Quasi-static Fading Channels Research Articles

Robust Communication via Decentralized Processing With Unreliable Backhaul Links

A source communicates with a remote destination via a number of distributed relays. Communication from source to relays takes place over a (discrete or Gaussian) broadcast channel, while the relays are connected to the receiver via orthogonal finite-capacity links. Unknowns to the source and relays, link failures may occur between any subset of relays and the destination in a nonergodic fashion. Upper and lower bounds are derived on average achievable rates with respect to the prior distribution of the link failures, assuming the relays to be oblivious to the source codebook. The lower bounds are obtained by proposing strategies that combine the broadcast coding approach, previously investigated for quasi-static fading channels, and different robust distributed compression techniques. Numerical results show that lower and upper bounds are quite close over most operating regimes, and provide insight into optimal transmission design choices for the scenario at hand. Extension to the case of nonoblivious relays is also discussed.

A General Upper Bound to Evaluate Packet Error Rate over Quasi-Static Fading Channels

We propose a new analytical approach to evaluate the average packet error rate (PER) of a conventional packet transmission system over a quasi static fading channel, by presenting an integral inequality lemma. The basic idea of the approach is that, given the PER for the AWGN channel as a function of signal-to-noise ratio (SNR), the average PER over Rayleigh fading channel can be generally upper bounded by a quite simple inequality, i.e.,1 - exp(-w <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> /γ̅), for both coded and uncoded schemes, where w <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> , defined by an integral expression, corresponds exactly to the inversion of coding gain; and this bound is tight in the high SNR region or for long packet systems. We further apply the integral inequality to extend our research to more general Nakagami-m fading channel.

Novel Power Adaptation Strategy for Space–Time-Coded Multiantenna Systems With Imperfect Channel State Information

This paper presents a strategy for allocating power in both space and time for beamforming space-time-coded multiantenna systems with imperfect channel state information at the transmitter (CSIT) over flat and quasi-static Rayleigh fading channels. We first develop a closed-form spatial-only (S-O) power allocation scheme based on a newly defined compressed signal-to-noise ratio (CSNR) criterion. The derived power allocation formula has a parameter (compression factor) that can be used to minimize the conditional bit error rate (BER). The BER performance of the new CSNR-based power allocation scheme is almost identical to the previous optimal S-O power allocation schemes, whereas its computation is more efficient. Using the CSNR-based power adaptation, we derive a joint spatio-temporal (S-T) power allocation method to minimize the average BER subject to a long-term (time) average of the transmit power constraint, which provides a large BER performance gain over the S-O power strategies and the existing S-T method. The practical issue of peak power constraint is also addressed.

Performance of super-orthogonal space–time trellis codes with transmit antenna selection

Super-orthogonal space-time trellis (SOSTT) codes provide a significant coding gain with respect to the conventional space-time trellis (STT) codes without increasing the decoding complexity at the receiver. Transmit antenna selection (TAS) is an important technique to solve the implementation complexity problems of multiple-antenna systems that arise from employing a separate RF chain for each antenna. This study treats a scheme combining SOSTT coding with TAS in order to exploit performance improvements provided by SOSTT codes while realising the promises made by the TAS technique. In the proposed scheme, transmit antennas that maximise the signal-to-noise ratio at the receiver are chosen and activated out of all available transmit antennas for transmission of the baseline SOSTT code, whereas all other transmit antennas are silent. The error performance of the proposed structure is investigated by deriving moment generating function (MGF)-based upper bound expressions on the pairwise error probability in quasi-static flat Rayleigh fading channels for both perfect and imperfect antenna subset selection. The performance analysis demonstrates that the proposed scheme provides full diversity order as if all transmit antennas were used when antennas are perfectly selected. Moreover, it is shown that this structure provides better error performance almost at the same decoding complexity compared to the previous STT coding structures with TAS in the literature.

On the Average Rate of Quasi-Static Fading Channels with ARQ and CSI Feedback

This letter studies the effect of channel side information on the achievable rates of quasi-static fading channels. The side information is obtained via combination of the standard channel state information (CSI) and automatic repeat request (ARQ) feedback. Demonstrating the general rate optimization problem, the results are obtained for different power allocation strategies. Simulation results show that considerable rate increment is achieved with as low as one bit feedback for each of these approaches.

