Showing papers on "Phase-shift keying published in 1989"

Delayed decision-feedback sequence estimation

Abstract: The authors delayed-decision-feedback sequence estimation (DDFSE) for uncoded PAM signals is considered. Estimates on the performance of the algorithm are given, and simulation results are provided for several examples. A more general form of DDFSE applicable to coded modulation systems is also presented. As an example, detection of trellis-coded QPSK (quadrature phase-shift keyed) signals over intersymbol interference channels is discussed. >

A pragmatic approach to trellis-coded modulation

Abstract: Since the early 1970s, for power-limited applications, the convolutional code constraint length K=7 and rate 1/2, optimum in the sense of maximum free distance and minimum number of bit errors caused by remerging paths at the free distance, has become the de facto standard for coded digital communication. This was reinforced when punctured versions of this code became the standard for rate 3/4 and 7/8 codes for moderately bandlimited channels. Methods are described for using the same K=7, rate 1/2 convolutional code with signal phase constellations of 8-PSK and 160PSK and quadrature amplitude constellations of 16-QASK, 64-QASK, and 256-QASK to achieve, respectively, 2 and 3, and 2, 4, and 6 b/s/Hz bandwidth efficiencies while providing power efficiency that in most cases is virtually equivalent to that of the best Ungerboeck codes for constraint length 7 or 64 states. This pragmatic approach to all coding applications permits the use of a single basic coder and decoder to achieve respectable coding (power) gains for bandwidth efficiencies from 1 b/s/Hz to 6 b/s/Hz. >

Bandwidth efficient coding for fading channels: code construction and performance analysis

Abstract: The authors apply a general method of bounding the event error probability of TCM (trellis-coded modulation) schemes to fading channels and use the effective length and the minimum-squared-product distance to replace the minimum-free-squared-Euclidean distance as code design parameters for Rayleigh and Rician fading channels with a substantial multipath component. They present 8-PSK (phase-shift-keying) trellis codes specifically constructed for fading channels that outperform equivalent codes designed for the AWGN (additive white Gaussian noise) channel when v>or=5. For quasiregular trellis codes there exists an efficient algorithm for evaluating event error probability, and numerical results which demonstrate the importance of the effective length as a code design parameter for fading channels with or without side information have been obtained. This is consistent with the case for binary signaling, where the Hamming distance remains the best code design parameter for fading channels. The authors show that the use of Reed-Solomon block codes with expanded signal sets becomes interesting only for large value of E/sub s//N/sub 0/, where they begin to outperform trellis codes. >

TCMP-a modulation and coding strategy for Rician fading channels

Abstract: The authors describe TCMP, a novel modulation strategy for Rician fading channels that multiplexes a time domain pilot sequence with trellis-coded data to permit coherent detection. This technique is shown to provide remarkably robust performance in the presence of fading. It is also shown that, when choosing trellis codes for fading channels, time diversity is of greater important than asymptotic coding gain. The motivation for studying this strategy is to find signaling schemes for transmitting data at a 4.8 kb/s rate over a mobile satellite channel with 5-kHz channel spacing. >

Quadrature-quadrature phase-shift keying

Abstract: Quadrature-quadrature phase-shift keying (Q/sup 2/PSK) is a spectrally efficient modulation scheme which utilizes available signal space dimensions in a more efficient way than two-dimensional schemes such as QPSK and MSK (minimum-shift keying) It uses two date shaping pulses and two carriers, which are pairwise quadrature in phase, to create a four-dimensional signal space and increases the transmission rate by a factor of two over QPSK and MSK However, the bit error rate performance depends on the choice of pulse pair With simple sinusoidal and cosinusoidal data pulses, the E/sub b//N/sub 0/ requirement for P/sub b/(E)=10/sup -5/ is approximately 16 dB higher than that of MSK Without additional constraints, Q/sup 2/PSK does not maintain a constant envelope, however, a simple block coding can provide a constant envelope This coded signal substantially outperforms MSK and TFM (time-frequency multiplexing) in bandwidth efficiency Like MSK, Q/sup 2/PSK also has self-clocking and self-synchronizing ability An optimum class of pulse shapes for use in Q/sup 2/PSK format is presented One suboptimum realization achieves the Nyquist rate of 2 b/s/Hz using binary detection >

