CDMA移动通信系统中的联合功率控制与多用户检测

功率控制和多用户检测是CDMA移动通信系统中克服远近效应、抑制多址干扰(MAI)的两项关键技术。这里简要介绍了CDMA移动通信系统中功率控制与多用户检测技术,阐述了联合功率控制与多用户检测技术的基本概念,重点综述了联合功率控制与线性多用户检测技术以及联合功率控制与非线性多用户检测技术的研究进展,并对今后的研究方向进行了概括性的描述。     

联合多用户调度与友好干扰的功率资源分配优化研究

物理层安全(Physical Layer Security,PLS)技术是一种利用无线信道固有物理属性来保护无线信道免受非法窃听的有效手段,受到了人们的广泛关注。因此,研究了联合多用户调度与友好干扰的功率资源分配优化问题,考虑存在信道估计误差以及多个窃听者通过协作方式获机密信息的情况,联合多用户调度策略与友好干扰选择,提出了联合多用户调度和随机干扰选择(Multiuser Scheduling and Random Jammer Selection,MS-RJS)方案和联合多用户调度和最佳干扰选择(Multiuser Scheduling and Optimal Jammer Selection,MS-OJS)方案,即选择最佳用户向基站传输机密信息的同时,选择友好干扰发射人工噪声降低窃听者的性能,并将传统多用户调度(Conventional Multiuser Scheduling,CMS)方案作为基准方案。对此,在通信系统总功率受限的情况下,以最小化所提方案的窃听概率和中断概率之和为目标,构建最佳用户与友好干扰之间的功率资源分配优化问题,并设计了一种基于黄金搜索的最佳功率分配迭代算法。实验结果表明,带有最佳功率分配因子的MS-RJS方案和MS-OJS方案相比于CMS方案具有显著的性能优势。     

扩频通信与扩频调制技术

Y99-61517-38 9915633码分多址系统的算法和性能(含7篇文章)=Session2:algorithms and performance CDMA systems[会,英]//1998 IEEE International Coanference on Comnmni—cations,Vol.1 of 3.—38～71(MaG)本部分共收入7篇文章,讨论了可供选择的宽带CDMA 系统的性能比较,基于宽带 CDMA 的 WLL(无线用户环路)系统的基站收发信机的实现,新用户对盲目自适应同步多用户直接序列(DS)CDMA 检测的影响,频率非选择性衰落信道上自举多用户 CDMA 检测器的性能,无线通信中最低中断率的最佳功率控制,基于信号干扰比的功率控制的 CDMA 蜂窝系统的多小区模拟结果,在 CDMA 系统中的快速前向链路功率控制。     

软件无线电技术在CDMA2000基站收发信机中的应用

文章在详细阐述了软件无线电的概念、系统结构、基本特性的基础上,分析软件无线电的优点和难点。结合CDMA2000标准,分析在CDMA2000的基站收发信机中,利用软件无线电技术平台,实现包括RAKE接收机、智能天线、多用户检测和快速功率控制在内的单片系统的方案。     

多用户检测技术及其算法选择的研究

本文在介绍了多用户检测技术的原理以及系统模型的基础上,着重分析对比了几种多用户检测算法的性能,并给出了不同情况下进行算法选择的准则。最后,本文分析了功率控制对多用户检测算法的影响。     

软件无线电技术在CDMA2000基站收发信机中的应用

文章在详细阐述了软件无线电的概念、系统结构、基本特性的基础上,分析软件无线电的优点和难点。结合 CDMA2000标准,分析在 CDMA2000的基站收发信机中,利用软件无线电技术平台,实现包括 RAKE 接收机、智能天线、多用户检测和快速功率控制在内的单片系统的方案。     

Turbo译码原理及其在CDMA多用户检测中的应用

研究了Turbo(并行级联码)译码原理及其在CDMA多用户检测中的应用。文中简述了Turbo译码原理及逐符号最大后验算法(symbol-by-symbol MAP),并将Turbo译码原理应用于CDMA系统的多用户检测,提出了基于Turbo译码原理的多用户检测接收机方案,通过计算机仿真验证该方案的性能。结果表明,本文所提出的方案经过4次迭代之后,其误码率接近单用户界,说明这种接收机可去除多址干扰(MAI)的影响。     

基于多用户MIMO-OFDM的联合发送技术研究

本文提出了一种多用户MIMO-OFDM的联合发送(JT)方案,给出了系统模型,并推导出了数据发送及检测算法。此方案可以大大降低移动终端的数据检测复杂度。通过在TD-SCDMA系统应用环境中的仿真和分析,表明多用户MIMO-OFDM的JT技术具有比多用户MIMO的JT技术更优越的误码率性能。     

一种低复杂度的空时多用户迭代检测方案

该文针对已有的对多用户空时编码系统的研究大都集中在多用户STTC和STBC方案, 提出一种联合Turbo-BLAST的多用户空时方案。在接收端,针对传统的基于符号干扰抵消(Symbol-Level Cancellation, SLC)与检测的迭代接收机复杂度仍然较高的前提下,提出一种低复杂度的基于比特级干扰抵消(Bit-Level Cancellation, BLC)的迭代检测方案。该方案在检测部分将M-QAM调制符号分解成为一系列的BPSK符号的线性组合,采用比特级的干扰抵消。理论分析和仿真结果表明,该文提出的方案在保持BLAST高频谱效率的同时,与传统检测方案相比,在不降低系统性能的前提下,计算复杂度得到了很大程度的降低。     

