交织OFDMA上行系统CFO估计算法的研究

文中对OFDMA系统中的子载波分配方法进行了研究,介绍了两种子载波分配方法的原理,对两种子载波分配方法进行了仿真,结果显示在频率选择性衰落信道中交织分配的OFDMA系统要比块分配的OFDMA系统获得更多的频率分集.给出了交织OFDMA系统上行链路的信号结构,由于发射机和接收机之间存在的载波频率偏移(CFO)将会影响子载波间的正交性,对多用户的CFO估计提出了一种估计算法,仿真的结果显示所提出的算法具有较好的性能.     

任意子载波分配OFDMA上行链路CFO估计及补偿方法

正交频分多址(OFDMA)技术是正交频分复用技术(OFDM)的扩展。与OFDM一样,它对载波频偏(CFO)相当敏感。该文针对多用户任意子载波分配的OFDMA上行链路系统提出一种基于导频辅助的CFO估计方法,并在此基础上给出一种低复杂度CFO补偿方法。仿真结果表明,该方法计算复杂度低,性能良好。     

OFDM系统上行链路的一种载波偏差估计算法

通过分析OFDM信号的特点,该文给出了OFDM系统上行链路的一种基于高倍钟采样的载波偏差估计算法.与采用循环前缀的载波偏差估计算法相比,该算法实现复杂度低,算法精度高,受用户子载波数目影响较小,适宜于多用户OFDM系统.计箅机仿真表明该算法具有优良的性能,优于采用循环前缀的载波偏差估计算法.     

Carrier Frequency Offset Compensation with Successive Cancellation in Uplink OFDMA Systems

Similar to OFDM systems, OFDMA systems also suffer from frequency mismatches between the receiver and the transmitter. However, the fact that each uplink user has a different frequency offset makes the compensation more challenging than that of OFDM systems. This letter proposes successive interference cancellation (SIC) for compensating the frequency offset in the uplink OFDMA systems. A decorrelator is used to remove the inter-carrier interference (ICI) within a user's signal and successive cancellation is applied to mitigate the multi access interference (MAI) arising due to the frequency difference among uplink users. The proposed algorithm is shown to eliminate the interference and has a manageable complexity.     

The Effect of Imperfect Carrier Frequency Offset Estimation on an OFDMA Uplink

In the uplink of Orthogonal Frequency-Division Multiple Access (OFDMA) systems, the user carrier frequency offsets result in inter-carrier-interference (ICI) and multipleuser-interference (MUI), leading to a degradation of the bit error rate (BER). This paper treats this uplink scenario and derives the average uplink capacity and the BER using the signal-to-interference-and-noise ratio (SINR) analysis. Adaptive power allocation is suggested to increase the capacity. When the frequency offsets are modeled as zero-mean Gaussian or Uniform random variables, the BER is derived as a closed-form infiniteseries. The series requires at least 50 terms to ensure sufficient accuracy.     

A Non-Pilot Aided Iterative Carrier Frequency Offset Estimator Using Optimal Filtering for an Interleaved OFDMA Uplink System

In an uplink transmission of a coded orthogonal frequency division multiple access (C-OFDMA) system, channel estimation, time and frequency synchronization has to be addressed. For this purpose a control data, i.e. a known training sequence called “preamble” and pilot sub-carriers are used. As an alternative to the classic scheme and in order to maximize the data rate, we propose a non-pilot aided estimator based on an iterative architecture that does not require pilot sub-carriers. Our approach combines 1/ the so-called minimum mean square error successive detector to estimate the signal sent by each user 2/ a recursive method estimating the CFOs. Various algorithms such as the extended Kalman filter, the sigma-point Kalman filters and the extended H _∞ filter are tested and their performances are compared in terms of convergence speed and estimation accuracy. When considering an interleaved OFDMA uplink system over a Rayleigh fading channel, simulation results clearly show the efficiency of the proposed algorithm in terms of CFO estimation and bit error rate performances.     

