Showing papers on "Phase-shift keying published in 1978"

Differential Encoding for Multiple Amplitude and Phase Shift Keying Systems

Abstract: Because of the symmetry in most two-dimensional signal constellations, ambiguities exist at the receiver as to the exact phase orientation of the received signal set. In PSK systems, this ambiguity is resolved by the use of differential encoding. This paper presents differential encoding techniques which can be used with a variety of symmetric signal sets to remove their phase ambiguity. While not proven to be optimum, the techniques do have low performance penalties relative to the uncoded performance. The key to reducing the performance penalty is to use the minimum amount of differential encoding necessary to resolve the ambiguity. Examples of encoding techniques for several common signal constellations are given, including their performance penalties.

Modern Electronic Communication

Abstract: 1 Introductory Topics 2 Amplitude Modulation: Transmission 3 Amplitude Modulation: Reception 4 Single-Sideband Communications 5 Frequency Modulation: Transmission 6 Frequency Modulation: Reception 7 Communications Techniques 8 Digital Communications: Coding Techniques 9 Wired Digital Communications 10 Wireless Digital Communications 11 Network Communications 12 Transmission Lines 13 Wave Propagation 14 Antennas 15 Waveguides and Radar

A Bandwidth Compressive Modulation System Using Multi-Amplitude Minimum Shift Keying (MAMSK)

Abstract: A bandwidth compressive modem making use of multiamplitude minimum shift keying (MAMSK) has been designed and implemented in a laboratory environment at microwave frequencies. This system achieves a substantial bandwidth reduction over binary PSK and operates within 0.5 dB of theoretical performance. A number of easily implemented microwave transmitters have been designed to generate the required set of 16 signals. The receiver has been designed to work at 1 Mbit/s and contains the necessary phase tracking, AGC, and symbol synchronization loops as well as a lock detector, SNR estimator and provisions for differential decoding. This paper describes this entire system and presents the experimental results.

Effect of Noisy Phase References on Coherent Detection of FFSK Signals

Abstract: Fast Frequency Shift Keying (FFSK) is a phase coherent binary FSK modulation technique with a deviation ratio of 0.5 and an ideal error rate performance equivalent to that of phase-shift keyed (PSK) modulation. Coherent reception of FFSK and PSK systems is degraded by imperfect receiver reference signals. The various forms of PSK modulation-binary (BPSK), conventional quadriphase (QPSK) and offset quadriphase (OK-QPSK)-as well as FFSK, exhibit the same ideal error rate performance but are not equally sensitive to imperfect carier phase reference. It is shown that while FFSK is similar in structure to OK-QPSK, its sensitivity to reference phase error is less. FFSK is shown to require 2.5 dB less receiver phase reference SNR for a specified detection loss than OK-QPSK.

Optimum Weighted PCM for Speech Signals

Abstract: Weighted digital modulation schemes which provide bit error probabilities matched to the PCM bits with respect to their sensitivity to digital errors are analyzed. The channel is additive, white Gaussian. The PCM system has arbitrary code, companding law and input signal density function. Especially optimum weighted PSK/PCM and QAM/PCM are given for speech signals. The average channel signal to noise ratio is kept constant when schemes are compared. We obtain a channel signal to noise ratio gain in threshold extension of 2 dB for standard 8 bit PCM. The performance of suboptimum schemes, where the number of different bit error probability levels are smaller than the number of PCM bits are also studied. Two levels per 8 bit PCM word yield more than half of the achievable gain (in dB) and 4 levels is almost equal to optimum.

On Low Crosstalk Data Communication and its Realization by Continuous-Frequency Modulation Schemes

Abstract: Modulation waveforms with continuous derivatives in conjunction with a receiver whose impulse response has continuous derivatives is shown to generate crosstalk interference in a correlation demodulator that decreases at least as the cube of the carrier spacing between waveforms. Constant envelope, continuous-frequency modulations called Continuous (Frequency) Shift Keying (CSK) are proposed which not only achieve this asymptotic crosstalk behavior but are better then Phase Shift Keying (PSK) and Minimum Shift Keying (MSK) for carrier spacings of at least 1.1 times and 2.0 times the data rate, respectively. CSK can be demodulated in Gaussian noise with no loss with respect to optimum hard-decision receivers of antipodal signals, i.e., with the same performance as PSK and MSK.

