Carrier Frequency Offset Compensation for an Interleaved OFDMA Uplink

This paper reports an investigation of the carrier frequency offset （CFO） compensation in the uplink of the orthogonal frequency division multiple access （OFDMA） system with interleaved subcarrier assignment. The presence of CFOs between the transmitters and the uplink receiver will destroy the orthogonality among the different subcarriers, resulting in inter-carrier interference and multiuser interference. This paper proposes a pseudoinverse CFO compensation method based on the signal structure. The proposed method can compensate the CFOs of all users simultaneously and isolate the signals from all users at the same time. Compared with the existing CFO compensation methods, the new method provides a considerable signal-to-noise ratio gain on the bit error rate performance and has a relatively low implementation complexity.     

基于压缩感知理论的频偏估计算法

针对基于交织子载波分配方式的OFDMA上行链路系统的频偏估计问题,提出了一种基于压缩传感理论的频偏估计算法.首先,利用频偏分布稀疏特性,构造出了一种具有稀疏结构的频偏估计模型;根据压缩感知理论,把OFDMA系统中频偏参数估计问题转化为凸优化问题并利用CVX求解最优稀疏向量;然后利用稀疏向量的非零元素位置有效地估计出系统中所有用户频偏信息.所提算法避免了子空间算法中特征值分解等复杂处理过程,从而更具有一定的实用性.仿真结果验证了所提算法的有效性.     

OFDMA系统中基于有限反馈的资源公平调度算法

OFDMA是下一代无线通信系统中在下行链路上实现大容量通信的一种有前途的技术,其中的关键技术之一是在共享信道的用户间公平合理地分配子载波和功率。分析了功率约束下系统最大吞吐量的实现方法,提出了一种基于有限反馈的资源公平调度算法,这种算法具有系统所需反馈信息量少、用户间公平性好等性能,并通过仿真进行了验证。     

An iterative interference cancellation based frequency offset estimation method for OFDMA uplink systems

In this paper, Moose scheme is used for frequency offset estimation in OFDMA uplink svstems due to that the signals from different users can be easily distinguished in frequency domain. However, differential multiple access interference （MAI） will deteriorate the frequency offset estimation performances, especially in interleaved OFDMA system. Analysis and simulation results manifest that frequency offset estimation by Moose scheme in block OFDMA system is more robust than that in interleaved OFDMA systern. And an iterative interference cancellation method has been proposed to suppress the differential MAI interference for interleaved OFDMA system, in which Moose scheme is the special case of the number of iteration is equal to one. Simulation results demonstrate that the proposed method can improve the performance with the increase of the number of iterations. In consideration of the performance and complexity, the proposed method with two iterations is selected. And the full comparison results of the proposed iterative method with two iterations and that with one iteration （conventional Moose scheme） are given in the paper, which sufficiently demonstrate that the performance gain can be obtained by the interference cancellation operation in interleaved OFDMA system.     

基于QoS保证的协作OFDMA系统无线资源分配算法

现有基于中继协作的正交频分多址接入(orthogo-nal frequency division multiple access,OFDMA)系统的无线资源分配算法主要面向单一业务和用户需求。该文研究了基于服务质量(quality of service,QoS)保证和异质业务的协作OFDMA系统无线资源分配问题,建立了以最大化系统效用函数为目标的模型,联合了功率控制、载波分配和中继选择。对于具有指数阶复杂度的原混合整数规划问题,通过引入QoS价格因子,将其转化为一个凸优化问题,并且提出了一个基于双层对偶分解的资源分配算法。仿真结果表明:该方法能显著提高系统对异质业务的支持能力,并保证用户之间的公平性。     

正交频分复用系统中采用离散导频的频偏估计方法

针对采用正交频分复用(OFDM)调制的欧洲数字电视地面广播系统，提出了采用离散导频的载波频偏估计方法。将接收信号中的离散导频与接收机本地生成的离散导频进行相关运算，由相关峰值的偏移量求得整数倍载波频偏，由相关峰值的相位求得每个符号的绝对相位偏转量，再由相邻两个符号的绝对相位偏转量之差求得单个符号时间间隔内的相位偏转，从而得到小数倍载波频偏。仿真结果表明，与传统的采用连续导频的载波频偏估计方法相比，在高斯白噪声信道和慢衰落信道下，采用离散导频的载波频偏估计方法的性能有明显的提高；在快衰落信道中性能则稍差，但仍然保持在系统性能允许的误差范围之内。将离散导频用于载波频偏估计可以提高系统的频谱利用率。     

