Motivated by the highly dynamic topology in wireless sensor networks with asynchronous duty cycle, and its impact on reliable data delivery, we propose a light-weight opportunistic forwarding (LWOF) scheme. Differing from other recently proposed schemes, LWOF neither employs historical network information nor a contention process to select a forwarder prior to data transmission. It takes advantage of the preamble in low power listening (LPL) media access control (MAC) protocols and dual-channel

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... communication to remove the overhead of making a forwarding decision. Along with LWOF, we propose an energyefficient MAC protocol (LWMAC) with a shortened preamble, to exploit the non-deterministic characteristics of opportunistic forwarding. The preamble length in LWMAC is a function of the node density and sleep duration. Simulation results show that LWOF, along with LWMAC, can provide reliable service of data delivery with less energy consumption.