Asynchronous speech encryption - formulation and simulation

Speech encryption techniques have always been very important for military communications, but most useful techniques require perfect synchronization between the transmitter and the receiver. This not only complicates the implementation, but makes the transmission very sensitive to channel conditions because slight synchronization error might completely break the transmission. In this paper, a general formulation for "asynchronous speech encryption" is proposed, in which the synchronization becomes completely unnecessary. It will be found that the two asynchronous techniques proposed recently become two special cases of the general formulation here. Also, an effective and practical method to evaluate the system performance when operated with a realistic telephone channel is developed and simulation results for such asynchronous techniques are presented finally.