基于混合精度量化的空时编码大规模MIMO系统性能

本文提出空时编码与混合量化结合的方法在有效降低系统功耗的同时增加传输分集增益,并对基于混合ADC结构的空时编码大规模多输入多输出（Multiple input multiple output,MIMO）系统性能进行了研究。采用加性量化噪声模型对系统性能进行分析,得到系统频谱效率,利用随机矩阵理论得到频谱效率的近似表达式,并通过仿真验证表达式的准确性,基于表达式分析系统中各个参数对系统性能的影响。仿真结果表明,在接收端使用混合精度量化的结构可以有效地降低大规模MIMO系统的功率损耗以及实际部署的成本,而且采用空时编码后,系统的发射分集增益增加了一倍。     

协同MIMO移动Ad Hoc网络中的一种新型Alamouti编码

针对协同MIMO(Multi-Input Multi-Output)移动ad hoc网络无线带宽相对有限、无线信道噪声干扰强烈而导致的信号传输质量不佳等问题,提出一种基于反相对称调制法的Alamouti空时编码方案。通过在编码过程中加入噪声相消运算环节而大大减小接收端接收到的噪声干扰强度;重点分析此种方案的编译码过程,并通过理论分析和系统仿真表明,相较于传统的Alamouti空时编码,此方案可使传输系统获得更优越的抗噪声性能和更小的传输误码率,大大提高了系统传输可靠性。     

一种新型的Turbo-MIMO收发机

通过结合HBLAST与VBLAST系统的特点以及Turbo编码的结构提出了一种应用于MIMO系统的新型BLAST收发系统Turbo-Like BLAST系统(TLBLAST).该系统实现了高速数据传输,此外每根天线可以采用不同的编码方式对数据实行不同等级的保护.接收端将软输入软输出检测器与迭代译码级联起来,经过迭代有效地提高了系统性能,并且与已有的VBLAST系统迭代接收结构复杂程度相当.仿真结果表明,在平坦Rayleigh衰落MIMO信道下TLBLAST系统性能优于HBLAST系统以及VBLAST系统.     

分布式MIMO系统容量最优的预编码设计

针对分布式多入多出(MIMO)系统各天线功率无法共享的问题,基于分布式MIMO系统各天线功率受限的假设,提出容量准则下的最优预编码矩阵设计方案。采用Lagrange对偶优化的方法,将原优化问题转化为其对偶问题,给出求解预编码矩阵的迭代算法流程,以及在不同天线配置和容量准则下的信号发射策略。仿真结果表明,在发射天线数目多于接收天线数目时或信道矩阵缺秩时,该迭代算法求得的预编码矩阵的容量性能优于已有次优解析解。     

交织复用空时码在协作中继网络中的应用

本文研究了一种基于交织复用(IDM)的分布式空时编码方案,对一种适用于该方案的迭代接收机结构进行性能分析。同时通过仿真,对所提出的协作编码方案进行性能评估。在相似环境下,通过比较本方案与其它协作空时码的性能,表明本方案由于采用了非正交的空时编码,具有多方面的优越性。同时它还可以采用灵活的发送天线数配置,反映到协作通信的场景,也就是对中继终端的数量没有特殊要求。     

基于GMD-DPC/THP的两组Alamouti非线性预编码系统

针对Alamouti空时块编码复用增益损失的问题,提出了两组Alamouti编码方案;在此基础上,为了改善系统的误码率（Bit Error Rate,BER）性能和简化接收端复杂度,提出将几何均值分解（Geometric Mean Decomposition,GMD）算法和非线性预编码技术相结合的两组Alamouti传输方案。本方案的设计方法为：首先等效出两组Alamouti空时块编码系统的信道矩阵;进而,通过GMD算法对等效信道矩阵进行收发端联合设计;最后,在发射端应用脏纸（Dirty Paper Coding,DPC）和Tomlinson-Harashima Precoding（THP）非线性预编码技术,消除发送信号间的干扰,从而使系统获得更好的误码率性能。通过仿真结果对比发现,提出的系统可以显著地改善误码率性能。     

