Showing papers on "Phase-shift keying published in 1985"

Performance of MRC Diversity Systems for the Detection of Signals with Nakagami Fading

Abstract: Bit error rate (BER) is analyzed theoretically for diversity reception in Nakagami fading environment using an M -branch maximal ratio combiner (MRC). Coherent and incoherent reception of frequency shift keying (FSK) are considered, using the multiple branch diversity system for both identical and different diversity branch fading parameters. The effect of correlation is also considered for the dual diversity case. The results are extended to include coherent phase shift keying (CPSK) and differential phase shift keying (DPSK).

Coherent lightwave communications

Abstract: The chief objective of this paper is to develop a fundamental understanding of the effects of laser phase noise on the performance of coherent lightwave communication systems. A comprehensive treatment applicable to a wide variety of coherent receiver designs under a broad range of conditions is provided. Our models and analytical tools are developed in sufficient detail to encompass a broad range of applications. Formulas are derived for the bit error rate in homodyne and heterodyne Phase Shift Keying (PSK), Differential Phase Shift Keying (DPSK), Frequency Shift Keying (FSK) and on-off keying. Estimates are provided of the penalties accrued due to phase noise. Based on detailed mathematical analysis and estimates, we made several findings. Near quantum-limited receiver sensitivity can be achieved with PSK using homodyne detection only at signaling rates 3000 times greater than the laser linewidth. A receiver sensitivity 3 to 6 decibels poorer than the quantum limit can be achieved with heterodyne rather than homodyne detection. DPSK, for example, can operate at rates only 300 times greater than the laser linewidth. At lower rates, FSK is an attractive candidate. It can be designed to be extremely tolerant of phase noise by using wide frequency deviations.

Performance of Noncoherent Direct-Sequence Spread-Spectrum Communications Over Specular Multipath Fading Channels

Abstract: The performance of coherent direct-sequence spread-spectrum communications over specular multipath fading channels is investigated. The average probability of error of the correlation receiver is derived for an arbitrary number of paths with deterministic or random gain coefficients. The gain coefficients, delays, and phase angles of any two distinct paths are modeled as mutually independent random variables. Numerical results for several values of the system and channel parameters are presented.

Convolutional Coding Combined with Continuous Phase Modulation

Abstract: Background theory and specific coding designs for combined coding/modulation schemes utilizing convolutional codes and continuous-phase modulation (CPM) are presented. In this paper the case of r = 1/2 coding onto a 4-ary CPM is emphasized, with short-constraint length codes presented for continuous-phase FSK, double-raised-cosine, and triple-raised-cosine modulation. Coding buys several decibels of coding gain over the Gaussian channel, with an attendant increase of bandwidth. Performance comparisons in the power-bandwidth tradeoff with other approaches are made.

The Role of AM-to-PM Conversion in Memoryless Nonlinear Systems

Abstract: A generalized proof is presented that AM-to-PM conversion can only degrade, never improve, the intermodulation-noise performance of memoryless nonlinear systems with random input signals having even probability density functions, and a measure of degradation is defined. It is also shown for such signals that AM-to-PM conversion causes a deterministic constant phase shift to be added to the argument of the signal component at the output but has no other effect on its phase. This class of inputs includes one or the sum of several PSK signals, as well as large ensembles that can be modeled as Gaussian noise. The latter are dealt with by using Bussgang's theorem on input-output cross correlation. In the proof, Bussgang's theorem is extended to the complex case, to include phase as well as amplitude nonlinearities, yielding a complex version of the theorem. For Gaussian inputs it is shown that the undistorted signal and the intermodulation noise at the output of such systems are uncorrelated.

Demodulation of optical DPSK using in-phase and quadrature detection

Abstract: A 140 Mbit/s optical DPSK system experiment employing a 90 degree optical hybrid to achieve in-phase and quadrature detection is reported. The principle of the optical hybrid is outlined and the effect of polarisation misalignment on the optical performance is compared with that for standard homodyne/heterodyne detection.

