共查询到20条相似文献,搜索用时 15 毫秒
1.
Hongyuan Zhang Mehta N.B. Molisch A.F. Jin Zhang Huaiyu Dai 《Wireless Communications, IEEE Transactions on》2008,7(1):155-165
Cooperative transmission by base stations (BSs) can significantly improve the spectral efficiency of multiuser, multi-cell, multiple input multiple output (MIMO) systems. We show that contrary to what is often assumed in the literature, the multiuser interference in such systems is fundamentally asynchronous. Intuitively, perfect timing-advance mechanisms can at best only ensure that the desired signal components -but not also the interference components -are perfectly aligned at their intended mobile stations. We develop an accurate mathematical model for the asynchronicity, and show that it leads to a significant performance degradation of existing designs that ignore the asynchronicity of interference. Using three previously proposed linear preceding design methods for BS cooperation, we develop corresponding algorithms that are better at mitigating the impact of the asynchronicity of the interference. Furthermore, we also address timing-advance inaccuracies (jitter), which are inevitable in a practical system. We show that using jitter-statistics-aware precoders can mitigate the impact of these inaccuracies as well. The insights of this paper are critical for the practical implementation of BS cooperation in multiuser MIMO systems, a topic that is typically oversimplified in the literature. 相似文献
2.
该文提出了一种多用户MIMO系统中预矩阵及其匹配接收矩阵的鲁棒性优化算法。针对信道估计误差构造均方误差代价函数,在发射功率受限的约束条件下联合设计发射和接收矩阵,推导出了采用线性多用户MMSE接收时的最优收发机迭代算法。仿真表明,系统具有良好的鲁棒性。 相似文献
3.
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
4.
In asynchronous slow frequency hopping Bluetooth networks, packet collisions diminish the total link throughput. However,
interference mitigation capability can reduce packet losses due to collisions. In this paper, an interference cancelling dual
decision feedback (IC-DDF) Bluetooth receiver is proposed and its performance is evaluated for slow fading indoor channels.
In addition to the bit error rate (BER) performance, the system level performance is evaluated by using the packet error rate
(PER). To integrate the BER performance into the PER performance, a new geometric interpretation of packet error rate is introduced
that uses an ensemble average of the received carrier to interference ratio (CIR). Also, a generalized packet collision probability
is derived to analyze total link throughput. 相似文献
5.
Xiaohua Li Fan Ng Taewoo Han 《Signal Processing, IEEE Transactions on》2008,56(2):675-685
Carrier frequency offset (CFO) mitigation is critical for orthogonal frequency-division multiplexing (OFDM)-based cooperative transmissions because even small CFO per transmitter may lead to severe performance loss, especially when the number of cooperative transmitters is large. In this paper, we show that cyclic prefix (CP) can be exploited to mitigate or even remove completely the CFO. The mitigation performance increases along with the CP length. In particular, long CP with length proportional to NI, where N is the fast Fourier transform (FFT) block length and I is the number of cooperative transmitters, can guarantee a complete CFO removal. While this comes with a reduction in bandwidth efficiency, the long CP in the proposed scheme is exploited to enhance transmission power efficiency in a way similar to spread-spectrum systems, and thus is different from conventional CP that degrades both bandwidth and power efficiency. An efficient CFO-mitigation algorithm is developed that has complexity at most O(NI 2), or even linear in N approximately in some cases. Implemented as a preprocessing procedure independently from cooperative encoding/decoding details, this algorithm makes the CFO problem effectively transparent to and thus has general applications in OFDM-based transmissions. 相似文献
6.
多部雷达信号间的共信道干扰是目前雷达传感网等面临的电磁兼容问题。适合于窄带雷达运用的传统捷变频与编码分集等方法无法有效解决高分辨宽带雷达共信道干扰问题。文中提出了一种波形与时间双分集的复合设计方法,通过多元码脉冲位置编码、伪随机序列阵脉冲压缩和脉冲积累的复合体制,为较好解决宽带雷达间的共信道干扰提供了
一种解决途径。仿真结果表明在共信道信干比大于-30dB 的前提下,所提出的设计波形具有明显的干扰抑制能力,计算结果验证了该设计的可行性与高效性。 相似文献
7.
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
8.
Polynomial Estimation of Time-Varying Multipath Gains With Intercarrier Interference Mitigation in OFDM Systems 总被引:3,自引:0,他引:3
In this paper, we consider the case of a high-speed mobile receiver operating in an orthogonal frequency-division multiplexing (OFDM) communication system. We present an iterative algorithm for estimating multipath complex gains with intersubcarrier interference (ICI) mitigation (using comb-type pilots). Each complex gain variation is approximated by a polynomial representation within several OFDM symbols. Assuming knowledge of delay-related information, polynomial coefficients are obtained from time-averaged gain values, which are estimated using the least-square (LS) criterion. The channel matrix is easily computed, and the ICI is reduced by using successive interference suppression (SIS) during data symbol detection. The algorithm's performance is further enhanced by an iterative procedure, performing channel estimation and ICI mitigation at each iteration. Theoretical analysis and simulation results for a Rayleigh fading channel show that the proposed algorithm has low computational complexity and good performance in the presence of high normalized Doppler spread. 相似文献
9.
10.
