Dynamic Polling Access Control for High Density Subscribers in Wireless WiMAX Networks

Abstract

IEEE 802.16標準提供支援QoS傳輸於無線都會網路中的即時服務，WiMAX採用輪詢存取控制為一個基地台 (Base Station)依次詢問多個用戶端 (Subscriber Stations)的機制，將會因為過多的用戶端節點數而增加輪詢延遲。Unicast polling較長輪詢延遲的缺點會產生一個長時間的等待而無法滿足即時服務的服務品質保證。因此，在這篇論文中我們提出了一個適性的輪詢機制去切換輪詢模式期能連續地支援即時輪詢服務 (real time Polling Service)。我們的方法包括兩個階段，第一，我們使用用戶端的節點數與剩餘的頻寬作為調整輪詢模式為單點與多點輪詢模式的v條件。第二，當基地台在多點輪詢的模式中，提出一個新的類似即時輪詢服務 (Quasi-rtPS)提供一個平均即時性流量的延遲，用來替代即時輪詢服務的最大延遲QoS參數。數值結果指出我們所提的方法勝過IEEE 802.16標準的平均延遲與網路利用率。此外，我們也評量一個基地台中不同的競爭時槽 (contention slots)與群組數量所產生的碰撞機率。

The IEEE 802.16 standard is proposed to support QoS-aware transmission of real-time service in WMANs. WiMAX adopts the polling access control for a Base Station (BS) to poll Subscriber Stations (SSs) in turn and it will increase polling delay when there is a lot of number of SSs within the BS. The disadvantage of long polling delay may not guarantee the quality of service (QoS) requirement of real-time service and cause long waiting time while not in unicast polling. Therefore, in this paper we propose an adaptive polling approach to switch the polling mode while continuously supporting real-time Polling Service (rtPS). The proposed approach consists of two phases. First, two hysteresises of number of SSs and residual bandwidth are adopted to determine the polling mode between the unicast and multicast polling modes. Second, a novel Quasi-rtPS service (QrtPS) that provides an Average Delay of real-time traffic instead of the Maximum Delay of rtPS is proposed to take over the rtPS service when the BS is in multicast polling. Numerical results demonstrate that the proposed approach outperforms the IEEE 802.16 standard in average delay and utilization significantly. Moreover, the collision probabilities of different contention slots and the number of groups within a BS are also evaluated for multicast polling.