Analysis of BPSK modulated asynchronous band-limited DS-CDMA systems with diversity receivers over generalised-K fading channels

The authors studied bit-error rate (BER) performance of asynchronous band-limited direct-sequence code-division multiple-access (DS-CDMA) systems with various diversity-combining receivers over Generalised-K fading channels. The effects of band-limited pulse shapes, multitone jamming, multiple-access interference as well as both flat and frequency-selective fading are considered. The Generalised-K model is adopted in order to include the effects of shadowing and fading of a wireless channel. The authors consider binary phase-shift keying as the modulation technique. The analytical expressions are valid for any arbitrary value of Generalised-K distribution parameters. Two types of band-limited pulses, namely spectrum raised cosine and Beaulieu-Tan-Damen (BTD) pulses, are incorporated in the analysis. Numerical results show that the system with BTD pulse outperforms the one with SRC pulse for various diversity-combining receivers under various channel conditions. Furthermore, by incorporating a minimum mean-square error stage in the multipath diversity receiver, the BER performance can be further improved.     

乘积合并接收的差分跳频通信系统在瑞利衰落信道上抗多音干扰的性能分析

在瑞利衰落信道上,在多音干扰和加性高斯白噪声共存的条件下,对采用乘积合并接收(PCR)方法的差分跳频(DFH)通信系统的误符号性能进行了理论分析.为验证理论分析的正确性,进行了相应的计算机仿真,将采用 PCR 方法的误符号性能与采用线性合并接收(LCR)方法的误符号性能作了比较.结果证实,在瑞利衰落信道上,DFH 通信系统采用乘积合并接收的方法要比采用 LCR 方法具有更好的抗多音干扰的性能.     

基于海面散射的莱斯MIMO信道容量研究

通过相关莱斯信道模型对海面散射水声多入多出(MIMO)信道容量进行了研究。从Helmholtz-Kirchhoff积分和Fresnel近似出发,得到海面散射信号的空间相关性,由于信道的协方差矩阵不可以表示成发射相关矩阵和接收相关矩阵的Kronecker积,通过Monte Carlo仿真研究了莱斯因子、接收信噪比和空间相关性对MIMO信道容量的影响。从对outage capacity和信道容量的CCDF(Complementary Cumulative Distribution Function)的仿真计算结果可以看出,莱斯衰落的MIMO信道容量并不总是小于瑞利衰落MIMO信道容量,当信道的空间相关性较大和接收信噪比较小时,由于信道的衰落作用将起主要作用,对于较小的收发阵元数,以非衰落的直达信号为主的莱斯MIMO信道容量将大于瑞利衰落的MIMO信道容量。     

Performance of turbo trellis coded/continuous phase modulation over MIMO channels

Bit error performance of turbo trellis coded/continuous phase modulation (TTC/CPM) is investigated for multiple input multiple output (MIMO) channels. The performance of TTC/CPM for 16-continuous phase frequency shift keying (CPFSK) over AWGN and Rician channels (for Rician channel parameter K=10 and 4 dB) is given for 1Tx-1Rx, 2Tx-1Rx and 2Tx-2Rx antenna combinations. Channel capacities of TTC-16CPFSK signals are obtained for these antenna configurations. TTC/CPM over MIMO fading channels is found to be very good, especially for low power applications     

Statistical characteristics of the envelope in diversity combining of two correlated Rayleigh fading channels

Performance of diversity systems is often evaluated under the assumption of perfect interleaving and characterised in terms of long-term parameters such as the average bit-error rate, which does not capture the dynamics of fading channels. Statistical characteristics (static and dynamic) of the envelope of two correlated Rayleigh fading channels are explored using a physical model. For two popular diversity-combining schemes, maximal ratio combining and selection combining, both static and dynamic (level-crossing rate) properties of correlated fading channels are derived. These results are very useful for performance evaluation of diversity systems without bit-level simulations. The results can also provide very useful characteristics such as average duration of fades, fading rate and outage probability for two-channel diversity systems and can be extended to multiple fading channels     

Performance of zero-forcing detectors over MIMO flat-correlated Ricean fading channels

The bit error rate (BER) performance of the zero-forcing (ZF) receiver over transmit-correlated flat Ricean fading channels is investigated. In particular, for a multiple-input multiple-output (MIMO) channel with M transmit and N receive antennas, an approximation for the average BER of each substream is derived. Then the system performance in receive-correlated flat Ricean fading channels is addressed. In this case, it is shown that the performance, when N ? M, is the same as that of transmit-correlated flat Ricean fading channels. A closed-form expression for the optimum transmit correlation coefficient, which achieves the maximum capacity (i.e. uncorrelated case), is also derived. As a result, a significant capacity gain is achieved by exploiting the knowledge of the Ricean channel. Extensive simulations are presented to validate and demonstrate the performance gain with different system parameters.     