空时分组码在TD-SCDMA系统中的应用技术研究

提出了一种空时分组码与TD-SCDMA系统联合检测算法相结合的新方法,提出在发送端两根天线采用基于数据域的域空时分组码编码方案,即以一个突发中的数据域为单位进行空时分组码的编码.接收端采用一根天线接收,算法可应用于多根天线,并对系统矩阵进行了扩充,对一个突发中的两个数据域同时进行译码.与传统的联合检测算法比较,由于采用了发送分集技术,性能有所提高.     

空时分组码在TD-SCDMA系统中的应用技术研究

提出了一种空时分组码与TD-SCDMA系统联合检测算法相结合的新方法,提出在发送端两根天线采用基于数据域的域空时分组码编码方案,即以一个突发中的数据域为单位进行空时分组码的编码。接收端采用一根天线接收,算法可应用于多根天线,并对系统矩阵进行了扩充,对一个突发中的两个数据域同时进行译码。与传统的联合检测算法比较,由于采用了发送分集技术,性能有所提高。     

基于改进OMP算法的毫米波大规模MIMO混合预编码设计

针对全连接单用户毫米波大规模MIMO系统,以最大化系统可达和速率为目标,提出一种基于改进的正交匹配追踪（orthogonal matching pursuit,OMP）算法的混合预编码方案。在既有的基于OMP算法的混合预编码基础上,首先,针对其迭代次数过多的问题,受多步长思想的启发,从阵列响应集合中选取与射频链路数目相等的最优的前多列矢量,从而求得模拟预编码矩阵;其次,针对其求逆运算复杂度高的问题,利用Hlder不等式及Schatten范数来逼近待优化的目标函数,从而求得最优的数字预编码矩阵。仿真结果表明,所提基于改进的OMP算法的混合预编码方案有效降低了运算复杂度,且在数据流数目与射频链数目相差较小时,其系统性能更优。     

基于改进粒子群算法的毫米波大规模MIMO混合预编码方案

针对毫米波大规模多输入多输出（MIMO）系统中基于传统粒子群优化（PSO）算法的混合预编码方案,在迭代后期收敛速度较慢以及容易陷入局部最优值的问题,提出了一种基于改进PSO算法的混合预编码方案。首先,随机初始化粒子的位置矢量和速度矢量,并以最大化系统和速率为目标求解初始群体最优位置矢量;其次,更新位置矢量和速度矢量,并随机地选择更新后的两个粒子的个体历史最优位置矢量进行加权求和作为新的个体历史最优位置矢量,从中挑选出若干个使系统和速率最大的粒子,将其个体历史最优位置矢量的加权平均值作为新的群体最优位置矢量,并与之前的群体最优位置矢量比较,经过多次迭代形成最终的群体最优位置矢量即为所求的最佳混合预编码矢量,并对其进行归一化;最后,根据归一化后的混合预编码矢量设计最终的模拟预编码矩阵和数字预编码矩阵。仿真结果表明,与基于传统PSO算法的混合预编码方案相比,所提改进方案在收敛速度与和速率上都得到优化;其收敛速度提高约100%,且性能可以达到全数字预编码方案的90%,因此,该改进方案能够有效提升系统性能且加快收敛。     

基于逐分量软干扰删除的迭代线性检测算法

提出了一种新型基于调制符号的分量进行干扰删除和线性最小均方误差滤波的软输入软输出检测算法,并采用软输入软输出的多入多出MIMO检测器和信道编码串行级联的迭代检测译码IDD结构。该算法充分利用正交调制符号同相分量和正交分量的独立衰落特性,达到检测中更加准确的软干扰删除。外信息转移EXIT图表明该算法比传统的逐符号软删除算法具有更低的临界信噪比。数值仿真也验证了提出的基于调制符号的分量删除的线性检测算法比采用调制符号级的删除具有更优的误码性能,并且仍然具有低复杂度的特性。     

