  By using joint modulation and customized constellation set, we show that
Quasi-Orthogonal Space-Time Block Code (QO-STBC) can be used to form a new
differential space-time modulation (DSTM) scheme to provide full transmit
diversity with non-coherent detection. Our new scheme can provide higher code
rate than existing DSTM schemes based on Orthogonal STBC. It also has a lower
decoding complexity than the other DSTM schemes, such as those based on Group
Codes, because it only requires a joint detection of two complex symbols. We
derive the design criteria for the customized constellation set and use them to
construct a constellation set that provides a wide range of spectral efficiency
with full diversity and maximum coding gain.
