Spectrum Efficiency of Weibull Fading Channels for Various Adaptation Policies with and Without Diversity Combining

In this paper, closed-form expressions for the capacities per unit bandwidth (spectrum efficiency) of Weibull fading channels are derived and plotted for (a) Switch and Stay Combining diversity case and (b) no diversity case for adaptation policies like: (i) Optimal Power and Rate Adaptation policy, (ii) Optimal Rate Adaptation with constant transmit power policy, (iii) Channel Inversion with Fixed Rate policy, and (iv) Truncated Channel Inversion policy. In addition, spectrum efficiency expressions for asymptotic approximations, upper bounds, approximations for low and high SNR cases are derived for the cases with and without diversity. The probability density function of capacity, and the complementary cumulative distribution function of capacity are derived and plotted from the moment generating function for the cases with and without diversity. Optimal power and rate adaptation policy provides the highest capacity and optimal rate adaptation with constant transmit power policy provides the highest capacity penalty over other policies for the no diversity and SSC diversity cases. Numerical results for spectrum efficiency are plotted for all adaptation policies with and without diversity.     

Spectrum Efficiency Evaluation for MRC Diversity Schemes Under Different Adaptation Policies Over Generalized Rayleigh Fading Channels

In this paper, closed-form expressions for the capacities per unit bandwidth for Generalized Rayleigh fading channels are derived for optimal power adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. The closed-form solutions are derived for the single antenna reception (without diversity combining) and MRC diversity reception cases. Optimal power adaptation policy provides the highest capacity over the other adaptation policies both with and without diversity combining. Truncated channel inversion policy suffers a large capacity penalty relative to the optimal power adaptation policy as the number of degrees of freedom is increased. However, with increase in diversity, the capacity penalty for the truncated channel inversion policy decreases. Capacity gains are more prominent for channel inversion with fixed rate policy as compared to the other adaptation policies.

Combining Pilot-Symbol-Aided Techniques for Fading Estimation and Diversity Reception in Multipath Fading Channels

A novel pilot-symbol-aided (PSA) fading estimation technique that combines the estimates from a conventional PSA technique and a bandwidth-efficient PSA technique to achieve better performances is proposed for digital signals in multipath fading channels. The conventional technique has better performances at low signal-to-noise ratios (SNRs), while the bandwidth-efficient technique is superior at high SNRs. Monte Carlo computer simulation has been used to assess the effects of the proposed combining technique on the bit-error-rate (BER) performances of 16-ary quadrature-amplitude-modulation (16QAM), with and without two-branch diversity reception, in a flat Rayleigh fading channel. Results have shown that the combining technique has the advantages of both of the conventional technique and the bandwidth-efficient technique and is more preferred for use with diversity reception. Man-Hung Ng received a BSc degree in Computer Studies from City University of Hong Kong in 1991. He worked as a computer programmer in Hong Kong from 1991 to 1995. In 1996, he obtained a MSc degree in Communication and Radio Engineering from King's College London. He joined the University of Hong Kong as a research assistant in 1997, and completed a PhD degree in mobile communications in 2001. He joined Lucent Technologies N.S. UK in 2001 and is now a principal standards engineer. Sing-Wai Cheung received the BSc degree in Electrical and Electronic Engineering from Middlesex University, U.K. in 1982 and the PhD degree from Loughborough University of Technology, U.K. in 1986. From 1986–1988, he was a post-doctorate research assistant in the Communications Research Group of King's College, London University. During 1988–1990, he was with the Radio and Satellite Communications Division in British Telecom Research Laboratories (now British Telecom Laboratories). He joined the Department of Electrical and Electronic Engineering at the University of Hong Kong in 1990 and is now an Associate Professor. He contributes regularly courses on mobile and satellite communications systems. His current research interests include modulation, coding, fading compensation and diversity and MIMO for mobile and satellite communications systems.     

Spectral Efficiency Evaluation for MRC Diversity Schemes Over Generalized Rician Fading Channels

In this paper, closed-form expressions for the capacities per unit bandwidth for generalized Rician fading channels are derived for power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. The closed-form solutions are derived for the single antenna reception (without diversity combining) and maximal-ratio combining (MRC) diversity cases. Truncated channel inversion adaptation policy is the best policy for the single antenna reception case, while the channel inversion with fixed rate policy is the best policy for the MRC diversity case. Constant transmit power policy provides the lowest spectral efficiency as compared to the other policies with and without diversity.     

