Asymptotic performance of a coded communication system with orthogonal signaling in partial band jamming

It is well known that a communication system using M-ary orthogonal signaling in additive white Gaussian noise can achieve capacity. However, in a worst case partial band jamming channel, orthogonal signaling fails to achieve capacity. In this paper, we show that a M-ary orthogonal system using coding and side information provides reliable communications in partial band jamming. In particular, the system can achieve capacity by using the ratio threshold test (RTT) to convert all errors due to the channel into erasures. For the worst case jamming scenario, the minimum E(b)/N(J) needed for error-free communications is shown to be 4ln2 (4.43 dB). The optimum code rate that minimizes E(b)/N(J) is 1/2. With hard decision decoding, the minimum E(b)/N(J) needed for error-free communications is 8 ln 2 (7.44 dB) with the optimum code rate at 1/4. Hence, asymptotically, the typical 3 dB gain obtained by using soft decisions is observed. Moreover, this gain in performance does not require additional information from the transmitter; RTT generates its side information entirely at the receiver.