Closed‐form analysis of multibranch switched diversity with noncoherent and differentially coherent detection

Exact closed‐form analytical expressions are derived for the average bit error probability of multibranch switched diversity systems over independent and identically Nakagami‐m distributed fading channels. Practical schemes that use noncoherent or differentially coherent symbol detection are considered. The general bit error probability expression derived in this paper includes as particular cases the following signaling formats: orthogonal binary signaling, correlated binary signaling, differential phase‐shift keying, and differential quadrature phase‐shift keying. Finally, we apply our analytical results to study the impact of the switching threshold selection on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

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     

Analysis of switched diversity systems on generalized-fadingchannels

The performances of switched diversity systems operating on generalized (Nakagami)-fading channels are analyzed using a discrete-time model. The average bit error rate (BER) of binary noncoherent frequency shift keying (NCFSK) on slow, nonselective Nakagami-fading channels is derived. Closed-form expressions that can be used to determine optimum switching thresholds (in a minimum error rate sense) are also derived. In addition, the use of optimum fixed thresholds is considered. It is found that a considerable amount of diversity gain can be obtained using an optimum fixed (rather than adaptive) switching threshold. Results are obtained for both independent and correlated Nakagami-fading branch signals. The effects of fading severity and the correlation coefficient on both the BER and on the optimum switching threshold are investigated. It is shown that useful diversity gain can be obtained with power correlation coefficients as high as 0.9 when the fading is strong. The results for a Rayleigh channel are obtained and presented as a special case of generalized-fading model     

Performance analysis of wireless multihop diversity systems

We study the performance of multihop diversity systems with non‐regenerative relays over independent and non‐identical Rayleigh fading channels. The analysis is based on the evaluation of the instantaneous end‐to‐end signal‐to‐noise ratio (SNR), depending on the type of the relay and the diversity scheme used. A closed‐form expression is derived for the average end‐to‐end SNR, when fixed‐gain relays and a maximal ratio combiner are used; also, an analytical expression formula for the average symbol‐error rate (ASER) for the above case is presented. The results show that, as expected, multihop diversity systems outperform conventional telecommunication systems in terms of ASER when the same amount of energy is assumed to be consumed in both cases. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance analysis of photovoltaic pumping systems using switched reluctance motor drives

A photovoltaic (PV) pumping system using a switched reluctance motor (SRM) is investigated in this work. the motor is supplied by a DC voltage through a simple switching circuit. This drive circuit is much simpler than the normal DC/AC inverter required to supply an induction motor. the efficiency of the SRM is considerably higher than that of equivalent DC or induction motors. In addition, because of its simple construction, the SRM is cheaper than these conventional drives. These advantages give the proposed system higher efficiency and lower cost compared with other systems. In this paper, which has a substantial tutorial content, a design example is studied in detail to explore the advantages of PV pumping systems based on the new drive. Study of the performance of the proposed system showed that the operating efficiency of the motor is about 85% during most of its working time. the matching efficiency between the PV array and the proposed system approaches 95%. the major part of the losses takes place in the pump and the riser pipes; this loss represents one-third of the total available energy.     

Performance analysis of MIMO systems with multiuser diversity

In this paper, we present a comprehensive performance analysis for multiple‐input multiple‐output (MIMO) systems with multiuser diversity over Rayleigh fading channels. We derive exact closed‐form expressions of the outage probability and the average bit error rate (BER) for different MIMO schemes, including the selective combining (SC), maximum ratio combining (MRC) and space‐time block codes (STBC). We also provide the explicit upper bounds on the BER performance. Finally, the mathematical formalism is verified by numeric results that study the interaction between the antenna diversity and the multiuser diversity. It is observed that the system performance is deteriorated as the number of transmit antennas increases in multiuser scenario, which is unlike the case in single‐user systems. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

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     

Performance analysis of multi-user diversity in heterogeneous cooperative communication systems

The heterogeneous cooperative relaying technique can be utilized to complete the hierarchical convergence for the multi-radio access networks, where the single heterogeneous cooperative relay is selected and the maximal-ratio combining (MRC) scheme is utilized to achieve the cooperative diversity gain. In order to evaluate performances of the hierarchical convergence mechanism, this paper theoretically investigates the key factors of the multi-user diversity (MUD) gain, the heterogeneous cooperative diversity gain and the large scale fading of the first and second links. The tight closed-form expressions in terms of the outage probability and the average symbol error rate are derived for evaluating how and with what factors impact on the system performance. The analytical and simulation results show that the number of heterogeneous cooperative relay nodes (HCRNs)M and the number of destination stations (DSs)K have great impacts on performances, and the order of outage probability is (M + 1)K. The large scale fading ratio of the first hop to the second hop also has a big impact on performances. Thus in the real network, we can utilize advanced radio resource management schemes to achieve a high multi-user diversity, instead of configuring too many HCRNs for the heterogeneous cooperative diversity gain. Furthermore, we can guarantee the transmission quality between the BS and HCRNs via the network planning to optimize the overall network performance.     

