多通道多介面無線隨意網路之漸層式傳輸功率控制協定

Abstract

在傳輸媒介共享的無線網路研究中，提出許多的傳輸功率控制協定來增加多重傳輸的數量以及減少干擾的影響，在本篇論文中，我們不嘗試提出一個新的傳輸功率控制協定，而是研究在每個通道都配置一個無線電傳輸設備的多通道無線網路環境中如何應用傳輸功率控制協定，而在多重跳躍通訊環境，單一無線電傳輸設備的傳輸端降低傳輸功率將會導致較低的網路連結率以及較長的傳輸路徑，另一方面，較低的傳輸功率能容納更多的傳輸端進行傳輸，因此，同時考慮傳輸路徑長度及傳輸媒介利用率這兩個參數來增加無線網路容量顯的更為重要，由於此動機，我們提出了一個可以應用在無線電傳輸介面並且獲得多重連結密度的傳輸功率控制協定，使得一個多重的網路拓樸擁有漸層式連結度在多個無干擾的通道中，稱之為漸層式傳輸功率控制協定（GradPC）。 在我們提出的漸層式傳輸功率控制協定（GradPC），基本通道被指定預設傳輸功率（無功率控制協定），而在其他非基本通道中，我們採用鄰近節點傳輸功率控制的方法來實現漸層連結密度，在漸層式傳輸功率控制協定（GradPC）配置所有無線電傳輸介面後，我們的協定執行以下兩個階段：(i) 一個變異DSR在基本通道尋找多重跳躍節點的路徑，(ii)當路徑確定後，無線電傳輸介面依選擇程序來分配合適之通道，由於漸層式傳輸功率控制協定（GradPC）同時考慮路徑長度和傳輸媒介利用率因素，因此模擬結果顯示了我們所提出的漸層式傳輸功率控制協定（GradPC）的確優於其他功率控制協定。

Various power control techniques have been proposed to boost aggregate network throughput by reducing the interference impact and encouraging more concurrent transmissions in medium-shared wireless systems. In this paper, we do not intend to devise new power control mechanisms. Rather, we investigate an interesting problem of how to apply power control techniques in a multi-channel networking environment, where every wireless node is equipped with multiple radio transceivers, each statically binding to a dedicated channel. For a single radio transceiver, more reduction on transmit power generally results in lower network connectivity, leading to a longer route (if path exists) for multi-hop communication (bad for end-to-end throughput). On the other hand, small transmit power helps accommodate more concurrent transmitters (good for aggregate throughput). For wireless ad hoc networks with multi-hop communication as the major behavior, how to take both route length and medium utilization into consideration to improve system capacity is thus important. Motivated by this, we propose to apply power control with different connectivity degrees on radio interfaces. Imagine several superposed network topologies having gradational connectivity levels over multiple non-interfering channels, hence the name, gradational power control (abbreviated as GradPC), is given. In our proposed GradPC protocol, a base channel is designated to use default transmit power (no power control on this radio). For other non-base radios, we adopt neighbor-based power control mechanisms to tailor the connectivity degree for each radio channel. After GradPC has successfully configured transmit power for all radios, our other corresponding protocols run in the following two phases: (i) a variant DSR is performed over the base channel to discover a multi-hop route, and (ii) once the route is ready, a radio selection procedure is activated to judiciously schedule the next link-layer packet sent over an appropriate channel. Simulation results demonstrate that the proposed GradPC along with its corresponding protocols outperform strategies with no power control and the same connected topology, by imposing gradational power levels on radios to balance the requirements for short route and high medium utilization.