Research On ACO-OFDM Based Optical Wireless Communication Transmission Technology

Optical wireless communication is a communication mode based on laser as the carrier of information transmission,it can realize high-speed bidirectional transmission of voice,data,multimedia image,and any cable medium is not necessary. But the optical transmission in the air may cause multipath effect, the problem can be solved by Orthogonal Frequency Division Multiplexing (OFDM) with its anti-interference ability in the multipath channel and OFDM technology has high spectrum efficiency and transmission rate. Optical wireless system uses intensity modulation and direct detection (IM/DD), so the signal must be non-negative and real. Asymmetrically-clipped optical OFDM (ACO-OFDM) is a unipolar mode with high optical power efficiency and transmission rate, so the ACO-OFDM technology is researched,solve the problem of the technology and improve communication performance of the system.The main work of the paper is as follows:Firstly, the background and significance of the paper are described, then the development history of Optical wireless communication and OFDM is introduced, then the technology principle of ACO-OFDM is analyzed in detail, and the simulation was finished in the ACO-OFDM system, at last the communication performance of error and the bandwidth efficiency is analyzed.Secondly,the problem of high peak-to-average power ratio (PAPR) is researched,and the definition and distribution of the system are analyzed, at the same time, the PAPR technology generally in wireless communication is introduced. Then the three technologies of companding transformation, active constellation extension, selective mapping in wireless communication are improved and the ACO-OFDM system is applied to realize the suppression of PAPR.Then,for the problem that traditional ACO-OFDM only utilize odd subcarrier demodulation and the problem that abandon the so-called "clipping noise" on even subcarrier,the paper uses the improved ACO-OFDM receiving technology, the information on even subcarrier of receivers is utilized, and combination with the information on odd subcarrier is applied. Under the condition of optimum weighted coefficient, the original information is restored, and the simulation was finished in optical wireless ACO-OFDM system. Compared with the traditional ACO-OFDM system, the improved ACO-OFDM system performance was improved by 2dB. ,Finally, for the problem of bandwidth efficiency in ACO-OFDM system, in this paper,the combination of ACO-OFDM and DCO-OFDM technology is adopted, ACO-OFDM technology is used on the odd subcarrier and the DCO-OFDM technology is used on the even subcarrier, and the information demodulated from the receiving ACO-OFDM is the same with traditional ACO-OFDM. The DCO-OFDM on the even subcarrier can be demodulated successfully by the process of interference elimination. Comparing with the traditional ACO-OFDM and DCO-OFDM system, the combined system improved the performance in optical power efficiency.