keywords: non-coherent channel, low-complexity(for detection) and near-optimal signaling

Bell Labs' current research over Information Theory covers space time modulation aspect. 

NEC Labs' work on UST. 

1.    J. Wang, NEC Laboratories America and X. Wang, NEC Laboratories America, "Optimum Design of Cayley Unitary Space-Time Coding for Noncoherent MIMO Communications", IEEE Transactions on Wireless Communications 5(7):1942-1951, 2006

2.    J. Wang, NEC Laboratories America, X. Wang, NEC Laboratories America and M. Madihian, NEC Laboratories America, "Design of Minimum Error-Rate Cayley Differential Unitary Space-Time Codes", IEEE Journal on Selected Areas in Communications 23(9):1779-1787, 2005

3.    G. Yue, NEC Laboratories America, X. Wang, NEC Laboratories America and M. Madihian, NEC Laboratories America, "Unitary Scrambling and Outer Code Design for MIMO Block Fading", Proceedings of the Thirty-Ninth Asilomar Conference on Signals, Systems and Computers 2005 pp. 1268-1272, 2005

 Samsung also holds patent on Diff STBC.

 However, it seems that my early expection on non-differential USTM did not present on diff USTM. DUST is more like differential PSK than USTM.