A multi-functional integrated 5G analog fronthaul in-band full-duplex communication method with simple RU

Abstract

This invention discloses a simple, multifunctional, integrated 5G analog fronthaul in-band full-duplex communication method for remote units (RUs). This method primarily relates to the fields of optical communication technology and microwave technology. The system structure of the method, as shown in Figure 1 of the specification, includes a laser, downlink vector signal, electrical local oscillator signal, downlink interference signal, target signal, reference signal, 90° electrical coupler, dual-polarization quadrature phase-shift keying modulator, phase modulator, single-mode fiber, optical coupler, polarization beamsplitter, polarization beam combiner, polarization controller, polarizer, and photodetector. The remote unit (RU) uses a single phase (PM) modulator to achieve self-interference cancellation (SIC) combined with anti-fiber dispersion transmission and down-conversion, eliminating the need for bias control and additional local oscillator (LO) branches, resulting in a simple structure. At the central office (CO), the carried downlink signal and local oscillator signal are single-sideband modulated to achieve anti-fiber dispersion transmission. The RU uses wavelength reuse technology to perform PM cascaded down-conversion on the signal received from the uplink, and the SIC is moved from the RU to the CO to simplify the RU. The entire link has no optical filter and is reconfigurable.

Description

Technical Field

[0001] This invention relates to the fields of optical communication technology and microwave technology, and mainly to optical radio frequency (RoF) technology, wireless access network technology, in-band full-duplex technology (IBFD) technology and self-interference cancellation technology (SIC). Background Technology

[0002] With the continuous increase in data rates and the number of users, the explosive growth in communication demand poses a huge challenge to broadband communication access. Next-generation broadband mobile communication presents new demands in terms of data capacity, network coverage, energy consumption, and latency. Currently, centralized radio access networks and cloud radio access networks, with the Common Public Radio Interface (CPRI) as the main interface standard, are the mainstream fronthaul networks. However, due to the need for high spectral efficiency and large data rates, the scalability of CPRI is limited. Compared to CPRI's digital fronthaul interface, RoF technology has advantages such as large bandwidth, high efficiency, and low latency, and has broad application prospects in fronthaul networks.

[0003] With the explosive growth of mobile traffic, wireless access technologies will adopt higher frequency bands, such as millimeter wave bands, to support high-speed transmission. The higher the frequency, the greater the signal attenuation during propagation, and the higher the base station density of 5G networks will be. As one of the two core components of modern base stations, simplifying RU infrastructure and reducing power consumption are crucial for building a fronthaul network architecture with low operating costs and high transmission efficiency.

[0004] To improve spectrum utilization efficiency and transmission capacity, IBFD (In-Frequency Directional Interference) technology was proposed. This technology enables simultaneous transmission and reception of signals on the same frequency, doubling spectrum utilization and data transmission rate, thus solving the problem of insufficient spectrum resources. However, in the application of IBFD technology, due to the close distance between the transmitting and receiving antennas and the limited isolation of the antennas themselves, the receiving antenna receives co-frequency interference (SI) signals transmitted by adjacent transmitting antennas. Furthermore, because the uplink and downlink frequencies are the same, SI signals cannot be filtered out. Moreover, the power of the locally transmitted signal is often greater than the received target signal (SOI), causing the SOI signal to be overwhelmed and undetectable, thus significantly reducing the system's communication performance. This results in co-frequency self-interference, making self-interference cancellation (SIC) crucial.

[0005] Traditional self-interference cancellation techniques include antenna self-interference cancellation, radio frequency (RF) self-interference cancellation, and digital self-interference cancellation. Among these three methods, RF self-interference cancellation is one of the most effective. It cancels interference by constructing a reference signal opposite to the received signal in the analog RF circuit and superimposing it on the received signal. However, due to electronic bottlenecks, the limited bandwidth of traditional electronic devices leads to problems such as nonlinearity, sensitivity to electromagnetic interference, and poor flexibility, which limits the performance and development of RF self-interference cancellation systems. Microwave photonics technology utilizes optical advantages to generate, transmit, and process RF or microwave signals. Compared to traditional electromagnetic microwave signal processing and transmission methods, microwave photonics technology has advantages such as large processing bandwidth, low transmission loss, low susceptibility to electromagnetic interference, and good tunability. It can easily process large bandwidth and high frequency microwave signals. Therefore, photon-assisted SiC methods have been extensively studied.

