A multi-dimensional multiplexing ultra-large capacity self-coherent digital analog radio over fiber access network

Abstract

The present invention discloses a multi-dimensional multiplexing ultra-large capacity self-coherent digital analog optical radio access network, comprising a central office (CU) and multiple remote radio units (RRUs). The CU is used to generate an optical frequency comb and replicate it into M sets, one of which is denoted as Comb_M, and the remaining M-1 sets are used as carrier optical frequency combs. The M-1 sets of carrier optical frequency combs are de-wavelength-division-multiplexed into N*(M-1) optical carriers and modulated to obtain multi-channel DA-RoF modulated signals. Each DA-RoF modulated signal and Comb_M signal are transmitted to an RRU side via a space-division multiplexing link. The RRU de-space-division-multiplexes the signal to obtain M-1 sets of wavelength-division-multiplexed signals and Comb_M signals. The Comb_M signals are replicated and de-multiplexed to obtain regenerated local oscillator light. Each RRU performs self-coherent detection based on one DA-RoF modulated signal and one remote regenerated local oscillator light, and recovers the DA-RoF signal through a simplified DSP process.

Description

Technical Field

[0001] This invention relates to the field of wireless access networks, specifically a mobile fronthaul access network that uses an optical frequency comb as a multi-channel carrier, simultaneously performs wavelength division multiplexing (WDM) and space division multiplexing (SDM) transmission, and employs digital analog radio over fiber (DA-RoF) transmission technology and a self-coherent architecture. This solution is suitable for 6G-oriented mobile fronthaul access networks and can significantly increase the number and scale of remote radio units (RRUs) supported by a single central office (CO), while also supporting access to ultra-high-capacity, carrier-aggregated wireless signals with extremely high modulation formats. Background Art

[0002] The centralized radio access network (C-RAN) bridges the gap between fiber networks and mobile wireless networks. A key component of C-RAN is mobile fronthaul: baseband signals concentrated in the central unit (CU) are distributed to remote radio units (RRUs) via a radio-over-fiber (RoF) system. Prior to 5G, digital RoF (D-RoF) technology based on the Common Public Radio Interface (CPRI) was widely used. D-RoF quantizes radio signals to 15 bits and transmits them using binary sequences, resulting in extremely low spectral efficiency: a CPRI rate exceeding 60 Gb / s is required for every 1 GHz of radio bandwidth. Analog RoF (A-RoF) offers a highly spectrally efficient alternative, but is limited by the link signal-to-noise ratio and struggles to support modulation formats higher than 64-QAM. With the surge in information traffic and advancements in mobile communication technology, a single radio interface in the 5G era will require an equivalent CPRI rate exceeding 100 Gb / s [eCPRI Specification, V2.0, “Common Public Radio Interface: eCPRI Interface Specification,” (2019)]. In the future 6G era, the peak rate of wireless signals will increase further by 10 times [S. Chen et al., “Vision, requirements, and technology trend of 6G: how to tackle the challenges of system coverage, capacity, user data-rate and movement speed,” IEEE Wireless Commun. 27(2), 218–228(2020)]. This requires each RoF channel to support an equivalent CPRI rate of the terabit per second. Secondly, due to limited wireless spectrum resources, 1024-QAM and even higher modulation formats will soon be used in wireless communications starting with 5G, requiring the RoF system to support a signal-to-noise ratio exceeding 32 dB [X. Liu, “Enabling Optical Network Technologies for 5G and Beyond” J. Light. Technol. 40, 358–367(2022)]. Third, the increasing density of RRUs deployed due to the use of millimeter-wave bands and ultra-high-density antenna arrays has made multi-dimensional multiplexing essential for access networks. Wavelength division multiplexing (WDM) and spatial division multiplexing (SDM) are currently the most promising multiplexing technologies. However, even in single-wavelength scenarios, traditional D-RoF and A-RoF technologies cannot simultaneously meet the capacity and signal-to-noise ratio requirements of the 6G era. The introduction of WDM and SDM further limits performance.

