Space-Time Coding for Multiuser Ultra-Wideband Communications

In this paper, we present the construction of full rate, fully diverse and totally real space-time (ST) codes for ultra-wideband (UWB) transmissions. In particular, we construct two families of codes adapted to real carrier-less UWB communications that employ Pulse Position Modulation (PPM), Pulse Amplitude Modulation (PAM) or a combination of the two. The first family is constructed from totally real cyclic division algebras. The second family encodes the pulses used to convey one information symbol and permits to achieve high performance levels with reduced complexity. Both families of codes permit to achieve the same coding gain independently from the size of the transmitted constellation. Moreover, for Time-Hopping (TH) multiple access channels, the amplitude spreading code associated with the second family of codes is taken to be user-specific. In this case, a simple design criterion is proposed, and spreading matrices constructed according to this criterion permit to reduce the level of multiple access interference.