Stimulated Brillouin scattering excited by a modulated pump wave in single-mode fibers

Abstract: The effects of modulation on the gain of stimulated Brillouin scattering (SBS) are discussed. Three different modulation techniques, i.e. frequency shift keying (FSK), amplitude shift keying (ASK), and phase shift keying (PSK) are considered. The results show that the SBS threshold depends on the ratio between the spontaneous Brillouin linewidth and the bit rate. The SBS threshold for ASK and FSK is 6 dB higher at high bit rates, whereas the SBS threshold for PSK increases by 10dB for each factor of 10 increase in the bit rate. >

Automatic modulation recognition of digitally modulated signals

Abstract: A modulation recognizer that automatically reports modulation types of constant-envelope modulated signals is developed using zero-crossing techniques. The zero-crossing sampler, as a signal conditioner, has the advantage of providing accurate phase transition information over a wide dynamic frequency range. Signal parameters, such as zero-crossing variance, carrier-to-noise ratio (CNR), and carrier frequency, are estimated. Phase-difference and zero-crossing-interval histograms play the roles of features for modulation recognition. The classifier performance is given in the form of a confusion matrix. The obtained simulation results demonstrate that reasonable average probability of correct classification is achievable at CNR=15 dB and higher. >

An all digital receiver architecture for bandwidth efficient transmission at high data rates

Abstract: Using the maximum-likelihood approach, algorithms for detection and synchronization are derived that are well suited for VLSI implementation. Special emphasis is placed on an all-digital implementation where carrier and clock synchronization do not require a feedback of signals to the analog part, which simplifies the analog front-end design (mixing oscillator and A/D converter sampling clock run at fixed frequency). An important advantage of the proposed algorithms is that a high clock rate is not required; only two-four times the symbol rate is needed, depending on amplitude quantization. Implementation aspects, e.g. architecture, and quantization, are considered. A prototype is described which was implemented to prove the feasibility of the concept and to evaluate the performance under practical conditions. >

Multi-symbol detection of M-DPSK

Abstract: The authors discuss optimal and suboptimal detection methods for improving the error performance when M-ary DPSK (differential phase shift keying) modulation is employed. All procedures use a block of N+1 measurements to produce N data decisions. The motivation is to lessen the energy penalty associated with classical DPSK detection and to approach the performance of fully-coherent detection, but without complicated feedback phase-tracking circuitry and the associated phase-acquisition time. The authors formulate optimal (block) detection under the assumption of unknown carrier phase. Performance analysis and simulation show significant improvement with increasing blocklength, but complexity increases exponentially in blocklength. Suboptimal methods are then proposed which have far less complexity, but retain the improvement over standard DPSK. The primary applications of the present work are in fast-acquisition TDMA (time-division multiple-access) systems with PSK modulation and in frequency-hopping systems using DPSK. >

Channel modeling and adaptive equalization of indoor radio channels

Abstract: The authors analyze the benefits of using a decision feedback equalizer (DFE) in the indoor radio environment and examine the results of performance predictions for different channel modelings. It is found that a QPSK/DFE modem with second-order diversity can operate at a data rate that is an order of magnitude higher than a QPSK (quadratic-phase-shift-keying) modem without equalization. A given set of measured profiles of the channel impulse response is interpreted using continuous and discrete channel models. The continuous channel model is represented by the delay power spectrum and the discrete channel model by the envelope delay power spectrum and the arrival rate of the paths. The sensitivity of the performance to the shape of the delay power spectrum, and the arrival rate of the paths is analyzed. >

