Design And Implementation Of Wifi-Over-Fiber Systems

Radio over Fiber (RoF) technique uses fiber to transmit RF, microwave and millimeter-wave signals, which combines the advantages of optical communications and RF microwave communications, now it’s broadly employed in wireless communication, military communication and other fields. RoF technique combining with the distributed antenna system constitutes a RoF wireless access system, it not only has the high-bandwidth, low loss advantages of optical communication, but also the flexibility, mobility characteristics of wireless communication. As one of the major wireless communication technologies which are closest to the client, WLAN (wireless local area network) technology standards have gone through802.11to802.11b/a/g/n of the change, and now it comes to the MIMO+OFDM. The rate of WLAN from the initial several megabits increased to hundreds of megabits, and now gradually popular use of stage IEEE802.11ac standard could provide at least the rate of500Mbps by using complex modulation formats up to256QAM and up to80MHz bandwidth. Due to its simple structure, WLAN now is widely employed in the public area of the business district, schools, airports, etc. This paper will evaluate the properties and do the design work of RoF distributed antenna system based on WLAN, this work is of great significance in providing convenient services, applications of network of things, safety and other aspects.The main contents of this paper involves two aspects:First, analysis of the RoF system structure and research of characteristics of RoF system, which includes the research and design of the key components in the system, such as RoF optical transceiver module, double WiFi frequency circulator, dual-band WiFi front-end amplifier module; the second is research of network performance parameters in the RoF-WLAN distributed antenna system, ultimately through analysis and comparation of system performance parameters.This paper firstly introduces the basic stucture unit of RoF system and each evaluation feature of the system performance. Then we independently designed the key components of the RoF system according to the significance of these indicators to meet the requirements of the target subject. In this part, it includes the schematic and PCB design and implementation of the photoelectric conversion module, radio frequency identification (RFID) circuit, dual-band circulator, dual-band WiFi amplifier, next the verification work of the performance characteristics of these modules member was done by the method of experimental tests, which will be specifically described in the subsequent body of this paper. Finally, by using these designed key components to build RoF experimental system to transmit WLAN signals, and combine these with diatributed antenna system, achieve the practical demonstration of multi-service transmission goal, finally we evaluate the performance and parameters of the whole system in experiment, and we get the actual measured results of the error vector magnitude(EVM) which is3%at2.4G band while3.3%at5.8G band, both are lower than upper limit of5.6%in IEEE standard. The spurious free dynamic range(SFDR) is91.96dB at2.4G band while90.6dB at5.8G band. By accessing intelligent terminal equipment for a long time observation and repeated experiments, finally complete the validation work of the feasibility and reliability in the dual-band WiFi system.