Rayleigh Fading Environments Research Articles

Energy Consumption Analysis and Energy Holes Avoidance for Gradient Based Routing in Wireless Sensor Networks

In wireless sensor networks(WSNs) using gradient based routing,the uneven energy dissipation among nodes can lead to energy holes and significantly reduces the lifetime of network.In this paper,we analyze the energy consumption of nodes on gradient sinking model in both free space and Rayleigh fading environment,and propose a scheme to avoid energy holes with nonuniform energy distribution,that is,a node is equipped with initial energy according to its energy consumption.Then,we investigate the upper and lower bounds of network lifetime in a WSN using gradient based routing by taking into consideration various factors such as communication interference,sleeping mechanism,etc.Simulation results indicate that our scheme can increase energy eFFIciency and prolong network lifetime.

Evaluation of True Polarization Diversity in Rician-Fading Environments

Multiple-input-multiple-output (MIMO) systems and reverberation chambers (RCs) have joined roads in recent years. This is due to the recently developed ability of RCs to produce a controllable environment that reduces the cost, time, and effort of evaluating the performance of MIMO handset antennas. This letter explores one of these new capabilities to evaluate systems that use true polarization diversity (TPD). Through a novel post-processing hybrid tool for the transformation of a Rayleigh-fading environment into a Rician one, the performance of TPD systems for different Rician fading is shown. Different arrays will be used for the purposes of comparison. This investigation demonstrates that TPD improves traditional orthogonal polarization also for Rician fading.

Effects of Doppler spread on adaptive orthogonal frequency division multiplexing channel capacity employing diversity in multipath environments

ABSTRACTThis paper derives the capacity of a fading channel with orthogonal frequency division multiplexing transmission employing diversity techniques and adaptive policies in Rayleigh fading environments. The effects of Doppler shift fd on channel capacity are analysed. The main contribution of this work is to model intercarrier interference as a function of fd and symbol duration Ts. Two diversity techniques are considered (i) maximal ratio combining (MRC) and (ii) selective combining (SC). Three adaptive policies are combined with MRC and SC to estimate the following channel capacity: (i) optimal rate adaptive; (ii) optimal power and rate adaptive; and (iii) channel inversion with fixed rate adaptive. Closed‐form expressions and bounds on channel capacity employing different diversity techniques are derived. Simulation results are given. Copyright © 2011 John Wiley & Sons, Ltd.

Performance analysis for optimum transmission and comparison with maximal ratio transmission for MIMO systems with cochannel interference

This article presents the performance analysis of multiple-input/multiple-output (MIMO) systems with quadrature amplitude modulation (QAM) transmission in the presence of cochannel interference (CCI) in nonfading and flat Rayleigh fading environments. The use of optimum transmission (OT) and maximum ratio transmission (MRT) is considered and compared. In addition to determining precise results for the performance of QAM in the presence of CCI, it is our another aim in this article to examine the validity of the Gaussian interference model in the MRT-based systems. Nyquist pulse shaping and the effects of cross-channel intersymbol interference produced by CCI due to random symbol of the interfering signals are considered in the precise interference model. The error probability for each fading channel is estimated fast and accurately using Gauss quadrature rules which can approximate the probability density function (pdf) of the output residual interference. The results of this article indicate that Gaussian interference model may overestimate the effects of interference, particularly, for high-order MRT-based MIMO systems over fading channels. In addition, OT cannot always outperform MRT due to the significant noise enhancement when OT intends to cancel CCI, depending on the combination of the antennas at the transmitter and the receiver, number of interference and the statistical characteristics of the channel.

Selection Relaying Schemes for Cooperative Wireless Networks With Adaptive Modulation

Due to the half-duplex transmission nature of cooperative protocols, almost all cooperative diversity systems suffer from low spectral efficiency. In general, adaptive modulation can offer a good tradeoff between spectral efficiency and bit-error-probability (BEP) performance of wireless communication systems. In this paper, we propose two adaptive modulation schemes for the cooperative system with detect-and-forward relaying that simultaneously exploit the cooperative diversity gain and improve the spectral efficiency of the system. In the first scheme, which is similar to conventional selection relaying, the relay decides independently whether to forward the source messages to the destination or not by comparing the instantaneous received signal-to-noise ratio (SNR) with a predetermined fixed threshold, which is independent of the instantaneous modulation scheme. In contrast, in the second scheme, the relay and the destination jointly decide whether the relay will participate in the second phase of the protocol or remain silent. This second scheme can be viewed as a combination of selection and incremental relaying and achieves higher spectral efficiency in comparison with its nonincremental counterparts. We evaluate the performance of the protocols in terms of the end-to-end BEP, the average spectral efficiency, and the outage probability for both identically and nonidentically distributed Rayleigh fading environments. In our analysis, we consider M-ary phase-shift keying ( M-PSK) modulation, M -ary pulse-amplitude modulation (M-PAM), and M-ary quadrature-amplitude modulation ( M-QAM) schemes and examine the impact of error propagation from the relay to the destination on the end-to-end performance of the system in detail. Moreover, we derive a closed-form expression for the optimal relaying threshold that effectively mitigates error propagation and minimizes the end-to-end BEP of the system. The high-SNR analysis demonstrates that both proposed schemes provide full diversity.

