Rayleigh fading channel

In order to adapt to the time-varying nature of wireless channels, various channel-adaptive schemes have been proposed to exploit inherent spatial diversity in wireless ad hoc networks where there are usually alternate forwarding nodes available at a given forwarding node. However, existing schemes along this line are designed based on heuristics, implying room for performance enhancement. Thereby, to seek a theoretical foundation for improving spatial diversity gain, we formulate the selection of the next-hop relay as a sequential decision problem and derive a general "Optimal Stopping Relaying (OSR)" framework for designing such spatial-diversity schemes. As a particular example, assuming Rayleigh fading channels, we implement an OSR strategy to optimize information efficiency (IE) in a protocol stack consisting of Greedy Perimeter Stateless Routing (GPSR) and IEEE 802.11 MAC protocols. We present an analysis of the algorithm for a single node. In addition, we perform extensive simulations (using QualNet) to evaluate the end-to-end performance of the proposed forwarding strategy. The results demonstrate the superiority of OSR over other existing schemes.

arXiv:cs/0612076v1 [cs.IT] 15 Dec 2006 SUBMITTED TO IEEE TRANSACTIONS ON INFORMATION THEORY 1 A New Approach for Capacity Analysis of Large DimensionalMulti-Antenna Channels W. Hachem(∗), O. Khorunzhiy, Ph. Loubaton, J. Najim and L. Pastur ...

Iterative threshold decoding of product and parallel concatenated block codes based on one step majority logic decodable (OSMLD) codes has proven to perform remarkably well on AWGN channels. For these codes to be applicable in wireless environment, their performance on fading channels must be examined. The purpose of this work is to study the performance of our iterative threshold decoding algorithm on the Rayleigh fading channel. Results have shown that the slope of the bit-error rate (BER) curve is as steep as for the Gaussian channel. We also present a comparison between our results and those for convolutional turbo code in terms of BER performance.

A statistical discrete-time model is proposed for simulating wideband multiple-input multiple-output (MIMO) fading channels which are triply selective due to angle spread, Doppler spread, and delay spread. The new discrete-time MIMO channel model includes the combined effects of the transmit filter, physical MIMO multipath channel fading, and receive filter, and it has the same sampling period as that of the MIMO receiver. This leads to very efficient simulation of physical continuous-time MIMO channels. A new method is also presented to efficiently generate the MIMO channel stochastic coefficients. The statistical accuracy of the discrete-time MIMO channel model is rigorously verified through theoretical analysis and extensive simulations in different conditions. The high computational efficiency of the discrete-time MIMO channel model is illustrated by comparing it to that of the continuous-time MIMO channel model. The new model is further employed to evaluate the channel capacity of MIMO systems in a triply selective Rayleigh fading environment. The simulation results reveal some interesting effects of spatial correlations, multipaths, and number of antennas on the MIMO channel capacity. Index Terms-Discrete-time channel model, multiple-input multiple-output (MIMO) channel, multiple-input multiple-output multipath channel capacity, Rayleigh fading, triply selective fading, wide-sense stationary uncorrelated scattering (WSSUS) multipath channel. I. INTRODUCTION T HE multiple-input multiple-output (MIMO) communication architecture has recently emerged as a new paradigm for high data rate wireless cellular communications in rich multipath environments. Using multiple-element antenna arrays at both the transmitter and receiver, which effectively exploits the spatial dimension in addition to time and frequency dimensions, this architecture shows channel capacity potential far beyond that of traditional techniques. In quasi-static, independent and identically distributed (i.i.d.) frequency flat Rayleigh fading channels, the MIMO capacity scales linearly with the number of antennas under some conditions [1], [2]. However, in practice,

In this paper we present a population declining ant colony optimization (PDACO) multiuser detector for asynchronous CDMA communications. Ant colony optimization (ACO) algorithms have already been used in multiuser detection in CDMA systems; however, as the pheromone accumulates, we may not get a global optimum because it stops searching early. PDACO can enlarge searching range through increasing the initial population of the ant colony, and the population declines in successive iterations. So, the performance of PDACO is superior with the same computational complexity. PDACO is applied to multiuser detection in asynchronous CDMA systems over slowly multipath Rayleigh-fading channels in this paper. Via computer simulations it is shown that the performance of PDACO detector is much better in bit-error rate and near-far effect resistance than conventional detector, ACO detector and genetic algorithm detector, and is close the optimal multiuser detector.

