Baseband processing unit, analog fronthaul system, signal processing method

Abstract

The present disclosure provides a baseband processing unit, including a first electro-optical modulator for modulating a baseband signal, the baseband processing unit also includes a second electro-optical modulator, the second electro-optical modulator is coupled to the input end of the first electro-optical modulator or the output end of the first electro-optical modulator, the second electro-optical modulator is used to receive a driving radio frequency signal and perform subcarrier modulation according to the driving radio frequency signal; the baseband processing unit adopts a two-stage electro-optical modulator structure, adds a second electro-optical modulator, and adjusts the operating frequency of the A‑ROF system by adjusting the frequency range of the driving radio frequency signal of the second electro-optical modulator, so that the working signal of the A‑ROF system can cover the millimeter wave band, thereby solving the compatibility problem in the low-frequency and high-frequency bands, achieving full coverage of the high and low frequency bands of 5G, and the operating frequency of the A‑ROF system is continuously adjustable. The present disclosure also provides an analog wireless fronthaul system and a signal processing method.

Description

Technical Field

[0001] The present disclosure relates to the technical field of wireless communications, and in particular to a baseband processing unit, an analog fronthaul system, and a signal processing method. Background Art

[0002] 5G systems have begun commercial use in the sub 6G frequency band (3.4-3.6GHz), however, domestic research on high frequency bands (26G and 40G) is not yet mature. Information access networks are very important. The 5G standard clearly defines three typical business scenarios where technical problems need to be overcome, including enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra-reliable low latency communications (uRLLC). Optical wavelength division multiplexing has great potential. Combined with OFDM (Orthogonal Frequency Division Multiplexing) / F-OFDM (Filtered Orthogonal Frequency Division Multiplexing, sub-band filtered orthogonal frequency division multiplexing) multiple access technology, it makes full use of high-frequency and low-frequency synchronous compatibility technical solutions. The above technologies can be superimposed, thereby greatly improving the capacity and reliability of mobile access systems. In addition, it has the characteristics of small size and low power consumption, making good technical reserves for the next system upgrade.

[0003] Radio-over-fiber access systems include digital fronthaul systems and analog fronthaul (A-ROF) systems. Systems operating at sub-6G frequencies often use digital fronthaul, which has the advantage of relatively low cost, but the disadvantage of occupying a large bandwidth and high latency. For 5G high-frequency bands, the use of analog fronthaul systems has technical advantages. At present, analog fronthaul systems do not cover the millimeter wave band, and there are limitations in their application. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present disclosure provides a baseband processing unit, an analog fronthaul system, and a signal processing method.

[0005] In a first aspect, an embodiment of the present disclosure provides a baseband processing unit, comprising a first electro-optical modulator for modulating a baseband signal, the baseband processing unit also comprising a second electro-optical modulator, the second electro-optical modulator being coupled to an input end of the first electro-optical modulator or an output end of the first electro-optical modulator, the second electro-optical modulator being used to receive a driving RF signal and perform subcarrier modulation according to the driving RF signal.

[0006] In some embodiments, the modulation mode of the second electro-optical modulator is suppressed carrier double sideband modulation.

[0007] In some embodiments, the baseband processing unit further includes an optical wave multiplexer, and the interval between each channel of the optical wave multiplexer is at least greater than twice the radio frequency frequency of the driving radio frequency signal.

[0008] In some embodiments, the baseband processing unit further includes a frequency division multiplexing unit and a code division multiplexing unit, and the code division multiplexing unit is used to perform code division multiplexing processing on multiple user code streams;

[0009] The frequency division multiplexing unit is coupled to the code division multiplexing unit and is used to perform frequency division multiplexing on each channel of user code stream that has undergone code division multiplexing.

[0010] In some embodiments, the code division multiplexing unit includes a codebook matrix, the number of rows of the codebook matrix is ​​the number of subcarriers in the frequency division multiplexing unit or the number of subcarriers after subcarrier grouping, and the number of columns of the codebook matrix is ​​the total number of user code streams, wherein the number of subcarriers is less than the total number of user code streams.

[0011] In some embodiments, the codebook matrix is ​​a sparse matrix.

[0012] In some embodiments, the frequency division multiplexing unit is an orthogonal frequency division multiplexing unit or an orthogonal frequency division multiplexing unit with sub-band filtering.

