最优多用户检测问题研究

DS-CDMA无线通信中的最优多用户检测属于NP完备组合优化问题,启发式方法是求解这类问题的有效方法,通过分析最优多用户检测问题的适应值曲面特征,研究设计了系列低计算复杂度、接近最优多用户检测性能的启发式算法.仿真结果表明,基于演化策略的多用户检测算法能够在中等规模用户数情况下提供与最优多用户检测相当的性能,而快速迭代局域搜索算法能够以较低的计算复杂度得到比其他局域搜索算法更好的解.     

一种实现最佳用户检测的非线性优化神经网络

本文提出并讨论了实现码分多址（CDMA）系统上最佳多用户检测（MUD）的一种神经网络方法。该方法通过将最佳多用户检测视为非线性优化组合问题，利用神经网络能有效求解非线性优化问题的优势，导出了一种非线性优化神经网络来实现最佳多用户检测，理论分析和计算机模拟表明，所提出的神经网络具有可实时应用的动态性能和较传统方法优越得多的误码率性能和抗多址干扰的性能。     

Asymptotic Analysis of General Multiuser Detectors in MIMO DS-CDMA Channels

We analyze decoupling structures of MIMO DS-CDMA channels with general multiuser detector front ends, using the replica method, in order to compare the space-time spreading (STS) and time spreading (TS) schemes. In the many- user limit, a MIMO DS-CDMA channel with the STS scheme is decoupled into a bank of single-user SIMO channels. On the other hand, a MIMO DS-CDMA channel with the TS scheme is decoupled into a bank of single-user MIMO channels. In view of performance, the STS scheme outperforms the TS scheme in the fast fading situation if transmit spatial correlations exist. In terms of complexity, the STS scheme does not require any space-time coding. On the other hand, the TS scheme does require space-time coding in order to achieve comparable performance to the STS scheme. The STS scheme improves the performance of communications and reduces the complexity of transmitter and receiver architectures.     

Optimum Power Allocation for Multiuser OFDM with Arbitrary Signal Constellations

This paper formulates power allocation policies that maximize the region of mutual informations achievable in multiuser downlink OFDM channels. Arbitrary partitioning of the available tones among users and arbitrary modulation formats, possibly different for every user, are considered. Two distinct policies are derived, respectively for slow fading channels tracked instantaneously by the transmitter and for fast fading channels known only statistically thereby. With instantaneous channel tracking, the solution adopts the form of a multiuser mercury/waterfilling procedure that generalizes the single-user mercury/waterfilling introduced in [1], [2]. With only statistical channel information, in contrast, the mercury/waterfllling interpretation is lost. For both policies, a number of limiting regimes are explored and illustrative examples are provided.     

最佳线性多用户信号检测器及其近似求解

本文提出了平均误比特率最小意义下的最佳线性多用户信号检测器，并给出了求解这种最佳线性多用户信号检测器的近似方法－训练单层感知器不。     

Optimum Multiuser Detector for Multipath Slow Fading Asynchronous CDMA Channels

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A New Algorithm for Optimum Multiuser Detection in Synchronous CDMA Systems

Optimum multiuser detection for Code Division Multiple Access (CDMA) systems requires the solution of an NP-hard combinatorial optimization problem. It is well known that the computational complexity of the optimum multiuser detector is exponential with the number of active users in the system. In order to reduce the complexity of the optimum multiuser detection, we propose a Reduced Complexity Maximum Likelihood (RCML) algorithm that includes a set of novel certain boundary rules and characteristics. We investigate the performance and complexity tradeoffs for the RCML algorithm by conducting a set of simulations; Maximum Likelihood (ML) detection as a reference for performance comparisons, and relaxation based Semidefinite Programming (SDPB) algorithm as a reference for complexity comparisons. We show that the RCML algorithm is a promising algorithm for its computational savings over relaxation based algorithms in lightly-to-moderately loaded CDMA systems, and for its optimality in highly loaded CDMA systems.     

TD-SCDMA的高频谱利用率探讨

文章通过对TD-SCDMA系统中所采用的关键技术,如智能天线、联合检测、同步CDMA以及动态信道分配等的分析,阐述了TD-SCDMA系统对比于其他移动通信系统所拥有的更高的频谱利用率,突出了其作为中国第一个拥有自主知识产权的国际通信标准在技术上的优势.     