Optimized opportunistic multicast scheduling (OMS) over wireless cellular networks

Optimized opportunistic multicast scheduling (OMS) is studied for cellular networks, where the problem of efficiently transmitting a common set of fountain-encoded data from a single base station to multiple users over quasi-static fading channels is examined. The proposed OMS scheme better balances the tradeoff between multiuser diversity and multicast gain by transmitting to a subset of users in each time slot using the maximal data rate that ensures successful decoding by these users. We first analyze the system delay in homogeneous networks by capitalizing on extreme value theory and derive the optimal selection ratio (i.e., the portion of users that are selected in each time slot) that minimizes the delay. Then, we extend results to heterogeneous networks where users are subject to different channel statistics. By partitioning users into multiple approximately homogeneous rings, we turn a heterogeneous network into a composite of smaller homogeneous networks and derive the optimal selection ratio for the heterogeneous network. Computer simulations confirm theoretical results and illustrate that the proposed OMS can achieve significant performance gains in both homogeneous and heterogeneous networks as compared with the conventional unicast and broadcast scheduling.

Volumetric-based detection scheme for multi-antenna FH/MFSK systems in the presence of multi-follower jamming

Follower partial-band jamming is an efficient strategy to degrade the performance of frequency hopping (FH) systems with M-ary frequency shift keying (MFSK) modulation. In this paper, a volumetric-based algorithm that uses a multi-element array is proposed to reject multi-follower jamming signals and carry out symbol detection in slow FH/MFSK systems over quasi-static flat fading channels. Specifically, based on using the proposed algorithm that can provide an estimate of the unknown spatial correlation of the received jamming components at the receiver antennas, jamming can be removed in the symbol detection process. The jamming rejection capability of this scheme is analyzed under a jamming dominant and a signal dominant environment. The much improved bit error rate (BER) performance that can be obtained is also verified in simulation studies.

Error-Rate Analysis for Bit-Loaded Coded MIMO-OFDM

Bit-loaded orthogonal frequency-division multiplexing (OFDM) with convolutional coding is a powerful technique for transmission over quasi-static frequency-selective fading channels. Further enhancements in data rate are achieved by combining loaded OFDM with multiple-input-multiple-output (MIMO) transmission. Motivated by the lack of appropriate error-rate analysis techniques for this popular type of transmission system, in this paper, we develop a novel analytical method for bit-error-rate (BER) and frame-error-rate (FER) estimation of bit-loaded coded OFDM and MIMO-OFDM systems using singular value decomposition (SVD), operating over frequency-selective quasi-static channels with nonideal interleaving. Then, we introduce three different applications of the proposed analysis. First, we compare the performance of several OFDM bit-loading schemes and propose a hybrid loading scheme that selects the best loading for each channel realization from a number of candidates. Second, we introduce three adaptive interleaving schemes: 1) selecting the best interleaver from a number of predefined interleavers; 2) a novel adaptive bit-interleaving algorithm based on the pairwise error probability; and 3) a spatial interleaving scheme for MIMO-OFDM-SVD systems with separate information sources. Third, we introduce an adaptive coded-modulation algorithm by using our BER and FER estimation techniques.

Cooperative Network Coding with Soft Information Relaying in Two-way Relay Cchannels

Network coding in wireless network can improve network throughput by exploiting the broadcast nature of the wireless network. Taking into consideration the error prone nature of wireless networks, we investigate the design of network coding implemented in physical layer, and propose a cooperative network coding scheme with soft information forwarding (SIR), which combines soft network coding and distributed turbo coding scheme in two-way relay channels (TWRC) in this paper. In order to mitigate the error propagation effect due to the imperfect decoding at the relay, soft network coding is deployed in the proposed scheme, where soft-input soft-output (SISO) encoder and decoder for recursive systematic convolutional (RSC) codes are implemented. Moreover, the soft information of both systematic bits and redundancy parity bits are forwarded at the relay by using higher-order constellations to achieve diversity gain. Aided by distance spectrum of turbo codes, concept of uniform interleaver, and Gaussian approximation of soft decoding information, union bound on the error performance of our scheme is analyzed. Both the analysis and simulation confirm that the proposed scheme achieves significant gain over conventional network coding in quasi-static fading channels.

