Showing papers on "Phase-shift keying published in 1976"

MSK and Offset QPSK Modulation

Abstract: Minimum shift keying (MSK) and offset keyed quadrature phase shift keying (OK-QPSK) modulation techniques are often proposed for use on nonlinear, severely band-limited communication channels because both techniques retain low sidelobe levels on such channels, while allowing efficient detection performance. A more detailed performance comparison of the two techniques on such channels is, therefore, of interest. In this paper a Markov process representation is developed which is applicable to either the MSK or OK-QPSK waveform. This representation is employed to illustrate the similarity between the modulation processes and to obtain the autocorrelations and power spectral densities of the two waveforms. This Markov process representation may be similarly employed with other modulation waveforms of the same class. The autocorrelations and power Spectral densities of MSK and offset QPSK provide initial insight to expected performance on band-limited channels. The results of a digital computer simulation are presented. The simulation compares the bit error rates (BER's) of MSK and offset QPSK on nonlinear, band-limited double-hop links such as encountered in satellite communications. The simmulation results are presented as E_{b}/N_{0} degradation with respect to ideal detection versus channel noise bandwidth. The error probability was used as a performance metric, and equal adjacent channel interference as a constraint. For the channels simulated, MSK is found to provide superior performance when the channel noise bandwidth exceeds about 1.1 times the binary data rate. For narrower bandwidths, offset QPSK provides superior performance.

Convolutional Code Performance in the Rician Fading Channel

Abstract: The performance of short constraint length convolutional codes in conjunction with binary phase-shift keyed (BPSK) modulation and Viterbi maximum likelihood decoding on the classical Rician fading channel is examined in detail. Primary interest is in the bit error probability performance as a function of E_{b}/N_{0} parameterized by the fading channel parameters. Fairly general upper bounds on bit error probability performance in the presence of fading are obtained and compared with simulation results in the two extremes of zero channel memory and infinite channel memory. The efficacy of simple block interleaving in combating the memory of the channel is thoroughly explored. Results include the effects of fading on tracking loop performance and the subsequent impact on overall coded system performance. The approach is analytical where possible; otherwise resort is made to digital computer simulation.

A Generalization of Minimum-Shift-Keying (MSK)-Type Signaling Based Upon Input Data Symbol Pulse Shaping

Abstract: In recent years, minimum-shift-keying (MSK) has gained increasing popularity as a modulation technique because of its desirable spectral properties. Quite often, the spectral concentration provided by MSK is not sufficient to meet requirements on out-of-band energy spillover. In these situations, one might apply additional input pulse shaping m such a way as to still maintain constant envelope signals. The properties of such MSK-type signals are the subject of this paper. Specific examples are included as illustrations of the theory both for the binary and M -ary cases.

Symbol Error Probabilities for M-ary CPFSK: Coherent and Noncoherent Detection

Abstract: Continuous-phase frequency shift keying (CPFSK) is discussed and theoretical predictions for symbol error probabilities are derived, where the memory inherent in the phase continuity is used to improve performance. Previously known results concluded that binary CPFSK can outperform coherently detected PSK at high SNR. New results presented here show that M -ary CPFSK outperforms more tranditionally used M -ary modulation systems. Specifically, coherently detected quaternary CPFSK with a five-symbol interval decision can outperform coherent QPSK by 3.5 dB, and octal coherent CPFSK with a three- symbol decision can outperform octal orthogonal signaling by 2.6 dB at high SNR. Results for coherently detected and noncoherently detected CPFSK are derived. These performance improvements are estimates derived from symbol error probability upper bounds. Monte Carlo simulation was performed which then verified the results.

Interference canceling method and apparatus

Abstract: Apparatus for canceling interference suitable for use in conjunction with stationary phased array antennas or transducer arrays designed for satellite or other communication systems employing N-phase PSK (Phase Shift Keying) modulation is disclosed. The techniques used in the apparatus involves processing of signals received by a main array and an auxiliary array of a phased array antenna so that an error signal is derived which is fed back to circuitry which modifies at least one signal received by the auxiliary array. The modified signal or signals are summed with the signal received by the main array so that a sum wave is generated whose interference component is minimal. The feedback circuitry exponentiates or raises the sum wave to the N th power to eliminate modulation, since the N th power of an N-phase PSK signal is a narrowband carrier. Then a term proportional to the desired signal raised to the N th power is filtered from the exponentiated sum wave and the remainder is utilized for error signal purposes. This technique operates without sacrificing bandwidth or degrading the desired signal and permits reception of signals with frequency spectra substantially overlapping one another.

