Outage performance of amplify-and-forward multiple-input multiple-output relay networks with outdated channel state information and co-channel interference

In this paper, we investigate the outage performance of a dual-hop amplify-and-forward(AF) multipleinput multiple-output(MIMO) relay network, considering beamforming transmission with outdated channel state information(CSI) and an arbitrary number of co-channel interferers at both the relay and the destination. The exact closed-form expression for the outage probability is derived, and the asymptotic behavior of the outage probability is also presented to provide further insights into the system performance. Our results show that the system suffers a diversity gain loss caused by the outdated CSI, and the interference only degrade the coding gain of the system. Moreover, increasing antennas can achieve more performance gains, however, the gains decrease as the delay of the CSI increases.     

STC-OFDM系统的post-IDFT多波束形成技术

提出了适用于空时编码-正交频分复用(OFDM)系统的后-逆离散傅立叶变换(post-IDFT)多波束形成技术.该技术通过对空频信道相关矩阵进行特征分解获得多个特征模式,再利用空时分组码(STBC)各发射分支信号的正交性使OFDM系统形成多个post-IDFT波束.接收端根据STBC传输矩阵的正交性对多波束解码.系统获得的空间分集增益为空频信道相关矩阵的特征值之和,最大空间分集增益与子载波波束形成方案相同,误码率比STC-OFDM的低.该技术将复杂度降低到子载波波束形成方案的1/S(S为OFDM系统的子载波数目),而且当波束维数(m)小于发射天线数目(M)时,可进一步减少M-m个IDFT模块     

Switching between antenna subset selection and quasi-orthogonal space-time block code in presence of correlation

We address the problem of adaptive modulation and coding scheme (AMCS) for a multi-input multioutput (MIMO) system in presence of time-varying transmitting correlation. Antenna subset selection and quasiorthogonal space-time block code (QOSTBC) have different error performances with different signal-to-noise ratios (SNRs) and in different spatial correlation scenarios. The error performance can be improved by selecting an appropriate transmission scheme to adapt to various channel conditions. The maximum distance criterion is the simplest and very effective algorithm for the antenna subset selection without needs of complex calculation and channel state information at transmitter (CSIT). The minimum error performance criteria and the simplified linear decision strategy are developed for constant transmission rate traffic to select the optimal transmission scheme. It can dramatically decrease algorithm complexity for obtaining error probability according to the known quantities comparing with using instant CSIT. Simulation results show that, remarkable performances including low SNR and weak spatial correlation at the expense of simple calculation and almost no bandwidth loss by adopting AMCS can be achieved. The proposed AMCS improves robustness of slowly varying spatial correlated channels.     

Simple closed-loop method to compensate interference asymmetry in time-division duplex MIMO-OFDM systems

In wireless communications systems with time-division duplex (TDD) deployment, channel reciprocity and symmetric interference between transmitter and receiver sides are two widely-adopted assumptions for the design of optimal adaptation transmission mode. However, in practice, there is an undesirable but non-negligible effect, namely the asymmetric interference, that makes the assumptions no longer valid. In this paper, a simple closed-loop feedback method of compensating interference asymmetry in TDD multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system is proposed. The system makes the estimated interference at transmit-side be able to track the instantaneous receive-side interference dynamically. The proposed method maintains constant frame error rate (FER) by adopting adaptive modulation coding (AMC) and power loading. The final simulations have verified the effectiveness of the new method.     

Robust optimization for the correlated MIMO downlink with imperfect channel state information

To reduce the performance deterioration induced by imperfect channel state information (CSI) in cor-related multiple input multiple output(MIMO) downlink, the linear transmit/receive filters should be optimized to be robust to imperfect CSI. A sub-optimization algorithm based on minimizing sum MSE conditional on available imperfect CSI estimates subject to a per-user power constraint is proposed. The algorithm adapts the existing MMSE algorithm from uncorrelated single-user MIMO system with perfect CSI to correlated MIMO downlink with imperfect CSI. Simulation shows that the suboptimal algorithm can effectively mitigate the performance loss induced by imperfect CSI and has a good convergence performance. In addition, the effect of spatial correlation on the performance of the proposed algorithm is also simulated.     

高速铁路环境下TD-SCDMA系统的多普勒频偏校正算法

高速铁路环境带来的大多普勒频偏会严重破坏移动通信系统性能.为消除大多普勒频偏的影响并且不增加终端的设备复杂度,本文提出一种低运算复杂度的TD-SCDMA系统多普勒（Doppler）频偏校正方案.方案首先利用系统上行时隙中训练序列（Midamble）的结构特点估计多普勒频偏.然后,根据时分复用系统的特点,利用上行时隙的多普勒频偏估计结果在基站端对下行时隙进行多普勒频偏预校正.仿真结果表明,所提出的多普勒频偏校正方案在高速铁路环境下可以取得良好的性能.     

