Postdetection diversity using differential phase detection forM-ary DPSK

Postdetection diversity that uses L differential phase detector outputs for data decision is described for M-ary differential phase shift keying (M-ary DPSK. Data decision is based on minimising the weighted sum of the errors of L DPD detector outputs. The squared geometric mean of the two consecutively received signal envelope samples is used as the branch weight. The simulation results on average bit error rate (BER) performances due to additive white Gaussian noise (AWGN), multipath Doppler spread, and delay spread of π/4-shift 4DPSK are reported     

Postdetection phase combining diversity for reception of faded DPSK signals

A new postdetection diversity scheme for the differential phase detection of faded DPSK signals is proposed. It combines the detector outputs in proportion to the squared value of each branch signal envelope. The average BER of pi /4-shift quaternary differential phase shift keying (QDPSK) with two-branch diversity is obtained through computer simulations assuming Rayleigh fading. It is found that the proposed diversity is superior to selection diversity by approximately 1.5 dB.<>     

Postdetection phase combining diversity

We propose a postdetection phase combining (PC) scheme for the two branch diversity reception of differential phase shift keying (DPSK) over multipath fading channels. The receiver has a differential phase detector (DPD) in each diversity branch, and the combiner weights each detector output in proportion to the vth power of the signal envelope at the detector's input. For π/4-shift QDPSK over frequency-flat Rayleigh fading channels, we find via computer simulation that the optimum weight factor is v=2, and that our simple, practical combining scheme performs almost as well as postdetection maximal ratio combining (MRC). We demonstrate similar relative performances for frequency-selective fading channels and for channels with co-channel interference (CCI)     

Improved-performance noncoherent weighted-coefficients diversity combiner for DPSK and NC-FSK signals in nonidentical Nakagami fading channels

It is well-known that noncoherent equal-gain combining (NC-EGC) is the simplest combining technique for noncoherent and differentially coherent communication systems. However, for nonidentical Nakagami-m channels (channels having nonuniform multipath intensity profile (MIP) and/or arbitrary non-integer fading parameters), the use of NC-EGC has three main disadvantages. First, its performance serves as a lossy upper bound to that of the optimum diversity combiner. Second, it results in complicated expressions for the system average error performance. Third, it incurs noncoherent combining loss (does not aid the use of diversity) at relatively low average signal-to-noise ratio (SNR). In this letter, we propose a modified version of the NC-EGC, which is a noncoherent combiner with weighting coefficients, to overcome the disadvantages of the conventional one. We show that this alternative combiner does provide improvements over the conventional N.C-EGC for all values of average SNRs, it does not incur any noncoherent combining loss, and it leads to a design of the receiver whose average error performance can be evaluated easily.     

Bit error rate analysis of reduced-state Viterbi differentialdetection of M-ary DPSK signals

A tight upper bound or bit error rate (BER) is derived for approximate maximum likelihood differential detection (DD) implemented by the reduced state Viterbi algorithm (VA) known as RSVDD. The BER performance of RSVDD is compared with Viterbi DD (VDD) for M-ary DPSK in additive white Gaussian noise (AWGN) channels     

Postdetection MRC diversity for pi /4-shift QDPSK mobile radio

Diversity reception using a postdetection maximal-ratio combiner (MRC) was experimentally investigated for pi /4-shift QDPSK signal transmission in Rayleigh fading environments. Two-branch postdetection MRC diversity reception provides a diversity gain, for a required E/sub b//N/sub 0/, of about 1.5 dB over selection diversity. It is also effective in reducing the impact of multipath channel delay spread. The average BER due to delay spread can be further reduced by a factor of about 1.5 times from selection diversity.<>     

A sectorized beamspace adaptive diversity combiner for multipathenvironments

The beam diversity technique is effective in combating multipath fading in wireless communications. In a beam diversity system, multiple receiving branches are formed with multiple antenna beams with distinctive patterns. These beams are synthesized in such a fashion that the fading phenomena observed at different branches are nearly uncorrelated. The disadvantage of such a system is the lack of adaptivity for cochannel interference (CCI) suppression. In this paper, an adaptive beam diversity combiner is proposed for sectorized signal reception. The diversity branches are formed with several adaptive beamformers whose response patterns encompass an angular sector in the field-of-view of the receiver. With a set of judiciously chosen weight vectors, effective diversity combining can be achieved inside the sector, and out-of-sector CCI can be suppressed via nulling. Simulation results confirm the efficacy of the proposed scheme     

Postdetection diversity receiver for DAPSK signals on the Rayleigh and Rician-fading channel