Phase error free LINC modulator

Abstract: A new technique for linear amplification with nonlinear components (LINC) is described LINC implementation is thought to be very difficult because of its sensitivity to phase error caused by the difference in electrical length between two power amplifier branches The allowable limit of phase error for achieving the 60 dB suppression of the adjacent channel interference (ACI) power is estimated for roll-off bandlimited offset QPSK (OQPSK) Then, a compensating method for this phase error is presented By using the proposed method, sufficient out-of-band spectrum suppression for mobile radio application is obtained An output power of 75 W and a power efficiency of 21% are experimentally confirmed

Generalized Viterbi algorithms for error detection with convolutional codes

Abstract: Presented are two generalized Viterbi algorithms (GVAs) for the decoding of convolutional codes. They are respectively, a parallel algorithm that simultaneously identifies the L best estimates of the transmitted sequence, and a serial algorithm that identifies the lth best estimate using the knowledge about the previously found l-1 estimates. These algorithms are applied to combined speech and channel coding systems, concatenated codes, trellis-coded modulation, partial response (continuous-phase modulation), and hybrid ARQ (automatic repeat request) schemes. As an example, for a concatenated code more than 2 dB is gained by the use of the GVA with L=3 over the Viterbi algorithm for block error rates less than 10/sup -2/. The channel is a Rayleigh fading channel. >

Design of coded CPFSK modulation systems for bandwidth and energy efficiency

Abstract: Consideration is given to the problems related to the design of M-ary continuous-phase frequency-shift keying (CPFSK) systems with modulation index h=J/M, combined with eternal rate r binary convolution encoders. The following questions are raised and answered: (1) how should different encoder-modulator systems be compared and how can comparable systems be recognized from the system parameters, i.e. M, h, and r?; (2) what are the limits on the information rate per unit bandwidth, versus signal-to-noise ratio, when reliable transmission is required?; (3) how does one choose the system parameters M, h, and r when the overall system has to achieve a specified performance?; and (4) how does one design the external rate r binary convolutional encoder to put in front of the M-ary CPFSK modulation system with h=J/M? A simple approximation for the bandwidth of a CPFSK signal is given and shown to be sufficiently accurate for system design purposes. The design of the external convolutional encoder is carried out in a novel way that leads to fewer states in the combined encoder-modulator system and thus yields improved performance for a given demodulation-decoding complexity compared to previous approaches for the design of coded CPFSK systems. >

Performance of interleaved trellis-coded differential 8-PSK modulation over fading channels

Abstract: The performance of trellis-coded differential octal phase-shift keying (coded 8-DPSK) with differentially coherent detection and soft-decision Viterbi decoding is investigated. A suitable receiver is presented whose signal processing is based on Nyquist signaling, requiring only one complex sample per modulation interval. Symbol synchronization and automatic frequency control are performed in a decision-directed way. Bit-error-rate (BER) performance over Gaussian, Rayleigh, and Rician channels is determined by means of computer simulations. The performance of coded 8-DPSK on the Gaussian channel is shown for a four-state convolutional trellis code. The unquantized outputs of up to three symbol detectors with delays of 1, 2, and 3 symbol periods are used for metric computation. The coding gain which includes losses due to timing and frequency synchronization errors is found to be 2.5 dB at BER=10/sup -5/ with respect to uncoded 4-DPSK. Much larger gains are achieved for fading channels if interleaving is applied. Using an eight-state trellis code the performance is determined on Rayleigh and Rician channels for various Doppler spreads and interleaver sizes. >

Rotationally invariant trellis-coded modulations with multidimensional M-PSK

Abstract: Using a multidimensional approach, the author discovers a large family of rotationally invariant trellis-coded M-PSK (M-ary shift keying) schemes, M>or=8, with nominal coding gains ranging from 3 to 5 dB and with bandwidth requirements the same as, or even less than, those of uncoded M/2-PSK schemes at the same information bit rate. The rotationally invariant schemes have performance and complexities comparable to the best known nonrotationally-invariant trellis-coded two-dimensional M-PSK schemes. Computer simulation results for these schemes, assuming an additive white-Gaussian-noise (AWGN) channel, are reported. >