EM-based turbo receiver design for low-density parity-check-coded MIMO-OFDM systems with carrier-frequency offset

The design of expectation-maximisation (EM)-based turbo receivers for low-density parity-check-coded multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems with the presence of carrier-frequency offset (CFO) is studied. First, starting from the maximum-likelihood principle, a novel EM-based CFO estimator for MIMO-OFDM systems is devised. This estimator iteratively provides the CFO estimate with the aid of pilot symbols. It is also capable of accommodating any space-time-coded-OFDM transmission. Then this CFO estimator is incorporated into the initialisation step of the turbo receiver. Simulation results show the effectiveness of the receiver design in combating CFO over unknown frequency-selective fading channels.     

Second-order statistics of dual-hop transmission with an amplify-and-forward relay over Rician and Weibull fading channels

The level-crossing rate (LCR) and average fade duration (AFD) are the second-order statistics that are useful for the design of adaptive transmission and coding systems over wireless fading channels. These second-order statistics are analyzed for dual-hop transmissions with a fixed-gain amplify-and-forward relay, where the Rician and Weibull fading channels are considered. To evaluate the LCR and AFD, we also derived the lower and upper bounds on the LCR and AFD which are useful when the exact closed-forms of the LCR and AFD are difficult to obtain. To illustrate the performance of the dual-hop relay channel, numerical results of the outage probability, the LCR and AFD are presented.     

Compact Rayleigh and Rician fading simulator based on random walk processes

This article describes a significantly improved sum-of-sinusoids-based model for the accurate simulation of time-correlated Rayleigh and Rician fading channels. The proposed model utilises random walk processes instead of random variables for some of the sinusoid parameters to more accurately reproduce the behaviour of wireless radio propagation. Every fading block generated using our model has accurate statistical properties on its own and hence, unlike previously proposed models, there is no need for time-consuming ensemble-averaging over multiple blocks. Using numerical simulation it is shown that the important statistical properties of the generated fading samples have excellent agreement with the theoretical reference functions. A fixed-point hardware implementation of the corresponding Rayleigh and Rician fading channel simulator on a field-programmable gate array (FPGA) is presented. By efficiently scheduling the operations, the reconfigurable fading channel simulator is compact enough that it can be efficiently used to simulate multipath scenarios and multiple-antenna systems (e.g. a 4 times 4 MIMO channel) using a single FPGA.     

Performance bounds of space-time block coding in rician and log-normal fading channels

Analytical expressions concerning the capacity and bit error rate (BER) of multiple-input multiple-output systems with space-time block coding (STBC) are derived. Two fading environments are examined, log-normal and Rician channels. A tight closed-form upper bound is presented for the BER of systems operating in log-normal fading environments in addition to an upper bound for the capacity of this type of systems. The latter bound applies to systems that operate under Rician fading as well. The analytical results were validated against ample numerical simulations for three STBC schemes and three phase-shift-keying modulations. The proposed bounds proved to be a tractable way to evaluate the system performance when no closed-form expression for the probability density function or the moment generating function is known     

Blind adaptive and iterative interference cancellation receiver structures based on the constant modulus criterion in multipath channels

Blind adaptive and iterative interference cancellation (IC) receiver structures for direct sequence code division multiple access systems in multipath channels are proposed. A code-constrained constant modulus design criterion based on constrained optimisation techniques and adaptive algorithms for receiver and channel parameter estimation are described for successive IC (SIC) and parallel IC (PIC) detectors and a new hybrid IC (HIC) scheme in scenarios subject to multipath fading. The proposed HIC structure combines the strengths of linear, SIC and PIC receivers and is shown to outperform the conventional linear, SIC and PIC structures. A novel iterative detection approach that generates different cancellation orders and selects the most likely symbol estimate on the basis of the instantaneous minimum constant modulus criterion is also proposed and combined with the new HIC structure to further enhance performance. Simulation results for an uplink scenario assess the algorithms, the proposed blind adaptive IC detectors against existing receivers and evaluate the effects of error propagation of the new cancellation techniques.     

