异步相干扩时光码分多址系统的干扰性能分析

从码字的非周期互相关函数出发,分析异步相干扩时光码分多址(OCDMA)系统的多址干扰(MAI)和差拍噪声(BN).干扰用户不同的传输时延,非周期互相关强度均值随之变化,差拍噪声和多址干扰也随之变化.给出了差拍噪声和多址干扰与非周期互相关强度均值的关系,讨论了异步相干扩时OCDMA系统的误码率(BER)与非周期互相关强度均值的关系.最后,以码长511的Gold码为例,针对干扰用户之间不同的传输时延,得到了异步相干扩时OCDMA系统的误码率上界与平均误码率性能.在平均误码率情况下,OCDMA系统能支持12个干扰用户,而在最差情况下(误码率上界),系统容纳的干扰用户数不超过4个.     

Interference and Queuing Delay Based Uplink Packet Access Control in Wideband Code-Division Multiple-Access Systems

In this letter, we propose a packet access control algorithm for non-real-time, interactive packet services via dedicated channels in the uplink of wideband code-division multiple-access (WCDMA) systems. We first derive an analytical expression of packet throughput as a function of packet queuing delay and the required signal-to-interference-plus-noise-density ratio. Based on such a relationship, we then propose a packet access control algorithm that not only maximizes the packet throughput per cell, but also provides quality of service (QoS) assurance. Practical aspects of a CDMA system such as the effects of power control inaccuracy and other cell interference are considered in the analysis.     

A Novel Effective Bandwidth Based Call Admission Control for Multimedia CDMA Systems

A novel Call Admission Control(CAC)scheme is proposed for multimedia CDMA systems.The effectivebandwidth of real time calls is reserved in the CAC with the consideration of active factors.The admission of non-real timecalls is controlled by the system according to the residual effective bandwidth left from real time calls.Simulation resultshave shown that the novel CAC has greatly enlarged the admission region for real time calls and make the transmission de-lay of non-real time calls under an acceptable level.     

Soft QoS in Call Admission Control for Wireless Personal Communications

In wireless multimedia communication systems, call admission control (CAC) is critical for simultaneously achieving a high resource utilization efficiency and maintaining quality-of-service (QoS) to mobile users. User mobility, heterogeneous nature of multimedia traffic, and limited radio spectrum pose significant challenges to CAC. QoS provisioning to both new calls and handoff calls comes with a cost of low resource utilization. This paper proposes a CAC policy for a wireless communication system supporting integrated voice and dataservices. In particular, soft QoS (or relaxed target QoS) is incorporated in the CAC policy to make compromises among different objectives.Numerical results are presented to demonstrate that (a) in dealing with the dilemma between QoS satisfaction and high resource utilization, how the resource utilization efficiency can be increased by introducing soft QoS; and (b) in accommodating different types of traffic, how the QoS of low priority traffic can be improved by specifying soft QoS to high priority traffic.     

一种新的CDMA系统多业务接入控制算法

文中提出一种新的CDMA系统中多业务接入控制算法。为了提高系统容量,在传统容量干扰受限的CDMA系统接入控制算法的基础上,考虑各种业务的激活因子,计算出系统接入呼叫用户后各个业务的中断概率,根据其中断概率是否满足QoS要求判断业务是否接入。仿真结果表明：所提算法的各种业务的阻塞概率明显低于传统算法,并且系统获得的性能改善随着桌些业务呼叫强度的增加而下降,从而证明了所提算法在系统容量上的优势。     

On Schemes for Multriate Support in DS-CDMA Systems

Different modulation schemes supporting multiple data rates in a Direct Sequence Code Division Multiple Access (DS-CDMA) system are studied. Both AWGN and multipath Rayleigh fading channels are considered. It is shown that the multi processing-gain scheme and the multi-channel scheme have almost the same performance. However, the multi-channel scheme may have some advantages due to easier code design and multiuser receiver construction. The drawback though, is the need for linear amplifiers also in mobile terminals. A multi-modulation scheme is also possible, but the performance for the users with the high data rates are significantly worse than for the other schemes. Furthermore multi chip-rate, parallel combinatory spread spectrum (PC/SS), pulse position modulation (PPM) and variable duty cycle schemes are discussed briefly.     

Capacity Analysis for Connection Admission Control in Indoor Multimedia CDMA Wireless Communications

In this paper, the capacity analysis for connection admission control is presented for the reverse-link transmission of a packetized indoor multimedia wireless communication system using direct sequence code division multiple access (DS/CDMA). Since CDMA is interference limited, the signal-to-interference-plus-noise ratio criterion is used to check if there is enough system resources (i.e., the CDMA channels and received signal power) for each new connection request. Taking into account the stochastical nature of multimedia traffic, the effective bit rate is used to characterize the resources required by each mobile user and a linear approximation is then used to find the total resources required by all the mobile users already admitted to the system and the new connection request. Transmission errors due to both base station buffer overflow and wireless channel impairments are considered. The capacity of multimedia traffic is determined in such a way that the utilization of the system resources is maximized and, at the same time, the required transmission bit error rate and transmission delay of all users admitted to the system are guaranteed. Computer simulation results are given to demonstrate the performance of the proposed method for capacity analysis.     

