Showing papers on "Phase-shift keying published in 1979"

Minimum shift keying: A spectrally efficient modulation

Abstract: The ever increasing demand for digital transmission channels, in the radio frequency (RF) band presents a potentially serious problem of spectral congestion and is likely to cause severe adjacent and cochannel interference problems. This has, in recent years, led to the investigation of a wide variety of techniques for solving the problem of spectral congestion. Some solutions to this problem include: 1) new allocations at high frequencies; 2) better management of existing allocations; 3) the use of frequency-reuse techniques such as the use of narrow-beam antennas and dual polarizing systems; 4) the use of efficient source encoding techniques; and 5) the use of spectrally efficient modulation techniques [l]. This article will consider the last approach and analyze, in particular, a modulation scheme known as minimum shift keying (MSK). The MSK signal format will be explained and its relation to other schemes such as quadrature phase shift keying (QPSK), offset QPSK (OQPSK), and frequency shift keying (FSK) pointed out. The main attributes of MSK, such as constant envelope, spectral efficiency, error rate performance of binary PSK, and self-synchronizing capability will all be explained on the basis of the modulation format.

Analysis of Direct-Sequence Spread-Spectrum Multiple-Access Communication Over Rician Fading Channels

Abstract: This paper is concerned with the performance of biphase direct-sequence spread-spectrum multiple-access communication for a general class of fading channels. The channels considered are those for which the channel output consists of a strong stable specular signal plus a faded version of this signal. Such channels, which are referred to as Rician fading (or Rice fading) or specular-plus-Rayleigh fading, are the result of a transmission medium which gives rise to a major stable communication path and a number of additional weaker communication paths. The fading channel is modeled as a general wide-sense-stationary uncorrelatedscattering (WSSUS) channel-a model which is general enough to exhibit both time and frequency selectivity and to impose no restrictions on the fading rate. For the general WSSUS model, results are obtained on the average signal-to-noise ratio at the receiver output in terms of the spread-spectrum signature sequences and the covariance function for the fading process. These results are then specialized to each of two important classes of WSSUS channels: time-selective fading channels and frequency-selective fading channels. Numerical evaluations are presented for specific examples of each of these two types of channels. Analytical expressions are derived for a spread-spectrum multiple-access system with random signature sequences, and the use of these expressions in preliminary system design is discussed.

A Comparison of Modulation Techniques for Digital Radio

Abstract: This paper describes and summarizes the characteristics of the modulation techniques most applicable to digital radio. The modulation techniques discussed are on-off-keying (OOK) with coherent and noncoherent detection, quadrature amplitude modulation (QAM), quadrature partial response (QPR), frequency-shift-keying (FSK) with noncoherent detection, continuous phase FSK (CP-FSK) with coherent and noncoherent detection, minimum-shift-keying (MSK), binary and quaternary phase-shift-keying (BPSK, QPSK) with coherent and differentially coherent detection, offset-keyed QPSK (OK-QPSK), M -ary PSK with coherent detection ( M = 8, 16 ), and 16-ary amplitude and phase-shift-keying (APK). Functional descriptions of these schemes are provided and their performance is compared in a series of tables summarizing the results of the literature of the past 20 years. The modulation schemes are compared with respect to ideal (white Gaussian noise) performance, spectral properties, signaling speed, complexity, and the effects on performance of interference, fading and delay distortion.

Analog and Digital Communication Systems

Abstract: Signal Analysis. Linear Systems. Probability and Random Analysis. Baseband Transmission. Amplitude Modulation. Angle Modulation. Source Encoding. Channel Encoding. Baseband Digital Communication. Digital Modulation. Design Consideration. Appendices: References Fourier Transforms Pairs Error Function Q Function.

