On the design of modern multilevel coded modulation for unequal error protection

Different error protection capabilities associated with different bit positions in a constellation are utilized to provide unequal error protection (UEP) with multilevel coding (MLC) on AWGN and fast/slow fading channels. Unlike previous work on this problem, the design tool in this paper is the symmetric information rate (SIR), which is well suited to the use of modern component codes. The constellation design problem is addressed from two perspectives: bits-to-symbol mapping, and positions of constellation points. Design guidelines of MLC for UEP are presented, and examples are shown to demonstrate the validity of the proposed method. It is further shown that the proposed design is especially desirable for communication over a slow-fading wireless channel, as it allows for a gradual performance degradation with the decreasing receive SNR. Throughput advantages are shown to support this claim.