功率约束条件下MIMO-OFDM下行广播信道自适应资源分配

该文分析了功率约束条件下MIMO-OFDM系统广播信道的发送优化问题,提出了两种不同准则下的多用户传输策略和功率分配方案,即最优空间距离OSD-DPC(Optimal Space Distance Dirty Paper Coding)方案和最大化信噪比波束成形MSNR-DPC(Max Signal to Noise Ratio Dirty Paper Coding)方案。数据结果表明,两种传输策略与理论上的最优传输方案性能非常接近,可以显著提高功率约束条件下的系统性能与容量。     

Optimal power control for Rayleigh-faded multiuser systems with outage constraints

How can we achieve the conflicting goals of reduced transmission power and increased capacity in a wireless network, without attempting to follow the instantaneous state of a fading channel? In this paper, we address this problem by jointly considering power control and multiuser detection (MUD) with outage-probability constraints in a Rayleigh fast-fading environment. The resulting power-control algorithms (PCAs) utilize the statistics of the channel and operate on a much slower timescale than traditional schemes. We propose an optimal iterative solution that is conceptually simple and finds the minimum sum power of all users while meeting their outage targets. Using a derived bound on outage probability, we introduce a mapping from outage to average signal-to-interference ratio (SIR) constraints. This allows us to propose a suboptimal iterative scheme that is a variation of an existing solution to a joint power control and MUD problem involving SIR constraints. We further use a recent result that transforms complex SIR expressions into a compact and decoupled form, to develop a noniterative and computationally inexpensive PCA for large systems of users. Simulation results are presented showing the closeness of the optimal and mapped schemes, speed of convergence, and performance comparisons.     

CDMA系统中基于代价函数的联合功率控制算法

在CDMA系统中，利用多用户检测中的干扰抑制效果可以降低对功率控制的要求。本文提出了一种新的基于代价函数的联合功率控制算法。在该算法中，除了需要对功率向量进行迭代更新以外，还要对接收机滤波器的抽头系数不断迭代更新。实验结果表明，采用本文提出的功率控制算法。在系统内用户发射总功率一定的条件下。可以使各用户获得更高的信干比服务质量，系统容量也具有进一步提高的潜力。     

CDMA系统中联合功率控制、波束赋形与多用户检测

应用功率控制、波束赋形和多用户检测可以有效地消除和减少CDMA系统中的干扰。本文结合波束赋形和多用户检测的特性，提出一种应用波束赋形增益和多用户相关矩阵的解相关算法。基于算法的复杂性，提出一种区分聚集用户进行多用户检测的的算法。由于波束赋形能够消减主瓣波束之外的多用户干扰，对聚集移动台采用解相关检测达到减少运算量和消除多用户干扰的目的。对算法进行了仿真分析，证明了本算法的优越性。     

Fast stochastic power control algorithms for nonlinear multiuser receivers

Uplink communication in a cellular radio network is considered where the base station in each cell employs linear or nonlinear (decision feedback) multiuser receivers. For any such receiver, the problem of interest is that of minimizing the total transmit power under the constraint that all the users of the network achieve their quality-of-service objective in terms of signal-to-interference ratio (SIR). When the solution is feasible for the desired SIR requirements, the optimum powers are computed with a distributed iterative power control strategy suitable for implementation at each base station. While the deterministic algorithm requires both in-cell and out-of-cell user information, the stochastic algorithm proposed in this paper can be implemented at the base stations in a truly distributed manner requiring knowledge of only in-cell parameters. Such an algorithm was proposed previously for the case where base stations use linear (single user) matched filter (MF) receivers. However, the feasibility region in terms of attainable SIRs for a well-designed multiuser receiver, particularly for a nonlinear receiver that employs decision feedback, is generally much larger than it is for the linear MF receiver. The stochastic power control algorithm in this paper, for linear or nonlinear multiuser receivers, converges in the mean-square sense to the minimal powers when the target SIRs are feasible. The second major focus of this paper is to improve the convergence properties of the conventional stochastic approximation based power control strategy by using the more recent results on averaging. Convergence issues of both the "nonaveraged" and "averaged" algorithms are investigated, and numerical examples are presented to demonstrate the performance improvement due to averaging.     

Asymptotic normality of linear multiuser receiver outputs

This paper proves large-system asymptotic normality of the output of a family of linear multiuser receivers that can be arbitrarily well approximated by polynomial receivers. This family of receivers encompasses the single-user matched filter, the decorrelator, the minimum mean square error (MMSE) receiver, the parallel interference cancelers, and many other linear receivers of interest. Both with and without the assumption of perfect power control, we show that the output decision statistic for each user converges to a Gaussian random variable in distribution as the number of users and the spreading factor both tend to infinity with their ratio fixed. Analysis reveals that the distribution conditioned on almost all spreading sequences converges to the same distribution, which is also the unconditional distribution. This normality principle allows the system performance, e.g., the multiuser efficiency, to be completely determined by the output signal-to-interference ratio (SIR) for large linear systems.     

