A Novel Genetic Algorithm for Adaptive Resource Allocation in MIMO-OFDM Systems with Proportional Rate Constraint

This paper considers base station allocation of subcarriers and power to each user to maximize the sum of user data rates, subject to constraints on total power, bit error rate, and proportionality among user data rates in Multiple Input Multiple Output Orthogonal Frequency Division Multiple access (MIMO-OFDMA) system. Previous allocation methods have been iterative nonlinear methods suitable for offline optimization. The subcarrier allocation is tackled using a novel algorithm which combines the aspects of both deterministic and Genetic Algorithms (GA). This modified GA gave very encouraging results as can be seen from the simulation results shown. The simulation results show a marked improvement in the performance of the algorithm as the number of users increase. The capacity attained from the subcarrier allocation scheme generated by our algorithm is found to be comparable to that attained by previous algorithms.     

单小区多用户下行OFDM系统资源分配算法研究

多用户正交频分复用(OFDM)系统中,充分利用多载波系统的多用户分集进行合理无线资源分配,能够显著提高系统容量和最大限度提高频谱利用率。经过广泛的研究,很多有效资源分配算法已经被提出来。重点讨论了单小区多用户OFDM系统关于子载波、比特及功率等无线资源的分配问题,介绍现有的研究成果,包括常见的模型及求解方法,并介绍近期的研究热点,包括多小区系统、多入多出(MIMO)系统等。     

一种多用户MIMO/OFDM下行链路保障QoS的自适应传输机制

在用户QoS参数限制下,该文提出一种在多用户MIMO/OFDM下行链路使系统总速率最大的资源分配机制。基站应用空分多址接入,使得每个子载波可支持多个用户,应用线性预编码方法抵消用户间的干扰,提出保障QoS的自适应功率、比特分配方案。该文并提出两种可应用到实际系统的低复杂度的比特加载和比特去除算法,仿真结果表明,该两种方法性能可非常接近最优遍历算法。     

Loading Schemes for Downlink OFDMA Systems

In this paper we study the subcarrier and bit allocation strategies for downlink OFDMA system.Our opti-mization objective is to find optimum subcarrier and bit assignment minimizing the total transmitted power with the con-straints on BER and data rate for all users.We divide this problem into three steps:resource allocation,subcarrier assign-ment and single-user power and bit allocation.For the first two steps we propose new algorithms.Various loading schemesconstitute by combining these algorithms as well as algorithms proposed in Ref.[6].Simulation results demonstrate thatour proposed suboptimal loading scheme can achieve performance closer to the near optimal algorithm in Ref.[8]withmuch lower complexity than schemes in Ref.[6].     

A Novel Circulant Approximation Method for Frequency Domain LMMSE Equalization

The coefficients of a Linear Minimum Mean Square Error (LMMSE) equalizer for a stationary random signal are defined by a Toeplitz system. The Toeplitz structure can be exploited to reduce computational complexity. In this paper we investigate the Levinson and Schur algorithm, as well as circulant embedding and circulant approximation methods applied to the Preconditioned Conjugate Gradient (PCG) method and Frequency Domain Equalization (FDE). We develop a novel circulant approximation method which improves the performance/complexity tradeoff. We show that the optimal choice of algorithms largely depends on the antenna configuration. Investigated configurations are Single Input Single Output (SISO), Single Input Multiple Output (SIMO) and Multiple Input Multiple Output (MIMO). All considered algorithms are benchmarked in terms of implementation complexity and capacity achieved by a High Speed Downlink Packet Access (HSDPA) receiver in a multipath fading scenario.     

下行多用户MIMO-OFDMA/SDMA系统动态资源分配

该文对下行多用户MIMO-OFDMA/SDMA系统动态资源分配算法进行了研究,在满足各种约束条件的前提下,以最大化系统吞吐量为目标建立了相应的优化模型。由于最优解难以获得,将整个优化过程分两步完成,第1步定义了一个用于度量配置多根天线的用户空间兼容性的指标,并根据该指标提出了相应的调度算法;第2步提出了两种次优的资源分配算法。仿真结果表明,所提算法优于传统的随机调度算法,与功率复用策略结合时,所提算法的性能接近于基于用户选择的最优分配算法的性能。     

Designing Fast Fourier Transform Accelerators for Orthogonal Frequency-Division Multiplexing Systems

Designing accelerators for the real-time computation of Fast Fourier Transform (FFT) algorithms for state-of-the-art Orthogonal Frequency-Division Multiplexing (OFDM) demodulators has always been challenging. We have scaled-up a template-based Coarse-Grain Reconfigurable Array device for faster FFT processing that generates special purpose accelerators based on the user input. Using a basic and a scaled-up version, we have generated a radix-4 and mixed-radix (2, 4) FFT accelerator to process different length and types of algorithms. Our implementation results show that these accelerators satisfy not only the execution time requirements of FFT processing for Single Input Single Output (SISO) wireless standards that are IEEE-802.11 a/g and 3GPP-LTE but also for Multiple Input Multiple Output (MIMO) IEEE-802.11n standard.     

