共查询到20条相似文献,搜索用时 31 毫秒
1.
Equalization for OFDM over doubly selective channels 总被引:5,自引:0,他引:5
In this paper, we propose a time-domain as well as a frequency-domain per-tone equalization for orthogonal frequency-division multiplexing (OFDM) over doubly selective channels. We consider the most general case, where the channel delay spread is larger than the cyclic prefix (CP), which results in interblock interference (IBI). IBI in conjunction with the Doppler effect destroys the orthogonality between subcarriers and, hence, results in severe intercarrier interference (ICI). In this paper, we propose a time-varying finite-impulse-response (TV-FIR) time-domain equalizer (TEQ) to restore the orthogonality between subcarriers, and hence to eliminate ICI/IBI. Due to the fact that the TEQ optimizes the performance over all subcarriers in a joint fashion, it has a poor performance. An optimal frequency-domain per-tone equalizer (PTEQ) is then obtained by transferring the TEQ operation to the frequency domain. Through computer simulations, we demonstrate the performance of the proposed equalization techniques. 相似文献
2.
The direct-conversion architecture is an attractive front-end design for multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. These systems are typically small in size and provide a good flexibility to support growing number of wireless standards. However, direct-conversion based OFDM systems are generally very sensitive to front-end component imperfections. These imperfections are unavoidable especially when cheaper components are used in the manufacturing process and can lead to radio frequency (RF) impairments such as in-phase/quadrature-phase (IQ) imbalance. These RF impairments can result in a severe performance degradation. In this paper, we propose training based efficient compensation schemes for MIMO OFDM systems impaired with transmitter and receiver frequency selective IQ imbalance. The proposed schemes can decouple the compensation of the transmitter and receiver IQ imbalance from the compensation of the channel distortion. It is shown that the proposed schemes result in an overall lower training overhead and a lower computational requirement as compared to a joint estimation/compensation of IQ imbalance and the channel distortion. 相似文献
3.
The aim of this article is to design a simple receiver, which can jointly estimate the frequency selective channel impulse response, frequency independent transmit/receive IQ imbalance, and carrier frequency offset with minimal training and implementation complexity. The estimation of carrier frequency offset is performed using 2 scalable solutions. To estimate the frequency selective channel impulse response and frequency independent transmit/receive IQ imbalance, we proposed 2 different estimation techniques. The first technique is an iterative approach stemming from a doubly linear model of the transmission system in the presence of transmit/receive IQ imbalance and frequency selective channel impulse response, while the second approach is a least squares solution. Both these schemes provide a good performance/complexity trade‐off. Although the iterative estimates of channel impulse response are not optimal, they do provide a near ideal bit error performance. The proposed scheme blends seamlessly with Institute of Electrical and Electronics Engineers 802.11 standard but can be adapted to work with any orthogonal frequency‐division multiplexing standard. 相似文献
4.
作为5G多载波技术强有力的候选对象,通用滤波多载波利用子带滤波技术抑制带外功率泄露,进而降低同步要求和获得更高的频谱效率。本文首先针对通用滤波多载波在慢时变多径信道下的性能进行了分析和研究;其次为消除多径信道所带来的干扰,提出了适用于该多载波系统的信道估计方案,该方案设计了具有重复样式的导频结构进行信道估计,复杂度低;最后针对通用滤波多载波在多径信道下容易遭受符号间干扰的问题,提出了基于干扰消除的Zero-Forcing均衡算法和基于迭代干扰消除的均衡算法,两种算法均能够在消除ISI的基础上进一步地消除ICI和IBI。仿真结果表明,本文提出的信道估计和均衡算法能有效消除通用滤波多载波技术在多径信道下所经受的ISI、ICI和IBI。 相似文献
5.
An MIMO-OFDM technique for high-speed mobile channels 总被引:1,自引:0,他引:1
Kyung Won Park Yong Soo Cho 《Communications Letters, IEEE》2005,9(7):604-606
In this letter, a new orthogonal frequency-division multiplexing (OFDM) technique for multiple-input multiple output (MIMO) channels is proposed to reduce interchannel interference (ICI) caused by high-speed mobiles in cellular environments. After analyzing the ICI caused by high-speed mobile channels using a simple curve fitting technique, the weighting factor for group transmission is optimized. Then, a new MIMO-OFDM technique, based on the weighting factor optimization, is proposed for reducing ICI caused by time-varying channels. Performances of the proposed technique are verified by using the I-METRA channel, proposed for an MIMO channel to 3GPP, and a MIMO-OFDM simulator designed for macrocellular mobile communication. It is shown by computer simulation that the proposed MIMO-OFDM technique is effective in reducing ICI and noise as well as in obtaining diversity gain even under highly-correlated fast fading channels, compared with the conventional MIMO-OFDM schemes. 相似文献
6.
Intercarrier Interference Suppression for OFDMA Uplink in Time- and Frequency-Selective Fading Channels 总被引:1,自引:0,他引:1
《Vehicular Technology, IEEE Transactions on》2009,58(6):2741-2754
7.
