Equal rate multilevel coding for the AWGN channel

We examine the use of layered modulation to form multilevel codes with unequal power allocations across the codewords. This departs from traditional coded modulation in that we do not enforce any particular constellation structure on the transmitted signals, but rather let the power allocations together with the sub-layered constellation determine the overall signal structure. We argue that the scheme can achieve the Gaussian capacity of the AWGN channel as the number of layers grows large, with each layer employing QPSK modulation with very low rate codes. A practical advantage of our scheme over traditional multilayered approaches is that the same coding rate is employed at each stage, allowing a single encoder and decoder; which removes the practical constraints of rate compatible code structures.