直接序列扩频多址通信系统中最佳线性多用户信号检测器研究

本文提出了平均误经特率最小意义下的最佳线性多用户信号检测器，并给出了救解这种最佳线性多用户信号检测器的近似方法－－训练单层感知器法，初步的研究结果表明；这种检测器的性能优于以往多种检测器。     

Achieving Long-Term Fairness and Optimum Multiuser Diversity Gain in Time-Varying Broadcast Channels

In this paper, a downlink system in which a single-antenna base station communicates with k single antenna users over a time-correlated fading channel is considered. It is assumed that each receiver knows its own channel state, while the rate of the channel variation for all users and the corresponding initial fading gains are known to the base station. The average (per channel use) throughput of the system is studied by applying various adaptive signaling schemes. Assuming a large number of users in the system, it is shown that using a scheduling scheme in which the base station transmits to the user with the maximum initial fading gain, while using a fixed codeword length for all users, achieves the order of the maximum throughput. Moreover, an alternative scheduling scheme is proposed (by accounting for users' delays) and shown to achieve the optimum long-term fairness, while preserving the order of the maximum throughput.     

Asymptotic Capacity of Static Multiuser Channels Under Optimal User Identification and Data Detection

We examine a multiple-access communication system in which multiuser detection is performed without knowledge of the number of active interferers. Using a statistical-physics approach, we compute the single-user channel capacity and spectral efficiency in the large-system limit and derive their limiting values for high SNR.     

多级降压收集极效率的优化

围绕着MDC的核心即提高效率问题,分析了MDC的物理模型,阐明了MDC的功率分布图并解释了其来源.利用MDC的入口条件生成的功率分布图,可以快速得到给定降压级数的MDC的最优化效率,以及各电极的最优化电位.在最优化电位附近进行模拟仿真,减小电位选择的盲目性,起到事半功倍的效果.     

Space-Time Blind Multiuser Detection for Multiuser DS-CDMA and Oversampled Systems

Novel space-time blind multiuser detection method for multiuser DS-CDMA and oversampled systems is presented. To achieve signal recovery, Khatri-Rao product structure of the space-time channel matrix of received signals and rank-1 projection strategy are exploited. Two blind signal detection algorithms based on Khatri-Rao product decomposition are proposed. Uniqueness of the Khatri-Rao decomposition is discussed. Simulation results show that the proposed algorithms have performance close to the non-blind Zero Forcing algorithm and still work well in the case of only few antennae in the receiving end.     

Multiuser projection receivers

A new multiuser receiver for synchronous code-division multiple-access (CDMA) systems with error control coding is proposed. The receiver achieves interference cancellation by projecting the undesired users onto the space spanned by the desired users' signal vectors. The detector calculates the least squares (LS) estimate of the interfering users data, that is used to yield an adjusted metric for maximum likelihood sequence estimation (MLSE) for the desired users' sequences. Simulation results indicate that close to optimal performance can be achieved when all but one of the users are projected using only a single user decoder for the desired user. Further, an adaptive receiver structure based on the recursive LS update is presented that is well-suited for DSP implementation due to it's computational efficiency     

CDMA多用户检测技术

首先分析了CDMA移动通信系统中采用多用户检测的必要性,然后介绍了各种多用户检测技术的工作原理,对各种多用户检测技术的特点进行了比较,最后提出了目前多用户检测技术的一些最新发展方向。     

Multiuser rate-based flow control

Flow and congestion control allow the users of a telecommunication network to regulate the traffic that they send into the network in accordance with the quality of service that they require. Flow control may be performed by the network, as is the case in asynchronous transfer mode (ATM) networks (the available bit rate (ABR) transfer capacity), or by the users themselves, as is the case in the Internet [transmission control protocol/Internet protocol (TCP/IP)]. We study both situations using optimal control and dynamic game techniques. The first situation leads to the formulation of a dynamic team problem, while the second one leads to a dynamic noncooperative game, for which we establish the existence and uniqueness of a linear Nash equilibrium and obtain a characterization of the corresponding equilibrium policies along with the performance costs. We further show that when the users update their policies in a greedy manner, not knowing a priori the utilities of the other players, the sequence of policies thus generated converges to the Nash equilibrium. Finally, we study an extension of the model that accommodates multiple traffic types for each user, with the switching from one type of traffic to another being governed by a Markov jump process. Presentation of some numerical results complements this study     

CDMA多用户检测技术

首先分析了CDMA移动通信系统中采用多用户检测的必要性 ,然后介绍了各种多用户检测技术的工作原理 ,对各种多用户检测技术的特点进行了分析比较 ,最后提出了目前多用户检测技术的一些最新发展方向。     

A Technique for Multiuser and Intercarrier Interference Reduction in Multiple-Antenna Multiuser OFDM Downlink

We propose a two-stage precoder/equalizer to suppress intercarrier interference (ICI) and multiuser interference (MUI) in downlink multiuser OFDM with multiple transmit antennas. The first stage, non-linear Tomlinson-Harashima preceding (THP) at the base station (BS) transmitter, mitigates the effect of the spatial inter-stream interference caused by transmission from multiple transmit antennas to decentralized users. In the second stage, each user's receiver employs low- complexity iterative linear minimum mean-square error (MMSE) equalization to suppress the ICI due to frequency offset. Our proposed technique virtually eliminates the bit error rate (BER) degradation due to normalized frequency offsets as high as 10%.