Diversity In Rayleigh Fading Channels Research Articles

Deep Learning-Based Channel Estimation Algorithm Over Time Selective Fading Channels

The research about deep learning application for physical layer has been received much attention in recent years. In this paper, we propose a Deep Learning (DL) based channel estimator under time varying Rayleigh fading channel. We build up, train and test the channel estimator using Neural Network (NN). The proposed DL-based estimator can dynamically track the channel status without any prior knowledge about the channel model and statistic characteristics. The simulation results show the proposed NN estimator has better Mean Square Error (MSE) performance compared with the traditional algorithms and some other DL-based architectures. Furthermore, the proposed DL-based estimator also shows its robustness with the different pilot densities.

Performance analysis of cognitive AF relay networks with multiuser switched diversity in Rayleigh fading channels

The multiuser switched diversity (MUSwiD) selection schemes are useful in reducing the required channel estimation load in wireless networks. In this paper, we propose and evaluate the performance of cognitive amplify-and-forward (AF) MUSwiD relay networks where a cognitive user is selected among a set of users for data reception. The selection process is performed such that the end-to-end (e2e) signal-to-noise ratio (SNR) of the selected user satisfies a predetermined switching threshold. Such a user that satisfies this threshold is scheduled instead of the best user to receive its message from the secondary source. In the proposed system, we consider a cognitive source, a cognitive relay, a set of cognitive users, and a primary user. In this paper, an upper bound on the e2e SNR of a user is used in deriving of closed-form approximations for the outage probability and average symbol error probability (ASEP) of the studied system in addition to deriving the ergodic channel capacity. To get more about system insights, the performance is studied at the high SNR regime where approximate expressions for the outage probability, SEP, diversity order, and coding gain are derived. The derived analytical and asymptotic expressions are verified by Monte-Carlo simulations, and some numerical examples are provided to illustrate the effect of some parameters such as number of users and switching threshold on the system performance. Findings illustrate that the diversity order of the studied cognitive AF multiuser switched diversity relaying network is the same as its non-cognitive counterpart. Also, results show that the asymptotic results tightly converge to the exact ones, and the analytical bounds are indeed very tight, validating the accuracy of our approach of analysis. Furthermore, findings illustrate that the proposed MUSwiD user selection schemes are efficient in the range of low SNR values, which makes them attractive options for practical implementation in emerging mobile broadband communication systems. In contrast, these selection schemes are shown to be inefficient in the range of high SNR values where the multiuser diversity gain is noticeably degraded when they are implemented.

Symbol Error Rate of Generalized Selection Combining with Signal Space Diversity in Rayleigh Fading Channels

Symbol Error Rate of Generalized Selection Combining with Signal Space Diversity in Rayleigh Fading Channels

A Novel Generalized Framework for Performance Analysis of Selection Combining Diversity

A novel generalized framework for performance analysis of selection combining diversity in Rayleigh fading channels is derived. It is shown that the performance of arbitrary systems used with selection combining diversity can be expressed in terms of only the performance of the system on a single branch Rayleigh fading channel. The results are valid for coded and uncoded transmission as well as for balanced (equal power) diversity branches and unbalanced (unequal power) diversity branches. The generalized framework encompasses both general noise and general interference, and allows correlated noise and correlated interference sources. Applications of the generalized framework to analytical, semi-analytical and simulation based performance evaluation of digital modulation schemes are discussed.

Performance Evaluation of Space-Time Block Codes from Coordinate Interleaved Orthogonal Designs in Shadowed Fading Channels

In this correspondence, we evaluate the symbol error rate (SER) and information outage probability (IOP) of space-time block codes (STBCs) from coordinate interleaved orthogonal designs (CIODs) in the composite channel of lognormal shadowing and Rayleigh fading. By applying the Gauss-Hermite quadrature integration, we derive an accurate closed-form approximation for the symbol pairwise error rate (SPER) and corresponding tight upper and lower bounds on the SER of STBCs from CIODs. An accurate closed-form approximate formula for the IOP is also derived by formulating the composite squared lognormal/chi-square probability density function and exploiting the high-signal-to-noise-ratio (SNR) approximation technique. Furthermore, we investigate the achievability of full diversity in Rayleigh fading channels with shadowing effects. Finally, various Monte Carlo simulations are performed to validate our theoretical results.