Digital Signal Design Concepts for a Time-Varying Rician Channel

Abstract: The problem of transmitting digital data reliably over a Rician channel, which is used to model the aircraft-satellite link, is treated by an integrated coding and modulation design approach. The results presented enable one to show that it is quite possible to achieve robust signaling which is fairly insensitive to the channel's surface scatter parameters, such as scatter path energy and Doppler spreads. These results illustrate that the scatter energy need not limit the effectiveness of transmitting digital data and, in fact, can improve the performance when operating in the region of low direct path SNR's. These concepts are exemplified by performance curves for frequencyshift keying (FSK) and differential phase-shift keying (DPSK) modulation formats combined with efficient channel measurement decoding algorithms. In addition, general analytical results for evaluating the bit error probability for binary and channel measurement decoders are presented.

Spectral occupancy of digital angle-modulation signals

Abstract: The spectral or band occupancy of an RF signal is often defined as the bandwidth that contains a specified fraction (usually 99 percent) of the modulated RF power. The band occupancy of binary and quaternary PSK signals with and without RF filtering and with modulation pulses of several shapes has been evaluated and the results presented in graphical and tabular form. For a binary FSK signal with phase deviation of ± π/2, sometimes called an FM-PSK signal, numerical values of the spectral occupancy with rectangular and raised-cosine signaling have been obtained and the results given in graphical form. For a binary PSK signal with signaling rate 1/T and with arbitrary baseband pulse shaping, we have derived a lower bound on the fraction of the continuous power contained outside any given band, but have not been able to get a bound on the total band occupancy. However, for an FM-PSK signal, a lower bound on the total band occupancy has been derived, and it is shown that the value of this lower bound for 99-percent power occupancy is 1.117/T. The 99-percent power occupancy bandwidth of an FM-PSK signal is 1.170/T with rectangular signaling and 2.20/T with raised-cosine signaling.

Better phase-modulation error performance using trellis phase codes

Abstract: We construct phase codes for use in phase- and frequency-shift modulation. A trellis structure allows simple decoding using the Viterbi algorithm. Even short codes give a large improvement in error performance.

Fast FSK signals and their demodulation

Abstract: The Fast FSK is a particular kind of FSK (Frequency Shift Keying) which is useful for the transmission of digital data over an r.f. channel which is limited in both bandwidth and power. This paper describes the performance of the Fast FSK, and outlines the practical circuits which demodulate it.

Unbalanced quadriphase demodulator

Abstract: A new and improved apparatus and method for demodulation of quaternary phase shift keyed (QPSK) data, particularly unbalanced QPSK, with phase adjustment of the output of a phase-locked loop local oscillator to reduce sensitivity to amplitude variations internal to the demodulator.

Kalman Filter Equalization for QPSK Communications

Abstract: The discrete complex Kalman filter is considered as an equalizer for quadrature phase-shift keyed (QPSK) systems in the presence of additive noise and intersymbol interference (ISI). When the channel is unknown, an adaptive Kalman equalizer is used in which the channel complex tap gains are estimated by decision feedback.

Candidate Receivers for Unbalanced QPSK

Abstract: Candidate receivers for unbalanced QPSK signal foremats have been studied. The fourth power receiver is shown to be an unsatisfactory choice unless the power division is close to 50-50 or 100-0. The Costas loop receiver which tracks on the high data rate signal of the unbalanced QPSK waveform is shown to perform satisfactorily. Approximate error rate computations, show that the Costas loop considered performs within a few tenths of a dB of the ideal receiver.

Bandwidth Occupancy in PSK Systems

Abstract: For phase-shift keying (PSK) systems a method has been presented to determine the filter parameters so that the degradation produced by the bandlimiting filters is tolerable and as many channels as possible can be accommodated in a given RF band. Thermal noise present in the system and intersymbol and interchannel interference are considered the major sources of impairment in the system, and these are the only sources of impairment considered in this paper. The method is here applied to a binary coherent PSK (CPSK) system when unequalized Butterworth and Chebyshev filters of different complexities are used as receiving filters, and suitable filter parameters have been determined.

An MSK Approach to Offset QASK

Abstract: This paper demonstrates that an offset quadrature amplitude-shift-keyed (OQASK) signal can be represented as an ncomponent version of a minimum-shift-keyed (MSK) signal. For example, the signal set obtained by summing two MSK signals which are 6 dB different in power and are formed by continuous phase, frequency modulating the same oscillator with two independent binary antipodal data streams, is spectrally equivalent to an OQASK signal set composed of 16 signals in which the symbol pulse is a half-cycle sinusoid rather, than the conventional rectangular form. Such generalizations as the above allow for potentially simpler implementation of spectrally shaped OQASK.

