  Space-Time block codes (STBC) from Orthogonal Designs (OD) and Co-ordinate
Interleaved Orthogonal Designs (CIOD) have been attracting wider attention due
to their amenability for fast (single-symbol) ML decoding, and full-rate with
full-rank over quasi-static fading channels. However, these codes are instances
of single-symbol decodable codes and it is natural to ask, if there exist codes
other than STBCs form ODs and CIODs that allow single-symbol coding?
  In this paper, the above question is answered in the affirmative by
characterizing all linear STBCs, that allow single-symbol ML decoding (not
necessarily full-diversity) over quasi-static fading channels-calling them
single-symbol decodable designs (SDD). The class SDD includes ODs and CIODs as
proper subclasses. Further, among the SDD, a class of those that offer
full-diversity, called Full-rank SDD (FSDD) are characterized and classified.