Distributed space-time-frequency coding for cooperative OFDM systems

A distributed space-time-frequency (STF) coding scheme is proposed for cooperative OFDM (C-OFDM) systems with three terminals over quasi-static frequency-selective Rayleigh fading channels. The outage probability is derived and its tight closed-form lower bound is presented. Asymptotic analysis indicates that the proposed scheme can achieve both spatial and multipath (frequency) diversity. The theoretical analysis of the proposed STF coded scheme is further implemented by the distributed group STF block coding (D-GSTFBC) scheme based on the subcarrier grouping technique. Simulation results confirm the previously introduced theoretical analysis.

Distance Spectrum and Expurgated Union Bound of Space–Time Trellis Codes in Quasi-Static Rician Fading Channels

This paper presents a technique to obtain an expurgated union bound on the frame error rate (FER) of space-time trellis codes (STTCs) on quasi-static Rician fading channels. We first present an algorithm to compute the distance spectrum of STTCs. The proposed algorithm iteratively manipulates the entries of the transition matrix of the product state transition diagram, which is convenient for symbolic computation. Then, a new method to identify the dominant quasi-static fading error events is proposed. Comparisons with simulated results reveal that the expurgated union bound on the FER (obtained using the limiting-before-average technique) using these dominant error events is tight.

On the average rate performance of hybrid-ARQ in quasi-static fading channels

The problem of efficient communication over a scalar quasi-static fading channel is considered. The single-layer transmission (SLT) and multi-layer transmission (MLT) schemes do not require any knowledge of the channel state information (CSI) at the transmitter, but their performance is also limited. It is shown that using Hybrid-ARQ (HARQ) can significantly improve the average rate performance, provided that the rate assignment between different ARQ rounds is carefully chosen. The average rate performance of several HARQ schemes is optimized and compared. In addition, optimal power allocation among retransmissions is derived and shown to further increase the average rate. This power allocation gain is remarkable at low signal-to-noise ratio (SNR), but becomes negligible at high SNR. Comparison of two different types of limited feedback, sequential feedback (ARQ) and one-shot feedback (quantized CSI), is made from several perspectives. Although the optimization problem is formed with respect to the average rate, simulation results give a comprehensive comparison under different metrics, including average rate, outage probability, and the combination of both. Substantial performance improvement is observed with even one ARQ retransmission in all simulations. More importantly, this gain appears to be robust with respect to the fading distributions.

Distributed Detection for Macrodiversity Enhanced Cellular Communication Systems

This paper considers the design of soft decision distributed detection schemes for achieving macrodiversity in uplink cellular communication systems with and without channel knowledge at the fusion center. Distributed detection macrodiversity (DDM) techniques are proposed where the quatizer thresholds of local detectors at base stations (radio access points) are optimized using a numerical global optimization algorithm called adaptive simulated annealing (ASA). The performance of such DDM schemes is studied for systems with and without channel coding, where the base stations employ multiple receive antennas over quasi-static Rayleigh fading channels. It is shown that properly designed quantizers for the local detectors, with a few resolution bits can make the performance very close to optimal macrodiversity that requires a much larger bandwidth from the connection links to the fusion center.

Joint Channel Estimation and Synchronization for MIMO–OFDM in the Presence of Carrier and Sampling Frequency Offsets

A pilot-aided scheme is proposed for the joint estimation and tracking of channel impulse response (CIR), carrier frequency offset (CFO) and sampling frequency offset (SFO) in burst mode, multiple-input-multiple-output (MIMO), and orthogonal frequency division multiplexing(OFDM) systems. First, a received signal model that takes into account nonlinear CFO/SFO effects is formulated. Then, based on the derived signal model and the received multicarrier signal samples containing the pilot tones in the frequency domain, an objective function that includes MIMO CIR, CFO, and SFO is introduced to develop a vector recursive-least-square (RLS)-based joint channel estimation and synchronization algorithm. The analysis and simulation results show that, over the large ranges of the CFO and SFO values, the proposed estimation and tracking scheme offers fast convergence, high stability, and a near-optimum receiver performance that is remarkably close to the ideal performance in the case of perfect channel estimation and synchronization over quasi-static Rayleigh multipath fading channels.

