Cross-layer packet scheduling for downlink multiuser OFDM systems

This paper proposes a channel and queue aware fair (CQAF) packet scheduling scheme for the downlink packet transmission in multiuser orthogonal frequency division multiplexing (OFDM) systems. By making use of the information on the channel conditions and the queue lengths, the proposed CQAF packet scheduling scheme efficiently allocates the subcarriers, transmission power and modulation level to users under the constraints of total transmission power, the number of subcarriers, bit-error-rate (BER) requirement and generalized processor sharing (GPS)-based fairness requirement. The numerical results show that the proposed CQAF packet scheduling scheme can reduce the transmission delay and queue length significantly while maximizing system throughput and maintaining fairness among users.     

Blind multiuser detection for MC-CDMA with antenna array

We investigate the characteristics of the received signal as trilinear model for multi-carrier code division multiple access (MC-CDMA) system with antenna array, and propose a blind multiuser detection method for MC-CDMA system in this paper. The trilinear-based multiuser detection algorithm (Trilinear-MUDE) that we presented exploits the versatile diversity in MC-CDMA system while require neither channel information nor statistical characteristics. The algorithmic performance indicates that the proposed algorithm is very close to the nonblind MMSE method, and better than minimum output energy (MOE) receiver and matched filter. Numerical results also reveal its compatibility in condition of small sampling sizes.     

DS-CDMA downlink systems with fading channel employing the generalized receiver

In this paper, we investigate a generalized receiver (GR) constructed on the basis of the generalized approach to signal processing (GASP) in noise employing by direct-sequence code-division multiple access (DS-CDMA) downlink wireless communication system with multipath fading. Transmitted signaling technique is based on using the orthogonal unified complex Hadamard transform spreading sequences. The use of GR allows us to maintain the orthogonality between users and reduce the multipath fading effect and interference from other users. A general multipath-fading model is assumed. Bit-error rate (BER) performance of system is evaluated by means of the signal-to-interference-plus-noise ratio (SINR) at the output of GR employed by DS-CDMA downlink wireless communication system. Using the orthogonal unified complex Hadamard transform spreading sequences as the transmitted signaling technique, we obtain that SINR at the GR output is independent of the phase offsets between different paths. If the Walsh–Hadamard (WH) spreading sequences are used as the transmitted signaling technique, the SINR at the output of GR employed by the same system is a function of squared cosine of path phase offsets. As a result, the BER performance of the last DS-CDMA downlink wireless communication system is worse in comparison with that of the first system. Comparative analysis between the BER performance of DS-CDMA downlink wireless communication systems employing both the GR and the Rake receiver, which consists of a bank of correlation receivers, with each individual receiver correlating with a different arriving multipath component, shows us a superiority of the first system over the second one both at high and low SINRs.     

基于OFDM的跨小区下行链路异步多用户检测

针对3GPP长期演进计划(LTE)下行链路的OFDMA传输以及基站之间异步部署的特点,引入了异步OFDM干扰消除问题来改善小区边缘用户的服务质量以及提高整个蜂窝系统的下行容量.在同步OFDM-IDMA原理的基础上,提出了低复杂度的基于滑动窗口的异步多用户检测算法.仿真结果表明,在窗口长度很小的情况下,该异步检测算法仍然可以在高信噪比区域接近同步的性能.     

Support vector machine multiuser receiver for DS-CDMA signals inmultipath channels

The problem of constructing an adaptive multiuser detector (MUD) is considered for direct sequence code division multiple access (DS-CDMA) signals transmitted through multipath channels. The emerging learning technique, called support vector machines (SVM), is proposed as a method of obtaining a nonlinear MUD from a relatively small training data block. Computer simulation is used to study this SVM MUD, and the results show that it can closely match the performance of the optimal Bayesian one-shot detector. Comparisons with an adaptive radial basis function (RBF) MUD trained by an unsupervised clustering algorithm are discussed.     

非理想功率控制和多用户检测在WCDMA高空平台通信系统中的联合应用

高空平台(HAPS)通信系统是近年来正处于先期研究的新型信息系统。理论分析了非理想功率控制和多用户检测(MUD)对HAPS通信系统上行链路的影响,分析这两种技术的工作原理,探讨在WCDMA应用中结合使用两种技术的可行性和方法。     

Advanced search algorithms for information-theoretic learning with kernel-based estimators

Recent publications have proposed various information-theoretic learning (ITL) criteria based on Renyi's quadratic entropy with nonparametric kernel-based density estimation as alternative performance metrics for both supervised and unsupervised adaptive system training. These metrics, based on entropy and mutual information, take into account higher order statistics unlike the mean-square error (MSE) criterion. The drawback of these information-based metrics is the increased computational complexity, which underscores the importance of efficient training algorithms. In this paper, we examine familiar advanced-parameter search algorithms and propose modifications to allow training of systems with these ITL criteria. The well known algorithms tailored here for ITL include various improved gradient-descent methods, conjugate gradient approaches, and the Levenberg-Marquardt (LM) algorithm. Sample problems and metrics are presented to illustrate the computational efficiency attained by employing the proposed algorithms.     

