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 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)     

Postdetection optimal diversity combiner for DPSK differentialdetection

Postdetection diversity reception weights and combines all the detector outputs before symbol decision to combat the effects of multipath fading. A theoretical analysis of a postdetection optimal diversity combiner that can minimize the symbol error probability for differential phase shift keying (DPSK) differential detection in the presence of multiplicative Rayleigh fading, and co-channel interference (CCI) is presented. The effect of unequal average powers among diversity branches is taken into account. It is shown that the postdetection maximal-ratio combiner (MRC) described previously by the author is not optimal unless all branches have the same average power. It is also found that the combiner optimized for the effect of CCI (fading induced random FM noise) should weight each branch detector output in inverse proportion to the average CCI power (desired signal power). Assuming two-branch diversity, calculated BER (bit-error-rate) performance of π/4-shift QDPSK due to AWGN, CCI, and random FM is presented. In addition, the BER due to multipath channel delay spread (which is not treated in the theoretical analysis) is also computed to find the optimal combiner     

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.<>     

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)     

Diversity improvement of voice signal transmission using postdetection selection combining in land mobile radio

This paper describes the effect of postdetection selection combining diversity on voice signal transmission for wide-band PM and narrow-band PM in a Rayleigh fading environment. First, the baseband average SNR versus the average CNR for a two-branch selection diversity with the syllabic compandor is derived in a closed form including the effect of the envelope correlation coefficient. Then, the dual selection diversity receiver, which shares an envelope detector with two branches in time division, and its performance are described. Finally, laboratory tests using a Rayleigh fading simulator are carried out with the result that an effective diversity improvement is obtained for a cross correlation coefficient in the range from 0 to 0.5.     

Selection diversity combining with multiple antennas for MM-waveindoor wireless channels

Presents predetection and postdetection combining schemes for selection diversity reception with multiple antennas for MM-wave indoor radio channels. For those combining schemes, a reduction in complexity is achieved by limiting the number of combined signals to small values and by increasing the number of received signals. Bit error rate (BER) performance of binary phase shift keying (BPSK) with predetection combining of selected signals (CSS) and BER performance of differential BPSK with postdetection CSS are analyzed for slow fading and Rayleigh-distributed envelope statistics. Predetection maximal ratio combining of signals that comes from a single group or several groups of diversity channels as well as postdetection combining of received signals for groups of channels are considered. In comparing predetection combining with groups (PCG) and predetection combining of the best signals (PCB), we observe that the required SNR for achieving a certain BER is approximatively the same (with PCG having a slight advantage of 0.5 dB) for a given number, N, of diversity channels and L combined signals. Furthermore. PCG is equivalent to PCB for L=N since both techniques then correspond to conventional predetection maximal ratio combining (MRC), PCG and PCB are also equivalent when L=1 as both schemes then correspond to conventional selection combining. A small degradation of approximately 2 dB in the required SNR is observed when postdetection diversity reception with groups (PDG) is used instead of PCG. For L=N, PDG reduces to post detection MRC. The PDG technique is considered more suitable than PCB or PCG for MM-indoor wireless systems     

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     

Soft-limiter RAKE receivers for coded DS/DPSK systems over pulsejammed multipath-fading channels

Two soft-limiter RAKE receivers are evaluated for coded direct-sequence/differential phase shift keying (DS/DPSK) signaling over a pulse jammed multipath-fading channel that use a combination of antenna and multipath diversity. One uses predetection selective (antenna) combining followed by postdetection equal gain (multipath) combining, and the other uses postdetection equal gain combining only. In either case, the postdetection diversity combiner output is soft-limited prior to decoding. It is shown that for increasing levels of diversity the soft-limiter becomes quite effective, resulting in a receiver performance that approaches a maximum likelihood (ML) soft decision receiver with perfect jammer state information     

Linear Diversity Analysis for M‐ary Square Quadrature Amplitude Modulation over Nakagami Fading Channels

We derive and analyze the exact closed‐form expression for the average bit error probability (BEP) of M‐ary square quadrature amplitude modulation (QAM) for diversity reception in frequency‐nonselective Nakagami fading. A maximal ratio combining (MRC) diversity technique with independent or correlated fading cases are considered. Numerical results demonstrate error performance improvement with the use of MRC diversity reception. The presented new expressions offer a convenient way to evaluate the performance of M‐ary square QAM with an MRC diversity combiner for various cases of practical interest.     

