共查询到20条相似文献,搜索用时 15 毫秒
1.
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. 相似文献
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Yuan Jing Fuliang Yin Zhe Chen 《Communications Letters, IEEE》2008,12(6):453-455
In this paper, an extended Hinfin filter-based carrier frequency offset (CFO) estimator is proposed for orthogonal frequency division multiplexing (OFDM) systems. The design criterion of the proposed estimator is to minimize the effect of worst-case disturbances (noise and model error) on the CFO estimation errors. This data-aided CFO estimator does not require any statistical knowledge of the disturbances. Moreover, its computational complexity is similar to that of the extended Kalman filter (EKF) method. Simulation results show that the proposed method can combat ICI effectively and obtain better bit error rate (BER) performance in the unknown noise for OFDM systems. 相似文献
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OFDM系统中载波间干扰消除方法性能分析 总被引:2,自引:0,他引:2
OFDM系统面临的一个主要问题是对频率偏移的敏感性,频率偏移将导致载波闻干扰(ICI)的产生,从而大大 降低系统性能。对由频率偏移而导致的ICI进行了理论分析,并对抑止ICI的三种方法:自消除方法(SC)、最大似然估计方法 (MLE)及扩展Kalman滤波方法(EKF)进行了仿真和性能比较。 相似文献
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OFDM系统中的资源调度 总被引:1,自引:0,他引:1
资源调度可以显著地改善通信系统的频谱效率和吞吐量。文中给出了OFDM下行链路中3种不同的时隙调度策略,这些策略都是以CDMA/HDR中比例公平算法(Proportional Fair)为基础。比较和分析了3种子带分配的方案。首先将OFDM的子载波划分为若干个子带,目的是减少系统的反馈量。所有的用户同时竞争所有的子带。仿真表明,子带的划分以16~32个比较合适,而调度可以将系统的吞吐量提高0.4~1倍,调度方案3实现了性能和复杂度的折衷,是一种好的选择。 相似文献
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Ashraf Y. Hassan 《Wireless Personal Communications》2017,97(2):1997-2015
Orthogonal-frequency-division-multiplexing (OFDM) systems suffer from Inter-carrier interference (ICI) when the orthogonality between subcarriers is lost. The orthogonality between subcarriers is lost due to two factors. The first is the Doppler-frequency shift in the subcarriers due to the relative motion between the transmitter and receiver. The second is the miss-synchronizations between the local oscillators in the receivers and the received OFDM signal. This paper proposes two methods to reduce the variance of the ICI signal. The first method uses a Fourier-transform based maximum-likelihood estimator (FT-MLE) to estimate the Doppler-shift in the channel. The receiver estimates the frequencies of the subcarriers by estimating the parameters of pilot signal and exploiting the strong relation between the subcarriers in the OFDM signal. The second methods depends on decreasing the value of the normalized Doppler shift by increasing the OFDM symbol rate. No estimation for the Doppler shift is required in this method. 相似文献
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OFDM系统的小区间干扰抑制技术研究 总被引:9,自引:0,他引:9
本文着重针对小区干扰消除技术对系统设计的要求进行了分析,提出了一种基于编码块分割的预定义频率资源块分配方法,以支持对多种带宽业务的小区间干扰消除.另外还提出了一种将小区间干扰协调和干扰消除合并使用的混合方法,可以在适应各种带宽业务的同时,实现系统频谱效率的最大化. 相似文献
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ISI和ICI是TD-LTE系统机制固有的干扰现象,也是TD-LTE系统必须消除和抑制的问题。通过对ISI和ICI产生机制及消除方法的定性分析与理论推导,可使广大工程技术人员对TD-LTE系统有全新的认识,为其管理、维护和优化TD-LTE系统提供帮助。 相似文献
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Vehicle-to-vehicle (V2V) communication has attracted much attention recently. In V2V communications mobility plays a major
role in yielding frequency dispersion of the channels, and thus accurately modeling of Doppler effect becomes a challenging
issue as the two fundamental assumptions of the Jack’s model may not be valid due to time-varying channel characteristics
in V2V communication systems. In this paper, we present a practical model to characterize V2V communication channel and its
corresponding Doppler spread spectrum is derived. In addition, we will study the impact of inter-carrier interference (ICI)
generated in an orthogonal frequency division multiplexing (OFDM) based V2V communication system. Compared with the classical
Jake’s channel model, our proposed new channel model is more accurate and fits in particular well for the performance assessment
of vehicle-to-vehicle communication systems. 相似文献
10.