[0003] Therefore, simultaneously improving the capacity, signal-to-noise ratio, and number of connected RRUs supported by the RoF system has become a research focus in the field of fronthaul access. Using a Kramers-Kronig receiver, Son Thai Le et al. achieved an equivalent CPRI rate of 1.53 Tb / s, but the modulation format was limited to 64QAM and only targeted the access of a single RRU [STLe et al., “1.53-Tbps CPRI-Equivalent Data Rate Transmission with Kramers-Kronig Receiver for Mobile Fronthaul Links,” ECOC, We4B.4 (2018)]. Compared with traditional solutions, A-RoF based on angle modulation can achieve a 6 dB and 9.5 dB SNR improvement at the cost of 2 times and 3 times the bandwidth [S.Ishimura et al., “SSBI-Free Direct-Detection System Employing Phase Modulation for Analog Optical Links” J.Light.Technol.38, 2719-2725 (2020)]. Che Di et al. have achieved a 26.2 GHz carrier aggregation wireless bandwidth while supporting the 256QAM standard [D.Che, “Digital SNR Adaptation of Analog Radio-over-Fiber Link Carrying up to 1048576-QAM Signals,” ECOC, Th3B-1(2020)], corresponding to an equivalent CPRI rate of 1.57Tb / s. However, angle modulation cannot be applied to complex signals, and spectral efficiency still needs to be improved. The research scenario is still targeted at the access of a single RRU. Xiang Liu proposed the DA-RoF technology as a competitive solution that can simultaneously achieve a high signal-to-noise ratio and large capacity [X.Liu, “Hybrid Digital-Analog Radio-over-Fiber (DA-RoF) Modulation and Demodulation Achieving a SNR Gain over Analog RoF of>10dB at Halved Spectral Efficiency” OFC, Tu5D.4(2021)]. DA-RoF technology splits the analog wireless signal into a probabilistically shaped digital part and an amplified residual analog part through quantization rounding operations and amplitude adjustment operations. After these two parts are time division multiplexed (TDM), a signal-to-noise ratio gain of more than 10dB can be obtained at the cost of twice the bandwidth.DA-RoF technology can also be extended to coherent detection systems, further quadrupling spectral efficiency [Q. Zhuge et al., “Transmission of Tb / s CPRI-equivalent rate using coherent digital-analog radio-over-fiber (DA-RoF) system” OFC, W4C.5 (2022)]. However, due to the completely random distribution of residual analog components in DA-RoF signals, symbol decision cannot be performed. Consequently, the carrier phase estimation (CPE) step required in traditional coherent systems cannot be performed, limiting the application of DA-RoF technology in coherent systems. Chenbo Zhang et al. proposed a self-coherent DA-RoF system based on remote optical frequency comb regeneration [C. Zhang et al., “14.1Tb / s CPRI-equivalent Rate 1024-QAM Transmission via Combs-cloned Self-homodyne WDM Digital-Analog Radio-over-Fiber System,” OFC, Tu2J.2 (2023)]. This system successfully recovered DA-RoF signals through multi-channel simultaneous self-coherent detection and increased the number of supported RRUs by utilizing optical frequency comb and wavelength division multiplexing technologies. However, there is still room for improvement in the multiplexing dimension, capacity, and number of RRUs supported by fronthaul systems. Summary of the Invention

[0004] In order to support ultra-large capacity and extremely high SNR fronthaul access networks in a single CU to multiple RRU (point-to-multipoint) architecture, the present invention proposes a multi-dimensionally multiplexed ultra-large capacity self-coherent digital analog optical radio access network. The present invention is based on an optical frequency comb and applies self-coherent detection technology to realize a multi-dimensionally multiplexed DA-RoF access network.

[0005] The present invention has three advantages:

[0006] 1) By using optical frequency combs and multi-core optical fibers, both spatial division multiplexing and wavelength division multiplexing are successfully applied simultaneously. The capacity and number of RRUs supported by the fronthaul access network are increased by more than two orders of magnitude compared to traditional solutions.

