Showing papers on "Phase-shift keying published in 1981"

Continuous Phase Modulation--Part I: Full Response Signaling

Abstract: The continuous phase modulation (CPM) signaling scheme has gained interest in recent years because of its attractive spectral properties. Data symbol pulse shaping has previously been studied with regard to spectra, for binary data and modulation index 0.5. In this paper these results have been extended to the M -ary case, where the pulse shaping is over a one symbol interval, the so-called full response systems. Results are given for modulation indexes of practical interest, concerning both performance and spectrum. Comparisons are made with minimum shift keying (MSK) and systems have been found which are significantly better in E_{b}/N_{0} for a large signal-to-noise ratio (SNR) without expanded bandwidth. Schemes with the same bit error probability as MSK but with considerably smaller bandwidth have also been found. Significant improvement in both power and bandwidth are obtained by increasing the number of levels M from 2 to 4.

Quadrature Overlapped Raised-Cosine Modulation

Abstract: A variation of an old but neglected pulse shaping technique, raised-cosine, is investigated. By overlapping raised-cosine pulses in each of two data streams and then by quadrature combining them, a simple QPSK/MSK type modulation results. This quadrature overlapped raised-cosine (QORC) modulation exhibits a hybrid structure of QPSK and MSK modulations. The power spectral density of QORC is shown to take on the form of the product of the power spectral densities of MSK and QPSK. The obvious consequences are that the power spectral density main lobe retains the width of the spectral density main lobe of QPSK, but the sidelobes drop off much faster (1/f^{6}) . A simple QORC modulator can be implemented similar to an MSK modulator. Several correlation type receivers are investigated and their performances calculated. Computer simulation results are used to compare end-to-end system performance of QORC and staggered QORC (SQORC) with MSK, QPSK, and staggered QPSK (SQPSK) for both linear and nonlinear satellite channels. The performance of QORC and SQORC compares very favorably with QPSK, SQPSK, and MSK. QORC performs particularly well in the presence of a nonlinear channel. The effect of phase equalization of the channel filter was investigated with outstanding performance improvement. The simulation results show that sidelobe regeneration caused by the channel nonlinearity is much less for SQORC than it is for the other modulation formats considered.

Coherent Detection of Frequency-Hopped Quadrature Modulations in the Presence of Jamming--Part I: QPSK and QASK Modulations

Abstract: This paper examines the performance of coherent QPSK and QASK systems combined with FH or FH/PN spread spectrum techniques in the presence of partial-band multitone or noise jamming. The worst-case jammer and worst-case performance are determined as functions of the signal-to-background noise ratio (SNR) and signal-to-jammer power ratio (SJR). Asymptotic results for high SNR are shown to have a linear dependence between the jammer's optimal power allocation and the system error probability performance.

The Effect of Phase Error on DPSK Error Probability

Abstract: Expressions are found for the effect of an error in the delay of the preceding signal, which provides the reference phase for the decoding of the present signal in differential phase-shift-keying reception. The signal-to-noise ratio is allowed to be different for the two signals that are compared by the receiver's phase detector. The results are applicable to both binary and quaternary DPSK. In addition, an approximation is obtained for the error probability when the two Signal-to-noise ratios are equal to the same large value.

A dynamic programming algorithm for simultaneous phase estimation and data decoding on random-phase channels

Abstract: The problem of simultaneously estimating phase and decoding data symbols from baseband data is posed. The phase sequence is assumed to be a random sequence on the circle, and the symbols are assumed to be equally likely symbols transmitted over a perfectly equalized channel. A dynamic programming algorithm (Viterbi algorithm) is derived for decoding a maximum {\em a posteriori} (MAP) phase-symbol sequence on a finite dimensional phase-symbol trellis. A new and interesting principle of Optimality for simultaneously estimating phase and decoding phase-amplitude coded symbols leads to an efficient two-step decoding procedure for decoding phase-symbol sequences. Simulation results for binary, 8 -ary phase shift keyed (PSK), and 16-quadrature amplitude shift keyed (QASK) symbol sets transmitted over random walk and sinusoidal jitter channels are presented and compared with results one may obtain with a decision-directed algorithm or with the binary Viterbi algorithm introduced by Ungerboeck. When phase fluctuations are severe and when occasional large phase fluctuations exist, MAP phase-symbol sequence decoding on circles is superior to Ungerboeck's technique, which in turn is superior to decision-directed techniques.