Jong-Bu Lim Chan-Ho Choi Gi-Hong Im 《Communications Letters, IEEE》2006,10(5):356-358
For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response, resulting in a loss of bandwidth efficiency. In this letter, the CP reconstruction (CPR) technique is first applied to a multi-input multi-output (MIMO)-OFDM system with insufficient CP. The intercarrier interference (ICI) from multiple transmit antennas is so large for MIMO system that it can not be sufficiently suppressed with the conventional CPR procedure used in single-input single-output (SISO) system. A new minimum mean-square error (MMSE) equalization and ordering process is proposed for MIMO system to suppress the ICI during the CPR procedure. By applying the proposed CPR algorithm to MIMO-OFDM system, we can obtain both the benefits of multiplexing gain and spectral efficiency gain. 相似文献
8.
The use of orthogonal frequency division multiplexing (OFDM) in frequency‐selective fading environments has been well explored. However, OFDM is more prone to time‐selective fading compared with single‐carrier systems. Rapid time variations destroy the subcarrier orthogonality and introduce inter‐carrier interference (ICI). Besides this, obtaining reliable channel estimates for receiver equalization is a non‐trivial task in rapidly fading systems. Our work addresses the problem of channel estimation and ICI suppression by viewing the system as a state‐space model. The Kalman filter is employed to estimate the channel; this is followed by a time‐domain ICI mitigation filter that maximizes the signal‐to‐interference plus noise ratio (SINR) at the receiver. This method is seen to provide good estimation performance apart from significant SINR gain with low training overhead. Suitable bounds on the performance of the system are described; bit error rate (BER) performance over a time‐invariant Rayleigh fading channel serves as the lower bound, whereas BER performance over a doubly selective system with ICI as the dominant impairment provides the upper bound. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
《Vehicular Technology, IEEE Transactions on》2008,57(5):2779-2791
10.
Analysis and characterization of intercarrier and interblock interferences for wireless mobile OFDM systems 总被引:2,自引:0,他引:2
Hsiao-Chun Wu 《Broadcasting, IEEE Transactions on》2006,52(2):203-210
OFDM has been applied in a wide variety of wireless communications in recent years since it has the advantage over the conventional single-carrier modulation schemes when enduring the frequency-selective fading. However, intercarrier-interference (ICI) and interblock interference (IBI) due to the Doppler effect, carrier frequency drift of local oscillators and multipath fading limit the capability of OFDM systems. In this paper, a new generalized mathematical model for intercarrier and interblock interferences is derived for wireless mobile OFDM systems, in which Doppler frequency drift, local carrier frequency offset, multipath fading, and cyclic prefix coding are all present in reality. Such a new ICI/IBI model can be applied for OFDM performance evaluation in different environments. This new formulation of IBI and ICI provides a generalized framework which includes special ICI models appearing in the previous literature. Besides, the derived OFDM performance evaluation analysis in this paper can greatly benefit OFDM designers for wireless multimedia networks and digital video broadcasting technologies. 相似文献
11.
Bounding performance and suppressing intercarrier interference in wireless mobile OFDM 总被引:2,自引:0,他引:2
While rapid variations of the fading channel cause intercarrier interference (ICI) in orthogonal frequency-division multiplexing (OFDM), thereby degrading its performance considerably, they also introduce temporal diversity, which can be exploited to improve performance. We first derive a matched-filter bound (MFB) for OFDM transmissions over doubly selective Rayleigh fading channels, which benchmarks the best possible performance if ICI is completely canceled without noise enhancement. We then derive universal performance bounds which show that the time-varying channel causes most of the symbol energy to be distributed over a few subcarriers, and that the ICI power on a subcarrier mainly comes from several neighboring subcarriers. Based on this fact, we develop low-complexity minimum mean-square error (MMSE) and decision-feedback equalizer (DFE) receivers for ICI suppression. Simulations show that the DFE receiver can collect significant gains of ICI-impaired OFDM with affordable complexity. In the relatively low Doppler frequency region, the bit-error rate of the DFE receiver is close to the MFB. 相似文献
12.
In order to enhance the anti-jamming capability of Cyberspace data-link (CDL) in the complex electromagnetic environment, the performance of jamming sensing of simultaneous transmit and receive based cognitive anti-jamming (SCAJ) receiver impaired by IQ imbalance is investigated. Firstly, energy detection (ED) based the jamming detection and false-alarm probabilities in closed-form for single- and multi-channel SCAJ receiver are derived. Then, the image channel interference cancellation (IC) scheme is proposed to mitigate the image channel crosstalk. Simulation results show that the false-alarm probability is increased by IQ imbalance, and the proposed interference cancellation scheme can reduce the adverse effect of IQ imbalance, thus the anti-jamming performance of SCAJ receiver in CDL system can be improved. 相似文献
13.
14.