[0006] Over the past decade, numerous photon-assisted SiC (Self-Conversion) methods have emerged, primarily falling into two categories: The first category utilizes Mach-Zehnder modulators, such as dual-drive Mach-Zehnder modulators, dual-parallel Mach-Zehnder modulators, dual-polarization binary phase-shift keying modulators, and dual-polarization quadrature phase-shift keying modulators, to achieve SiC. This method suffers from inherent DC drift issues, often requiring additional bias control devices, resulting in a complex RU (Realizer Unit) structure. However, it can integrate SiC with down-conversion and fiber dispersion-resistant transmission functions. The second category uses phase (PM) modulators to achieve SiC. This method eliminates DC drift problems, eliminates the need for bias control, and has a simple RU structure, but its functionality is limited. In summary, existing solutions cannot simultaneously integrate SiC with fiber dispersion-resistant transmission and frequency conversion functions while maintaining RU simplicity. Summary of the Invention

[0007] To address the problems existing in the background technology, this invention proposes a simple, multifunctional, integrated 5G analog fronthaul in-band full-duplex communication method with a simple RU (Radio Unit). This method has three main advantages: First, the RU structure is simple. It uses a single PM modulator, eliminating the need for bias control, and employs wavelength reuse technology, eliminating the need for an additional local oscillator (LO) branch. It uses photon-assisted SiC (Self-Conversion) technology, avoiding the shortcomings of traditional electrical domain microwave signal processing, and moves the SiC from the RU to the central office (CO) to simplify the RU. Second, it is multifunctional and integrated. Single-sideband modulation of the carried signal at the CO end enables dispersion-resistant transmission, while PM cascaded frequency conversion at the RU end enables SiC-based down-conversion. Third, the entire link does not use optical filters, therefore different signal frequency bands can be designed for different transmission requirements, and the system is reconfigurable.

[0008] The technical solution adopted by the present invention to solve the technical problem is as follows: the device includes a laser (LD), a downlink vector signal (DS), an electric local oscillator signal (LO), a downlink interference signal (SI), a target signal (SOI), a reference signal (SR), a first 90° electrical coupler, a second 90° electrical coupler, a dual polarization quadrature phase shift keying modulator (DP-QPSK), a phase modulator (PM), a first single-mode fiber (SMFa), a second single-mode fiber (SMFb), an optical coupler (OC), a polarization beam splitter (PBS), a polarization beam combiner (PBC), a first polarization controller (PC1), a second polarization controller (PC2), a third polarization controller (PC3), a first polarizer (Pol1), a second polarizer (Pol2), a first photodetector (PD1), and a second photodetector (PD2). The DP-QPSK integrates two dual parallel Mach-Zehnder modulators (DP-MZM). The first dual parallel Mach-Zehnder modulator (DP-MZM1) and the second dual parallel Mach-Zehnder modulator (DP-MZM2) are integrated in a polarization multiplexing manner. Sub-modulators X-MZM1 and X-MZM2 are embedded in the main modulator of DP-MZM1, and sub-modulators Y-MZM1 and Y-MZM2 are embedded in the main modulator of DP-MZM2. Its schematic diagram is shown in Appendix Figure 1 of the specification. The key feature is that the continuous optical carrier output from the LD enters the DP-QPSK. The DS signal is injected into the first 90° electro-coupler and then split into two paths, which are applied to the two RF input ports of DP-MZM1. The LO signal is injected into the second 90° electro-coupler and then split into two paths, which are applied to the two RF input ports of DP-MZM2. The output of the DP-QPSK modulator is transmitted via the SMFA and then input to the OC for power splitting. One optical signal passes through PC1 and Pol1 and is input to PD1 for up-conversion before being sent to the transmitting antenna for downlink signal transmission. The other optical signal passes through PC2 and PBS to separate the X and Y polarization states. The X-polarized light is used as a reference signal, and the Y-polarized light is selected for wavelength reuse and input to the PM modulator. The SOI signal received by the receiving antenna is mixed with the SI signal and loaded into the PM modulator for uplink modulation. After PM cascaded down-conversion, the X-polarized and Y-polarized light are then combined through PBC and input to the SMFb for transmission. Rotating PC3 and Pol2 completes amplitude matching between the SI and SR signals, and the signal is input to PD2 for interference cancellation and uplink signal reception.

