IMT—2000CDMA宏小区蜂窝无线网络的仿真

ＩＭＴ－２０００ＣＤＭＡ宏小区蜂窝无线网络的仿真,是为评估当前在第三代移动通信系统中较具实力的Ｗ－ＣＤＭＡ和ｃｄｍａ２０００技术而开发的。仿真包括链路级和系统仿真两部分,主要分析研究、验证了评估了两种ＣＤＭＡ无线传输技术的性能以及ＣＤＭＡ无线网络的频谱效率／系统容量。     

Cellular CDMA capacity with out-of-band multihop relaying

In this paper, we consider the capacity of cellular code division multiple access (CDMA) when there is out-of-band ad hoc traffic relaying. The mobile stations (MSs) are dual-mode, having both ad hoc and cellular CDMA radios. An active MS is free to choose any available relay station (RS) within its ad hoc radio coverage area for dual-hop communication with the CDMA base station (BS). Communications between the RSs and the MSs use bandwidth which is available to the ad hoc radio and does not consume the CDMA capacity. Using this mechanism, CDIVIA interference can be reduced by dynamically selecting RSs which have more favorable CDMA link characteristics. Several relay station selection criteria are considered, namely, ad hoc relaying with low relative interference (ARRI), with best link gain (ARLG), and with shortest distance (ARSD). The relay station selection protocols are compatible with existing wireless local area network (WLAN) standards such as IEEE 802.11. An analytic model is used to compute the effects on uplink and downlink CDMA capacities when out-of-band relaying is added. The results show that very significant capacity improvements are possible by using these criteria compared with conventional CDMA with hard or soft handoff. Ad hoc relaying which dynamically tracks CDMA link quality can achieve greater capacity improvements than that using a distance-based relay station selection. Relaying, which considers both signal and interference conditions, achieves better capacity than that based on signal link quality alone.     

Adaptive arrays for narrowband CDMA base stations

Base station antenna arrays are a promising method for providing significant capacity increases in cellular mobile radio systems. This paper examines receiver structures and algorithms to assess the potential capacity gains from the employment of multiple receiver antenna elements, of different sizes, for code division multiple access (CDMA) systems. It considers antenna arrays for the mobile to-base station or reverse link of a CDMA cellular system such as the IS-95 standard. It begins with an introduction to CDMA communication systems and also addresses the general topic of antenna array receivers. Channel modelling is then discussed, as this will influence the design of CDMA receivers. The specific form of receiver array processing algorithms is then discussed and some performance comparisons provided. Finally, the most important reason for implementing antenna array systems, the capacity gains which are achievable, is indicated     

Centralised power control in CDMA cellular mobile systems

Efficient power control is of great importance in the design of high capacity cellular radio systems. Optimum power control scheme, in the sense that it minimises the outage probability, has been fully investigated for FDMA/TDMA cellular systems. The authors propose optimum power control and several centralised power control algorithms for CDMA cellular systems. Simulation results indicate that the optimum power control scheme outperforms the perfect average power control algorithm by ~1.9 dB under the IS-95 defined radio condition     

A novel dynamic cell configuration scheme in next-generation situation-aware CDMA networks

To balance the time-varying traffic load between cells, caused by user mobility and diverse applications, it is crucial for next-generation code-division multiple-access (CDMA) cellular networks to configure cell coverage and capacity dynamically. In this paper, we show that pilot power allocation is highly coupled to other facets of radio resource management. We propose a novel dynamic cell configuration scheme for multimedia CDMA cellular networks, based on reinforcement-learning, which takes into account pilot, soft handoff, and maximum link power allocations, as well as call admission control mechanisms. Simulation results demonstrate the effectiveness of the proposed scheme in situation-aware CDMA networks.     

Advantages of CDMA and spread spectrum techniques over FDMA andTDMA in cellular mobile radio applications

A unified theoretical method for the calculation of the radio capacity of multiple-access schemes such as FDMA (frequency-division multiple access), TDMA (time-division multiple access), CDMA (code-division multiple access) and SSMA (spread-spectrum multiple access) in noncellular and cellular mobile radio systems is presented for AWGN (additive white Gaussian noise) channels. The theoretical equivalence of all the considered multiple-access schemes is found. In a fading multipath environment, which is typical for mobile radio applications, there are significant differences between these multiple-access schemes. These differences are discussed in an illustrative manner revealing several advantages of CDMA and SSMA over FDMA and TDMA. Novel transmission and reception schemes called coherent multiple transmission and coherent multiple reception are briefly presented     

Design and analysis of cellular mobile communications system basedon DQRAP/CDMA MAC protocol

Future third-generation mobile communication systems will need multi-access control (MAC) protocols suitable for multimedia code division multiple access (CDMA) radio communications. Distributed queueing random access protocol (DQRAP)/CDMA is a general purpose MAC protocol oriented to the CDMA environment. Analytical model expressions and computer simulations have shown its capacity to achieve near-optimum performance under heterogeneous traffic scenarios in a unicellular environment. A cellular environment has been designed to verify that DQPAP/CDMA maintains its near-optimum performance in a packet switched mobile communication system. A new handover technique based on the protocol is proposed to further improve the system performance     

