Low rate code designs for multilevel signaling

In this letter we present a new approach to designing codes with spectral efficiencies between 0.5 and 1 bit/dimension using multilevel signaling. Traditionally, code design techniques for these rates use high rate codes with binary signaling. However, from constrained channel capacity results, we know that for spectral efficiencies between 0.5 and 1 bit/dimension, the use of low rate codes with multilevel signaling can result in significant gains compared to the conventional approach. We present several examples of bit interleaved coded modulation using low rate turbo codes and a 16QAM signal set that demonstrate this advantage.