[0007] 2) While using M-1 fiber cores to transmit wavelength-division multiplexed DA-RoF signals to multiple RRUs, the remaining fiber core transmits a complete set of unmodulated optical frequency combs. The unmodulated optical frequency comb is co-origin with the signal carrier, and after demultiplexing, power splitting, and amplification, each comb tooth serves as the local oscillator light for each signal channel. This allows all channels to use self-coherent detection, eliminating the need for CPE and frequency offset estimation (FOE). This solves the problem of symbol decision difficulty in the analog portion of the DA-RoF signal in coherent systems. Simultaneously, the simplified digital signal processing (DSP) process reduces RRU power consumption and link latency.

[0008] 3) Coherent detection is used in each channel of the fronthaul access network. By increasing spectrum efficiency by a factor of four, each RRU can achieve an equivalent CPRI rate of Tb / s, meeting 6G requirements. Compared with direct detection systems, the power budget is more than an order of magnitude better.

[0009] 4) Through DA-RoF technology, the restored original carrier aggregation wireless signal has an extremely high signal-to-noise ratio and can support ultra-high-order modulation formats from 1024-QAM to 1048576-QAM.

[0010] The technical solution adopted in the present invention is:

[0011] A mobile fronthaul access network employing digital analog radio over fiber (DA-RoF) technology and a self-coherent architecture uses an N-wavelength optical frequency comb as a light source and an M-core multi-core optical fiber as a fronthaul link. M-1 groups of wavelength division multiplexed DA-RoF signals are transmitted through M-1 fiber cores, and an unmodulated N-wavelength optical frequency comb is transmitted through the remaining fiber core, acting as a self-coherent local oscillator at the remote end. The network comprises the following steps:

[0012] 1) Use N-wave optical frequency comb as the CU side light source with a repetition frequency of f r , generating N waves with a frequency interval of f r The optical frequency comb is replicated into two identical sets using an optical power splitter. One set is retained directly, denoted as Comb_M. The other set is amplified by an erbium-doped fiber amplifier (EDFA) and then replicated into M-1 identical carrier frequency combs using a 1-input, M-1-output power splitter, resulting in a total of N*(M-1) optical carriers. Note that the number and order of the power splitters can be changed; the goal is to replicate one optical frequency comb into M-1 carrier frequency combs and one retained optical frequency comb.

[0013] 2) On the CU side, M-1 demultiplexing devices are used to demultiplex the M-1 carrier frequency combs into N*(M-1) independent optical carriers. The DA-RoF signal to be transmitted is modulated onto each optical carrier, resulting in a total of N*(M-1) DA-RoF modulated signals. Each DA-RoF modulated signal is generated by DA-RoF modulation of the same or different carrier aggregated wireless signals. Using M-1 wavelength division multiplexing devices, the N*(M-1) DA-RoF modulated signals are wavelength-division multiplexed into M-1 groups, still following the distribution of the M-1 carrier frequency combs, to form M-1 groups of wavelength-division multiplexed signals.

[0014] 3) The fronthaul link uses M-core multi-core fiber as the transmission medium. Through the multi-core fiber fan-in device, M-1 groups of wavelength-division multiplexed (DA-RoF) modulated signals are transmitted through the first core to the M-1th core of the M-core fiber. The Comb_M signal, which is retained without signal modulation, is transmitted through the Mth core. On one side of a large number of RRUs, the fan-out device demultiplexes the signals of the M cores, obtaining the transmitted M-1 groups of wavelength-division multiplexed signals and one set of unmodulated Comb_M signals.

[0015] 4) On a side with a large number of RRUs, the unmodulated Comb_M is replicated into M-1 sets of unmodulated N-wavelength optical frequency combs through an EDFA and an M-1-input power splitter. This is then replicated through M-1 wavelength division multiplexers to obtain N*(M-1) comb teeth, corresponding to N*(M-1) remote local oscillator (LO) signals. If the LO power is low, additional EDFAs can be added at appropriate locations.

