Fast Rayleigh Fading Channels Research Articles

Blind adaptive modulation systems for wireless channels with binary feedback

AbstractIn this paper, we investigate the performance of a blind adaptive modulation scheme that does not require any channel knowledge and just uses binary feedback, thereby decreasing feedback load. Retransmission of erroneous packet is not considered. In particular, we present an analytical framework for the performance evaluation of a simple wireless system in terms of receiver and transmitter structure. The system requires no knowledge of the channel and relies on a binary feedback. Slow and fast Rayleigh fading channel conditions are considered. The paper includes the derivation of the closed‐form expressions of the spectral efficiency. In some cases, closed‐form expression for packet error rate (PER) are derived. Our results show relatively high PER but some applications can still operate in a satisfactory fashion in these conditions, such as voice communication. Using coded modulation with high coding gain and increasing the number of blocks per time slot decrease the PER even more. An advantage of this system is that it uses a low complexity receiver, which sends binary feedback. Copyright © 2006 John Wiley & Sons, Ltd.

Performance of multicarrier DS/SSMA over fast Rayleigh fading channels with Doppler diversity

The significant loss in performance of multicarrier direct-sequence spread-spectrum multiple-access systems over fast-fading channels is investigated. First, the channel model for individual subchannels is obtained, using a canonical decomposition to a wide-sense stationary (WSS), uncorrelated scattering channel. Next, a receiver structure, which features both Doppler diversity and frequency diversity, is presented and analyzed. It is found that large Doppler spreads cause the average magnitude of the desired signals to diminish dramatically. Expressions for the bit-error rate are derived for both uncoded and coded systems by applying the standard Gaussian approximation. Numerical results, which show that Doppler diversity is preferable over frequency diversity in fast-fading channels, are provided for different combinations of the diversity orders. Numerical results, which show that the intersymbol and intersubchannel interference can be effectively suppressed, and the multiple-access interference tends to degenerate into a WSS process with the statistical periodicity destroyed by the fast-fading channels, are also provided.

QPSK differential space time coding on different unitary matrices sets and initializations

AbstractThis paper investigates a distinct set of complex unitary matrices for differential space time coding by using QPSK modulation. The numerical results show that the proper selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels. Copyright © 2005 John Wiley & Sons, Ltd.

QPSK Differential Space Time Coding on Different Unitary Matrices Sets and Initializations

This letter investigates a distinct set of complex unitary matrices for differential space time coding by using QPSK modulation. The numerical results show that the properly selection of the initial transmission matrix and the set of unitary matrices can efficiently improve the bit error rate (BER) performance, especially for the antennas correlated fading channel. The computer simulations are evaluated over slow and fast Rayleigh fading channels.

Adaptive MLSD receiver employing noise correlation

A per-survivor processing (PSP) maximum likelihood sequence detection (MLSD) receiver is developed for a fast time-varying frequency-selective Rayleigh fading channel with coloured additive noise, which follows an autoregressive (AR) model with unknown parameters. The correlation between noise samples is exploited to considerably enhance the performance of the communications. The maximum likelihood criterion is employed based on unknown noise parameters. This criterion has some desired properties, e.g. it has a unique joint minimum at the true values of the channel and the noise parameters. The new PSP–MLSD algorithm detects the input data and jointly estimates the noise and the channel parameters all together. The proposed structure can be viewed as a traditional PSP–MLSD receiver combined with an adaptive whitening filter. In a coloured noise environment, this scheme offers a faster tracking property, more accurate estimation of the channel and a substantially lower error probability compared with the traditional PSP–MLSD structure. The signal-to-noise ratio (SNR) improvement achieved by the proposed receiver, which can be called the noise whitening gain (NWG), is almost equal to the ratio of the energy of the additive noise to the energy of the unpredictable noise component. The square of the NWG gives also an accurate approximation for the bit error rate (BER) improvement ratio obtained by using the proposed algorithm compared with the traditional one.

Opportunistic beamforming based on multiple weighting vectors

In order to improve the throughput of the opportunistic beamforming, the authors generalize the opportunistic beamforming by using multiple random weighting vectors at each time slot. The base station chooses the best weighting vector and performs the opportunistic beamforming with this optimum vector. For the case of equally strong independent fast Rayleigh fading channels, the throughput of the proposed scheme is analytically approximated and the optimum number of random weighting vectors per time slot is obtained. Numerical results demonstrate that the proposed scheme considerably improves the throughput compared to the conventional opportunistic beamforming for a low/realistic number of users.

