Research On Technologies Of Narrow-Band Interference Avoidance In OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) technology as an effective means of high-spectral efficiency in wireless environment, with the advantages of its strong anti-multipath fading and resistance to inter-symbol interference ability, efficient spectrum utilization, etc., stand out from the many attractive core technology of the next-generation broad-band wireless communication systems.However, OFDM system is susceptible to a crowded band's traditional Narrow-Band Interference (NBI); therefore, the study in NBI suppression of OFDM system has important and far-reaching significance.For the issues that OFDM system's performance is vulnerable to be impacted by NBI, drawing on the technical ideas of avoiding NBI in Transform Domain Communication System (TDCS), using of the technical features that the OFDM system can close the sub-carriers flexible, this paper presents an improved OFDM system, which has the capacity of NBI detection, evaluation, and avoidance. What's more, this paper studies its key technologies, namely, NBI avoidance technologies in OFDM system and its Peak to Average Power Ratio (PAPR) reduction techniques.First, this paper gives the mathematical model of OFDM system, also it describes the main processes of OFDM system's transmitter and receiver in brief, buildind the OFDM system's simulation model; it analyses the characteristic of OFDM signal in time and frequency domain; mainly, from the two aspects of the power and bandwidth of NBI, the paper takes the detailed analysis of the impact of the NBI on OFDM system.Then, taking the main ideas of avoiding NBI in TDCS as premises, this paper presents a proved OFDM system, which has the capacity of NBI avoidance; it focus on the establishment of a comprehensive mathematical model of the proved OFDM system; simulation results verified that the technical feasibility and the effectiveness of NBI avoidance technologies for OFDM system.Finally, taking into account the problem that the PAPR of OFDM system may be too high, this paper applies conventional classic technology of PAPR reduction, which is the technology of PAPR reduction in OFDM system based on clipping and combined it with technical characteristics of improved OFDM system, and thus the technology of PAPR reduction based on clipping for improved OFDM system is proposed; Simulation results show that the method can reduce the PAPR of improved OFDM system to some extent, however the system's BER increases slightly.