[0016] 5) For M-1 sets of wavelength-division multiplexed signals, M-1 demultiplexers are used to generate N*(M-1) DA-RoF modulated signals. These N*(M-1) signals and the N*(M-1) remote local oscillator (LO) optical signals from 4) are transmitted to the N*(M-1) RRUs on the RRU side. In each RRU, the corresponding signals and the regenerated LO undergo autocoherent detection. A simplified DSP process that excludes the CPE and FOE stages is used to recover the transmitted DA-RoF signal. DA-RoF demodulation is then used to recover the received carrier-aggregated radio signal.

[0017] For DA-RoF modulation in 2), the steps include:

[0018] 1) Normalize the amplitude of the original carrier aggregation wireless signal S0 and then perform amplitude matching to divide it into the digital part S D and the analog part S A During the division, the constellation point scale of the digital part and the amplitude relationship between the digital and analog parts can be controlled by flexibly adjusting the three factors A, B and C. D=B[Round(AS0+C)-C] / A, analog part S A =2A(S0-S D / B). Where A is the quantization factor, used to control the scale of the digital constellation points, such as 49QAM, 81QAM, or 121QAM; B is the amplitude scaling factor, used to control the amplitude ratio of the digital and analog parts of the DA-RoF signal; C is the quantization offset, used to adjust the parity of the constellation points; Round() is the rounding function.

[0019] 2) The digital part S D and the analog part S A Perform time division multiplexing splicing to generate DA-RoF signals and complete DA-RoF modulation. The splicing here is not limited to time division multiplexing.

[0020] 3) Before actual access network deployment, laboratory-level scanning of factors A, B, and C can be performed to determine the factors A, B, and C that best adapt to the access network channel conditions and achieve the highest carrier aggregation wireless signal-to-noise ratio.

[0021] 4) DA-RoF modulation is not limited to the 1-level digital part, but also includes the cascaded DA-RoF modulation of multiple-level digital parts. For the DA-RoF signal of M-level digital parts and 1-level analog part, it can be recorded as S D1 S D2 …S DM S A Here, an additional intermediate quantity E is introduced i To describe the residual part of the i-th level. For the original wireless signal (i = 0), E0 = S0; for i ≥ 1, the relationship between the levels is SD i =B i [Round(A i E i-1 +C i )-C i ] / A i , E i =E i-1 -S Di / B i For the final simulation part S A , S A =E M 2A M Here, A i 、B i and C i are the quantization factor, amplitude scaling factor, and quantization offset of the i-th level digital part, respectively. Thus, the modulation generates a cascaded DA-RoF signal of the M-level digital part and the 1-level analog part.

[0022] Through DA-RoF modulation of M-level digital part and 1-level analog part, the original wireless signal to be sent can be completely transparently split into (M+1)-level time division multiplexing symbols and transmitted to the RRU side through the fronthaul link. i 、B i and C i After scanning optimization, the RRU can be immune to the noise of the fronthaul link after the decision stage; the last-stage residual analog part is amplified multiple times on the CU side and is greatly compressed at the RRU after the fronthaul link, so the link noise it carries is also greatly suppressed. Therefore, the DA-RoF modulation of the M-level digital part and the 1-level analog part can break through the physical noise limitation of the fronthaul link at the cost of (M+1) times the bandwidth requirement, achieving a huge improvement in the signal-to-noise ratio: each cascade of the 1-level digital part can improve the signal-to-noise ratio by more than 10dB, and improve the QAM modulation format by more than 4 times. The specific performance can be seen in the positive effect 1) and the attached Figure 4 )~8).

[0023] For DA-RoF demodulation in 5), the steps include:

[0024] 1) De-time-division multiplexing the DA-RoF signal recovered by the DSP and normalize its amplitude;

[0025] 2) After adjusting the amplitude of the digital and analog parts, they are combined to restore the received carrier aggregation signal

[0026]

[0027] 3) The demodulation process is not limited to a single-level digital part and may include multiple-level digital parts, the operation of which is the DA-RoF modulation operation.

[0028] 4) is the reverse operation.