This paper offers performance analysis of decodeand-forward protocol employing selection combining (SC) at the destination. For an arbitrary number of relays, BER for M PSK of the system is investigated in both independent identically distributed (i.i.d) and independent but not identically distributed (i.n.d.) Rayleigh fading channels. A variety of simulations are performed and show that they match exactly with analytic ones. In addition, our results also show that the optimum number of relays depend not only on channel conditions (operating SNR) but also on modulation scheme which we exploit.

In this work, a channel estimation technique based on Artificial Neural Networks (ANN) has been proposed as an alternative to pilot based channel estimation technique for Space-Time Block Coded Multiple-Input Multiple-Output (STBC- MIMO) systems over Rayleigh fading channels. ANNs, due to their high degree of adaptability, can be used for modelling the nonlinear phenomenon of channel estimation and for decoding the degraded symbols over severely faded channel. Two different ANN structures, namely Multilayer Perceptron (MLP) and Recurrent Neural Networks (RNN) have been trained and tested extensively for estimating the channel in STBC- MIMO systems with Binary Phase Shift Keying (BPSK) modulation scheme. Simulated results in terms of Bit Error Rates (BER) vs. Signal to Noise Ratio (SNR) have been used to compare the effectiveness of the learning capability of the two ANN structures over wireless fading channel. RNN structures are found to outperform the MLP, both in terms of training...

When the mechanisms of fading channels were first modeled in the 1950s and 1960s, the ideas were primarily applied to over-the-horizon communications covering a wide range of frequency bands. The 3-30 MHz high-frequency (HF) band is used for ionospheric communications, and the 300 MHz-3 GHz ultra-high-frequency (UHF) and 3-30 GHz super-high-frequency (SHF) bands are used for tropospheric scatter. Although the fading effects in a mobile radio system are somewhat different than those in ionospheric and tropospheric channels, the early models are still quite useful to help characterize fading effects in mobile digital communication systems. This tutorial addresses Rayleigh fading primarily in the UHF band. That affects mobile systems such as cellular and personal communication systems (PCS). Part I of the tutorial itemizes the fundamental fading manifestations and types of degradation

Multi Carrier Code Division Multiple Access (MC-CDMA) is an attractive choice for high speed wireless communication as it avoids the problem of Inter Symbol Interference (ISI) and also exploits frequency diversity. In order to support multiple users with high speed data communications, the MC-CDMA technique is used to address these challenges. MC-CDMA experiences severe multipath fading which badly affects its performance. When transmission over fading channel multi-cell interference occurs and this degrades the performance of the system. This paper specially analyzes the BER performance under Rayleigh fading channel conditions of MC-CDMA in presence of AWGN (Additive White Gaussian Noise) using BPSK modulation for different number of subcarrier, different number of users using MATLAB program, and finally the paper also presents a comparison between simulated results, which shows the reduction in BER performance.

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.

In this paper, Multi-Carrier Code Division Multiple Access (MC-CDMA) technique combined with several Space-Time Block Codes (STBC) is analyzed in the case of transmit antennas and receive antennas to provide a diversity order of for a 1 or 2 bps/Hz spectral efficiency. A general method to decode STBC from ort hogonal designs associated with MC-CDMA is proposed. Two Single-user Detection

Reverberation chambers (RC) are a popular tool for laboratory wireless communication performance evaluation, and their standardization for Over-The-Air (OTA) measurements is underway. Yet, the inherent limitations of single-cavity RCs to emulate isotropic Rayleigh-fading scenarios with uniform phase distribution and high elevation angular spread put their representation of realistic scenarios into jeopardy. Recent advances in the last few years, however, have solved all these limitations by using more general mode-stirred reverberation chambers (MSC), wherein the number of cavities, their stirring and coupling mechanisms, and their software postprocessing algorithms is far from simple, representing a new era for wireless communications research, development, and over-the-air testing. This article highlights recent advances in the development of second-generation mode-stirred chambers for wireless communications performance evaluation.

El maltrato animal comprende una gama de comportamientos que causan dolor innecesario o estrés al animal, esto abarca desde la negligencia en los cuidados básicos, hasta el asesinato malicioso. Existen dos tipos de crueldad animal, el maltrato directo, que consta de la falta intencional en proporcionar los cuidados básicos, la tortura, la mutilación o el asesinato de un animal, y el maltrato indirecto.