[0009] The present invention includes the following steps in operation: (1) The optical carrier output from the LD at the CO end of the architecture is injected into the dual polarization quadrature phase shift keying modulator DP-QPSK. (2) After the downlink vector signal DS is injected into the first 90° electro-coupler, it is split into two paths and loaded onto the two RF input ports of DP-MZM1. After the local oscillator signal LO is injected into the second 90° electro-coupler, it is split into two paths and loaded onto the two RF input ports of DP-MZM2. The DC bias voltage is adjusted so that X-MZM1 operates at the quadrature point (QTP), X-MZM2 operates at QTP, and the master mode operates at -QTP. Y-MZM1 operates at the minimum point (MITP), Y-MZM2 operates at MITP, and the master mode operates at QTP. The carried DS signal is subjected to single-sideband modulation, and the LO signal is subjected to single-sideband modulation with suppressed carrier. The spectrum of the modulation is shown in the appendix of the instruction manual. Figure 2 As shown in (a). (3) The modulated signal output by the DP-QPSK modulator is transmitted to the RU terminal through the SMFa and then input to the OC power splitter into two paths. (4) One optical signal is input to PD1 via PC1 and Pol1 to achieve up-conversion and then sent to the transmitting antenna to complete the downlink signal transmission. Its spectrum before beat frequency is shown in the appendix of the instruction manual. Figure 2 As shown in (b). (5) Another optical signal is separated into X and Y polarization states by PC2 and PBS. The X polarization state light is used as a reference signal, and the Y polarization state light is selected for wavelength reuse and input into the PM modulator. The target signal SOI received by the receiving antenna is mixed with the interference signal SI and loaded into the PM modulator to complete the uplink modulation. (6) After completing the PM cascade downconversion, the X-polarized light and the Y-polarized light are combined through the PBC and then transmitted to the CO end through the SMFb. (7) At the CO end, rotate PC3 and Pol2 to complete the amplitude matching of SI signal and SR signal, and input to PD2 to complete interference signal cancellation and uplink signal reception.

[0010] This invention proposes a simple, multifunctional, integrated 5G analog fronthaul in-band full-duplex communication method using a single RU (Radio Unit). The RU achieves SiC (Silicon Integrated Circuit) combined with fiber dispersion-resistant transmission and downconversion using a single PM (Microwave Module) modulator, eliminating the need for bias control and additional LO (Local Receiver) branches, resulting in a simple structure. At the CO (Cooperative Optical Unit) end, single-sideband modulation of the carried downlink and LO signals achieves fiber dispersion-resistant transmission. The RU employs wavelength reuse technology to perform PM cascaded downconversion on the uplink received signal, and the SiC is moved from the RU to the CO to simplify the RU. The entire link is filterless and reconfigurable. Attached Figure Description

[0011] Figure 1 is a schematic diagram of a simple, multi-functional, integrated 5G analog fronthaul in-band full-duplex communication method for RU. Wherein: Figure 1(a) shows the link architecture of the proposed method. Figure 1(b) shows the specific structure of the DP-QPSK modulator. Figure 2 The spectrum of the nodes marked in Figure 1(a) is shown. Figure 2 (a) is the output spectrum of DP-QPSK. Figure 2 (b) is the spectrum before PD1 beat frequency. Figure 2 (c) is the spectrum of PBC2 after beam combining. Figure 2 (d) is the spectrum output after Pol2. Figure 3 shows the electrical spectrum and constellation diagram of the received downlink 16-QAM microwave vector signal, as well as the measured error vector amplitude (EVM). Figure 3(a) shows the electrical spectrum of a 16-QAM microwave vector signal with a downlink center frequency of 27.5 GHz. Figure 3(b) shows the constellation diagram of the downlink received 16-QAM microwave vector signal with a center frequency of 27.5 GHz and a signal error vector amplitude (EVM) of 4.22%. Figure 4 The images show a comparison of the spectra of PC3 and Pol2 with and without SIC operation enabled. Figure 5 shows the self-interference cancellation spectrum of the 27.5 GHz interference signal converted to the center frequency of 2.5 GHz in different broadband ranges without SOI signal. Figure 5(a) shows the intermediate frequency electrical spectrum before and after 100M broadband SIC. Figure 5(b) shows the intermediate frequency electrical spectrum before and after 50M broadband SIC. Figure 5(c) shows the intermediate frequency electrical spectrum before and after 25M broadband SIC. Figure 6 This is a curve showing the relationship between SIC depth and SI frequency. Figure 7 shows the recovery performance of the received uplink SOI signal. Figure 7(a) shows the spectrum before and after 100MHz broadband SI elimination. Figure 7(b) shows the SOI signal demodulation constellation diagram when the SIC function is not enabled, with a signal error vector amplitude (EVM) of 43.91%. Figure 7(c) shows the SOI signal demodulation constellation diagram when the SIC function is enabled, with a signal error vector amplitude (EVM) of 7.9%. Detailed Implementation