[0029] Compared with the prior art, the present invention has the following positive effects:

[0030] 1) This invention uses DA-RoF technology to cut and splice the waveform of wireless signals. On the basis that traditional ARoF systems usually only support 64QAM signals, only a single-stage digital and analog part is required to improve the signal-to-noise ratio by more than 11dB (see Appendix Figure 8 ) to support the 1024-QAM signal required for the post-5G and 6G eras (see Appendix Figure 4 ); 4096-QAM signal is supported by cascading 2-level digital and 1-level analog parts (see Appendix Figure 5 ); through the cascade of 3-level digital and 1-level analog parts, it supports 16384-QAM and 65536-QAM signals (see attached Figure 6 );

[0031] Finally, through the cascade of 4-level digital part and 1-level analog part, the fronthaul access of 1048576-QAM signal is supported (see Appendix Figure 7 ), providing solutions for future higher-order applications.

[0032] 2) While transmitting M-1 groups of wavelength-division multiplexed signals, the present invention also transmits a complete set of unmodulated optical frequency combs to a large number of RRUs through the remaining fiber core. The unmodulated optical frequency comb is co-origin with the signal carrier, and each comb tooth can serve as the co-origin local oscillator light for each signal after demultiplexing and power splitting. This allows all channels to use self-coherent detection, eliminating the need for CPE and frequency offset estimation (FOE). This solves the problem of the analog portion of DA-RoF signals being unable to make symbol decisions in coherent systems. Simultaneously, the simplified digital signal processing (DSP) process reduces RRU power consumption and link latency.

[0033] 3) Due to the advantage of 4 times the capacity of the coherent system, the present invention can achieve a single-channel CPRI equivalent rate of >1Tb / s, meeting the needs of the 6G era.

[0034] 4) By leveraging wavelength division multiplexing (WDM) of optical frequency combs and spatial division multiplexing (SDM) of multi-core optical fibers, the present invention can achieve a total link capacity improvement of more than two orders of magnitude compared to conventional solutions, achieving a link capacity of hundreds of Tb / s CPRI equivalent rates (supporting 204 Tb / s 1024-QAM signals in the experiment), and simultaneously supporting the simultaneous access of hundreds of remote RRUs (174 in the experiment), thereby enabling the simultaneous access of tens of thousands of 5G users (34,800 corresponding to the experimental data), providing a promising solution for fronthaul access networks with ultra-large capacity, ultra-high RRU access numbers, and ultra-high modulation formats (see the attached results for the above results). Figure 8 ). BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the schematic diagram of a multi-channel self-coherent hybrid digital-analog optical wireless access network based on remote optical frequency comb regeneration.

[0036] Figure 2 f r =28GHz, N=29 optical comb spectrum diagram.

[0037] Figure 3 This is a spectrum diagram of a 29-channel wavelength division multiplexing DA-RoF signal, demonstrating a total of 6 corresponding wavelength division multiplexing signals, corresponding to the injection of 6 fiber cores.

[0038] Figure 4This is the constellation diagram after the 1024-QAM wireless signal received from fiber core 2 and CH-3 is recovered and demodulated through the DA-RoF signal. The transmitted DA-RoF signal is a cascade of a level 1 digital part and a level 1 analog part. The 1024-QAM signal bandwidth corresponding to a single channel is 20 GHz.

[0039] Figure 5 This is the constellation diagram after DA-RoF signal recovery and demodulation of the 4096-QAM wireless signal received from fiber core 2 and CH-3. The transmitted DA-RoF signal is a cascade of a two-level digital section and a one-level analog section. The 4096-QAM signal bandwidth corresponding to a single channel is 14.7 GHz (each channel transmits a 22 GBaud dual-skew DA-RoF signal).

[0040] Figure 6 This is the constellation diagram after the 16384-QAM wireless signal received from fiber core 2 and CH-3 is recovered and demodulated through the DA-RoF signal. The transmitted DA-RoF signal is a cascade of a three-level digital part and a one-level analog part. The 16384-QAM signal bandwidth corresponding to a single channel is 10 GHz.

[0041] Figure 7 This is the constellation diagram after the 1048576-QAM wireless signal received from fiber core 2 and CH-3 is recovered and demodulated through the DA-RoF signal. The transmitted DA-RoF signal is a cascade of a four-level digital part and a one-level analog part. The 1048576-QAM signal bandwidth corresponding to a single channel is 8 GHz.

