SENSORS: Cooperative Diversity for Wireless Sensor Networks

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0329908Anders Host-MadsenUniversity of HawaiiThis project considers the communication between sensors in a wireless sensor network. The capacity of such wireless sensor networks is limited both by the interference between different transmissions and by the impairments of the wireless channel, such as fading. This project investigates using cooperative diversity to overcome the limitations of the wireless communication. The gains promised by cooperative diversity are substantial, and the impact on the design of wireless sensor networks could be considerable. Simple forms of cooperative diversity can be build into wireless sensor networks in the near term relatively easily, while more advanced forms can be incorporated in future wireless networks as technology develops. Cooperative diversity can also have a large impact on military networks, both communications networks and sensor-actuator networks. In cooperative diversity, several nodes form a kind of coalition to assist each other with the transmission. The sources jointly act like a multi-antenna transmit array, and the destinations act like a multi-antenna receive array through interchange of messages. There are three advantages from this: diversity, since different paths might fade independently, a power gain through beamforming, and interference mitigation through cooperation on messages transmission. The gain from cooperative diversity is both an increase in rate, measured by ergodic capacity, and diversity, measured by outage or outage capacity. Preliminary results already show very large gains while still hinting at the further considerable gains that can be obtained by optimum signaling. The work planned in this project is 1) Deriving upper and lower bounds for the Shannon capacity of cooperative diversity in fading channels. 2) Developing near-optimum signaling methods for cooperative diversity. 3) Developing simple signaling methods that can be utilized by even simple sensors.