Performance analysis of adaptive loading OFDM under Rayleigh fading

In this paper, we investigate the performance of adaptive loading orthogonal frequency-division multiplexing (OFDM) under Rayleigh fading with maximal ratio-combining (MRC) diversity at the receiver. We assume that channel-state information is available at both the transmitter and the receiver. Closed-form expressions for the lower bound on the average capacity of OFDM transmission under Rayleigh fading are provided for ideal MRC diversity. Simple approximate expressions for the average capacity of the Rayleigh-fading channel are also provided for the high signal-to-noise ratio (SNR) case. In the second part of this paper, a maximum-rate adaptive-loading strategy is derived for uncoded quadrature-amplitude-modulation modulated OFDM. Simple lower bound expressions and high-SNR approximations are provided for the average spectral efficiency of the maximum-rate adaptive-loaded uncoded OFDM under Rayleigh-fading channel conditions. According to the results, the performance of the uncoded adaptive-loading OFDM is about 8.5 dB inferior to the capacity bound at 10/sup -5/ symbol error probability under frequency-selective Rayleigh fading.     

Rayleigh衰落信道下多载波DS-CDMA系统性能分析

本文基于多载波传输技术，提出了一种多载波码分多址模型。并在Rayleigh衰落信道下对其误码性能进行了分析。分析及仿真结果表明，系统具有降低多址干扰的能力，同传统的单载波直接序列码分多址系统相比，能支持更大的用户容量。本系统能满足第三代移动通信系统对高速数据传输的要求。     

Performance analysis of coherent TCM systems with diversityreception in slow Rayleigh fading

Coherent trellis-coded modulation (TCM) systems employing diversity combining are analyzed. Three different kinds of combining are considered: maximal ratio, equal gain, and selection combining (SC). First, the cutoff rate parameter is derived for equal gain combining (EGG) and SC assuming transmission over a fully interleaved channel with flat slow Rayleigh fading, which permits comparison with previously derived results for maximal ratio combining (MRC). Then, tight upper bounds on the pairwise error probabilities are derived for all three combining techniques. These upper bounds are expressed in product form to permit bounding of the bit error rate (BER) via the transfer function approach. In each case, it is assumed that the diversity branches are independent and that the channel state information (CSI) can be recovered perfectly. Also included is an analysis of MRC when the diversity branches are correlated-the cutoff rate and a tight upper bound on the pairwise error probability are derived. It is shown that with double diversity a branch correlation coefficient as high as 0.5 results in only slight performance degradation     

Optimization of an OFDM Rayleigh fading system

An OFDM cellular system operating in a Rayleigh fading environment is described and its spectral efficiency is estimated in terms of the theoretically achievable average channel capacity (in the Shannon sense) per user. The analysis covers the operation over a downlink cellular time‐varying link and leads to a simple novel closed‐form expression for the optimal number of individual OFDM subcarriers, based on the maximization of the achieved spectral efficiency. Copyright © 2006 John Wiley & Sons, Ltd.     

SINR analysis of FFH/OFDM over frequency selective Rayleigh fading channel

Fast frequency hopping/orthogonal frequency division multiplexing (FFH/OFDM) has been previously proposed to achieve frequency diversity over frequency selective channels. However, the performances of the FFH/OFDM scheme have been usually calculated using simulations over empirical channel models in earlier works. The main aim of this paper is to theoretically expose the diversity of the FFH/OFDM signal over statistical models, specifically Rayleigh distributed, for frequency selective fading channels. In order to achieve this aim, we first derive the decision variables and the signal‐to‐interference noise ratios of the FFH/OFDM signal at the output of minimum mean square error and zero forcing receivers. For various levels of quadrature amplitude modulation used in FFH/OFDM, the performances are calculated and validated via simulations. The results show that FFH/OFDM in case of zero forcing equalization does not provide any diversity gain even over a frequency selective channel. However, in case of minimum mean square error equalization, it brings significant diversity gain at high signal‐to‐noise ratio (SNR) values with the rise of number of sub‐carriers. Moreover, the FFH/OFDM with four quadrature amplitude modulation scheme provides better performance than that of the conventional OFDM even at low SNR values, as well as a significant diversity gain at high SNR values. Copyright © 2016 John Wiley & Sons, Ltd.     

