無線CDMA通訊系統媒介存取控制協定設計之考量與服務品質保證

Abstract

對於下一代multi-services無線CDMA通訊系統，為達到服務品質要求系統可以藉由安排不同等級的功率給不同型態的流量服務，使得每個使用者能滿足所需。利用功率控制達到QoS的方法已有很多的研究，最佳的功率控制結果在[4]已計算出。三種服務品質的要素為：頻寬（傳輸速率）、延遲、和可靠度。功率控制的CDMA系統只將傳輸頻寬和可靠度考慮進去，並沒有考慮延遲服務品質的問題。關於延遲服務品質的問題，可以利用其它的方法來完成。例如：呼叫允入控制、排程方法….等。在[1]中提出了一些access control的方法來確保real-time的封包（packet）能夠在一定的時間內傳送完成。這些方法減少了碰撞發生，降低封包流失。從[1]的結果發現在整合語音和資料的系統中，動態優先權(DP)的方法似乎是最好的選擇。然而，動態優先權的方法必須將Deadline訊息加入所要傳送的封包中，而且基地台（base station）根據所有使用者所傳來的Deadline訊息做排序，使有較高優先權的使用者能夠接收到基地台所傳來的知會（ACK）訊息。當接收到知會（ACK）訊息，使用者將緩衝器中最前面的封包傳給基地台。根據動態優先權方法的原則，本篇論文提出一個分散式優先權安排（Distributed Priority Assignment）的方法預計可以減少用戶端和基地台的複雜度。在未來以服務品質為基礎無線CDMA通訊系統，分散式優先權安排的方法也許是一個不錯的選擇。

For next-generation multi-services CDMA wireless system, CDMA has inherent capacity to control the quality-of-services (QoS) requirements by assigning different power levels to each traffic type. Toward this, optimum power control schemes have been investigated. The three components of QoS are bandwidth (rate), delay, and reliability. The delay aspect of QoS specification will not be discussed in the power controlled CDMA system. The delay issue has to be considered in connection with the definition of service class, call admission control schemes, and scheduling algorithms. To guarantee delivery of packets with time constraints, several access control schemes had been proposed in [1]. These access schemes totally eliminate the possibility of packet loss caused by collision. From the results of [1], the DP (Dynamic Priority) scheme seems to be a good choice for an integrated voice/data system. The DP scheme, however, must insert the Deadline information into the transmitted packet and the BS sorts the Deadline information of all users. After sorting the Deadline information, the BS know which user has higher priority and sent ACK messages to high priority users. Users transmit one packet at the head of its buffer in the adequate power level when receiving ACK message from the BS. According to the principle of the DP scheme, we propose a Distributed Priority Assignment scheme to reduce the complexity of both mobiles and base station. This maybe a solution of future QoS based wireless CDMA network.