Diversity Combining Options and Low-Complexity MMSE Equalization for Spread Spectrum OFDM Systems in Frequency Selective Fading Channels

This paper compares diversity combining schemes for the downlink of spread spectrum orthogonal frequency division multiplexing (SS-OFDM) systems in frequency selective fading channels. In particular, symbol-level combining after despreading is compared to chip-level combining under maximal ratio combining (MRC) of signals from different diversity branches and minimum mean-square error (MMSE) equalization of spreading sequences. Symbol-level combining takes place after the operations of MMSE equalization and despreading, whereas the operations of equalization and despreading occur after MRC if chip-level combining is used. Chip-level combining combines diversity samples in an efficient manner while reducing inter-code interference (self-interference) that results from the loss of orthogonality of spreading sequences due to a frequency selective channel. This method is shown to be superior to symbol-level combining when the diversity branches are uncorrelated, and when the branches differ only due to subcarrier interleaving. An MMSE equalization method with significantly reduced complexity for partially loaded systems is also presented, based on the premise of chip-level combining. Novel expressions for the bit error rate (BER) of the two methods, as well as the extension of the analysis to partially loaded systems are given. The extensions of chip-level combining and low-complexity equalization of a partially loaded system to an OFDM system with 2-dimensional spreading are also presented. The results are relevant to antenna diversity as well as temporal diversity achieved though re-transmission within an ARQ scheme. This paper was presented in part at WCNC 2005, New Orleans, LA, USA, March 13–17, 2005. Robert Novak was born in Edmonton, Canada in 1974. He received the B.Sc. degree in Engineering Physics with Distinction at the University of Alberta, Canada in 1997. He receieved the Ph.D. degree in Electrical Engineering from the University of Alberta in 2006. He was with Telecommunications Research Laboratories (TRLabs) from 1997 to 2006. He is currently with the Wireless Technology Lab of Nortel Networks, in Ottawa, Canada. His main research interests include adaptive techniques for orthogonal frequency division multiplexing (OFDM) systems, spread spectrum techniques, multi-user communications, diversity combining, and high speed packet data systems for mobile radio applications. Witold A. Krzymień received his M.Sc. (Eng.) and Ph.D. degrees (both in Electrical Engineering) in 1970 and 1978, respectively, from the Poznań University of Technology in Poznań, Poland. He received a Polish national award of excellence for his PhD thesis. Since April 1986 he has been with the Department of Electrical & Computer Engineering at the University of Alberta, Edmonton, Alberta, Canada, where he currently holds the endowed Rohit Sharma Professorship in Communications & Signal Processing. In 1986, he was one of the key research program architects of the newly launched TRLabs, Canada's largest industry-university-government pre-competitive research consortium in the Information & Communication Technology area, headquartered in Edmonton. His research activity has been closely tied to the consortium ever since. Over the years Dr. Krzymień has also done collaborative research work with Nortel Networks, Ericsson Wireless Communications, German Aerospace Centre (DLR – Oberpfaffenhofen), Telus Mobility and the University of Padova (Italy). He held visiting research appointments at Twente University of Technology (Enschede, The Netherlands; 1980–1982), Bell-Northern Research (Montréal, Canada; 1993–1994), Ericsson Wireless Communications (San Diego, USA; 2000), Nortel Networks Harlow Laboratories (Harlow, UK; 2001), and the Department of Information Engineering at the University of Padova (2005). His research is currently focused on broadband high throughput packet data access for mobile and nomadic users, employing multi-carrier signalling, multiple antenna techniques and link adaptation, as well as on the related MAC and network layer issues of hybrid ARQ, packet scheduling and relaying. Dr. Krzymień is a Fellow of the Engineering Institute of Canada, and a licensed Professional Engineer in the Provinces of Alberta and Ontario, Canada. From 1999 to 2005 he was the Chairman of Commission C (Radio Communication Systems and Signal Processing) of the Canadian National Committee of URSI (Union Radio Scientifique Internationale). He received the 1991/1992 A.H. Reeves Premium Award from the Institution of Electrical Engineers (U.K.) for a paper published in the IEE Proceedings, Part I.     