[0012] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments:

[0013] Figure 1 is a schematic diagram of a simple multi-functional integrated 5G analog fronthaul in-band full-duplex communication method for RU. In this embodiment, the device shown in Figure 1 includes a laser (LD), a downlink vector signal (DS), an electrical local oscillator signal (LO), a downlink interference signal (SI), a target signal (SOI), a reference signal (SR), a first 90° electrical coupler, a second 90° electrical coupler, a dual polarization quadrature phase shift keying modulator (DP-QPSK), a phase modulator (PM), a first single-mode fiber (SMFa), a second single-mode fiber (SMFb), an optical coupler (OC), a polarization beam splitter (PBS), a polarization beam combiner (PBC), a first polarization controller (PC1), a second polarization controller (PC2), a third polarization controller (PC3), a first polarizer (Pol1), a second polarizer (Pol2), a first photodetector (PD1), and a second photodetector (PD2). The DP-QPSK integrates two dual-parallel Mach-Zehnder modulators (DP-MZM). The first dual-parallel Mach-Zehnder modulator (DP-MZM1) and the second dual-parallel Mach-Zehnder modulator (DP-MZM2) are integrated in a polarization multiplexing manner. Sub-modulators X-MZM1 and X-MZM2 are embedded in the main modulator of DP-MZM1, and sub-modulators Y-MZM1 and Y-MZM2 are embedded in the main modulator of DP-MZM2. The continuous optical carrier output from the LD enters the DP-QPSK. The DS signal is injected into the first 90° electro-coupler and then split into two paths, which are applied to the two RF input ports of DP-MZM1. The LO signal is injected into the second 90° electro-coupler and then split into two paths, which are applied to the two RF input ports of DP-MZM2. The DS signal is subjected to single-sideband modulation, and the LO signal is subjected to single-sideband modulation with a suppressed carrier to achieve fiber dispersion-resistant transmission. The modulated spectrum is shown in the appendix of the instruction manual. Figure 2 As shown in (a). The output of the DP-QPSK modulator is transmitted through the SMFa and then input to the OC for power splitting. One optical signal is input to the PD1 via PC1 and Pol1 to achieve up-conversion and is then sent to the transmitting antenna to complete the downlink signal transmission. Its spectrum before beat frequency is shown in the appendix of the instruction manual. Figure 2As shown in (b). Another optical signal is separated into X and Y polarization states via PC2 and PBS. The X-polarized light is used as a reference signal, and the Y-polarized light is selected for wavelength reuse and input into the PM modulator. The SOI signal received by the receiving antenna is mixed with the SI signal and loaded into the PM modulator to complete uplink modulation. After PM cascaded downconversion, the X-polarized light and Y-polarized light are then combined via PBC and input into SMFb for transmission. The spectrum is shown in the appendix of the instruction manual. Figure 2 As shown in (c). Rotating PC3 and Pol2 completes the amplitude matching of the SI signal and the SR signal; the cancellation principle diagram is shown in the appendix of the instruction manual. Figure 2 As shown in (d). The comparison spectra of PC3 and Pol2 with and without SIC operation are shown in the appendix of the instruction manual. Figure 4 As shown in the diagram. Finally, the signal is input to PD2 to complete interference cancellation and uplink signal reception.

