The performance of a wireless sensor network is limited by the available bandwidth of the shared wireless channel. For the need to share the available bandwidth sensors contend for concurrent transmissions. The simultaneous transmissions by the neighbouring nodes are the main source of interference at the intended receiver sensor. In this paper, we derive the successful decoding probability of receiver sensor in presence of interference and Rayleigh fading channel. We introduce the concept of circular influence zone, to impose a restriction on the aggregated interference from the distant neighbours at an intended receiver sensor. We provide an insight about the critical sensor density which yields an optimal trade-off between the achievable coverage and receiver decoding probability in presence of co-channel interference.