基于子空间的交织OFDMA上行载波频偏估计

为了实现采用交织子载波分配方法的正交频分多址(orthogonal frequency division multiplexing access,OFDMA)上行链路多个用户频偏的联合估计,提出一种基于子空间的两阶段频偏搜索方法。由于多重信号分类法(multiple signal characteristic,MUSIC)的采用,使得该方法具有较高的精确度,并且该方法不需要知道接入的用户个数及用户所占用的子信道;因此适用于随机分配子信道的情况。仿真结果表明:当信噪比大于5 dB时,其标准均方根误差小于子载波间隔的1%,满足宽带无线接入系统关于载波频率偏差应小于子载波间隔2%的频率同步要求。     

基于子空间的交织OFDMA上行载波频偏估计

为了实现采用交织子载波分配方法的正交频分多址(orthogonal frequency division multiplexing access,OFDMA)上行链路多个用户频偏的联合估计,提出了一种基于子空间的两阶段频偏搜索方法。由于多重信号分类法(multiple signal characteristic,MUSIC)的采用,使得该方法具有较高的精确度。并且该方法不需要知道接入的用户个数及用户所占用的子信道,因此适用于随机分配子信道的情况。仿真结果表明:当信噪比大于5dB时,其标准均方根误差小于子载波间隔的1%,满足宽带无线接入系统关于载波频率偏差应小于子载波间隔2%的频率同步要求。     

基于集成神经网络的信道估计方法研究

为解决噪声以及信号干扰等因素严重影响接收端信道估计的问题,提出一种基于集成神经网络的信道估计方法,利用多个改进后的神经网络来提取带噪导频信号与原始导频信号之间的非线性关系模型,根据其输出误差来计算差异度值,并结合差异度对其进行集成,得到训练完成的集成神经网络模型,通过集成神经网络模型来获取信道估计结果;与最小二乘(least squares,LS)估计方法相比,该方法不仅可以提高通信的可靠性,而且还能减少导频开销提高通信有效性;在不同的调制方式下,当误码率相同时,算法所需的信噪比LS算法均要更低;基于正交频分复用(orthogonal frequency division multiple,OFDM)通信系统进行仿真,结果证明,该方法具有优良的性能。     

多业务正交频分复用多址系统中的机会公平调度算法

研究了宽带正交频分复用多址(OFDMA)系统中存在多种不同业务时的无线资源管理问题,给出了多业务情况下基于效用公平的公平调度算法.仿真结果表明,基于效用公平的算法,可以保证各用户间的吞吐量符合比例公平原则,并能明显增加系统总吞吐量.     

正交频分多址接入系统的上行载波同步跟踪方法

为了解决上行正交频分多址系统中频率偏差导致多用户干扰和载波间干扰的问题,提出了一种载波同步跟踪方法。该方法使用了时频同步跟踪环路,从数据子载波提取相位误差,并利用频域插值补偿多个用户的估计频偏。该方法只需要一个快速Fourier变换(FFT)单元,降低了系统实现复杂度。仿真结果表明:该方法对不同的子载波分配方式具有鲁棒性,与无频偏系统的理想接收性能相比,误码率性能损失小于0.5 dB。此外,该方法可以在10~20个正交频分复用(OFDM)符号内快速收敛。与传统的导频辅助跟踪方法相比,提高了频谱利用率,抗噪声和抗多径衰落性能有明显改善。     

Guardband Analysis for Distributed OFDMA with User Heterogeneity

This paper presents an in-depth analysis of the interference strength and required guardband width between coexistent users for distributed orthogonal frequency division multiple access (OFDMA).In dynamic spectrum access networks,the cross-band interference between spectrally adjacent users is considered harmful with frequency guardbands inserted between spectrum blocks to eliminate the interference.However,the strength of the cross-band interference depends heavily on the user heterogeneity in different OFDM configurations.The cross-band interference due to the three user heterogeneity artifacts of power heterogeneity,sampling rate heterogeneity,and symbol length heterogeneity is investigated to determine the required guardband width.Analytical and simulation results show that the greater user heterogeneity requires larger guardbands with the sampling rate heterogeneity having the greatest effect.These results can be used to assist the design of spectrum allocation strategies.     

