New collision-channel model for packet-switched CDMA networks

Packet conflicts in a distributed CDMA network vary with different code protocols which determine packet structure. Improperly designed packet structure is responsible for unrecoverable packet collisions in the channel, resulting in an unacceptably small throughput and large delay. A novel collision-channel model is presented to analyse the network performance concerning the packet contention nature for different CDMA code protocols.<>     

Multiuser detection for packet-switched CDMA networks with retransmission diversity

In this paper, multiuser detection is developed with exploitation of retransmission diversity. A maximum likelihood detector (MLD) that has the same order of complexity as the MLD using only the data in one transmission is developed. It is shown that the retransmission diversity increases the minimum signal distance and, therefore, significantly improves the performance of MLD. The linear MMSE, decorrelating, and MF detectors are developed under two design approaches. In the first approach,we have considered the weighted sum of outputs of a number of linear detectors, where each is implemented for one transmission. The optimum set of weights that maximizes the signal-to-interference-and-noise ratio (SINR) is obtained. In the second approach, a linear detector jointly utilizes the statistics collected from all transmissions. When the SINR of a linear detector is the same in each transmission, the retransmission diversity is shown to increase the SINR by 10log/sub 10/J dB for a packet of J transmissions. The limiting bit error rate for these three linear detectors in large networks with random spreading sequences is obtained in closed form, which enables further network throughput evaluation.     

Capacity plane of CDMA system for multimedia traffic

In a wireless CDMA system for multimedia services, the maximum number of concurrent users satisfying the QoS (Quality of Service) requirements is evaluated in both single-cell and multi-cell environments. A simple upper-bounded hyperplane concept is also formulated to visualise the capacity of a multimedia CDMA system. With this capacity plane, the tradeoffs between the level of system resources needed for a certain user and that needed for others are illustrated, analytically, within the concept of resource management     

Capacity evaluation of a cellular CDMA system operating in the63-64-GHz band

A cellular asynchronous code-division multiple access (A-CDMA) system operating in the 63-64-GHz band for short-range communications is analyzed. A simple propagation model for the 63-64-GHz band is first introduced and discussed. The system capacity, expressed as the maximum number of users per cell, is then analytically derived and favorably compared with other CDMA schemes operating in conventional frequency bands (i.e., below 2 GHz). Also, simple expressions for the system bit error rate (BER) are analytically derived for different cases and validated through computer simulations. Finally, power requirements are derived and the impact of atmospheric conditions is evaluated. It turns out that the use of the 63-64-GHz band significantly increases the capacity of A-CDMA, and proves to be suitable for cellular systems and personal communication networks (PCNs) provided that adequate power margins are taken into account in the design of the system     

Throughput evaluation of a satellite-switched CDMA (SS/CDMA) demandassignment system

This paper presents throughput evaluation of a satellite-switched code-division multiple-access (SS/CDMA) system which operates under demand assignment control. SS/CDMA provides both multiple access and switching to a geostationary multibeam satellite. Multiple access is resolved by space, frequency, and code division. Space division is introduced by the multibeam antennas that provide frequency reuse in each beam. The spectrum is then channelized into frequency bands where each band is accessed by code division for both the uplink and downlink. The satellite on-board performs the switching function, which is also based on compatible code-multiplexed switching. The switch may route both circuit calls and data packets which are assigned upon request. The on-board code-division switch operates under the control of a channel assignment algorithm. We provide channel assignment algorithms for optimum, suboptimum, and random switch operation. The system throughput has been evaluated for each case and compared. Performance analysis has been carried out for the case of the optimum switch scheduling. The analysis is based on a discrete-time Markovian model, and provides the call-blocking probabilities and data packet delays. Computer simulations have been used to evaluate the performance of the optimum, suboptimum, and random cases. It is shown that the circuit call-blocking probabilities achieved for these cases are almost the same. The optimum algorithm achieves the minimum data packet delay, while the performance of the suboptimum algorithm is slightly better than the random one. Furthermore, data packets may be routed via the switch with limited delays, even with a heavy load of circuit calls     

