共查询到20条相似文献,搜索用时 15 毫秒
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In this paper we consider how Orthogonal Space-Time Block Codes (OSTBC) can be used in the presence of feedback from the receiver
to the transmitter. First, we survey how some of the feedback techniques for AWGN channels with fading can be applied to OSTBC.
Then we consider a simple scheme with diagonal weighting. The optimal diagonal weighting matrix, which minimizes the probability
of error, is derived. The optimal weights depend on the channel and, hence, a feedback becomes necessary. However, the required
feedback can be accomplished using log2 (n
t) bits, where n
t is the number of transmit antennas. Simulations show that relatively significant gains can be achieved with the diagonal
weighting scheme.
In a practical system it is quite possible that the bits that are fed back to the transmitter are in error. In that case we
show that there will be a loss of diversity. To overcome this loss, we develop weighting schemes that are error tolerant and
always perform better than the unweighted OSTBC (even in the presence of feedback errors). 相似文献
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在某些MIMO(multiple—input multlple-output)衰落环境下,发射或者接收信号不相关,但是系统的信道容量依然很低,这种现象称之为Keyhole效应.本文针对Keyhole衰落MIMO信道,在任意的收发天线数目下,对正交空时分组码进行了性能分析,通过矩生成函数的分析方法,分析了Keyhole信道可以提供的分集增益,给出严格的封闭的符号错误概率表达式.并且针对收发天线数目不相等的情况,给出简洁的近似结果.在Keyhole衰落信道下的计算机仿真表明,,严格的分析结果与仿真结果一致,在高信噪比下,近似表达式也与仿真的结果吻合。 相似文献
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In this paper, we concern the channel estimation for a wireless communication system in which the techniques of multiple-input multiple-output, code division multiple access (CDMA) and orthogonal space-time block codes (OSTBCs) are integrated together for the purpose of achieving high data rate. We show that a composite channel information (CCI) vector can be formed, which contains the effects of channel state information, spreading coding and OSTBCs. From the standpoint of the MUltiple SIgnal Classification method, such CCI vector must lie in the signal subspace spanned by the dominant eigenvectors of the received data covariance matrix. Also, this CCI vector is located in another subspace which is associated with the CDMA and OSTBC codes and can be computed off-line. Using the vector space projections method, this CCI vector can be viewed as the intersection of these two subspaces and thus can be computed by alternative projections. In order to reduce the computation complexity, we propose an equivalent but computationally effective single-step solution in which the channel estimation amounts to searching for the principal eigenvector of a certain matrix with moderate size. Additionally, only one training block is required to overcome the problem of sign ambiguity. Numerical results demonstrate that, in addition to improving the bandwidth efficiency, the proposed method offers better performance in terms of channel estimation accuracy and bit-error-rate as compared with the standard nonblind least-squares channel estimation approach. 相似文献
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On Space-Time Block Codes from Complex Orthogonal Designs 总被引:4,自引:1,他引:3
Space-time block codes from orthogonal designs recently proposed by Alamouti, and Tarokh-Jafarkhani-Calderbank have attracted considerable attention due to the fast maximum-likelihood (ML) decoding and the full diversity. There are two classes of space-time block codes from orthogonal designs. One class consists of those from real orthogonal designs for real signal constellations which have been well developed in the mathematics literature. The other class consists of those from complex orthogonal designs for complex constellations for high data rates, which are not well developed as the real orthogonal designs. Since orthogonal designs can be traced back to decades, if not centuries, ago and have recently invoked considerable interests in multi-antenna wireless communications, one of the goals of this paper is toprovide a tutorial on both historical and most recent resultson complex orthogonal designs. For space-time block codes from both real and (generalized) complex orthogonal designs (GCODs) with or without linear processing, Tarokh, Jafarkhani and Calderbank showed that their rates cannot be greater than 1. While the maximum rate 1 can be reachedfor real orthogonal designs for any number of transmit antennas from the Hurwitz–Radon constructive theory, Liang and Xia recentlyshowed that rate 1 for the GCODs (square or non-square size) with linear processing is not reachable for more than two transmit antennas.For GCODs of square size, the designs with the maximum rates have been known, which are related to the Hurwitz theorem.In this paper, We briefly review these results and give a simple and intuitive interpretation of the realization. For GCODs without linear processing (square or non-square size), we prove that the rates cannot be greater than 3/4 for more than two transmit antennas. 相似文献
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在多输入多输出(MIMO)解码转发(DF)双向中继系统中,分别设计了两种信道状态信息(CSI)情况下的系统传输策略,并推导了系统中断概率的闭合表达式.当已知完全CSI时,采用(最大比发送-最大比接收)MRT-MRC技术设计波束形成和合并向量;当未知完全CSI时,设计了基于有限反馈的传输策略,并采用随机向量量化和Grassmann两种码本进行数值仿真验证.仿真结论显示,所设计的双向中继传输策略的中断概率性能明显优于其他策略,所推导的闭合表达式能准确地表征系统中断概率性能. 相似文献
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Capacity Analysis for Transmit Antenna Selection Using Orthogonal Space-Time Block Codes 总被引:1,自引:0,他引:1
Antenna selection for multiple-input multiple-output (MIMO) where only a subset of antennas at the transmitter and/or receiver are activated for signal transmission is a practical technique for the realization of full diversity. Despite extensive research, closed-form capacity expressions for MIMO systems employing transmit antenna selection (TAS) and orthogonal space-time block codes (OSTBCs) are not available. We thus derive the exact closed-form capacity expressions when an OSTBC is employed and N transmit antennas out of total Lt antennas are selected for transmission. The expressions are valid for a frequency-flat Rayleigh fading MIMO channel and avoid numerical integration methods 相似文献