Orthogonal Discrete Frequency-Coding Waveform design for MIMO radar

Design of orthogonal code sets with ideal correlation properties is crucial for orthogonal Multiple Input Multiple Output（MIMO）radar.A modified Genetic Algorithm（GA）is proposed to numerically design orthogonal Discrete Frequency-Coding Waveforms（DFCWs）with good correlation properties for MIMO radar.Some of the designed results are presented,and their correlation properties are better than those presented in literatures.The effect of Doppler frequency shift on the performance of these signals is simply investigated.Simulation results and comparisons show that the proposed algorithm is more effective for the design of DFCWs with superior aperiodic correlation properties.     

大规模MIMO系统中收发联合阈值天线选择算法

在大规模多输入多输出(massive MIMO)系统中使用天线选择算法可提高能效和系统吞吐量,然而适用于传统MIMO系统的天线选择算法具有高复杂度,很难用于massive MIMO系统。为优化天线选择算法,以算法复杂度和系统容量为优化目标,提出了收发联合阈值天线选择算法。该算法在发射端使用最大范数双向天线选择算法进行天线选择,在接收端使用分组maxvol算法并通过仿真实验结果的预设阈值进行天线选择。仿真实验表明,收发联合阈值天线选择算法在降低复杂度的同时可以提高系统容量,与递增天线选择算法相比,系统容量最多可提高52.2 bit/s/Hz。提出的天线选择算法可以满足不同天线相关度和信噪比的传输环境。     

CFAR Detectors for MIMO Radars

CFAR (Constant False-Alarm Rate) processors are useful for detecting radar targets in a background for which the parameters in the statistical distribution are not known. A variety of CFAR techniques such as CA (Cell Averaging), Go (Greatest Of), SO (Smallest Of), OS (Ordered Statistics) and ACMLD (Automatic Censored Mean-Level Detector) processors have been proposed for SISO (Single Input–Single Output) radars in a non-homogeneous background. In this paper, conventional CFAR algorithms including CA, SO, OS and ACMLD processors are generalized for MIMO (Multiple Input–Multiple Output) radars. The exact expressions for false-alarm probabilities of the proposed algorithms in a homogeneous background are presented. In addition, the detection performance of the proposed detectors is studied by means of simulation in the presence of interfering targets and also colored Gaussian clutter. Besides, the proposed CFAR processors are compared, and it is shown that the ACML-based algorithm is superior to the other investigated methods.     

Low complexity margin adaptive resource allocation in downlink MIMO-OFDMA system

We study the downlink multiuser Multiple Input Multiple Output-Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) system for margin adaptive resource allocation where the Base Station (BS) has to satisfy individual Quality of Service (QoS) constraints of the users subject to transmit power minimization. Low complexity solutions involve beamforming techniques for multiuser inter-stream interference cancellation. However, when beamforming is introduced in the margin adaptive objective, it becomes a joint beamforming and resource allocation problem. We propose a sub-optimal twostep solution which decouples beamforming from subcarrier and power allocation. First a reduced number of user groups are formed and then the problem is formulated as a convex optimization problem. Finally an efficient algorithm is developed which allocates the best user group to each subcarrier. Simulation results reveal comparable performance with the hugely complex optimal solution.     

OFDM-UWB系统基于用户速率的多用户动态资源分配算法

在原有动态资源分配算法基础上,提出了一种基于用户速率需求的动态资源分配算法。该算法在满足用户数据速率需求和服务质量要求(QoS)的前提下,以用户公平性为原则,分步执行子载波和比特分配来降低系统总的发射功率。首先,通过比较不同子载波对用户速率的影响,引入速率影响因子,对子载波进行分配;然后为每个用户子载波分配比特,并根据用户速率需求进行比特调整。为了进一步降低系统的复杂度,提出了一种通过子载波分组来完成子载波比特分配的方法。仿真结果表明,该算法能够降低系统功耗、误码率和系统复杂度。     

一种低复杂度MIMO-OFDMA系统的自适应子载波分配算法

本篇论文提出一种多用户多输入多输出正交频分复用系统(MIMO-OFDMA)下行链路具有信道变化实时性的动态子载波分配算法.文中采用奇异置分解,将每个子载波的MIMO衰落信道分解为独立的并行子信道,利用子信道通对各子载波容量的求解推导出本文算法.此次优的算法在满足各个用户数据速率和BER要求的同时,能减小发射功率.仿真结果也证明了这一点.     

