Adaptive Retransmission Diversity with Packet Combining for Slotted DS/CDMA Packet Radio Networks

A time diversity automatic repeat-request (ARQ) scheme is investigated for slotted random access direct-sequence code-division multiaccess (DS/CDMA ALOHA) wireless packet radio networks on multipath Rayleigh fading channels. The receiver retains and processes all the retransmissions of a single data block (packet) using predetection diversity combining, instead of discarding those which are detected in error. This effectively improves the system throughput and delay characteristics especially at small values of signal-to-noise ratio (SNR) per bit. A simple and practical selection combining rule is proposed, which lends itself to a low-complexity receiver structure and specifically suitable for high data rate transmissions. Owing to the stochastic nature of the multiple access interference, the new maximum output selection diversity (MO/SD) system yields superior performance in comparison to the traditional maximum SNR selection diversity (SNR/SD) model. The bit error rate performance, throughput and the average number of transmissions required to transmit a packet successfully with and without forward error correction (FEC) are evaluated. Numerical results reveal that the proposed adaptive retransmission diversity with packet combining provides a considerable advantage over the conventional slotted DS/CDMA ALOHA without incurring a substantial penalty in terms of cost or complexity.     

Joint adaptive modulation and diversity combining with feedback error compensation

This letter investigates the effect of feedback error on the performance of the joint adaptive modulation and diversity combining (AMDC) scheme which was previously studied with an assumption of error-free feedback channels. We also propose to utilize adaptive diversity to compensate for the performance degradation due to feedback error. We accurately quantify the performance of the joint AMDC scheme in the presence of feedback error, in terms of the average number of combined paths, the average spectral efficiency, and the average bit error rate. Selected numerical examples are presented and discussed to illustrate the effectiveness of the proposed feedback error compensation strategy with adaptive combining. It is observed that the proposed compensation strategy can offer considerable error performance improvement with little loss in processing power and spectral efficiency in comparison with the no compensation case.     

Effects of channel-estimation errors on receiver selection-combining schemes for Alamouti MIMO systems with BPSK

The bit-error rate (BER) of binary phase-shift keying in Rayleigh fading, using the Alamouti transmission scheme and receiver selection diversity in the presence of channel-estimation error, is studied. Closed-form expressions for the BER of log-likelihood ratio selection, signal-to-noise ratio (SNR) selection, switch-and-stay combining selection, and maximum ratio combining are derived in terms of the SNR and the cross-correlation coefficient of the channel gain and its corrupted estimate. Two new selection schemes, space-time sum-of-squares combining selection diversity and space-time sum-of-magnitudes selection diversity, are proposed and proven to provide almost the same performance as SNR selection, but with much simpler implementations. The effects of channel-estimation errors on each selection scheme are examined.     

Soft-decision Viterbi decoding with diversity combining formulti-beam mobile satellite communication systems

Diversity combining methods for mobile satellite communication systems employing convolutional encoding and soft-decision Viterbi decoding are evaluated. Computer simulation clarifies that the pre-Viterbi-decoding maximal ratio combining method has better performance than other methods in Rician fading channels. The simulation results agree with the Pe (bit error probability) performance derived from the numerical analysis for slow fading using the approximate Pe performance of Viterbi decoding in AWGN (additive white Gaussian noise) channels and the probability density function of Rician fading. Applying this diversity method to the multi-beam mobile satellite communication systems, a satellite beam diversity reception scheme is proposed. A computer simulation result shows that the proposed scheme decreases the packet error rate of the control signals to less than 1/100 around the satellite beam boundary     

Performance evaluation of various decision schemes for frequencydemodulation of narrow-band digital FM signals in land mobile radio