不平衡业务下CDMA蜂窝系统的呼叫接入控制方案

针对 CDMA蜂窝系统区间业务不平衡的情况 ,文中提出了一种呼叫接入控制方案 ,在重负荷小区为邻区即将到来的呼叫预留部分资源 ,预留的大小随呼叫阻塞情况自适应地调整。仿真结果显示 :该方案能很好地解决区间业务不平衡的问题 ,而且与基于固定资源预留的呼叫接入控制方案相比 ,还能获得低的系统呼叫阻塞率     

3G动态预留呼叫接纳控制算法研究

第三代移动通信技术支持不同服务质量(QoS)的多媒体业务,而呼叫接纳控制(CAC)技术是移动通信中的关键技术之一.本文提出一种动态预留呼叫接纳控制算法,该算法根据小区中各业务的话务量预测各业务所需信道教,从而为切换业务和新业务预留一定的信道.通过比较动态预留算法与新呼叫受限算法和中断优先级算法的性能,得出动态预留算法在降低语音和数据业务的呼叫阻塞率、中断率方面有明显的改善,是一种比较理想的呼叫接纳控制算法.     

WCDMA系统中高速下行分组接入的接纳控制策略

高速下行分组接入(HSDPA)技术是WCDMA对于下行链路分组数据的增强,其分组数据的调度由基站(NodeB)中的MAC hs实体完成。在HSDPA的接纳控制中,数据业务的接纳控制由无线网络控制器(RNC)完成,其判决依据是当前资源的使用状况,这样就需要Node B能通过Iub接口向RNC提供详细的资源使用状况。通过针对HSDPA中流类业务、交互/后台类业务接纳控制的特点,分别从资源的分配、判别门限的设定等方面进行了分析和阐述,并给出了HSDPA中接纳控制的基本流程示意图。     

Scalable Schemes for Call Admission and Handover in Cellular Networks with Multiple Services

The introduction of new service categories withdifferent bandwidth requirements, e.g., data and multimedia, to cellularmobile radio networks makes many of the traditional mechanisms for controlingtraffic unusable orless efficient. The call admission and the handover handling are of the mostsensitive issues in this extension to new services. The performance of allservices includingthe traditional voice and the new services can be dramatically affected ifappropriate schemes are not used. In this paper, we propose call admission andhandover handling schemes for a cellular mobile network that offers twoservice types: voice and data. The data connections are assumed to transmitatdifferent transmission rates that are integer multiples to that of one radiochannel. In the case of congestion, the base station asks the active dataconnections to reduce their transmission rate in order to provide freechannels for the newly arrived request of both service types. This isbasically intended for incoming handover requests. The request will berejected if the transmission rate of the active connections reaches a givenminimum rate. Similar mechanism can also be used for new call arrivals, butsome priority can be given to handovers by setting a higher transmission ratethreshold for the new call rejection. As an extension to the proposedscalability, aqueuing of new calls is also proposed and analyzed. Analytical models werebuilt for the two proposed schemes together with the traditional channelreservation scheme. The effect of different traffic and configurationparameters on the performance measures like the grade of service, blockingprobabilities, and utilization, are studied using the proposed technique.Results show that the proposed schemes provide very good performance and morefairness among the different service types.     

On Admission Control and Scheduling of Multimedia Burst Data for CDMA Systems

In order to support transmissions of multimedia data (high data rate and burst) with performance guarantees in a wideband CDMA system, it is crucial to design a judicious algorithm for burst data admission control and scheduling. However, in the current literature there are only simple techniques (such as first-come-first-served and equal sharing) suggested for tackling the problem. Indeed, these existing schemes are not designed for optimizing the precious bandwidth resources while providing performance guarantees (e.g., a user admitted with a certain data rate can enjoy the assigned rate without interruption). In this paper, we first present our novel integer programming formulation of the burst data admission control and scheduling problem. The objective of the optimization can be maximizing the utilization of the bandwidth resources or minimizing the delays of the user transmissions. Taking into account all the important factors such as mobility, power control, and soft handoff, our formulation induces an algorithm for generating an optimal admission control solution which consists of: (1) the burst data rate (in terms of the number of channels); (2) the burst duration; and (3) the burst start time. For practical implementation, we also suggest a near-optimal version of the algorithm, which is evaluated via static and dynamic simulations, and comparisons with two existing schemes.     

QoS Performance Bounds and Efficient Connection Admission Control for Heterogeneous Services in Wireless Cellular Networks

Quality-of-Service (QoS) performance and connection admission control (CAC) for heterogeneous services in wireless multiple access networks are investigated. The heterogeneous services include constant bit rate (CBR), variable bit rate (VBR) and available bit rate (ABR) services. Multiple access control is handled by a polling-based scheme with non-preemptive priority. Tight delay variation (jitter) bounds for CBR connections and delay bounds for VBR connections are derived. A CAC scheme based on the derived bounds is developed. The CAC makes use of user mobility information to reserve an appropriate amount of system resources for potential handoff connections to achieve low handoff connection dropping rate (HCDR). Simulation results show that the proposed CAC scheme can achieve both low HCDR and high resource utilization.     