Power Spectra of Multi-h Phase Codes

Abstract: A procedure is presented for calculating the power spectrum of the class of digital continuous-phase signals known as multi- h phase codes. These signals have been shown to have attractive power advantages over other uncoded digital schemes such as QPSK, and represent a bandwidth-efficient alternative to other coding. techniques. The method is general, handling M -ary signaling, various frequency pulse shapes, and arbitrary sets of modulation indices. Numerical results are shown for several specific codes. In addition, the issue of spectral lines is resolved, and simple spectral approximations are developed.

The Use of the Fourier-Bessel Series in Calculating Error Probabilities for Digital Communication Systems

Abstract: Using the theory of spherical symmetric random vectors one can find an expression for the error probability of a wide variety of digital communications systems. These expressions, however, are in the form of Bessel integrals which are usually difficult to solve. In this paper we show how the Fourier-Bessel series can be used to solve the integrals numerically. The calculation error is found to depend on two series parameters which can be manipulated to make the error arbitrarily small. Two examples are used to show the utility of the technique. In the first the probability of error for a CPSK communications system operating in Gaussian noise and cochannel interference is found. In the second the error performance for a multilevel ASK communications system operating in the same corrupting environment is determined. The Fourier-Bessel series technique is a valuable practical tool for solving these and other signal detection problems.

Performance of Offset Quadriphase Spread-Spectrum Multiple-Access Communications

Abstract: New analytical results are obtained on the performance of quadriphase spread-spectrum multiple-access communications. The primary performance parameter considered is the signal-to-noise ratio at the receiver output. This parameter includes the effects of multiple-access interference and channel noise, and it has been shown to give a reliable estimate of the average probability of error.

Data communication system

Abstract: A data communication system for general purposes having a new ternary carrier frequency shift keying (TCSK) signal The system is applied to a utility load control by transmission of a sub-carrier of an FM broadcast channel It is decoded by a receiver, SCA decoder, TCSK filter and a two level or binary converter and used to communicate to a pre-programmed microprocessor which enables various load control functions to be performed The general system also is given for a QPSK (quadraphase shift keying) operating system A data transmission filter is split between the transmitter and receiver and is operated in cascade to give individual interference filtering at each end of the transmission while also providing combined action and wave shaping A high accuracy FM decoder using zero crossing detection enables data recovery with simple circuits A novel random time load restoration circuit for ramp-up is disclosed A fail safe relay operator is also disclosed The TCSK employs a novel 19 character hex code format which is 8 bit microprocessor compatible and directly usable for other purposes such as ASCII message transmission Both QPSK and TCSK systems offer command structures of variable length so as to permit truncation of message and reduce total message transmit time

Calculation of error probability for MSK and OQPSK systems operating in a fading multipath environment

Abstract: A technique is given for determining the error-rate performance of a class of digital communication systems operating with fading multipath interference. The approach uses a truncated series to represent the fading process and takes into account the effects of intersymbol interference caused by linear filtering in the receiver or channel. Application of the method to the cases of minimum shift keyed (MSK) and offset quadriphase shift key (OQPSK) systems reveals a slight performance advantage for MSK.

Decoding with approximate channel statistics for bandlimited nonlinear satellite channels

Abstract: Expressions for the cutoff rate of memoryless channels and certain channels with memory are derived assuming decoding with approximate channel statistics. For channels with memory, two different decoding techniques are examined: conventional decoders in conjunction with ideal interleaving/deinterleaving, and maximum likelihood decoders that take advantage of the channel memory. As a practical case of interest, the cutoff rate for the band-limited nonlinear satellite channel is evaluated where the modulation is assumed to be M-ary phase shift keying (MPSK). The channel nonlinearity is introduced by a limiter in cascade with a traveling wave tube amplifier (TWTA) at the satellite repeater while the channel memory is created by channel filters in the transmission path.

A Simulation Study of Two Bandwidth-Efficient Modulation Techniques

Abstract: Signal space coded signaling systems have the potential of achieving significant error-rate improvement without the bandwidth expansion normally encountered when error-correcting codes are used. This paper investigates two such systems by means of computer simulation. A band-limited, nonlinear channel is assumed and both systems exhibit performance improvenment compared to uncoded systems.

