Abstract
Nonlinear feedback communication schemes proposed up to now have been restricted to coherent channels. This paper describes a scheme which not only lacks this restriction but yields performance better than the coherent ones that have been analyzed. Block coded orthogonal signals together with incoherent receiver forms are used on both forward and feedback links. It is assumed that the transmitter has a high peak power capability. However, it is shown that by increasing the code length the duty cycle of this mode can be made sufficiently small so that the contribution to average power is negligible. It is found that the probability of error for every message is upper-bounded by exp[-E(R)T], where T represents the code length and E(R) is a function of the transmission rate, R , the capacities of the forward and feedback channels, and a parameter that determines the rate with which the duty cycle decreases with increasing code length. When the forward and feedback capacities are equal, say C , the E(R) versus R curve can be made to approach a curve that starts at 2C and decreases monotonically to the value C at R = C . This contrasts with the corresponding curve without feedback which starts at C/2 and decreases to zero at R = C . The main advantage of information feedback over no feedback, namely E(R = C) > 0 , where C is the forward channel capacity, can also be obtained even when the capacity of the feedback channel is less than that of the forward. To obtain such behavior, existing schemes require that the feedback channel capacity be at least as great as the forward.
|
