Design And Research On Index Modulated OFDM System

In these days the bandwidth resources are restricted serious, so how to reduce the bandwidth overhead and improve the information transmission ability of system are the key problems that need urgent solve in next generation communication system. To solve these problems, based on the theory of spatial modulation, a new modulation mode called index modulated orthogonal frequency division multiplexing(IM-OFDM), which use the activation state of subcarrier to transmit information had been proposed. This modulation mode improves the spectrum efficiency of OFDM system. With respect to the research of IM-OFDM system, there are some existing research results, but still lack of the research of subcarrier activation strategy. Base on the existing work, we analysis the condition that the ideal subcarrier activation strategy should satisfy and propose the ideal subcarrier activation strategy. To reduce the complexity, we proposed two other strategy which called gray code subcarrier activation strategy and equiprobable subcarrier activation strategy. At last we through the simulation to demonstrated the effectiveness of the proposed schemes. The simulation shows that the new subcarrier activation strategy can improve the performance of the system in BER compare to the traditional activation strategy.In addition, pilot-assisted channel estimation is an effective channel estimation method in OFDM system. But the pilot make the system lose degree of freedom in time and frequency. Now the IM-OFDM system inherits the thought of OFDM system, that the pilot position is fixed. To solve this problem, we try to take the pilot position as a serial number bearing unit to improve the frequency efficiency. Thus, this paper proposed two pilot design schemes. The pilot position in one of the schemes is equal interval distribution while another scheme is unequal. Then we analysis which pilot position detect algorithm and channel estimation method should be use and through the simulation to demonstrated the effectiveness of the proposed schemes. The simulation shows that the new scheme can improve the performance of the system compare to the pilot position fixed IM-OFDM system, both in BER and spectrum efficiency.