Research On The Effects Of BPF Group Delay On The Performance Of OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is a special multi-carrier transmission method. Its advantages are confrontation on frequency selective fading, and improve the utilization of spectrum at the same time. It can not only increase the system capacity, more importantly, it can transmit out multimedia services with plenty of information including audio, data, video and so on, with high-quality through broadband channel, which meets the requirement of multimedia communication.Significant results in the key technologies of OFDM, such as carrier synchronization, channel estimation, phase noise and so on have achieved in theory and practice. Because OFDM signal containing multiple frequency components, so the effect of the transmitter radio frequency (RF)group delay characteristics on the OFDM system is a problem that should not be overlooked. The OFDM system is very strict in orthogonality of sub-carries, thus it is extremely sensitive to the filter group delay. If the group delay characteristic of BPF is non-ideal, when the OFDM RF modulation signal passes the BPF, the different frequency components of the signal will be delayed for different time, which will make the orthogonality of the sub-carriers damaged, and result in inter-career interference (ICI).This paper is to research the effects of the RF BPF group delay characteristics on the bit error rate (BER) of the OFDM receiver. First of all, the reasons of the effects of BPF group delay on the OFDM system is deduced in theory. The deduced result shows that the non-ideal group delay characteristic of BPF will cause interference on the output signal of the OFDM system. Then by simulation, the different extent of the effects of different group delay characteristics of BPF on the OFDM receiver is found. Eventually the relationship between the BER and group delay is shown in picture. In the simulation, the modulations such as BPSK, QPSK,π/4-QPSK, 8PSK, 16QAM and 64QAM are taken in the OFDM system. Finally, the difference of the effects of the same group delay characteristic on the OFDM system under the different modulation modes, as well as the difference of the effects of the same modulation mode on the OFDM system under the different group delay characteristic is analysed. At last, the relationship of BER and BPF group delay is shown. The result of the research supplies a reference to the design of group delay of BPF in the RF system.