Performance of Noncoherent Direct-Sequence Spread-Spectrum Multiple-Access Communications

Abstract: The performance of noncoherent reception in direct-sequence spread-spectrum multiple-access communications systems is investigated for additive white Gaussian noise channels. Analytical and numerical results on the probability of error are presented for binary and M -ary frequency-shift-keying data modulation with noncoherent demodulation and differential-phase-shift-keying data modulation with differentiallycoherent demodulation. Both synchronous and asynchronous systems are analyzed. Systems which employ deterministic as well as random signature sequences are considered. The multiple access capability of noncoherent DS/SS systems is evaluated and compared to that of coherent DS/SS systems with the same parameters. The comparison shows that the loss in the performance of DS/SSMA systems due to noncoherent reception can be considerably larger than the loss incurred to noncoberent single-user systems operating in additive Gaussian noise.

QPSK modulator or demodulator using subharmonic pump carrier signals

Abstract: The present invention relates to a QPSK modulator or demodulator for modulating two different input bit streams with a subharmonic pump carrier signal to produce an appropriately encoded QPSK output signal. The subharmonic pump carrier signal used is a submultiple of a predetermined microwave or millimeter-wave carrier frequency. The QPSK modulator or demodulator is capable of being fabricated on a planar substrate using appropriate stripline filters and a mixer diode in each of an in-phase and quadrature signal path. A fin line arrangement, also capable of fabrication on the substrate, can be used to introduce an appropriately phased subharmonic pump carrier signal into each of the in-phase and quadrature signal paths before each mixer diode. Each mixer diode mixes the associated data bit stream and one of the two appropriately phased pump carrier signals to produce separate output signals which modulate along separate orthogonal axes, which output signals are combined to produce the QPSK modulator output signal.

Coherent Hybrid DS-SFH Spread-Spectrum Multiple-Access Communications

Abstract: The performance of synchronous and asynchronous hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access communications over additive white Gaussian noise channels is examined. Systems employing binary or quaternary phase-shift-keying modulation with coherent demodulation are investigated. Both deterministic and random signature sequences and frequency-hopping patterns are considered and several possible assignments for them are discussed. It is shown that the multiple-access capability of hybrid spread-spectrum is superior to that of pure frequency-hopped spread-spectrum, and inferior to that of pure direct-sequence spread-spectrum for systems with identical bandwidth expansion which employ the same data modulation and demodulation scheme and random hopping patterns and signature sequences.

Data modem system

Abstract: A data modem system incorporates, digital filters (11, 21, 59, 60) in transmitter and receiver units having intermediate frequency stages which operate at a frequency which is an integral multiple of the modulation symbol rate. This enables filtering, modulation and demodulation to be carried out in a relatively simple manner using digital hardware, with conversion between different forms of modulation such as QPSK, BPSK and offset BPSK being possible without substantial hardware modifications. In one embodiment of the invention, the receiver employs a phase estimating circuit (124) to compensate for phase and frequency errors arising when a free-running local oscillator is used as an alternative to one controlled via a phase-locked loop.

SQAM - A new superposed QAM modem technique

Abstract: A spectral and power efficient modulation techniquesuperposed quadrature amplitude modulation (SQAM-is introduced. In SQAM, the premodulation baseband signal is a double-interval ( 2T_{s} ) raised-cosine pulse superposed with weighted single-interval (T s ) raisedcosine pulses. Our results indicate that SQAM has spectral advantages over OQPSK, QBL, and MSK, and better P(e) performance than MSK, IJF-OQPSK (or SQORC), and TFM.

BPSK system with sounder to combat Rayleigh fading in mobile radio communication

Abstract: A simple method is proposed to remove random FM from a fast Rayleigh faded binary phase shift keying (BPSK) signal and the great improved performance of reducing the irreducible error is presented. In the mobile radio environment, there happens inevitably a fast Rayleigh fading which causes random FM. The phase error of the reference signal due to random FM will degrade the bit error rate (BER) performance, even if the signal-to-noise ratio is sufficiently high. In the realization of reliable mobile communication, removal of this random FM is an unavoidable theme. Proposed strategy is to transmit a sounding continuous wave (CW) together with a BPSK signal, each phase being kept orthogonal and each power being kept the same. This CW wave is also used as the reference signal in coherent reception. The BER performance of this system is worse by 3 dB than that of the coherent BPSK in a slow Rayleigh fading environment.

