| The requirements for transmission capacity and data rates in communication network are rapidly increasing at an amazing speed in human society with the continuous updating of mobile terminals such as smartphones,smart devices and laptops.Hence,the mobile communication system is facing new challenges.We not only need to explore new technologies such as novel multiple access technique and high order modulation to improve the spectral efficiency but also develop high frequency bands,achieving all-spectrum access based on high-frequency and low-frequency networking in mobile communications,because of spectrum as scarce resources in the mobile communication.In the current centralized/cloud radio access network(C-RAN)proposed by China Mobile,the part transmitted over the optical fiber is digital mobile fronthaul(MFH)based on the common public radio interface(CPRI)protocol.Although this structure is simple and easy to deploy,the limited transmission capacity due to the digitization of samples from the radio domain,it cannot meet the demand for large capacity and high data rate.However,the MFH based on radio over fiber(RoF)has become research focus in recent years for the reason that it can meet large capacity and high data rate requirements as well as achieve all-spectrum access.The application of MFH based on RoF in all-spectrum access wireless network is studied in this paper.Firstly,all-spectrum access technology,C-RAN architecture and RoF are introduced.Secondly,the transmission of radio signals is derived and analyzed theoretically in the MFH based on RoF.Finally,a novel analog MFH architecture has been proposed according to continuous wide area seamless coverage and high data rate requirements in hotspot area in 5 G with the help of the advantages of all-spectrum access and RoF.(1)A novel analog MFH architecture which can provide different services for users by using different frequencies and data rates according to the client rate requirements is proposed.In the analog MFH architecture,the radio signals at different frequencies for different services that 2.4 GHz band is utilized for wide-area seamless coverage to meet daily network requirements,28 GHz band is supplied to meet temporary high data rate requirements such as HD movies downloading,and 60 GHz band is employed as supplementary for seamless coverage to meet ultrahigh data rate requirements in hotspot areas.High-frequency and low-frequency hybrid networking is achieved for supporting the conventional seamless telecommunication networks and large capacity and high data rate requirements in hotspot area.(2)The 60 GHz optical millimeter-wave signal in the radio remote unit(RRU)can be sequentially transmitted over fiber to multiple further RRUs possibly working as a supplementary to realize the future plug and play flexible networking in the hotspot areas as well as increasing the coverage of millimeter-wave signal to meet high data rate requirements of different hotspot areas in wide domain.(3)With the development of denser and denser deployment and increasing quantity required of RRU,colorless RRU is an inevitable choice in order to deploy flexibly and save costs.A full-duplex MFH architecture with colorless RRU based on RoF has been proposed,which colorless RRU and F-RRU are achieved by utilizing the technology of polarization multiplexing and power splitters.Also high-frequency and low-frequency based on all-spectrum access is achieved for supporting the conventional seamless telecommunication networks and improvement of data rates in hotspot area. |
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