Capacity estimation for a multicode CDMA system with SIR-basedpower control

Capacity estimation in code division multiple access (CDMA) systems is an important issue which is closely related to power control. Strength-based power control has been assumed in most analyses in which other cell interference was considered as a known and fixed variable. However, in signal-to-interference ratio (SIR)-based power-control systems, power control and other cell interference are closely related to each other and capacity can be obtained by considering this relationship. This study derives the reverse-link capacity of an SIR-based power-controlled multicode CDMA system supporting heterogeneous CBR and on-off traffic in a multiple cell environment. Mean and variance statistics of total other cell interference, and the effects of traffic and propagation parameters on system capacity are investigated     

Capacity of complexity-constrained noise-free CDMA

An interference-limited noise-free CDMA downlink channel operating under a complexity constraint on the receiver is introduced. According to this paradigm, detected bits, obtained by performing hard decisions directly on the channel's matched filter output, must be the same as the transmitted binary inputs. This channel setting, allowing the use of the simplest receiver scheme, seems to be worthless, making reliable communication at any rate impossible. We prove, by adopting statistical mechanics notion, that in the large-system limit such a complexity-constrained CDMA channel gives rise to a non-trivial Shannon-theoretic capacity, rigorously analyzed and corroborated using finite-size channel simulations.     

Optimising delay and throughput in packet-switched CDMA networkwith collision resolution using stack algorithm

The authors address the effect of code division multiple access (CDMA) on the performance of wireless packet-switched networks. Although CDMA can enhance throughput, the delay at small traffic loads suffers from bandspreading. For imperfect signal separation at the receiver, performance benefits from CDMA may be lost. The capacity of the particular stack algorithm addressed for collision resolution can be enhanced from 0.32 to ~0.40 if a 10 dB spreading gain with perfect signal separation is employed     

CDMA接入信道的容量分析

本文简要介绍了CDMA接入信道的特性,随后给出了接入信道容量的概念和计算方法,最后提出了优化接入信道容量的建议.     

CDMA寻呼信道的容量分析

本文介绍了一种估算CDMA IS-95寻呼信道容量的方法,可用于指导无线网络的设计和规划.     

CDMA覆盖容量优化策略

随着我国手机用户骤增和通信网络的庞大，为用户提供优质的通信服务已成为各个运营商工作的重中之重。为此，一大批从事网络优化的工程技术人员日夜奋战在第一线，以自己的艰辛劳动和聪明才智努力为用户服务，同时也积累了许多宝贵的经验。为了不断提高我国网络优化工作的水平，本刊特开设“网络优化”栏目，为广大工程技术人员提供一个交流的平台。欢迎大家踊跃投稿（投稿信箱：dcw@dcw．org．cn）。     

多载波CDMA容量的研究

该文对多载波CDMA容量规划进行了详细的理论和数学分析,推导出多载波CDMA上下行链路的容量的表达式,利用拉格朗日乘数求极值的方法,分别得到多载波CDMA话音和数据业务上下行链路最大容量;同时得出一个非常重要的结论：只有当即基站最大发射功率平均分配给每个子载波时,多载波CDMA系统才能获得最大的容量。该文还对影响容量的因素进行了仿真,各业务的容量随平均路径损耗的增加急剧下降。由此揭示了容量和覆盖的内在关系：容量和覆盖是相互制约的一对矛盾,容量的增加就意味着覆盖的减小,反之亦然。无论上下行链路,当功率达到一定程度时,再通过增大功率来提高容量并不是行之有效的方法。最后,通过对GSM,WCDMA,多载波CDMA 3个系统容量的比较,得出多载波CDMA下行链路频谱效率为WCDMA频谱效率的1.7倍,GSM 的2.7倍;上行链路频谱效率为WCDMA频谱效率的2.1倍,GSM 的2.4倍的结论。     

平流层CDMA通信系统的容量分析

针对平流层通信中利用多波束天线进行分空分复用的特点，对平流层CDMA通信系统的容量进行了分析，并考虑了有功率控制和无功率控制两种情况的区别，给出了相关的表达式。最后，通过计算机仿真得到了在特定天线条件下的系统容量。     

