Abstract: Concerning the collision and access failure which are very likely to occur when the intensity of the users’ access increases, a random access packetbased strategy was proposed. The users were divided into several groups according to the strategy; certain subframes formed a superframe to enable different users to send Uplink Synchronization Code (SYNCUL) to the corresponding subframe of superframe when the users needed random access information, and based on it, priority was set for the users from different groups. Compared with the general strategy, packetbased strategy has greatly improved the success rate of the users’ access, and grouping based on priority was adopted to ensure a higher success rate for advanced users. The theoretical analysis and simulation results show that the proposed packetbased strategy can significantly improve the system Quality of Service (QoS) and could be an effective measurement for decreasing the probability of collision in random access.

Key words: TD-SCDMA, trunking, random access, Quality of Service (QoS), priority

摘要： 在用户接入强度大时，容易产生碰撞导致随机接入失败。针对这个问题，提出一种基于分组的随机接入策略。该策略将用户分为若干组，若干子帧组成一个超帧，用户进行随机接入时，在超帧对应子帧上发送上行同步码，在此基础上，为不同组别用户设定不同优先级。与一般不分组的情况进行对比，基于分组的随机接入策略提高了用户接入成功率，基于优先级的分组进一步保证了高优先级用户更高的接入成功率。理论分析和仿真结果表明，所提出的分组策略能够明显改善系统的服务质量，是一种有效降低随机接入碰撞概率的方法。

关键词: TD-SCDMA, 集群, 随机接入, QoS, 优先级