In general Mode S Identification of Friend or Foe (IFF) interrogator frame format consists of 56 bits of which 4 bits (10-13) are the interrogator identifier and 16 bits (17-32) are the spare bits which is usually left free. In this paper, these 16 bits are utilized to send the encoded interrogator identity. Objective is to estimate the interrogator identity and validate it with the interrogator identifier. Reed Muller algorithm is used to encode the interrogator identifier. These 56 bits are transmitted using Binary phase shift keying (BPSK) technique. The transponder will demodulate and decode the received signals using Hadamard algorithm to estimate and validate the interrogator identity. Simulated results show that it is possible to estimate the correct interrogator identity with up to 3 bits error. Since, probability of detection is mainly depends on noise level, received signal’s SNR is also estimated using two algorithms, based on iterative maximum likelihood criterion. © Research India Publications.