Design And Performance Analysis Of O-OFDM Symbol Decomposition With Serial Transmission System In Visible Light Communication

Visible light communication(VLC)provides short-range,ultra-wideband,cable-free information transmission using visible light emitted by common light-emitting diode(LED)as the carrier,which is an ideal complementary technology to traditional radio frequency(RF)communication.Optical orthogonal frequency division multiplexing(O-OFDM)technology tackles the problems of inter symbol interference,narrowband interference and low spectral efficiency of VLC systems.However,O-OFDM signals with large peak-to-average ratio(PAPR)are susceptible to non-linear distortion.The operating range of physically available LED is restricted,and the LED operating range exhibits non-linear characteristics.LED is regarded as the non-coherent light source.VLC employs intensity modulated direct detection(IM/DD)technique,which is susceptible to non-linear distortion that deteriorates the system error vector magnitude(EVM)and bit error rate(BER)performance.Therefore,this thesis takes the visible light communication O-OFDM system as the research object and conducts the research focusing on the LED non-linear distortion suppression method.We propose the O-OFDM symbol decomposition with serial transmission system,the adaptive O-OFDM symbol decomposition with serial transmission system,and the optimal signal-to-noise ratio O-OFDM symbol decomposition with serial transmission system.The specific research contents are as follows:1.The O-OFDM symbol decomposition with serial transmission(SDST)system is proposed.The O-OFDM symbol is decomposed by amplitude clipping,followed by serially framing,and it is finally input to a single LED.Compared with traditional iterative signal clipping(ISC)system,the SDST system requires a single LED,which reduces the system synchronization requirements.It is simple to hardware implement,convenient to deploy,and avoids the problem of BER degradation caused by the channel gain difference.The expression of the system theoretical signal-to-noise ratio is derived and the simulation models using the Monte Carlo bit error rate and the error vector magnitude are built.Results demonstrate that the performance of EVM and BER enhance significantly as the symbol decomposition times increase;however,the information transmission rate slightly decreases,and the direct current biases will affect the performance of EVM and BER.2.The adaptive O-OFDM symbol decomposition with serial transmission(ASDST)system is proposed.The maximum symbol decomposition times are fixed first,and then the OOFDM symbol is decomposed by amplitude clipping.For each decomposition,the input symbol is subtracted from the output symbol and determining whether the subtraction value equals zero.If it is zero,the symbol decomposition is terminated;if it is non-zero,the symbol decomposition is continued until the difference between the input and output symbols of certain symbol decomposition equals zero or the maximum symbol decomposition times are attained,which avoids the possibility of abundant all-zero symbols in ISC and SDST systems.The information rate,optical power and signal-to-noise ratio expressions of the ASDST system are derived.Monte Carlo simulations are performed to investigate the average symbol decomposition times,average optical power,average EVM and average BER.The results show that ASDST reduces the average symbol decomposition times,thus reducing optical power consumption,improving BER performance and information transmission rate.3.The optimal signal-to-noise ratio O-OFDM symbol decomposition with serial transmission(OSNR-SDST)system is proposed.According to the maximum times of symbol decompositions,the bit signal-to-noise ratios are calculated for symbol decomposition once,symbol decomposition twice,and until the maximum times of symbol decompositions.Comparing the signal-to-noise ratio for different symbol decomposition times,the O-OFDM symbol is decomposed according to the times of maximum signal-to-noise ratio.The problem of fixed symbol decomposition times in ISC and SDST systems is avoided;meanwhile,the problem that ASDST system requires excessive decomposition times to completely decompose O-OFDM symbol at low symbol variances is also avoided.Monte Carlo simulations are performed to investigate the connection between the O-OFDM symbol variances and the optimal times of symbol decompositions as well as the system performance.The results show that OSNR-SDST improves BER performance while reducing the symbol decomposition times,further saving LED optical transmit power and improving the system information transmission rate.As the central device of visible light communication,the non-linear characteristics of LED directly affect the performance,communication rate and hardware design of visible light communication systems.The research results of this thesis certainly have important theoretical significance and practical value.