A design of 2 by 2 unitary space-time codes from sphere packing theory with optimal diversity product of code size 6

In this paper, we propose some designs of 2/spl times/2 unitary space-time codes by using sphere packing theory. In particular, we present an optimal 2/spl times/2 unitary space-time code of size 6 in the sense that it reaches the maximal possible diversity product for 2/spl times/2 unitary space-time code of size 6. The construction and the optimality of the code of size 6 provide the precise value of the maximal diversity product of a 2/spl times/2 unitary space-time code of size 6.