Joint Estimation of the Timing and Frequency Offset for Uplink OFDMA

Inheriting all the advantages of Orthogonal Frequency Division Multiplexing (OFDM), plus the ability to offer a fine level of bit granularity and dynamic subcarrier allocation for multiuser diversity, the Orthogonal Frequency Division Multiple Access (OFDMA) has emerged as a potential candidate for multiple access technique for future broadband wireless networks. However, the benefits of OFDMA come with stringent requirements on synchronization, especially in the uplink. Unless the timing offsets (TOs) and carrier frequency offsets (CFOs) among users in the uplink are kept under tolerable ranges, inter-symbol interference (ISI), inter-channel interference (ICI) and multi-user interference (MUI) will occur, which degrade the overall system performance severely. Accurate estimation of TOs and CFOs is required for each user, so that they can be accounted for at the user’s side or compesated for at the base station. This paper proposes a novel method to estimate jointly TOs and CFOs in the time-domain for multi-user in the OFDMA uplink. The method is shown to offer good accuracy, while maintaining a reasonable complexity compared to conventional estimation schemes.     

An Iterative CFO Estimation Using MVDR Criterion for Interleaved OFDMA Uplink Systems

This letter presents an iterative carrier frequency offset (CFO) estimator based on the minimum variance distortionless response criterion for interleaved orthogonal frequency division multiple access uplink systems, without using specific training sequences. The proposed estimator iteratively searches for the correct CFO vector by minimizing the objective function using a first-order Taylor series approximation of the CFO vector with the one initially given. However, the proposed estimator is not only can estimate CFO, but also has less computational load. Several computer simulation results are provided for illustrating the effectiveness of the blind estimate approach.     

多小区OFDMA系统频偏补偿算法

针对OFDMA系统对频率偏移敏感的特性,在频率偏移估计的基础上重点研究了多小区OFDMA系统的频率偏移的补偿算法。就三个小区的情形,利用频域和时域两种补偿算法对其基站频率偏移做了小数位的补偿。仿真结果表明：频域补偿的效果比时域补偿好,而作为一种新的尝试,时域补偿所涉及的计算量减小了很多。     

一种提高MTC上行频偏估计的LTE算法

为了解决低复杂度MTC UEs能量消耗的增加,针对LTE/LTE-A基站开发了一种新的基于极大似然(ML)的上行载波频偏估计技术,该方法在低覆盖范围内稳健且准确,提高了MTC UEs的上行能量效率.     

MU-MIMO-OFDM上行频偏与信道联合跟踪

本文提出了一种在MU-MIMO-OFDM （Multiple-User Multiple-Input-Multiple-Output Orthogonal-Frequency-Division-Multiplexing）上行链路中,联合跟踪残留频偏（Residual Carrier Frequency Offset,RCFO）和信道的算法.本算法采用EM （Expectation Maximization）方法求解该非线性问题,并使用变分推断来近似原来复杂的隐变量的后验概率.在估计RCFO时,考虑了信道估计误差的概率分布,从而降低了信道估计误差对跟踪性能的影响.仿真中,本算法达到了较高的跟踪精度,尤其是在高信噪比时没有误差平台问题.     

基于旋转不变技术实现多用户交织OFDM频偏估计

本文提出一种针对多用户交织OFDM载频偏移估计的算法。首先介绍上行链路中交织OFDM的信号结构,利用其周期性质,形成特定的数据矩阵,利用旋转不变技术(ESPRIT)实现载频偏移估计。这种估计方法不需要利用任何训练序列或导频信号,进一步提高了系统频带利用率,降低了计算复杂度。仿真表明,该估计算法在信噪比大于零的情况下也能获得较好的频偏估计。     

WiMAX OFDMA初始测距中的多用户频偏估计

测距过程是移动WiMAX标准中的重要过程,用于解决远近效应及同步问题。该文针对WiMAX OFDMA上行链路的初始测距,提出了两种适用于多用户的载波频偏估计方法。方法1采用参考测距信号与接收信号的时域相关提取期望测距信号,并利用相关结果的相位估计测距用户的频偏;方法2采用参考测距信号与接收到的两个相邻OFDM符号的频域相关提取期望测距信号,并利用两次结果的相位差估计测距用户的频偏。仿真实验证明基于频域相关的方法更适合于在一个测距时隙内存在多个测距用户的情况,并且不易受定时偏差估计误差的影响。     

Low Complexity Carrier Frequency Offset and Channel Estimation for Multiuser OFDMA Networks

Wireless Personal Communications - Multiple carrier frequency offsets exist in the orthogonal frequency-division multiple access (OFDMA) uplink receivers, and consequently induce inter-carrier...     

