Reducing complexity with less than minimum delay space-time lattice codes

Recently, several papers have been concentrating on reducing the decoding complexity of high-rate space-time codes. While the research has led to some impressive reductions in decoding complexity, the geometric methods so far used appear to have faced some fundamental limits. In this paper, we study what happens if we let go of the assumption of full diversity and study the possibility of reducing the complexity, while holding on to a high code rate, by reducing the length of codes. We will develop some tools that can be used to measure the changes we will encounter when reducing the code length. We will also study the achievable diversity-multiplexing gain trade-off (DMT) of codes with less than minimum delay (LMD) and discuss some code constructions.