Analysis of Multipath Outage with Applications to 90-Mbit/s PSK Systems at 6 and 11 GHz

Abstract: An analytical study to predict multipath fading outages in terrestrial digital radio systems is described. The method, which is quite general, makes specific use of previously reported statistics on multipath fading. It is applied, in this study, to 6- and 11-GHz systems carrying 90 Mbits/s per RF channel. For purposes of comparing alternate approaches, three different modulations are considered, namely, (i) conventional QPSK at 45 Mbits/s, using two polarizations per channel; (ii) Offset-QPSK at 45 Mbits/s using two polarizations per channel; and (iii) 8-level PSK at 90 Mbits/s, using one polarization per channel. In all cases, a fourthorder Butterworth transmit filter is assumed which enforces FCC spectral emission requirements. The channel is treated as a two-path propagation medium, the receiver is assumed to be coherent, and various practical assumptions are invoked regarding the recovered carrier phase, timing phase, receive filter response, bit error rate objectives and fade margin. Results are given in terms of expected yearly fraction of multipath outage per repeater hop vs. hop length. We find that the choice of operating band has only a minor effect on the results; that OffsetQPSK systems suffer somewhat more multipath outage than conventional QPSK systems; that 8-level systems suffer more multipath outage than 4-level systems (although this difference may be offset by cross-polarization effects in the latter); and that all the approaches considered require repeater spacings of 15 mi or less in order to meet short-haul outage objectives over average terrain.

Receiving circuit in an interference-suppressing communications system comprising narrow-band conventional message modulation and additional pseudo-noise phase shift keying

Abstract: A receiving circuit for an interference-suppressing communications system having a narrow-band conventional message modulation and additional pseudo-noise phase shift keying (PN-PSK), has a pseudo-random generator whose pseudo-random sequence is identical to the pseudo-random sequence provided by the system transmitter. The pseudo-random generator actuates a phase-shift keying element to cancel the phase shift modulation produced at the transmitter. A matched filter or correlation network for correlation of the pseudo-random sequence at the receiver with the pseudo-random sequence contained in the received signal is provided. The message modulation impairs the function of the matched filter or the correlation network. The degrading influence of message modulation is to be eliminated, at least, reduced. To this end, a demodulation circuit is provided which receives the entire received signal and the signal present after removal of the phase-shift keying to provide an input for the matched filter or correlation network. This signal only exhibits the pseudo-noise phase-shift keying contained in the received signal, but no longer has the message modulation.

Method of and apparatus for transmitting and recovering offset QPSK modulated data

Abstract: Bit timing references are derived at a receiver for a carrier modulated by OQPSK. A carrier is transmitted with a constant reference phase modulation during a first interval. During a subsequent, second interval the carrier is transmitted with rotational phase modulation representing binary bit values so that orthogonal components phase modulate the carrier with a predetermined bit sequence. A receiver responds to the constant phase modulated carrier to lock the frequency and phase of a phase lock loop oscillator of a carrier recovery loop. Synchronization at the receiver is achieved in response to a reception of the rotational phase modulation, while maintaining the frequency and phase lock. A carrier recovery loop of the receiver is activated to a decision directed operation after bit synchronization has been achieved. Decision directed operation is achieved by sampling and comparing components derived in orthogonal channels of the carrier recovery loop while the receiver is responsive to the rotational phase modulation. The bandwidth of a filter used in achieving bit synchronization is reduced after there has been a decay of transients in the carrier tracking loop resulting from a transition between locking of the loop and initiation of the decision directed operation. Then the bandwidth of a filter in the carrier tracking loop is adjusted as a function of the quality of the received rotational modulated suppressed carrier.

Bandwidth Efficiency and Probability of Error Performance of MSK and Offset QPSK Systems

Abstract: In this paper a model of Minimum Shift Keying (MSK) is introduced, an analysis of which shows that the theoretical maximum bandwidth efficiency of MSK is 2 bits/s/Hz, the same as for Quadrature Phase Shift Keying (QPSK) and Offset Quadrature Phase Shift Keying (Offset QPSK). The filtering necessary to achieve minimum spectrum width as well as a raised cosine spectrum while maintaining the condition of zero intersymbol interference for Offset QPSK is reviewed, and the equivalent filtering for MSK derived. In addition, partioning of this filtering between transmitter and receiver for optimum probability of error (P e ) versus receiver input signal to noise ( S/N ) ratio is given. Computer simulation results are presented for a MSK system and an Offset QPSK system, both filtered for 0%, 50% and 100% excess bandwidth raised cosine spectrum. The results show fully open eyes at the decision threshold input for all cases. They also show that when filtered to give the same spectrum the different system have identical P e versus S/N performance, S/N being defined at the input to the receiver decision threshold, i.e., after all the filtering for the desired raised cosine spectrum. This performance is best for 100% excess bandwidth filtering and worst for 0% excess bandwidth filtering.

