Optimum reserved resource allocation scheme for handoff in CDMA cellular system

CDMA cellular systems support two types of handoff: soft handoff and hard handoff. Soft handoff has many advantages over hard handoff. Qualitatively, this feature provides more reliable handoff between base stations as a mobile moves from one cell to the adjacent one. Quantitatively, it considerably increases both the capacity of a heavily loaded multicellular system and the coverage of each individual cell in a lightly loaded system. In this paper, in order to increase the probability of soft handoff at the time of handoff, optimum reserved resource allocation scheme for handoff in CDMA cellular system is proposed, which allocates reserved resource to each frequency channel according to the number of neighbor cells using the same frequency channel. Performance analysis results show that the proposed scheme has higher probability of soft handoff at the time of handoff and higher total call processing performance which is a function of both new calls accepted probability and soft handoff probability than the conventional scheme allocating reserved resource irrelevantly to frequency channels being used by neighbor cells.     

基于功率控制CDMA容量优化的应用

为了克服CDMA系统的远近效应和边缘效应,解决CDMA网络容量受限的问题,采用了功率控制技术,对前向链路减小基站发射功率,对反向链路调整移动台发射功率,降低系统内的干扰水平,满足用户QoS要求,有效提高CDMA系统容量。理论阐述了功率控制技术与CDMA系统容量的关系,从系统载扰比分析入手验证了功率控制对CDMA系统容量的影响,得到了基于功率控制技术两种容量优化方法即远近控制和C/I控制。实际案例仿真结果表明,通过优化功率控制参数的方法能够有效地提升CDMA系统的容量,促使CDMA网络软容量达到最佳,为CDMA网络优化人员提供可以借鉴的思路和方法。     

WCDMA和CDMA2000接入信道的比较和仿真

根据接入信道承载的数据类型，提出了在第三代移动通信系统中接入信道的设计要求。通过对WCDMA和CDMA2000接入信道、增强接入信道的分析，比较了两种系统所使用接入技术的优劣。还给出了接入信道仿真程序的设计思路。基于该仿真程序，可以得到两种接入信道的仿真结果，分析得出WCDMA的接入性能要优于CDMA2000的结论。     

Optimal timeslot and channel allocation considering fairness for multicell CDMA/TDD systems

The CDMA/TDD system is a highly attractive solution to support the next generation cellular mobile systems which provide unbalanced multimedia services between downlink and uplink. In this paper, we analyze the interference for downlink and uplink timeslots in a multicell CDMA/TDD system. We also mathematically formulate an optimal timeslot and channel allocation problem considering capacity fairness among cells, which is to maximize the system capacity under the given traffic unbalance, and propose an efficient algorithm based on the simulated annealing technique. Extensive experimental results show that the proposed scheme yields a good performance, and fairness among cells improves with a decrease in the system capacity.     

一种基于无线信道的多维马尔可夫规划模型

针对3G系统支持多业务的特点,提出了一种基于多维状态马尔可夫模型(Markov)的无线信道容量规划方法。该方法的关键是建立话音业务和其他各类数据业务准确的业务模型,并将每类业务的服务需求映射成对无线信道的实际需求。对呼损率、业务呼叫到达率以及无线信道配置间的关系进行了深入分析。通过分析无线信道容量与业务呼叫到达率的关系,给出了系统扩容的依据。     

编码多载波CDMA在下行Rice衰落信道下的性能分析

文中讨论了一种新的CDMA体制,即将OFDM调制技术应用于CDMA的MC-CDMA。从理论上分析了编码MC-CDMA经过下行Rice衰落信道的性能,针对接收端采用分集与Viterbi译码相结合的接收技术,给出下行链路的误码率表达式,并模拟了性能曲线。     

基于多维状态Markov模型的一种无线信道规划方法

针封3G系统支持多业务的特点，本文提出一种基于多维状态马尔可夫模型（Markov）的无才信道容量规划方法。该方法的关键是建立话音业务和其它各类数据业务准确的业务模型，并将每类业务的服务需求映射成封无才信道的实际需求。本文对呼损率、业务呼叫到达率以及无才信道配置间的关系进行了深入分析。通过分析无线信道容量与业务呼叫到达率的关系，给出了系统扩客的依据。     