Reducing ICI effect in OFDM system using low‐complexity Kalman filter based on comb‐type pilots arrangement

AbstractIn OFDM systems, time‐varying channels destroy orthogonality between subcarriers causing Inter‐Carrier Interference. To reduce this effect, a Kalman filter, as a benchmark, is used for channel estimation, based on comb‐type pilot arrangements of the OFDM system. An advantage of comb‐type pilot arrangements in channel estimation is the ability to track the variation of the channel caused by Doppler frequency. Kalman method has been proposed to estimate the channel frequency response (CFR) at the pilot locations, then CFR, at data subchannels, is obtained by means of interpolation between estimates at pilot locations. The low‐complexity Kalman method is introduced to reduce the complexity of the system while achieving the same BER/SNR. Different types of interpolations have been also compared such as Low‐pass, Spline‐cubic and Linear interpolation methods. The BER/SNR performance of BPSK modulation schemes are considered for time varying Rayleigh fading channels. Our results has shown that the low‐complexity Kalman estimation, used with the pilot arrangement and a suitable interpolation method, gives almost the same performance as that of the Kalman method specially for low SNR values and hence the effect of Doppler shift effect is controlled. Copyright © 2010 John Wiley & Sons, Ltd.

A novel rate-2 full diversity algebraic space-time code

Orthogonal space-time block codes (OSTBCs) have attracted considerable attention due to their low complexity linear decoding and full diversity in Rayleigh fading channels. However, OSTBCs exist only for certain numbers of transmit antennas and do not provide full code rate when more than two transmit antennas are used. In this paper, a novel rate-2 algebraic space-time code that combines coordinate-interleaving and group precoding is proposed. By properly choosing the designed parameters, the coding scheme can achieve full diversity order and high coding gain. The receiver adopts polynomial complexity sphere decoding algorithm to get maximum likelihood (ML) performance. Analysis and simulations illustrate that the new code exhibits significant performance gain over the conventional OSTBCs and diagonal algebraic space-time code.

Benefits, variants and applications of cyclic delay diversity

AbstractCyclic delay diversity (CDDx) is a simple multiple antenna technologyxs 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. Copyright © 2008 John Wiley & Sons, Ltd.

시변 레일리 페이딩 채널에서 이중 판정 궤환 방식을 이용한 STBC 검출 알고리즘

이 논문에서는 시변 레일리 페이딩 채널에서 STBC(Space Time Block Code)의 신호 검출 방법을 연구한다. 하나의 블록 내의 두 심볼 구간 동안 채널 환경이 변하는 경우, 채널 행렬의 직교성이 성립하지 않고 두 심볼간에 간섭이 발생한다. 이러한 채널에서 수신 성능을 개선하기 위해서 joint ML 검출 방식이 제안되었으나, 계산복잡도가 증가한다. 이를 줄이기 위해서 판정 궤환(decision feedback) 방식이 제안되었으나, joint ML 방식에 비해 수신 성능이 떨어진다. 이에 이 논문에서는 joint ML 검출 방법을 사용하는 경우에 비해 수신기의 복잡도를 줄이는 동시에 기존의 판정 궤환 방식에 비해 성능이 개선된 이중 판정 궤환 방식을 이용한 새로운 STBC 검출 알고리즘을 제안한다. In this paper, we study STBC(Space Time Block Code) detection scheme in time varying Rayleigh fading channel. When the channel is varying during the time duration of STBC, the channel matrix of orthogonal STBC is not orthogonal. To get the optimum reception performance in this channel, joint ML detection scheme may be used, however this scheme requires high computation complexity. Decision feedback scheme is proposed to reduce the computation complexity with less reception performance. In this paper, we propose a novel STBC detection algorithm using double decision feedback which is less complex than the joint ML scheme and outperforms the conventional decision feedback scheme.