Optimal training design and placement for MIMO orthogonal frequency division multiplexing channel estimation

This paper deals with optimal training design and placement over multiple orthogonal frequency division multiplexing(OFDM) symbols for the least squares(LS) channel estimation in multiple-input multipleoutput(MIMO) OFDM systems.First,the optimal pilot sequences over multiple OFDM symbols are derived by co-cyclic Jacket matrices based on the minimum mean square error(MSE) of the LS channel estimation.Then,an enhanced channel estimation method using sliding window is proposed to improve further the performanc...     

A Reduced Complexity Time-Delay Tracking and Channel Estimation for OFDM Systems

Introduction OFDM[1]is a special case of multicarrier trans-mission, where a single datastream is transmittedover a number of orthogonal subcarriers. Becausethe symbol duration increases for the lower rateparallel subcarriers, the relative amount of disper-sion in time caused by multipath delay spread is de-creased. Intersymbol interference is eliminated al-most completely by introducing a guard time in ev-ery OFDM symbol. Due to these advantages,OFDM is widely exploited for the communica…     

A Semi—blind Adaptive Beamforming Algorithm for Wideband Coherent CDMA

This paper presented a novel semi-blind adaptive beamforming algorithm specially designed for wideband coherent CDMA mobile communication systems with multiplexd control and data channels. The presented algo-rithm uses a parallel structure to exploit not only the desired user‘s pseudo noise sequence but also the information from multiplexed pilot and data symbols, thus help achieve faster convergence and lower bit error rate. Monte Carlo simulation results verified the performance improvement in terms of BER.     

Relay Selection and Power Allocation in Amplify-and-Forward Cognitive Radio Networks: A Special Spectrum Sharing Scheme

In this paper, we present a special spectrum sharing scheme that is a joint optimization of relay selection and power allocation at the secondary transmitter, where the primary user is incapable of supporting its target signal-to-noise ratio(SNR). Specifically, the selected secondary transmitter assists the primary user with achieving its target SNR via two-phase cooperative amplify-and-forward relaying. By searching for the candidate secondary transmitters which have already satisfied the primary user's target SNR, we can select the optimal secondary transmitter. This optimal secondary transmitter not only satisfies the primary user's target SNR,but also maximizes the throughput of the secondary user. We study this joint optimization problem such that the secondary user's throughput is maximized under the constraint that satisfies the primary user's target SNR.Numerical results show that our scheme can maximize the throughput of the secondary user, and can obtain the win-win solution for the primary and secondary systems.     

自供电路侧单元能量-时延均衡分组调度策略

考虑了自供电路侧单元在分组传输过程中能量收集、车辆到达与车速的随机性, 基于受限马尔科夫决策模型建立分组调度系统模型, 研究了分组平均传输时延与能量消耗; 分析了在能量队列约束下最小分组平均传输时延的优化问题, 提出了自供电路侧单元能量-时延均衡分组调度策略, 通过仿真试验分析了最优分组调度策略性能, 并与贪婪中继方案和Q-learning算法进行对比。仿真结果表明: 该分组调度策略具有双门限结构, 系统通过自供电路侧单元的能量队列状态以及到达车辆的车速状态确定决策变量, 使系统可以在考虑能量利用效率的前提下降低监测数据分组的平均传输时延, 保证自供电路侧单元在能量存储不溢出不耗尽的同时, 最小化系统分组平均传输时延; 在单分组发送模型中, 提出的分组调度策略的平均传输时延相比贪婪中继方案降低了15.7%, 相比Q-learning算法降低了13.5%;在批量分组发送模型中, 其分组平均传输时延相比贪婪中继方案降低了20.4%, 相比Q-learning算法降低了11.5%。      

连续流交叉口信号协调配时及延误模型

为解决连续流交叉口车辆二次停车和人-车冲突问题,防止车辆排队溢出,破坏连续流交叉口稳定的运行状态,提出人-车信号协调优化控制策略。根据车流运行特征,协调主、预信号配时,优化信号相位方案,以车均延误最小为目标构建优化模型。通过仿真对比可知,本文模型计算的延误估算误差在5%以内。通过案例分析可知,现状方案南北左转车均延误和车均停车次数是优化方案的2倍以上,说明优化方案避免了车辆二次停车;从整个交叉口来看,优化方案在两种流量场景下,车均延误分别降低了27.8%、18.5%,提升了交叉口运行效率。通过敏感性分析发现,移位左转车道长度在100 m时,综合效益最佳。     

基于分组合并的多信道停等ARQ性能

从信道数、合并方式、分组丢失率、传输延迟等方面,分析了在Rayleigh衰落信道下具有分组合并的多信道停等ARQ性能.分析结果表明:对于多信道停等ARQ,需根据分组传输时间和往返延迟时间合理安排停等ARQ的信道数,以使ARQ系统性能达到最佳;根据信道质量,采用合适的分组合并方式可减少接收处理延迟;为获得恒定分组传输延迟和系统吞吐率,可根据分组丢失率要求和信道质量调整最大传输次数.     