[0013] On the other hand, an embodiment of the present disclosure further provides an analog wireless fronthaul system, comprising the baseband processing unit as described above.

[0014] In some embodiments, the analog wireless fronthaul system further includes a radio remote unit, the radio remote unit includes an optical wave demultiplexer, and the optical wave demultiplexer is connected to the optical wave multiplexer of the baseband processing unit via optical fiber coupling.

[0015] In some embodiments, the optical fiber includes a single-mode optical fiber and a dispersion compensating optical fiber for performing dispersion compensation on the single-mode optical fiber.

[0016] In some embodiments, the analog wireless fronthaul system also includes a user terminal, and the baseband processing unit is the baseband processing unit as described above; the user terminal includes a code division multiplexing decoding unit and a frequency division multiplexing demodulation unit, and the frequency division multiplexing demodulation unit is used to demodulate the frequency division multiplexing signal received from the radio frequency remote unit; the code division multiplexing decoding unit is coupled to the frequency division multiplexing demodulation unit, and is used to perform code division multiplexing decoding processing on the demodulated signal.

[0017] In another aspect, an embodiment of the present disclosure further provides a signal processing method, comprising: performing at least two-level modulation on a received signal, wherein the performing at least two-level modulation on the received signal comprises:

[0018] receiving a driving radio frequency signal, and performing subcarrier modulation according to the driving radio frequency signal;

[0019] The received baseband signal is modulated.

[0020] In some embodiments, performing subcarrier modulation according to the driving RF signal includes:

[0021] Subcarrier modulation is performed according to the driving RF signal so that the frequency of the output signal is twice the frequency of the driving RF signal.

[0022] In some embodiments, after performing at least two-level modulation on the received signal, the method further comprises:

[0023] The signals after two-stage modulation are subjected to optical wavelength division multiplexing processing.

[0024] In some embodiments, before performing at least two-level modulation on the received signal, the method further includes:

[0025] Carry out code division multiplexing processing on multiple user code streams;

[0026] The user code streams that have undergone code division multiplexing are subjected to frequency division multiplexing.

[0027] In some embodiments, the signal processing method includes:

[0028] The signal processed by optical wavelength division multiplexing is transmitted to the radio remote unit through optical fiber, so that the radio remote unit demultiplexes the received signal and sends the demultiplexed signal to the user terminal through the antenna.

[0029] The baseband processing unit provided in the embodiment of the present disclosure includes a first electro-optical modulator for modulating a baseband signal, and the baseband processing unit also includes a second electro-optical modulator, the second electro-optical modulator is coupled to the input end of the first electro-optical modulator or the output end of the first electro-optical modulator, and the second electro-optical modulator is used to receive a driving radio frequency signal and perform subcarrier modulation according to the driving radio frequency signal; the baseband processing unit of the embodiment of the present disclosure adopts a two-stage electro-optical modulator structure, and adds a second electro-optical modulator. By adjusting the frequency range of the driving radio frequency signal of the second electro-optical modulator, the operating frequency adjustment of the analog wireless fronthaul (A-ROF) system is achieved, so that the working signal of the A-ROF system can cover the millimeter wave band, thereby solving the compatibility problem in the low-frequency and high-frequency bands, achieving full coverage of the high and low frequency bands of 5G, and the operating frequency of the A-ROF system is continuously adjustable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of two-stage modulation of a BBU provided in an embodiment of the present disclosure;

[0031] Figure 2 A schematic diagram of the BBU structure provided in an embodiment of the present disclosure;

[0032] Figure 3 A schematic diagram of a code division-frequency division joint multiplexing process provided in an embodiment of the present disclosure;

[0033] Figure 4 A schematic diagram of the A-ROF system structure provided in an embodiment of the present disclosure;

[0034] Figure 5 A schematic diagram of the structure of an A-ROF system transmitter with a two-stage MZM modulation structure provided in an embodiment of the present disclosure;

[0035] Figure 6 A schematic diagram of an A-ROF system for a two-way direct transmission scenario provided by an embodiment of the present disclosure. DETAILED DESCRIPTION

[0036] Example embodiments will be described more fully below with reference to the accompanying drawings, but the example embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. On the contrary, the purpose of providing these embodiments is to make the present disclosure thorough and complete and to enable those skilled in the art to fully understand the scope of the present disclosure.

