在無線感測網路中探討Glossy之網路特性的實作與研究

Abstract

在設計WSN的資料收集協定時，如何設計一個有效率的頻道存取一直是十分重要的課題。而Glossy是目前一個相當新穎的協定，它主要是讓不同感測節點的無線電同步傳送，以達成電磁波的建設性干涉，進而讓多個節點可以同時存取頻道，並減少因CSMA的頻道探測及TDMA的時間排程所造成的延遲。然而，Glossy的網路特性卻尚未被清楚了解，因此本篇研究著重在探討各種網路特性對Glossy的影響。首先，此研究驗證我們具有能力將Glossy移植到我們的testbed上，並且確立其可行性。此外，我們研究不同的網路特性像是封包生成速率、封包大小以及無線電發送訊號強度對Glossy的影響。結果顯示當封包生成速率較快的情況下，感測結點無法正常啟動運作；另外，當訊號強度變小，Glossy的效能也會明顯地隨著封包大小所影響。因此，當應用上需要較快的封包生成速率或較大的封包時，Glossy不適合當作資料收集協定。

Efficient channel access in WSN has always been significant in the design of data collection protocol. The state-of-the-art flooding-based protocol, Glossy, focuses on multiple senders’ simultaneous transmissions with constructive interference to access 802.15.4-based channel, reducing latency for channel sampling of CSMA or slot scheduling of TDMA. However, the properties of Glossy are still not completely understood. This study is to investigate the impact of distinct network characteristics on Glossy. We first verify our ability sufficient to use it and its feasibility on our local testbed. Furthermore, we investigate the effect of various factors such as packet generation rate, packet size and transmission power. Our results showed that Glossy has limitation on faster generation rate. Also, when radio power is close to the sensitivity threshold, tradeoff appears between packet length and time synchronization accuracy. Thus, applications with long packet and high packet generation rate is less suitable to use Glossy as data collection protocol.