CDMA通信卫星系统容量分析

对基于码分多址(CDMA)体制的通信卫星系统及其容量进行了分析,从系统的角度,提出了CDMA体制的通信卫星系统容量的数学模型。定量分析了用户数量与系统的扩频增益、抗干扰能力指标、卫星转发器饱和功率等的关系,容量分析的结果可供人们在选择和设计通信卫星系统时参考。     

宏分集对于CDMA系统前向容量的影响

宏分集可以有效地克服大尺度衰落的影响.对于CDMA反向信道而言,采用宏分集可以有效地改善信道质量并提高反向容量.与此相比,有关宏分集对CDMA前向信道的影响的研究则并不多见.本文深入分析了多天线宏分集下的CDMA系统前向容量并发现,在传统CDMA系统中,无论采用何种功率分配方案,宏分集都会导致前向容量损失.在分析容量损失原因的基础上,我们进一步提出了一种新的发送分集方案.在该方案下,前向容量不仅得到较大的提高,而且会随着参与宏分集的基站数目的增多进一步增大.     

On the Teletraffic Capacity of Optical CDMA

The capacity of an optical CDMA (OCDMA) network has traditionally been defined as the number of continuously transmitting circuits supported by the network. In this paper, we use teletraffic models to determine the teletraffic capacity of a circuit-switched OCDMA network where circuits carry bursty traffic. Our analysis is independent of the OCDMA implementation or spreading code. In conventional networks, e.g., a wavelength-routed-network (WRN), new circuits are blocked when all wavelengths are occupied. In OCDMA, when the number of codewords exceeds the number of network subscribers, new circuits need not be blocked. Instead, capacity is limited by multiple-access interference: when the number of actively transmitting circuits becomes excessive, the bit-error rate of all circuits on the network degrades, causing an outage. We find that through statistical multiplexing, the capacity of OCDMA exceeds that of a WRN, except when circuit activity is very high, while the constraints on outages are more stringent than those blocking. In such cases, we show how OCDMA with call admission control can be used to match or exceed the capacity of a WRN. Overall, our analysis shows that OCDMA is well suited to applications when conventional blocking is undesirable, and/or circuits carry bursty traffic.      

Capacity of a band-limited CDMA MMSE receiver-based system whencombined with trellis or convolutional coding

This paper examines the achievable capacity of a direct-sequence spread-spectrum multiple-access system based on an adaptive minimum mean-square-error (MMSE), single-user receiver over a Gaussian channel. The effect of using both trellis and convolutional codes of varying rates and complexity is investigated in relation to the effect on the maximum number of users and the achievable bit-error rate for a given number of users. A system based on a matched filter receiver is presented for the purposes of comparison. It has been found that, over the band-limited channel considered, the use of convolutional coding reduces the total system capacity for the high efficiency MMSE receiver while still providing a coding gain for a small numbers of users. The use of trellis codes however leads to increased system capacity     

CDMA系统下行链路容量研究

本文从基本的码分多址(CDMA)理论出发,根据WCDMA系统建立系统模型,从基站发射功率受限和小区间的相互干扰与影响的角度入手,结合计算机仿真,对CDMA系统的下行链路的容量特性作了分析与计算,分析了传播环境、小区半径、切换门限等参数对下行容量的影响,并使用计算机仿真对分析结果作了验证.对比表明,该分析结果与计算机仿真所得结果吻合的较好,可以作为分析、设计CDMA网络的基础.     

Capacity and power control for CDMA microcells

Capacity and power control issues are considered for urban CDMA microcells that operate on channels characterized by log-normal shadowing and Nakagami fading. The effects of fading on the desired and interfering signals, variations in the shadow standard deviation, imperfect power control, and the requiredE _b /N _o for satisfactory link operation are investigated. It is shown that the reverse channel is relatively insensitive, and the forward channel very sensitive, to shadow and fading variations. Power control error is shown to significantly degrade reverse channel capacity. Twobiased forward channel power control strategies are introduced to enhance existing unbiasedbalancing forward channel power control algorithms.This research has been supported by BNR Inc.     

CDMA无线容量分析与测试方法探讨

从CDMA软容量的特点出发，根据CDMA的噪声受限理论并与实测技术相结合，研究CDMA无线容量的算法，分析影响无线容量的各种因素，探讨无线容量的测试方法。