Narrow-band interference rejection using real-time Fourier transforms

Abstract: An analysis is presented of a BPSK-PN (binary phase shift-keyed with pseudonoise) demodulator when present narrowband interference is attenuated using transform domain filtering. The signal of interest is a wideband direct-sequence spread-spectrum signal (DS-SS). The interference is a narrowband signal which may be of high power and which is either intentionally or unintentionally collocated in frequency and interfering with the signal of interest. The effect of windowing the input signal by a rectangular or Hamming windows as well as the use of an overlap and save scheme is presented. It is shown that the Hamming window far outperforms the rectangular window, and that the interference is for all purposes completely eliminated when the Hamming window is used in conjunction with the overlap and save scheme. The criterion used to evaluate the effectiveness of the different interference rejection techniques is the bit error rate (BER) as measured at the output of the demodulator. >

Throughput performance of an unslotted direct-sequence SSMA packet radio network

Abstract: A spread-spectrum multiple-access (SSMA) packet radio network model is presented. The topology is a fully connected network with identical message generation processes at all radios. Packet lengths are exponentially distributed, and packets are generated from a Poisson process, resulting in a Markovian model. This network model accounts for the availability of idle receivers in a finite population network. The model also allows the performance of the radio channel to be specified in detail. The channel considered is a BPSK (binary phase-shift keying) direct-sequence SSMA radio channel with hard-decision Viterbi decoding. An analysis of the Viterbi decoder leads to a bound on its performance which is valid for a system with a varying probability of error, as is the case for the network under consideration. The approximate analysis yields lower bounds on throughput and probability of successful packet transmission. Results are given which show the effects on throughput of the received energy-to-noise density ratio, the number of chips per symbol, and the number of radios, as well as the improvement due to error control coding. >

Noncoherent detection of pi /4-QPSK systems in a CCI-AWGN combined interference environment

Abstract: The performance of pi /4-QPSK modems in a cochannel interference (CCI) and additive white Gaussian noise (AWGN) environment is studied. Three differential detection models are described and modified to improve the BER (bit error rate) performance of the detector: (1) baseband differential detection, (2) IF (intermediate frequency) band differential detection, and (3) FM-discrimination detection. Computer simulation results show that, if optimal filter separation is used, the three differential detection schemes can achieve optimal performance for differential detection. The simulation results also show that, for a stationary environment without Rayleigh fading at 15-dB signal-to-interference ratio (CIR), the BER is only 1.3-dB degraded at P/sub e/=10/sup -2/ compared to an AWGN-only environment. If CIR decreases to 9 dB, however, the eye-diagram closes and an error floor of 10/sup -3/ occurs even without noise. The impact of random FM on differential detection is also studied. >

Diversity selection using coding in a portable radio communications channel with frequency-selective fading

Abstract: It is shown that the degradation in the performance of wideband digital transmission systems due to intersymbol interference can be reduced by utilizing diversity selection using coding A BCH (31, 21, 5) double-error-correcting code and QPSK (quadrature-phase-shift-keying) modulation with coherent detection are used for this study The probability of word error is taken to be the measure of system performance Analytic expressions are derived for the word error probability; these expressions simplify the simulation processes It is found that a diversity selection algorithm using coding can reduce the floor of word error probability, and hence increase the dynamic range of received power before the word error probability reaches that floor >

Multichannel CPFSK coherent optical communications systems

Abstract: A detailed theoretical analysis of multichannel coherent CPFSK communications systems is presented. The analysis accounts for the crosstalk between adjacent channels, the intersymbol interference and correlation between noise samples stemming from the limited IF bandwidth the non-Gaussian statistics of the noise at the decision gate, and the impact of the laser phase noise. It is found that the IF bandwidth needed to avoid intersymbol interference is 2.2 bit rates for a modulation index m=1; it is larger for other modulation index values. For m=1, receiver sensitivity is within 1 dB of the shot noise limit, and the electrical domain channel spacing can be as small as 2.05 bit rates with 1-dB sensitivity penalty. The foregoing conclusions are valid for a negligibly narrow linewidth; the degradation due to phase noise is shown to be modest as long as the linewidth does not exceed 1% of the bit rate if m=1. Larger linewidth can be tolerated if the modulation index is larger than unity. >

