PARMA: a PHY/MAC aware routing metric for ad-hoc wireless networks with multi-rate radios

Ad-hoc wireless networks with multi-rate radios (such as 802.11a, b, g) require a new class of MAC/PHY aware metrics that take into account factors such as physical-layer link speed and MAC-layer channel congestion. Conventional "layer 3" ad-hoc routing algorithms typically make routing decisions based on the minimum hop-count (MH). Use of the MH metric leads to the selection of paths with few hops, but one or more of these hops may turn out to be low-speed radio links due to adaptive rate selection at the physical layer We investigate a new cross-layer routing metric that takes into account both physical layer link speed and estimated channel congestion, thus aiming to minimize end-to-end delay that includes both transmission and access times. The proposed "PARMA" routing metric thus helps to spread the traffic across the "good links and nodes" in the network, increasing network capacity and reducing packet loss and delay. The paper presents the design and implementation of the proposed PARMA metric for proactive ad-hoc routing protocols, such as DSDV. DSDV modifications for incorporating the MAC/PHY aware metric into an ns-2 simulation model are given. Simulation results for typical multi-rate 802.11 ad-hoc network scenarios show that the proposed cross-layer PHY/MAC aware metric achieves significantly higher network throughput and decreases network congestion by selecting paths with high bit-rate links, while also avoiding areas of MAC congestion.