Multiuser detection algorithm based on belief propagation in multiple-input multiple-output systems

In MIMO (multiple-input, multiple-output) systems, signals from differenttransmitting antennas interfere at each receiving antenna and multiuser detection (MUD)algorithms may be adopted to improve the system performance. This paper proposes anovel multiuser detection algorithm in MIMO systems based on the idea of "beliefpropagation" which has achieved great accomplishment in decoding of low-densityparity-check codes. The proposed algorithm has a low computation complexityproportional to the square of transmitting/receiving antenna number. Simulation resultsshow that under low signal-to-noise ratio (SNR) circumstances, the proposed algorithmoutperforms the traditional linear minimum mean square error (MMSE) detector while itencounters a "floor' of bit error rate under high SNR circumstances. So the proposedalgorithm is applicable to MIMO systems with channel coding and decoding. Although inthis paper the proposed algorithm is derived in MIMO systems, obviously it can be appliedto ordinary code-division m     

Performance of Dual-Polarized DSTTD-IDMA system over correlated frequency selective channels

In this correspondence, we present the performance of Dual-Polarized double space–time transmit diversity (DSTTD) aided multiple-input multiple-output (MIMO) interleave division multiple access (IDMA) scheme over correlated frequency-selective channels for downlink communication. DSTTD system is realized by employing two space–time block code units at the base station (BS). We employ two Dual-Polarized antennas both at the BS and mobile stations. We consider maximum-likelihood ratio detection algorithm at the receiver to detect the signals and to mitigate the effects of multiple access interference and multi stream interference. We implement iterative type turbo decoding algorithm to enhance bit error rate (BER) performance. We evaluate the performance of Dual-Polarized DSTTD-IDMA system based on Stanford University Interim channel models and Long-Term Evaluation channel model. Our simulation results reveal that DSTTD-IDMA system with Dual-Polarized antenna requires higher SNR than uni-polarized antennas. However, it provides the advantage of replacing two uni-polarized antennas by a single Dual-Polarized antenna.     

低复杂度的大规模MIMO上行链路软输出信号检测

针对信道矩阵维度高以及接收信号复杂的情况,提出了一种适用于大规模MIMO系统上行链路信号检测的混合迭代算法,即结合自适应阻尼雅克比(damped Jacobi,DJ)算法和共轭梯度(conjugate gradient,CG)算法。首先利用CG算法为自适应阻尼雅克比迭代算法提供有效的搜索方向;随后提出切比雪夫方法消除松弛参数对信号检测的影响,在降低算法复杂度的同时加快收敛速度;最后,利用信道编译码中的比特似然比近似求解软信息,以提升检测性能。通过理论分析算法的复杂度,仿真在不同判决方式下对不同检测算法进行误码率对比,并对混合迭代算法的收敛进行了分析。仿真结果表明,混合迭代算法在少量迭代次数下快速收敛并近似达到最佳MMSE检测性能,且算法复杂度远低于MMSE算法。     

上行多用户MIMO系统检测算法及抗远近效应研究

上行多用户MIMO通信系统必须抑制用户间的共信道干扰,本文提出了一种基于最大信号干扰噪声比准则的多用户干扰抑制算法,并且给出了其在存信在道估计误差时的改进算法。与BD算法相比,该算法考虑了噪声的影响,性能有较大的提升。然后提出了一种信号重组方法将Alamouti空时编码用于上行多用户系统中,以进一步提升系统的检测性能。最后针对存在远近效应时算法的局限性,提出了一种分组优化算法,以保证各用户均能达到所期望的容量。仿真结果表明本文所提算法具有优异的性能。     