Fade margin calculation for channels impaired by Rician fading

Abstract: Excess path loss due to multipath severely restricts the performance of power limited mobile networks such as those using satellite-aided links. To reduce multipath related losses, the higher elevation angle of the spacecraft can be exploited by utilizing mobile antennas which reduce the strength of the multipath reflections in favor of the line-of-sight signal. The presence of a strong and stable path in a fading link will change the envelope statistics of the received waveform from Rayleigh to a more favorable Rician distribution. It is determined that the excess path loss, or fade margin, of a Rician channel when coherent detection of binary phase shift keying (BPSK) or quaternary phase shift keying (QPSK) signals is considered. The results are presented parametrically such that they can be applied to a wide range of propagation characteristics from heavy fading to nonfading situations. Furthermore, similar results are also given for the case where only limited coverage is provided.

Comparison of High-Level Modulation Schemes for High-Capacity Digital Radio Systems

Abstract: This paper presents a comparative study of four 2n-state quadrature amplitude modulation techniques, namely, 16, 32, 64, and 128 QAM, in a digital radio system environment. The effects of filtering, interference, amplifier nonlinearities, and selective fading are investigated using computational and simulation methods. Increase of the carrier-to-noise ratio (CNR) at a fixed symbol error probability (10^{-3} ) is taken as a robustness criterion.

QPSK transmission system having phaselocked tracking filter for spectrum shaping

Abstract: A system for transmitting digital data employs an angle modulated carrier signal having constant amplitude and a limited spectrum. The system comprises an offset quadrature phase shift key (QPSK) modulator with a "tracking filter" phaselocked loop at the output of the QPSK modulator. The phaselocked loop has a voltage controlled oscillator which produces a constant amplitude carrier signal at the output of the loop, and also has a low pass loop filter which reduces the spectrum of the phase modulated carrier signal. Additional spectrum shaping is obtained by connecting L-R-C circuits to the low pass loop filter to eliminate predetermined frequency components from the output of the loop.

An Analysis of the Sensitivity of Digital Modulation Techniques to Frequency-Selective Fading

Abstract: This Paper investigates the sensitivity to frequency-selective fading of different modulation techniques commonly used in digital radio systems. The modulation methods considered are phase-shift-keying ( M ary PSK), nonoffset and offset quadrature amplitude modulation ( M -ary QAM), and quadrature partial response signaling (QPRS). The performances of these methods during multipath fading are compared on the basis of the "signatures" calculated for idealized systems. Results are presented from which the relative outage probability was determined, assuming a propagation channel with frequency-selective Rician fading.

Speech and data communications over 942 MHz TAB and TTIB single sideband mobile radio systems incorporating feed-forward signal regeneration

Abstract: The transmission of speech and data over 942 MHz pilot tone single sideband (SSB) mobile radio links is the main concern of this paper. It has been found that the use of feedforward signal regeneration enables a speech quality to be obtained in the Rayleigh fading environment which is superior to that achieved by a 25 kHz Advanced Mobile Phone Service (AMPS) type FM system and markedly superior to that obtained with a 12.5 kHz FM system. A new optimized form of SSB, phase-locked transparent tone-in-band (TTIB), is shown to be capable of achieving coherent data transmission such as M-ary phase shift keying (PSK) in the presence of Rayleigh fading without the usual "high-level" irreducible error rates. The signal processing described has wide application from line to satellite communications.