Channel switching control policy for wireless mesh networks

Dynamic channel assignment algorithms allow wireless nodes to switch channels when their traffic loads exceed certain thresholds. These thresholds represent estimations of their throughput capacities. Unfortunately, the threshold estimation may not be accurate due to co-channel interference (CCI) and adjacent-channel interference (ACI), especially with high traffic loads in dense networks. When the link capacity is over-estimated, these channel assignment algorithms are not effective. This is because the channel switch is not triggered even with overloaded data traffic and the link quality decreases significantly as the channel is overloaded. When the link capacity is under-estimated, the link is under-utilized. Moreover, when link traffic load increases from time to time, channel switch occurs frequently. Such frequent channel switches increase latency and degrade throughput, and can even cause network wide channel oscillations. In this paper, we propose a novel threshold-based control system, called balanced control system (BCS). The proposed threshold-based control policy consists of deciding, according to the real time traffic load and interference, whether to switch to another channel, which channel should be switched to and how to perform the switch. Our control model is based on a fuzzy logic control. The threshold which assists to make the channel switch decisions, could be deduced dynamically according to the real-time traffic of each node. We also design a novel dynamic channel assignment scheme, which is used for the selection of the new channel. The channel switch scheduler is provided to perform channel-switch processing for sender and receiver over enhanced routing protocols. We implement our system in NS2, and the simulation results show that with our proposed system, the performance improves by 12.3%–72.8% in throughput and reduces 23.2%–52.3% in latency.     

码分多址在移动卫星通信系统中的信道容量分析

本文介绍了码分多址(CDMA)联接的移动卫星通信系统及其在不同波束情况下,其信道容量的计算方法。给出了单波束固定天线系统、扫描波束CDMA系统、多波束CDMA系统和CDMA扫描波束回程键的信道容量表达式,并对结果进行了详细分析。对正在着手规划和建立我国的移动卫星通信系统具有一定的参考价值。     

基于SATA的嵌入式直接存储系统

研究嵌入式高速存储系统的应用问题,分析传统数据存储系统存在的不足,提出一种基于SATA的嵌入式直接存储系统设计方法。该方法参照完整实现SATA物理层和链路层协议,根据嵌入式存储需求组合SATA传输层和应用层协议建立DMA控制模块,在现场可编程门阵列中构建符合SATA标准的存储通道。SATA存储通道实现数据到SATA存储设备的直接存储,通过扩展SATA存储通道实现存储系统带宽及容量的扩展。实验结果表明,该方法能解决带宽瓶颈和通用性问题,达到良好的存储效果。     

Performance evaluation of cyclic prefix CDMA systems with frequency domain interference cancellation

Direct-sequence code division multiple access (DS/CDMA) systems transmitting over multipath channels suffer from intersymbol interference (ISI) and multiple access interference (MAI). Recently, DS/CDMA with frequency domain equalization (FDE) has attracted much attention for its ability to obtain an excellent performance even in strong frequency selective fading channels. However, the presence of residual interference after the FDE degrades the orthogonality among the spreading codes and hence the BER performance deteriorates. Parallel interference cancellation (PIC) is an effective method to suppress the MAI and improve the CDMA system capacity. In this paper, we propose three interference cancellation architectures for downlink cyclic prefix CDMA systems. The common thread between these three architectures is their implementation in frequency domain. A comparison between such architectures is presented. Simulation results show that the combination of PIC and FDE provides an efficient solution to suppress the MAI in downlink CDMA systems over frequency selective fading channels.     

Power Control for Cellular Communications with Time‐Varying Channel Uncertainties

