Analysis of switched diversity TCM-MPSK systems on Nakagami fadingchannels

Space diversity reception and forward-error correction coding are powerful techniques to combat multipath fading encountered in mobile radio communications. In this paper, we analyze the performance of a discrete-time switched diversity system using trellis-coded modulation multiple phase-shift keying (TCM-MPSK) on slow, nonselective correlated Nakagami (1960) fading channels. Analytical upper bounds using the transfer function bounding technique are obtained and illustrated by several numerical examples. A simple integral expression for calculating the exact pairwise error probability is presented. The use of optimum adaptive and fixed switching thresholds is considered. Monte Carlo simulation results, which are more indicative of the exact system performance, are also given     

Optimization of multi-branch switched diversity systems

A performance optimization based on the optimal switching threshold(s) for a multi-branch switched diversity system is discussed in this paper. For the conventional multi-branch switched diversity system with a single switching threshold, the optimal switching threshold is a function of both the average channel SNR and the number of diversity branches, where computing the optimal switching threshold is not a simple task when the number of diversity branches is high. The newly proposed multi-branch switched diversity system is based on a sequence of switching thresholds, instead of a single switching threshold, where a different diversity branch uses a different switching threshold for signal comparison. Thanks to the fact that each switching threshold in the sequence can be optimized only based on the number of the remaining diversity branches, the proposed system makes it easy to find these switching thresholds. Furthermore, some selected numerical and simulation results show that the proposed switched diversity system with the sequence of optimal switching thresholds outperforms the conventional system with the single optimal switching threshold.     

Performance analysis of multibranch switched diversity systems

We investigate the performance of multibranch switched diversity systems. Specifically, we first derive generic formulas for the cumulative distribution function, probability density function, and moment-generating function of the combined signal power for both switch-and-stay combining (SSC) and switch-and-examine combining (SEC) schemes. We then capitalize on these expressions to obtain closed-form expressions for the outage probability and average error rate for various practical communication scenarios of interest. As a byproduct of our analysis we prove that for SSC with identically distributed and uniformly correlated branches, increasing the number of branches to more than two does not improve the performance, but the performance can be different in the case the branches are not identically distributed and/or not uniformly correlated. We also show that, in general, the SEC performance improves with additional branches. The mathematical formalism is illustrated with a number of selected numerical examples.     

Markov chains and performance comparison of switched diversity systems

Switch-and-stay combining (SSC) diversity systems have the advantage of offering one of the least complex solutions to mitigating the effect of fading. In this paper, we present a Markov chain-based analytical framework for the performance analysis of various switching strategies used in conjunction with SSC systems. The resulting expressions are quite general, and are applicable to dual-branch diversity systems operating over a variety of correlated and/or unbalanced fading channels. The mathematical formalism is illustrated by some selected numerical examples, along with their discussion and interpretation. As a result, this paper presents a thorough comparison and highlights the main differences and tradeoffs between the various SSC switching strategies.     

Unified analysis of switched diversity systems in independent andcorrelated fading channels

The moment generating function (MGF) of the signal power at the output of dual-branch switch-and-stay selection diversity (SSD) combiners is derived. The first-order derivative of the MGF with respect to the switching threshold is also derived. These expressions are obtained for the general case of correlated fading and nonidentical diversity branches, and hold for any common fading distributions (e.g., Rayleigh, Nakagami-m, Rician, Nakagami-q). The MGF yields the performance (bit or symbol error probability) of a broad class of coherent, differentially coherent and noncoherent digital modulation formats with SSD reception. The optimum switching threshold (in a minimum error rate sense) is obtained by solving a nonlinear equation which is formed by using the first-order derivative of the MGF. This nonlinear equation can be simplified for several special cases. For independent and identically distributed diversity branches, the optimal switching threshold in closed form is derived for three generic forms of the conditional error probability. For correlated Rayleigh or Nakagami-m fading with identical branches, the optimal switching threshold in closed form is derived for the noncoherent binary modulation formats. We show previously published results as special cases of our unified expression. Selected numerical examples are presented and discussed     

一类离散切换系统的性能分析

针对一类含有不确定性和时滞的离散切换系统,探讨了H∞性能分析问题。假设所考虑的线性不确定性具有线性分式形式,综合利用Lyapunov-Krasovskii函数和Finsler’s引理,给出判断系统满足H∞性能界γ的充分条件,并且γ的上界可以通过求解一组线性矩阵不等式获得。最后通过一个数值算例说明方法的有效性。     

Orthogonal switched beams for downlink diversity transmission

A downlink transmission scheme in a switched-beam antenna system for providing diversity and beamforming simultaneously based on the space-time block coding technique is proposed. The scheme involves selecting multiple beams based on the uplink reception of the switched-beam antenna system, and determining multiple orthogonal beams from the selected beams. With the orthogonal transmit beams, the proposed switched-beam antenna system outperforms conventional switched-beam systems and approaches the optimal performance achievable by a much complex adaptive antenna system.     

A small theorem on the nonlinearity of switched systems

A criterion for actual examination the nonlinearity of some systems composed of switched linear elements is given.     

A switched diversity receiving system for mobile radio

A low cost switched diversity receiving system has been developed for use in UHF-FM mobile radio. The input of a single receiver is switched back and forth between two antennas upon command from a signal level sensing logic circuit. The system has been measured on simulated Rayleigh fading channels and has been found to give a significant improvement to both voice and data signals.     