Noncoherent detection of convolutionally encoded continuous phase modulation

Abstract: The authors consider the error probability at large signal-to-noise ratios of rate-1/2 convolutionally encoded CPFSK (continuous-phase frequency-shift keying) with an optimum noncoherent detector on an additive white Gaussian noise channel. The performance is given in terms of a parameter called the minimum squared normalized equivalent Euclidean distance which plays the same role mathematically as the minimum squared normalized Euclidean distance used for coherent detectors. It is shown that by introducing convolutional coding the error performance is significantly improved. The authors propose a decoding algorithm for these convolutionally encoded CPM schemes which is based on a limited tree search algorithm and uses the maximum-likelihood decision rule for noncoherent detection. Computer simulations show that the degradation in error performance compared to the performance of the optimum coherent Viterbi detector is less than 1 dB with a relatively simple noncoherent detector on an additive white Gaussian noise channel for most of the schemes considered. >

Distribution line communications using CSMA access control with priority acknowledgements

Abstract: The authors describe the use and performance of CSMA (carrier-sense multiple access) with priority acknowledgements for medium access control on distribution power line communication networks. Such networks suffer from highly variable, ever-changing, and unpredictable signal-to-noise ratio. The architecture of the CSMA implementation is described, along with its advantages relative to other access control schemes. The best packet length, in terms of throughput maximization, was found to approximate 1000 bits. Delay-throughput performance is measured, and the particular effects on performance of the power-line channel behavior are ascertained. Extensive tests were conducted on intrabuilding lines using channel bit rates from 1200 to 19200 bits/s, with FSK (frequency-shift keying) and spread-spectrum PSK (phase-shift keying) modems transmitting at 3 V RMS at frequencies ranging from 40 to 120 kHz. The reported results include potentially difficult cases involving transmission across power phases. >

Probability of error for selection diversity as a function of dwell time

Abstract: An expression is derived for the probability of error of an Nth-order selection diversity system for the case where the receiver is forced to swell on one channel for several symbols before being allowed to make a decision regarding the best channel. It is found that the time-varying nature of a fading channel causes significant degradation of the probability of error when the dwell time becomes longer than about 10% of the inverse of the fading bandwidth of the channel. The onset of degradation is a function of the signal-to-noise ratio and of the order of diversity. Specific probabilities of error are calculated for differential phase-shift keyed modulation (DPSK). However, the calculations can be done for any other modulation technique. >

Optical phaselock receiver with multigigahertz signal bandwidth

Abstract: We have built a balanced pin FET receiver which employs two signal amplification paths for homodyne detection of multigigabit-per-second, pilot-carrier PSK optical signals. Using narrow-line 1.51µm semiconductor lasers, we have employed this receiver to phaselock a local oscillator to a 295 pW pilot carrier with 8° RMS phase error.

5 Gbit/s direct optical DPSK modulation of a 1530-nm DFB laser

Abstract: 5 Gb/s direct optical differential-phase-shift-keying (DPSK) modulation of a 1530-nm distributed feedback (DFB) laser is demonstrated using injection current modulation with a bipolar signal format. Delay demodulation is performed using an interferometer with a delay time T equal to the duration of one bit. The input and differentially encoded nonreturn to zero (NRZ) signals are shown. The bipolar modulation current signal is basically the time derivative of the NRZ signal. There was no degradation of the optical DPSK signal due to thermal frequency modulation of the laser. The direct DPSK modulation technique avoids the insertion loss and systems complexity of external DPSK modulators. >

The effects of delay spread on 2-PSK, 4-PSK, 8-PSK and 16-QAM in a portable radio environment

