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.