Application Research Of Broadband Optical Communication Modulation Technology For Indoor Multi-user Acces

In recent years,with the emergence of new network application scenarios such as virtual/augmented reality（VR/AR）,artificial intelligence（AI）,big data and cloud computing,there is an urgent need for higher-quality access networks to meet people’s demand for high-performance communication terminals.Therefore,high-speed,large-bandwidth and flexible access data receive-transmit and transmission have become the goal of the future development of a new generation of access systems.Passive optical network（PON）access system has become the most promising broadband access system because of its large transmission capacity,low-cost budget,wide access bandwidth,less electromagnetic radiation and easy compatibility with existing telecommunication access networks.At present,the shortage of radio frequency（RF）spectrum resources has become increasingly prominent,which has brought unprecedented pressure to traditional wireless communication.Visible light communication（VLC）technology uses light emitting diode（LED）as the light source.It has rich spectrum resources that can be used without application,and the advantages of strong confidentiality and saving optoelectronic device resources.It supports low-energy lighting while transmitting data and has received extensive attention from the academic community.Therefore,in PON and VLC access systems,it has great research significance and practical value to study and apply broadband modulation technology to further improve transmission rate,communication capacity,spectrum utilization and access flexibility of indoor multi-user terminals.In this paper,the structure and principle of PON and VLC high-speed access systems are described and analyzed.The multi-dimensional bandwidth signal processing methods such as orthogonal frequency division multiple access（OFDMA）technology,Polarization division multiplexing（PDM）technology and multi-color multiplexing technology are studied to improve the access performance of communication network end users.The application performance of various broadband modulation technologies such as quadrature amplitude modulation（QAM）,pulse position modulation（PPM）,minimum frequency shift keying（MSK）and orthogonal frequency division multiplexing（OFDM）in the system is studied.The main research process and research contents are as follows:A broadband optical access system scheme for high-speed data receive-transmit and transmission in the 6 GHz band is designed.The 1.25 Gbit/s non-return-to-zero on-off keying（NRZ-OOK）signal is modulated by the 6GHz subcarrier and transmitted over a 20 km standard single-mode fiber,and then assigned to four optical network units（ONUs）to achieve broadband signal access.To a certain extent,it reduces the bandwidth resource burden of the access system in the 2.4 GHz and 5 GHz Wi Fi bands and alleviates the shortage of spectrum resources.A broadband optical access system with a transmission rate of 50 Gbit/s using 16/32QAM-OFDMA technology is designed,which supports simultaneous transmission of four high-speed downlink signals.The system configuration is simplified by self-mixing detection technology to reduce the cost budget.The research results show that the 16QAM-OFDMA system has better receiving sensitivity,lower computational complexity and better anti-interference ability,but it is not as good as the 32QAM-OFDMA system in terms of communication capacity and bandwidth utilization.A full-duplex broadband optical access system scheme using 32QAM-OFDMA technology and NRZ-OOK technology is designed,which supports three 32QAM-OFDMA signals downlink transmission and one NRZ-OOK signal error-free uplink transmission at the same time.The ONU is passive,which reduces the system complexity and budget cost of the user’s side.A broadband optical access system scheme combining PDM technology and OFDMA technology is designed.The downlink transmission of six 32QAM-OFDMA signals is realized by using only one external cavity laser,and the communication capacity is doubled compared with that without PDM.The results show that when the received optical power is larger than-14d Bm,the bit error rate（BER）of the six downlink signals can be lower than 10^-3.A multi-color multiplexing VLC broadband wireless access system scheme using PPM technology is designed to support the transmission of three signals while providing lighting for the indoor environment.The transmission performance of the traditional NRZ-OOK modulation signal is compared and analyzed.The results show that the receiver sensitivity of the 16-PPM signal is higher when the BER is the same.A scheme of multi-color multiplexing VLC broadband wireless access system based on PPM and MSK modulation technology is designed,and the transmission performance of4-PPM-MSK signal is compared with that of MSK modulation signal.The results show that 4-PPM-MSK signal has lower BER when the received optical power is the same.In order to promote the construction of rural information network,realize the broadband wireless access of rural residents in mountainous areas and maximize the utilization of resources.A multi-user access system scheme combining PON and VLC technology is designed.The64QAM-OFDMA technology is used to access three downlink transmission signals to the rooms,and then the PPM-MSK multi-color multiplexing VLC technology is used to undertake three channels of data and transmit to each terminal user.In the uplink,the signal is modulated and encoded by the alternative mark inversion（AMI）code,and the error-free uplink transmission of the signal is realized.