Joint Distortion Model for Progressive Image Transmission Using Error Correcting Arithmetic Codes

A novel joint source channel distortion model was proposed, which can essentially estimate the average distortion in progressive image transmission. To improve the precision of the model, the redundancy generated by a forbidden symbol in the arithmetic codes is used to distinguish the quantization distortion and the channel distortion, all the coefficients from the first error one to the end of the sequence are set to be a value within the variance range of the coefficients instead of zero, then the error propagation coming from the entropy coding can be essentially estimated, which is disregarded in the most conventional joint source channel coding (JSCC) systems. The precision of the model in terms of average peak-signal-to-noise has been improved about 0.5 dB compared to classical works. An efficient unequal error protection system based on the model is developed, and can be used in the wireless communication systems.     

Simulation and Analysis of Typical Mobile Radio Channels

In this paper, the bit error rate (BER) performance for typical mobile radio channels is simulated and analyzed based on a tapped delay line model. The investigation is focused on the propagation environments determined by the average delay profile and the Doppler spectra. The profile characteristics and their influences on channel behavior are also examined.     

Performance Analysis of AF Relaying Based on Water-filling Power Allocation over Nakagami-m Fading

This paper investigates exact performance of an amplify-and-forward(AF) relay system based on water-filling power allocation in Nakagami-m fading environment, where m is a nonnegative integer plus one half.We first offer the cumulative distribution function(CDF) and probability density function(PDF) of the received signal-to-noise ratio(SNR) at a destination. Then outage probability, moments of SNR, higher-order statistics of the capacity are explicitly conducted. Especially, average symbol error rate(SER) under an additive white generalized Gaussian noise(AWGGN) is developed for water-filling power allocation scheme. While the average SER subjected by an additive white Gaussian noise(AWGN) can be regarded as a special case. Finally, all theoretical formulas are truly attested by various simulation results.     

Joint distortion model for progressive image transmission using error correcting arithmetic codes

A novel joint source channel distortion model was proposed, which can essentially estimate the average distortion in progressive image transmission. To improve the precision of the model, the redundancy generated by a forbidden symbol in the arithmetic codes is used to distinguish the quantization distortion and the channel distortion, all the coefficients from the first error one to the end of the sequence are set to be a value within the variance range of the coefficients instead of zero, then the error propagation coming from the entropy coding can be essentially estimated, which is disregarded in the most conventional joint source channel coding （JSCC） systems. The precision of the model in terms of average peak-signal-to-noise has been improved about 0.5 dB compared to classical works. An efficient unequal error protection system based on the model is developed, and can be used in the wireless communication systems.     

Improving Mobility Management for All-IP Radio Heterogeneous Network Using SCTP

IntroductionFuture mobile communication network willconsist of multiple traffics and access technologies.It is to certainty a radio heterogeneous network(RHN) because none of the current networks canprovide ubiquitous coverage and all-around ser-vices[1]. Future mobile terminal will be multi-modethat maintains connectivity to different radio accesspoints, so RHN should be scalable and support theevolution and upgrade of individual network ele-ments. All-IP architecture is an inevitable way…     

Performance analysis of AF relaying based on water-filling power allocation over Nakagami-<Emphasis Type="Italic">m</Emphasis> fading

This paper investigates exact performance of an amplify-and-forward (AF) relay system based on water-filling power allocation in Nakagami-m fading environment, where m is a nonnegative integer plus one half. We first offer the cumulative distribution function (CDF) and probability density function (PDF) of the received signal-to-noise ratio (SNR) at a destination. Then outage probability, moments of SNR, higher-order statistics of the capacity are explicitly conducted. Especially, average symbol error rate (SER) under an additive white generalized Gaussian noise (AWGGN) is developed for water-filling power allocation scheme. While the average SER subjected by an additive white Gaussian noise (AWGN) can be regarded as a special case. Finally, all theoretical formulas are truly attested by various simulation results.     

衰落信道下两发送天线MIMO系统V-BLAST算法研究

对两发送天线MIMO系统在相关瑞利和莱斯信道下V—BLAST检测算法的性能进行了分析,推导出最优和固定检测两种方案中第一步和第二步的误码率．相对于独立同分布瑞利信道,考察了相关瑞利信道和莱斯信道对接收信噪比的影响;相对于固定检测方案,讨论了最优检测算法对信噪比的提升．理论分析和仿真结果表明,瑞利信道相关性或莱斯信道的直达波分量会减弱最优检测方案对信噪比的提升．