Analytical study of binary differential impulse radio-ultra wide band over single-mode fibre systems using two receiver structures

A binary differential impulse radio-ultra wide band (IR-UWB) communication scheme over a singlemode optical fibre is examined. For a receiver structure, the conventional electrical receiver as well as an optical receiver structure, which is similar to the optical receiver used for digital, optically phase-modulated differential phase shift keying, are considered. The optical receiver can alleviate the IR-UWB receiver implementation challenges and it is studied for the first time in the context of IR-UWB. Considering various important noises, for example, phase noise, laser intensity noise, thermal noise and shot noise, analytical expressions for the error probability of the aforementioned receivers are derived. The mathematical models for optical components including laser diode and single-mode fibre, along with the analytical expressions for the receiver?s error probability, are used to evaluate the overall performance of an UWB communication system over a fibre transmission medium. Furthermore, the electrical receiver is compared with the optical receiver and it is shown that the performance of the optical receiver can be as good as that of the electrical receiver and even better. The impact of wireless channel fading, bias current of laser diode and the coherence time of laser diode on the UWB over fibre system performance is also examined.     

Non-coherent improved-gain diversity reception of binary orthogonal signals in Nakagami-q (Hoyt) mobile channels

A novel non-coherent receiver with diversity reception for binary orthogonal signals in non-identical Nakagami-g (Hoyt) fading channels (channels having arbitrary average fading powers and arbitrary fading parameters) is proposed. A closed-form expression for the average bit error probability of the proposed receiver is derived, which is given in terms of elementary functions, and can be readily evaluated numerically. In addition, the results clarify that the proposed receiver does not incur non-coherent combining loss, and at the same time, lower bounds the performance of the conventional non-coherent equal-gain combining (NC-EGC) receiver. Simulation results are provided to validate the mathematical analysis.     

Maximum a posteriori channel estimation for cooperative diversity orthogonal frequencydivision multiplexing systems in amplify-andforward mode

Transmit diversity-orthogonal frequency-division multiplexing (OFDM) systems have been proposed to mitigate the detrimental effects of channel fading. However, owing to the space and power limitations, the use of multiple transmit antennas is not practical in certain wireless devices, such as portable terminals and wireless sensors. Therefore cooperation among users at the physical layer has been proposed recently. Here, space-time block coded in amplify-and-forward (AF) relaying mode has been proposed as cooperative diversity for OFDM systems (CO-OFDM) in the presence of perfect channel-state information. Then, the channel estimation techniques for CO-OFDM systems in AF mode based on pilot symbols are investigated over frequency-selective channels. In particular, expectation-maximisation (EM) based maximum a posteriori (MAP) channel estimation is developed and compared with comp-type pilot-aided channel estimation (PACE) based the maximum likelihood (ML) estimator and the least minimum mean-square error (LMMSE) channel estimation techniques for CO-OFDM systems. To overcome the drawback owing to the receiver complexity, the Karhunen-Loeve expansion with the optimal truncation property is also considered. Simulation results that demonstrate the overall performance advantage of the EM-MAP based receiver over the PACE-ML and PACE-LMMSE based receivers are presented.     

Bit error rate analysis of diversity M-phase-shift keying receivers in weibull fading with cochannel interference

In this study, the effect of introducing cochannel interference (CCI) on the performance of diversity receivers operating over the Weibull fading channel is thoroughly investigated. More specifically, the authors derive novel bit error rate (BER) expressions for the dual-branch selection combining (SC) and post-detection equal gain combining (EGC) diversity M-PSK receivers with possibly correlated branches operating over Weibull fading channels in presence of CCI. A characteristic function (CF)-based approach is used to achieve this goal. For the EGC correlated branches case, because of lack of existence of a closed-form expression for the CF of the sum of two Weibull random variables (RVs), the authors revert to using the Pade′ approximation (PA) technique to approximate this CF by a rational function and hence an approximate BER expression is obtained. Various results pertaining to the effect of fading severity of both the desired signal and the interferers, the effect of the number of interferers and the effect of correlation between diversity branches for different M-PSK modulations are presented. The obtained results are verified by comparison with Monte Carlo simulations and excellent agreement is observed.     