A single-chip MSK coherent demodulator for mobile radio transmission

Abstract: Design and performance of a single-chip minimum shift keying (MSK) coherent demodulator fabricated by complementary metal oxide semiconductor-integrated circuit (CMOS-IC) technology is described. The demodulator consists of a phase detection circuit, carrier recovery circuit, data recovery circuit, and timing-clock recovery circuit. For the carrier recovery circuit, three types of Costas-loop are reviewed from the viewpoint that MSK modulation format has a close relationship to binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). Among these loops, a loop of center-frequency locking scheme modified from a BPSK Costas-loop, termed MSK Costas-loop in this paper, is adopted for IC implementation. Digital IC design techniques are next described. Utilizing the sample-and-hold operation of the digital devices, a divided-frequency locking scheme of the quadrature coherent demodulation is proposed. Finally, IC demodulator performance is experimentally shown in the static and Rayleigh fading environments. The bit error rate performance and error-burst characteristic are measured. It is concluded that the single-chip coherent demodulator is suitable for digital mobile radio application.

A comparison of multipath distortion characteristics among digital modulation techniques

Abstract: In a digital mobile radio transmission, long-delayed multi-path propagation causes frequency selective fading, resulting in signal waveform distortion and hence bit error rate (BER) degradation. Comparison of multipath distortion among various digital modulation techniques (binary, quaternary, offset quaternary, and minimum phase shift keying (BPSK, QPSK, OQPSK and MSK)) is made using a two-ray propagation model, which is a fundamental model to evaluate multipath tolerant capability. The analysis clarified the multipath conditions causing severe distortions and also the mechanisms of eye pattern degradation, showing the superiority of BPSK in multipath tolerance.

Optical source linewidth criteria for heterodyne communication systems with PSK modulation

Abstract: The performance of an optical heterodyne communication system is analysed for the cases of phase-shift keying (PSK) with synchronous electrical demodulation and differential PSK with non-synchronous demodulation. The combined effect on the system performance from the shot noise, quantum phase noise of the optical sources and the pulse shaping are considered. From the results, criteria are given for the maximum linewidth of the transmit and local optical sources to satisfy a given degradation in the optical receiver sensitivity.

A 120 mb/s qpsk modem designed for the intelsat tdma network

Abstract: This paper presents the major aspects of a 120 Mb/s QPSK modem developed for use within the INTELSAT TDMA network. Particular attention is focused upon the most important elements of the modem, namely the pre-modulation lowpass filters, the demodulator AGC, the carrier and symbol timing recoveries and the demodulator filtering strategy. In addition to the modem description, details of a burst mode bit error rate test equipment will also be given. This test equipment was especially designed to simulate a practical TDMA working environment thus enabling the modem's burst mode performance to be evaluated in laboratory conditions. Finally, the modem's measured probability of bit errors versus Eb/No, and the probability of clock and carrier cycle skips versus Eb/No are presented. Results of the modem performance both in IF and RF loop-back are shown. The modem RF loop-back performance was evaluated using an INTELSAT V satellite simulator.

On binary differential detection for coherent lightwave communication

Abstract: Motivated by the communication problems caused by phase noise in those semiconductor lasers that may be used for fiber-optic data transmission, we consider heterodyned binary Differential Phase-Shift Keying (DPSK) in conjunction with high-rate (short time chip) redundancy as provided by repetition or by more complex coding techniques. In surprising contrast to repetitive coherent phase-shift keying where only a loss of a 2/π (2 db) in power is incurred in the limit of infinitely many infinitesimal time chips, we show that DPSK requires, in this limit, an infinite number of photons per bit. This is true regardless of the coding scheme used with the DPSK modulation. Next we find the bandwidth expansion that minimizes the number of received photons per bit required to hold the error rate at 10−9 for two situations: first for a simple repetition code, and then for a repeated (24, 12) Golay code with maximum likelihood detection. The performance of the latter is assumed to be representative of other optimally detected codes of the same rate, such as convolutional codes with Viterbi decoding. Explicit curves relating required photons per bit to the bandwidth expansion are given for B/R ratios of 0.01 to 10, where B is the laser linewidth and R is the data rate. An example of the results is that for B/R = 0.1 and a bandwidth expansion of 10, about 23 photons per bit are required for the repeated Golay code to perform as well as uncoded DPSK without phase noise (which requires 20 photons per bit for Pe = 10−9). If B/R = 0.01 the bandwidth expansion is reduced to 2, and 12 photons per bit are required, thus outperforming the phase-stable, but uncoded, situation.