적응 공간 다중화 MIMO 시스템을 위한 효율적인 전력 할당 알고리즘

Water-filling 알고리즘은 적응 MIMO 시스템의 ergodic 용량을 최대화하는 효율적인 전력 할당 방식이지만 이산 변조 지쉬discrete modulation index)를 사용하는 실제의 시스템의 경우 과도한 잉여 전력(residual power)으로 인해 스펙트럼 효율이 감소하는 단점이 있다. 본 논문에서는 water-filling 알고리즘의 잉여 전력을 효율적으로 재할당 함으로써 적응 MIMO 시스템의 스펙트럼 효율을 향상시키는 새로운 전력 할당 알고리즘을 제안한다. 알고리즘의 성능을 검증하기 위해 터보 코드가 적용된 적응 MIMO 시스템을 구성하고 다양한 환경에서 시뮬레이션을 수행한다 시뮬레이션 결과, 레일리이 페이딩 환경에서 SNR이 20dB일 때 제안된 알고리즘의 스펙트럼 효율이 기존의 water-filling 알고리즘에 비해 대략 8.9% 향상됨을 알 수 있었다. While the water-filling algorithm is an efficient power allocation method that maximizes the ergodic capacity of adaptive MIMO systems, its excessive residual power causes spectrum loss in real systems employing discrete modulation indices. In this paper we propose new power allocation algorithms that improve the spectral efficiency of MIMO systems by efficiently reallocating the residual power of the water-filling algorithm. We apply the proposed algorithms to the adaptive turbo-coded MIMO system to verify their performance through computer simulation in various environments. Simulation results show that the spectral efficiency of the proposed algorithms is better than that of the water-filling algorithm by about 8.9% at SNR of 20dB in Rayleigh fading environments.

Optimal SNR-based selection relaying scheme with M -ary modulations in cooperative wireless networks

Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, especially when the source-relay channel state information (CSI) is not available at the destination. In this study, the authors investigate the SNR-based selection relaying scheme in a multi-relay cooperative network (with R potential relay nodes) and examine the impact of the error propagation on the end-to-end performance of the system. The authors derive closed-form expressions for the end-to-end symbol error probability (SEP) of the system for both identically distributed and non-identically distributed Rayleigh fading environments. In the analysis, the authors consider M-ary phase shift keying (M-PSK), M-ary pulse amplitude modulation (M-PAM) and M-ary quadrature amplitude modulation (M-QAM) schemes. They also propose a class of geometry-independent thresholds that effectively mitigate the error propagation and provide full diversity of order R+1. Furthermore, for the special case of single-relay network, the authors derive closed-form expressions for the optimal thresholds that minimise the end-to-end SEPs.

Impact of Opportunistic Scheduling on Cooperative Dual-Hop Relay Networks

This letter advocates the performance of a multiuser relay network (MRN) equipped with a single amplify-and-forward (AaF) relay over Rayleigh fading environments. We derive new expressions for the cumulative distribution function (CDF) of the highest instantaneous end-to-end signal-to-noise ratio (SNR) taking into consideration the two cases of fixed gain relays and variable gain relays. Relying on these statistical results, we derive new expressions for the outage probability and symbol error rate (SER), both of which are obtained in exact closed form. Furthermore, we derive simple asymptotic outage probability and SER. Our asymptotic results confirm that opportunistic scheduling has no impact on the diversity order. We further prove that the array gain is what determines the SNR advantage of opportunistic scheduling over the single user scenario.

Outage Analysis of a Cooperative Multi-hop Wireless Network for Rayleigh Fading Environment

This paper presents an information theoretic outage analysis for physical layer of a cooperative multihop wireless network. Our analysis shows that cooperation by selecting a proper relay at each hop increases the coverage or data rate of the network. In our analysis we consider both symmetric and asymmetric network model. We also investigate the availability of cooperative relay at each hop and show that end-to-end performance of the network depends on the relay selection procedure at each hop. We also verify our analytical results with simulations.

