A Technique for Improving the Efficiency of M-ary Signaling

The coding gain of M -ary communication systems using orthogonal alphabets have been shown to improve by using concatenated orthogonal codes, each of length m = \sqrt{M} . In the receiver, a two-stage MF/correlator and ML detection are utilized to provide the final decision through only 2(m- 1) comparisons instead of the (M- 1) comparisons normally required. A coding gain of 8 dB for P_{e} = 10^{-5} is obtained with m = 2^{l0} only. Higher coding gain is obtained with higher order concatenation.