Binary decoding of concatenated turbo codes and space-time block codes for quaternary modulations

Space-time block (STB) coding is one of the key techniques used to combat fading in multiantenna wireless communication systems. STB coding provides diversity gain while having a simple decoding. However, when further gains are needed, an outer channel code has to be concatenated. Turbo codes are channel codes that have been shown to perform close to the Shannon limits in AWGN channels. Moreover, they have a relatively low-complexity binary MAP decoding. However, this complexity increases exponentially with the number of bits per symbol. In this paper, a system consisting on an outer turbo code concatenated with an STB code is considered. A general formulation for STB decoding based on a least squares criteria is given in order to allow binary turbo decoding while using quaternary modulations such as QPSK. This binary decoding results in a higher global rate at no complexity cost. A normalization algorithm of STB codes is also given in order to present a fair comparison in terms of energy between MIMO (multiple-input multiple-output) and single-antenna systems.