Quaternion Orthogonal Design based Sphere Decoder for MIMO Systems

In Land Mobile Satellite Communication system, MIMO (Multiple Input Multiple Output) Polarization Diversity along with spatial and temporal diversity is studied and analyzed. In general diversity, schemes offer better link reliability. Therefore, to achieve this, a combination of space, time and polarization diversity schemes is proposed. In this work, Orthogonal Space- Time Polarization Block Codes is generalized using quaternions which is a generalization of an orthogonal complex number. To decode OSTPBC, Sphere Decoding algorithm is used. Sphere Decoding is an effective technique to find the solution of Maximum Likelihood Decoding. But computational complexity is still high in the traditional Sphere Decoding. To further reduce the complexity of SD, Contraction Factor scheme is introduced which will speed up the contraction in each layer of the sphere radius and reduce the decoding complexity.