In this paper, the optimum decision boundaries for (N, M) differential amplitude phase-shift keying on the Rayleigh-fading channel are analyzed. A postdetection maximal ratio combining (MRC) and weighted maximal ratio combining (WMRC) diversity receivers are proposed. In the Rayleigh-fading channel, assuming a high signal-to-noise ratio and a small normalized Doppler frequency, the analytical optimum decision boundaries are obtained. In addition, it is shown that an outer optimum decision boundary is the inverse of the inner optimum decision boundary. In the proposed MRC receiver, the decision at each branch is made based on the minimum distance criterion. The performance of the MRC receiver is analyzed, in terms of the union bound for bit error probability. The proposed WMRC receiver assigns weighting factors to the decision variable at each branch, based on the optimum decision boundaries. The performance of the WMRC is investigated through computer simulation and compared with those of MRC and equal gain combining (EGC). From the results, the performances of MRC and WMRC are found to be better than those of the EGC receiver on both the Rayleigh- and Rician-fading channels. It is also found that the performance improvement of WMRC over MRC is more pronounced as the number of diversity branches increases     

Switched diversity with feedback for DPSK mobile radio systems

Switched diversity with feedback for differential phase shift keying (DPSK) mobile radio is discussed. The technique uses multiple transmit antennas at the base station but only one receive antenna at the mobile. The base station transmits with one antenna that is switched when the mobile informs the base station that the received signal has fallen below a fixed level. The implementation of switched diversity with feedback in a digital mobile radio system is first described, and then the bit error rate performance of the system is analyzed with fading as a function of several design parameters. Implementation of the system is shown to be relatively simple, yet the system is shown to reduce substantially the required received Eb/N0for a given error rate at the mobile as compared to a system without diversity. For example, with five transmit antennas the required received Eb/N0for a 10^-3bit error rate is 13 dB less. The system capacity and availability assuming 32 kb/s audio and flat fading is then discussed. It is shown that with three-corner base station diversity and four transmit antennas at each base station, 126 two-way circuits per cell can be used in a fully loaded 40-MHz bandwidth system with a ten-percent probability that the error rate exceeds 10^-3.     

Postdetection selection diversity effects on digital FM land mobile radio

The postdetection selection diversity effects on a binary digital FM system are theoretically analyzed in the fast Rayleigh fading signal environment encountered in the typical UHF or microwave land mobile radio channels. Both differential and discriminator detections are considered for demodulation of digital FM signal. The average error rate is presented by a simple closed form including both effects of Rayleigh envelope fading and random FM noise. A few examples of numerical results for minimum shift keying (MSK) are graphically presented.     

Time diversity in DPSK noisy phase channels

Differential phase shift keying (DPSK) in the presence of both additive white Gaussian noise and a phase impairment, modeled by a Brownian motion is considered. A time-diversity scheme is used for mitigating the effects of phase noise. This scheme renders a repetition coding approach where the transmitter sends multiple replicas of each data bit. An upper bound on the bit error probability, relying on a bivariate moment-generating function admitted by certain real functionals of the phase sample-path, is derived. The approach taken yields a trackable analysis, which rigorously adheres the phase noise effects. The impact of an incomplete statistical characterization on the tightness of the resultant bound is addressed. The theory, which is applicable to assess the design and performance of general heterodyned lightwave systems using (delay) differential demodulation (as DPSK and CP-FSK, or continuous phase frequency-shift keying), is exemplified and explicit results for the considered time-diversity DPSK scheme are provided. The optimum design of the diversity level is discussed and it is concluded that power efficient transmission is feasible even at bit rates comparable with the signal linewidth     

Low complexity multilevel coding for multiple-symbol differentialdetection

Power and bandwidth-efficient multilevel coding matched to noncoherent transmission with multiple-symbol differential detection is discussed. A simplified metric calculation is proposed, which has a computational complexity comparable to conventional differential detection, but offers almost the entire performance gain provided by multiple-symbol differential detection     

Postdetection switched combining - a simple diversity scheme with improved BER performance

This paper develops, analyzes, and optimizes a simpler form of dual-branch switch-and-stay combining (SSC), namely, one that relies on the output signal plus noise rather than the instantaneous signal-to-noise ratio (SNR) to trigger the switching between the diversity branches. Analysis supported by numerical results show that the newly proposed postdetection SSC scheme outperforms predetection SSC and this performance gain increases as the channel conditions improve in terms of average SNR and/or severity of fading. In brief, when simplicity of implementation is of primary concern, as is the case, for example, in mobile units, the proposed scheme offers an attractive low-complexity solution to mitigate the deleterious effects of multipath fading.     

Simple error probability derivation for binary DPSK over fast Rician channels with diversity

Bit error probability (BEP) performance of binary differential phase shift keying (DPSK) with differential detection over the nonselective, fast Rician fading channels with combining diversity reception is analysed. The analytical approach that exists in previously published literature for computing the BEP relied on a special case of the derivation given by Proakis that was concerned with the probability that a general quadratic form in complex Gaussian random variables is less than zero. However, evaluating the various coefficients required in the derivation leads to a computationally intensive solution. A simple derivation is presented which leads to a new, alternative BEP expression.     