非数据辅助的QAM信号载波频偏估计算法

研究了正交幅度调制（Quadrature Amplitude Modulated ,QAM）信号的非数据辅助载波频率偏移估计算法。针对一些算法主要适用于低阶QAM信号以及计算复杂度较高等问题,提出一种基于加权相位直方图的载波频偏估计算法。该算法通过分析零频偏下的相位概率密度函数与加权相位直方图的关系,采用多级估计方法,对该相位直方图二阶矩的峰值进行测量,从而得到频偏估计值。进一步地,本算法通过联合快速傅里叶变换（Fast Fourier Transform,FFT）算法实现多级估计过程,从而简化计算过程降低计算复杂度。仿真结果表明,信噪比较高时,该算法在无信噪比、星座图以及前导信息等辅助信息条件下同样具有较好的估计性能。      

Improved Carrier Frequency Offset Estimation in OFDM Systems

1　Introduction　OrthogonalFrequencyDivisionMultiplexing(OFDM )isaneffectivetransmissionschemetocombatmultipathfading[1 ] .Byinsertingaguardin tervalbetweensymbolblockscalledcyclicprefix ,theInterSymbolInterference (ISI)canbemitigat ed.OFDMwasadoptedasthemodulationschemeforaDigitalAudioBroadcasting(DAB)system[2 ]andADSL (AsymmetryDigitalSubscriberLoop) [3]andwasalsoproposedastheterrestrialHDTVtransportinEurope[4] .　OFDMsystemsareverysensitivetocarrierfre quencyoffset,andcarrie…     

Blind Estimation of Carrier Frequency Offset and DC Offset for OFDM Systems

In this letter, a blind joint carrier frequency offset and DC offset (DCO) estimator for OFDM systems is proposed. By exploiting the underlying subspace of the received OFDM signals after the time-domain-average based coarse DCO cancellation, the proposed estimator can achieve excellent performance, which is demonstrated by simulations.     

Blind Residual Carrier Frequency Offset and Timing Offset Estimation Using Improved Minimum Output Variance Approaches in Uplink MC-CDMA Systems

This paper deals with blind residual carrier frequency offset (CFO) and timing offset (TO) estimation based on minimum output variance (MOV) criterion without devoting training sequence and pilot symbol for uplink multicarrier-code division multiple access (MC-CDMA) systems. It has been shown that the performance of MOV estimator is degraded because the effect of noise and wideband spread-spectrum signals. In conjunction with spreading code-aided and subspace projection techniques, we present an improved code-aided MOV (ICMOV) estimator to achieve the high accuracy estimate for the noisy case. Due to more accuracy residual CFO estimate can provide more accuracy residual TO estimate, this paper also present a decision-directed ICMOV (DD-ICMOV) approach to improve the estimation performance of ICMOV estimator. Computer simulations are provided for illustrating the effectiveness of the proposed approaches.     

一种宽范围低复杂度的载波频偏估计算法

针对短突发通信系统存在的频偏估计相位模糊问题,本文提出了一种宽范围低复杂度的时域相关频偏估计算法——基于相位解模糊的部分互相关算法.该算法利用自相关算法思想和相关代数知识消除了其复乘运算,再利用基于蒙特卡罗仿真的解相位模糊算法解决了其相位模糊问题,从而适应大频偏下的短突发通信环境.最后仿真结果表明,与经典的M&M、AC和Giugno时域算法相比,在保证了较大估计范围的同时,该算法具有更高的估计精度和更低的复杂度,适用于低时延高可靠的短数据包传输.     

一种数据辅助的载波频差估值算法

在许多频率估值算法中,估值范围和估值精度是难以同时兼顾的一对矛盾。本文通过对这一问题进行分析,提出了一种具有高性能和低复杂度的估值算法。仿真结果表明,对于数据辅助的ＢＰＳＫ,在Ｅｂ／Ｎ０＞ ０ｄＢ时,本算法的频差估值范围为符号速率的±４０％ ,估值方差接近克拉美—劳界（ＣＲＢ）,与文献［２］提出的算法相比,在相同的性能下,其硬件实现代价减小了３～５ 倍