分集合并及Rake接收抗多径衰落技术

该文主要针对无线通信系统信号传播特点,首先分析了影响无线通信系统性能的多径衰落形成的原因,介绍了几种常见的抗多径衰落技术;接下来从技术原理、实现方式、应用效率等方面对分集合并与Rake接收技术在抗多径衰落效应上的表现进行分析比较;随后结合两种技术的发展现状,总结出多维分集与广义混合合并两个主要研究方向;最后对分集合并及Rake接收技术跟均衡与信道编码相结合的发展前景进行展望。     

Frequency-Selective Fading Effects in Digital Mobile Radio with Diversity Combining

we analyze the effects of frequency-selective fading in a cellular mobile radio system that uses 1) phase-shift keying (PSK) with cosine rolloff pulses, and 2) space diversity with maximal-radio combining. The distorting phenomena with which we deal are multipath fading (which produces the frequency selectivity), shadow fading, and cochannel interference. The relevant quality measure is defined to be the bit error rate averaged over the multipath fading, denoted by (BER). The relevant system performance characteristic is defined to be the probability distribution for (BER), taken over the ensemble of shadow fadings and locations of the desired and interfering mobiles. To obtain numerical results, we use a combination of analysis and Monte Carlo simulation, invoke widely accepted models for the multipath and shadow fadings, and assume a cellular system with seven channel sets and centrally located base stations. The outcome is a set of performance curves that reveal the influences of various system and channel parameters. These include: the number of modulation levels (two or four), the diversity order, the shape of the multipath delay spectrum, and the standard deviation (or delay spread, τ0) of the multipath delay spectrum. Practical factors accounted for in these assessments include fading- and interference-related timing recovery errors and combiner imperfections. Our results highlight the importance of the ratiotau_{0}/T, whereTis the digital symbol period. They show that the delay spectrum shape is of no importance fortau_{0}/T leq 0.2, but can have a profound influence fortau_{0}/T geq 0.3. We also find that using 4-PSK leads to better detection performance, in certain cases, than using 2-PSK.     

Performance Analysis of Switch and Stay Combining Diversity for Beaulieu-Xie Fading Model

Wireless Personal Communications - Beaulieu-Xie (BX) fading model is adequate for Femtocell and high-speed railway applications. In this paper, the performance evaluation of dual branch switch and...     

Ordered Statistic Analysis for Diversity Combining Schemes over Nakagami-m Fading Channel

Order diversity combining technique is one of efficient methods to lower the complexity but not to significantly degrade performance. Recently, Eng and Milstein [1] proposed a novel order-combining technique, called the second order diversity combining (SC2) and third order diversity combining (SC3) and applied to Rayleigh fading channel. SC2 and SC3 schemes mean that the two (three) signals with the first two (three) largest amplitudes among the branches are chosen and coherently combined. However, when compared to Rayleigh distribution, the Nakagami-m distribution [10] provides a more general and versatile way to model wireless channel. For the reason, the bit error rate (BER) performance of proposed schemes were then analyzed with order statistic method and compared to the traditional diversity technique over Nakagami fading environment in this paper. The results are compared to maximal ratio combining (MRC), and conventional selection combining (SC) in coherent reception and to equal gain combining (EGC) in noncoherent reception. The results show that SC is in performance the worst for either in coherent or in noncoherent schemes, as expected. The performance differences between SC2 (SC3) and MRC (EGC) are not significant when the diversity order L 3, but the difference will increase when L 5. It is worth noting that the result of [1] is a special case with fading figure, m = 1. It is also observed the performance is much affected by the number of diversity branches L, the fading figure m, and the signal-to-noise ratio (SNR).     

Performance Analysis of Diversity Combining Algorithms in Shadowed Fading Channels

A compound fading model incorporating short term fading and shadowing proposed recently is used to analyze the performance of wireless systems employing microscopic diversity to mitigate the effects of flat fading. This model can account for the presence of different levels of fading and shadowing and provide an analytical solution for the probability density function of the signal-to-noise ratio. Using that model, the performances of MRC and SC diversity combining algorithms were studied. The amount fading (AF) following diversity implementation was calculated and it is seen that the decline in the amount of fading is bound by the level of shadowing present, with the MRC providing a larger decrease in the amount of fading than the SC algorithm. The effect on the error rates was studied using the example of the coherent BPSK modem. Results show that the performances of wireless systems can be analyzed using the compound model for the shadowed fading channels. P.M. Shankar received his M. Sc (1972) in Physics from Kerala University, India, M. Tech (1975) in Applied Optics and Ph. D. in Electrical Engineering (1980) from Indian Institute of Technology, Delhi, India. He was a visiting scholar at the School of Electrical Engineering, University of Sydney, Australia, from 1981 to 1982. He joined Drexel University in 1982 and is currently the Allen Rothwarf Professor of Electrical and Computer Engineering. He is the author of the textbook ‘Introduction to Wireless Systems’, published by John Wiley & Sons, 2002. His research interests are in Fading Channels, Wireless communications, and Statistical signal processing for medical applications.     