[0037] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0038] The terms used herein are only used to describe specific embodiments and are not intended to limit the present disclosure. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It will also be understood that when the terms "comprising" and / or "made of" are used in this specification, the presence of the features, wholes, steps, operations, elements and / or components is specified, but the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or groups thereof is not excluded.

[0039] The embodiments described herein may be described with reference to plan views and / or cross-sectional views by means of idealized schematic diagrams of the present disclosure. Therefore, the example illustrations may be modified according to manufacturing techniques and / or tolerances. Therefore, the embodiments are not limited to the embodiments shown in the accompanying drawings, but include modifications of the configurations formed based on the manufacturing process. Therefore, the regions illustrated in the accompanying drawings have schematic properties, and the shapes of the regions shown in the figures illustrate the specific shapes of the regions of the elements, but are not intended to be limiting.

[0040] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted as having an idealized or overly formal meaning unless explicitly defined as such herein.

[0041] The present disclosure provides a baseband processing unit (Base band Unite, BBU), such as Figure 1 As shown, the baseband processing unit includes a first electro-optical modulator and a second electro-optical modulator, the first electro-optical modulator is used to modulate the baseband signal, the second electro-optical modulator is coupled to the input end of the first electro-optical modulator or the output end of the first electro-optical modulator, and the second electro-optical modulator is used to receive a driving RF signal and perform subcarrier modulation according to the driving RF signal.

[0042] The baseband processing unit provided by the embodiment of the present disclosure includes a first electro-optical modulator for modulating a baseband signal, and also includes a second electro-optical modulator. The second electro-optical modulator is coupled to the input end of the first electro-optical modulator or the output end of the first electro-optical modulator, and is used to receive a driving radio frequency signal and perform subcarrier modulation according to the driving radio frequency signal. The baseband processing unit of the embodiment of the present disclosure adopts a two-stage electro-optical modulator structure and adds a second electro-optical modulator. By adjusting the frequency range of the driving radio frequency signal of the second electro-optical modulator, the operating frequency adjustment of the A-ROF system is achieved, so that the operating signal of the A-ROF system can cover the millimeter wave band, thereby solving the compatibility problem in the low-frequency and high-frequency bands, achieving full coverage of the high and low frequency bands of 5G, and the operating frequency of the A-ROF system is continuously adjustable.

[0043] The second electro-optical modulator and the first electro-optical modulator are connected in series to form a two-stage modulation structure. The second electro-optical modulator is coupled to the input end or the output end of the first electro-optical modulator. That is to say, baseband signal modulation can be performed first, or subcarrier modulation can be performed first. That is, the corresponding positions of the first electro-optical modulator and the second electro-optical modulator can be interchanged. In the embodiment of the present disclosure, baseband signal modulation is performed first and then subcarrier modulation is performed as an example for explanation.

[0044] The two-stage modulation structure is adopted to facilitate integrated design. Two electro-optical modulators can be realized at one time on the same optoelectronic integrated chip. This series structure shares one active laser, which has lower manufacturing cost, small size and better anti-interference performance.

[0045] The second-level electro-optical modulation implements subcarrier modulation. The frequency of the input driving RF signal determines the location of the wireless communication frequency of the A-ROF system. When the frequency of the driving RF signal (i.e., the subcarrier) changes, the frequency of the output signal of the baseband processing unit also changes. It should be noted that the bandwidth of the second electro-optical modulator must be greater than or equal to the frequency of the driving RF signal.

[0046] In some embodiments, the modulation method of the second electro-optical modulator is suppressed carrier double-sideband modulation, so that a twice-frequency RF signal output can be achieved. That is, when the frequency of the RF signal input by the second electro-optical modulator is continuously adjusted in the range of 1GHz-30GHz, an analog wireless fronthaul signal with a carrier varying in the range of 2GHz-60GHz can be obtained.

[0047] In some embodiments, the type of the first electro-optic modulator can be a direct modulator or an external modulator, wherein the external modulator includes an intensity modulator, a phase modulator, and an IQ (In-phase Quadrature) modulator. The modulation mode of the first electro-optic modulator can be double-sideband modulation or single-sideband modulation.