We consider the design of channel codes for improving the data rate and/or the reliability of communications over fading channels using multiple transmit antennas. Data is encoded by a channel code and the encoded data is split into n streams that are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. We derive performance criteria for designing such codes under the assumption that the fading is slow and frequency nonselective. Performance is shown to be determined by matrices constructed from pairs of distinct code sequences. The minimum rank among these matrices quantifies the diversity gain, while the minimum determinant of these matrices quantifies the coding gain. The results are then extended to fast fading channels. The design criteria are used to design trellis codes for high data rate wireless communication. The encoding/decoding complexity of these codes is comparable to trellis codes employed in practice over Gaussian channels. The codes constructed here provide the best tradeoff between data rate, diversity advantage, and trellis complexity. Simulation results are provided for 4 and 8 PSK signal sets with data rates of 2 and 3 bits/symbol, demonstrating excellent performance that is within 2-3 dB of the outage capacity for these channels using only 64 state encoders.

Cyclic delay diversity (CDD) is a simple multiple antenna technology which provides additional diversity in Rayleigh fading channels, and therefore, improves the system performance. We recall the principles of CDD and discuss the properties and impact of this transmit (TX) antenna diversity technology. Different applications motivate variations of the CDD principle. This variants are briefly introduced and discussed. We show the application to several types of wireless systems, in particular terrestrial digital video broadcasting, cellular mobile radio communications systems and a wireless communications system using adaptive bit loading (ABL). Simulation results highlight the benefits of CDD for these kind of systems.

Maximum Likelihood (ML) detection of differentially encoded M-PSK signals on Rayleigh fading channels is investigated. It is shown that the solution to this problem can be related to previous results [l] and leads to the implementation of a receiver structure based on the Viterbi Algorithm and employing per-survivor processing. The error rate performance of this receiver is evaluated by means of computer simulations for both trellis-coded and uncoded systems.

The performance of maximal ratio combining for space diversity reception in digital cellular mobile radio systems is studied for communications in the presence of multiple cochannel interference (CCI) sources and is compared to optimum combining. The main contribution of the paper is that the analysis accounts for fading of the signal of interest (SOI) as well as the cochannel interference (CCI). The paper considers BPSK signalling in flat, quasi-static channels. Rayleigh or Rice fading is assumed for the SOI, while CCI is assumed subject to Rayleigh fading. Channels associated with interference sources are assumed independent and identically distributed. Using a multivariate statistical analysis approach and assuming equal-power interference sources, analytical expressions are derived for the density function of the array output signal-to-interference ratio (SIR), the outage probability, and the average probability of bit error with maximal ratio combining. Earlier results obtained for optimum combining and Rayleigh fading are extended to the case when the SOI is subject to Rice fading. A limited analysis of the equal gain combiner is also presented.

It is well-known that for single-input and single-output (SISO) narrow-band transmission on frequency-flat fading channels, uncoded communication with only receiver channel state information (Rx-CSI) leads to extremely poor reliability performance whereas transmitter CSI (Tx-CSI) allows us approach the reliability of an additive white gaussian noise (AWGN) channel via power control. In this paper, we propose a novel approach to achieve reliability close to the AWGN channel for uncoded transmissions on SISO frequency-flat Rayleigh fading channels without Tx-CSI. Our approach employs pseudo-random phase precoding (PRPP) of modulation symbols prior to temporal multiplexing, and joint-detection at the receiver that has polynomial complexity in the precoder size. With a precoder size of 400 binary symbols, we demonstrate that the proposed system achieves performance within 0.1 dB of the AWGN channel at a bit error rate of 0.00001, and is also robust to fading correlation and channel estimation errors. Furthermore, we present extensions to multiple-user multiple-input and multiple-output (MU-MIMO) systems and wideband transmission schemes such as orthogonal frequency-division multiplexing (OFDM) and single carrier frequency-domain multiple access (SC-FDMA) systems. We show, through extensive simulations, that i) with 8-by-8 MIMO system per-stream AWGN channel reliability is achieved with 8 spatial streams and 50 channel uses, ii) for a 5 user multiple-access channel with one antenna per user and 5 antennas at the receiver, 80 channel uses eliminates fading and interference complexity while simultaneously providing a power gain of approximately 6.9 dB, and iii) for OFDM and SC-FDMA systems with single antenna at the transmitter and two antennas at the receiver, within 0.1 and 0.3 dB of the matched-filter bound performance is achieved with a precoder size of 96 and 400 symbols, respectively.