On the performance of phase-shift-keying systems

Abstract: Coherent phase-shift keying (CPSK) and differential phase-shift keying (DPSK) are widely used modulation methods in digital communications Bandwidth efficiency, good noise immunity, constant envelope, and simplicity of implementation make these schemes particularly attractive for use over the satellite, terrestrial radio and voiceband telephone channels While system analyses abound in the literature, treatment is usually restricted to the additive Gaussian channel Important issues determining ultimate performance, such as the joint effect of intersymbol interference and the acquisition of carrier phase have not been adequately addressed The main purpose of this paper is to develop analytical tools that can be used to assess system performance under practical operating conditions Pure coherent demodulation schemes such as CPSK are ideals which are rarely achieved in practice, and carrier phase must be estimated prior to and/or during data transmission This requires start-up time, as well as added equipment, and the fidelity of the phase estimate ultimately determines performance In contrast, DPSK is independent of carrier phase, since decisions are made on phase differences However, this comes at a price, and it is known that ideal multiphase DPSK suffers an asymptotic performance penalty of 3 dB in signal-to-noise ratio (s/n) over ideal CPSK We develop a new rigorous method for calculating the error rates of both CPSK and DPSK, under a variety of operating conditions In particular, we find that the intersymbol interference penalty for quaternary DPSK is about 1 dB worse in s/n than for CPSK We demonstrate that the detection efficiency of CPSK approaches the ideal, provided that the s/n of the phase-recovery circuit is about 10 dB more than that at the receiver input Alternatively, for the same s/n, a 10-baud phase-locked loop integration time is required to achieve near-ideal performance

MSK and OK-QPSK signal demodulator

Abstract: An MSK or OK-QPSK data signal demodulator includes a filter and limiter for filtering and amplitude limiting the data signal, a timer for generating a timing signal indicating elapsed time and a microcomputer coupled to the limited data signal from the limiter and the timing signal from the timer. The microcomputer is interrupted by each transition of the limited data signal and stores the timing signal from the timer. An interrupt routine of the microcomputer extracts the clock offset, which is an estimate of the relative location of the bit boundaries, and the phase intercept, which is an estimate of the phase of the data signal at the bit boundaries, from the timing signals.

Comments on Transmission System Using Pseudonoise Modulation of Linear Chirps

Abstract: The combination of phase shift keying (PSK) with different chirp waveforms is investigated in respect to its signal form and spectrum shape. A reasonable compromise for low probability of exploitation and jam sensitivity is found for a system where the chirp bandwidth is in the vicinity of the bitrate of the pseudonoise code.

The Impact of Pulsed RFI on the Coded BER Performance of the Nonlinear Satellite Communication Channel

Abstract: The coded bit error rate (BER) performance of a satellite communications system, wherein the satellite repeater contains an arbitrary nonlinearity and the system operates in the presence of pulsed radio frequency interference (RFI), is examined. A major result is an analytic method for determining soft decision statistics of the receiver demodulator output in which pulsed RFI effects are accounted for. It is further demonstrated how this result can be analytically applied to the approximate determination of the BER at the output of the Viterbi decoder when convolutional coding is employed. Computed results specialize the nonlinearity to either a hard limiter or clipper, in conjunction with an arbitrarily specified AM/PM characteristic. Performance curves examine BER sensitivity to RFI duty cycle, form of RFI (CW or noise), and various coding/decoding conditions.

Analysis of Coherent Satellite Communication Systems in the Presence of Interference and Noise

Abstract: This paper presents the analysis and evaluation of bit error probabilities of coherent MPSK nonlinear satellite communication systems, in which there is uplink noise, downlink noise, and CW tone interference with random phase uniformly distributed over the interval [0, 2π]. The evaluation of bit probabilities also includes intersymbol interference whose statistical distribution is constructed through a two-dimensional moment technique. This moment technique is as effective and accurate as the standard Gauss quadrature formulas (GQF), yet more versatile than GQF for evaluating an expectation over random variables. Some numerical examples for the performance of satellite channels are illustrated.

Receiver for pseudo-randomly phase-modulated signals

Abstract: In a receiver within a communications system operating with pseudo-random phase shift keying, the AGC level regulation which serves to stabilise the useful signal level, in contrast to current practice, is located only downstream of the bandspread-reversing phase restore key (4). Narrowband AGC amplifiers can then be used. A receiver designed according to the invention is used in interference-immune spread-spectrum communications systems which operate with pseudo-random phase shift keying.

Quaternary Transmission Over Satellite Channels with Cascaded Nonlinear Elements and Adjacent Channel Interference

Abstract: The performance of coherent QPSK, offset QPSK, and MSK modulation systems is investigated via computer simulation for TDMA transmission over satellite channels with cascaded nonlinear elements, up- and downlink fades, intersymbol interference, adjacent channel interference, and thermal noise. Three satellite transponder concepts are considered: TWTA transponders nominally operated at their saturation power under clear sky conditions, TWTA transponders nominally operated at input overdrive, and hard-limiting transponders. The performance of these modulation techniques in terms of bit error rate versus energy per information bit over thermal noise power density E_{b}/N_{0} has been evaluated for the three system concepts as a function of various system parameters. For transponder BT products in the range of 1.5-2.0, modem filter characteristics and waveform shaping have been carefully and nearly "optimally" selected to combat adjacent channel interference, which is the major source of impairments, especially under uplink fades. It has been found that, for certain system environments, MSK and OQPSK outperform QPSK. As a byproduct of this investigation, various means to minimize the effects of adjacent channel are proposed.