[0042] Figure 8 Experimental results show that on one side of multiple RRUs, 174 RRUs can be connected and transmitted simultaneously, with a total 1024-QAM wireless signal bandwidth of 174*20=3480GHz and a CPRI equivalent rate of 204Tb / s.

[0043] (a) is the signal-to-noise ratio of the DA-RoF symbols and the corresponding 1024-QAM wireless signals for a total of 58 channels on cores 4 and 7.

[0044] (b) is the signal-to-noise ratio of the DA-RoF symbols and the corresponding 1024-QAM wireless signals for a total of 58 channels on cores 3 and 6.

[0045] (c) shows the signal-to-noise ratio of the DA-RoF symbols and the corresponding 1024-QAM wireless signals for a total of 58 channels on cores 2 and 5.

[0046] Figure 1: 1-CU side seed light, 2-cascaded intensity-phase modulator, 3-RF source with repetition frequency fr, 4-optical comb flattening module (such as Waveshaper), 5-first Erbium-doped fiber amplifier (EDFA), 6-one-input two-output optical power splitter, 7-IQ modulator, 8-second EDFA, 9-first one-input six-output optical power splitter, 10-seven-core fiber fan-in device, 11-seven-core fiber, 12-seven-core fiber fan-out device, 13-DA-RoF signal wavelength division multiplexer, 14-third E DFA, 15-second one-input six-output optical power splitter, 16-first wavelength division multiplexing module (such as Waveshaper), 17-fourth EDFA, 18-polarization controller, 19-coherent receiver, 20-first polarization-maintaining EDFA, 21-single-bias IQ modulation module, 22-arbitrary signal generator, 23-second polarization-maintaining EDFA, 24-polarization multiplexing simulator, 25-channel selection module, 26-fifth EDFA, 27-second wavelength division multiplexing module (such as Waveshaper). DETAILED DESCRIPTION

[0047] The solution of the present invention is described in further detail below with reference to the accompanying drawings.

[0048] The principle of the present invention is as follows Figure 1 As shown in Figure 2. In CU, narrow linewidth laser 1 is used as seed light and injected into cascaded intensity and phase modulator 2. Cascaded modulator 2 is repetition frequency f r The high-power RF source 3 drives N=29 optical frequency combs. The present invention uses the optical comb flattening module Waveshaper4 to flatten the optical frequency comb, and after amplification by the first EDFA5, it is copied into two sets of combs through the power divider 6. One set of combs is directly retained and recorded as Comb_M. In the experiment, due to the number of IQ modulators, the other set of optical frequency combs is modulated on the N-wave carrier by the IQ modulator 7 at the same time. After amplification by the second EDFA8 and the one-input six-output power divider 9, 6 groups of wavelength division multiplexing signals are output. Each group of signals has a total of 29 wavelength division channels, and a total of (M-1)*N=6*29=174 DA-RoF signals. In actual applications, these 174 signals are modulated separately. Note that in the demonstration of the present invention, f r =28GHz, N=29, M=7. The specific values ​​can be adjusted according to actual needs.

[0049] The present invention uses a seven-core optical fiber 11 as the transmission medium. Six wavelength-division multiplexed signals are injected into the second through seventh cores of the seven-core optical fiber 11 through a seven-core optical fiber fan-in 10. An unmodulated optical comb, Comb_M, is injected into the first core of the seven-core optical fiber 11. After transmission through the seven-core optical fiber 11, the six wavelength-division multiplexed signals and the unmodulated optical comb, Comb_M, are separated at a large number of RRUs using a seven-core optical fiber fan-out 12. For each set of wavelength-division multiplexed signals, a corresponding de-wavelength division multiplexer 13 is used to separate 174 DA-RoF signals. The unmodulated optical comb Comb_M is amplified by the third EDFA 14 and replicated into six optical combs via a one-input, six-output power splitter 15. The corresponding de-wavelength division multiplexing module 16 is then used to separate 174 remote local oscillators. Each local oscillator is amplified by the corresponding fourth EDFA 17 and passes through a polarization controller 18 before being input into the corresponding RRU along with the DA-RoF signal. In the 174 remote RRUs, the corresponding remote local oscillators and DA-RoF signals undergo self-coherent detection in a coherent receiver 19. After a simplified DSP process that does not include the CPE and FOE, the transmitted DA-RoF signal is recovered and demodulated by DA-RoF to obtain the carrier aggregation wireless signal sent by the CU.