[0014] In this example, the specific implementation steps of the method are as follows: Step 1: At the CO end, LD1 generates a continuous light wave with a working wavelength of 1553.60nm, a linewidth of 15kHz, and a power of 16dBm, which is injected into a DP-QPSK modulator with a half-wave voltage of 5V and an insertion loss of 6dB. X-MZM1 and X-MZM2 operate in QTP, with the master mode operating in -QTP; Y-MZM1 operates in MITP, Y-MZM2 operates in MITP, with the master mode operating in QTP. Step 2: A 16-QAM microwave vector signal with a symbol rate of 100 MSym / s, a carrier frequency of 2.5 GHz, and a power of 0 dBm is used as a DS signal and split into two equal-power electrical signals via a 90° electro-coupler. These signals are then input to the two RF input ports of DP-MZM1. A single-tone signal with a carrier frequency of 25 GHz and a power of 14 dBm is used as a LO signal and split into two equal-power electrical signals via a 90° electro-coupler. These signals are then input to the two RF input ports of DP-MZM2. Step 3: Transmit the modulated optical signal output from DP-QPSK to the RU end via a 25km SMFa. Step 4: At the RU end, the received optical signal is split into two equal-power optical signals via the optical coupler OC. One optical signal is connected to PD1 for photoelectric detection after passing through PC1 and Pol1, and the detected electrical signal is sent to an oscilloscope for analog-to-digital conversion and digital baseband demodulation. The electrical spectrum and reconstructed constellation diagram of the received downlink 16-QAM microwave vector signal up-converted to 27.5GHz are shown in Appendix Figure 3 of the manual, with an EVM of 4.22%. Step 5: The other optical signal from the RU end is separated into X and Y polarization states after passing through PC2 and PBS. The X-polarized light is used as a reference signal, and the Y-polarized light is selected for wavelength reuse and input into the PM modulator. The target signal SOI with a symbol rate of 50 MSym / s and a carrier frequency of 27.5 GHz received by the receiving antenna is mixed with the interference signal SI with a symbol rate of 100 MSym / s and a carrier frequency of 27.5 GHz and loaded into the PM modulator to complete the uplink modulation. Step 6: After completing PM modulation, combine the X-polarized light and Y-polarized light through PBC2 and then transmit them to the CO end through the 25km SMFb. Step 7: At the CO end, rotate PC3 and Pol2 to complete the amplitude matching of the SI signal and SR signal. Input the signal to PD2 to complete interference signal cancellation and uplink signal reception. Send the SOI signal to the oscilloscope for analog-to-digital conversion and digital baseband demodulation. The recovery performance of the received uplink SOI signal is shown in Appendix Figure 7 of the manual. Figure 7(a) shows the electrical spectrum before and after downconversion to a center frequency of 2.5GHz at a 100M broadband SIC. From Figures 7(b)-(c), it can be seen that before SIC is turned on, its EVM is 43.91%, and the target signal cannot be recovered. After SIC is turned on, its EVM is 7.9%, and the target signal can be recovered. Step 8: Change the bandwidth of the interference signal and measure the self-interference cancellation depth of the 27.5GHz interference signal converted to the center frequency of 2.5GHz in different bandwidths under the condition of no SOI signal. The results are shown in Appendix Figure 5 of the manual. As can be seen from Figure 5, the cancellation depth of the 100MHz bandwidth is 31.3dB, the cancellation depth of the 50MHz bandwidth is 34.5dB, and the cancellation depth of the 25MHz bandwidth is 37.4dB. Step Nine: Change the frequency of the uplink signal, switching the SI signal frequency from 5.5GHz to 27.5GHz in 2GHz increments, and correspondingly change the LO signal frequency to maintain the intermediate frequency signal frequency at 2.5GHz. The measured curve of SiC depth as a function of frequency is shown in the appendix of this document. Figure 6 As shown, the depth of the single-tone SiC is consistently above 60dB, and the depth of the 100MHz broadband SiC is consistently above 30dB, demonstrating good performance over a wide frequency range.