《Wireless Communications, IEEE Transactions on》2007,6(8):2881-2893
Time-varying multipath channels distort the orthogonality between subchannels in orthogonal frequency-division multiplexing (OFDM) transmission. The loss of sub-channel orthogonality causes inter-subchannel interference (ICI), which limits the achievable bit-error probability (BEP) at high signal-to-noise ratio (SNR). In this paper, we propose a simple but very effective ICI self-cancellation algorithm. A pre-processor and a post-processor arc inserted in the transmitter and receiver, respectively. The pre-processor adds diversity to the frequency- domain symbols by time-domain periodical extension, while the post-processor uses this diversity to make most of the ICI self- cancelled. Our algorithm can provide a trade-off between ICI reduction and system throughput by adjusting the length of periodical extension. For the full-extension scheme, we show that the ICI can be completely removed if the channel variation of each path is linear with time within one extended symbol interval. We further propose an equivalent implementation of the post-processor such that the complexity of the receiver is the same as the standard OFDM receiver. This implementation also enables our algorithm to be readily combined with other OFDM algorithms of channel estimation, synchronization, coding, and so on that do not consider the ICI effect. Applying the proposed algorithm of ICI reduction makes these algorithms more applicable in fast-fading channels. To provide more insight on the ICI cancellation, we derive the equivalent channel effect of our algorithm. We also analyze the variance of ICI and observe the density function of the residual ICI in our algorithm, based on which we show a procedure to derive a BEP upper bound. The proposed algorithm is further validated by simulation and the comparison with another ICI self-cancellation algorithm. 相似文献
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Marabissi D. Fantacci R. Papini S. 《Wireless Communications, IEEE Transactions on》2006,5(11):3068-3076
In orthogonal frequency division multiple access systems clusters of subcarriers are assigned to different users for parallel data transmissions. The subcarriers are overlapped, but orthogonal to each other such that there is no intercarrier interference (ICI). However, synchronization errors among users cause the loss of the orthogonality and introduce ICI resulting in multiple-access interference. Synchronization between users is particularly difficult in the uplink channel where the user signals are potentially asynchronous and affected by different frequency offsets due to misalignment in carrier frequencies and Doppler shifts. This paper proposes a method to lower the effects of different frequency offsets among user signals in an OFDMA uplink system. The multiple access interference due to the user frequency misalignments is reduced by reconstructing and removing the interfering signals in the frequency domain. An approach based on the selective cancellation method, is proposed and its performance is analyzed by means of theoretical analysis and computer simulations. The effectiveness of the proposed system has been evaluated in the case of ideal and no-ideal frequency offset estimation and has been compared with that of the classical successive and parallel cancellation schemes. Simulation results show that the proposed approach allows performance close to the ideal case, i.e., with ideal frequency synchronization among users, with a low increase of the implementation complexity. Moreover, it is also highlighted here, that the successive cancellation method slightly outperforms the selective scheme, at the expense of a higher computational complexity and processing delay 相似文献
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Guixia Kang Philipp Hasselbach Yu Yang Hasselbach P. Klein A. 《Communications Letters, IEEE》2007,11(3):237-239
