Channel-quality-aware multihop broadcast for single and multi-channel wireless sensor networks

Abstract

Improvements in hardware technologies enable small size of sensor nodes with low cost, which are composed of a processor, memory, and a radio transceiver. Untethered/unattended operation of wireless sensor networks (WSNs) is very attractive for a large number of applications due to no human intervention. Sensor nodes are generally deployed in environments where exhausted batteries are difficult to be charged or replaced. Since communication between sensor nodes is the most energy consuming operation, the primary goal to design communication protocols for WSNs is to maximize energy efficiency to prolong network lifetime.

Multihop broadcast is a fundamental service for high-level operations in WSNs such as query propagation, route discovery, and network configuration and reprogramming. The purpose of multihop broadcast is to convey a broadcast message to all nodes in a network. A source node of multihop broadcast produces burst traffic in a short time period, and these broadcast messages are spread across the whole network. This inherent broadcast mechanism causes serious broadcast redundancy and collision, and it can hinder transmission of sensing data for data gathering which is the intrinsic goal of WSNs. Therefore, it is essential that multihop broadcast should be performed with the minimum number of transmissions and collisions. In this dissertation, we present multihop broadcast mechanisms for both single and multi-channel WSNs.

First, we propose EMBA, an efficient multihop broadcast protocol for asynchronous single channel WSNs where each node independently wakes up according to its own schedule. Our scheme adopts a technique of the 2-hop forwarder's guidance. A node transmits broadcast messages with guidance to neighbor nodes. The guidance presents how the node forwards the broadcast message to neighbor nodes. The 2-hop forwarder's guidance deterministically selects forwarding nodes to transmit broadcast messages through links that have good quality. This technique reduces redundant transmissions, collisions, and retransmissions. We implement EMBA and other single channel based multihop broadcast protocols and show that EMBA outperforms other protocols in terms of various performance metrics. EMBA achieves lower message cost than the conventional protocols in terms of the number of collisions and redundant transmissions, and the number of byte transmitted.

Second, we propose Multi-channel EMBA (M-EMBA), efficient multihop broadcast for asynchronous multi-channel WSNs. Our scheme employs two channel-quality-aware forwarding policies of the improved forwarder's guidance and fast forwarding to improve multihop broadcast performance. The improved forwarder's guidance allows forwarders to transmit broadcast messages with the simplified guidance to their receivers through channels with good quality. This technique is the improved version of the 2-hop forwarder's guidance of EMBA to reduce overhead of guidance exchange. Fast forwarding allows adjacent forwarders to send their broadcast messages simultaneously through different channels that have good quality, which helps to reduce multihop broadcast latency and improve multi-channel broadcast utility. We evaluate the multihop broadcast performance of M-EMBA through theoretical analysis of the system design and empirical simulation-based analysis. We implement M-EMBA and compare it with other multi-channel based broadcast schemes. The performance results show that M-EMBA outperforms these protocols in both light and heavy network traffic. M-EMBA reduces message cost in terms of goodput, total bytes transmitted, as well as broadcast redundancy and collision. M-EMBA also achieves a high broadcast success ratio and low multihop broadcast latency. Finally, M-EMBA significantly improves energy efficiency by reducing average duty cycle.