UEP MIMO-OFDM with Beamforming- Combining for Imperfect Channel Information

In this paper, unequal error protection (UEP) adaptive multiple-input multiple-output (MIMO) system using orthogonal frequency division multiplexing (OFDM) is considered. Our proposed transmission scheme consists of three stages. The inner stage is a UEP adaptive loading, which is introduced to fulfill a certain UEP profile by distributing bits and power across the unitarily transformed eigenbeams. The next stage is a variable size beamforming to adaptively utilize the channel eigenbeams. The final stage is a post combiner that uses a linear-spatial equalizer to withstand the rapid wireless channel variation and resolve the undesired CSI error effects. For the case of imperfect channel state information (CSI), we studied the performance of different beamforming-combining techniques for time varying channel conditions and different correlation models using an intuitive and a robust bit-loading. The results are promising and fulfill the proposed UEP profile. Moreover, the robust bitloading seems to be a reliable technique in case of CSI uncertainties.