改進無線區域網路的頻寬公平性

Abstract

由於無線區域網路的應用日廣及頻寬的不足，有效分配目前無線區域網路IEEE802.11 標準環境下的頻寬是一個值得探討的議題。但目前針對無線頻寬管理議題的討論多利用PCF與DCF結合或是與IEEE802.11標準不相容的方法達成頻寬管理的目的，在現實商業化產品中存在建置困難與無法推廣的問題。因此我們提出一個利用Uplink Data Dropping (UDD) 改進 co-DRR演算法在純DCF無線區域網路環境下無法達成上下行間頻寬公平分配的問題。UDD根據一個動態機率丟棄超用上行頻寬的無線節點的DATA封包以降低上行鏈路的傳送速度，達到提供下行鏈路較大頻寬的目的。同時能夠達到各無線節點間頻寬的公平分配。從模擬的結果可以看出，相對於未使用UDD前co-DRR上下行頻寬的比率由30%降到8%,能夠有效的提升上下行的頻寬比率到90%，同時分配給各台機器的上下傳頻寬量也能夠達到一定程度的公平性與延展性。

With an increasing number of users, fairly sharing the limited bandwidth in wireless LAN (WLAN) between mobile hosts has received more attention. Although many solutions were presented, most of them can only be deployed on a QoS-aware but IEEE 802.11-incompatible, or PCF-supported WLAN to achieve the bandwidth sharing. This study proposes a DCF-only IEEE 802.11 compatible scheme, Uplink Data Dropping (UDD), to solve the unfair problem in the cooperative deficit round robin (co-DRR) scheduling algorithm which utilizes PCF to keep fair sharing between uplink and downlink traffic. UDD punishes the MHs occupying excess bandwidth by dropping their data packets with a dynamic ratio, which forces the congestion-aware traffic sent from these MHs to decrease their rate and leave the transmission chance to downlink traffic. Simulation results show UDD can hold the fairness ratio between uplink and downlink at 90% when the ratio in co-DRR is degraded to 30% or even 8%.