A Unified Approach to Power control in Large Energy-Constrained CDMS Systems

A unified approach to power control is proposed for maximizing utility in terms of energy efficiency in code-division multiple access (CDMA) networks. The approach is applicable to a large family of multiuser receivers including the matched filter, the decorrelator, the linear minimum mean-square error (MMSE) receiver, and the (nonlinear) optimal detectors. It exploits the linear relationship between the transmit power and the output signal-to-interference-plus-noise ratio (SIR) for each user in the large-system limit. Suppose that each user seeks to selfishly maximize its own energy efficiency, a unique Nash equilibrium is shown to exist and be SIR-balanced, thus extending a previous result on linear receivers. A unified power control algorithm for reaching the Nash equilibrium is proposed, which adjusts transmit powers iteratively by computing the large-system multiuser efficiency, which is independent of instantaneous spreading sequences. The convergence of the algorithm is proved for linear receivers, and is demonstrated via simulation for the multiuser maximum likelihood detector. Moreover, the performance of the algorithm in finite-size systems is studied and compared with that of a conventional power control scheme, in which user powers depend on the instantaneous spreading sequences.     

Joint Frequency-Domain Multiuser Turbo Equalization with Successive Interference Cancellation for Doubly-Selective Fading Channels

A novel multiuser separation and equalization scheme is proposed for single carrier wireless communication systems integrating frequency-domain (FD) multiuser turbo equalization (MUTE) and successive interference cancellation (SIC). The proposed iterative structure consists of multiple layers of detection, and at each layer the user with strongest power is processed by a frequency-domain multiuser equalizer to yield the soft extrinsic information on the coded bits of that user, which is delivered to a channel decoder after deinterleaving. The extrinsic information gleaned by the decoder is fed back to both the current and previous multiuser equalizers for the next iteration as a-priori information. The soft symbols of the current user are evaluated by the a-posteriori information of coded bits provided by the multiuser equalizer, and the interference reconstructed by the current user’s soft symbols is canceled out from the received signals in frequency domain. The interference-canceled signals are fed forward to subsequent layers for detection of other users. The proposed scheme effectively mitigates multiple access interference and intersymbol interference by an iterative (turbo) detection method. Numerical simulation examples demonstrate that the proposed FD MUTE with SIC outperforms the traditional MMSE multiuser equalizer over the severely doubly-selective channels, and the bit-error-rate performance tends to be better with the increase of iterations.     

QoS-constrained opportunistic scheduling for sc-fdma with iterative multiuser detection

This letter proposes a quality-of-service (QoS) constrained opportunistic scheduling for a single-carrier frequency division multiple access (SC-FDMA) scheme. The SC-FDMA scheme considered in this letter employs an iterative multiuser detection using frequency-domain equalization (IMDFDE), which allows several users to share a common set of subcarriers. In order to improve spectral efficiency and guarantee QoS of assigned users, the proposed method chooses users by iteratively performing user selection. At each user selection for a set of subcarriers, the scheduler takes into account multiuser interference from previously assigned users of corresponding subcarriers and QoS constraint. Simulation results show that the proposed method provides higher spectral efficiency compared with round-robin and max-SNR.     

Is multiuser detection beneficial to mixed service UMTS networks?

The main objective of this paper is to investigate linear multiuser detection for the uplink of present mixed service UMTS Terrestrial Radio Access Network (UTRAN) Frequency Division Duplex (FDD) networks in terms of system capacity, system coverage as well as power reduction. For the system performance assessments we apply a two-stage power control multiuser detection algorithm where the users are detected by a multiuser block detection. We evaluate the UTRAN FDD load control parameter noise rise and show corresponding system capacity bounds for different service mixes carried over dedicated channels with data rates up to 64 kbit/s. Note that for typical UTRAN FDD services the signal-to-noise operating points of a multiuser detector are very low (less than 0 dB). These low signal-to-interference-plus-noise ratios (SINR) operating points severely limit multiuser detection performance gains. Compared to single-user-matched filtering the minimum mean square error (MMSE) detector leads to fairly modest system capacity gains up to 60% dependent on the service mix assumed while the decorrelator is even worse. With respect to coverage as well as mobile station power, MMSE detection indicates fair to high improvements.     

Spatiotemporal Sensing in Cognitive Radio Networks

Cognitive radio networks need to continuously monitor spectrum to detect the presence of the licensed users. In this paper, we have exploited spatial diversity in multiuser networks to improve the spectrum sensing capabilities of centralized cognitive radio (CR) networks. We develop a fixed and a variable relay sensing scheme. The fixed relay scheme employs a relay that has a fixed location to help the cognitive network base station detect the presence of the primary user. The variable relay sensing scheme employs cognitive users distributed at various locations as relays to sense data and to improve the detection capabilities. This effectively reduces the average detection time by exploiting spatial diversity inherent in multiuser networks. Finally, we study the network outage probabilities to compare the performances of the fixed and variable relay schemes.