Soft Decision Demodulation for PCM Encoded Speech Signals

Abstract: The effect of digital errors in PCM encoded speech signals transmitted over a noisy channel is reduced by using soft decision demodulation at the receiver. The reliability information supplied by the soft decision demodulator is used to point out likely transmission errors, especially in the most significant PCM bits. When a likely transmission error is identified, the corresponding PCM word is rejected by the receiver and replaced by a predictor estimate or an interpolation estimate if delayed decisions are used. We have analyzed soft decision demodulation schemes for standard PCM encoded speech signals transmitted over the Gaussian channel with coherent PSK (phase shift keying). A signal to noise ratio gain in E_{b}/N_{0} of the order of 1-2 dB is Obtained at low input signal levels. The gain depends on the performance of the predictor or, alternatively, the interpolator. No modifications of the transmitter are required to obtain this improvement. The suggested soft decision schemes are optional at the receiver. The comparisons are made with hard decision demodulation.

On the Calculation of Squaring Loss in Costas Loops with Arbitrary Arm Filters

Abstract: The calculation of the optimum performance of suppressed carrier receivers with Costas loop tracking is directly related to evaluating the loop's so-called squaring loss. Recent work by the author and others presented specific numerical results for this loss when the input data were biphase- L (Manchester coded) and the Costas loop arm filters were of the n -pole Butterworth type. These results were largely obtained by numerical integration on a digital computer. This paper presents a partial fraction expansion technique for arriving at closed form expressions for squaring loss for Costas loops with arbitary arm filters and NRZ as well as Manchester coded data. Specific closed form results are given for one and two pole Butterworth filters as examples.

Effects of Thermal Noise, Filtering and Co-Channel Interference on the Probability of Error in Binary Coherent PSK Systems

Abstract: An analytical method for evaluating the bit error probability in Binary Coherent Phase Shift Keying (BCPSK) systems is presented. The system impairments considered are additive Gaussian noise, intersymbol interference and co-channel interference. The method is based on the power series expansion of the characteristic function of the interferences. Each characteristic function is expanded in a power series and its coefficients are averaged analytically with respect to the random phase and the bit timing alignment. Numerical examples are given to illustrate the method and to provide design data for system designers.

Performance of Maximum-Likelihood Receiver in the Nonlinear Satellite Channel

Abstract: A computer-simulation algorithm is described for calculating the performance of a maximum-likelihood (ML) receiver in the nonlinear satellite communications channel. It is assumed that performance is dominated by isolated single errors and that the channel can be approximated by one of finite memory, M \leq 10 bits. The algorithm employs the brute force method of comparing the wave forms of all sequence pairs of length 2M - 1 bits that differ in their M 'th bit, and in spite of the large number of sequences involved requires only modest computer time. Examples for a rudimentary channel employing a traveling wave tube at saturation with modulation formats QPSK, O-QPSK, and MSK are computed and ML performance is compared to that of suboptimum receivers using bit-by-bit decision or discrete ML sequence estimation. Results indicate that the inherent channel degradation that cannot be corrected by appropriate receiver design is not great even for transmission at the Nyquist rate limit as defined relative to the 3 dB bandwidth of a link employing 6-pole Butterworth filters.

Error Probability Performance of Unbalanced QPSK Receivers

Abstract: A simple technique for calculating the error probability performance and associated noisy reference loss of practical unbalanced QPSK receivers is presented. The approach is based on expanding the error probability conditioned on the loop phase error φ in a power series in φ and then, keeping only the first few terms of this series, averaging this conditional error probability over the probability density function of φ. Doing so results in an expression for the average error probability which is in the form of a leading term representing the ideal (perfect synchronization references) performance plus a term proportional to the mean-squared crosstalk. Thus, the additional error probability due to noisy synchronization references occurs as an additive term proportional to the mean-squared phase jitter \sigma_{\phi}^{2} directly associated with the receiver's tracking loop. Similar arguments are advanced to give closed-form results for the noisy reference loss itself.

Four-phase staggered shift keying modulator system

Abstract: A four phase staggered phase shift keying modulator system having means to modulate a voltage controlled oscillator generating the carrier by positive or negative pulses of a predetermined duration to shift the phase of the carrier by +90° or -90°, the positive or negative being produced by individual coding of a series of applied pulses.

