In many process Wireless Sensor Networks (WSNs) are based on received signal strength indication (RSSI).the advantage of RSSI are interms of complexity and energy consumption. But the RSSI values in the indoor environment are unstable due to the fading caused by multi path propagation. In wireless sensor network we compute RSSI based localization algorithm in spatial diversity. We consider many kinds of single and multiple antenna systems they are Single Input Single Output (SISO) system, Single Input Multiple Output (SIMO) system, Multiple Input Single Output (MISO) system and Multiple Input Multiple Output (MIMO) system. For comparing the antenna systems trilateration and multilateration localization algorithms are used. Multiple antenna systems used in spatial diversity will improve the accuracy. We use three diversity combining techniques at the receiver: Maximal Ratio Combiner (MRC), Equal Gain Combining (EGC) and Selection Combining (SC). Multiple antennas used at both the side provide better performance. Finally MRC diversity combining technique outperforms EGC that as well outperforms SC. For estimating the target position we use trilateration and multilateration. By comparing both the algorithm multi lateration algorithm present better results compared with the trilateration algorithm At last we find that MRC performs the best and SC is the worst.