Power control in a code‐division multiple access (CDMA) based cellular network is a challenging problem because the communication channels change rapidly because of multipath fading. These rapid fluctuations cause detrimental effects on the control efforts required to regulate the signal‐to‐interference plus noise ratios (SINRs) to the desired level. Thus, there is a need for power‐control algorithms that can adapt to rapid changes in the channel gain caused by multipath fading. Much of the previous work has either neglected the effects of fast fading, assumed that the fading is known, or assumed that all the link gains are known. In this paper, we model the effects of fast fading and develop practical strategies for robust power control based on SINR measurements in the presence of the fading. We develop a controller for the reverse link of a CDMA cellular system, and use a Lyapunov‐based analysis to prove that the SINR error is globally uniformly ultimately bounded. We also utilize a linear prediction filter that utilizes local SINR measurements and estimates of the Doppler frequency that can be derived from local SINR measurements to improve the estimate of the channel fading used in the controller. The power‐control algorithm is simulated for a cellular network with multiple cells, and the results indicate that the controller regulates the SINRs of all the mobile terminals (MTs) with low outage probability. In addition, a pulse‐code‐modulation technique is applied to allow the control command to be quantized for feedback to the transmitter. Simulation results indicate that the outage probabilities of all the MTs are still within the acceptable range if at least 3‐bit quantization is employed. Comparisons to a standard algorithm illustrate the improved performance of the predictive controller.     

基于MABC的中继系统资源分配策略

针对MABC的中继系统,对资源配置策略的优化问题进行研究,并将功率分配问题和中继选择问题相结合。基于此,提出了一种存在干扰情况MABC模型的多中继系统资源分配策略（IS-MABC-OPOR）。考虑双向中继系统干扰信号对其传输性能的影响,以通信链路信道容量最大化为优化目标,利用拉格朗日方法,对通信链路上的各节点进行了最优功率分配和最佳中继选择,给出了通信链路信道容量最大意义下的资源分配数学表达式。仿真结果表明,该链路的信道容量受中继节点位置以及链路总功率的制约,相比于等功率分配方案（EPA）、随机功率分配方案（RPA）和在所提方案的基础上加大干扰信号的信道增益,IS-MABC-OPOR方案有效提高了系统的信道容量,从而实现资源能够满足更高速率的业务传输需求。     

Optimal admission control algorithms for scheduling burst data in CDMA multimedia systems

The third generation mobile communication systems are widely envisioned to be based on wideband code division multiple access (CDMA) technologies to support high data rate (HDR) packet data services. To effectively harness the precious bandwidth while satisfying the HDR requests from users, it is crucial to use a judicious burst admission control algorithm. In this paper, we propose and evaluate the performance of a novel jointly adaptive burst admission algorithm, called the synergistic burst admission control algorithm to allocate valuable resources (i.e., channels) in wideband CDMA systems to burst HDR requests. We consider the spatial dimension only, and by that we mean the algorithm performs scheduling and admission control, for the current frame only, based solely on the selection diversity in the geographical and mobility aspects. The scheduler does not exploit the temporal dimension in that it does not make allocation decisions about future frames (i.e., requests that do not get allocation are simply ignored and such requests will be treated as new request in future frames). In the physical layer, we use a variable rate channel-adaptive modulation and coding system which offers variable throughput depending on the instantaneous channel condition. In the MAC layer, we use the proposed optimal multiple-burst admission algorithm, induced by our novel integer programming formulation of the admission control and scheduling problem. We demonstrate that synergy could be attained by interactions between the adaptive physical layer and the burst admission layer. Both the forward link and the reverse link burst requests are considered and the system is evaluated by dynamic simulations which takes into account of the user mobility, power control and soft handoff. We found that significant performance improvement, in terms of average packet delay, data user capacity and coverage, could be achieved by our scheme compared to the existing burst assignment algorithms.     

基于UKF的CDMA系统信道参数估计

CDMA系统信道时间延迟估计是一个非线性的迭代过程。UKF算法能够避免EKF由于线性化非线性系统而带来的误差过大等问题,比EKF估计的更加精确。利用UKF算法对CDMA系统信道的幅度衰减参数与延时参数进行了估计。在研究中考虑到了多址干扰和远近效应对信道参数的影响,仿真结果表明UKF算法能有效地抑制远近效应及多址干扰,估计出无线信道参数。     

基于DSP的信号处理实验系统的设计和开发

以TI公司的数字信号处理器(DSP)TMS320VC5416为CPU,设计了CDMA通信系统中反向链路信号处理过程的实验系统。CDMA反向链路信号处理过程比较复杂,不易观察。而利用DSP高速和精确的运算能力﹑丰富的通用输入输出口(需要配置)和其软件开发平台CCS中丰富的显示信号特征的功能,实验者能够多角度的观察和研究信号处理结果。给出了硬件电路设计和作为例子的多角度观察OQPSK调制。     