While rapid variations of the fading channel cause intercarrier interference (ICI) in orthogonal frequency-division multiplexing (OFDM), thereby degrading its performance considerably, they also introduce temporal diversity, which can be exploited to improve the performance. In this paper, we first derive a matched-filter bound (MFB) for OFDM transmissions over doubly selective Rayleigh fading channels, which benchmarks the best possible performance if ICI is completely canceled without noise enhancement. We then derive universal performance bounds which show that the time-varying channel causes most of the symbol energy to be distributed over a few subcarriers, and that the ICI power on a subcarrier mainly comes from several neighboring subcarriers. Based on this fact, we develop low-complexity minimum mean-square error and decision-feedback equalizer (DFE) receivers for ICI suppression. Simulations show that the DFE receiver can collect significant gains of ICI-impaired OFDM with affordable complexity. In the relatively low Doppler frequency region, bit-error rate of the DFE receiver is close to the MFB.

In this paper, we present a log-likelihood ratio (LLR) based approach to analyze the bit error rate (BER) performance of quadrature amplitude modulation (QAM) on Rayleigh fading channels without and with transmit diversity. We derive LLRs for the individual bits forming a QAM symbol both on flat fading channels without diversity as well as on channels with transmit diversity using two transmit antennas (Alamouti's scheme) and multiple receive antennas. Using the LLRs of the individual bits forming the QAM symbol, we derive expressions for the probability of error for various bits in the QAM symbol, and hence the average BER. In addition to being used in the BER analysis, the LLRs derived can be used as soft inputs to decoders for various coded QAM schemes including turbo coded QAM with transmit diversity, as in high speed downlink packet access (HSDPA) in 3G.

New Over-The-Air (OTA) measurement technology is wanted for quantitative testing of modern wireless devices for use in multipath. We show that the reverberation chamber emulates a rich isotropic multipath (RIMP), making it an extreme reference environment for testing of wireless devices. This complements thereby testing in anechoic chambers representing the opposite extreme reference environment: pure Line-of-Sight (LOS).

This report, presents an analytical framework for analyzing two-branch diversity systems for a Rayleigh fading channel. In many cases the fading received at both branches (i.e. a two-antenna element system) is correlated because of the proximity of the antenna elements to each other. It is also not uncommon for a diversity system to use antennas with different patterns or polarizations, this usually results in differences in average signal-to-noise ratios at both branches depending on which element is better matched to the signal environment. As will be shown, the performance of a diversity system depends greatly on the envelope correlation, average power imbalance and the combining scheme used on both branches.

In this paper, we propose a new method of channel estimation for asynchronous additive white Gaussian noise channels in satellite communications. This method is based on signals correlation and multiuser interference cancellation which adopts a successive structure. Propagation delays and signals amplitudes are jointly estimated in order to be used for data detection at the receiver. As, a multiuser detector, a single stage successive interference cancellation (SIC) architecture is analyzed and integrated to the channel estimation technique and the whole system is evaluated. The satellite access method adopted is the direct sequence code division multiple access (DS CDMA) one. To evaluate the channel estimation and the detection technique, we have simulated a satellite uplink with an asynchronous multiuser access.

Previous work on receivers suitable for correlated Rayleigh fading channels is examined. The analysis is generalized to complex signaling. It is demonstrated that the error performance of a standard receiver is weakly dependent on the structure of the fading process, and that an appropriate receiver may exploit this structure to give greatly improved performance. Two receiver structures, based on the classic estimator correlator derivation of Kailath, are considered. These structures are able to lower the error floor of a receiver in a correlated, Rayleigh fading channel. The performance limitation is found to be due to the form of the receiver used, rather than a fundamental channel capacity type of limit, and the appropriate receiver structure is able to virtually eliminate the asymptotic error. The performance of both standard and optimal receivers is examined analytically and verified through simulation.

In this paper, we design capacity approaching lowdensity parity-check (LDPC) codes in the low signal-to-noise ratio (SNR) regime for flat Rayleigh fading channels with channel side information at transmitter and receiver. We use the structure advocated by Caire et al, which uses a single codebook with dynamic power allocation. The extrinsic information transfer (EXIT) function method is used to design the LDPC codes which approach the channel capacities. We also study the EXIT function properties of various demappers.