[0050] The optical frequency comb is amplified by the IQ modulator 7 through the first polarization-maintaining EDFA 20 to amplify the DA-RoF signal carrier optical comb. The DA-RoF signal is modulated onto each comb tooth through the arbitrary waveform generator 22 and the single-bias IQ modulation module 21. The attenuated wavelength-division-multiplexed single-bias DA-RoF signal is further amplified by the second polarization-maintaining EDFA 23. Polarization multiplexing is achieved through a polarization multiplexing simulator, thereby simulating the output of a set of wavelength-division-multiplexed double-bias DA-RoF signals with N = 29 wavelengths.

[0051] The demultiplexer 13 selects a group of wavelength division multiplexing channels to be demodulated through the channel selection module 25. The fifth EDFA 26 amplifies the group of wavelength division multiplexing channels and the second demultiplexing module Waveshaper 27 separates the group of N=29 wavelength division multiplexing channels.

[0052] Figure 2 The N=29 wave comb used in the demonstration was shown; Figure 3 The image shows a set of wavelength-division multiplexed signals, each modulating a 20GBaud dual-skew DA-RoF signal. Six such wavelength-division multiplexed signals are injected into six fiber cores. Figure 8The SNR of six wavelength-division multiplexing (WDM) signals, totaling 174 channels of carrier-aggregated (CA) radio signals, transmitted over six fiber cores on the RRU side, is demonstrated, as is the SNR of the fronthaul DA-RoF signal. The SNR of all 174 channels exceeds 32dB, meeting 1024-QAM requirements and representing an improvement of more than 11dB compared to the SNR of the fronthaul DA-RoF signal. Each channel transmits a 20GHz bandwidth, 1024QAM radio signal, for a total CPRI equivalent rate of 204Tb / s. Figures 4 to 7 The constellation diagrams of 1024-QAM to 1048576-QAM signals transmitted from the third wavelength division multiplexing channel of the second fiber core using 2nd to 4th level DA-RoF cascade technology are respectively shown.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Those skilled in the art may modify or make equivalent substitutions for the technical solutions of the present invention without departing from the spirit and scope of the present invention. The scope of protection of the present invention shall be based on the claims.

Claims

1. A multi-dimensional multiplexing ultra-large capacity self-coherent digital analog radio over fiber access network, characterized in that: It includes a central office (CU) and multiple remote radio units (RRUs); The central office CU is used to generate N waves with a frequency interval of f r The optical frequency comb is obtained and copied into M sets, one of which is denoted as Comb_M, and the remaining M-1 sets of optical frequency combs are used as carrier optical frequency combs. The M-1 sets of carrier optical frequency combs are then de-wavelength-division-multiplexed into N*(M-1) independent optical carriers, and the DA-RoF signal to be transmitted is modulated on each optical carrier to obtain N*(M-1) DA-RoF modulated signals. The N*(M-1) DA-RoF modulated signals and the unmodulated Comb_M signal are then fanned into the spatial division multiplexing fronthaul link through a multi-core optical fiber fan-in device and transmitted to the fan-out device on the RRU side. The fan-out device demultiplexes the received signal to obtain M-1 groups of wavelength division multiplexing signals and a set of unmodulated Comb_M signals; then the unmodulated Comb_M signals are copied into M-1 sets of unmodulated N-wave optical frequency combs and demultiplexed to obtain N*(M-1) wave comb teeth as N*(M-1) remote regenerated local oscillator lights; the M-1 groups of wavelength division multiplexing signals are demultiplexed to obtain N*(M-1) DA-RoF modulated signals; then the N*(M-1) DA-RoF modulated signals and N*(M-1) remote local oscillator lights are respectively transmitted to N*(M-1) RRUs; then each RRU performs self-coherent detection based on the received DA-RoF modulated signal and remote regenerated local oscillator light, and recovers the DA-RoF signal through a simplified DSP process; then the recovered DA-RoF signal is DA-RoF demodulated to recover the received wireless signal; the simplified DSP process is a DSP process that does not include the CPE and FOE links.