多小区OFDMA系统中低开销的基站协作资源分配算法

基站协作是多小区正交频分多址接入(OFDMA)系统中降低共信道干扰的有效手段。为了降低收集各小区信息所需的开销,提出一种新的基站协作资源分配算法。算法由各基站计算本小区的业务负荷及所有子信道对本小区的价值,并发送至中心节点。根据这两类信息,资源首先由中心节点分配至各小区,再由各基站分配至用户。该算法的开销仅约为现有方法的2/U(U为协作小区的总用户数)。与无基站协作的方法相比,该算法仍可获得30%以上的用户容量或吞吐量增益。结果表明:本算法兼具实用性和有效性,有望应用于新一代移动通信系统。     

Performance evaluation of the fixed relay in OFDMA systems

Performance of fixed relays in orthogonal frequency division multiple access (OFDMA) systems, especially the coverage and capacity performance at the cell edge, is evaluated in this paper.Two methods, theoretical analysis and calculation and Monte Carlo simulation, are used for the evaluations.By theoretical analysis and calculation, frequency efficiency equation of a relay is introduced and numerical results are calculated.Monte Carlo simulation results also verify that the calculation method is reasonable.The evaluation shows that a relay can increase system performance to a certain level if it is designed appropriately, otherwise it will be harmful for the system performance, even to reduce it.     

用于跳频分量选取的修正适应度距离比粒子群算法

跳频信号参数估计是跳频信号截获、干扰的前提,而传统Cohen类时频分析方法存在核函数选择的瓶颈.结合匹配追踪和智能计算的思想,将多峰函数粒子群优化算法引入跳频信号时频分析领域.在分析粒子适应度和粒子间距2个影响粒子搜索行为的关键因素的基础上,提出了基于改进的适应度-距离比测度的多峰函数粒子群优化算法,并应用于跳频分量自适应选取.该方法不需要跳频信号的任何先验知识和粒子群小生境参数的人为设置.理论分析和仿真结果表明,与基于环形拓扑结构、单一共享适应度信息的粒子群优化算法相比,算法成功率和参数估计精度进一步改善,该方法的邻域搜索机制和跳频分量选取具有可行性和有效性.     

802.16e系统周期测距的软件设计和实现

测距作为WiMAX上行链路调整时间偏置、功率信息和载波频率的一种方法,在系统接入和通信过程中起着重要作用。深入研究了基于ARM处理器的802.16e系统正交频分多址(orthogonal frequency division multiple ac-cess,OFDMA)物理层的周期测距的软件设计与实现,给出了802.16e系统OFDMA物理层的周期测距算法和流程、周期测距码的发射和检测原理以及周期测距模块的C语言设计。在搭建的测试平台上进行链路测试,结果表明此方案是可行的。     

超宽带系统中盲自适应降秩接收机

针对超宽带系统中的多址干扰和码间干扰问题,提出了一种低复杂度的盲自适应接收机,该接收机首先采用多级维纳滤波算法抑制多址干扰并提取期望信号各多径分量;再进一步采用紧缩近似投影子空间跟踪方法估计信道并进行最大比合并,提高输出信干噪比。仿真结果表明,其误码性能优于匹配滤波器、传统Rake接收机、解相关Rake接收机和基于恒模算法的自适应接收机,且收敛速度较快、复杂度较低。     

A Novel Minimum Output Variance Estimator for Carrier Frequency Offset in OFDM Systems

In orthogonal frequency-division multiplexing (OFDM) systems, the carrier frequency offset (CFO) destroys the orthogonality among subcarriers which degrades system performance. Various CFO estimation methods have been developed to compensate for the CFO at the receiver. This paper describes a novel minimum output variance method for OFDM systems with CFO in additive white Gaussian noise channels. This method utilizes the phase and the amplitude of the received signal and reduces the mean square error of the CFO by about 3 dB compared with the original minimum output variance method.     

A new satellite to satellite tracking algorithm from Doppler-shifted frequency measurements

A new satellite to satellite tracking (SST) algorithm from Doppler-shifted frequency measurements is proposed. The estimation principle is demonstrated and the mathematic model of SST is established. The state estimation methods for a user (the cooperative case) and target satellites (the non-cooperative case) are presented based on particle swarm optimization (PSO). The Cramer-Rao lower bounds (CRLB) are deduced as well. Performance of the new algorithm is validated through computer simulations, which proved that the proposed method is effective in terms of the estimation quality compared with CRLB and superior in accuracy to the Bearings-Only (BO) method in almost all simulation cases except for the case that an enough long tracking arc-length is obtained for a user satellite.     

基于傅立叶变换的OFDM信道估计方法研究

分析了无线OFDM 系统中基于傅立叶变换的信道估计方法,提出了在低信噪比情况下使用LMMSE估计的一种改进方法和在高信噪比情况下使用不需要先验信息的LS估计的改进方法。仿真结果表明，在无线多径慢衰落信道条件下，该改进方法都能够有效对抗频率选择性和先验信息的估计偏差对信道估计的影响，在估计性能与算法复杂度之间取得良好折衷。