[0048] It should be noted that the baseband processing unit of the embodiment of the present disclosure may also adopt a modulation structure of more than two levels. For example, a three-level modulation structure can achieve a 4-fold frequency signal output, but a corresponding filtering link must also be added to eliminate low-order interference signals.

[0049] In some embodiments, Figure 2 As shown, the baseband processing unit may also include an optical wave multiplexer, which is used to combine a series of optical signals carrying information but with different wavelengths (i.e., optical signals of each channel) into one beam, and the interval between each channel of the optical wave multiplexer is at least greater than twice the RF frequency of the driving RF signal.

[0050] The optical wave multiplexer can be WDM (Wavelength Division Multiplexing), CWDM (Coarse Wavelength Division Multiplexer), DWDM (Dense Wavelength Division Multiplexer) or AWG (Arrayed Waveguide Grating).

[0051] In some embodiments, the baseband processing unit may also include a frequency division multiplexing (FDM) unit and a code division multiplexing (CDM) unit, the code division multiplexing unit is used to perform code division multiplexing processing on multiple user code streams; the frequency division multiplexing unit is coupled to the code division multiplexing unit to perform frequency division multiplexing processing on each user code stream that has been processed by code division multiplexing.

[0052] The baseband processing unit of the disclosed embodiment realizes code division-frequency division joint multiplexing through a frequency division multiplexing unit and a code division multiplexing unit. Compared with the existing OFDMA (Orthogonal Frequency Division Multiple Access) solution, the number of users of the A-ROF system can be increased by more than 50% (that is, the overload rate can reach more than 1.5 times), thereby increasing the scale of large-scale Internet of Things mMTC, and the bit error rate is significantly reduced. The two-dimensional multiplexing technology of code domain and frequency domain, applied to the A-ROF system, can increase the user access volume of C-RAN (central control-cloud radio access network), and can design and select different codebook matrices according to the needs of the scene to achieve different overload rates, which is more flexible and adaptable to a wide range of applications.

[0053] In some embodiments, the frequency division multiplexing unit is an OFDM unit or a F-OFDM unit.

[0054] In some embodiments, the code division multiplexing unit includes a codebook matrix, the number of rows of the codebook matrix is ​​the number of subcarriers in the frequency division multiplexing unit or the number of subcarriers after subcarrier grouping, and the number of columns of the codebook matrix is ​​the total number of user code streams, wherein the number of subcarriers is less than the total number of user code streams.

[0055] In order to reduce the decoding complexity of the signal receiving end (ie, the user terminal), reduce the decoding operation amount, and thus reduce chip resource consumption and hardware cost, in some embodiments, the codebook matrix may be a sparse matrix.

[0056] The following combination Figure 3 The code division-frequency division joint multiplexing process is described in detail. Figure 3As shown, firstly, a codebook matrix M is designed. The codebook matrix M has K rows and N columns (K<N). The codebook matrix can be flexibly designed and selected to achieve different overload rates. Then, the subcarriers of the frequency division multiplexing unit (for example, OFDM) are divided into several groups, each group contains K=4 subcarriers, and each subcarrier corresponds to one row of the codebook matrix M; after being mapped by the codebook matrix M, N=6 virtual subcarrier frequency resources are output, that is, N=6 users can be supported. Since K<N, the overload rate N / K=1.5 (greater than 1), and the 6 users are mapped to the 4 orthogonal subcarriers of OFDM through the codebook matrix M, thereby achieving the effect of increasing the number of users and realizing the joint multiplexing of information in the frequency domain and the code domain.

[0057] In some embodiments, there may be multiple code division multiplexing units and multiple frequency division multiplexing units, and each frequency division multiplexing unit corresponds to each code division multiplexing unit one by one, so as to realize multiple code division-frequency division joint multiplexing parallel processing.

[0058] In the embodiments of the present disclosure, Figure 2 As shown, there are multiple code division multiplexing units and one frequency division multiplexing unit. The frequency division multiplexing unit is coupled to each code division multiplexing unit respectively, and can perform frequency division multiplexing processing on the output signals of each code division multiplexing unit at the same time.

[0059] In the embodiments of the present disclosure, Figure 2 As shown, the baseband processing unit may further include: a multiplier and a driving amplifier unit, the multiplier is coupled to the frequency division multiplexing unit and the driving amplifier unit respectively, the driving amplifier unit is connected to a two-stage electro-optical modulator, wherein the first-stage modulation may be a first electro-optical modulator or a second electro-optical modulator.

