 
Summary: LowComplexity SQRbased Decoding Algorithm
for QuasiOrthogonal SpaceTime Block Codes
Luay Azzam and Ender Ayanoglu
Center for Pervasive Communications and Computing
Department of Electrical Engineering and Computer Science
University of California, Irvine
Abstract In this paper, we propose a new decoding algorithm
for quasiorthogonal spacetime block codes (QOSTBCs) which
achieves near Maximum Likelihood (ML) performance while
substantially reducing the decoding complexity. We show that
for a system with rate r = ns/T, where ns is the number of
transmitted symbols per T time slots; the proposed algorithm
decomposes the original complexvalued system into a parallel
system with ns 2×2 realvalued components, thus allowing for a
simple decoding of one real symbol at a time. For a square QAM
constellation with L points (LQAM), this algorithm achieves
full diversity by properly incorporating twodimensional rotation
using the optimal rotation angle and the same rotating matrix
for any number of transmit antennas (N 4). We show that
the complexity of this algorithm is linear with the number of