The decision feedback equalizer (DFE), three-level eye, and maximum-likelihood sequence estimator (MLSE) decision schemes for frequency demodulation of 16-kb/s GMSK signals are evaluated. Laboratory experimental results on bit error rate (BER) and block error rate (BKER) performances are presented. In additive white Gaussian noise channels, two-bit DFE achieves the best BER performance, whereas MLSE is the best for cochannel interference-limited channels. BKER performance was also examined. The three-level eye decision is a bit-by-bit decision, and thus has superior performance because there is no error propagation. In fading environments, however, this superiority tends to diminish because bursty errors due to deep fades predominate rather than error propagation effects. Some of the laboratory experimental results have been confirmed with field experiments at a 1.45-GHz carrier frequency     

Performance Analysis of Generalized Sort, Switch, and Examine Combining

Examples of low-complexity diversity combining schemes are, among others, the generalized selection combining (GSC) scheme and the generalized switch-and-examine combining (GSEC). In this paper, we propose a new low-complexity combining scheme, termed generalized sort-switch-and-examine combining (GSSEC), that, in a sense, can be considered as a hybrid GSC/GSEC scheme. A generic expression for the moment-generating function of the GSSEC output SNR in general independent, identically distributed fading channels is derived, and is then applied to the analysis of its error performance     

A Hybrid Selection/Equal-Gain Combining over Correlated Nakagami-m Fading Channels

A new type of hybrid selection/equal-gain combining (HS/EGC) scheme is proposed and analyzed. This scheme dynamically selects the best combination of branches by a simple test and combines them in equal-gain combining (EGC) manner. As a result, the scheme always shows better performance than conventional EGC and selection diversity (SD), and close to maximal-ratio combining (MRC). As an exemplary performance indicator, its average output SNR for dual correlated Nakagami-m fading channels is calculated and demonstrated in comparison with other diversity schemes     

Adaptive selection/maximal-ratio combining based on error detection of multidimensional multicode DS-CDMA

A novel two-dimensional diversity combining is proposed for the uplink in a single cell which employs multidimensional multicode direct-sequence code-division multiple-access signaling and two receive antennas. First, the signaling is combined with precoding to obtain a constant envelope signal that is suitable for the uplink, and the resulting error detection is applied to the diversity combining. Based on the error detection, an adaptive selection-combining/maximal-ratio combining (SC/MRC) is performed, for which initial data detection is made by the SC to avoid the combining loss of the very noisy paths. When the initial SC is unreliable (indicated by the error detection), the MRC is attempted to fully exploit the space and multipath diversity. The adaptive SC/MRC is generalized to further increase the diversity gain over the MRC, offered by the error-detection capability. Through analysis and simulation results, it is shown that the adaptive SC/MRC and its generalized diversity receiver outperforms the other schemes in terms of the symbol-error rate, and also its bit-error rate can be lower than that of the variable spreading factor scheme using a single code.     

Performance of multiuser diversity reception in Rayleigh fadingCDMA channels

Error probability of an adaptive multiuser diversity receiver is evaluated in terms of channel fading rate and the number of code-division multiple access users. Fading-induced performance loss, which leads to the error probability floor, is established for the proposed coherent combining scheme and compared to that of the differentially coherent receiver with equal-gain combining     

Frequency offset receiver diversity for differential MSK

A new receiver diversity scheme for differential detection of minimum shift keying (MSK) is proposed. The signal from each receiving branch is translated to a different IF frequency. The IF signals are summed and then detected by a common differential detector. The diversity scheme does not need phase adjusters, signal quality measurement circuits or a switching controller; moreover the error rate performance is equivalent to that of postdetection equal gain combining diversity, which needs plural complete receiving systems. Theoretical analysis and computer simulation results show that the diversity gain of the proposed scheme is about 13 dB at a 10^-3error rate under Rayleigh fading and 5 dB under Rician fading when the signal-to-interference power ratio is 10 dB. The static error rate performance improvement was confirmed by experimental test results. Simulation results with data from mobile propagation studies are also shown. Even in heavily shadowed cases, the probability that fading attenuation is less than 17 dB is improved from 80 to 99 percent, and a 7 to 13 dB improvement in margin requirement for 99 percent of time operation is achieved.     