认知频谱共享系统最大比例合并分集的性能分析

研究了一个认知频谱共享系统,该系统是由一个次用户发射机、一个次用户接收机和一对主用户发射机和接收机组成,次用户接收机利用最大比合并策略提高系统性能。首先分析了来自主用户发射机的干扰对频谱共享系统中断概率的影响。经过一些运算得到了中断概率确切的封闭表达式,为评价系统关键参数的联合作用提供了有效手段,如次用户接收机天线的数目、次用户最大的发射功率、干扰温度限制以及主用户发射功率等。另外,还对系统中断概率的渐近性能进行了研究,揭示了次用户系统中断概率具有饱和现象。最后,分析了该系统分集复用增益。仿真结果表明,该中断概率确切封闭表达式与Monte Carlo仿真结果非常吻合,干扰温度约束和主用户的干扰对中断概率具有显著的不利影响,增加次用户接收机的天线数目可提高系统性能。     

Performance analysis of multiuser selection diversity in SIMO spectrum sharing systems

In this paper, a performance analysis is presented for user selection schemes in a single‐input multiple‐output spectrum sharing system. In the considered system, multiple secondary users try to use the licensed spectrum of a primary user in an opportunistic manner, in which an interference constraint for the primary user is satisfied. In this paper, we first use 2 conventional user selection schemes for single‐input multiple‐output spectrum sharing system and analyze the system performance for each scheme. We then propose a new user selection scheme that can overcome the limitations of those 2 conventional user selection schemes. As for the performance analysis, the average channel capacity, the outage probability, and the bit error rate performances of the system using the presented user selection schemes are analyzed and mathematical closed‐form expressions for the outage probability are derived. The performances of the system are evaluated using the derived mathematical formulas in different cases. In addition, Monte Carlo simulation results are also provided to show the accuracy and correctness of the performed analysis.     

Performance analysis of dual switched diversity over correlated Weibull fading channels with co‐channel interference

This paper studies the performance of switch and stay combining (SSC) diversity in the presence of co‐channel interference over correlated Weibull fading channels. SSC diversity based on signal‐to‐interference ratio (SIR) is a low‐complexity and a very efficient technique that reduces fading and co‐channel interference influence. New closed‐form expressions for the probability density function and cumulative distribution function of the output SIR's are derived. These formulas are used in a detailed analysis of the average output SIR and outage probability. The influence of fading severity and correlation coefficient on the optimum switching threshold and system performance is investigated. Monte Carlo simulations are performed to verify obtained theoretical results and determine average bit error rate in detecting binary phase‐shift keying (BPSK), differential BPSK and quadrature amplitude modulation signals. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

双发射天线选择正交空时码分集系统性能分析

针对任意Nakagami衰落信道,分析了多输入多输出(MIMO)系统中采用双发射天线选择正交空时码的平均误码率(ASER)性能。利用矩生成函数方法,推导出采用相干检测的二进制相移键控/二进制频移键控(BPSK/BFSK)、多进制相移键控(MPSK)和多进制正交幅度调制(MQAM)的精确ASER闭合解析式,对不同条件下的系统性能做了数值仿真,验证了分析结果的正确性。     

Performance analysis of discrete feedback schemes for downlink multiuser diversity in OFDMA systems

This paper analyzes discrete feedback of various feedback schemes for multiuser diversity in a multiple subchannel environment. In these schemes of full feedback, fixed feedback, adaptive feedback, and threshold-based feedback, users report a quantized discrete value to indicate their modulation and coding scheme instead of feeding back the full values of the channel state. A closed-form expression of the sum-rate capacity is developed to evaluate the feedback schemes. By comparing the feedback schemes in terms of the sum-rate capacity and the feedback load, this paper provides guidance for the selection of a feedback scheme. Additionally, a mixed-feedback scheme is proposed to reduce the amount of allocated feedback resources in the threshold-based feedback scheme, where the base station adjusts the capacity-feedback tradeoff by controlling two parameters, namely the number of subchannels and a threshold.     

Bifurcation analysis of switched dynamical systems with periodically moving borders

This paper describes a method for analyzing the bifurcation phenomena in switched dynamical systems whose switching borders are varying periodically with time. The type of systems under study covers most of power electronics circuits where two or more dynamical systems are cyclically switched according to the interaction of the state variables and some periodically moving borders. In particular, the complex bifurcation behavior of a voltage feedback buck converter is studied in detail. The analytical method developed in this paper allows bifurcation scenarios to be clearly revealed in any chosen parameter space.