Space-Time Adaptive MMSE Multiuser Decision Feedback Detectors With Multiple-Feedback Interference Cancellation for CDMA Systems 总被引:1,自引:0,他引:1
In this paper, we propose a novel space-time minimum mean square error (MMSE) decision feedback (DF) detection scheme for direct-sequence code-division multiple access (DS-CDMA) systems with multiple receive antennas, which employs multiple-parallel-feedback (MPF) branches for interference cancellation. The proposed space-time receiver is then further combined with cascaded DF stages to mitigate the deleterious effects of error propagation for uncoded schemes. To adjust the parameters of the receiver, we also present modified adaptive stochastic gradient (SG) and recursive least squares (RLS) algorithms that automatically switch to the best-available interference cancellation feedback branch and jointly estimate the feedforward and feedback filters. The performance of the system with beamforming and diversity configurations is also considered. Simulation results for an uplink scenario with uncoded systems show that the proposed space-time MPF-DF detector outperforms existing schemes such as linear, parallel DF (P-DF), and successive DF (S-DF) receivers in terms of bit error rate (BER) and achieves a substantial capacity increase in terms of the number of users, compared with the existing schemes. We also derive the expressions for MMSE achieved by the analyzed DF structures, including the novel scheme, with imperfect and perfect feedback and expressions of signal-to-interference-plus-noise ratio (SINR) for the beamforming and diversity configurations with linear receivers. 相似文献
11.
12.
This paper presents joint power allocation and interference mitigation techniques for the downlink of spread spectrum systems
which employ multiple relays and the amplify and forward cooperation strategy. We propose a joint constrained optimization
framework that considers the allocation of power levels across the relays subject to an individual power constraint and the
design of linear receivers for interference suppression. We derive constrained minimum mean-squared error (MMSE) expressions
for the parameter vectors that determine the optimal power levels across the relays and the linear receivers. In order to
solve the proposed optimization problem efficiently, we develop joint adaptive power allocation and interference suppression
algorithms that can be implemented in a distributed fashion. The proposed stochastic gradient (SG) and recursive least squares
(RLS) algorithms mitigate the interference by adjusting the power levels across the relays and estimating the parameters of
the linear receiver. SG and RLS channel estimation algorithms are also derived to determine the coefficients of the channels
across the base station, the relays and the destination terminal. The results of simulations show that the proposed techniques
obtain significant gains in performance and capacity over non-cooperative systems and cooperative schemes with equal power
allocation. 相似文献
13.
Fan-Shuo Tseng Wen-Rong Wu Jwo-Yuh Wu 《Wireless Communications, IEEE Transactions on》2009,8(10):4928-4933
This paper considers transmitter precoding in an amplify-and-forward cooperative system where multiple antennas are equipped at the source, the relay, and the destination. Existing methods for the problem only consider the design of the relay precoder. To further improve the performance, we include the source precoder into the design. Using a minimum-meansquare- error (MMSE) criterion, we propose a joint source/relay precoder design method, taking both the direct and relay links into account. It is shown that the MMSE is a highly nonlinear function of the precoding matrices, and a direct minimization is not feasible. To facilitate analysis, we propose to design the precoders toward first diagonalizing the MSE matrix of the relay link. This imposes certain structural constraints on both precoders that allow us to derive an analytically tractable MSE upper bound. By conducting minimization with respect to this bound, the solution can be obtained by an iterative water-filling technique. 相似文献
14.
We propose a blind user identification detection (UID) scheme based on linear prediction algorithm for asynchronous direct-sequence code-division multiple-access systems over multipath fading channels. Numerical results show that both the false alarm rate and bit error rate of the proposed algorithm are better than those of the existing subspace-based UID algorithms. 相似文献
15.
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
16.
Yue Shang Xiang-Gen Xia 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2007,53(11):4119-4126
Shift-full-rank (SFR) matrices are matrices that have full row rank no matter how their rows are shifted. SFR matrices have been used lately as generator matrices for a family of space-time trellis codes to achieve full diversity in asynchronous cooperative communications, where the numbers of columns of the SFR matrices correspond to the memory sizes of the trellis codes. A systematic construction of SFR matrices, including the shortest (square) SFR (SSFR) matrices, has been also previously proposed. In this paper, we study a variation of SFR matrices with a relaxed condition: limited-shift-full-rank (LT-SFR) matrices, i.e., the matrices that have full row rank no matter how their rows are shifted as long as the shifts are within some range called delay tolerance. As the generator matrices for the previously proposed space-time trellis codes, LT-SFR matrices can guarantee asynchronous full diversity of the corresponding codes when the timing errors are within the delay tolerance. Therefore, due to the relaxed condition imposed on LT-SFR matrices, more eligible generator matrices than SFR matrices become available. 相似文献
17.
This paper investigates subset antenna transmission (SAT) for multiple-input multiple-output (MIMO) systems in the presence
of strong dominant co-channel interferer. The capacity gain from SAT is investigated in the context of optimal antenna subset
selection and power allocation. The SAT does not require channel state information of the co-channel interference, and achieves
capacity gains by distributing the transmit power equally over a selected subset of the transmit antennas. The capacity gain
of the SAT method is analyzed in terms of transmit power and eigenvalues of channel matrix, and its performance in V-BLAST
MIMO systems with various signal constellations is evaluated by computer simulation. 相似文献
18.
针对终端直通(D2D)用户复用蜂窝下行资源时,基站对D2D接收端干扰较严重的问题,该文提出一种基于Null-space的基站下行预编码策略。该策略通过在基站预编码时加入对D2D用户干扰抑制的考虑,使得基站在将下行波束对准其调度的蜂窝用户的同时,在D2D用户方向上形成零陷,从而有效地抑制基站对D2D用户的干扰。考虑到实际系统中基站难以获取完美信道信息,又进一步推导了信道估计误差对预编码性能的影响。仿真结果表明,该文提出的基于Null-space的预编码策略能有效提高D2D用户的吞吐量,但这种性能增益很大程度上依赖于基站到D2D用户信道估计的准确性。 相似文献
19.
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