Dual-turbo receiver architecture for turbo coded MIMO-OFDM systems

This paper presents a novel architecture of iterative receivers with two layers of iterations for turbo coded multiple-input and multiple-output orthogonal frequency-division multiplexing(MIMO-OFDM)systems,where soft messages are passed not only between the MIMO detector and the turbo decoder,but also between the two component decoders within the turbo decoder.We first derive the factor graph representation of a turbo coded system as a basic building block for developing the iterative receivers.Then,a new soft message passing schedule over the factor graph is proposed,resulting in the proposed dual-turbo receiver architecture(DTRA).In DTRA,the MIMO detector and the turbo decoder work concurrently,and the soft messages for both layers of iterations are updated instantaneously,instead of the block-based exchange of soft messages in the conventional iterative receivers.In so doing,the processing latency can be greatly reduced while low computational complexity can be achieved.     

Performance optimization of iterative receiver for wireless communications based on realistic channel conditions

Adopting orthogonal frequency division multiplexing (OFDM) to low-density parity check (LDPC) coded multiple-input multiple-output (MIMO) is attractive scheme for wireless communication systems. An iterative receiver design for LDPC coded MIMO-OFDM system is proposed as the foundation for enhancing the wireless link performance can deliver the coverage, speed, throughput and reliability. However, in previous works, evaluations are basically assumed for a certain channel scenario and it is inefficient in incorporating different channel scenarios. The aim of this paper is to improve the system range for equivalent error rate, while not significantly increasing system complexity compared to conventional iterative receiver solution under realistic channel environment. We show that our proposed iteration adaptation at receiver can considerably adopt the system to realistic change environment, and reach very high reliability. Simulations of our optimization reveal superior error rate performance and lower computational cost vs. conventional LDPC coded MIMO OFDM system. Our simulation results also capture the effects of realistic vs. typical channel fading types (i.e., Rician vs. Rayleigh, respectively) and fading parameter models (average vs. random azimuth spread and K factor) on system performance and complexity.     

多用户CDMA系统中Turbo-BLAST迭代检测算法

将V-BLAST结构和CDMA技术相结合,构造了多用户CDMA系统模型,提出了一种联合多用户检测和Turbo迭代思想的多用户检测算法.该方案首先利用解相关算法对接收信号进行空时多用户检测.以去除用户间干扰.然后再对期望用户的接收信号进行软干扰抵消迭代检测,以去除天线间干扰.解相关后数据检测仅和单个用户的天线数目有关,算法复杂度较低.仿真结果表明,构造的空时多用户模型可使各用户检测相对独立,有利于已有单用户Turbo-BLAST方案的应用.     

Performance of multiuser CDMA system with space-time block coding in MIMO Rayleigh fading channels

In this paper, by introducing orthogonal space-time coding scheme, the multiuser CDMA systems with different space time codes are given, and corresponding system performance is investigated over Rayleigh fading channel. A low-complexity multiuser receiver scheme is developed for space-time coded CDMA systems. The scheme can make full use of the complex orthogonality of space-time coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, average bit error rate (BER) of the system is derived in detail, and tight closed-form approximation expressions of BER are attained. Simulation results on average BER are in agreement with the theory analysis. The results show that the proposed scheme can achieve almost the same performance as the existing scheme. Moreover, on the condition of same system throughput and concatenation of channel code, the given full-rate space-time coded CDMA system has lower BER than the full-diversity space-time coded CDMA systems.     

STBC MC-CDMA系统自适应MBER多用户检测算法

针对MC-CDMA(Multicarrier code division multiple access)系统,描述了其时变多径衰落环境下采用空时分组编码(Space-time block coding,STBC)的同步上行链路模型,提出一种基于最小误比特率(Minimum biter-ror rate,MBER)的多用户检测算法。利用内核密度估计和梯度下降的方法,推导了该算法自适应实现形式。对具有2个发射天线和2个接收天线的STBC MC-CDMA同步上行链路系统进行了自适应MBER检测算法的计算机仿真。结果表明:当系统负荷较小时,该算法误码性能较好;当系统负荷较大时,该算法误码性能有所下降,但仍然优于具有类似计算复杂度的MMSE(Minimum mean squared error)自适应检测算法。