Carrier reproducing circuit for phase shift keying signals

Abstract: A frequency converter converts the frequency of a PSK signal into a frequency of a carrier to be reproduced. A carrier reproducing circuit including a PLL circuit reproduces the carrier. The intended data contained in the reproduced carrier is demodulated. A frequency correction data generator forms correction data according to a bit error rate of the demodulated data, and superposes the correction data on a control voltage to a voltage controlled oscillator of the PLL circuit.

Throughput Performance of a Direct Sequence CDMA Packet Radio Network

Abstract: : A Code Division Multiple Access (CDMA) spread spectrum packet radio network model is presented. The topology is a single-hop fully connected network with identical users. The network model allows the performance of the radio links to be specified in detail. A model of a BPSK Direct Sequence (DS) CDMA radio channel with convolutional Forward Error Correction (FEC) coding is used. A refinement of the network model takes into account the restriction that half- duplex radios cannot transmit and receive simultaneously. Single hop throughput and probability of successful first transmission are derived. The effects on throughput and probability of successful first transmission are derived. The effects on throughput of the received signal strength Eb/No, the number of chips per bit N and the number of users M are shown. A channel load sense access protocol is introduced in which radios are blocked from transmitting when the channel is heavily loaded. The increase in throughput due to this protocol is shown for zero and for non-zero propagation delay. (rh)

Combined trellis coding with asymmetric modulations

Abstract: The use of asymmetric signal constellations combined with optimized trellis coding to improve the performance of coded systems without increasing the average or peak power, or changing the bandwidth constraints of a system is discussed. The trellis code, asymmetric signal set, and Viterbi decoder of the system model are examined. The procedures for assigning signals to state transitions of the trellis code are described; the performance of the trellis coding system is evaluated. Examples of AM, QAM, and MPSK modulations with short memory trellis codes are presented.

Weak-Signal DPSK Detection in Narrow-Band Impulsive Noise

Abstract: The weak-signal receiver for binary differential phase-shift keying (DPSK) in additive noise is derived, and its performance in terms of the error probability in the most general narrow-band impulsive (nonGaussian) noise model, Middleton's class A noise, is analyzed.

Coded octal PSK system performance disturbed by imperfect recovered phase reference

Abstract: There have been various investigations on the PSK modulation technique which is encoded by a convolutional code. For the bandwidth constrained transmission, such as satellite communications, it is important to hold a high information transmission rate. From this viewpoint, the coded 8-phase PSK (8PSK) system seems advantageous. This paper investigates the coded 8PSK system performance using the theoretical analysis and computer simulation when disturbed by the recovered carrier phase error and jitter. The results obtained here should be useful for coded PSK modem design.

Bit synchronization of differentially detected MSK and GMSK

Abstract: The filter-square bit synchronizer has been previously proposed and shown to give near optimum performance for coherent PSK systems In this paper, the same bit synchronization scheme is analyzed for a differentially detected GMSK system It is shown that the filter-square bit synchronizer can successfully work in a differential phase detection receiver By making linear approximations appropriate for high loop signal-to-noise ratio operation (the usual case of interest in tracking), it is demonstrated that the mean-square bit sync jitter of differentially detected GMSK system reveals striking similarities both qualitatively and quantitatively in comparison with that of a coherent PSK system

Error correction scheme

Abstract: An error correcting scheme for processing data which is transmitted on a broadband and/or CATV network and utilizes the IEEE 802.4 three-level duobinary AM/PSK (phase shift keying) coding format. The error correcting scheme utilizes two thresholders. One of the thresholders makes data (1 or 0) decisions while the other thresholder makes non-data or no non-data (non-data) decisions. Pattern matching and windowing are used to detect non-data symbols which are corrected if the non-data symbols deviate from a predetermined pattern. The template used in the pattern matching is determined from the state of a demodulator.