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.<>     

High reliability of real-time visual data transmission using superposition coding with receiver diversity

Supporting visual data applications in the real-time communication systems are among the most challenging issues over the next generation wireless communication systems. This challenge is further magnified by the fact that the quality of reception is highly sensitive to transmission delay, data losses and bit error rate (BER) in such applications. In this paper, we proposed Superposition Coding with Receiver Diversity (SPC-RD) scheme, which employs unequal error protection (UEP) to improve the error performance, maximize the received signal to noise ratio (SNR) and optimize the reliability of the transmission system. In the transmitter side, the visual data is divided into a number of different priority layers based on their effects on the reception quality. These layers are modulated individually where the highest priority layer is modulated with the highest UEP level against error-prone channels, and vice versa. These modulated signals are then superimposed together and transmitted via wireless Single-Input Multiple-Output (SIMO) Rayleigh fading channel. In the receiver side, three different diversity combining approaches; selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) are considered. The combined signal is then passed through a multiuser demodulator so-called the ordered successive interference cancellation (O-SIC) demodulator to reconstruct and separate the data layers. This demodulation technique is evaluated and compared with the traditionally maximum likelihood joint detection (MLJD) technique. Extensive simulations have been carried out to validate the various assertions. Under the assumption of equal transmission power, the simulation results illustrate that the proposed SPC-RD scheme provides a SNR gain of 14.5 dB over the Rayleigh fading channel at the diversity order of three for the acceptable BER level of 10^?3 when BPSK scheme is exploited compared to the traditional equal error protection system. In addition, the proposed scheme with O-SIC demodulation technique achieves almost similar performance compared to MLJD technique but using less computational complexity.     

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     

A mobile radio single-frequency "Two-way" diversity system using adaptive retransmission from the base

This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "two-way diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.     

A Mobile Radio Single-Frequency "Two-Way" Diversity System Using Adaptive Retransmission from the Base

This paper describes an adaptive retransmission system capable of providing a UHF (1 GHz) mobile radio channel with "twoway diversity." The system is unique in that all signal processing associated with the diversity combining is done at the base station. A two-branch prototype of the system, without modulation, was field tested to determine its adaptive retransmission performance. These tests indicate that the statistics of the fading envelope at both the base and mobile stations closely agree with those predicted by theory for an equal gain combiner with correlation between the branches.     

Diversity Improvement of Voice Signal Transmission Using Postdetection Selection Combining in Land Mobile Radio

This paper describes the effect of postdetection selection combining diversity on voice signal transmission for wide-band PM and narrow-band PM in a Rayleigh fading environment. First, the baseband average SNR versus the average CNR for a twobranch selection diversity with the syllabic Compandor is derived in a closed form including the effect of the envelope Correlation coefficient. Then, the dual selection diversity receiver, which shares an envelope detector with two branches in time division, and its performance are described. Finally, laboratory tests using a Rayleigh fading simulator are carried out with the result that an effective diversity improvement is obtained for a cross correlation coefficient in the range from 0 to 0.5.     

Performance limits of M-FSK with Reed-Solomon coding and diversity combining

This paper examines the asymptotic (M/spl rarr//spl infin/) performance of M-ary frequency-shift keying (M-FSK) in multi-channels, or multiple frequency-nonselective, slowly fading channels, with coding, side information, and diversity reception. In particular, Reed-Solomon (RS) coding is considered in conjunction with the ratio-threshold test (RTT), which generates side information regarding the reliability of received symbols. The asymptotic performance of orthogonal signaling in multichannels with maximal ratio combining (MRC), postdetection equal gain combining (EGC), hybrid selection combining (H-SC), and selection combining (SC) is derived for an arbitrary statistical fading model and diversity order. The derivations reveal that coherent and noncoherent implementations of diversity combining schemes yield the same performance asymptotically. In addition, the asymptotic results are evaluated assuming a Nakagami-m fading model, and the effect of fading severity, diversity order, code rate, and side information upon the performance of the various diversity combiners is investigated. The minimum signal-to-noise ratio (SNR) required to achieve arbitrarily reliable or error-free communication, as well as the associated optimal RS code rate, are determined for various cases.     

Level crossing rate and average fade duration of MRC and EGC diversity in Ricean fading

The average level crossing rate and average fade duration of the output signal of a maximal ratio combiner (MRC) and equal gain combiner (EGC), operating on independent Ricean fading input branch signals, are derived. Exact, closed-form results are obtained for MRC diversity, while precise expressions for EGC diversity are presented with an infinite series method. The results are valid for an arbitrary number of independent, identically distributed diversity branches, isotropic scattering, and a specular component perpendicular to the line of motion of the mobile.     

On the performance of a maximum-likelihood code-acquisitiontechnique for preamble search in a CDMA reverse link

The performance of a maximum likelihood (ML) code-acquisition technique is analyzed for slotted-mode preamble search in the code-division multiple access (CDMA) reverse link. The probabilities of detection, miss, and false alarm are derived analytically for multiple H ₁ cell cases, based on the statistics of the CDMA noncoherent demodulator output in a frequency-selective Rayleigh fading channel. The probability density function (PDF) of a decision variable is also derived by considering the fading characteristics of the received signal for both single- and dual-antenna cases. The performance of the code-acquisition technique is evaluated numerically with emphasis on the effects of postdetection integration, fading rate, antenna diversity, and so on     

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