Antenna pairing for space-frequency block codes in edge-excited distributed antenna systems

Space-frequency block codes (SFBC) combined with frequency switched transmit diversity (FSTD) is used in the downlink of 3GPP LTE system, where all transmit antennas are collocated at eNodeBs. However, all transmit antennas serving a cell are distributed at the cell edge in edge-excited distributed antenna systems. The performance of SFBC is greatly affected by the different large scale fading from different remote antenna units. In this paper, we investigate the tradeoff between the coding gain and average receive SNR of SFBC in DAS layout and propose to set apart the two antennas of SFBC transmission as far as possible. The optimal antenna pairing schemes in the edge-excited DAS cells compatible with 3GPP LTE system are those with the maximized average distance of SFBC transmission. According to the system level simulations in multicell environment, the 5% outage spectrum efficiency and average throughput per cell of SFBC transmission are improved by as much as 21.8% and 11.6% respectively in DAS3 cells, compared with those in LTE system. The DAS6 cells achieve even high gains in outage spectrum efficiency by 123.6% and average throughput per cell by 22.5%.