適用於具指向性天線與功率控制無線隨意網路之跨層設計

Abstract

無線隨意網路 (wireless ad hoc network) 是由多個可任意移動位置之行動主機所組成，相較於有基礎結構之網路，無線隨意網路擁有較靈活之傳輸方式，然而傳統使用全方向性天線之無線隨意網路傳輸易造成網路擁擠。將指向性天線應用在無線隨意網路中能夠顯著地提升空間再使用的可能性而減緩網路擁擠程度，進而提昇網路整體資料流量。為了能完全發揮指向性天線的特性，許多指向性媒介接取控制 (directional medium access control) 協定被提出。然而這些指向性媒介接取控制協定卻引起了新類型的隱藏節點 (hidden node) 和封鎖問題，導致資料流量隨之下降。在本論文中，吾人針對使用指向性天線的實體、媒介接取控制與路由協定提出一整合性的設計。吾人提出之M-null指向性天線模型搭配指向性媒介接取控制不只能夠指向性地傳送封包，也能形成M個波束形成之零點 (beamforming null) 以消除來自其他方向的干擾。如此一來隨意節點不只能充份地達到空間再使用，也能透過解決隱藏節點和封鎖問題而明顯地增加資料流量。此外為了有效處理指向性天線強增益對遠方通訊之干擾，吾人提出了功率控制之跨層設計。透過控制傳送功率，能使得在鄰近範圍內的二組或以上的節點可同時進行資料傳輸，因而大大地提昇網路整體資料流量，此外也可降低功率消秏。最後，相較於使用全向性天線和基本指向性天線的系統，吾人藉由電腦模擬驗證本論文所提的系統架構可大幅度地改進網路的整體效能。

A wireless ad hoc network is a collection of wireless mobile hosts that are dynamically and arbitrarily located in a certain area. Compared with infrastructure networks, ad hoc network has more flexible ways of communication. However, the conventional ad hoc network uses omnidirectional antennas, which may result in network congestion. Using directional antennas can increase the potential for spatial reuse to alleviate network congestion significantly, leading to higher total network throughput. In order to exploit the benefit of directional antenna, many directional MAC (DMAC) protocols are proposed. However, these DMAC protocols induce new types of hidden terminal and blocking problems, which decrease the network throughput performance drastically. In this thesis, we propose an integrated design of physical, MAC and routing protocols with the use of directional antennas. An M-null directional antenna model with DMAC is proposed to transmit packets directionally and form M beamforming nulls to eliminate interference from other direction. Therefore, ad hoc nodes can adequately achieve spatial reuse, and the throughput performance is improved significantly due to addressing the hidden terminal as well as blocking problems. Furthermore, to deal with the high directional antenna gain which may potentially interfere with communications taking place far away, we propose a cross-layer design of power control protocol. Through controlling transmission power, simultaneous data transmissions of two or more pairs of nodes located in each other’s vicinity may be allowed and thus the network total throughput is enhanced drastically. In addition, power consumption is reduced. Finally, we evaluate the performance of the proposed system architecture by computer simulations, and confirm that the throughput performance is improved greatly over omnidirectional and basic directional antenna communications in ad hoc networks.