Performance of a New DS-CDMA Synchronization System Using Cycle-and-Add Property

This paper proposes a novel PN (Pseudo Noise) synchronization system using Cycle-and-Add property of M-sequence featuring fast acquisition in DS-CDMA (direct sequence-code division multiple access). Fast acquisition is carried out by generating a PN sequence in a simple multiplicative action of a received signal with its delayed one. This multiplicative action is similar to differentially coherent detection and realizes an anti-fading property. Easy implementation is materialized by the fact that the system is mostly composed of baseband devices. The principle, performance evaluation and the detection probability of synchronization for the proposed method are shown. Furthermore, detection probability of synchronization in a fast Rayleigh fading channel is shown for the performance evaluation.

Optimal Constellation Labeling for Iteratively Decoded Bit-Interleaved Space–Time Coded Modulation

We consider the design of iteratively decoded bit-interleaved space-time coded modulation (BI-STCM) over fast Rayleigh-fading channels with N/sub t/ transmit and N/sub r/ receive antennas. We propose the design criterion to achieve the largest asymptotic coding gain inherited in the constellation labeling. In particular, for orthogonal space-time block codes, the labeling design criterion reduces to maximizing the (-N/sub t/N/sub r/)th power mean of the complete set of squared Euclidean distances associated with all error-free feedback events in the constellation. Based on this power mean criterion, we show that the labeling optimization problem falls into the category of quadratic assignment problems for constellations of any shape and with an arbitrary number of transmit and receive antennas. For a set of practical values of N/sub t/ and N/sub r/, we present optimal labeling maps for 8-PSK, 16-QAM, and 64-QAM constellations.

Adaptive Blind Multiuser Detection over Flat Fast Fading Channels Using Particle Filtering

We propose a method for blind multiuser detection (MUD) in synchronous systems over flat and fast Rayleigh fading channels. We adopt an autoregressive-moving-average (ARMA) process to model the temporal correlation of the channels. Based on the ARMA process, we propose a novel time-observation state-space model (TOSSM) that describes the dynamics of the addressed multiuser system. The TOSSM allows an MUD with natural blending of low-complexity particle filtering (PF) and mixture Kalman filtering (for channel estimation). We further propose to use a more efficient PF algorithm known as the stochastic M -algorithm (SMA), which, although having lower complexity than the generic PF implementation, maintains comparable performance.

Systematic and optimal cyclotomic lattices and diagonal space-time block code designs

In this correspondence, a new and systematic design of cyclotomic lattices with full diversity is proposed by using some algebraic number theory. This design provides infinitely many full diversity cyclotomic lattices for a given lattice size. Based on the packing theory and the concrete form of the design, optimal cyclotomic lattices are presented by minimizing the mean transmission signal power for a given minimum (diversity) product (or equivalently maximizing the minimum product for a given mean transmission signal power). The newly proposed cyclotomic lattices can be applied to both space-time code designs for multi-antenna systems and linear precode design for signal space diversity in single antenna systems over fast Rayleigh fading channels. Although there are some cyclotomic lattices/space-time codes existing in the literature, most of them are not optimal.

Space–Time Trellis Codes With Linear Transformation for Fast Fading Channels

A space-time trellis code with linear transformation (STTC-LT) is presented. The upper bound on the pairwise error probability (PEP) is derived and a new design criterion is proposed. It is shown that the performance of STTC-LT over fast Rayleigh fading channels depends on the weighted square product distance (WSPD). Simulation results are provided for QPSK signal sets. They show that the proposed scheme is superior by about 8 dB and 10 dB to the conventional beamforming and Tarokh-Seshadri-Calderbank codes (TSC) at the bit error rate (BER) of 1.0e-4 over fast fading channels.