14-GHz MIC 16-ns Delay Filter for Differentially Coherent QPSK Regenerative Repeater

Abstract: A parallel-coupled microstrip fused silica filter at 14 GHz was developed as a 16-ns delay element for application to direct detection with a differentially coherent quaternary PSK (DQPSK) demodulator/regenerator module of an onboard regenerative repeater for future satellite-switched time-domain multiple-access (SS-TDMA) satellite communications systems. Design considerations, experimental results of the 14-GHz bandpass delay element, and a technique for precision measurement of the fused silica filter delay phase temperature coefficient are presented. In addition, the expected DQPSK demodulator performance is evaluated by simulation analysis using a comprehensive transmission channel modeling program.

Imperfect Carrier Recovery Effect on Filtered PSK Signals

Abstract: Coherent demodulation of a PSK signal requires the generation of a local carrier phase reference. Methods are given to determine the detection loss caused by noisy phase recovery and its use in the coherent detection of filtered BPSK and QPSK signals. It is assumed that the phase noise can have a static part and a random component with a Tikhonov-type distribution. The static part is mostly due to offset frequency tracking of the PLL used to recover the carrier, while the random component is due to thermal noise present in the carrier recovery loop and is also due to the random nature of the phase modulation. It is shown that the probability of error of BPSK and QPSK can be expressed as a finite sum of a set of strictly alternating converging series when the number of ISI terms is finite. Upper and lower bounds on the probability of error have been derived when this number becomes infinite and we show how this error rate can be computed with any desired accuracy. Numerical results are presented for various values of static error and phase noise variance when the transmit and receive filters are 4-pole Butterworth filters. For filtered PSK signals and for a bit error rate of 10-6, our results show that the additional degradation in presentday receiver systems due to imperfect carrier recovery can be less than 0.1 dB for BPSK and less than 1 dB for QPSK.

Performance of Phase Comparison Sinusoidal Frequency Shift Keying

Abstract: Some communication systems require the close packing of many signals into a fixed bandwidth while precluding an absolute phase reference at the receiver and time synchronization between the signals. This paper investigates the bit error performance in the presence of white Gaussian noise of PCSFSK, which has been found to be very bandwidth efficient under the above conditions; much more efficient than DQPSK. PCSFSK is found to perform slightly better than an upper bound on the performance of DQPSK for high signal-signal-to-noise ratios and somewhat worse for low signal-to-noise ratios, while allowing much closer packing of unsynchronized signals.

Error-signal generation for pseudonoise tracking loops

Abstract: The paper discusses various alternative error functions for the delay-lock tracking-loop used for synchronisation of received and locally-generated sequences in communications and ranging systems which employ a pseudonoise subcarrier. For each error function, a variety of structures for generating it are given.

An Integrated DQPSK Demodulator for 14-GHz Satellite Communications Applications

Abstract: An MIC assembly for direct DQPSK demodulation at 14 GHz is described. A time delay of 16.6 ns (120 Mbit/s) is achieved by edge-coupled bandpass filters. Quadrature phase detection is provided by a novel MIC topology that causes RF and IF ports to occur in adjacent pairs. An electronic phase shifter provides near linear phase shift with bias voltage. Temperature compensation maintains the phase errors to within 5/spl deg/ for a 20/spl deg/C temperature change.

1.6-Gb/s 16-Level Superposed APSK Modem with Baseband Signal-Processing Coherent Demodulator

Abstract: A 1.6-Gb/s 16-level superposed APSK modem using a newly developed baseband signal-processing coherent demodulator is described. ln the modulator, the superposing modulation method is adopted in which two QPSK carriers having different levels are superposed so that the combined signal forms a 16-level APSK carrier. Sixteen signal points are arranged in lattice form on the signal space. In the demodulator, a newly developed carrier recovery loop is adopted in which quantizing error signals are detected in the process of data regeneration; they are used for generating the phase error signal to control a VCO. The principles of operation and theoretical analysis of this carrier recovery loop is described, through which it is shown that the recovered carrier has inherently low-pattern jitter power. Furthermore, it features a very simple circuit configuration. The circuit configurations of an experimental modem and some important test results are deseribed in detail. It is shown that the modem has improved performance characteristics in such a high-speed region as 1.6 Gb/s while its circuit configuration is much simplified.

Modulation and Coding Study for the Advanced Narrowband Digital Voice Terminal.