Combined frequency and phase-shift keying

Abstract: In previous letters, the constraints necessary for the elimination of i.s.i. in both binary and multilevel f.s.k. were discussed. It is now shown that a system with simultaneous phase and frequency modulation is possible, both modulations being detected with zero i.s.i. In terms of energy per bit required at the receiver input for a given error rate, a 4-phase 2-frequency system is shown to be superior to an equivalent 8-state multiphase or combined phase/amplitude system.

Synchronization of QAM Signals in the Presence of ISI

Abstract: A data-aided carrier reconstruction method is described for quadrature amplitude modulation (QAM) data communications over narrow-band transmission channels. Previous analyses of this problem have assumed an "infinite" bandwidth of the communication link, so that negligible intersymbol interference (ISI) resulted. On the contrary, when ISI takes place, a different structure must be used which operates on sampled data. The performance of this structure is expressed analytically as a function of 1) the statistics of the message symbols, 2) the characteristics of the channel, and 3) the parameters of the tracking system. Excellent agreement has been found between the theory and the results of a computer simulation.

Transmission Characteristics of an M-ary Coherent PSK Signal Via a Cascade of N Bandpass Hard Limiters

Abstract: This paper provides a general analysis of the transmission characteristics of a coherent PSK signal, where an M -ary coherent signal is transmitted via a repeater system composed of a cascade of N bandpass hard limiters. The probability density function of a composite phase of the signal and noise over the system is newly derived to obtain an error probability. In addition, the comparison with the repeater system composed of a cascade of N linear amplifiers is made to clarify the features of the transmission characteristics. It is found that the probability density function of the composite phase over the system is symmetric about each input carrier-to-noise power ratio (CNR), and it reduces to some well-known results. It is also shown that for a reasonably large input CNR in each stage, the presence of the bandpass hard limiter (BPHL) provides some improvement, but that for small input CNR it causes degradation in performance.

On the Use of Polarity Coincidence Correlation Techniques for Differential Phase-Shift-Keyed Demodulation

Abstract: The use of polarity coincidence correlation techniques can allow efficient use of digital logic elements for binary differential phase-shift-key demodulation. For the case of sinusoidal signals in the presence of additive Gaussian noise it is shown that an ideal hard limiter at the input to the demodulator adds no degradation to the bit error rate performance.

Error Probability in Binary Digital Communication in the Presence of an Interfering Signal

Abstract: The presence of an interferring signal i(t) in a binary coherent symmetric channel is investigated. The probability of error is maximum when i(t) is antipodal to the transmitted signal, so(t) or s1 (t). The error probability is derived in the presence of a delayed interfering signal - so (t - r), where r is the time delay. An example of phase shift keying signals is given.

A bandwidth-compressive modulation system

Abstract: The phrase 'bandwidth-compressive modulation' means that the compression is achieved not by removing redundancy from the data (data compression), but rather by modulating the carrier phase and amplitude with blocks of data bits. The modulation described here is quadrature amplitude shift keying (QASK), a logical extension of quadrature phase shift keying, (QPSK, or quadriphase). QASK is a cost-effective form of combined phase-and-amplitude modulation. That is, n-bit QASK, like most phase-amplitude forms of modulation, requires considerably less transmitter power than comparably performing n-PSK, while among the class of all n-bit phase-modulation types, n-bit QASK performs nearly optimally but requires the least circuit complexity. A simple, unique microwave transmitter is described which provides high-rate QASK modulation with 4:1 bandwidth compression. A suppressed carrier multiple-loop QASK receiver provides the necessary phase tracking, automatic gain control (AGC), and symbol timing.

Carrier and symbol synchronization system performance study

Abstract: Results pertinent to predicting the performance of convolutionally encoded binary phase-shift keyed communication links were presented. The details of the development are provided in four sections. These sections are concerned with developing the bit error probability performance degradations due to PN despreading by a time-shared delay locked loop, the Costas demodulation process, symbol synchronization effects and cycle slipping phenomena in the Costas loop. In addition, Costas cycle slipping probabilities are studied as functions of Doppler count time and signal-to-noise conditions. The effect of cycle slipping in the symbol synchronizer is also studied as a function of channel Doppler and other frequency uncertainties.