In this paper, the Bit Error Rate (BER) performance of Fast Fourier Transform-based Orthogonal Frequency Division Multiplexing system (FFT-Based OFDM) is compared with Discrete Cosine Transform-based Orthogonal Frequency Division Multiplexing system (DCT-Based OFDM) using Binary Phase Shift Keying (BPSK) as a modulation technique over Additive White Gaussian Noise environment (AWGN) and Multipath Rayleigh Fading environment. From the results it is clear that, the BER shift in case of DCT-Based OFDM is less as compared to FFT-Based OFDM. In addition to this we have also compare the BER performance of FFT-Based & DCT-Based OFDM over Additive White Gaussian Noise environment and Multipath Rayleigh Fading environment and it is observed that Bit Error Rate performance of FFT-Based & DCT-Based OFDM over AWGN is better than Multipath Rayleigh Fading environment.

In this paper, we propose a technique to reduce the number of trellis states in BCJR-type algorithms, i.e., algorithms with a structure similar to that of the well-known algorithm by Bahl, Cocke, Jelinek, and Raviv (BCJR). This work is inspired by reduced-state sequence detection (RSSD). The key idea is the construction, during one of the recursions in the reduced-state trellis, of a "survivor map" to be used in the other recursion. In a more general setting, two distinct survivor maps could be determined in the two recursions and used jointly to approximate the a posteriori probabilities. Three examples of application to iterative decoding are shown: 1) coherent detection for intersymbol interference (ISI) channels; 2) noncoherent detection based on an algorithm recently proposed by the authors; and 3) detection based on linear prediction for Rayleigh fading channels. As in classical RSSD, the proposed algorithm allows significant state-complexity reduction with limited performance degradation.

Space-time trellis codes provide both diversity gain and coding gain. There are two different design criteria proposed for spacetime trellis codes (STTCs), namely the rank and determinant criteria (RDC) and the Euclidean distance design criteria (EDC). In this paper, we present the performance of STTCs over Nakagami fading channels. Our results show that the STTCs designed for Rayleigh fading channels & Recian fading channels are also suitable for Nakagami fading channels. Nakagami fading channel models are considered more versatile than other channel models. In Gong et al. presented the performance of the STTCs over Nakagami fading channels. In this paper, we also present the performance of the STTCs designed using the EDC over Nakagami fading channels.

The principle of coding in the signal space follows directly from Shannon's analysis of waveform Gaussian channels subject to an input constraint. The early design of communication systems focused separately on modulation, namely signal design and detection, and error correcting codes, which deal with errors introduced at the demodulator of the underlying waveform channel. The correct perspective of signalspace coding, although never out of sight of information theorists, was brought back into the focus of coding theorists and system designers by Imai's and Ungerböck's pioneering work on coded modulation. More recently, powerful families of binary codes with a good tradeoff between performance and decoding complexity have been (re-) discovered. Bit-Interleaved Coded Modulation (BICM) is a pragmatic approach combining the best out of both worlds: it takes advantage of the signal-space coding perspective, whilst allowing for the use of powerful families of binary codes with virtually any modulation format.

In this letter, we consider the adaptive decodeand-forward (DF) and amplify-and-forward (AF) cooperativediversity systems with the th best-relay selection scheme. In the best-relay selection scheme, from the set of relays the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the th best relay. We derive closed-form expressions for the symbol error probability, outage probability and asymptotic error probability. In particular, we derive a closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function (MGF) of the output SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. All these expressions are derived over identical and non-identical Rayleigh fading channels. Results show that with the th best relay the diversity order is equal to ( − + 2) where is the number of relays.

