Performance evaluation of multimedia mobile communication networks based on chip-level traffic volume

本文提出了一种DS-CDMA系统中扩频码的动态重新分配方案，称为RDA（Region Division Assignment），通过重构码树来缓解码阻塞问题，从而有效地提供所有支持速率的服务。我们比较了RDA的性能与传统的OVSF码分配方案（CONV），和动态OVSF码分配方案（DCA）。计算机仿真结果表明，在大流量条件下，RDA算法的阻塞概率低于DCA算法。仿真结果还表明，DCA的计算时间明显大于RDA。讨论了TDMA和W-CDMA频谱共享系统（TDMA/W-CDMA重叠系统）在蜂窝结构下的共存问题。在该系统中，两个系统共享相同的频带以提高频谱效率。在AWGN信道下，计算了系统前向链路（下行链路）的误码率和频谱效率。考虑到路径损耗和阴影衰落损耗，应用干扰消除（IC）的W-CDMA在频谱效率上显示出与诸如TDMA系统或W-CDMA系统的基于单个多址的系统相比的显著差异。干扰抵消可以显著改善频谱重叠系统的误码率，通过仿真研究了新的呼叫信道限制方案（NCCL）解析模型的有效性。NCCL通过参数α限制新呼叫接入总信道数，而切换呼叫不限制接入总信道数。针对低移动性用户的仿真模型，重点研究了用户的移动性和参数α对新接入和切换阻塞概率的影响。

We proposed a dynamic reassignment scheme of spreading codes for DS-CDMA systems so called RDA (Region Division Assignment) by reconstructing the code tree to mitigate the code blocking problem in order to efficiently provide the services for all supported rates. We compare the performance of the RDA with the conventional OVSF-code assignment scheme (CONV), and the dynamic OVSF-code assignment scheme (DCA). The computer simulation results show that the blocking probability of RDA is lower than that of DCA under the heavy traffic condition. The simulation results also show that the calculation time of DCA is significantly larger than that of RDA. Furthermore, RDA is shown to be able to simultaneously handle much more voice sources than DCA.The co-existence of TDMA and W-CDMA spectrum sharing system (TDMA/W-CDMA overlaid system) with cellular architecture is discussed. In this system, both systems share the same frequency band to improve the spectrum efficiency. BER and spectrum efficiency of the system are calculated for the forward link (down-link) in the presence of AWGN channel. Taking into account the path loss and shadow fading loss, W-CDMA applying interference cancellation (IC) shows a substantial difference in spectrum efficiency than a single multiple access-based system such as TDMA system or W-CDMA system. The interference cancellation can significantly improve BER of the spectrum overlaid system.We investigate the validity of the analytical model of new call channel limiting scheme (NCCL) by means of simulation. NCCL limits new calls to access the total channels with parameter α while handover calls have no restriction to access the channels. We focus on the effects of users' mobility and the parameter α on the blocking probabilities of new and handover good match to the simulation model for low mobility users.