基于TD-LMS算法的OFDMA上行链路载波频率偏移消除

提出了一种时域自适应最小均方误差算法(TD-LMS)来消除正交频分多址接入(OFDMA)系统上行链路的各载波频率偏移引起的干扰.该算法首先对OFDMA系统接收端的时域信号进行估计,并利用估计量来预消除载波频率偏移,然后在时域内进行残留频率偏移消除.仿真结果表明,在相同的仿真条件下,与最小二乘算法相比,该算法可以获得3dB的增益,且对各用户的频率偏移有明显的消除效果.     

基于TD-NLMS的航空移动通信OFDM系统载波频率偏移消除

针对航空移动通信中时变的信道环境和多普勒频移造成的子载波间干扰(ICI),提出了一种时域自适应归一化最小均方误差算法(TD-NLMS)来消除航空移动信道正交频分复用(OFDM)系统中载波频率偏移引起的干扰.该算法首先对接收的时域信号进行频偏预估计和预补偿,然后对剩余载波频移进行消除.仿真结果表明:在航空移动信道环境中,新算法可以很好的对旋转相位进行补偿,与最小二乘算法相比,误码率性能有明显提高,可以实现对载波频率偏移的消除.     

基于求根MUSIC算法的低复杂度OFDMA频偏盲估计

为了解决OFDMA系统频率同步困难的问题,针对子载波交织分配的OFDMA上行链路提出了一种基于多项式求根的多用户载波频偏盲估计算法.首先对接收信号的协方差矩阵进行特征值分解,并利用噪声子空间的特征向量构造一个多项式,然后求解最接近于单位圆的K个根来获得各个载波频偏.此算法的优点是能够在一个OFDMA符号块内同时估计出所有用户的载波频偏而无需信道状态、训练序列和导频等先验信息,同时在低信噪比下也具有良好的准确性.通过仿真表明,相对于一般的谱峰搜索方法,算法不仅减少了噪声对频偏估计的影响,而且有着更低的计算复杂度和更高的分辨率.     

稀疏信道下基于变换域的上行OFDMA信道估计方法

单用户正交频分复用(OFDM)系统通常使用插入的频域导频获得信道频域响应(CFR),将此CFR变换到时域进行滤波以获得更准确的信道估计。上行正交频分多址接入(OFDMA)系统中由于每个用户信号占用不同的子载波且经过的信道不同,使用上述方法会由于窗函数畸变产生能量泄漏。该文提出一种时域滤波频域补偿(TFFC)方法,使用补偿向量对时域滤波后的CFR进行补偿,降低变换域算法中由于畸变引起的能量泄漏,并给出在稀疏信道条件下该补偿向量的简化解。仿真表明:采用该方法,上行OFDMA信道估计的性能得到很大改善。     

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.     

一种改进的MIMO-OFDM系统频偏估计方法

针对传统的2个训练符号的载波频偏估计算法提出一种改进算法,并设计出一种新的频偏估计器对多入多出正交频分复用(MIMO-OFDM)系统的不同信道的整数频偏和小数频偏进行估计.该算法仅利用单个训练符号来进行频偏估计,其训练符号采用正交性良好的Walsh序列来设计,用以区分不同的信道;利用同一训练符号内相邻的偶数子载波上数据的差分关系完成整数频偏估计.仿真结果表明,新的频偏估计器可以获得较好的载波频偏估计性能.     

基于多臂赌博机的卫星通信系统子载波分配算法

为了提升卫星通信系统的频谱效率,在卫星系统采用正交频分多址(Orthogonal Frequency Division Multiple Access, OFDMA)传输技术的情况下,提出了一种基于多臂赌博机(Multi-Armed Bandit, MAB)的子载波分配算法。首先,建立基于OFDMA的卫星系统上行链路多用户传输模型。然后建立以用户总速率最大化为目标,以用户最大发射功率和用户服务质量为约束条件的资源分配问题。接着,利用MAB能在环境信息部分未知时在线学习摇臂选择策略的特性来求解该优化问题,并获得子载波分配方案。仿真结果表明,所提算法能实现系统子载波的自适应分配,同时用户总速率与贪婪算法在已知信道状态信息下获得的用户总速率几乎相同。     

交织正交频分多址上行频偏和定时同步联合盲估计算法

提出了一种基于功率谱叠加的交织正交频分多址系统上行链路载波频偏和定时同步联合估计算法.该算法利用同一用户在各个子载波上具有相同载波频偏的特点,采用一个未受之前符号污染的循环前缀样值,通过抽取自相关矩阵,将属于同一用户的子载波在功率谱上进行叠加,得到更尖锐的谱峰,从而实现对载波频偏的精确估计.对不同时刻估计到的谱峰量级进行比较,可同时实现定时同步.仿真结果表明,算法在估计精度上明显优于循环平稳算法,当一帧中的符号数较大时,算法的估计精度略优于子空间法,且计算复杂度更低.     