Novel scheduling strategy for downlink multiuser MIMO system: Particle swarm optimization

In this paper the scheduling problem in downlink multiuser MIMO system is described as an optimization problem and particle swarm optimization (PSO) algorithm is introduced to address such problem. Two PSO scheduling methods with different objective functions applicable to different requirements on capacity and complexity are investigated. One is the capacity based PSO(C-PSO) scheduling method aiming at achieving the near optimal capacity; and the other is the lower bound of eigenvalue based PSO (LBE-PSO) scheduling method with the purpose of reducing computational complexity and at the same time achieving as large as possible capacity gain. Furthermore, convergence analysis of PSO from both the particle and the velocity aspects is also presented to derive the convergent condition, which is validated by several examples of different parameter values. Simulation results reveal that the C-PSO can obtain nearly the same capacity as the exhaustive search method with lower complexity, while the LBE-PSO provides a viable approach by striking a better tradeoff between capacity and computational complexity.     

基于粒子群优化的多用户MIMO下行链路调度算法

将多用户MIMO下行链路调度问题描述为一优化问题,并引入粒子群优化(particle swarm optimization,PSO)算法进行求解.针对容量和复杂度有不同要求的应用场合,给出了两类采用不同目标函数PSO调度算法:基于容量PSO(C-PSO)调度算法和基于特征值下界PSO(LBE-PSO)调度算法.C-PSO算法目标是获得接近最优容量的性能;而LBE-PSO算法旨在有效降低算法复杂度的同时尽可能获得高的容量增益.进一步,从粒子和速度两方面对PSO算法的收敛性进行分析并得出收敛条件,然后通过不同参数值的实例对其进行验证.仿真结果表明,C-PSO算法能够以较低的复杂度获得接近穷搜索算法的容量,而LBE-PSO调度算法则提供了一种能够在容量和复杂度之间很好折中的调度方案.     

新的基于仿射投影算法的盲多用户检测器

多径衰落信道下的盲自适应多用户检测算法的运算复杂度通常都比较大,将基于仿射投影算法的盲多用户检测器与RAKE分集技术相结合,提出了一种盲自适应接收算法。该接收算法平衡了收敛速度和计算复杂度之间的矛盾,具有相对较好的收敛性能及较小的运算复杂度。通过模拟实验比较了几种算法的收敛、跟踪及误码性能,结果表明该方法具有明显的整体优势。     

Ant colony input parameters optimization for multiuser detection in DS/CDMA systems

In this work a simple and efficient methodology for tuning the input parameters applied to the ant colony optimization multiuser detection (ACO-MuD) in direct sequence code division multiple access (DS-CDMA) is proposed. The motivation in using a heuristic approach is due to the nature of the NP complexity posed by the wireless multiuser detection optimization problem. The challenge is to obtain suitable data detection performance in solving the associated hard complexity problem in a polynomial time. Previous results indicated that the application of heuristic search algorithms in several wireless optimization problems have been achieved excellent performance-complexity tradeoffs. Regarding different system operation and channels scenarios, a complete input parameters optimization procedure for the ACO-MuD is provided herein, which represents the major contribution of this work. The performance of the ACO-MuD is analyzed via Monte-Carlo simulations. Simulation results show that, after convergence, the performance reached by the ACO-MuD is much better than the conventional detector, and somewhat close to the single user bound (SuB). Flat Rayleigh channels is initially considered, but the input parameter optimization methodology is straightforward applied to selective fading channels scenarios, as well as to joint time-spatial wireless channels diversities.     

Blind joint maximum likelihood channel estimation and data detection for SIMO systems

A blind adaptive scheme is proposed for joint maximum likelihood (ML) channel estimation and data detection of single- input multiple-output (SIMO) systems.The joint ML optimisation over channel and data is decomposed into an iterative optimisation loop.An efficient global optimisation algorithm called the repeated weighted boosting search is employed at the upper level to optimally identify the unknown SIMO channel model,and the Viterbi algorithm is used at the lower level to produce the maximum likelihood sequence estimation of the unknown data sequence.A simulation example is used to demonstrate the effectiveness of this joint ML optimisation scheme for blind adaptive SIMO systems.     