Performance Evaluation of Two-Hop Wireless Link under Rayleigh and Nakagami-m Fading Channel for 8-PSK and 16-QAM

One of the major challenges in wireless communications, especially in urban area, is to detect the digital data under different fading environment and additive white Gaussian noise (AWGN). In a two-hop wireless links, each link is affected by fading and noise which degrades the overall performance of the communication system. In this paper performance of two-hop link is analyzed under Rayleigh and Nakagami-m fading environments separately for 8-PSK and 16-QAM modulation schemes. The objective of the paper is to observe the relative impact of two fading environments on the two above mentioned modulation schemes if no combining scheme or error correction measure is taken on the repeater station.

Generalised selection combining diversity performance of multi-element antenna systems via a stochastic electromagnetic-circuit methodology

A stochastic electromagnetic-circuit methodology for evaluating the generalised selection combining (GSC) diversity performance of coupled and arbitrarily terminated multi-element antenna (MEA) systems when operating in Rayleigh fading environments is proposed. The methodology is based on the effective length matrix, which connects the incident electric fields to the received voltage and current vectors, and on the newly introduced stochastic generation of realistic propagation environments by means of the angular power density functions and the cross polarisation power ratio of the incoming plane waves. The generated statistical ensemble of voltage and current vectors is then used to determine the receive GSC diversity performance metrics, that is mean effective gain (MEG), envelope correlation coefficient (ρe) and effective diversity gain (EDG). Two compact MEA configurations comprising two and four printed inverted F antennas (IFA) operating in a uniform propagation scenario at the 5.2 GHz band are investigated under various GSC schemes, which include the selection (SC) and the maximal ratio (MRC) as special cases. The simulated values of MEG, ρe and EDG under the MRC scheme are in excellent agreement to those obtained from well-established closed-form methodologies.

Signal detection performance in Rayleigh fading environments with a moving antenna

The performances of a single-antenna handheld receiver in detecting a narrowband signal in a Rayleigh fading environment that is temporally static but decorrelates spatially are analysed. Of interest is comparing the detection performance of a static antenna with that of a moving antenna subject to constant processing time. It is shown that the net processing gain resulting from randomly moving the antenna relative to keeping it static can be large, namely over 11 dB in some cases, which is significant for numerous indoor applications. It is further demonstrated that, for a given utilisation scenario, there is an optimum number of spatial samples that maximise the processing gain advantage of the moving antenna. Generally, if the spatial trajectory of the antenna becomes too large, then the loss associated with the signal decorrelation dominates and undermines the gains achieved by the increased spatial diversity. Practical implementation issues including the sensitivity of the proposed method to trajectory estimation are investigated. An extensive set of measurements based on CDMA 2000 signals propagated from outdoor terrestrial base stations and captured in indoor multipath environments using static and moving antennas are utilised to experimentally substantiate these theoretical findings.

BER of OFDM with diversity and pulse shaping in Rayleigh fading environments

This paper derives the bit error rate (BER) of Orthogonal Frequency Division Multiplexing (OFDM) systems with pulse shaping for ICI reduction employing L th-order maximal ratio combining (MRC) diversity in Rayleigh fading environments. The probability density function of the signal-to-interference ratio per bit γ in the presence of the total average inter-carrier interference (ICI) power P ICI is also derived. Simulation results are given and discussed.

Analytical matched filter bound for M-QAM hierarchical constellations with diversity reception in multipath rayleigh fading channels

In this paper, we derive matched filter bound (MFB) expressions for the performance of hierarchical quadrature amplitude modulations (M-HQAM) over time-discrete multipath Rayleigh fading environments with diversity. The expressions are valid for multipath environments where different paths and antennas can be correlated. Since hierarchical constellations are usually employed to achieve unequal bit error protection, the MFB expressions are given in terms of the individual bit error rate (BER) for the different bit streams. Although typically the MFB is obtained assuming slow time varying channels, fast varying channels are also considered in this paper.

Effects of asynchronous MAI on average SEP performance of OFDMA uplink systems over frequency-selective Rayleigh fading channels

This paper investigates the effects of asynchronous multiple access interference (MAI) on the performance of orthogonal frequency-division multiple access (OFDMA) uplink systems in frequency-selective Rayleigh fading environments. We first analyze the MAI and its statistical characteristics using the Gaussian approximation. Then the analytical expression for the uncoded average symbol error probability (SEP) is obtained with various modulation schemes. Comparison with simulation results shows a tight agreement of the proposed analysis over a wide range of asynchronous timing errors and for various numbers of asynchronous users. Numerical examples show that when asynchronous timing errors reside within the guard interval, a performance of uncoded SEP- 10-3 can be feasible even in high dispersive environments. Furthermore, the effect of the Gaussian approximation is examined, and the performance comparison between interleaved- and block-type subcarrier allocation schemes is provided.

