receivers which use polarity-type Costas loops for the carrier recovery of unbalanced quadrature phase-shift keyed (QPSK), asynchronous QPSK or binary PSK (BPSK) signals in the presence of periodic data patterns. The potential false-lock frequencies are first identified. Expressions for both true-lock and false-lock components are also derived, thereby allowing numerical evaluation of various key parameters for cases of practical interest.

Wang, James June-Ming↗
NASA NTRS1989

Generalized Multiple-Trellis-Coded Modulation

Generalized multiple-trellis-coded modulation technique combines multiple trellis coding (more than one channel symbol per trellis branch transmitted) with symmetrical M-ary phase-shift keying. Transmitter puts out k M-ary code symbols for every b input binary symbols. Throughout performances, b/k, of trellis-coded multiple-phase-shift-keying channels compared with computational cutoff rates, R0, of multiple-phase-shift keying. Performs better than conventional trellis-coded modulation technique, with no increase in complexity.

Divsalar, D.↗
NASA NTRS1988

A lower bound on the minimum Euclidean distance of trellis-coded modulation schemes

A lower bound on the minimum free Euclidean distance of trellis-coded modulation (TCM) is derived that guarantees the existence of good TCM codes of any complexity. The bound is used to compare trellis codes combined with phase-shift keying, pulse amplitude modulation, and quadrature amplitude-shift keying modulation. This random coding bound is the first lower bound on the free distance of trellis codes, is tighter than any upper bound for large constraint lengths, and predicts the asymptotic performance of TCM when the complexity of the code becomes large. The bound can be used with any code rate and any modulation scheme and shows that the free distance increases linearly with the constraint length for large values of the constraint length.

Rouanne, Marc↗
NASA NTRS1990

Trellis-coded multidimensional phase modulation

A 2L-dimensional multiple phase-shift keyed (MPSK) (L x MPSK) signal set is obtained by forming the Cartesian product of L two-dimensional MPSK signal sets. A systematic approach to partitioning L x MPSK signal sets that is based on block coding is used. An encoder system approach is developed. It incorporates the design of a differential precoder, a systematic convolutional encoder, and a signal set mapper. Trellis-coded L x 4PSK, L x 8PSK, and L x 16PSK modulation schemes are found for L = 1-4 and a variety of code rates and decoder complexities, many of which are fully transparent to discrete phase rotations of the signal set. The new codes achieve asymptotic coding gains up to 5.85 dB.

Pietrobon, Steven S.↗
NASA NTRS1990

A novel demodulator/detector for digital and analog signals on LMR channels

The design, implementation, and performance of an all-digital demodulator/detector suitable for differentially encoded phase-shift keying (DPSK), continuous-phase frequency-shift keying (CPFSK), frequency-shift keying (FSK), and analog FM are discussed. In this demodulator/detector, two detectors, one noncoherent and another differentially coherent, operate simultaneously to provide data detection and automatic frequency control (AFC). Test results indicate that the system provides improved performance over the conventional analog quadrature detector for two-period raised-cosine (2RC) CPFSK modulation in additive white Gaussian noise (AWGN) and Rayleigh fading channels. Being all-digital, the demodulator/detector is well suited for integrated circuit implementation. In addition, the system performs as well as the analog quadrature detector for analog FM voice transmissions, thereby maintaining full compatibility with analog land mobile radio (LMR) transmissions.

Saulnier, Gary J.↗
NASA NTRS1990

DS/LPI autocorrelation detection in noise plus random-tone interference

An analysis is presented of a frequency-noncoherent, two-lag autocorrelation statistic for the wideband detection of random binary phase-shift keying (BPSK) signals in noise plus random multitone interference. It is shown that this detector is quite robust to the presence or absence of interference and its specific parameter values contrary to an energy detector. The rule assumes knowledge of the data rate and the active scenario under H0. The purpose of the paper is to promote the real-time autocorrelation domain and its samples (lags) as a viable approach for detecting random signals in dense environments.

Hinedi, Sami↗
NASA NTRS1990

Trellis coded modulation for transmission over fading mobile satellite channel

The combination of trellis coding and multiple phase-shift keyed (MPSK) signaling with asymmetry (nonuniform spacing) to the signal set is disclosed with regard to its suitability for a fading mobile satellite communication channel. For MPSK signaling, introducing nonuniformity in the phase spacing between signal points provides an improvement in performance over that achievable with trellis codes symmetric MPSK signaling, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Block interleaving may be used to reduce error and pilot tone(s) may be used for improving the error correction performance of the trellis decoder in the presence of channel fading.