WCDMA系统中的差分最小均方误差多用户检测算法研究

针对现有自适应多用户检测算法需要训练比特、不能适应快衰落信道的问题,提出适用于WCDMA系统的基于差分最小均方误差（DMMSE）准则的自适应多用户检测算法。该算法结合二级扩频体制的特点,根据具有相同综合扩频码的相邻接收符号幅度变化的比率变化自适应调整横向滤波器的权系数,由于该方法更能刻画多址干扰的变化规律,因此可有效地抑制多址干扰。仿真结果表明,在多普勒频移的传播环境下,DMMSE算法的误码性能优于现有自适应MMSE算法。     

一种DS-CDMA系统扩频码和参数盲估计方法

传统DS-CDMA系统扩频码盲估计方法以主元分析为基础,若各用户扩频码非正交(即存在多址干扰)则将导致扩烦码估计失效.本文通过码域映射,信息码盲分离以及相应的信号处理手段,实现了多用户情况下的扩频码、延时信息以及信息码的盲估计.该方法无需已知任何同步信息,允许系统存在较差的信噪比和多址干扰.仿真实验表明,对异步DS-CDMA系统该方法有效可行.     

Efficient recursive algorithms for detection of abrupt changes insignals and control systems

This paper addresses a number of open problems concerning the generalized likelihood ratio (GLR) rules for online detection of faults and parameter changes in control systems. It is shown that with an appropriate choice of the threshold and window size, these GLR rules are asymptotically optimal. The rules are also extended to non-likelihood statistics that are widely used in monitoring adaptive algorithms for system identification and control by establishing Gaussian approximations to these statistics when the window size is chosen suitably. Recursive algorithms are developed for practical implementation of the procedure, and importance sampling techniques are introduced for determining the threshold of the rule to satisfy prescribed bounds on the false alarm rate     

Recursive identification algorithms to design fault detection systems

This paper deals with the recursive identification of the parity space based fault detection systems. We propose two such algorithms that update the eigenstructure after every new measurement with significantly less computational cost. Its immediate application is in the design of adaptive parity space based residual generators. The method improves the fault detection performance against uncertain changes, especially the frequent shifts in operating points, or parameter variations. The algorithms are compared with the existing techniques and applied to the hybrid simulation platform of continuously stirred tank heater.     

面向多用户检测的蚁群算法及其改进

基于蚁群算法建立了一个多用户检测问题的模型,在这个模型中,蚁群算法得到了简化并且更加利于并行计算.随后将基于优化排序的蚂蚁系统用于多用户检测,并通过分析算法的缺陷提出了一种蚁群算法与进化规划相结合的混合算法,扩大了搜索空间,降低了搜索陷入局部极小的概率.通过对多用户检测问题的试验仿真表明,改进算法不仅操作简单,而且全局搜索能力有了显著的提高.     

采用非线性串行干扰消除的DS-CDMA系统中最优检测顺序的研究

在采用串行干扰消除的DS-CDMA系统中,不同的检测顺序导致不同的系统性能。研究在这样的系统中如何调整检测顺序以最小化总发射功率的问题。不同于已有研究,考虑非理想情况下的非线性串行干扰消除接收机,并且外小区干扰不再假设为独立于用户发射（接收）功率。在这样的前提下,根据给定检测顺序下最优功率分配的表达式,推导出了能够最小化总发射功率的最优检测顺序。仿真实验展示了不同检测顺序下系统的发射功率要求,证实了最优检测顺序有助于降低总发射功率。相应地,可将基于最优检测顺序的功率分配机制用于实际系统。     

基于离散粒子群优化的多用户MIMO用户选择*

为了在降低计算复杂度的同时获得良好的性能,给出了一种基于离散粒子群优化的多用户MIMO用户选择方法.该方法基于sum-MSE预编码,所支持的用户数目取决于接收方的子流数之和,改变了传统的用户选择方法支持的用户接收天线数之和不大于发送天线数的限制.当移动台子流个数小于接收天线数时,所研究的用户选择方法可以增加同时服务的用户个数,获得更高的系统和容量.仿真结果表明,该方法能够在系统性能和复杂度之间进行良好的折中.     

Power-time resource allocation for downlink SWIPT-assisted cooperative NOMA systems

We study a downlink cooperative non-orthogonal multiple access(NOMA) system in which a base station(BS) serves two paired users on the same frequency band simultaneously, and the near user acts as an energy-constrained relay for the far user since there is no direct link between the BS and the far user due to physical obstacles or heavy shadowing. To replenish energy of the near user for relaying, we enable the near user to harvest energy from BS signals by adopting the simultaneous wireless inf...