Correction to 'Error Performance of Differentially Coherent Detection of Binary DPSK Data Transmission on the Hard-Limiting satellite Channel'

Abstract: The error performance of differentially coherent detection of a binary differential phase-shift keying (DPSK) system operating over a hard-limiting satellite channel is derived. The main objective is to show the extent of error rate degradation of a DPSK system when a power imbalance exists between the two symbol pulses that are used in a bit decision interval. Consideration is also given to the DPSK error rate performance for the special case of {\em uncorrelated} uplink and {\em correlated} downlink noises at the sampling instants in adjacent time slots. Error probabilities are given as functions of uplink signal-to-noise ratio (SNR) and downlink SNR with different levels of SNR imbalance and different downlink SNR and uplink SNR as parameters, respectively. Our numerical results show that 1) as long as the symbols are equiprobable, the error probability is not dependent upon the downlink noise correlation, regardless of whether there is a power imbalance; 2) error performance is definitely affected by the power imbalance for all cases of symbol distributions; and 3) the error probability does depend upon downlink noise correlation for all levels of power imbalance if the symbol probabilities are not equal.

MSK and Offset QPSK Modulation with Bandlimiting Filters

Abstract: It is considered by some that minimum shift keying (MSK) is spectrally more efficient than quaternary phase-shift keying/offset quadrature phase-shift keying (QPSK/OQPSK). An analytical method is presented here for determining the detection efficiencies of MSK and QPSK/OQPSK when the constant-envelope signal is passed through a set of filters and when the resulting signal is corrupted by Gaussian noise. The detection efficiency of MSK is compared with that of QPSK/OQPSK when a four-pole Butterworth filter is used as a transmit filter and for two different receive filter functions. When the two-sided 3-dB bandwidth of the transmit filter is between approximately 1.00/T and 1.50/T, it is shown that the detection efficiency of MSK is not substantially different from that of QPSK/OQPSK. For more severe bandlimiting of the signal, the performance of MSK is shown to be inferior to that of QPSK/OQPSK. It is, therefore, concluded that MSK does not have significantly better detection efficiency when the effect of bandlimiting filters is taken into account.

Spectrally Efficient Communication via Fading Channels Using Coded Multilevel DPSK

Abstract: This paper investigates the use of multilevel differential phase-shift keying with forward error-correcting coding as a technique for achieving limited bandwidth, yet reliable communication over a class of fading channels. Error rate bounds based on the cutoff rate are computed to show that multilevel modulation can be used to allow significant coding gains, while maintaining or reducing the bandwidth of the transmitted signal.

Suboptimal reception of binary CPSK signals

Abstract: A general class of binary continuous-phase shift keying (CPSK) signals is defined, of which continuous-phase FSK (CPFSK) and continuous-phase chirp (CPC) signals are special cases. The structure and performance of suboptimal average matched filter (AMF) receivers with multibit observation are considered; both coherent and noncoherent detection of binary CPSK signals are investigated. Expressions suitable for numerical evaluation of such suboptimal CPSK receivers in the additive white Gaussian noise (AWGN) environment are given, and simplified expressions are derived for special cases. In particular, the coherent AMF receiver with optimised CPC and CPFSK signal parameters is shown to be equivalent to a generalised inphase and quadrature receiver. The relation between crosstalk and filter orthogonality is clarified for non-coherent AMF detection. Numerical examples for CPFSK and CPC signals are given.

Required Transmit Filter Bandwidths in Digital Radio Systems

Abstract: Widely used digital radio modulations such as quaternary phase shift keying (QPSK), minimum shift keying (MSK), and sinusoidal frequency shift keying (SFSK) usually require some form of transmit filtering to ensure compliance with spectrum emission rules. Typically, radio transmit filters are of a specified type, such as fourthorder Butterworth, where the bandwidth parameter (\beta) is a design variable. We specify β to be optimal for a particular filter when it has the largest value for which the transmitted signal satisfies the emission rules, and we present numerical solutions for β over a wide range of conditions. These data can be used in design studies that compare contending modulation/transmit filter combinations. The solutions given are for systems subject to the spectral limits of FCC Docket 19311. The types of modulation considered are generalizations of those cited above; the types of transmit filters considered are Butterworth and Chebyshev filters of various orders; and β is tabulated as a function of channel width-to-symbol rate ratio for numerous modulation/filter combinations. While computed specifically, for the 6 GHz common carrier band, the results are also valid, to within a few percent, for the 4 and 11 GHz bands.