結合上傳功率與頻寬之配置於IEEE 802.16j 穿透式中繼網絡

Abstract

IEEE 802.16j中定義利用relays的方式來加強WiMAX網路容量，目前的研究主要都是注重在增加傳輸的速率，來達到改善網路的傳輸效能，不過增加MSs的上傳速度，會造成MSs的耗電量增大，減少使用電池的MSs待機時間。在本篇論文中，我們主要針對IEEE 802.16j 穿透式中繼網絡，提出頻寬配置的解決方法，同時考慮如何在上傳功率與耗電量之間，取得平衡。在頻寬配置的問題中，我們以滿足所有的MSs上傳資料為第一目標，在此前提之下，進一步達到減少所有MSs耗電量加總的第二目標。尤其是頻寬配置的問題在網路傳輸頻寬飽和時，更是重要。我們在此論文中證明頻寬配置的問題是NP-complete的問題，並且提出了一個兩階段的演算法。第一階段，我們先利用 Relay Station 來達到建立多個平行上傳的目標，第二階段，如果還有剩餘的資源，我們利用改變MSs的上傳速率和上傳路徑，來減少耗電量，達到節能的目標。模擬結果顯示我們提出的方法，跟目前已提出的方案比較，可以節省90%的總耗電量。

The IEEE 802.16j standard is defined to enhance WiMAX networks with relay capacity. Under the transparent mode, existing studies only target at improving network throughput by increasing the transmission rates of mobile stations (MSs). Nevertheless, using a higher transmission rate could harm MSs in term of their energy consumption, especially for those battery-powered devices. In the paper, we consider a bi-objective uplink optimization problem in an 802.16j transparent-relay network to balance between rates and energy costs. In this joint power-and-bandwidth allocation problem, it asks how to arrange the frame space with satisfying MSs’ demands as the first goal and minimizing their total energy consumption as the second goal if the first goal can be met. This bi-objective problem is more meaningful when the network works under a non-saturated condition. We prove this problem to be NPcomplete and develop an energy-efficient heuristic, which has two key designs. First, we exploit relay stations to allow more concurrent uplink communications. Second, when there are remaining resources, we lower down some MSs’ transmission powers by adjusting their transmission rates and paths to save their energy. Simulation results show that our heuristic can save up to 90% of MSs’ energy as compared to existing results.