UO1TCQ 12 1AGU O JJC 2Offl.C bucbp urnX pc dnoq ipori cxbjci bci.w22ou bLoAqcq qrn njj cLcq ucjnqu © © JÔÔQ P b11J KU1UJ91J rjj UJU2 LCaCLAGq 2JJOLi 2GCt!0U2 Oj 1QX U01 O cxccq tMO JQ2G91Cp obu!ou2 CXbL22q LG flJO2C O C 1UJJOL uq UO JO2C Oj JJC ,41!OIJ9I BnCn o cououjc JJJT2 bthL 12 b9 O I4EI2 LC2C9LCjJ bLOLUJ IU pUCLIJPOU1J J.Lvq uq JIJA2I1JCUr VUA NLCP JQ NV O3J18 JOO N 9CJJ(12CU2 wvnowir Bfll EVfl OI ECOI4ONIC BE2EVBCH JOLjUU bbcL tXI bJ KLI111

It is shown that the level crossing rate (LCR) of a Rayleigh distributed stochastic process is proportional to the second centralized moment of the normalized power spectrum of the underlying complex Gaussian process. This proportionality factor is independent of the power spectrum. The relation can be applied for estimating the rms delay spread of time-dispersive (= frequency-selective) radio channels from swept-frequency power measurements, where the rms delay spread is proportional to the LCR in the frequency-domain, independent of the channel impulse response.

Cooperative diversity is a promising technology for future wireless networks. In this paper, we derive the average bit error rate (BER) and outage probability (P out) for differential equal gain combining (EGC) in cooperative diversity networks. The considered network uses adaptive decode-and-forward (DF) relaying over independent non-identical Nakagami-m fading channels. In adaptive DF relaying among M relays, that can participate, only C relays (C ≤ M ), with good channels to the source, decode and then forward (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using differential EGC. We first derive a simple exact expression for the equivalent SNR at the destination. Second, we derive the expressions of the PDF and the MGF of this equivalent total SNR at the destination. Then the MGF is used to determine the error and outage probabilities of adaptive DF with an arbitrary number of relays. Furthermore, we found (in terms of MGF) the SNR moments, the average signal-to-noise ratio (SNR) and the amount of fading. Computer simulations are used to validate our analytical results. Results show the significant performance improvement due to the use of the adaptive DF cooperative diversity. Also, results show that the performance of the adaptive DF differential EGC is comparable to the adaptive DF maximum ratio combining (MRC) performance.

In this paper an approach to the performance analysis of signal-to-interference (SIR) based selection combining (SC) operating over the Rayleigh fading channels experiencing an arbitrary number of multiple, Rayleigh cochannel interferers is presented. We have presented a general analysis of multibranch SC where each branch experiences an arbitrary number of multiple equal power co-channel interferers. Useful closed form expressions are derived for the probability density function (PDF) and cumulative distribution function (CDF) at the output of the combiner. Also an outage analysis is performed in order to show the effects of the number of multiple interferers, diversity order and input SIR unbalance to the system performances.

Searching for spectrum holes in practical wireless channels where primary users experience multipath fading and shadowing, with noise uncertainty, limits the detection performance significantly. Moreover, the detection challenge will be tougher when different band types have to be sensed, with different signal and spectral characteristics, and probably overlapping spectra. Besides, primary user waveforms can be known (completely or partially) or unknown to allow or forbid cognitive radios to use specific kinds of detection schemes! Hidden primary user's problem, and doubly selective channel oblige the use of cooperative sensing to exploit the spatial diversity in the observations of spatially located cognitive radio users. Incorporated all the aforementioned practical challenges as a whole, this paper developed a new multi-stage detection scheme that intelligently decides the detection algorithm based on power, noise, bandwidth and knowledge of the signal of interest. The proposed scheme switches between individual and cooperative sensing and among featured based sensing techniques (cyclo-stationary detection and matched filter) and sub-band energy detection according to the characteristics of signal and band of interest.Compared to the existing schemes, performance evaluations show reliable results in terms of probabilities of detection and mean sensing times under the aforementioned conditions. Keywords spectrum sensing,local and cooperative,cognitive radio, sub-band energy detection, probability of detection, mean detection time

An infinite series representation for the moment generating function of the sum of squared arbitrarily correlated Rayleigh random variables is presented. Based on the derived formula, corresponding analytical expressions for the probability density and cumulative distribution functions are extracted. As an application for the aforementioned sum, exact analytical expressions for the outage and the average error probability, as well as, the channel average spectral efficiency of multibranch maximal-ratio diversity receivers operating over identically distributed and arbitrarily correlated Rayleigh fading channels are obtained. Our analysis is verified by comparing numerically evaluated results with extensive computer simulation ones.