Abstract: Computer simulation results are presented of a study of delay spread on digital modulations with different constellations in a quasi-static multipath radio channel. Unfiltered 2-, 4-, and 8-PSK and 16-QAM with a rectangular signaling pulse are compared first, followed by 4- and 16-QAM with a raised-cosine Nyquist pulse. The bit error rate performances averaged over fading samples under the influence of the intersymbol interference caused by delay spread are compared for modulations of different levels. It is found that 4-level modulation is the most desired method for both performance and implementation in a quasistatic, frequency-selective fading radio channel. Both the spectral and the power efficiencies can be enhanced using Nyquist signaling pulses. >

Optimal decoding in fading channels: a combined envelope, multiple differential and coherent detection approach

Abstract: A maximum likelihood sequential decoder for the reception of digitally modulated signals with single or multiamplitude constellations transmitted over a multiplicative, nonselective fading channel is derived. It is shown that its structure consists of a combination of envelope, multiple differential, and coherent detectors. The outputs of each of these detectors are jointly processed by means of an algorithm. This algorithm is presented in a recursive form. The derivation of the new receiver is general enough to accommodate uncoded as well as coded (e.g. trellis-coded) schemes. Furthermore, reduced complexity, near-optimal versions of the algorithm are also presented. Performance evaluation results for a reduced-complexity trellis-coded QPSK (quadrature phase shift keying) system have demonstrated that the proposed receiver dramatically reduces the error floors caused by fading. At E/sub b//N/sub 0/=20 dB the new receiver structure results in bit error rate reductions of more than three orders of magnitude compared to a conventional Viterbi receiver, while being reasonably simple to implement. >

BER evaluation for phase and polarization diversity optical homodyne receivers using noncoherent ASK and DPSK demodulation

Abstract: An analysis of the performance of phase diversity receivers using amplitude-shift keying (ASK) and differential phase-shift keying (DPSK) is presented. Both (2*2) and (3*3) multiport receivers are investigated. Asymptotic methods are used to estimate the bit error rate (BER) and signal-to-noise power ratio (SNR) dependence for each type of the receiver. The analysis favors the squarers as the demodulators for ASK whose performance approaches that of the ideal heterodyne detector in the limit of large SNR. A modification of the ASK ((3*3)) receiver which cancels the local oscillator intensity noise is proposed. Receivers which comprise polarization and phase diversity techniques are also investigated for both ASK and DPSK. Their performance is independent of the polarization state of the received signal, and the value of SNR required to obtain the BER of 10/sup -9/ is only a few tenths of a decibel greater than that needed by the phase diversity receivers. >

Offset DPSK with differential phase detector in satellite mobile channel with narrow-band receiver filter

Abstract: An expression is derived for the error probability of M-ary offset differential phase-shift keying (DPSK) with the differential phase detector and narrowband receiver filter in the satellite mobile (Rician) channel, which includes as special cases the Gaussian and land mobile (Rayleigh) channels. The error probability is computed as a function of various system parameters for M=2, 4, and 8 symbols and third-order Butterworth receiver filter. Both symmetric and conventional DPSK systems are considered. The optimal normalized bandwidth is close to 1.0. Symmetric and conventional DPSK differ significantly in error probability only for M=2 and in the lower range filter bandwidth. In most cases, symmetric DPSK outperforms conventional DPSK. This was particularly noted when the time delay between the specular and diffused signal components was taken into account. >

Trellis coded noncoherent QAM: a new bandwidth and power efficient scheme

Abstract: The authors introduce the concept of noncoherently detected, multilevel/phase trellis coded schemes. They derive the optimal noncoherent decoding algorithm for trellis coded QAM (quadrative-amplitude-modulated) signals. Further, two reduced complexity decoder structures are proposed and analyzed. The first is based on a reduced state algorithm, whereas the second one uses a novel algorithm that combines both envelope and multiple differential detection. The two decoders have been evaluated for a 16-QAM signalling format by means of computer simulation. The results indicate that the proposed schemes have performance gains of up to 5 dB over equivalent conventionally detected noncoherent systems. >