System design and analysis of MIMO SFBC CI-OFDM system against the nonlinear distortion and narrowband interference

The CI-OFDM (carrier interferometry orthogonal frequency division multiplexing) system has been widely studied in the multi-carrier communication system. This CI-OFDM system spreads each information symbol across all N sub-carriers using orthogonal CI spreading codes. The CI-OFDM system can show the advantage of PAPR (peak to average power ratio) reduction and frequency diversity gains without any loss in the communication throughput. On the other hand, a great attention has been devoted to MIMO (multiple input multiple output) antenna array systems and space-time-frequency processing. In this paper, focusing on the two Tx (transmit) / one Rx (receive) antennas and two Tx / two Rx antennas configuration, we evaluate the performance of MIMO OFDM and MIMO CI- OFDM system. SFBC (space frequency block coding) coding is applied into both MIMO OFDM system and MIMO CI-OFDM system. For CI-OFDM realization, digital implemented CI-OFDM structure is used in which CI code spreading operation and carrier allocation are separately processed by simple IFFT type operation. From the simulation results, it is shown that MIMO SFBC CI-OFDM reduces PAPR significantly compared with MIMO SFBC-OFDM system. The out-of band re-growth of signal spectrum in MIMO SFBC CI-OFDM system is much smaller than MIMO SFBC OFDM. In the NBI (narrow band interference) channel MIMO SFBC CI-OFDM system achieves considerable BER improvement, compared with the MIMO SFBC-OFDM system in which error floor occurs in most of SNR range. So, it can be expected that MIMO SFBC CI-OFDM system is very useful for the high speed communication system in the situation of nonlinear HPA (high power amplifier) and NBI channel.