Performance Analysis of Joint Adaptive Modulation and Diversity Combining Over Fading Channels

Both adaptive modulation and diversity combining represent important enabling techniques for future generations of wireless communication systems. In this paper, capitalizing on recent developments in adaptive combining, we propose three joint adaptive modulation and diversity combining (AMDC) schemes. With these schemes, the modulation mode and diversity combiner structure are adaptively determined based on the fading channel condition and error-rate requirement. We accurately analyze these three AMDC schemes in terms of processing power consumption, spectral efficiency, and error-rate performance. Selected numerical examples show that the proposed AMDC systems meet the target error-rate requirement while achieving high spectral efficiency with low processing power consumption     

Simple Average BER Formulas for M-ary Orthogonal Signals with Noncoherent Diversity Combining in Nakagami-m Fading Channels

This paper presents simple and exact expressions for the average bit error rate (BER) of M-ary orthogonal signals with noncoherent diversity combining in independent as well as arbitrarily correlated nonidentically distributed Nakagami-m fading channels. The expressions are given in terms of elementary functions, and they do not involve numerical integrals or complicated functional operations. In addition, they are valid for the generalized case when the channels have arbitrary average signal- to-noise ratios (SNRs) as well as nonidentical fading parameters. Simulation results are provided to validate the analytical results.     

Error Probability Distribution and Density Functions for Weibull Fading Channels With and Without Diversity Combining

In this letter, a detailed theoretical analysis of probability distribution and density functions of probability of error in a wireless system is considered. Closed form expressions for distribution and density functions of the probability of error are derived for Weibull fading channels for the cases of (i) No Diversity (ND), (ii) Selection Combining (SC) diversity, and (iii) Switch and Stay Combining (SSC) diversity. Numerical results are plotted and discussed in detail for the various cases.     

Diversity Combining and SNR Estimation for Turbo-Coded Frequency-Hopped Spread-Spectrum in Partial-Band Interference and Fading Channels

We compare different combinations of the repetition diversity order L and code rate R for turbo-coded Frequency-Hopped Spread-Spectrum (FH/SS) communication systems in the presence of fading and partial-band Gaussian interference. For a fixed overall channel code rate R/L we show that using the lowest code rate and no repetition diversity always performs better than using a higher code rate and some repetition for both coherent and non-coherent schemes. We then propose a simple maximum-likelihood-based method for signal-to-noise-ratio (SNR) estimation in Non-Coherent Binary Frequency Shift Keying (NCBFSK) without training symbols. Except for impractically small hop sizes of 8 bits or less we obtain performance virtually equal to that of perfect SNR knowledge but with much less complexity than iterative schemes previously proposed. For the case of Coherent Binary Phase Shift Keying (CBPSK) we derive the Expectation Maximization (EM) estimate of the SNR without training symbols and iteratively feed the estimator with the extrinsic information from the turbo decoder. The performance for CBPSK is near that of perfect SNR knowledge for hop sizes of 64 bits or more. Unlike previously proposed methods for CBPSK the EM estimate of SNR does not require knowledge of the noise and interference variance, received bit energy, or the fading channel model.

A Quantitative Analysis of Spectrum Efficiency of Various Diversity Combining Schemes in the Presence of Co-channel Interference

Wireless Personal Communications - Content Addressable Memory (CAM) is used in high speed searching applications and also in data compression. Recently in the network computing era, fast lookup...     

Multi-user Opportunistic Spectrum Access with Channel Impairments

In this paper, we study the impact of sensing error and channel fading on the decision process of a multiple secondary user network in a primary network whose channel occupancy states are modelled as a Bernoulli process. We present a randomized access strategy to maximize total secondary network throughput. The proposed method guarantees that the probability of collision between primary and secondary users in each channel is less than the predefined value of P_c = ξ. To find the optimal access strategy, we formulate secondary network throughput as an optimization problem. Then, using the KKT method to find the solution, we break the original problem into multiple sub-problems. Then, we employ an iterative algorithm and a sifting technique to reduce the number of sub-problems and find the final solution. The solution contains both the SUs access strategies and their detector operating points. In other words, we present a solution for the cross layer design in cognitive radio networks. At the end, we compare our results with two other heuristic strategies (1) equi-probable strategy and (2) weighted strategy and show that the proposed method outperforms them in terms of total throughput.     