[0015] In summary, this invention proposes a simple, multifunctional, integrated 5G analog fronthaul in-band full-duplex communication method using a single RU (Radio Unit). The RU achieves SiC (Self-Integrated Circuit) combined with fiber dispersion-resistant transmission and down-conversion using a single PM modulator, eliminating the need for bias control and additional LO (Local Outgoing Node) branches, resulting in a simple structure. At the CO (Cooperative Optical Unit) end, single-sideband modulation of the carried downlink and LO signals achieves fiber dispersion-resistant transmission. The RU employs wavelength reuse technology to perform PM-cascaded down-conversion on the uplink received signal, and the SiC is moved from the RU to the CO to simplify the RU. The entire link is filterless and reconfigurable.

[0016] In summary, the above-described embodiments are merely examples of the present invention and are not intended to limit the scope of protection of the present invention. It should be noted that those skilled in the art can make several equivalent modifications and substitutions based on the content disclosed in the present invention, and the center frequency of the radio frequency signal, the signal bandwidth, and the modulation format can all be changed. These equivalent modifications and substitutions, as well as adjustments to the frequency range, should also be considered within the scope of protection of the present invention.

Claims

1. A simple, multifunctional, integrated 5G analog fronthaul in-band full-duplex communication method, comprising a laser (LD), a downlink vector signal (DS), an electrical local oscillator signal (LO), a downlink interference signal (SI), a target signal (SOI), a reference signal (SR), a first 90° electrical coupler, a second 90° electrical coupler, a dual polarization quadrature phase shift keying modulator (DP-QPSK), a phase modulator (PM), a first single-mode fiber (SMFa), a second single-mode fiber (SMFb), an optical coupler (OC), a polarization beam splitter (PBS), a polarization beam combiner (PBC), a first polarization controller (PC1), a second polarization controller (PC2), a third polarization controller (PC3), a first polarizer (Pol1), a second polarizer (Pol2), a first photodetector (PD1), and a second photodetector (PD2). The DP-QPSK integrates two dual-parallel Mach-Zehnder modulators (DP-MZM). The first dual-parallel Mach-Zehnder modulator (DP-MZM1) and the second dual-parallel Mach-Zehnder modulator (DP-MZM2) are integrated in a polarization multiplexing manner. Sub-modulators X-MZM1 and X-MZM2 are embedded in the main modulator of DP-MZM1, and sub-modulators Y-MZM1 and Y-MZM2 are embedded in the main modulator of DP-MZM2. Its schematic diagram is shown in Appendix Figure 1 of the specification. Its key feature is that... The continuous optical carrier output from the LD enters the DP-QPSK. The DS signal is injected into the first 90° electro-coupler and split into two paths, which are loaded onto the two RF input ports of DP-MZM1. The LO signal is injected into the second 90° electro-coupler and split into two paths, which are loaded onto the two RF input ports of DP-MZM2. The DS signal is subjected to single-sideband modulation, and the LO signal is subjected to single-sideband modulation with suppressed carrier. The output of the DP-QPSK modulator is transmitted through the SMFA and then input to the OC for power splitting. One optical signal passes through PC1 and Pol1 and is input to PD1 for up-conversion and then sent to the transmitting antenna to complete the downlink signal transmission. The other optical signal passes through PC2 and PBS to separate the X and Y polarization states. The X-polarized light is used as a reference signal, and the Y-polarized light is selected for wavelength reuse and input into the PM modulator. The SOI signal and SI signal received by the receiving antenna are mixed together and loaded into the PM modulator to complete the uplink modulation. After PM cascaded down-conversion, the X-polarized light and Y-polarized light are then combined through PBC and input into SMFb for transmission. Rotating PC3 and Pol2 completes the amplitude matching of the SI signal and SR signal, and inputting it to PD2 completes interference signal cancellation and uplink signal reception.

2. The simple, multi-functional integrated 5G analog fronthaul in-band full-duplex communication method according to claim 1, characterized in that, The RU (Remote Receiver) can achieve SIC (Self-Converting IC) combined with fiber dispersion-resistant transmission and down-conversion using a single PM modulator, without the need for bias control or an additional LO (Local Receiver) tributary, resulting in a simple structure. At the central office (CO), single-sideband modulation is performed on the carried downlink and LO signals to achieve fiber dispersion-resistant transmission. The RU uses wavelength reuse technology to perform PM cascaded down-conversion on the signals received from the uplink, and the SIC is moved from the RU to the CO to simplify the RU. Simultaneously, the entire link has no optical filters and is reconfigurable.

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