Robust power control of CDMA cellular radio systems with time-varying delays

Power control is an important factor to increase communication link quality and system capacity in the direct-sequence code-division multiple access (DS-CDMA) cellular radio systems. The Smith prediction filter can achieve the unbiased asymptotic tracking about a desired target signal to interference noise ratio (SINR) under the fixed round-trip delay. However, it is sensitive to the variation of round-trip delay. In order to track the desired SINR with the time-varying round-trip delay, a multiple-mode Smith prediction filter, which combines the multiple Smith predictors with a likelihood function, is proposed for the power control of CDMA systems. The proposed scheme can compensate for the unknown time-varying round-trip delay. Simulation results show that the performance of the proposed multiple-mode power control method is robust to time-varying round-trip delay in the CDMA cellular radio systems.     

The capacity of a spread spectrum CDMA system for cellular mobileradio with consideration of system imperfections

There has been much interest in the use of spread spectrum code division multiple access (CDMA) techniques for cellular mobile radio. To date, spread spectrum has been used mainly for military applications, in which the inherent transmission security and immunity to deliberate jamming are important. Spread spectrum systems, however, possess various other features such as multiple access and multipath rejection capability, which make their use attractive within the mobile radio environment. However, the current interest has been principally motivated by the work of Gilhousen et al. (see IEEE Trans. Vehic. Technol., vol.VT-40, no.2, p.303, 1991) in which it is claimed that the CDMA option may offer capacity improvement over more conventional frequency and time division multiple access, FDMA and TDMA, techniques. Within this paper, the relative capacities of a basic FDMA and CDMA system are examined. It is shown that, in the absence of capacity-enhancing features such as voice activity detection and cell sectorization, the capacity of each system is comparable. The paper then assesses the sensitivity of the CDMA system to typical propagation conditions, power control errors, and realistic antenna patterns and shows that the capacity of a CDMA system may be significantly reduced under nonideal conditions     

On the radio capacity of TDMA and CDMA for broadband wireless packet communications

Studies of the capacity of cellular systems, stated in terms of the admissible number of remote users, have generally been limited to voice telephony. We address the problem of comparing the interference-limited performance of code-division multiple-access (CDMA) and time-division multiple-access (TDMA) systems in a packet-switched environment. The objective is to determine whether the capacity advantages claimed for circuit-switched CDMA still apply in a packet-switched environment, where the natural time diversity of bursty transmission may be a significant factor. Under a set of specific assumptions about the wireless environment (including path loss, shadow fading, multipath delay spread, cochannel interference, power control, and coding), we evaluate the number of users that can be admitted to the system while maintaining some desired quality-of-service (QoS) level. Four different classes of users with different characteristics and requirements are considered. The system capacity is found to depend significantly on the QoS objectives, which might be stated in terms of availability of some specified signal-to-interference level, packet-loss rate, or mean tolerable delay. The main finding is that strict requirements imposed on the radio access level tend to favor CDMA, whereas if some form of packet recovery is allowed at the higher layers (implying a relaxed set of requirements on the radio interface), then a somewhat higher capacity may be achieved by TDMA.     

CDMA系统中天线系统的调整

在CDMA系统中天线系统的调整对CDMA系统整体性能都会产生影响，本分析了天线系统的干扰和天线系统对小区覆盖的影响，讨论了天线系统的调整在CDMA无线网络优化过程中的应用。     

Microcell engineering in CDMA cellular networks

The demand for cellular radio services is growing rapidly, and in heavily populated areas the need arises to shrink the cell sizes and “scale” the clustering pattern. The extension of the service into the PCN domain, mostly in-buildings and in pedestrian areas, further enhances this trend. The vision of the “third generation” cellular systems incorporates micro- and picocells for pedestrian use, with macrocells for roaming mobiles. Connectivity between all these cells, while maximizing total system capacity, is the main challenge facing the “third generation architects.” The CDMA cellular system, which shares the same frequency channel across the system (reuse pattern of one) and applies soft handoff between the cells, has already shown, both by analysis and by tests, to have full connectivity between the microcells and the overlaying macrocells without capacity degradation. The parameters involved in the engineering of a heterogeneous CDMA network are discussed in the paper. Factors that determine the size of the cell, the soft handoff zone, and the capacity of the cell clusters are analyzed, and engineering techniques for overlay-underlay cell clustering are outlined     

A flexibly configurable spatial model for mobile radio channels

The application of multiple directive antennas, i.e., directional diversity, may lead to significant capacity benefits in cellular mobile radio systems. A flexibly configurable statistical channel model for mobile radio systems using directional diversity is presented. The parameters of this model, which is available as a FORTRAN77 program, can be easily adjusted to various propagation areas such as, for example, rural, urban, microcellular, and picocellular environments. Therefore, the model is well suited to perform simulations, evaluations, and comparisons of mobile radio systems. Simulation results concerning a code-division multiple-access (CDMA) mobile radio system which uses multiple directive base station (BS) antennas in combination with joint detection illustrate the application of the presented channel model     