An OCDMA Scheme to Reduce Multiple Access Interference and Enhance Performance for Optical Subscriber Access Networks

We propose a new optical code division multiple access (OCDMA) scheme for reducing multiple access interference (MAI) and enhancing performance for optical subscriber access networks using modified pseudorandom noise (PN)‐coded fiber Bragg gratings with bipolar OCDMA decoders. Through the bipolar OCDMA decoder and the modified PN codes, MAI among users is effectively depressed. As the data are encoded either by a unipolar signature sequence of the modified PN code or its complement according to whether the data bit is 1 or 0, the bit error ratio (BER) can be more improved with the same signal to interference plus noise ratio over the conventional on‐off shift keying‐based OCDMA system. We prove by numerical analysis that the BER of the proposed bipolar OCDMA system is better than the conventional unipolar OCDMA system. We also analyze the spectral power distortion effects of the broadband light source.     

时分双工环境下的分组预约多址(PRMA/TDD)协议及其性能

在分析标准分组预约多址（PRMA／FDD）协议的基础上,提出了时分双工环境下的分组预约多址（PRMA／TDD）协议,理论分析和计算机仿真均表明,PRMA／TDD与PRMA／FDD的性能相近,可以较大幅度地提高系统的容量。     

基于缓冲区门限的ATM网业务流量控制分析

ＡＴＭ网中许多流量控制策略是基于缓冲区门限的，即根据缓冲区占有情况采取输入业务降速等控制。但以往的文献对这类控制策略的分析缺乏普遍性。本文对这类控制策略建立数学模型，并利用推广的流体流法对Ｏｎ－Ｏｆ业务在这种控制策略下的性能进行理论分析。文中通过数值实验得到一些重要结论。它们对这类控制策略的实现具有指导意义。     

Precoding for Minimization of Envelope Variations in Multicode DS-CDMA Systems

A multicode direct-sequence code-division multiple-access system experienceslarge envelope variations as a result of a sum of many independently spreadsignals. However, large envelope variations is problematic because it reducesthe spectral efficiency, the efficiency of the power amplifiers and theperformance. All these effects depend on the non-linear amplifiers thatgenerally are used in handsets. It would of course be possible to use a linearamplifier but then the power efficiency is drastically reduced. In this paperwe analyze the envelope variations of a multicode signal in terms of thecrest factor and find that it increases as the square root of thenumber of used codes. As a consequence it is only possible to use themulticode scheme for a few parallel codes. To reduce the envelope variationsa precoder is introduced. This precoder is a non-linear high-rate block codeespecially designed for the set of spreading codes used. However, the precodercan be made independent of the spreading codes if a user-specific spreadingcode is concatenated with a set of Hadamard or Conference sequences. Theresulting spreadig codes are orthogonal. Also, the precoder is independent ofthe user-specific spreading code, and can thus be used for all users. Afterprecoding the crest factor is significantly reduced and the performance, dueto introduced coding gain, improved. Algorithms for the design of precoderswith both reduced envelope variation and good performance are presented.Furthermore, simulations show that a precoded multicode system outperforms anuncoded multicode system in a single-user as well as in a multiuserenvironment.     

Optimum Power Assignment for Maximum Throughput in CDMA Personal Communication Systems with Integrated Voice/Data Traffic

A CDMA personal communication system with integrated voice/data traffic is considered, in which the link error performance is controlled according to the voice error rate requirement, and the acceptable data traffic error rate is ensured by ARQ. Optimum power assignment (or allocation) between voice and data users is investigated to maximize the total system throughput. A graphical method (the tangent method) is described to obtain this optimum power allocation. The maximum throughput is expressed as a function of other system parameters. The tangent method is further used to measure the impact of transmission quality on the maximum data throughput. Numerical results and a design example are given for a power controlled wideband IS-95 type wireless personal communication system.     

A New Approach for Performance Evaluation of TCP over Interference-Limited Wireless Channels

A new metric for performance evaluation of transport control protocol(TCP) over wireless channels based on the interference-limited characteristics of code division multiple address(CDMA) system is proposed. According to the new metric, the performance of TCP over CDMA correlated channel for different protocol parameters and different versions is investigated. The results show that appropriate selection of protocol parameters and packet error rate(PER) operation point can improve significantly the capacity of packet-switched CDMA-based network.     

A New Approach for Performance Evaluation of TCP over Interference-Limited Wireless Channels over Interference Wireless Channels

A new metric for performance evaluation of transport control protocol(TCP) overwireless channels based on the interference-limited characteristics of code division multipleaddress(CDMA) system is proposed.According to the new metric,the performance of TCP over CDMAcorrelated channel for different protocol parameters and different versions is investigated.The resultsshow that appropriate selection of protocol parameters and packet error rate(PER) operation point canimprove significantly the capacity of packet-switched CDMA-based network.