Research On NOMA-VLC System Based On Polar Codes And Its Power Allocation Algorithm

With the rapid development of communication technology,how to improve the quality of communication technology is very important.In terms of channel coding technology,polar codes proposed by Arikan is the only coding scheme that can theoretically reach the Shannon capacity limit,and have been widely used in various digital communication systems due to its excellent performance,such as 5G,visible light communication(VLC)and other fields.As a communication technology that uses visible light as a carrier in space,VLC not only can avoid electromagnetic interference,but also makes full use of the visible light spectrum to replace traditional radio frequency communication,which has gradually attracted people’s attention.In this paper,polar codes are combined with nonorthogonal multiple access(NOMA)-VLC communication system,and its error correction performance and power allocation algorithm are studied.The main contents and innovations of the full text are summarized as follows:(1)In order to improve the reliability of NOMA-VLC system,a NOMA-VLC system based on polar codes scheme is proposed in view of the occlusion effect of VLC channel and the error propagation caused by successive interference cancellation(SIC)decoding.The transmitting end of the system performs NOMA hybrid superposition coding operation on the information sequence encoded by polar codes;the decoding end adopts a SIC joint successive cancellation(SC)decoding scheme based on the SC decoding of polar codes.The simulation results show that when the bit error rate(BER)is 10-4 and fixed power allocation factor α=1/9、code length is 1024,and the polar code rate is 0.5,compared with NOMA-VLC system,user 1(user with poor channel status)obtains 4.2dB gain and user 2(user with good channel status)obtains at least 4dB gain in the NOMA-VLC system based on polar codes.(2)Aiming at the problem that power allocation in NOMA-VLC system based on polar codes will affect the bit error rate,fairness and system capacity of users,a dynamic power allocation algorithm is proposed from the aspects of user service quality and fairness.The algorithm first ensures that the transmission speed of users with poor channel status is not lower than the minimum transmission rate,and then allocates the remaining power to users with good channel status,so as to maximize the objective function of the total rate.Compared with the fixed power allocation algorithm(α=1/9),when the signal-to-noise ratio(SNR)is 10dB,the total rate of the NOMA-VLC system based on polar codes using the dynamic power allocation algorithm is increased by 38.2%.(3)Aiming at the requirement of system capacity improvement in multi-user scenarios,a collaborative NOMA-VLC system based on polar codes is designed on the basis of the above system.Users with good channel status not only serve as destination nodes to receive information sequences sent by the LED,but also act as relays node to transmit information to users with poor channel status.A dynamic power algorithm that satisfies cooperative communication is proposed.The simulation results show that when the BER is 10-4 and fixed power allocation factor α=1/9,compared with the NOMA-VLC system based on polar codes,user 1(user with poor channel status)in the cooperative system can obtain a gain of 0.9dB;when the SNR is 24dB and fixed power allocation factor α=1/9,compared with the NOMA-VLC system based on polar codes,the total transmission rate of the cooperative system is increased by 20.0%;when the dynamic power allocation algorithm is adopted,the outage probability performance of user 1(user with poor channel status)in the cooperative system is improved compared with that in the non-cooperative system.