Study Of Precoded OFDM System Based On Cognitive Radio Technology

Cognitive radio technology can aware the "spectrum hole" in wireless communication environment; and makes full use of the spectrum through a certain way to increase spectrum utilization efficiency. The technology solves the tense situation of radio spectrum resources as wireless communication technology development and the users demand increasing. As an intelligent wireless communication system it has the ability of cognition and reconfigure. It can rationally communicate using free spectrum with dynamic changing secondary users' configuration parameters, and doesn't cause interference to the working authorized users.OFDM technology has high spectral efficiency and the ability of anti-multipath interference. It may achieve high speed data transmission as a hot candidate for 4G communication. In addition, OFDM technology achieves well control of spectrum resources through combination or cutting frequency, and effectively uses spectrum for data transmission, that meets the requirements of cognitive radio. The combination of OFDM and cognitive radio technology not only eases the situation of current short supply radio spectrum and uneven distribution, but also achieves rational allocation and fully utilizing of radio spectrum.This paper first introduces the basic principle of OFDM technology and its related technical knowledge, and describes the basic principles of cognitive radio technology and the advantages combined with OFDM. In cognitive radio conditions, adaptive OFDM system can improve spectrum efficiency and maximize its system capacity. Then we analyses the system performance of ZP-OFDM and make simulation analysis of NC-OFDM system. In the last, it focuses on the precoded OFDM system without CP based on cognitive radio. Cognitive radio makes the user of OFDM real-time change communication configuration parameters including modulation, coding, frequency, bandwidth and transmission power etc according the perceived status of wireless spectrum, so as to avoid interference to the authorized users in data transmission. The system makes these configuration parameters precoded into a pseudo-random sequence and transmits it with OFDM symbols. In this way, the system eliminates the specific control signaling for the transmission of communication configuration parameters, also improves the spectrum utilization efficiency and reduces the transmission power to increase system capacity.