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。     

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.     

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.     

Interference-Cancellation-Based Carrier Frequency Offset Estimation for OFDMA Uplink Transmissions

A carrier frequency offset (CFO) estimator was developed based on an interference cancellation scheme for an orthogonal frequency division multiplex access uplink. An initial CFO estimate was first obtained based on the received training signals at each user’s prescribed subcarrier positions. Then, the received training signals were compensated by using the initial CFO estimates in the frequency domain and the multi-user interferences were estimated. Finally, the interference-cancelled training signals were...     

一种基于PN序列的上行多用户OFDM系统载波频偏估计算法

针对多用户正交频分复用(OFDM) 系统上行链路中的载波频偏估计问题, 提出一种基于伪噪声(PN)序列的载波频偏(CFO)估计算法。该算法将不同相位的PN序列作为各个用户的训练序列, 利用训练序列良好的自相关性估计出存在CFO 情形下不同用户的信道参数, 再根据两个训练周期内信道参数的相位变化获得各用户的CFO估值。理论分析和仿真结果表明本算法具有优 良的估计性能。     

A time domain multiple-CFOs and CIRs estimation algorithm over wireless multimedia sensor networks

Channel parameters estimation in an orthogonal frequency division multiple access(OFDMA)systemfor the receiver station is a multi-dimensional(MD)optimization problem,because every user node has aseparate local oscillator and every transmitter to receiver link has individual carrier frequency offset(CFO)and channel impulse response(CIR)parameters .In order to reduce the computational complexityfor MD optimization,a time domain CFOs and CIRs estimation algorithm over the OFDMA based wirelessmultimedia sen...     

基于LTE-Advanced上行链路的多级迭代干扰消除检测算法

针对先进的长期演进(long term evolution advanced,LTE-Advanced)上行链路多输入多输出(multiple-input multiple-output,MIMO)单载波频分多址(single carrier frequency division multiple access,SC-FDMA)系统载波频率偏移(carrier frequency offset,CFO)的影响,提出了基于多级迭代干扰消除检测算法.将传统的单级串行干扰消除(successive interference cancellation,SIC)和并行干扰消除(parallel interference cancellation,PIC)进行混合迭代形成多级的迭代干扰消除检测算法以降低MIMO SC-FDMA系统的误比特率.理论分析和仿真结果表明两级PIC迭代检测算法和SIC+ PIC混合迭代检测算法都能实现MIMO SC-FDMA系统CFO干扰消除的目的,降低了MIMO SC-FDMA系统的误比特率,提高了系统的性能.     

一种相关编码正交频分复用系统的载波频偏估计算法

基于相关编码正交频分复用(OFDM)系统，提出了一种新的数据辅助载波频偏估计技术，利用相关编码OFDM系统的频域幅度特性估计载波频率偏移，增大了频偏估计的跟踪范围，同时采用改进的迭代估计剩余频偏方法，消除载波间干扰对频偏估计的影响，提高了估计精度．仿真结果表明，与传统的基于数据辅助频偏估计技术相比，该技术的跟踪估计范围增大为(-1，1)，且在较高信噪比的估计均方误差明显降低。     

Coordinated multipoint transmission and reception based on multicarrier time division multiple access

Coordinated multipoint ( CoMP) transmission and reception is a technique to reduce intercell interference and increase the cell edge throughput. In order to get maximum CoMP gain the networks and terminals involved in CoMP communication should be robust against time and frequency offset due to asynchronism between terminals and base stations. However, the modulation techniques proposed in LTE-Advanced standard (SC-FDMA and OFDM A) are quite sensitive to frequency offset because of DFT/IDFT used in the modulation systems, which brings difficulties for commercial implementation of CoMP technique based on LTE-Advanced. To relax the synchronization requirement in CoMP system, in this paper we introduce a CoMP technique based on a new multicarrier modulation scheme-multicarrier time division multiple access (MC-TDMA). In comparison with SC-FDMA and OFDMA, the MC-TDMA modulation can significantly improve the CoMP performance in case of carrier frequency offset. Simulation shows that at 20% of carrier frequency offset the CoMP system with MC-TDMA modulation can also keep high performance, while the system with SC-FDMA and OFDMA is totally lost in work.