An Opportunistic Forwarding Scheme Exploiting both Long Progress and Adaptive Rate in Wireless Networks

Suhua TANG
Mehdad N. SHIRAZI
Oyunchimeg SHAGDAR
Ryutaro SUZUKI
Sadao OBANA

Publication
IEICE TRANSACTIONS on Communications   Vol.E91-B    No.10    pp.3241-3250
Publication Date: 2008/10/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e91-b.10.3241
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Network
Keyword: 
geographic routing,  multipath fading,  opportunistic forwarding,  rate adaptation,  

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Summary: 
In Mobile Ad hoc Networks (MANET) geographic routing is characterized by local forwarding decision. Links with a long progress are preferred under the greedy forwarding rule. However in a real system long links tend to have a high packet loss rate due to multipath fading. A sub-optimal solution may separately exploit path diversity or rate adaptation. In this paper we study channel efficiency of multi-hop forwarding and try to jointly optimize rate adaptation and forwarder selection in geographic routing by the tradeoff between progress and instantaneous rate. We define a new metric -- Bit Transfer Speed (BTS) -- as the ratio of the progress made towards the destination to the equivalent time taken to transfer a payload bit. This metric takes overhead, rate and progress into account. Then we propose a packet forwarding scheme that Opportunistically exploits both long Progress and Adaptive Rate (OPAR) by a cross-layer design of routing and MAC. In OPAR each node selects for a packet the forwarder with the highest BTS. The forwarder changes as local topology (progress), packet size (overhead ratio) or channel state (data rate) varies. Simulation results show that compared with the normalized advance (NADV) [7] scheme and contention-based forwarding (CBF) [17] scheme, OPAR has lower packet loss and can effectively reduce channel occupation time by over 30% in the scenario with moderate mobility speeds.