COHERENCY CRITERION FOR THE BINARY SYMMETRIC CHANNEL.

For the purpose of communication system planning, predictions of system performance based upon models of an ideal coherent channel are extensively used. Previous work has demonstrated the deleterious effects of RF phase error on channel performance by machine computation of an integral derived by statistically averaging over the phase error. The required receiver performance in deriving the RF phase for detecting binary coherent signals is examined and a criterion is generated which, when satisfied, allows the use of the familiar performance formula derived from the idealized coherent channel mode. The criterion is obtained without resorting to machine computation. The Tikhonov probability distribution for the RF reference phase error is used. Some implications of the criterion for low capacity coherent channels are exhibited. In particular, the advantages of coding to reduce the energy to noise density ratio are examined. In this regard, carrier-present and suppressed-carrier coherent channels are contrasted. Author