Carrier recovery circuit for use in a multi-level phase shift keying demodulator

Abstract: In a demodulator for use with a multi-level phase shift keying (p.s.k.) signal having N phase levels, the p.s.k. signal which includes a carrier signal is frequency multiplied by a factor N in a multiplier filtered and frequency divided by the factor N to enable the carrier signal to be reconstituted at a terminal. To enable the demodulator to work at different data rates, and to enable filters to have sufficiently precise characteristics, the received p.s.k. signal is initially converted to base-band in mixers to which is applied a locally generated signal nominally at the carrier frequency.

Combined coherent frequency and phase shift keying modulation system

Abstract: A system of modulation and demodulation for the transmission of binary data in the presence of multipath. The binary data modulates the phase of the carrier and the same binary data, after a delay of "δ" bits, also modulates the frequency of the carrier. Following reception, the binary data is obtained either by frequency demodulation or by a method of coherent phase shift demodulation wherein the mark or the space frequency is selected for detection of each bit in accord with the bit received "n" bits previously. The system selects between the demodulation methods to obtain one which operates satisfactorily in the instant electromagnetic environment.

Planar QPSK demodulator

Abstract: A microwave integrated circuit (MIC) quadrature phase shift keying (QPSK) modulator uses a novel arrangement of couplers to permit the IF ports to be adjacent one another so that, in mixer applications, it is unnecessary for the circuitry to leave the plane of the MIC. A symmetrical arrangement of the MIC ensures near-perfect phase orthogonality of the RF2 split and the power/phase identity of the RF1 split.

Digital Communication Systems in Impulsive Atmospheric Radio Noise

Abstract: Analyses are presented of the performance of binary and M-ary coherent and noncoherent communication systems operating in the impulsive atmospheric radio noise environment. The receiver is usually a maximum likelihood detector for white Gaussian interference and therefore has the form of a parallel bank of matched filters followed by decision circuitry. By employing a Poisson or generalized Shot noise model for the impulsive noise with a suitable probability density function (pdf), closed-form expressions and bounds of error probabilities for M-ary noncoherent and coherent amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK) systems are obtained and the results discussed.

16 QAM Modulation for High Capacity Digital Radio System

Abstract: A computational method allowing the calculation of bit error rate in the presence of filtering and some other impairments is described for 16 QAM modulation; a breadboard working at a bit rate of 140 Mbits/s has been implemented and experimental results are compared with calculated values. The possible use of this modulation type for a high capacity digital radio-relay system is considered. Some parameters are introduced for this purpose, especially the net fade margin parameter. In the case of the 140 Mbit/s system in the 10.7-11.7 GHz frequency band, 4 PSK and 8 PSK modulation types are compared with 16 QAM. System gain, frequency arrangement, nodal capacity and outage performances are evaluated.

The Specification and Design of Bandlimited Digital Radio Systems

Abstract: This paper presents an introductory discussion of the factors related to specification and design of bandlimited digital transmission systems. Two classes of band limited signaling pulses are considered: raised cosine and partial response. These signaling pulses are generated by using pulse shaping filters on the output of conventional QPSK, MSK, or QASK modulators. Realization of bandwidth efficient digital transmission systems is reduced to a problem of designing a special class of filters. Performance evaluation indicates information densities of up to 4.2 bits/s/ Hz can be achieved with theoretically no impairment in error performance as compared to the ideal nonbandlimited channel. Computer-aided design methods for realization of the necessary pulse shaping filters are described.

Design and Performance of an Adaptive Kalman Receiver for Synchronous Data Transmission

Abstract: A class of multilevel linear-modulation data-transmission systems, over unknown, slowly time-varying, and bandlimited channels is considered. It is shown how sequence estimation in the presence of Gaussian noise and intersymbol interference can be carried out by means of a discrete Kalman estimator. Moreover, the receiver can be provided with data-aided adaptive loops for performing channel identification, carrier recovery, and timing extraction. A computational method is presented to evaluate the average probability of error of the overall system in the presence of inter-symbol interference, additive noise, and phase-and sampling-synchronization errors. The method is based upon nonclassical one-and two-dimensional quadrature rules, which are outlined in the Appendix. As an example, numerical performance results related to a phase-shift-keying (PSK) system are given. The results are obtained by means of general-purpose and system-oriented computers.

