資料無線下載服務的天線傳送功率動態控制

Abstract

在行動通訊網路中，透過各基地台間的無線電訊號覆蓋來增進無線服務覆蓋率。對無線下傳資料服務來說，基地台間的無線電覆蓋可提供虛擬軟式交遞機會，但也增加基地台間的訊號干擾，以至於減少可獲得的資料率。在本論文中，我們將介紹一種在下傳資料服務下的基地台功率控制策略。藉由一個門檻的假設，動態調整基地台功率來降低基地台間的訊號干擾，以期增加系統總處理量並有效處理空間上及時間上熱點基地台問題。另外，為了減少基地台變動功率的頻率，我們也提出另一種方式，即假設兩個門檻來降低此種磁滯效應。由數據顯示出我們所提的功率控制策略能夠有效的增加系統總處理量、減少延遲時間並且解決空間、時間上的熱點問題。In cellular networks, wireless service coverage is improved through partly radio coverage overlays between neighboring access point transmitters (APTs). For wireless forward link data services, the overlay provides virtual soft handoff opportunities, but also introduces significant intercell interference which reduces feasible service data rate. In this thesis, we investigate APT power level control strategy for wireless forward link data services. We assume that the transmission power of each APT is adjustable between a default high level and a low level if necessary. The objective is not only to improve system throughput by reducing intercell interference but also to adapt APT power level activity to alleviate the impact of temporal and spatial traffic variation among cells. These are achieved by utilizing a simple search-and-lock algorithm which coordinates APT power level activity essentially according to traffic loads and traffic spatial distributions. Moreover, we consider that the frequency of switching APT power levels is an important measure of system complexity. We then propose a hysteresis approach using two thresholds to damp down the frequency of changing APT power activity patterns besides using a single threshold. In addition, we study the effect of adapting APT power level activity on the behavior of the proportional fair scheduler for forward link data services. Our study shows that proposed power level control strategies are able to yield many favorable performance features in terms of throughput, latency, temporal and spatial traffic hot spot relief, in particular when path loss exponent is small or traffic loads are distributed increasingly toward cell boundaries. Additionally, service opportunities by the proportional fair scheduler drift toward users in the far field where fading gains from changing antenna power patterns are more significant.