Analysis of the Principal Component Combining with Weight Estimation for DPSK Signals

We analyze the principal component combining with differential detection (PCC-DD) with weight estimation for the demodulation of DPSK signals in diversity systems. The estimated weight vector is considered to be the principal component of the exponentially weighted sample correlation matrix of the signals at diversity channel outputs. We arrive at closed form expressions for the approximate bit error rate (BER) for the scenario where channel gains are fixed, and the approximate average BER for the scenario where channel gains are independent identically Rayleigh distributed. The analysis provides accurate BER approximation, and is justified by the results from computer simulations. We also arrive at a rule of thumb about the value of the forgetting factor of the exponentially weighted sample correlation matrix should be selected for PCC-DD to yield good performance under time varying Rayleigh fading channels

On the average crossing rates in selection diversity

This letter presents new results on the average crossing rate of the combined signal of a selection diversity in Rayleigh fading channels. Exact closed-form expressions are derived for the inphase zero crossing rate, inphase rate of maxima, phase zero crossing rate, and the instantaneous frequency zero crossing rate of the output of the selection combiner. The utility of the new theoretical formulas, validated by Monte Carlo simulations, are briefly discussed as well

Feedback outage correlated with CQI and its impact on multiuser diversity in Rayleigh fading channels

This letter addresses a feedback outage when the channel condition of the feedback channel is correlated with that of the traffic channel the quality information of which is being carried by the feedback, and its impact on the multiuser diversity in flat Rayleigh fading channels. The correlation is described by the time delay as well as the frequency separation between the traffic and the feedback channel. The average capacity is provided in terms of the time and the frequency factor. With numerical investigations, we show that the capacity degradation due to the feedback outage is generally saturated at the great frequency separation approximately over 45 MHz (e.g., in present IS-95 cellular systems), within which it fluctuates depending on the feedback delay

SER Analysis of QAM with Space Diversity in Rayleigh Fading Channels

This paper derives the symbol error probability for quadrature amplitude modulation(QAM) with L-fold space diversity in Rayleigh fading channels. Two combining techniques, maximal ratio combining(MRC) and selection combining(SC), are considered. The formula for MRC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an additive white Gaussian noise(AWGN) channel over a chi-square distribution with 2L degrees of freedom. The obtained formula overcomes the limitations of the earlier work, which has been limited only to deriving the symbol error rate(SER) of QAM with two branch MRC space diversity. The formula for SC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an AWGN channel over the distribution of the maximum signal-to-noise ratio among all of the diversity channels for SC space diversity. No analysis for QAM with SC space diversity has been reported yet. Analytical results show that the probability of error decreases with the order of diversity. We can also see that the incremental diversity gain per additional branch decreases as the number of branches becomes larger. On the other hand, the performance of 16 QAM with MRC becomes much better than that of SC as the number of branches becomes larger. By giving the order of diversity, L, and the number of signal points, M, we have been able to obtain the SER performance of QAM with general space diversity. These results can be used to determine the order of diversity to achieve the desired SER in land mobile communication system employing QAM modulation.

Markov characterization of channels with soft decision outputs

It is shown that a methodology based on hidden Markov models is applicable to the modeling of slowly varying Rayleigh fading channels with additive Gaussian noise and soft decision outputs. The fading is considered to be frequency nonselective, and ideal demodulation is considered throughout. To prove the validity of robustness of the modeling technique, various results that show good agreement between the simulated channels and the models found are presented. Two soft decision statistical distributions, namely, the soft burst and soft burst interval distributions, are defined and compared. To illustrate the accuracy of the models obtained, the simulation and model outputs are compared for a convolutional encoder with Viterbi decoding and various degrees of interleaving.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>