MVDR‐combining‐aided diversity and spatial multiplexing for MIMO multi‐cellular networks with cochannel interference

Two multiple‐input multiple‐output (MIMO) schemes (a diversity scheme and a spatial multiplexing scheme) that employ the minimum variance distortionless response (MVDR) combining are proposed for multi‐cellular networks with cochannel interference. With the receive diversity provided by the MVDR combining, the proposed diversity scheme can be benefited by both the transmit diversity and the receive diversity, also, the proposed spatial multiplexing scheme can be benefited by both the receive diversity and the spatial multiplexing. The proposed MIMO schemes do not require the space‐time coding or the successive interference cancellation, thus they can result in less computational complexity than space‐time block code (STBC) and vertical‐Bell Labs layered space‐time (V‐BLAST). We show that the capacity of the proposed diversity scheme is close to or larger than that of STBC for the noise‐corrupted case and is much larger than that of STBC for the interference‐corrupted case. We also show that the capacity of the proposed spatial multiplexing scheme can be much larger than that of V‐BLAST for the interference‐corrupted case and the noise‐corrupted case, and the proposed spatial multiplexing scheme can achieve good compromise between diversity and spatial multiplexing. Copyright © 2011 John Wiley & Sons, Ltd.     

On the feedback error compensation for adaptive modulation and coding scheme

In this paper, we consider the effect of feedback error on the performance of the joint adaptive modulation and diversity combining (AMDC) scheme which was previously studied with an assumption of perfect feedback channels. We quantify the performance of two joint AMDC schemes in the presence of feedback error, in terms of the average spectral efficiency, the average number of combined paths, and the average bit error rate. The benefit of feedback error compensation with adaptive combining is also quantified. Selected numerical examples are presented and discussed to illustrate the effectiveness of the proposed feedback error compensation strategy with adaptive combining. Copyright © 2011 John Wiley & Sons, Ltd.     

A Parallel Concatenated Convolutional-Based Distributed Coded Cooperation Scheme for Relay Channels

In this paper, we investigate a coded cooperation diversity scheme suitable for L-relay channels operating in the soft-decode-and-forward (soft-DF) mode. The proposed scheme is based on parallel concatenated convolutional codes (PCCC). To improve the overall performance through diversity, the coded cooperation operates by sending the systematic and the first parity outputs via L?+?1 independent fading paths. Instead of using only a centralized turbo code system at the source node, we have proposed a DCC scheme, where the first recursive systematic coding is done at both source and relay nodes. At the destination, the received replicas are combined using the maximal ratio combining (MRC). The entire codeword, comprising the MRC sequence and the second parity part, is decoded via the maximum a-posteriori (MAP) algorithm and turbo decoding principle. We analyze the proposed scheme in terms of bit error rate (BER). In fact, we define the explicit upper bounds for error rate assuming Binary phase shift keying (BPSK) transmission for fully interleaved channels with channel state information (CSI). We use the Rayleigh fading channels with independent fading. Our study shows that the full diversity order is achieved when the source-relay link is more reliable than the other links. Otherwise, the diversity decreases. However, in both cases, it is shown that significant performance improvements are possible to achieve over non-cooperative coded systems. Theorical and simulation results are presented to demonstrate the efficacy of the proposed scheme.     

Coherent detection of biorthogonal signals over Rayleigh fadingchannels

A practical coherent detection scheme for biorthogonal signals over Rayleigh fading channels is proposed. The proposed scheme improves the bit error rate (BER) performance compared to the noncoherent detection schemes for biorthogonal signals. It also outperforms the coherent and noncoherent detection schemes for orthogonal signals with comparable bandwidth efficiency. The BER performance for a Rayleigh fading channel with two path diversity combining is obtained by computer simulation. The results show that the required average signal-to-noise ratio per bit γ_b can be reduced by as much as 1.4 dB when we use this system in the CDMA cellular reverse link     

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.     