基于CDMA的Ad hoc网络MAC协议吞吐量研究

网络吞吐量性能是衡量一个通信网络性能的一个重要指标,基于CDMA技术的Ad hoc网络扩频码的分配方案对系统吞吐量性能有着重要的影响,研究了如何充分利用CDMA多址接入能力提高Ad hoc信道利用率等网络性能.通过建立网络状态的马尔可夫模型,提出一种分析吞吐量性能的方法,该方法适用于同时存在背景噪声和多址干扰的情况.最后,通过数值仿真分析了扩频增益和信噪比对吞吐量性能的影响,并对网络参数进行了优化配置.该研究成果对基于CDMA技术的Ad hoc网络设计和优化提供了理论依据.     

基于天线选择的全双工中继干扰抑制

在全双工中继协作通信系统中,中继发送端和接收端之间的干扰严重影响了系统的传输性能,因此干扰抑制是全双工模式下的关键问题。与引入权重矩阵的抑制方法不同,介绍了一种在中继发送端和接收端同时进行天线选择的干扰抑制方法。在多天线中继衰落信道系统中,基于最小化干扰信道的信道容量准则,中继发送端和接收端均选择合适的天线子集。在该抑制方法的基础上,理论分析了系统信道容量的闭式表达。仿真结果表明,天线选择方案改善了系统的信道容量和误码率性能,干扰抑制效果明显,同时降低了系统的复杂性。     

基于合作似然检测和球形译码的多用户多输入输出多跳中继系统

针对多输入输出(MIMO)系统在传输数据过程中的误码率(BER)和信道容量优化问题,提出一种基于合作似然检测和球形译码的多用户MIMO多跳中继系统。首先,该系统构建二阶协作的MIMO中继系统模型对信道数据的中继传输过程以及路径损耗、阴影衰落情况进行分析;接着,通过球形译码来推导出等效的最大似然规则进行对数正态阴影衰落检测;最后提出最大调和平均信道功率选择策略,基于相关性链路度量和最大信道功率阈值为用户选择误码率更小的接入链路,从而改善多用户MIMO系统的性能。实验仿真结果显示,与基于互信息最大化的多用户MIMO多跳中继系统以及基于解码转发和多入多出技术正交空时分组编码(STBC)的中继系统相比,该系统在数据传输过程中的平均比特误码率分别降低了27.4%和32.6%,平均信道容量分别提高了9.5%和12.7%,因此在减少误码率和提高信道容量上具有较好的效果。     

Blind information-theoretic multiuser detection algorithms for DS-CDMA and WCDMA downlink systems

Code division multiple access (CDMA) is based on the spread-spectrum technology and is a dominant air interface for 2.5G, 3G, and future wireless networks. For the CDMA downlink, the transmitted CDMA signals from the base station (BS) propagate through a noisy multipath fading communication channel before arriving at the receiver of the user equipment/mobile station (UE/MS). Classical CDMA single-user detection (SUD) algorithms implemented in the UE/MS receiver do not provide the required performance for modern high data-rate applications. In contrast, multi-user detection (MUD) approaches require a lot of a priori information not available to the UE/MS. In this paper, three promising adaptive Riemannian contra-variant (or natural) gradient based user detection approaches, capable of handling the highly dynamic wireless environments, are proposed. The first approach, blind multiuser detection (BMUD), is the process of simultaneously estimating multiple symbol sequences associated with all the users in the downlink of a CDMA communication system using only the received wireless data and without any knowledge of the user spreading codes. This approach is applicable to CDMA systems with relatively short spreading codes but becomes impractical for systems using long spreading codes. We also propose two other adaptive approaches, namely, RAKE-blind source recovery (RAKE-BSR) and RAKE-principal component analysis (RAKE-PCA) that fuse an adaptive stage into a standard RAKE receiver. This adaptation results in robust user detection algorithms with performance exceeding the linear minimum mean squared error (LMMSE) detectors for both Direct Sequence CDMA (DS-CDMA) and wide-band CDMA (WCDMA) systems under conditions of congestion, imprecise channel estimation and unmodeled multiple access interference (MAI).