Abstract: : A study was performed of modulation and coding techniques to support development of specifications for an advanced narrowband digital voice terminal. Emphasis was on the development of a signal design for HF radio transmissions. The results indicate that transmission channel effects can be significantly reduced by the application of forward acting error correction coding to the most sensitive bits of the digital voice signal. A recommendation is made to use the Golay (24, 12) code, with soft decision decoding, to protect 44 percent of each frame of data generated by a linear predictive encoder. This would result in a transmission rate of 3466.6 bps for an input of 2400 bps using multi-tone four phase differentially coherent phase shift keying. (Author)

Some Effects of Phased-Array Dispersion on Digital Error Rates

Abstract: Some calculations of the effect of phased-array dispersion on degrading phase-shift-keyed (PSK) error rates are presented. The results are given in the form of curves of the bit error rate versus the ratio of array "fill-time" (propagation time across the array) to signaling interval. Values of this ratio in the range 0.5 to 0.8 are required to degrade the error rate by a factor of 2. These results were obtained for both linear and square arrays, and for rectangularpulse signaling over single-pole and two-pole Butterworth equivalent low-pass channels, as well as for impulsive signaling over an idealized channel with a raised-cosine frequency response.

Experimental Evaluation of MSK and Offset Keyed QPSK Through Satellite Channels

Abstract: Laboratory test measurements show nearly equivalent error rate performance of MSK and OKQPSK modulation formats for channels having bandwidths approximately equal to the bit rate bandwidth and typical associated phase delay characteristics. High quality MSK and OKQPSK transmitters and a versatile modular receiver have been designed and constructed to eliminate differences associated with varying degrees of hardware quality when the performance of the various modulation formats is compared. The selection of a modulation format should, therefore, be strongly directed by considerations other than error rate, such as complexity, sensitivity to alignment, and compatibility with differential coding. INTRODUCTION In recent years MSK has become an increasingly popular modulation technique for signaling through band limited channels in which data must be efficiently packed into the restricted bandwidth. 2, 3 MSK appears attractive for such signaling because more of its energy is concentrated toward the band center, and less in sidelobes, when compared to the other most popular digital modulation techniques, QPSK and offset keyed QPSK (OKQPSK). Each of these three signaling techniques is equivalent to a bi-orthogonal set; therefore, they perform identically in a non-band limited channel. The objective of this study is to compare the performance of MSK and OKQPSK when operating through various degrees of channel bandlimiting. Data were collected with a laboratory test modem with a 1.5 GHz carrier operating at 80 Mbps, and include both integrate and dump and passive data filters. The results indicate that for severely band limited channels offset QPSK outperforms MSK, while with more moderate band limiting MSK is better. The results also indicate that incorporation of high quality phase equalizers yields better performance improvement with MSK than with OKQPSK. LABORATORY MODEM A high quality, flexible 80 Mbps laboratory modem capable of operating in either MSK or OKQPSK modes with a 1.5 GHz carrier was developed. The 80 Mbps rate was selected because it is both low enough to allow accurate simulation of distortion, and high enough to evaluate performance at low error rates. To ensure modulation format differences are not masked by hardware implementation, extensive effort was given to the construction of nearly ideal performing transmitters and receivers. Figure 1 is the block diagram of the 80 Mbps evaluation modem. This modem includes MSK and OKQPSK transmitters, which were switched into the modem as required, and a versatile modular receiver capable of demodulating MSK with sinusoidal weighting, MSK with no weighting, and OKQPSK. A matched filter receiver is one in which a received signal is correlated with its stored replica followed by an integration operation. For an undistorted MSK signal, the required operation is correlation of the received signal with the recovered carrier and a sinusoid at half the symbol rate. Such a matched filter configuration for MSK is referred to as MSK with sinusoidal weighting. When the MSK signal is correlated with only the recovered carrier, this receiver is referred to as MSK with no weighting. Demodulation of an OKQPSK signal requires correlation with only the recovered carrier. The digital test modem was implemented so that its configuration could be altered from matched MSK (sinusoidal weighted correlation) to matched OKQPSK, or to unmatched MSK (no weighting) by passive component adjustments only. This makes possible the use of the same receiver components and guarantees identical receiver characteristics for each demodulation scheme considered. The modem was assembled in the following configurations for the study.