CDMA的基本原理及其在数字蜂窝通信中的应用

本文首先介绍了蜂窝通信的无线传输环境以及分多址的基本原理，然后介绍了在数字蜂窝系统中采用ＣＡＤＭ技术的优越性及其不足之处，并针对此不足简单地介绍了国内外在此方面的研究动向。     

Dispersive fading effects in CDMA radio systems

The effect of multipath delay spread in a code division multiple access (CDMA) radio communications system where multiple PN receivers are used is reported. Ten multipath power delay profiles obtained from measurements in New York City are examined. Results show that the increase of interference due to diffuse uncaptured energy is approximately 1-1.4 dB on the average. This increase in interference results in at least 20% capacity reduction in CDMA radio systems.<>     

Known and novel diversity approaches as a powerful means to enhancethe performance of cellular mobile radio systems

The main requirements to be met by third generation mobile radio systems are high cellular spectrum efficiency and high flexibility. The authors focus on high cellular spectrum efficiency, which is difficult to achieve due to the time variance and frequency selectivity of the mobile radio channel and due to interference. It is known that the degrading effects of these adverse characteristics of the mobile radio channel and of interference can be mitigated by diversity. The way how diversity influences cellular spectrum efficiency is derived in general. As a reference point, the types of diversity used in GSM are analyzed. In GSM, the potential for diversity enhancement inherent in code-division multiple-access (CDMA) is not exploited. A joint detection code-division multiple-access (JD-CDMA) system concept aimed at third generation mobile radio systems has been proposed which introduces a CDMA feature into systems based on time-division multiple-access (TDMA) and frequency-division multiple-access (FDMA) like GSM and also advanced TDMA (ATDMA). The gains achievable by different types of diversity in GSM as well as in the JD-CDMA system concept are investigated. It is shown that considerable gains can be achieved by different types of antenna diversity and by exploiting the additional diversity potential of CDMA. Therefore, third generation standards should be flexible in order to allow the use of as many types of diversity as possible to enhance the cellular spectrum efficiency     

多媒体CDMA系统在功率约束条件下的业务容量分析

码分多址接入（CDMA）技术可以灵活地支持无线多媒体业务传输。该文分析了多小区环境下CDMA系统上行链路的多媒体业务容量，主要讨论了用户最大发射功率约束条件在不同用户激活因子情况下对系统容量的影响。分析和计算结果表明用户最大发射功率约束使系统的容量有所降低。     

Capacity Estimation in Multiple-Chip-Rate DS/CDMA Systems Supporting Multimedia Services

This paper is concerned with capacity estimation in multiple-chip-rate (MCR)DS/CDMA systems supporting multimedia services with different informationrates and quality requirements. Considering both power spectral density (PSD)over a radio frequency (RF) band and the effect of RF input filtering onthe receiver, capacity that satisfies the requirementof the bit energy-to-interference PSD ratio is derived.The optimum value of the received power which causes the leastinterference for other users while maintaining an acceptablequality-of-service(QoS) requirement is also derived. The results show that system performanceisstrongly affected by a selected channel assignment strategy. Therefore, it is critical to efficiently assign radio resources in MCR-DS/CDMA systems that support high capacity and a low blocking rate.     

Spread-spectrum techniques for fiber-fed microcellular networks

It is well known that for a specified radio capacity, the peak performance [such as the minimum bit error rate (BER) or probability of outage] of subcarrier multiplexing (SCM)-based fiber-fed microcellular systems is limited by the nonlinearity of the optical source. Conversely, for a specified performance, the maximum radio capacity is restricted by the source nonlinearity. It is the goal of this paper to examine the robustness of a code-division multiple-access (CDMA)-based system in the presence of these nonlinearities. This is done by comparing the error and outage probabilities of a CDMA-based system to that of a conventional SCM system, which utilizes frequency-division multiple access (FDMA). It is shown that a CDMA system can relax the bounds on the performance or capacity. However, this improvement is obtained at the expense of large chunks of bandwidth. An alternative hybrid CDMA/FDMA approach is examined, wherein the inherent benefits of both CDMA and FDMA techniques are utilized. Performance evaluation shows that the hybrid system achieves the same system requirements in a more spectrally efficient manner     

Adaptive Resource Allocation for MC‐CDMA and OFDMA in Reconfigurable Radio Systems

This paper studies the uplink resource allocation for multiple radio access (MRA) in reconfigurable radio systems, where multiple‐input and multiple‐output (MIMO) multicarrier‐code division multiple access (MC‐CDMA) and MIMO orthogonal frequency‐division multiple access (OFDMA) networks coexist. By assuming multi‐radio user equipment with network‐guided operation, the optimal resource allocation for MRA is analyzed as a cross‐layer optimization framework with and without fairness consideration to maximize the uplink sum‐rate capacity. Numerical results reveal that parallel MRA, which uses MC‐CDMA and OFDMA networks concurrently, outperforms the performance of each MC‐CDMA and OFDMA network by exploiting the multiuser selection diversity.