Simon, Marvin K.↗
NASA NTRS1990

The performance of trellis-coded MDPSK with multiple symbol detection

The idea of using a multiple (more than two) symbol observation interval to improve error probability performance is applied to differential detection of trellis-coded multiple phase-shift keying (MPSK) over an additive white Gaussian noise (AWGN) channel. An equivalent Euclidean distance measure per trellis branch is determined for this detection scheme. This is used to define an augmented (larger multiplicity) trellis code whose distance measure is the conventional squared Euclidean distance typical of conventional trellis-coded modulation on the AWGN. Such an augmented multiple trellis code is a convenient mathematical tool for simplifying the analysis. Results are obtained by a combination of analysis (upper Chernoff bounds and asymptotic large-SNR approximations) and computer simulation. It is shown that only a slight increase (e.g., one symbol) in the length of the observation interval will provide a significant improvement in bit error probability performance.

Divsalar, Dariush↗
NASA NTRS1991

Pi/4-QPSK modems for satellite sound/data broadcast systems

The use of pi/4-quadrature phase-shift keying (QPSK) modems for satellite sound broadcast systems (SSBS) broadcasting to mobile or portable receivers is proposed. Three different differential detectors (including the FM-discriminator followed by integrate-sample-and-dump filter) and a novel coherent detector are discussed. The degradation caused by the frequency offset between the local oscillator (LO) and the unmodulated carrier (CR) in the baseband differential detector is studied. The performance of both coherently and differentially detected pi/4-QPSK in a Gaussian channel is also studied. It is shown that with a frequency offset of more than 3 percent of the symbol rate, the performance degradation is more than 1 dB at 0.0001. The out-of-band power of the nonlinearly amplified bandlimited pi/4-QPSK signals is reduced from -13 dB to -37 dB if a 2-dB output back-off amplifier is used instead of a hardlimiter. The performance of the pi/4-QPSK is equivalent to that of QPSK, although the pi/4-QPSK has the advantage of less spectrum restoration after nonlinear amplification. The coherent demodulator and differential decoder avoid the three-level detection and achieve the same bit-error-rate performance as DEQPSK with a simple circuit.

Liu, Chia-Liang↗
NASA NTRS1991

An improved pi/4-QPSK with nonredundant error correction for satellite mobile broadcasting

An improved pi/4-quadrature phase-shift keying (QPSK) receiver that incorporates a simple nonredundant error correction (NEC) structure is proposed for satellite and land-mobile digital broadcasting. The bit-error-rate (BER) performance of the pi/4-QPSK with NEC is analyzed and evaluated in a fast Rician fading and additive white Gaussian noise (AWGN) environment using computer simulation. It is demonstrated that with simple electronics the performance of a noncoherently detected pi/4-QPSK signal in both AWGN and fast Rician fading can be improved. When the K-factor (a ratio of average power of multipath signal to direct path power) of the Rician channel decreases, the improvement increases. An improvement of 1.2 dB could be obtained at a BER of 0.0001 in the AWGN channel. This performance gain is achieved without requiring any signal redundancy and additional bandwidth. Three types of noncoherent detection schemes of pi/4-QPSK with NEC structure, such as IF band differential detection, baseband differential detection, and FM discriminator, are discussed. It is concluded that the pi/4-QPSK with NEC is an attractive scheme for power-limited satellite land-mobile broadcasting systems.

Feher, Kamilo↗
NASA NTRS1990

Acquisition of the QPSK demodulator in the presence of interference

The acquisition behavior of the tracking and data relay satellite system (TDRSS) receiver (a quadrative phase-shift keying (QPSK) demodulator using a dither lock detector) in the presence of interference from another user has been analyzed using a simulation model. The demodulator is composed of an automatic gain control, a QPSK Costas loop, a frequency sweep unit, lock test units, and a control unit. The simulation model has been tested for the following variables: signal and interference Doppler frequencies and phase offsets (with respect to initial voltage control oscillator setup), signal-to-interference ratio (SIR), and signal I/Q power ratio. The simulation results are discussed.

Ghazvinian, Farzad↗
NASA NTRS1992

Acquisition Performances Of QPSK Carrier-Tracking Loops

Report presents comparative study of acquisition performances of several types of carrier-signal-tracking loops for reception of quadrature phase-shift keying (QPSK) signals. Loops classified into three types: maximum a-posteriori, (MAP) estimation loop, Costas cross-over loop, and generalized Costas loop. Mathematical models developed. In-phase and quadrature signals generated numerically and processed according to loop algorithms. Results show though MAP loop produces smallest squaring loss at all signal-to-noise ratios, others sometimes exhibit shorter acquisition time and greater probability of acquisition.

Hinedi, Sami M.↗
NASA NTRS1990

A Tone-Aided/Dual Vestigial Sideband (TA/DVSB) system for mobile satellite channels

Tone-aided modulation is one way of combatting the effects of multipath fading and Doppler frequency shifts. A new tone-aided modulation format for M-ary phase-shift keyed signals (MPSK) is discussed. A spectral null for the placement of the tone is created in the center of the MPSK signal by translating the upper sideband upwards in frequency by the same amount. The key element of the system is the algorithm for recombining the data sidebands in the receiver, a function that is performed by a specialized phase-locked loop (PLL). The system structure is discussed and simulation results showing the PLL acquisition performance are presented.

Saulnier, Gary J.↗