This paper deals with the case of a high speed mobile receiver operating in an orthogonal-frequency-divisionmultiplexing (OFDM) communication system. Assuming the knowledge of delay-related information, we propose an iterative algorithm for joint multi-path Rayleigh channel complex gains and data recovery in fast fading environments. Each complex gain time-variation, within one OFDM symbol, is approximated by a polynomial representation. Based on the Jakes process, an autoregressive (AR) model of the polynomial coefficients dynamics is built, making it possible to employ the Kalman filter estimator for the polynomial coefficients. Hence, the channel matrix is easily computed, and the data symbol is estimated with free inter-sub-carrier-interference (ICI) thanks to the use of a QRdecomposition of the channel matrix. Our claims are supported by theoretical analysis and simulation results, which are obtained considering Jakes' channels with high Doppler spreads.

In this paper, we consider an orthogonal-frequency-division-multiplexing (OFDM) mobile communication system operating in downlink mode in a time-varying multipath Rayleigh channel scenario. We present a Mean Square Error theoretical analysis for a multipath channel complex gains estimation algorithm with inter-sub-carrier-interference (ICI) reduction using a comb-type pilot. Assuming the presence of delayrelated information, the time average of the multipath complex gains, over the effective duration of each OFDM symbol, are estimated using LS criterion. After that, the time-variation of the multipath complex gains within one OFDM symbol are obtained by interpolating the time-averaged symbol values using lowpass interpolation. Hence, the channel matrix, which contains the channel frequency response and the coefficients of ICI, can be computed and the ICI can be reduced by using successive interference suppression (SIS) in data symbol detection. The algorithm's performance is further enhanced by an iterative procedure, performing channel estimation and ICI suppression at each iteration. Theoretical analysis and simulation results show a significant performance improvement for high normalized Doppler spread (especially after the first iteration) in comparison to conventional methods.

This paper proposes a structure that combines iterative equalization and turbo decoding, denoted as spatial turbo coding (STC), for single carrier signaling to achieve near capacity performance in multipath-rich fading channels. Instead of multiplexing the encoded bits in the time domain as in the standard turbo codes, the proposed STC transmits coded bits in the space domain by employing multiple-input multiple-output (MIMO) transceiver to exploit space diversity, path diversity and coding gains through the decoding branches at the receiver. The considered MIMO detector is a MIMO frequency domain softcancelation and minimum mean square error equalizer (FD/SC-MMSE). Extrinsic Information Transfer (EXIT) chart analysis confirms that bit-error-rate (BER) pinch-off is achieved in 64path Rayleigh fading channels with equal average path gains power which is just by about 1dB away from the static channel capacity/dimension of 2×2 MIMO systems.

This paper deals with the on-line estimation of time-varying frequency-flat Rayleigh fading channels based on training sequences and using H ∞ filtering. When the fading channel is approximated by an autoregressive (AR) process, the AR model parameters must be estimated. As their direct estimations from the available noisy observations at the receiver may yield biased values, the joint estimation of both the channel and its AR parameters must be addressed. Among the existing solutions to this joint estimation issue, Expectation Maximization (EM) algorithm or crosscoupled filter based approaches can be considered. They usually require Kalman filtering which is optimal in the H 2 sense provided that the initial state, the driving process and measurement noise are independent, white and Gaussian. However, in real cases, these assumptions may not be satisfied. In addition, the state-space matrices and the noise variances are not necessarily accurately estimated. To take into account the above problem, we propose to use two crosscoupled H ∞ filters. This method makes it possible to provide A. Jamoos (B) robust estimation of the fading channel and its AR parameters.

Real world source coding algorithms usually leave a certain amount of redundancy within the coded bit stream. Shannon already mentioned that this redundancy can be exploited at the receiver side to achieve a higher robustness against channel errors. In this paper, we show how joint source-channel decoding can be performed in a way that is applicable to any mobile communication system standard. Considerable gains in terms of bit error rate or signal-to-noise ratio (SNR) are possible dependent on the amount of redundancy. However, an even better performance can be achieved by changing also the transmitter sided source and channel encoders. We propose an encoding concept employing low-dimensional quantization. Keeping the gross bit rate as well as the clean channel quality the same, it decreases the complexity of the source encoder and the decoder significantly. Finally, we give an application of our methods to spectral coefficient coding in speech transmission over a Rayleigh fading channel resulting in channel SNR gains of about 2 dB as compared to state-of-the-art (de-)coding and bad frame handling methods.