A single-hop wireless sensor network for distributed detection has been considered in the majority of the existing literature. However, a wireless sensor network for an event detection application with cheap and short range sensors is likely to be a multihop network. Here we consider a distributed detection problem in a multihop wireless sensor network with tree topology. We propose an optimum multibit decision fusion rule derived from the previously known optimum likelihood ratio for a

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... op network with star topology. Subsequently, we present an efficient multibit decision fusion rule for a multihop wireless sensor network with tree topology. Through numerical results, the proposed scheme is shown to achieve a significant improvement in detection accuracy over existing distributed detection schemes.