Model-based channel estimation for OFDM signals in Rayleigh fading

This paper proposes a robust pilot-assisted channel estimation method for orthogonal frequency division multiplexing (OFDM) signals in Rayleigh fading. Our estimation method is based on nonlinear regression channel models. Unlike the linear minimum mean-squared error (LMMSE) channel estimate, the method proposed does not have to know or estimate channel statistics like the channel correlation matrix and the average signal-to-noise ratio (SNR) per bit. Numerical results indicate that the performance of the proposed channel estimator is very close to the theoretical bit error propagation lower bound that is obtained by a receiver with perfect channel response information     

Performance analysis of optimum combining in antenna array systems with multiple interferers in flat Rayleigh fading

In this letter, we examine the statistical distribution of the signal-to-interference-plus-noise ratio (SINR) of the optimum combining (OC) technique in receive-antenna diversity systems. We decompose the SINR into two components by projection onto the interference subspace for systems with more antennas than interferers. For the case when the number of interferers is larger than the number of antennas, upper and lower bounds on performance are provided.     

BER of OFDM in Rayleigh fading environments with selective diversity

This paper derives the analytical bit error rate (BER) of orthogonal frequency division multiplexing (OFDM) systems employing selective diversity in Rayleigh fading environments. First, the probability density function (pdf) of inter‐carrier interference (ICI) power in Rayleigh fading environments is derived. Second, the pdf of the signal‐to‐interference ratio (SIR) is then derived. The cumulative distribution function (cdf) and hence pdf of the SIR with selective diversity are then given in the third and fourth steps. Using the BER expressions of binary phase shift keying (BPSK) and differential BPSK (DBPSK) modulation in an added white Gaussian noise (AWGN), the corresponding BER expressions of OFDM systems can then be derived. Detailed discussions are given. Possible future work is also outlined. Copyright © 2009 John Wiley & Sons, Ltd.     

Matched filter bound for OFDM on Rayleigh fading channels

A matched filter bound (MFB) analysis is presented, in which the normalised Doppler rate is unrestricted, and thus applicable to OFDM signalling. In contrast to the static channel case, the optimal matched filter receiver is shown to be time varying and the probability of error is shown to depend on the transmitted pulse shape     

Performance analysis of amplify-and-forward relaying with hybrid-ARQ in Rayleigh fading channels

Hybrid automatic repeat request (HARQ) is a well-known technique for improving system throughput and link performance of wireless communication systems, including cooperative communication systems. The amplify-and-forward (AF) relaying method is one of the most attractive cooperative diversity schemes because of its low complexity. In this article, the end-to-end performance in terms of block error rate (BLER) and normalized throughput of AF relaying with HARQ transmission under the Rayleigh fading channel is analyzed. Numerical results validate the proposed analysis and demonstrate the gain of HARQ schemes in AF relaying systems. This analytical method can be extended to the systems with other HARQ protocols and other cooperative relaying schemes.     

GF(2p)LDPC编码的相位调制OFDM系统在瑞利衰落信道的性能

OFDM是一项能有效对抗高速无线通信中多径衰落的关键技术，为了进一步提高OFDM系统的误码性能，许多信道编码技术已被应用于OFDM系统中，二元域LDPC码以其近香农限的误码性能和较低的译码复杂度成为研究的热点。在AWGN信道下，多元域LDPC码比等效码长的二元域LDPC码有更好的纠错性能。本文提出了一种将多元域LDPC码经过MPSK调制后用于OFDM系统的新方法。仿真结果表明，在多径衰落信道下，通过合理选择多元LDPC码域的阶数和调制的方法，多元域LDPC编码的高阶调制OFDM系统比等效码长的二元域LDPC编码OFDM系统具有更好的性能，并且由于采用了多元域LDPC的快速BP译码，译码复杂度只是稍有增加。     

Performance analysis of imperfect closed-loop power control over Rayleigh fading

The performance of closed-loop power control in code division multiple access systems considering several non-ideal conditions such as multiple power control, group delays, channel estimation error, and power control command bit error probability is investigated.     

Performance analysis of MIMO–OFDM in various outdoor fading environments

Multiple-input Multiple-output (MIMO) technology is being combined with Orthogonal Frequency Division Multiplexing (OFDM) for use in next generation broadband wireless communication systems, and there has been an increase in the study of MIMO–OFDM systems. IEEE 802.11n specification uses MIMO–OFDM system to improve network throughput and coverage over the two previous standards, 802.11a and 802.11g, in indoor and outdoor environments, respectively. With an extended range of about two hundred meters in the outdoor environment, the use of 802.11n has increased. This paper analyzes the effect of shadowing, moving user and foliage in outdoor environment. There is a special need to analyze performance measures such as Spectral Efficiency and Bit Error Rate (BER), and this is the subject matter of interest in this paper.     

Performance analysis of coded modulation with generalized selection combining in Rayleigh fading

We consider coded modulation with generalized selection combining (GSC) for bandwidth-efficient-coded modulation over Rayleigh fading channels. Our results show that reception diversity with generalized selection combining can conveniently trade off system complexity versus performance. We provide a number of new results by calculating the cutoff rate, and by deriving analytical upper bounds on symbol-interleaved trellis-coded modulation (TCM) and bit-interleaved-coded modulation (BICM) with GSC. All are verified by simulation. We show that our new bounds on TCM with GSC, which includes maximum ratio combining and selection combining as special cases, are tighter than the previously derived bounds. A new asymptotic analysis on the pairwise error probability, which can be used as a guideline for designing coded modulation over GSC channels, is also given. Finally, we show that BICM with iterative decoding (BICM-ID) can achieve significant coding gain over conventional coded modulation in a multiple-receiving-antenna channel.     

