on acquisition technique (ASEAT). Time Synchronization of Non-Coherent FH/MFSK Systems multitone jammer whose presence in only one of a sequence of n1 hops might be sufficient to cause the failure of that specific acquisition trial. (Each time this occurs the process must repeat the acquisition trial until a clean record of n1 successive hops is received without a single jammed tone.) The reason for this vulnerability again stems from the fact that the spectral estimation process is performed on a hop-by-hop basis, thus making no use of the inter- ference rejection capability associated with the FH despreading process. Finally, we point out that the ASEAT is also applicable to hybrid SS systems such as FH/TH and FH/DS [6]. 3.2 TIME SYNCHRONIZATION OF NON-COHERENT FH / MFSK SYSTEMS Time synchronization of a conventional (non-spread) non-coherent MFSK receiver, with additive white Gaussian noise (AWGN) as the only source of disturbance, is typically achieved by transmitting a known synchronization sequence (say frequency f1 followed by f2) which is repeated as often as nec- essary until the desired degree of time synchronization accuracy is obtained. In the presence of this sequence, spectral estimates are formed from discrete (fast) Fourier transforms of the received signal plus noise over one data sym- bol interval and evaluated at the two frequencies, f1 and f2. The ratio of the difference of these two spectral estimates to twice their sum is then the maximum-likelihood estimator of the time of transition from f1 to f2 relative to the receiver's present time origin [11], [12]. It is emphasized that it is the transitions in the data from f1 to f2, and vice versa, that allow the determi- nation of time synchronization by the above approach. In a non-coherent FH/MFSK receiver, it is sufficient to transmit a single frequency tone corresponding to a specific data symbol and allow the fre- quency hopping to cause the necessary frequency transitions for estimation of time synchronization. As such, the timing estimate i