Research On Fronthaul Access Technology Based On RoF

With the rapid development of big data,Internet of Things,cloud computing and other technologies and people's preference for mobile communications,the data traffic of mobile networks will usher in explosive growth.Mobile access networks are facing challenges in terms of high speed,low latency,and large capacity.Research on new technologies such as full spectrum access technology,millimeter wave technology,and massive MIMO technology has been carried out at home and abroad.Millimeter wave technology can utilize rich spectrum resources and can increase the transmission capacity of wireless access,but the line-of-sight propagation and coverage are small.The full-spectrum access technology based on high and low frequency cooperative networking can simultaneously utilize the large transmission capacity and transmission capacity of the millimeter wave frequency band.The advantages of wide coverage in low frequency bands increase system capacity and enhance user experience.The mobile access fronthaul network is the main component of the wireless access network.The current digital fronthaul network based on the CPRI protocol under the C-RAN architecture has the advantages of simple structure and high tolerance to nonlinearity,but it also faces the digitalization of analog signals.It is difficult to meet the requirements of mobile networks because of the high bandwidth requirements and processing delays.The RoF-based analog fronthaul technology transmits analog wireless signals in the optical domain.It has the advantages of high spectrum efficiency and low delay,and can realize high and low frequency cooperative networking,so it has become a research hotspot in recent years.This article mainly studies the fronthaul access technology based on RoF.First,the fronthaul network,high and low frequency cooperative networking technology,RoF-based fronthaul technology and other content are summarized,and then at the theoretical level,it aims at the simulation MFH network based on RoF technology.The signal transmission process was deduced in detail.Finally,according to the 5G candidate frequency bands released by the ITU,taking full advantage of the advantages of RoF technology and high and low frequency cooperative networking technology,a new MFH link structure based on analog RoF technology was proposed.The thesis work mainly includes the following two aspects:(1)Two MFH downlink schemes based on electric domain up-conversion are proposed.The first is a low-complexity,high-,medium-,and low-frequency signal mixed transmission analog MFH downlink scheme based on electrical domain upconversion.This scheme loads an IF signal carrying high-,mid-,and low-frequency signal data information and a radio frequency local oscillator signal onto the light wave.After the signal is transmitted through the optical fiber,it is recovered by photoelectric detection,and finally the RF-OFDM signal and the radio frequency local oscillator signal in the photocurrent are extracted;the second is the electric domain up-conversion high,middle and low frequency mixed transmission MFH downlink structure based on the optical filtering method.This solution loads the IF signal carrying high,medium and low frequency band signal data information and two radio frequency local oscillator signals on the light wave.The optical signal is transmitted by SSMF and divided into two paths through an IL.One of them contains the signal data information carrying high,medium and low frequency bands.O-OFDM signal,the signal is restored to the original IF signal through photoelectric detection,and the other path contains two optical carriers separated by a certain frequency interval.The signal is restored to a radio frequency local oscillator signal with the frequency of the difference between the two optical frequency components through photoelectric detection..The mid-band signal in the two schemes is generated by the IF signal supporting temporary high-rate services and the radio frequency local oscillator signal after being passed through the mixer 1,and its frequency is the sum of the two frequencies;the high-band signal is generated by the signal supporting the ultra-high-rate service The radio frequency local oscillator signal after the frequency and the double frequency is generated by the mixer 2,and the signal frequency is the sum of the two frequencies.By building a system simulation link,the spectrum and frequency spectrum of the transmitted RF-OFDM signal are analyzed in detail,and according to 3 GPP standards and simulation data,the EVM of eight RF-OFDM signals varies with SSMF link length,modulation depth,and reception.The changes of optical power and laser linewidth are studied in depth.The results show that the first scheme based on up-conversion in the electrical domain is more effective.(2)A high-,middle-and low-frequency mixed transmission MFH downlink scheme based on optical domain up-conversion is proposed.In order to avoid frequency conversion of low-frequency and mid-frequency signals at the receiving end,the position of the frequency band can be determined in advance;in order to reduce the requirements of the MFH link electro-optical conversion device,the up-conversion of millimeter wave signals is completed based on the optical domain,and the up and down of DP-DDMZM The DDMZM of the two arms respectively perform upper sideband OSSB modulation and lower sideband OSSB modulation,and then combine the signals to obtain optical carriers separated by a certain frequency interval and optical signals supporting ultra-high-speed services in hotspots,which can be retained after photoelectric detection The photocurrent component of the signal amplitude and phase information in the high frequency band.Set up a simulation link to analyze the spectrum and spectrum of the transmitted signal in the system.According to 3GPP standards and simulation results,the EVM of RF-OFDM signals in the three frequency bands of high,medium and low varies with SSMF link length,modulation depth,received optical power,The laser linewidth changes have been studied in depth.The scheme is compared with the high,middle and low frequency mixed transmission MFH downlink scheme based on electrical domain upconversion.The results prove that the optical domain-based upconversion structure is simple,the receiver sensitivity is lower,and the performance is better than that based on electrical domain.Frequency conversion scheme.