Optimum multiuser noncoherent DPSK detection in generalized diversity Rayleigh-fading channels

The jointly optimum multiuser noncoherent detector for differential phase-shift keying (DPSK) modulation over the generalized diversity Rayleigh-fading (GDRF) channel is derived and analyzed. The GDRF channel includes time/frequency/receiver antenna diversity and allows fading correlations between the various diversity branches of each user. Noncoherent detection here refers to the case where the receiver has neither knowledge of the instantaneous phases nor of the envelopes of the users' channels. Upper and lower bounds on the bit-error probability of the optimum detector are derived for a given user. For fast fading, when the fading coefficients vary from one symbol interval to the next (but are still essentially constant over one symbol interval), the detector asymptotically (for high signal-to-noise ratios (SNRs)) reaches an error floor, which is bounded from below and above for different fast fading scenarios. For slow fading, when the channel is constant for at least two consecutive symbol intervals, the upper bound is shown to converge asymptotically to the lower bound. Thus, the asymptotic efficiency of optimum multiuser DPSK detection can be determined and is found to be positive. In contrast to coherent detection, however, it is smaller than unity in general. Since the asymptotic efficiency is independent of the interfering users' signal strengths, the optimum detector is near-far resistant. While optimum multiuser detection is exponentially complex in the number of users, its performance provides the benchmark for suboptimal detectors. In particular, it is seen that the previously suggested post-decorrelative detectors can be far from satisfactory.     

Optimum diversity combiner based multiuser detection fortime-dispersive Rician fading CDMA channels

Multiuser detection for asynchronous code division multiple access (CDMA) data transmission over the time-dispersive two-path Rician fading channel is considered. The multiuser maximum likelihood sequence detector (MLSD) is derived, and an equivalence of the fading channel to an asynchronous Gaussian intersymbol interference (AGISI) CDMA channel is established. However, the MLSD is found to be implementationally infeasible and this motivates the derivation of the optimum linear detector with near/far resistance as the performance criterion. The optimally near/far resistant linear time-invariant K-user detector is shown to consist of a cascade of a 2 K input/K output linear multiuser diversity combining filter followed by a K input/K output decorrelator that is designed for the equivalent AGISI/CDMA channel. This detector solves the near/far problem and also supports significantly higher bandwidth efficiencies for CDMA communication over the fading channel than does the conventional near/far limited single-user diversity combiner. The performance penalties incurred by multiuser detectors designed for the Gaussian channel when used over the Rician fading channel are also analytically characterized. It is shown that these penalties can be significant, making the case for the use of multiuser detectors optimized for this fading channel, particularly the optimum linear detector due to its relative implementational simplicity     

Combined adaptive RAKE diversity (ARD) and coding for DPSK DS/CDMAmobile radio

A diversity combining scheme, adaptive RAKE diversity (ARD), is proposed for a differential phase-shift keying (DPSK) direct sequence code division multiple access (DS/CDMA) mobile communications system. The ARD scheme minimizes the mean squared errors in the diversity combiner output. This suppresses the effects of the interference only paths in the time window for path diversity combining. Bit error rate (BER) performances with the proposed ARD and conventional equal gain combining (EGC) schemes are evaluated through laboratory experiments and compared. Block error rate (BKER) performance with the ARD scheme is also evaluated experimentally. Based upon the BKER evaluation results, an error correction scheme is proposed that is suitable for error occurrence characteristics of ARD output     

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

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^-9 is only a few tenths of a decibel greater than that needed by the phase diversity receivers     

Performance of diversity combining techniques for DS/DPSK signalingover a pulsed jammed multipath-fading channel

The effectiveness of antenna and spread-spectrum diversity is evaluated for direct-sequence differential phase-shift-keyed signaling over a worst-case pulse-jammed multipath-fading channel. Two diversity combining techniques are proposed. One uses predetection selective combining followed by postdetection equal-gain combining, and the other uses only postdetection equal-gain combining. The use of coding with hard and soft decision decoding is also considered. It is shown that the proposed diversity techniques can provide a significant improvement in the performance of coded antijam systems operating over jammed multipath-fading channels     

Balanced phase diversity receiver in 565 Mbit/s DPSK transmission system

565 Mbit/s DPSK optical transmission experiments with a balanced phase diversity receiver are reported. by employing a bulk optical 90 degrees hybrid in the input stage and a silicon bipolar multiplier IC in the demodulator and AFC stages, a system with a receiver sensitivity of -48.5 dBm and long-term stability was realised.<>