Performance analysis of joint switched diversity and adaptive modulation

In this paper, a simple and practical system based on a switched diversity scheme with adaptive modulation is presented. This system provides a reduced number of channel estimation while offering the optimum spectral efficiency given by a selection diversity system. In addition, the switching threshold is easily manipulated so as to make an efficient use of the tradeoff between spectral efficiency and channel estimation overhead. An extension of switched diversity into a multiuser scheduling is later also considered. This switch-based multiuser access scheme results in a lower average feedback load than that for the optimal selection-based multiuser scheme. Numerical results show that we can obtain a trade-off between spectral efficiency and the feedback load by choosing the switching threshold appropriately.     

Improving the performance of switched diversity with post-examining selection

Switched diversity offers one of the lowest complexity solution for fading mitigation. The receiver employing switched combining schemes. seeks and uses an acceptable diversity path for data reception. However, when no acceptable path is found after all paths have been examined, the receiver ends up randomly choosing an unacceptable path. In this paper, we consider the performance improvement of switched combining schemes. In particular, we modify conventional multi-branch switch and examine combining (SEC) schemes in a way that the best path is selected when no acceptable path is found after all paths have been examined. We carry out a thorough performance versus complexity tradeoff study on the resulting scheme: SEC with post-examining selection and illustrate the study with some selected numerical examples.     

Performance analysis of a rate-adaptive dual-branch switched diversity system

In this letter, a performance analysis of a dualbranch switched diversity system operating on statistically independent and identically distributed Nakagami-m flat-fading channels is presented. An adaptive coded modulation (ACM) scheme is employed to increase the spectral efficiency of the system. The ACM scheme consists of a set of multidimensional trellis codes originally designed for additive white Gaussian noise channels, where the codes are based on quadrature amplitude modulation (QAM) signal constellations of varying size. The performance is evaluated by assuming perfect channel knowledge at both transmitter and receiver and instantaneous feedback of channel state information, conveyed from the receiver to the transmitter on an error-free feedback channel. The optimal switching threshold of the switched diversity combiner, maximizing the average spectral efficiency, is identified for spatially uncorrelated antenna branches.     

Closed-form analysis of dual-branch switched diversity with binary nonorthogonal signalling

An exact closed-form analytical expression is derived for the average bit error probability of dual-branch switched diversity over Rayleigh fading. A practical scheme is considered employing binary nonorthogonal signalling with noncoherent detection. The analytical results are useful to evaluate the performance?bandwidth trade-off in systems that intentionally employ nonorthogonal signalling.     

多天线无线数据通信系统中多用户分集的研究

研究当接收天线不少于发送天线时多输入多输出(MIMO)系统的多用户分集能力。首先从理论上分析了发送天线个数等于1和2时最大似然接收和迫零接收系统的平均吞吐量和调度增益,以及仿真分析了发送天线个数大于2时系统性能。理论分析和仿真表明：在多用户的MIMO系统中,接收的平均信噪比、用户个数、收发天线个数、接收机的结构等对于多用户分集有很大的影响。当发送天线个数为1时,接收天线较少(1,2,3)和平均信噪比为．10dB时调度增益很大,但调度增益随着天线个数和发送功率增大急剧下降。和最大似然接收相比,迫零接收具有更大的多用户分集增益,因此迫零接收机的吞吐量可以很容易超过最大似然接收机。     

New results on the BER of switched diversity combining over Nakagami fading channels

New closed-form bit error rate (BER) expressions are derived for multibranch switched combining (SWC) systems with independent Nakagami faded diversity branches having integer Nakagami 717-parameters. Constellations considered include BPSK, M-PSK, M-PAM and M-QAM. The analysis is also applicable to the generalized hierarchical PAM and QAM modulation formats.     

Modelling and simulation of frequency selective fading using switched antenna diversity

Simulation results for differential MSK in both flat and selective fading environments are presented together with the improvements offered by two and three branch antenna diversity. The results show that for short range communication systems diversity may be considered, up to a point, as an effective alternative to channel equalisation.<>     

Single-receiver diversity systems

Diversity reception techniques can help to combat fast fading in urban areas, and this paper describes some predetection combining systems designed to be compatible with existing standard receivers. Quantitative results show that a worthwhile improvement in quality of reception can be Obtained with small numbers of antennas. There are advantages to be gained if, in future receiving systems, the diversity technique is incorporated directly into the receiver design.     

开关电容滤波器的系统设计与实现

通过合理选择滤波器的类型和阶数,利用低Q值二级滤波器放在高Q值二级滤波器的前级,给每一级分配不同的增益使得每一级的输出峰值相同.从开关电容电路的原理入手,分析了开关电容电路和电容编程阵列,最终设计一个可编程开关电容6阶带通滤波器.选择合适的运算放大器参数.可编程滤波器系统共需3路时钟控制,滤波器编程参数控制模块用于实现芯片内部程序存储器编程控制.通过对设计的开关电容滤波器进行仿真,结果基本与设计目标吻合.     

多时滞离散切换系统反馈镇定

研究一类具有多时滞子系统的离散切换系统的稳定性分析和反馈镇定问题。通过状态变量的转换，将时滞切换系统变为不含时滞项的切换系统。以LMI形式给出了在任意切换信号作用下多时滞离散切换系统渐近稳定的充分性条件，以及系统状态反馈镇定、输出反馈镇定的控制器设计。并通过两个仿真实例验证所设计控制方案的有效性。