The Key Technologies Research Of CI-OFDM Systems

The Orthogonal Frequency Division Multiplexing (OFDM) system has attracted extensive attention since the property of high-speed broadband transmission , robustness to multipath interference, balanced simple, anti-impulsive noise and so on. However, OFDM signal has high PAPR (peak to average power ratio) because of the superimposition of multi-carrier signals with large number of sub-carriers. The high PAPR seriously affects the performance of OFDM systems.Recently, a new kind of technique called CI-OFDM (carrier interferometry orthogonal frequency division multiplexing) has been widely studied. In the CI-OFDM technique, each information symbol is sent simultaneously over all carriers and the each carrier for the symbol is assigned a corresponding orthogonal CI spreading code. This CI-OFDM system not only can reduce PAPR problem significantly but also achieve frequency diversity gains without any loss in throughput. This paper focuses on studying the performance of different CI spreading codes in OFDM and we evaluate the performance of MIMO OFDM and MIMO CIOFDM system.Firstly, based on the wireless channel characteristics and channel model, we discuss the main principles of the OFDM system. Build simulation platform, and get the performance curves of OFDM system in the ideal environment CSI.Secondly, Several CDMA spreading sequences are applied to CI-OFDM, comparing the performance of different CI spreading codes in OFDM. From the theoretical analysis and MATLAB simulation, Bit Error Rate (BER) gradually diminishes with the increase of subcarriers and is nothing to do with CI spreading codes. Moreover, Peak-to-Average Power Ratio (PAPR) is determined by the autocorrelation and cross-correlation of each CI spreading codes and invariant to signal sequences.Finally, combine CI-OFDM and MIMO. SFBC (space frequency block coding) and STBC (space time block coding) are applied into both MIMO OFDM system and MIMO CI-OFDM system. From the theoretical analysis and MATLAB simulation, STBC-CI-OFDM and SFBC-CI-OFDM systems have the same performance in the frequency and time selected channel, and SFBC- CI-OFDM and STBC- CI-OFDM system achieves considerable BER improvement, compared with the SFBC-OFDM and STBC-OFDM system.