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Chadi Abou-Rjeily 《Communications, IEEE Transactions on》2009,57(3):602-605
In this paper, we propose orthogonal Space-Time (ST) codes for binary Pulse Position Modulations (PPM). Unlike the well known orthogonal ST codes, the proposed schemes verify the additional constraint of achieving a full transmit diversity order without introducing any phase rotations. This renders the proposed codes suitable for Free-Space Optical (FSO) communications with direct detection and for Ultra-WideBand (UWB) communications. At the receiver side, optimal detection can be achieved with linear operations and the proposed codes can be also applied with On-Off Keying (OOK). 相似文献
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We study coding techniques for the single-relay non-orthogonal amplify-and-forward half-duplex relay fading channel. Unlike the multiple-antenna case, we show that 2times2 rotations induce large gains in outage probability with no increase in decoding complexity under iterative probabilistic decoding. We compare rotated and unrotated turbo-coded schemes and show that they both perform close to their corresponding outage limits. 相似文献
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We present a simple closed-form expression for the BER of orthogonal space-time block codes (OSTBCs) with MMSE channel estimation, assuming PAM and QAM constellations and flat Rayleigh block fading. The BER expression is exact for a certain class of OSTBCs, and provides a very accurate approximation for other OSTBCs. 相似文献
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Abdulkarem Hussein Mohammed Almawgani Motea Alsamawi Waled Hussein Al-Arashi 《Wireless Personal Communications》2017,97(4):5277-5287
Slow fading channel is one of the most important channels, which appears widely in a cellular mobile system. It has several problems such as bad effects of fading, which causes an attenuation to the signal. This paper presents a new scheme in cooperative communication system under slow fading channel to enhance and increase the quality of communication systems performance. This new scheme is called a cooperative multiple input–multiple output Antenna. The main idea of this scheme depends on transmitting multi copy of message via two paths. It’s performance has been compared with MIMO technique in term of outage probability. The results show that the negative effects of fading are mitigated and the outage probability and diversity gain are enhanced. Furthermore, the reliability in communication system under slow fading channel is improved. 相似文献
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Linear space-time block codes (STBCs) have proven their effectiveness in performance improvement of wireless multiple-input multiple-output communication systems. Their successful decoding, however, requires reliable channel knowledge at the receiver. In this paper, we present a semiblind channel estimation method for linear STBC without the usual code orthogonality condition. We provide a set of identification conditions that are mostly verifiable a priori in terms of code parameters and antenna array configuration. We also present a simple channel estimation algorithm. Finally, we provide simulation results that illustrate the performance of the proposed scheme 相似文献
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1 IntroductionRecently,anewspace timecodeadaptedtomultipleantennaswirelessfadingchannelhasbeenproposed[1~6] .Thecodesarethejointdesignofcoding ,modulation ,transmissionandreceptiondi versityto providethebesttradeoffbetweendatarates,diversityadvantageandcodes… 相似文献
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In MIMO systems, space-time block code (STBC) is good solution for improving system performance. Among the STBCs, coordinate interleaved orthogonal designs (CIODs) combined with QR-decomposition-based decision-feedback decoding (QR-DDF) allow achieving good performance for time-selective fading channels. However, half of entries in codeword matrix of CIODs are zeros. These zero entries result in high peak-to-average power ratio (PAPR) and also impose a severe constraint on hardware implementation of the code when turning off some of the transmitting antennas whenever a zero is transmitted. In this paper, we propose a new design of space-time block codes without zero entry in codeword matrix (NZE-STBCs) for time-selective fading channels. The main advantage of the proposed NZE-STBCs is that its peak-to-average ratio (PAPR) is 3 dB lower than that of CIODs, and its hardware implementation is also easier due to eliminating on-off switchers without sacrificing performance. Moreover, similar as CIODs, the proposed NZE-STBCs can use low complexity QR-DDF decoder over time-selective fading channels to enhance performance and reduce decoding complexity. Simulation results show that the proposed NZE-STBCs outperform CIODs for three transmit antennas while performing the same for two and four transmit antennas. 相似文献
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In this letter, we propose a low complexity Maximum Likelihood (ML) decoding algorithm for orthogonal spacetime block codes (OSTBCs) based on the real-valued lattice representation and QR decomposition.We show that for a system with rate r = K/T, where K is the number of transmitted symbols per T time slots, the proposed algorithm decomposes the original complex-valued system into a parallel system represented by 2K real-valued components, thus allowing for a simple and independent detection of the real and imaginary parts of each complex transmitted symbol. We further show that for square L-QAM constellations, the proposed algorithm reduces the decoding computational complexity from /spl pdelta/(L) for conventional ML to /spl pdelta/(?L) without sacrificing the performance. 相似文献