Channel capacity of dual-branch diversity systems over correlated Nakagami-m fading with channel inversion and fixed rate transmission scheme

Closed-form expressions are derived for the channel capacity of dual-branch maximal ratio combining, equal gain combining, selection combining, and switch and stay combining (SSC) diversity systems over correlated Nakagami-m fading for the channel inversion with fixed rate transmission scheme. Since some of the final capacity expressions contain infinite series, the series are truncated and upper bounds on the truncation errors are presented. An expression is also derived that can be used to numerically determine the optimum adaptive switching threshold for the capacity of a dual-branch SSC system over correlated Nakagami-m fading channels. A closed-form expression for the optimum adaptive switching threshold is derived, however, for the case of independent branches. The corresponding expressions for Rayleigh fading are obtained as a special case of Nakagami-m fading. Finally, numerical results are presented, which are then compared to the capacity results that the authors previously obtained for the rate adaptation with constant power transmission scheme.     

Concatenated bit-interleaved coded modulation and orthogonal space-time block codes over fading channels

The authors analyse concatenated bit-interleaved coded modulation and orthogonal space-time block codes (OSTBC) over fading channels in the absence and presence of channel state information (CSI) in receiver. The authors derive analytical expressions for bit and frame error probabilities based on which corresponding designing rules are proposed. The analytical results are for arbitrary rate of constituent STBC and arbitrary convolutional code, and for CSI-aware receiver is for any number of transmit and receive antennas. Simulation results are presented to confirm the validity of the proposed designing rules. Moreover, the simulation results show that the proposed system outperforms concatenated trellis coded modulation and OSTBC.     

Upper bounds on the error probability of coded space?time block coded systems with diversity reception

New union bounds are derived for space-time block coded systems over Rayleigh fading channels. Both maximal ratio combining and generalised selection combining are considered as combining schemes at the receiver. The union bounds are easy to be evaluated using the transfer function of the code. Furthermore, the bounds are general to any coding scheme with a known weight distribution. Results show that the proposed union bounds are tight to simulation results for wide ranges of diversity orders and signal-to-noise ratio values.     

Performance analysis of rectangular quadrature amplitude modulation with combined arbitrary transmit antenna selection and receive maximal ratio combining in nakagami-m fading

The average symbol error probability (SEP) performance of arbitrary rectangular quadrature amplitude modulation in the context of arbitrarily ordered transmit antenna selection and receive maximal ratio combining diversity system is analysed. The channel gains are assumed to follow Nakagami-m fading distribution with in general arbitrary fading parameters. Exact expressions for the average SEP performance are derived for the general case of unequal in-phase and quadrature decision distances as well as distinct in-phase and quadrature modulation orders. The results generalise many previous case studies, and can be used to investigate the impact of various diversity-combining schemes and different modulation and channel parameters on the system average SEP performance.     

Performance analysis of multiple-input multipleoutput singular value decomposition transceivers during fading and other cell interference

A generalised method is derived to compute the error probabilities of singular value decomposition (SVD)-based receivers for a multiple-input multiple-output (MIMO) system with uncoded transmission. The method can be used for a wide class of flat fading environments, including independent and identically distributed (i.i.d.) and semi-correlated Rayleigh and i.i.d. Ricean channels. Although the method is applied to equal-power binary phase shift keying, it can easily be extended to higher-order M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) signal constellations and adaptive 'water-filling' schemes. The error probability curves derived from closed-form formulas and simulations demonstrate very close agreement. The error performances of channel inversion, minimum mean square error and zero forcing receivers are compared with the SVD receiver for a single-user system. The impact of multiple users is considered by studying the performance of an adaptive MIMO SVD transmission scheme operating in a cellular environment. In particular, the effect of inter-cell interference on the performance of the scheme is quantified, modelling the interference as increased Gaussian noise. A number of cellular layouts are examined and the impact of the resulting singal-to-interference and noise ratio on the constellation sizes that can be supported, the BER and so on is considered. The primary metric used for our performance analysis is the error-free transmission rate, which is derived for our adaptive system. For the cellular scenarios considered, it can be found that the effect of interference is considerable and the performance of the adaptive MIMO SVD scheme is only marginally better than that provided by conventional diversity methods.