Envelope Fluctuation Statistics of Filtered PSK and Other Digital Modulations

Abstract: Radio signals derived using constant-envelope digital modulations (e.g., PSK, FSK and variations thereon) are impervious to the nonlinear characteristics of high-power RF amplifiers such as TWT's. However, constant-envelope modulations that must be heavily filtered to meet spectrum emission requirements, or intrinsically spectrumefficient modulations such as Quadrature Partial Response Signaling (QPRS), exhibit envelope fluctuations that render them vulnerable to amplifier nonlinearities. This paper describes a study, based on the use of Monte Carlo computer simulations, of the RF envelope variations associated with different digital modulations. Simulations and statistical analyses of these variations have been conducted for both filtered PSK and QPRS. The PSK category includes such special cases as Staggered Quaternary PSK (SQPSK); Minimum Shift Keying (MSK); L -ary PSK with cosine rolloff shaping (divided equally between transmitter and receiver); and linear phase modulation using shaped (nonrectangular) baseband pulses. The primary fluctuation measure used in the study is the dynamic range, in decibels, between the 10th and 90th percentiles of the RF envelope. This quantity, D , is presented for the various modulations considered and for various types of transmit filtering, with filter bandwidth-to-symbol rate ratio treated as a variable. The numerical results show the tradeoff between envelope constancy and spectrum efficiency among the most widely used digital radio approaches. For QPRS modulations, D is typically in the range 11-16 dB; for heavily filtered PSK modulations, the range of D lies roughly 6 dB lower, but other sources of distortion are more prominent.

Optimum Modulation and Channel Filters for Nonlinear Satellite Channels

Abstract: This is a comparative study of three modulation schemes: QPSK, Offset QPSK(OQPSK), and MSK, in nonlinear satellite channels with adjacent channel interference. Two kinds of typical satellite channel models are used for performance evaluation: one is an INTELSAT type narrow band model and the other is a domestic type wide band model. The transmitter filter and receiver filter are optimized for each combination of modulation scheme, channel model, and an input back-off condition for nonlinear amplifiers. All the combinations considered here have the optimum division of the Nyquist shaping between transmitter filter and receiver filter in common. The filters are a wide band sharp cut-off transmitter filter with flat inband response and a gently rolled-off Nyquist receiver filter with an aperture equalizer ( x/\sin x or 1-(2x)^{2}/\cos x equalizer). With these optimized filters, comparisons are made with respect to the bit error rate (BER) performance and phase jitter of the recovered carrier. OQPSK and MSK show superior BER performance to QPSK in the wide band model. However, in the narrow band model, QPSK shows the best BER performance among the three modulation schemes. The phase jitter in the recovered carrier is small for all modulation schemes in the wide band model. But, in the narrow band model, the phase jitter in OQPSK and MSK is four times larger than in QPSK. Generally QPSK is the most preferable modulation scheme in the narrow band model: OQPSK and MSK are most preferable for the wide band model.

The Effects of the Amplitude and Delay Slope Components of Frequency Selective Fading on QPSK, Offset QPSK and 8 PSK Systems

Abstract: Amplitude and delay slope are significant components of inband distortion resulting from multipath fading. In this paper, we present and compare computer simulated results of signal to noise ( S/N ) degradation for probability of error (P e ) of 10-4, due to these distortion components on Quadrature Phase Shift Keying (QPSK), Offset Quadrature Phase Shift Keying (Offset QPSK) and 8 Phase Shift Keying(8 PSK)systems. For all systems the transmitter and receiver filtering is modeled so as to provide a 50% excess bandwidth raised cosine spectrum at the receiver detector input. The QPSK and Offset QPSK systems are studied with bit rates of 44.7 Mbits/s, the so-called T3 rate, and the 8 PSK system is studied with bit rates of 44.7 Mbits/s and 67 Mbits/s, a 67 Mbit/s 8 PSK system having the same modulated frequency spectrum as 44.7 Mbit/s QPSK and Offset QPSK systems. When the frequency spectrum is the same for all systems, then for a given amplitude slope, results show that QPSK is the least degraded, followed by Offset QPSK, then 8 PSK, and for a given delay slope, Offset QPSK is the least degraded, followed by QPSK, than 8 PSK. When the bit rate is the same for all systems, then for a given amplitude slope, QPSK is the least degraded. 8 PSK is less degraded than Offset QPSK for values of amplitude slope less than 0.47 dB/MHz, but more degraded for higher values. For equal bit rates and a given delay slope, Offset QPSK is the least degraded, followed by 8 PSK, then QPSK. By relating degradation results to published information on the occurrence of amplitude and delay slope distortion components during multipath fading, estimates of S/N degradation for a P e of 10-4due to these distortion components as a function of frequency selective fade depth are made. Finally, measured S/N degradations for a P e of 10-4due to amplitude and delay slope on a 44.7 Mbit/s Offset QPSK system with filtering similar to the computer model are presented and compared to the computer simulation results.

