Improved design criterion for good space-time trellis-codes under block fading channels

The design criteria for space-time codes under block fading channels are the rank criterion and the determinant criterion, which are widely cited in the literature. These criteria are not very tight under some circumstances. In this letter, we derive a tighter design criterion for space-time codes. Based on our criterion, we have found good space-time codes by computer search. The complexity of systematic search for good space-time codes is a big obstacle to get good codes. Using our new design criterion, the complexity of search is dropped down dramatically. Simulations show that our new codes have superior performance over the existing codes.