Performance comparison of selection combining schemes for binary DPSK on nonselective Rayleigh-fading channels with interference

This paper is concerned with the error performance analysis of binary differential phase shift keying (DPSK) with differential detection over the nonselective Rayleigh-fading channel with selection diversity reception and with an additive, correlated, Gaussian interference process in each diversity channel. The fading process is assumed to have an arbitrary Doppler spectrum with arbitrary Doppler bandwidth. The selection schemes investigated are: 1) the selection combining (SC) scheme based on signal-to-noise power ratio (SNR); 2) the SC scheme based on signal-plus-noise (S+N); and 3) the SC scheme based on maximum output (MO). New, exact, closed-form bit-error probability (BEP) expressions are derived, and a performance comparison among the three SC schemes and combining diversity reception is given. The results obtained reduce to previously known results when the correlated interference process is absent, and when the fading process does not fluctuate over the duration of several symbol intervals. The results indicate that the performance of each scheme depends on the tradeoff between the number of diversity branches, the SNR, the interference level, and the correlation of the interference process. However, the SC-(S+N) scheme generally performs worse than the SC-SNR scheme, the SC-MO scheme and combining diversity reception scheme. The findings presented here are not only of fundamental theoretical value, but are also of practical interest to the designers of future mobile communication systems.     

An MGF-based performance analysis of generalized selectioncombining over Rayleigh fading channels

Using the notion of the “spacing” between ordered exponential random variables, a performance analysis of the generalized selection combining (GSC) diversity scheme over Rayleigh fading channels is presented and compared with that of the conventional maximal-ratio combining and selection combining schemes. Starting with the moment generating function (MGF) of the GSC output signal-to-noise ratio (SNR), we derive closed-form expressions for the average combined SNR, outage probability, and average error probability of a wide variety of modulation schemes operating over independently, identically distributed (i.i.d.) diversity paths. Because of their simple form, these expressions readily allow numerical evaluation for cases of practical interest. The results are also extended to the case of non-i.i.d. diversity paths     

Optimum selection diversity for BPSK signals in Rayleigh fadingchannels

We propose a new selection diversity scheme, called |ar|-selection diversity, that selects the branch providing the largest magnitude of log-likelihood ratio (LLR). The LLR for BPSK signals in fading channels is found to be proportional to the product of the fading amplitude and the matched filter output after phase compensation. The proposed |ar|-selection diversity scheme is shown to be optimal in the sense of minimizing the bit error rate (BER), and outperform existing selection diversity schemes. We also propose a suboptimal selection diversity scheme, called |aw|-selection diversity, that does not require a phase compensation in the selection process, thereby significantly reducing implementation complexity. We show that the proposed |ar|-selection and |aw|-selection diversity schemes exhibit significant power gains over existing selection diversity schemes in Rayleigh fading channels     

Clipped diversity combining for channels with partial-bandinterference. II. Ratio-statistic combining

For pt.I see ibid., vol.COM-3, no.12, p.1320 (1987). Ratio-statistic combining is proposed for mitigating partial-band interference in systems with diversity transmission and frequency-hop signaling. Systems with noncoherent demodulation and binary orthogonal signaling are covered. The partial-band interference is Gaussian, and Gaussian quiescent noise is included in the analysis to account for wideband noise sources. The exact probability of error is found for a receiver using ratio-statistic combining, and this is compared to the exact error probabilities for receivers with optimum combining with perfect side information, clipped-linear combining, the ratio-threshold test with majority-logic decoding, and self-normalization diversity combining. Numerical results are also given for a frequency-hop system which uses ratio-statistic combining for channels with Rayleigh fading and partial-band interference. It is determined that ratio-statistic combining is an excellent diversity combining scheme for systems with partial-band interference and fading