2. The ultra-large capacity self-coherent digital analog radio over fiber access network according to claim 1, characterized in that: The method for the central office CU to perform DA-RoF modulation on the wireless signal is as follows: first, the amplitude of the wireless signal S0 is normalized and then the amplitude is aligned, and the first-level digital part S D and the first level simulation part S A ; Among them, S D =B[Round(AS0+C)-C] / A,S A =2A(S0-S D / B); A is the quantization factor, which is used to control the scale of the digital constellation points; B is the amplitude scaling factor, which is used to control the amplitude ratio of the digital part and the analog part in the DA-RoF signal; C is the quantization bias, which is used to adjust the parity of the constellation points; then the digital part S D and the analog part S A Perform splicing to generate DA-RoF signals and complete DA-RoF modulation.

3. The ultra-large capacity self-coherent digital analog radio over fiber access network according to claim 2, characterized in that: The method for the central office CU to perform DA-RoF modulation on the wireless signal is as follows: first, the amplitude of the wireless signal S0 is normalized and then the amplitude is adjusted, and the signal is divided into an M-level digital part S D1 S D2 ···S DM and Level 1 Analog Section S A The DA-RoF signal is introduced by introducing the intermediate quantity E i Describe the residual part of the i-th level, the original wireless signal E0 = S0; for i = 1 ~ M, the relationship between the levels is S Di =B i [Round(A i E i-1 +C i )-C i ] / A i , E i =E i-1 -S Di / B i ;Simulation part S A =E M 2A M ; A i 、 B i and C i are the quantization factor, amplitude scaling factor and quantization bias of the digital part of level i respectively.

4. The ultra-large capacity self-coherent digital analog radio over fiber access network according to claim 3, characterized in that: The method for DA-RoF demodulation of the recovered DA-RoF signal is as follows: first, the recovered DA-RoF signal is de-time-division-multiplexed and amplitude normalized; then, the digital part and the analog part are amplitude-adjusted and combined to recover the received carrier aggregation signal.

5. The ultra-large capacity self-coherent digital analog radio over fiber access network according to claim 1, 2 or 3, characterized in that: The central office CU includes an optical power splitter and a light source. The optical power splitter is connected to the output end of the light source and is used to divide the N waves generated by the light source into a frequency interval of f r The optical frequency comb is replicated into two identical sets of outputs, one of which is denoted as Comb_M, and the other is amplified by an erbium-doped fiber amplifier and input into an M-1-input power splitter to replicate the same M-1 sets of optical frequency combs, thereby obtaining N*(M-1) optical carriers.

6. The ultra-large capacity self-coherent digital analog radio over fiber access network according to claim 5, characterized in that: The central office CU uses M-1 de-wavelength division multiplexing devices to de-wavelength-division multiplex M-1 sets of carrier optical frequency combs into N*(M-1) independent optical carriers; and modulates the DA-RoF signal to be transmitted on each optical carrier to obtain N*(M-1) DA-RoF modulated signals.

7. The ultra-large capacity self-coherent digital analog radio over fiber access network according to claim 1, characterized in that: The fronthaul link is an M-core multi-core optical fiber; M-1 groups of wavelength division multiplexing DA-RoF modulated signals are transmitted respectively through the first core to the M-1th core of the M-core multi-core optical fiber; the unmodulated Comb_M signal is transmitted through the Mth core of the M-core multi-core optical fiber; then the unmodulated Comb_M signal is amplified by EDFA and passed through an M-1 input and output power splitter to be copied into M-1 sets of unmodulated N-wave optical frequency combs; then, through M-1 demultiplexers, N*(M-1) wave comb teeth are obtained, corresponding to N*(M-1) far-end local oscillator lights.

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