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)     

Error rate performance of digital FM mobile radio withpostdetection diversity

An analysis of bit error rate (BER) in a binary digital FM system with postdetection diversity is presented. Expressions for the average BER due to additive white Gaussian noise (AWGN), random FM noise and delay-spread in the multipath channel are derived for reception using differential demodulation (DD), and frequency demodulation (FD) assuming independent fading signals. Calculated results for MSK show that the BER performance is strongly dependent on the RMS-delay/bit-duration ratio and that the delay-spectrum shape is of no importance when the receiver predetection filter product is optimized for the effect of AWGN. The effect of fading correlation on the diversity improvement is also analyzed for a two-branch case with multiplicative Rayleigh fading signals. Expressions for the average BER due to AWGN and random FM noise are derived. Calculated results are shown for the average BER due to random FM noise assuming a horizontally spaced antenna system at a mobile station. It is shown that the use of small antenna spacings leads to a diversity improvement greater than that obtainable for the case of independent AWGN     

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.<>     

Error analysis of noncoherent M-ary FSK with postdetection EGC overcorrelated Nakagami and Rician channels

We analyze the performance for the noncoherent reception of M-ary orthogonal frequency shift keying with postdetection equal gain combining over a correlated fading channel. Two kinds of correlated fading statistics are considered: (1) Nakagami fading in which the diversity branches can have unequal signal-to-noise ratios (SNRs) as well as different m-parameters and (2) Rician fading in which the diversity branches can have unequal SNRs. Using the characteristic function of the combiner output SNR, closed-form expressions for the symbol error probability are obtained     

BER performance owing to random FM noise for QDPSK mobile radio with diversity reception

BER performance owing to random FM noise is investigated for QDPSK with postdetection selection diversity reception in a multiplicative Rayleigh fading environment. Experimental results for 16 Kbit/s QDPSK using a Rayleigh fading simulator are reported. It is shown that diversity reception can significantly reduce the impact of random FM noise.<>     

Unified analysis of postdetection diversity for binary digital FMmobile radio

An analysis is presented of postdetection diversity using both selection combining and general combining for the reception of a binary digital FM signal in a Rayleigh fading environment. Noncoherent (differential and frequency) demodulation is assumed. In the general combiner, the output of each branch demodulator is weighted by the νth power of the demodulator input signal envelope (weighting factor). The optimum weighting factor is found to be ν=2. It is shown that postdetection general combiners using weighting factors of ν=1 and 2 correspond to predetection equal-gain and maximal-ratio combiners, respectively. A closed-form solution and a fairly simple expression are derived for the average bit error rate. Numerical calculations show that the postdetection two-branch diversity gain is only about 0.9 dB inferior to the predetection system when minimum shift keying (MSK) is used     

Postdetection selection diversity reception with correlated,unequal average power Rayleigh fading signals for π/4-shift QDPSKmobile radio

The diversity gain degradations due to fading correlation and unequal average power are investigated for practical, two-branch postdetection selection diversity reception. The average bit error rate (BER) of π/4-shift QDPSK is theoretically analyzed taking into account additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread; exact diversity gain degradations are calculated. Simple and useful approximate expressions for the gain degradations are also presented     

Post-detection diversity Nakagami fading channels with correlatedbranches

We derive a closed-form expression for the performance of the post-detection product detector combiner (PDC) operating on L correlated branches in Nakagami (1960) fading. We consider the 2-DPSK signaling scheme and nonselective slow fading. The average bit error rate (BER) obtained with this scheme is compared to the ideal predetection MRC, showing limited loss. Moreover, the post-detection PDC is shown to outperform the selection diversity combiner (SDC) under the considered case of Nakagami fading     

Antenna diversity combining and finite-tap decision feedbackequalization for high-speed data transmission

The next-generation wireless communication systems are expected to support high-speed data transmission. Associated with high transmission rates, however, is the problem of multipath intersymbol interference (ISI) due to frequency-selective fading. Decision feedback equalization (DFE) and antenna diversity combining are two practical techniques for combating multipath ISI. Through simulations we investigate the performance of diversity combining, together with DFE, under various numbers of antenna branches and equalization taps, in a quasistationary frequency-selective fading environment with additive white Gaussian noise (AWGN) and cochannel interference (CCI). We consider joint optimization combining and power selection diversity combining. We simulate the combiner, using quaternary phase shift keying (QPSK) modulation with up to four antenna branches. Our results show that using antenna diversity and DFE with joint optimization combining provides performance improvement with lower computational complexity, as compared to that of using either DFE or diversity combining alone for combating ISI     

Average BER Analysis for $M$-ary FSK Signals in Nakagami-$q$ (Hoyt) Fading With Noncoherent Diversity Combining

This paper analyzes the average bit error rate (BER) of noncoherent M-ary frequency-shift keying (FSK) signals over multichannel nonidentically distributed Nakagami-q (Hoyt) fading employing diversity combining. The first part of the paper considers the conventional postdetection noncoherent equal-gain combiner (NC-EGC), in which a Fourier series inversion formula is employed to derive a simple and rapidly converging series-based expression for the system average BER. This expression is valid for arbitrary values of received average signal-to-noise ratios (SNRs) and fading parameters. The derived expression is then compared with some existing ones in the literature, and the results show a large reduction in computational complexity, particularly when M and/or the diversity order increases. In the second part, a new noncoherent combiner is proposed to achieve improvements over the conventional NC-EGC. It is also shown that this new combiner results in a simple closed-form expression for the system average BER that is given in terms of elementary functions; hence, it can be easily numerically evaluated with noticeable computation efficiency.     