Performance analysis of TAS/MRC-based scheme in time-varying Rayleigh fading channels

This paper investigates a Multiple-Input Multiple-Output (MIMO) scheme combining Transmit Antenna Selection and receive Maximal-Ratio Combining (TAS/MRC) in time-varying Rayleigh fading channels. We first present new closed-form expressions for optimal received Signal-to-Noise Ratio (SNR), which is expressed in polynomial form. These are used to analyze ergodic capacity, outage probability and Bit Error Rate (BER) of TAS/MRC systems. Numerical results are presented to validate the theoretical analysis.     

Performance analysis of optimum combining with multiple interferersin flat Rayleigh fading

This paper is a performance analysis of optimum combining in the presence of multiple equal power interferers and noise when the number of interferers is less than the number of antenna elements. Desired signal and interferers are subject to flat Rayleigh fading, and the propagation channels are independent. An approximate expression of the probability density function of the output signal-to-interference-plus-noise ratio (SINR) is derived analytically. It is then applied to obtain the cumulative distribution function of the SINR, and the bit-error rate (BER) of some binary modulations, including coherent binary phase-shift keying. In the case of a single interferer, an exact analysis is performed to prove the validity of the approximation. In the case of multiple interferers, the accuracy of the approximation is assessed through simulations. Although limited to equipower interferers, this analysis is a convenient way of assessing the performance of optimum combining in some typical situations and comparing it with that of maximal-ratio combining. The final results are remarkably simple and provide a useful complement to previous analyzes, especially in the region of reasonably high BERs which are of practical interest     

Performance analysis of various 16 level modulation schemes under Rayleigh fading

The average bit error rate (BER) performances of 16 square/star QAM and 16 CPSK/DPSK under Rayleigh fading are theoretically analysed and compared. 16 star QAM is inferior to 16 square QAM, which achieves the best performance, by approximately 4 dB in the required average E/sub b//N/sub 0/; however, when compared with differentially encoded square QAM, the performance inferiority is less than 2 dB.<>     

瑞利衰落信道下差分跳频通信系统的性能分析

介绍了一种新型的短波跳频通信技术--差分跳频,频率转移函数设计和信号的检测方法是差分跳频中的关键技术.针对逐符号检测和按序列检测两种信号检测方法,分别就差分跳频通信系统在瑞利衰落信道条件下的性能进行了理论分析,同时做出相应的计算机仿真.结果证实了,差分跳频通信技术和按序列检测方法的结合,使通信系统在瑞利衰落信道条件下的性能得到了比较显著的提升.     

Theoretical analysis of ICI self-cancellation in OFDM systems over Rayleigh flat-fading channels

Orthogonal frequency division multiplexing (OFDM) has been widely used for its robustness against multipath fading and low-complexity implementation. However, OFDM system, especially with large number of subcarriers and high modulation order, is severely affected by the phase noise of oscillators and carrier frequency offset (CFO). On the other hand, self-cancellation schemes have received a lot of attention due to their simple implementation and high efficiency to suppress inter-carrier interference (ICI) in OFDM systems. Among those ICI self-cancellation methods, symmetric conjugate symbol repetition (SCSR) has been proven to have the best bit error ratio (BER) performance for phase noise suppression. In this paper, the performance of OFDM systems with SCSR ICI self-cancellation in the presence of both phase noise (PHN) and CFO are investigated, and analytical expressions are derived to calculate error probability evaluated by symbol error ratio (SER) over additive white Gaussian noise (AWGN) and Rayleigh flat fading channels. An approach of second order approximation of PHN/CFO has been performed to estimate the residual ICI, which could provide more accurate results. Simulation results show perfect agreement with those obtained by theoretical analysis, which could be used to estimate OFDM system error probability, facilitating the design of the overall system.     

正交频分复用技术在协作通信下的应用

协作分集技术利用其他用户进行协作传输,可以获得一定的分集增益,但是在频率选择性衰落信道下性能不很乐观。为了对抗频率选择性衰落,采用正交频分复用(ODFM)技术与协作分集技术相结合的方法,研究了基于OFDM技术的协作通信,对在不同调制技术、不同信道估计方法下系统的性能进行了比较,为了进一步提高系统性能,对传统S&C算法进行了改进并应用于该系统中,仿真实验结果表明,改进的定时同步算法性能优于传统的S&C算法。