Two-hop forwarding in wireless networks
Shivendra S. Panwar, Sathya Narayanan · 2006
Wireless networks are becoming increasingly popular in both local area networks (LAN) and wide area networks (WAN). All known wireless technologies define multiple rates to allow wireless nodes to choose the best modulation scheme based on the environment. Due to the variations in wireless channel, a wireless network generally contains a collection of high data rate (HDR) nodes and low data rate (LDR) nodes. The presence of LDR nodes in the network has a negative effect on the performance of wireless networks. In this thesis, we propose cooperation between HDR nodes and LDR nodes to reduce the negative impact of the LDR nodes in the network. We present three advantages in extending the widely deployed IEEE 802.11 MAC to support cooperation among nodes by enabling two-hop transmissions in the infrastructure mode. The first advantage is higher available bandwidth in a multi-rate 802.11 network. The second advantage is the potential increase in the number of VoIP calls that can be carried in a 802.11 network. As a third advantage we demonstrate that the total energy consumption of the network for a given throughput reduces due to cooperation among the nodes. These advantages accrue assuming every node in the network is capable and willing to participate in two-hop forwarding, which is unrealistic due to the widespread adoption of the legacy MAC protocol. In order to achieve incremental deployment of two-hop forwarding, we address the backward compatibility of any proposed modifications and ensure that there are sufficient incentives for HDR nodes to forward data bits for LDR nodes. Hence, we analyze the use of two-hop forwarding from the forwarding nodes perspective. The analysis presented demonstrates that the forwarding node can achieve significant benefits on throughput, media-access-delay and even the power expended in transmitting a given number of its own bits. Based on these benefits, we show that it is in the interest of a HDR node in a 802.11 network to participate in two-hop forwarding schemes. Since this is a win-win situation for the HDR node we conclude that the incremental deployment of cooperative communication in multi-rate wireless networks under well-defined constraints is realistic.