A Novel Cooperative-Aided Transmission in Multi-Hop Wireless Networks

Cooperative transmission protocols attract a great deal of attention in recent years as an efficient way to increase the capacity of multi-hop wireless networks in fading environments. In this paper, we propose and analyze a cooperative transmission method, called Cooperative-Aided Skipping multi-Hop protocol (CASH), for multi-hop wireless networks with Rayleigh fading environments. For performance evaluation, we compare and verify the results of the theoretical analysis with the results of simulations.

A Compact Reverberation Chamber for Hyper-Rayleigh Channel Emulation

Recent propagation measurements conducted for emerging applications such as vehicle-to-vehicle communications and wireless sensor systems have illustrated that present worst-case channel models are not sufficient to characterize the small-scale propagation effects seen. New theoretical models have thus been proposed but existing emulation environments do not create sufficiently severe channel conditions. In this work we present the design of a compact, reconfigurable channel emulator (CRCE) specifically designed to create Ricean, Rayleigh and hyper-Rayleigh fading environments in a repeatable manner. The bench-top sized chamber leverages concepts seen in reverberation chambers but in addition to a mechanical stirrer varies the multipath environment through the use of multiple antennas. Emulated channels illustrating space-, time- and frequency-selective behaviors are presented.

A Scheduling Algorithm for Minimizing the Packet Error Probability in Clusterized TDMA Networks

We consider clustered wireless networks, where transceivers in a cluster use a time-slotted mechanism (TDMA) to access a wireless channel that is shared among several clusters. An approximate expression for the packet-loss probability is derived for networks with one or more mutually interfering clusters in Rayleigh fading environments, and the approximation is shown to be good for relevant scenarios. We then present a scheduling algorithm, based on Lagrangian duality, that exploits the derived packet-loss model in an attempt to minimize the average packet-loss probability in the network. Computer simulations of the proposed scheduling algorithm show that a significant increase in network throughput can be achieved compared to uncoordinated scheduling. Empirical trials also indicate that the proposed optimization algorithm almost always converges to an optimal schedule with a reasonable number of iterations. Thus, the proposed algorithm can also be used for bench-marking suboptimal scheduling algorithms.

On the statistics of cognitive radio capacity in shadowing and fast fading environments

In this paper we consider the capacity of the cognitive radio (CR) channel in different fading environments under a "low interference regime". First we derive the probability that the "low interference regime" holds under shadow fading as well as Rayleigh and Rician fast fading conditions. We demonstrate that this is the dominant case, especially in certain practical CR deployment scenarios. The capacity of the CR channel depends critically on a power loss parameter, ¿, which governs how much transmit power the CR dedicates to relaying the primary message. We derive a simple, accurate approximation to ¿ in Rayleigh and Rician fading environments which gives considerable insight into system capacity. We also investigate the effects of system parameters and propagation environment on ¿ and the CR capacity. In all cases, the use of the approximation is shown to be extremely accurate.

Performance of Gaussian and hyperbolic scattering channels in mobile OFDM systems

This paper estimates the inter-carrier-interference power P ICI of Gaussian and hyperbolic scattering channels in a mobile orthogonal frequency division multiplexing (OFDM) system by using their angle-of-arrival (AoA) probability density functions (pdf). The P ICI difference of the two channels is estimated and plotted as functions of ( τ , ζ ) , ( τ , ϵ ) and ( τ , f d T s ) , where τ is the ratio of the coverage distance D and effective radius R eff , ζ frequency tracking, f d maximum Doppler spread, T s symbol duration and ϵ travelling direction of a user equipment. Experimental P ICI difference for ϵ = 0 , ζ = 0 and f d T s = 0.05 is obtained and plotted with the simulated results for comparison purposes. The ICI power is also plotted against ( f d T s , ϵ ) , ( f d T s , ζ ) , and ( ζ , ϵ ) for specific values of τ . Detailed analyses on the performance of the hyperbolic and Gaussian AoA pdfs are given. Relative merits of each pdf are discussed. Closed-form bit error rate (BER) expressions of OFDM communication systems in an added white Gaussian noise (AWGN) channel and Rayleigh fading environment using bipolar phase shift keying (BPSK), OFDM-BPSK, are derived as functions of P ICI and phase noise to validate the effectiveness of the approximate Gaussian and hyperbolic AoA pdfs. Future work is also outlined.