QDPSK signal transmission performance with postdetection selectiondiversity reception in land mobile radio

The bit error rate (BER) performance of 16-128 kb/s Nyquist raised-cosine filtered quaternary differential phase-shift keying (RC-QDPSK) signal transmission was experimentally investigated. Two-branch postdetection selection diversity reception was employed. Measured results are presented for the BER performance due to additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread. Field BER measurements were also conducted at a carrier frequency of 1.45 GHz in an area characterized by high-rise buildings and in an area surrounded by mountains. The results show that postdetection selection diversity is a simple yet powerful technique to improve the BER performance in fading mobile radio channels     

Experimental evaluation of combined postdetection diversity andconcatenated channel coding

The combined effects of postdetection diversity reception and concatenated channel coding are experimentally evaluated for π/4-shift QDPSK signal transmission over a Rayleigh fading channel. Two-branch postdetection diversity reception using maximal ratio combining (MRC) and selection combining (SC) are considered. The concatenated channel coding uses the Reed-Solomon (15,k) code of GP(2 ⁴) as the outer code and the BCH (7,4) code as the inner code (k=9,11,13). Measured bit error rate (BER) performance results are presented under cochannel interference (CCI) and multipath channel delay spread, as well as additive white Gaussian noise (AWGN)     

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.<>     

Experimental evaluation of postdetection diversity reception ofnarrow-band digital FM signals in Rayleigh fading

Postdetection diversity is attractive for narrowband digital FM signal reception because the cophasing function, which may be difficult to realize in a fast Rayleigh fading environment, is not required. The combining scheme evaluated here is to weight each frequency demodulator (FD) output in proportion to the νth power of the received signal envelope of that branch. Maximum diversity improvement can be obtained with ν=2 (this combiner is referred to as a postdetection maximal ratio chamber (MRC)). Experimental results are presented on postdetection diversity reception in the Gaussian minimum shift keying (GMSK) signal transmission system. Diversity combining and FD-decision algorithms (decision feedback equalizer (DFE) and maximum-likelihood sequence estimator (MLSE)) are performed by software on a computer using the data of the sampled FD output and received signal envelope obtained from a laboratory transmission system. It is shown that the MRC can attain about a 1-dB larger diversity gain than the selection combiner (SC) when two-branch diversity is used. The degradations of two-branch diversity improvement caused by the differences between demodulator sensitivities and between received signal envelope detector gains are evaluated     

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 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.     

Performance of 16 kbit/s GMSK transmission with postdetection selection diversity in land mobile radio

Through laboratory simulation tests and field experiments in the Tokyo metropolitan area, 16 kbit/s Gaussian filtered minimum shift keying (GMSK) transmission performance has been experimentally clarified in the 920 MHz land mobile radio environment. The experimental results agree closely with theory, and they show that fast multipath fading severely degrades average bit error rate (BER) performance in GMSK transmission. However, a space diversity reception technique using a postdetection selection combining scheme is able to efficiently mitigate the fast multipath fading.     

Performance of 16 kbit/s GMSK Transmission with Postdetection Selection Diversity in Land Mobile Radio

Through laboratory simulation tests and field experiments in the Tokyo metropolitan area, 16 kbit/s Gaussian filtered minimum shift keying (GMSK) transmission performance has been experimentally clarified in the 920 MHz land mobile radio environment. The experimental results agree closely with theory, and they show that fast multipath fading severely degrades average bit error rate (BER) performance in GMSK transmission. However, a space diversity reception technique using a postdetection selection combining scheme is able to efficiently mitigate the fast multipath fading.     

Micro- and macrodiversity MDPSK on shadowed frequency-selectivechannels

The performance of M-ary differential phase shift keying (MDPSK) on frequency-selective slow Rayleigh fading, lognormal shadowed channels with diversity combining is analyzed for mobile and portable applications. The use of L-branch equal gain postdetection microdiversity combining to mitigate the effects of fading and P-port macrodiversity to alleviate the effects of shadowing are investigated. Four performance criteria are considered for a frequency-selective multipath fading, intersymbol interference channel. These are, the short term bit error rate (BER), the irreducible BER, the complementary distribution over the lognormal shadowing of the average BER, and the probability that the instantaneous BER exceeds a threshold value, averaged over a spatial environment. Closed-form expressions for the four performance criteria are obtained. The BER and outage performance results show that diversity combining is an effective method for improving the system performance (and hence system reliability), when the normalized delay spread is not large. It is also seen that, in most cases, 4DPSK gives the best performance followed by 8DPSK and 2DPSK, respectively, for a given information throughput     

A transmitter diversity for MSK with two-bit differential detection

Transmitter diversity is a technique that is effective for mitigating signal transmission degradation caused by multipath fading which is one of the most serious problems in land mobile radio. A frequency-offset transmitter diversity is proposed for a land mobile radio system that employs minimum-shift keying (MSK) and two-bit differential detection. It is shown that high transmission efficiency can be obtained in comparison with the other frequency-offset transmitter diversity. In addition, the diversity effect on the bit error rate (BER) performance is equivalent to that of postdetection equal gain combining diversity. The BER performance improvement was confirmed by the experimental test results.