Low PAPR STBCs from Complex Partial-Orthogonal Designs (CPODs)

Space-time codes from complex orthogonal designs (CODs) with no zero entries offer low peak to average power ratio (PAPR) and avoid the problem of turning off antennas. But CODs for 2^alpha antennas with alpha + 1 complex variables, with no zero entries are not known in the literature for alpha ges 4. In this paper, a method of obtaining no zero entry (NZE) codes, called complex partial-orthogonal designs (CPODs), for 2^alpha+1 antennas whenever a certain type of NZE code exists for 2^alpha antennas is presented. This is achieved with slight increase in the ML decoding complexity for regular QAM constellations and no increase for other complex constellations. Since NZE CODs have been constructed for 8 antennas our method leads to NZE CPODs for 16 antennas. Moreover, starting from certain NZE CPODs for n antennas, a construction procedure is given to obtain NZE CPODs for 2n antennas. The class of CPODs do not offer full-diversity for all complex constellations. For the NZE CPODs presented in the paper, conditions on the signal sets which will guarantee full-diversity are identified. Simulations results show that bit error performance of our codes under average power constraint is same as that of the CODs and superior to CODs under peak power constraint.