Adaptive space-time-frequency coding schemes for MIMO OFDM

In this paper, some novel results on adaptive space-time-frequency (STF) coding schemes for multiple-input multiple-output (MIMO) OFDM systems are illustrated. Such schemes result from the concatenation of conventional channel codes with orthogonal space-time block codes (STBCs). In the proposed channel codes, adaptivity can be implemented by adjusting the constellation/energy of the inner STBC code on a subcarrier by subcarrier basis via a space-frequency water-filling procedure and/or modifying some parameters, like the code rate and codeword size, of the outer code. Numerical results show that, in a MIMO OFDM systems with one or two receive antennas, using Alamouti´s STBC, and without outer coding, STBC adaptivity can yield an appreciable energy gain over an unloaded system operating at the some data rate. The use of an additional outer code can provide a further substantial gain, at least for high signal-to-noise ratios.