Research On LDPC-OFDM Coded Modulation Technology In Wireless Ultraviolet Communication

Wireless ultraviolet(UV)communication utilizes the scattering effect of various particles in the atmosphere to realize information transmission.It has the advantages of anti-interference,non-line-of-sight(NLOS),high confidentiality,etc,and has broad application prospects.However,the scattering can cause serious inter symbol interference(ISI)problem,which leads to higher bit error rate(BER)while limiting the rate of UV communication,and reduces the perform ance of UV communication system.Low-Density Parity-Check(LDPC)code is a channel coding scheme with excellent error correction performance and close to the Shannon limit.Orthogonal Frequency Division Multiplexing(OFDM)has the advantages of high spectrum utilization and strong anti-interference ability,etc.Combining the advantages of these two technologies,this thesis studies the LDPC-OFDM coded modulation technology in wireless UV communication to achieve the purpose of suppressing ISI and reducing the system error rate.The details are as follows:(1)The construction of check matrix,encoding algorithm and decoding algorithm in LDPC codes are systematically studied.The binary phase shift keying subcarrier modulation and on-off keying are used to simulate under the NLOS UV communication model.The results show that the subcarrier modulation method has better performance.After LDPC coding,the BER of the receiver decreases significantly.In addition,the effects of decoding algorithm,code length,maximum iteration number and code rate on the performance of LDPC codes are simulated and compared.The results show that the performance of LDPC codes can be effectively improved by using soft decision decoding algorithm,setting appropriate code length and number of iterations,etc.(2)The wireless UV OFDM system is designed,and the Direct Current Biased Optical OFDM(DCO-OFDM)is simulated.The results show that OFDM technology can effectively suppress ISI in UV communication and improve system communication rate.In order to further improve the communication quality,the LDPC code is applied to the UV OFDM system,and the different modulation orders,the number of subcarriers and the UV communication system settings are simulated.The results show that the smaller the modulation order and the less number of subcarriers,the lower BER of the system performance.When combining OFDM with LDPC coding,the UV OFDM system modulated by 16QAM(Quadrature Amplitude Modulation)has been improved significantly.When using LDPC(1536,768)code and the error rate is 10-5,which can bring 13.2dB coding gain.In summary,the LDPC-OFDM technology can suppress ISI,improve communication rate,and reduce system error rate,which can effectively improve the performance of NLOS wireless UV communication system.