Properties and performance of space-time bit-interleaved coded modulation systems in fast Rayleigh fading channels

In this paper, we investigate the properties and performance of space-time bit-interleaved coded modulation (ST-BICM) systems in fast Rayleigh fading channels. We first show that ST-BICM with QPSK signaling in fast fading channels possesses the uniform distance property, which makes performance analysis tractable. We also derive the probability distribution of the squared Euclidean distance between space-time symbols assuming uniform bit-interleaving. Based on the distribution, we show that the diversity order for each codeword pair becomes maximized as the frame length becomes sufficiently long. This maximum diversity order property implies that the bit-interleaver transforms an ST-BICM system over transmit diversity channels into an equivalent coded BPSK system over independent fading channels. We analyze the performance of ST-BICM in fast fading channels by deriving an FER upper bound. The derived bound turns out very accurate, requiring only the distance spectrum of the binary channel codes of ST-BICM. Numerical results demonstrate that the bound is tight enough to render an accurate estimate of performance of ST-BICM systems.

Average probability of packet error with diversity reception over arbitrarily correlated fading channels

AbstractClosed form expressions for the average probability of packet error (PPE) are presented for no diversity, maximum ratio combining (MRC), selection combining (SC) and switch and stay combining (SSC) diversity schemes. The average PPE for the no diversity case is obtained in two alternative expressions assuming arbitrarily correlated Nakagami and Rician fading channels. For the MRC case, L diversity branches are considered and the channel samples are assumed to follow Nakagami distribution and to be arbitrarily correlated in both time and space. For the SC diversity scheme with L diversity branches, two bounds on the average PPE are derived for both slow and fast fading channels. The average PPE in this case is obtained in an infinite integral form for Nakagami channels while it is reduced to a closed form expression for the Rayleigh case. The average PPE is also derived in the case of SSC diversity with dual branches for both slow and fast Rayleigh fading channels. The new formulas are applicable for all modulation schemes where the conditional probability of error has an exponential dependence on the signal‐to‐noise ratio. The average PPE is then used to obtain a modified expression for the throughput for network protocols. In general, the diversity gain exhibits a little diminishing effect as the number of diversity branches increases. In addition, the system is found to be more sensitive to the space correlation than to the time correlation. The effects of different system parameters and diversity schemes are studied and discussed. Specific figures about the system performance are also provided. Copyright © 2004 John Wiley & Sons, Ltd.

Space-Time Coding Ambiguities in Joint Adaptive Channel Estimation and Detection

This paper studies the error propagation effect that is caused by certain ambiguities in joint data detection-channel tracking algorithms for transmission diversity schemes. Here, we use a space-time (ST) receiver based on the maximum a posteriori (MAP) method that takes into account the channel estimation error assuming the unknown channel to have a given complex multivariate Gaussian probability density function (pdf) (i.e., a Ricean channel). The decision criterion that is expressed in quadratic form represents either a linear detector or a noncoherent-nonlinear detector in extreme cases. Then, the channel pdf for the next iteration is updated by estimates of the second-order statistics of the channel coefficients, and a very simple decision-directed adaptive algorithm is derived for adaptive channel estimation. The adaptive algorithm can efficiently track a fast Rayleigh fading channel and, as a result, achieves robust performance. However, the occurrence of two types of ambiguities initiated in deep fades result in error propagation. Some remedies called space-time ambiguity remedies (STARs) are proposed to prevent error propagation. A new time-varying space-time coding (TVST) scheme is suggested as a bandwidth-efficient method to combat the permutation ambiguity impairment. This coding scheme, in conjunction with a differential detector, can resolve the ambiguity problem.

Performance and design of space-time coding in fading channels

The pairwise-error probability upper bounds of space-time codes (STCs) in independent Rician fading channels are derived. Based on the performance analysis, novel code design criteria for slow and fast Rayleigh fading channels are developed. It is found that, in fading channels, the STC design criteria depend on the value of the possible diversity gain of the system. In slow fading channels, when the diversity gain is smaller than four, the code error performance is dominated by the minimum rank and the minimum determinant of the codeword distance matrix. However, when the diversity gain is larger than, or equal to, four, the performance is dominated by the minimum squared Euclidean distance. Based on the proposed design criteria, new codes are designed and evaluated by simulation.