Efficient Pulse Shaping Using MSK or PSK Modulation

Abstract: The increasing requirement for high data rate, bandwidth efficient digital radio systems has led to the development of MSK-type modulation methods designed to achieve a compact signal spectrum. These modulation methods include sinusoidal frequency shift keying (SFSK), special MSK-type pulse shapes, and multiamplitude minimum shift keying (MAMSK). When more compact signal spectra are required, bandlimited filtering must be introduced. This note considers the use of conventional MSK or PSK modulators followed by newly developed bandlimited pulse shaping filters. With this approach, it is shown that MSK and offset QPSK modulators yield identical signals on the channel when filtered by properly designed bandlimited pulse shaping networks.

Binary CPSK Performance Analysis for Saturating Band-Limited Channels

Abstract: An expression is derived for the error probability of binary CPSK signals received over a soft-limited channel in the presence of pre- and post-limiter additive Ganssian noise. Although this expression is not in closed form, it may be efficiently evaluated to any desired accuracy using a recurrence method developed in the appendix. System performance is also evaluated when the signals are subjected to bandlimiting as well as Gaussian noise preceding the limiter. Moment space techniques are used to obtain upper and lower bounds on the errorrate in terms of the error-rate in the presence of Gaussian noise alone. Numerical examples are presented for a channel which includes a Chebyshev filter preceding the limiter. These illustrate that the bounds are tight enough for most practical purposes.

Error performance of differentially coherent detection of binary DPSK data transmission on the hard-limiting satellite channel

Abstract: [51 A. M. Kagan, Yu. V. Linnik, and C. R. Rao, Characterization Problems in Mathematical Statistics. New York: Wiley, 1913. E. T. Jaynes, “Prior probabilities,” IEEE Trans. Syst. Sci. Cybern., vol. SSC-4, no. 3, Sept. 1968. 0. E. Lanford, “Entropy and equilibrium states in classical statistical mechanics,” in Statistical Mechanics and Mathematical Problems. Berlin: Springer-Verlag, 1973. S. L. Zabell, “A limit theorem for conditional expectations with applications to probability theory and statistical mechanics,” Ph.D. dissertation, Harvard University, Cambridge, MA, Aug. 1974. H. Chemoff, “A measure of asymptotic efficiency for tests of a [61

A Decision-Directed Carrier Recovery Loop for Duobinary Encoded Offset QPSK Signals

Abstract: The Canadian RD-3 digital radio system will utilize duobinary encoded, offset QPSK modulated signals. This complex signal structure is such that a conventional fourth order nonlinearity and phase-locked loop cannot be used for carrier recovery. In this paper, a decision-directed phase-lock loop is proposed for carrier recovery and demodulation of these signals. The equations describing loop operation are obtained, and the effective phase-detector characteristic is examined. Fokker-Planck techniques are then employed to approximately find the steady-state probability density function of the phase error, and this is used to find an upper bound on the average probability of error.

Performance of unbalanced QPSK in the presence of noisy reference and crosstalk

Abstract: The problem of transmitting two telemetry data streams having different rates and different powers using unbalanced quadriphase shift keying (UQPSK) signaling is considered. It is noted that the presence of a noisy carrier phase reference causes a degradation in detection performance in coherent communications systems and that imperfect carrier synchronization not only attenuates the main demodulated signal voltage in UQPSK but also produces interchannel interference (crosstalk) which degrades the performance still further. Exact analytical expressions for symbol error probability of UQPSK in the presence of noise phase reference are derived.