| With the gradual deployment of the fifth generation communication system(5G),the vigorous development of the Internet of things,big data,blockchain,cloud computing,artificial intelligence and other services,provides an unprecedented experience for people's life and work style,politics and economy,and then brings a great demand for network capacity.The rapid growth of business traffic has caused severe challenges to mobile communication.Due to the increasing shortage of medium and low frequency radio spectrum resources and the urgent demand for high-speed wireless broadband access,people turn their attention to the high-frequency millimeter wave band with more abundant spectrum resources.However,due to the limited bandwidth and other electronic bottlenecks,it is more difficult and costly to generate millimeter wave signals by traditional electrical methods.At the same time,when high-frequency signal is transmitted in the air,the transmission distance of millimeter wave signal is greatly restricted due to the attenuation characteristics of atmospheric channel.The generation and transmission technology of millimeter wave signal and vector millimeter wave signal based on radio over fiber(RoF)can not only generate high frequency carrier more simply and flexibly,but also realize long-distance and low loss transmission of millimeter wave signal based on optical fiber link,which has a very wide application prospect in the future wireless access network.This paper focuses on the realization of optical millimeter wave system,and makes a deep study on the key issues in the production of millimeter wave signal with high frequency multiplication factor,the generation of vector millimeter wave signal and the RoF transmission of vector signal.The main research results are as follows:1.Aiming at the problems of complex structure,difficult precise synchronization,poor tunability,weak system stability and high cost in the process of high frequency multiplication millimeter wave signal generation,three new schemes for millimeter wave signal generation are proposed.The first scheme is based on a single Mach Zender modulator and photon frequency multiplication technology to realize the generation of frequency tunable millimeter wave signals.Compared with other reported generation schemes of millimeter wave signal,this scheme just employs one Mach Zender modulator,and optical filter is not needed,which is simpler in structurea and tunable,and the system is more stable and higher.It is demonstrated that the 40GHz millimeter wave signal is generated by using 10GHz RF source as the local vibration.The second scheme is based on two Mach Zender modulators in parallel and combine with photon frequency multiplication technology to generate the frequency tunable 12 tupling frequency millimeter wave signal.In the scheme,the generation of 120GHz millimeter wave signal is realized by using 10GHz RF source as the local vibration.In the third scheme,two Mach Zehnder modulators are connected in parallel with optical attenuator and optical phase shifter respectively,and the photonic frequency multiplication technology is combined to realize the generation of frequency tunable 16 tupling frequency millimeter wave signal.In the scheme,it is demonstrated that 160GHz millimeter wave signal can be generated by using a 10GHz RF source as local oscillator.Compared with the reported optical millimeter wave generation schemes,these three schemes are simpler in structure,lower in cost and more stable in performance.At the same time,they do not need any optical filter,so that the adjustable bandwidth range of the system is wider.2.In view of the increasing trend of service types and carrier frequency bands in wireless access network in the future,and the phase out of sequence problem caused by linear multiplication of phase in frequency multiplication of mm-wave with modulated vector data,a new generation scheme of cost-effective frequency quadruple vector millimeter wave based on precoding assistant technology is proposed.In this scheme,based on the parallel connection of two Mach Zehnder modulators,the asymmetric sideband fourth harmonic vector millimeter wave signal is generated without any optical filter.Aiming at the information disorder caused by phase multiplication in the process of vector millimeter wave frequency multiplication,a precoding scheme is proposed to precompensate the vector signal at the transmitter,and finally the vector millimeter wave signal is received without changing the structure and algorithm of the receiver.Through simulation,a 20GHz RF source is used to generate an 80GHz W-band vector millimeter wave signal based on precoding technology,and 16 phase shift keying(16PSK)signal with 10Gbit/s and 20Gbit/s is demonstrated,which is transmitted for 10km by optical fiber.3.To solve the problem of information disorder caused by phase multiplication in the process of vector millimeter wave frequency multiplication,and reduce the Euclidean distance of phase constellation points caused by vector millimeter wave generation scheme of precoding,which is sensitive to fiber dispersion and noise,unable to use high-order modulation format and narrow tuning bandwidth in optical fiber transmission,four novel schemes for vector millimeter wave signal generation without precoding are proposed.In the first scheme,two Mach Zehnder modulators are used to realize the optical single sideband modulation,respectively,so that one single sideband signal modulates the vector information,and the other single sideband signal does not modulate the vector information.Then the phase difference between the two Mach Zehnder modulators is controlled to suppress the optical carrier.Finally,the vector millimeter wave signal generation with frequency multiplication and phase information without damage is realized.In this scheme,a 65 GHz V-band orthogonal frequency division multiplexing(OFDM)vector millimeter wave signal is generated,and the orthogonal phase shift keying(QPSK)OFDM signals with different symbol rates are carried for 50 km transmission over optical fiber.In the second scheme,a single Mach Zehnder modulator is used to generate orthogonal frequency division multiplexing vector millimeter wave signals without precoding.Compared with the first scheme,the structure of this scheme is simpler,which just employs a single Mach zendel modulator to realize the optical double single sideband modulation without an optical filter,and can generate a vector millimeter wave signal with frequency multiplication and no phase damage.This scheme demonstrates the generation of OFDM vector millimeter wave signal with a frequency of 30GHz,and carries different symbol rate hexadecimal quadrature amplitude modulation.The 16QAM OFDM signal is transmitted for 20km by optical fiber.To further simplify the structure and reduce the complexity of the system,the third scheme is orthogonal frequency division multiplexing vector millimeter wave signal generation based on two parallel phase modulators.Due to no DC bias voltage for phase modulator,there is no need to use additional electronic circuit to control the drift of the bias point.The insertion loss of the phase modulator is lower than that of the Mach Zehnder modulator.Based on this scheme,50GHz OFDM vector millimeter wave signal modulated by QPSK is generated,which carries QPSK signals with symbol rates of 2.5Gbaud/s and 5Gbaud/s for back-to-back and 10km optical fiber transmission.The fourth scheme is a multi frequency vector millimeter wave generation scheme based on single-phase modulator without precoding.In the scheme,only one phase modulator is used to generate multi frequency modulated and unmodulated optical sideband signals.According to different requirements,wavelength selection switch is used to select two optical sideband signals with different frequency intervals to beat frequency for multi frequency vector millimeter wave signals generation.The two selected optical subcarriers with asymmetric order,and can have several different combinations,such as(-1,2),(-1,3),(-2,1),(-3,1),etc.Taking this combination(-2,1)as an example,a 48GHz QPSK modulated vector millimeter wave signal is generated based on optical communication simulation software.The generated vector millimeter wave carries QPSK signals with symbol rates of 1Gbaud/s and 2Gbaud/s for back-to-back and 20km transmission. |
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