Adaptive modulation based MC-CDMA systems for 4G wireless consumer applications

Adaptive modulation based MC-CDMA systems can play a vital role in future generation consumer communication electronics. Adaptive modulation, combined with MC-CDMA based transmission technology, is a promising way to increase the data rate that can be reliably transmitted over the wireless radio channels. For 4G wireless networks, which demand very high data rate up to 100 Mbits/s with the constraints limiting higher data rate being severe ISI due to multipath and limited spectrum, such kind of adaptive modulation based multi-carrier systems applied to a wide-area environment, can achieve very large average user throughputs. In this paper, adaptive modulation based M-ary PSK, M-ary QAM, M-ary CPM, M-ary MHPM and GMSK systems applied to a turbo coded MC-CDMA system in a Rayleigh fast fading channel environment have been investigated and the BER performance of all these digital modulation techniques have been compared. Results of the comparative study indicate that the continuous phase modulation schemes like CPM, MHPM, and GMSK gives better performance as compared to PSK and QAM schemes. At most of the time, the MHPM systems outperforms both GMSK and CPM. The PSK and QAM based systems perform well till the number of users are around 10. As a whole, the adaptive MHPM system is found to give the optimum performance among the considered digital modulation schemes for the MC-CDMA system in a 4G environment.

Analysis and measurement of FM click rate in fast Rician fading channel

For the prediction of the error probability performance of a digital frequency modulation (FM) receiver that uses a limiter-discriminator-integrator (LDI) detector, expressions for the rates of "clicks" are needed. Recently, formulas for FM click rates valid for the slow Rician fading channels have been derived by N.P. Secord et al. (see ibid., vol.42, p.197-204, 1993) by taking expectation of the classical click-rate formulas of Rice, which is valid for the additive white Gaussian noise (AWGN) channel, over the Rician distribution. We derive and present new closed-form expressions for average FM click rates for the fast Rician fading channels, taking into account the effect of Doppler spread or fading bandwidth. We exploit the fact that the multipath component of the Rician process can be combined with the AWGN into another Gaussian process, so that the classical click-rate analysis of Rice can be applied. An experiment using modern equipment is conducted, and the measured click rates match the theory closely for both the fast Rician and Rayleigh fading channels.

Multisampling decision-feedback linear prediction receivers for differential space-time modulation over rayleigh fast-fading channels

Novel decision-feedback (DF) linear prediction (LP) receivers, which process multiple samples per symbol interval in conjunction with optimal sample combining, are proposed for differential space-time modulation (DSTM) over Rayleigh fast-fading channels. Performance analysis demonstrates that multisampling DF-LP receivers outperform their symbol-rate sampling counterpart in fast fading substantially. In addition, an asymptotically tight upper bound on the pairwise error probability is derived. In view of this bound, the design criterion of DSTM for fast fading is the same as that for block-wise static fading. To avoid the estimation of the second-order statistics of the channel, a polynomial-model-based DF-LP receiver is proposed. It can approach the performance of the optimum DF-LP receiver at high signal-to noise ratios, provided fading is moderate.

Maximum-likelihood frame timing instant and frequency offset estimation for OFDM communication over a fast Rayleigh-fading channel

A novel maximum-likelihood (ML) technique for frame timing instant and frequency offset estimation in an orthogonal frequency-division multiplexing system is investigated. By taking advantage of the cyclic prefix within the guard interval, the proposed technique can accurately estimate the frame timing instant and frequency offset with no assistance from pilot symbols. The proposed technique also takes fast Rayleigh fading into consideration for the purpose of wireless applications. Furthermore, several combining techniques are also investigated in order to improve the performance of the proposed estimators. Extensive simulation experiments show that the proposed techniques can effectively achieve lower estimation errors in frame timing and frequency offset estimation.

Neural network space diversity combination and ring coding for multicarrier CDMA over fast fading channels

Multicarrier CDMA is a major candidate to fulfil the requirements of 3G mobile systems. A novel scheme is developed combining modulo-S ring TCM with RNN-based adaptive space diversity for multicarrier CDMA systems with single-antenna transmitter and multiple-antenna receiver. The nonlinear RTRL algorithm for antenna diversity combining combats the distortive effects of the communication channel and reduces the interference. Ring TCM channel coding and RNN space diversity are evaluated in 16-QAM multicarrier CDMA systems transmitting over Rician and Rayleigh fast fading channels with a maximum Doppler frequency of 96 Hz. Modulo-4 ring TCM codes of 16 and 64 states have been designed. The RNN system is shown to be superior to the linear algorithms in channels dominated by multipath fading, inter-symbol interference and multiple access interference. The complexity of the RNN structure is comparable to that of the linear techniques. The joint utilisation of RNN based diversity, ring TCM and binary TCM coding schemes has been implemented. Whereas coding and space diversity do not provide sufficient benefit separately, the combination of both produces an increase in performance.