Performance evaluation for PCC-OFDM systems impaired by carrier frequency offset over AWGN channels

Orthogonal frequency division multiplexing （OFDM） is sensitive to carrier frequency offset （CFO）, which destroys the orthogonality and causes inter-carrier interference （ICI）. ICI self-cancellation schemes based on polynomial cancellation coding （PCC-OFDM） can evidently reduce the sensitivity to CFO. In this paper, we analyze the performance of PCC-OFDM systems impaired by CFO over additive white gaussian noise （AWGN） channels. Two criteria are used to evaluate the effect of CFO on performance degradations. Firstly, the closed-form expressions of the average carrier-to-interference power ratio （CIR） and the statistical average ICI power, both of which reflect the desired power loss, are presented. Simulation and analytical results show that the theoretical expressions depend crucially on the normalized frequency offset and are hardly relevant to the number of subcarriers. Secondly, by exploiting the properties of the Beaulieu series, the effect of CFO on symbol error rate （SER） and bit error rate （BER） performance for PCC-OFDM systems are exactly expressed as the sum of an infinite series in terms of the charac- teristic function （CHF） of ICI. We consider the systems modulated with binary phase shift keying （BPSK）, quadrature PSK （QPSK）, 8-ary PSK （8-PSK）, and 16-ary quadrature amplitude modulation （16-QAM）, and all above modulation schemes are mapped with Gray codes for the evaluations of BER.     

OFDM移动接收中的迭代干扰消除

针对正交频分复用系统在高速移动接收中存在快变衰落信道难以估计、子载波间干扰(ICI)过大的问题,提出基于迭代结构的信道估计算法和ICI消除算法。利用信道解码器输出判决信息,通过离散傅里叶变换实现信道估计,并对时变信道进行线性近似,以较低的计算复杂度消除子载波间的干扰。仿真结果表明,该方法可以对抗10%~15%的归一化多普勒频移。     

存在多个载波频率偏移的分布式STBC-OFDM系统的均衡技术

本文研究了存在载波频率偏移的分布式空时分组编码(DSTBC)正交频分复用(OFDM)系统(DSTBC-OFDM)的性能。首先给出存在多个载波频率偏移的DSTBC-OFDM系统的接收信号模型,然后提出一种频域均衡技术来抑制符号检测时的载波间干扰(IC I)以及符号间干扰(ISI)。仿真结果表明这种均衡技术在各分布式发送端间的载波频率之差较小时具有优异的性能,同时,通过把接收端的频率设置为各发送端频率的平均值可以获得更好的性能。     

OFDM系统在多径衰落信道下的时钟同步

为消除时钟同步误差对正交频分复用（OFDM）系统的影响，提出了一种可工作在多径衰落信道下的时钟同步方法.该方法分为时钟频偏估计和时钟频偏补偿两个步骤，在估计时钟频偏时，利用了相邻符号的相邻导频之间的相关性；在补偿时钟频偏时，采用了数字内插环路，这使得时钟同步模块可在全数字接收机中实现.该方法的一个好处是，当存在载波频偏时仍可正常工作，这说明时钟同步可在载波同步之前完成.结果表明，该方法具有足够大的时钟频偏捕捉范围，可用于IEEE802.11a系统和DVB-T系统的接收机中.     

一种基于分布式频域线性卷积码的低计算复杂度的均衡算法

在本文中,考虑了基于分布式频域线性卷积空频码(distributed frequency-domain linear convolutivespace-frequency codes,DFLC-SFC)的协同通信系统。该协同通信系统考虑了多个载波频率偏移(multiple carrierfrequency offsets,MCFOs)的影响,同时假定中继结点到目的结点的信道是平坦衰落的。通过数学推导,该系统模型得到了简化。因此,本文最终得到了等价的限带模型,同时也分析了关于最终等价信道矩阵的限带属性。在此限带模型的基础之上,本文提出了一种应用LDHH矩阵分解的"限带"块最小均方误差(minimum mean square error,MMSE)均衡方法。进一步地,为了实现相应的限带操作,本文还定义了一类特殊的掩码矩阵。相比较于那些传统的MMSE均衡方法,本文所提出的均衡方法在保持较满意的系统性能的前提下,具有相对较低的计算复杂度。     

ICI74-1氨合成催化剂运行总结

介绍ICI74-1氨合成催化剂的特性,特殊工况的操作,运行10年的评估。     

Inter-Carrier Interference Cancellation for OFDM Systems with Macrodiversity and Multiple Frequency Offsets

Macrodiversity provides improved coverage in wireless communications. It isused in single frequency networks (SFN), and in some cellular systems, whena mobile is in a soft handoff. The combination of OFDM and macrodiversity isvery attractive for the ability of OFDM to cope with delay spread resultingfrom macrodiversity. However, such system is very sensitive to poor frequencysynchronization among transmitters, which results in multiple frequencyoffsets. These cause inter-carrier interference (ICI), which severely degradesperformance. In this paper we quantify the degradation, providing expressionsfor the receiver SINR, and find the optimum receiver frequencysynchronization. Furthermore, we propose to mitigate ICI degradation usinglinear and decision feedback interference cancellation. In each case, weprovide a solution using both the decorrelating and the MMSE criteria.Simulation results show that, for macrodiversity OFDM, our approach resultsin significantly improved performance and robustness to frequency offsets.     

Subcarrier and power allocation algorithm based on inter-cell interference mitigation for OFDMA system

This article proposes a dynamic subcarrier and power allocation algorithm for multicell orthogonal frequency division multiple access (OFDMA) downlink system, based on inter-cell interference (ICI) mitigation. Different from other ICI mitigation schemes, which pay little attention to power allocation in the system, the proposed algorithm assigns channels to each user, based on proportional-fair (PF) scheduling and ICI coordination, whereas allocating power is based on link gain distribution and the loading bit based on adaptive modulation and coding (AMC) in base transceiver station (BTS). Simulation results show that the algorithm yields better performance for data services under fast fading.     

OFDM电力线载波通信系统中同步技术研究

OFDM(Orthogonal Frequency Division Multiplexing)系统能够对抗电力线环境中的频率选择性衰落、多径干扰、脉冲噪声等。由于符号定时偏差和载波频率偏差将会产生较为严重的符号间干扰(ISI)和信道间干扰(ICI),从而降低OFDM系统性能,所以OFDM关键技术之一同步技术的好坏占有较为重要的地位。本文对OFDM同步技术做了系统的研究和分析,给出四种同步算法,能够较好地进行符号定时同步和载波频偏估计,可针对不同的电力线通信环境选用不同的同步算法。     

OFDM系统中载波间干扰抑制方法

在高速移动通信环境下,OFDM系统在传输过程中出现的多普勒频移和收发两端本地振荡器之间的频率偏差,形成子载波间干扰(ICI)并造成系统性能降低。在分析子载波间干扰机制的基础上,讨论了自消除方法和分段均衡方法,并提出一种利用加窗技术改进的分段均衡方法。仿真结果表明,采用该改进的分段均衡方法能更好地改善系统的性能,有约2 dB的信道估计增益。