The combination of Space–Time Coded Multiple Input Multiple Output systems (STC-MIMO) with Orthogonal Frequency Division Multiplexing
(OFDM) is recently being investigated as an effective means of providing high-speed data transmission over dispersive wireless
channels. The strengths of the two techniques coalesce and render MIMO-OFDM systems robust to ISI and IBI. However, the decoding
and demodulation of STC-OFDM needs reliable channel knowledge at the receiver, unless differential modulation techniques are
used. Semi-blind methods for channel estimation are seen to provide the best trade-off in terms of bandwidth overhead, computational
complexity and latency. The conventional Expectation-Maximization (EM) algorithm for semi-blind channel estimation improves
a pilot-based estimate with a two step process; however, it is computationally complex to implement. In this paper, we propose
a variant of the EM method, referred to as ML-EM, for semi-blind estimation of doubly dispersive channels in space–time coded
MIMO-OFDM systems. Here, the conventional EM algorithm is coupled with the ML decoder for space time block codes (STBCs).
The technique shows good performance, even in highly correlated antenna arrays, and is computationally simpler than conventional
EM. The method incurs a training overhead of less than 1%, and performs close to exact CSI through iterative processing at
the receiver. 相似文献
15.
《Vehicular Technology, IEEE Transactions on》2009,58(9):4848-4859
16.
为克服OFDM系统中的符号块间干扰(IBI)和载频间干扰(ICI),基于满信道状态信息(CSI)的发端预处理算法已被提出,系统性能得以提高并简化了接收机。不过,反馈满CSI将占用紧张的频谱资源,并且在一些实时性要求高的系统中也是不现实的。为解决这一问题,基于部分CSI反馈提出了一种预处理优化算法,并对优化矩阵的3种处理方案进行了分析与讨论。仿真结果表明,所建议的优化算法能有效地抑制IBI和ICI,提高系统的性能。与已有的基于满信道信息的发端预处理传输方案相比,在满足一定服务质量要求的情况下,本方案的频谱效率得以提高,反馈量和计算复杂度明显降低。 相似文献
17.
A Comparison of Frequency-Domain Block MIMO Transmission Systems 总被引:2,自引:0,他引:2
《Vehicular Technology, IEEE Transactions on》2009,58(1):165-175
Block transmission techniques, with appropriate cyclic prefix and frequency-domain processing schemes, have been shown to be excellent candidates for digital transmission over severely time-dispersive channels, allowing good performance with implementation complexity that is much lower than traditional time-domain processing schemes. Orthogonal frequency-division multiplexing (OFDM) modulation is the most popular block transmission technique. Single-carrier (SC) modulation using frequency-domain equalization (FDE) is an attractive alternative approach based on this principle. In this paper, we propose two new receiver structures for multiple-input-multiple-output (MIMO) channels employing SC (MIMO-SC) modulation and FDE schemes. These receivers have a hybrid structure with frequency-domain feedforward and time-domain feedback filters for intersymbol interference (ISI) and interference cancellation. The proposed schemes are compared with different MIMO systems employing OFDM modulation (MIMO-OFDM) receivers in terms of performance [bit error rate (BER) and throughput] and complexity. Our performance results show the superiority of MIMO-SC approaches relative to MIMO-OFDM in terms of the BER performance for the simulated scenarios. Also, the simulation results show that the proposed hybrid MIMO-SC receivers yield a higher throughput than a MIMO-OFDM system. 相似文献
18.
How to compensate the detrimental impact of intercarrier interference (ICI) on BER performance is the key issue of signal detection for orthogonal frequency division multiplexing (OFDM) systems in doubly selective channels. In this paper, we propose an optimal linear ICI suppression algorithm with successive detection based on oversampling at the receiver, by which the OFDM systems can benefit from doubly selective channels for achieving both the multipath diversity and Doppler diversity. To reduce the additional computational complexity caused by oversampling, a low complexity implementation method for this algorithm is also presented. Simulations results show that the proposed algorithm can enhance the BER performance with the increase of the Doppler spread and the oversampled factor. 相似文献
19.
鉴于MIMO-OFDM(多输入多输出-正交频分复用)系统中时域信道方法的灵活性和低带宽开销的特点,本文采用Steiner训练符号设计方法设计MIMO-OFDM系统中的时域训练符号,给出传统CDMA系统的Steiner信道估计器在MIMO-OFDM系统中的实现过程,解决了MIMO-OFDM时域信道估计矩阵求逆的问题,降低了时域信道估计的实现复杂度。并进一步提出了采用接收天线DOA(波达方向)改进的Steiner信道估计方法,提高了信道估计的精度,获得了一定程度的性能增益,增强了时域信道估计方案的实际可行性。 相似文献
20.
Jinho Choi 《Wireless Communications, IEEE Transactions on》2007,6(11):3994-4003
In this paper, we derive an iterative receiver for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. As MIMO-OFDM is considered for future cellular systems, the iterative receiver is investigated when the co-channel interference (CCI) exists. It is assumed that the CCI's are also OFDM signals. Since a joint detection of the desired signal and CCI is difficult, we only detect the desired signal, while the CCI is assumed to be a (colored) noise. This approach can avoid the channel estimation and detection of the CCI and keep the complexity of the receiver low. The proposed iterative receiver estimates the channel impulse response of the desired signal and the covariance matrix of the CCI for the detection based on a generalized expectation- maximization (GEM) algorithm. Through GEM iterations, we can observe the performance is improved. 相似文献