Turbo Processing for Joint Channel Estimation, Synchronization, and Decoding in Coded MIMO-OFDM Systems

This paper proposes a turbo joint channel estimation, synchronization, and decoding scheme for coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The effects of carrier frequency offset (CFO), sampling frequency offset (SFO), and channel impulse responses (CIRs) on the received samples are analyzed and explored to develop the turbo decoding process and vector recursive least squares (RLSs) algorithm for joint CIR, CFO, and SFO tracking. For burst transmission, with initial estimates derived from the preamble, the proposed scheme can operate without the need of pilot tones during the data segment. Simulation results show that the proposed turbo joint channel estimation, synchronization, and decoding scheme offers fast convergence and low mean squared error (MSE) performance over quasistatic Rayleigh multipath fading channels. The proposed scheme can be used in a coded MIMO-OFDM transceiver in the presence of multipath fading, carrier frequency offset, and sampling frequency offset to provide a bit error rate (BER) performance comparable to that in an ideal case of perfect synchronization and channel estimation over a wide range of SFO values.

Threshold-based frame error rate analysis of MIMO systems over quasistatic fading channels

Proper selection of a signal-to-noise ratio threshold largely determines the tightness of an approximation to the frame error rate of a system over a quasistatic fading channel. It is demonstrated that the expression for the optimal threshold value, which has been established for single-input single-output (SISO) channels, remains unchanged for the general case of multiple-input multiple-output (MIMO) channels.

Rate optimization to minimize distortion for source-channel coded H-BLAST with SIC decoding

As joint source and channel coding schemes, layered transmission schemes for a successive refinable source (SRS) are recently studied over quasi-static fading channels. In this letter, we consider spatial layered transmission for a SRS with successive interference cancellation (SIC) decoder over quasistatic multi-input multi-output (MIMO) fading channels. We show that if the distortion function can be factorized, the minimum average distortion can be obtained by individual rate optimization for each layer when zero-forcing (ZF) SIC receiver is employed over Rayleigh fading channels.

Performance of Block Space-Time Code in Wireless Channel Dynamics

In this work, we observe the behavior of block space-time code in wireless channel dynamics. The block space-time code is optimally constructed in slow fading. The block code in quasistatic fading channels provides affordable complexity in design and construction. Our results show that the performance of the block space-time code may not be as good as conventionally convolutional coding with serial transmission for some channel features. As channel approaches fast fading, a coded single antenna scheme can collect as much diversity as desired by correctly choosing the free distance of code. The results also point to the need for robust space-time code in dynamic wireless fading channels. We expect that self-encoded spread spec-trum with block space-time code will provide a robust performance in dynamic wireless fading channels.

Finite-SNR Analysis and Optimization of Decode-and-Forward Relaying Over Slow-Fading Channels

We provide analytical results on the finite signal-to-noise ratio (SNR) outage performance of packet-based decode-and-forward relaying over a quasi-static fading channel, with different types of transmitter channel state information (CSI). At the relay, we consider repetition coding (RC) and parallel coding (PC). At the destination, we consider receivers based on selection combining (SC), code combining (CC), and maximum-ratio combining (MRC) (the latter only for the case of RC at the relay). Based on available CSI, we optimize the number of channel uses consumed by the source and by the relay for each packet. In doing so, we consider three different protocols that make use of different combinations of long-term CSI, 1-bit CSI, and complete CSI, respectively, at the source node. Several interesting observations emerge. For example, we show that for high SNRs, SC and CC provide the same outage probabilities when the source has perfect CSI.

Non-coherent Receivers for Orthogonal Space-Time CPM

Continuous phase modulation (CPM) is a non-linear modulation technique whose power and bandwidth efficiency make it an attractive choice for mobile communication systems. Current research has focused on devising encoding rules for using CPM over multiple-input multiple-output (MIMO) systems in order to obtain the improved bit error rate (BER) and high data rates promised by MIMO technology. In this paper, optimal and suboptimal non-coherent receivers for a class of CPM signals called orthogonal space-time CPM (OST-CPM) are derived under a quasi-static fading channel assumption. The performance of these receivers is characterized and shown to achieve the same diversity order as that of the corresponding optimal coherent receiver.