Reduced Complexity Decoding of Space Time Trellis Codes in the Frequency Selective Channel

An iterative approach is developed for decoding Space Time Trellis Codes (STTCs) in frequency selective Multiple Input Multiple Output (MIMO) channels. The method uses the Partitioned Viterbi Algorithm (PVA) as an equaliser for the MIMO system. It is used iteratively with a STTC decoder that provides soft outputs using the Soft Output Viterbi Algorithm (SOVA). It is shown through simulation that the iterative procedure achieves a performance within 2.0dB of Maximum Likelihood (ML) decoding, at a FER of 10^?2, but suffers a small diversity loss. It is also shown that the complexity of the iterative approach is lower than that of ML decoding.     

多入单出正交空时分组码系统的调制识别

在现代无线通信系统中,采用正交空时分组码(STBC)的多天线发射技术是提高通信速率和可靠性,并且能够实现简单译码的关键技术。该文针对瑞利信道系统模型,提出一种适用于多入单出正交空时分组码(OSTBC)的调制识别算法。该算法通过对接收到的数据进行重排,将多入单出的系统模型转化为类似多入多出的系统模型,并且根据信源的特殊性用最大似然的思想实现调制类型的识别。仿真结果验证了所提算法的有效性。     

WiMAX系统中导频和信道估计

WiMAX系统中物理层多址方案采用了正交频分多址接入(OFDMA),并根据上、下行链路的不同特点,定义了多种导频图案。当OFDMA和多输入多输出(MIMO)技术结合时,导频图案也需要变化来支持多天线。WiMAX系统中MIMO-OFDMA有五种导频模式,包括下行部分使用子信道(DL-PUSC)、下行完全使用子信道(DL-FUSC)、下行可选完全使用子信道(DL-OFUSC)、上行部分使用子信道(UL-PUSC)和上行可选部分使用子信道(UL-OPUSC)。通过分析时域LS、频域LS和基于FFT的信道估计方法下的仿真结果,可以得出每种模式下的最优信道估计方案。     

Use of linear programming for dynamic subcarrier and bit allocation in multiuser OFDM

An adaptive subcarrier allocation and an adaptive modulation for multiuser orthogonal frequency-division multiplexing (OFDM) are considered. The optimal subcarrier and bit allocation problems, which are previously formulated as nonlinear optimizations, are reformulated into and solved by integer programming (IP). A suboptimal approach that performs subcarrier allocation and bit loading separately is proposed. It is shown that the subcarrier allocation in this approach can be optimized by the linear-programming (LP) relaxation of IP, while the bit loading can be performed in a manner similar to a single-user OFDM. In addition, a heuristic method for solving the LP problem is presented. The LP-based suboptimal and heuristic algorithms are considerably simpler to implement than the optimal IP, plus their performances are close to those of the optimal approach.     

多用户OFDM系统的次最优分配算法

本文提出了一种多用户OFDM系统中次最优的自适应载波、比特和能量分配算法。此算法利用各子载波的瞬时特性,在保证各个用户服务质量(QoS)的前提下,通过合理地分配子载波并调整各个子载波调制等级,达到降低总发射功率的目的。该算法相对于最优算法具有简单、公平、高效的特点。仿真实验表明,该算法的性能接近最优算法。     

基于量子遗传算法的多通道通信信号盲反卷积算法研究

本文在分析多输入多输出盲反卷积的网络结构和算法模型的基础上，提出了一种基于输出信号上下文信息的盲反卷积算法，并提出一种采用量子遗传算法的新的优化求解方法，对仿真的通信信号分离的结果表明算法的有效性。     

Rate adaptive resource allocation for OFDM downlink transmission

In this paper, we present a multiuser rate adaptive resource allocation for OFDM downlink transmission. This new algorithm assign one bit at a time to user that has the minimum total power in the subcarrier that requires the least additional power. Simulation results show that the proposed algorithm achieves a higher capacity than previous existing algorithms and distributed the overall capacity more fairly among users.