On Optimal Power Allocation over Time-Varying Rayleigh Fading Channels for Maximum-Ratio Combining in Diversity Systems with Partial CSI

Wireless Personal Communications - This paper studies the problem of optimal power allocation (OPA) over independent but not necessarily identically distributed time-varying Rayleigh fading...     

Diversity Cutoff Rate Evaluation of the Rayleigh and Rician Fading Channels

This paper presents expressions for the cutoff rate R0diversity transmission over the Rayleigh and Rician fading channels withM-ary orthogonal signaling. These expressions include the unquantized R0forD-fold diversity, which upper bounds the channel performance, and hard decision and four- and eight-level soft decision quantized R0expressions. Tradeoffs betweenDand the number of quantization levels for equivalent performance are presented for the unquantized and quantized channels. These tradeoffs illustrate the reduction in signal energy, system bandwidth, and system complexity by increasing the number of quantization levels, thereby allowing a reduction inD.     

Performance Analysis of Multiband Complex Wavelet Based MC-CDMA System with Space Diversity Combining in Rayleigh Fading Channel

In this paper, the multiband complex wavelet used as multi-carrier basis function is optimized. On the basis of analyzing the principle of multi-carrier code division multiple access (MC-CDMA), a new multiband complex wavelet based MC-CDMA (MBCW-MC-CDMA) system model is proposed, and space diversity combining (SDC) technique is employed to improve the system performance further. The uplink performance of proposed MBCW-MC-CDMA system with SDC technique is investigated in Rayleigh fading channel, and corresponding bit error rate (BER) analysis is given in detail. Without any cyclic prefix (CP), the system can avoid the decrease of spectrum efficiency and data rate of conventional MC-CDMA with CP. By comparison, our scheme outperforms real wavelet packet based MC-CDMA and slightly outperforms conventional MC-CDMA with CP via utilizing superior properties of the optimized multiband complex wavelet. Theoretical analysis and simulation result show that the application of SDC technique can improve the proposed system ability to combat spatial fading and various interferences effectively. Moreover, the proposed system based on SDC technique has superior BER performance over conventional DFT and SDC based MC-CDMA system and real wavelet packet and SDC based MC-CDMA system. Xiangbin Yu received the M.S degrees in Communication and Information Systems from Hohai University, Nanjing, China, in 2001; and his Ph.D. in Communication and Information Systems in 2004 from National Mobile Communications Research Laboratory at Southeast University, China. Now he is working as a Postdoctoral Researcher in Information and Communication Engineering Postdoctoral Research Station at Nanjing University of Aeronautics and Astronautics, Nanjing, China. His research interests include multi-carrier digital communication, space-time coding and digital signal processing in modern communications. Xiaodong Zhang received the M.S degrees from Nanjing University of Posts and Telecommunications, Nanjing, China, in 1998. In 2002, he received the Ph.D. degree from Southeast University, Nanjing, China. His research interests include contemporary signal processing and digital communications. DaZhuan Xu received the M.S degrees and Ph.D. in Communication and Information Systems from Nanjing University of Aeronautics and Astronautics in 1986 and 2001, respectively. He is now a full professor in Nanjing University of Aeronautics and Astronautics, Nanjing, China. Prof.Xu is a Senior Member of China Institute of Electronics (CIE). His research interests include digital communications, soft radio, coding theory, medical signal processing. Guangguo BI was graduated from Nanjing Institute of Technology, Nanjing, China, in 1960. He is now a professor in the Department of Radio Engineering of Southeast University, Nanjing, China. Prof.Bi is a fellow and a member of the board of Director of the China Institute of Communications, and a senior member of IEEE. His research interests include digital communications, personal communications network, spread spectrum communications, and intelligent information processing. He has published more than 200 papers in above areas.     

Diversity and Coding for FH/MFSK Systems with Fading and Jamming--Part I: Multichannel Diversity

The performance of diversity and/or coding is evaluated for FH/MFSK signaling over Rayleigh fading channels in the presence of jamming. The effects of partial-band tone and partial-band noise jamming on uncoded and coded systems are considered. The results indicate that FH/MFSK signaling with diversity provides satisfactory performance for jammed fading channels. For coded FH/MFSK signaling over fading channels, noise jamming may be more effective than tone jamming. The amount of improvement resulting from the use of diversity in conjunction with coding depends upon many factors, including the nature of the channel, the degree of channel state information available at the decoder, the type of decoding, and the modulation alphabet size.