In this letter, the design of pilots aiming at mitigating the inter-cell interference in MIMO OFDM systems is addressed. It is shown that if an ideal channel between interferer and receiver is assumed, pilots resulting in a variation coefficient of zero, and therefore best performance on system level, can be designed. The properties of these pilots are described, and numerical calculations as well as simulation results are presented to verify the theoretical analysis 相似文献
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Dynamic Downlink OFDM Resource Allocation With Interference Mitigation and Macro Diversity for Multimedia Services in Wireless Cellular Systems 总被引:2,自引:0,他引:2
《Vehicular Technology, IEEE Transactions on》2006,55(5):1555-1564
This paper presents efficient dynamic resource allocation schemes with interference mitigation techniques for multimedia services in downlink orthogonal frequency-division multiplexing mobile cellular systems. Performance of the proposed algorithms is evaluated in terms of user quality-of-service and system spectral efficiency. It is shown that the best subcarrier allocation scheme with interference mitigation and macrodiversity techniques gives significant performance gains in terms of system spectral efficiency. Furthermore, sharing the system bandwidth among real-time stream-type voice and bursty data services can support much larger system loads than having a hard division. 相似文献
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一种OFDM系统中的同频干扰消除算法 总被引:4,自引:1,他引:3
该文研究正交频分复用(OFDM)系统中的同频干扰(CCI)问题。基于正弦信号模型,该文提出一种基于最小均方误差(MMSE)准则的干扰时域估计与消除算法,并进行仿真验证。仿真结果表明:与现有算法相比,该文提出的方法可以更为有效地抑制单频模型的CCI。同时,该文提出的方法对干扰进行时域估计与消除,减小了时频变换后的干扰能量泄漏,并具有不依赖于信道估计,避免直接清零造成的有用信息损失等优点。 相似文献
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在基于OFDM的蜂窝移动通信网络中,影响系统性能的主要干扰来自小区间干扰。小区间的干扰协调技术是提高系统性能的有效手段之一。首先,给出了干扰协调的软频率复用原理。然后,按照资源在时域上调度粒度的不同将干扰协调技术分为三类,即静态干扰协调、动态干扰协调和半静态干扰协调,并分析了各自的优缺点。最后,通过两个干扰协调方案实例说明干扰协调在3G长期演进系统中的应用。 相似文献
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Radio Resource Allocation Algorithms for the Downlink of Multiuser OFDM Communication Systems 总被引:4,自引:0,他引:4
《Communications Surveys & Tutorials, IEEE》2009,11(3):92-106
This article surveys different resource allocation algorithms developed for the downlink of multiuser OFDM wireless communication systems. Dynamic resource allocation algorithms are categorized into two major classes: margin adaptive (MA) and rate adaptive (RA). The objective of the first class is to minimize the total transmit power with the constraint on users? data rates whereas in the second class, the objective is to maximize the total throughput with the constraints on the total transmit power as well as users? data rates. The overall performance of the algorithms are evaluated in terms of spectral efficiency and fairness. Considering the trade-off between these two features of the system, some algorithms attempt to reach the highest possible spectral efficiency while maintaining acceptable fairness in the system. Furthermore, a large number of RA algorithms considers rate proportionality among the users and hence, are categorized as RA with constrained-fairness. Following the problem formulation in each category, the discussed algorithms are described along with their simplifying assumptions that attempt to keep the performance close to optimum but significantly reduce the complexity of the problem. It is noted that no matter which optimization method is used, in both classes, the overall performance is improved with the increase in the number of users, due to multiuser diversity. Some on-going research areas are briefly discussed throughout the article. 相似文献
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基于并行干扰抵消的OFDM/OQAM系统中的信号检测方法 总被引:1,自引:0,他引:1
在多径衰落信道中,基于交错正交幅度调制的正交频分复用(OFDM with Offset QAM, OFDM/OQAM)系统使用迫零均衡器进行信号检测时,不能完全消除信道复数特性和滤波器实数正交特性引入的时域符号间干扰和频域子载波间干扰,及信道估计误差导致的误码率性能损失。该文利用对数据初始判决并重构相邻载波及符号间干扰的思想,通过分析采用迫零均衡信号检测时的残余干扰与信道估计误差干扰,提出了一种基于并行干扰抵消和迫零均衡器结合的OFDM/OQAM信号检测方法,并在IEEE 802.22 技术标准的两种典型多径衰落信道中进行了计算机仿真与比较研究。仿真结果表明,与基于迫零均衡的检测方法相比,基于并行干扰抵消的迭代信号检测方法在误码率为1%时,可获得1 dB至2 dB的性能提升。 相似文献