[0060] The present disclosure also provides a simulated wireless fronthaul system, such as Figure 4 As shown, the analog wireless fronthaul system includes a baseband processing unit, and the baseband processing unit is the baseband processing unit as described above.

[0061] The analog wireless fronthaul system provided by the embodiment of the present disclosure includes a baseband processing unit, the baseband processing unit includes a first electro-optical modulator for modulating a baseband signal, and also includes a second electro-optical modulator, the second electro-optical modulator is coupled to the input end or the output end of the first electro-optical modulator, and is used to receive a driving radio frequency signal and perform subcarrier modulation according to the driving radio frequency signal; the baseband processing unit of the embodiment of the present disclosure adopts a baseband processing unit with a two-stage electro-optical modulator structure, and a second electro-optical modulator is added. By adjusting the frequency range of the driving radio frequency signal of the second electro-optical modulator, the operating frequency adjustment of the A-ROF system is achieved, so that the operating signal of the A-ROF system can cover the millimeter wave band, thereby solving the compatibility problem in the low-frequency and high-frequency bands, achieving full coverage of the high and low frequency bands of 5G, and the operating frequency of the A-ROF system is continuously adjustable.

[0062] It should be noted that, in the A-ROF system, the baseband processing unit exists in the form of a BBU pool, that is, the A-ROF system includes a BBU pool, and the BBU pool includes multiple baseband processing units.

[0063] In the embodiments of the present disclosure, Figure 4 As shown, the analog wireless fronthaul system also includes a remote radio unit (RRU), which includes an optical wave demultiplexer. The optical wave demultiplexer is connected to the optical wave multiplexer of the baseband processing unit through optical fiber coupling, and is used to demultiplex the received signal (the signal is the signal output by the optical wave multiplexer in the BBU), that is, to separate the optical signals of different wavelengths.

[0064] In some embodiments, the radio remote unit may also include: an optical filter, a photoelectric conversion unit, a filter, a power amplification unit, an antenna, etc. After the radio remote unit completes a series of processes such as demultiplexing, filtering, photoelectric conversion, and amplification, the signal is sent to the user terminal (User Experience, UE) through the antenna.

[0065] The photoelectric conversion unit can be a photodetector, avalanche photodetector (APD) or PIN detector, and its bandwidth covers the highest frequency of the A-ROF system. The antenna, power amplifier unit and filter can be wideband or narrowband, as long as they can cover the frequency range of the A-ROF system passband signal. The antenna can be a single-input single-output structure, a multiple-input multiple-output (MIMO) structure, or a large-scale MIMO structure.

[0066] By changing the frequency of the subcarrier RF signal (i.e., the driving RF signal) of the second electro-optical modulator in the A-ROF system, the frequency of the modulated signal output by the optoelectronic conversion unit in the RF remote unit can be achieved, and the signal is sent to the user terminal through the antenna.

[0067] In some embodiments, the optical fiber includes a single-mode optical fiber and a dispersion-compensating optical fiber, and the dispersion-compensating optical fiber is used to perform dispersion compensation on the single-mode optical fiber.

[0068] In some embodiments, an optical wave multiplexer and an optical wave demultiplexer are respectively used in the BBU and the RRU, and a single optical fiber transmits multiple signals simultaneously, thereby improving the capacity of the A-ROF system. The number of channels of the optical wave multiplexer can be selected to be 4, 8, 16, 32, 64, 128, etc. The frequency is within 40G, and the optical frequency interval between channels can be selected to be 50G or 100G. When the frequency is greater than 40G, the channel interval is 100G.

[0069] The baseband processing unit, the optical fiber and the radio remote unit form a signal transmitting end of the A-ROF system. In some embodiments, the analog wireless fronthaul system also includes a user terminal, which is a signal receiving end of the analog wireless fronthaul system, including a code division multiplexing decoding unit and a frequency division multiplexing demodulation unit. The frequency division multiplexing demodulation unit is used to demodulate the frequency division multiplexing signal received from the radio remote unit; the code division multiplexing decoding unit is coupled to the frequency division multiplexing demodulation unit to perform code division multiplexing decoding processing on the demodulated signal.

[0070] The user terminal receives the signal sent by the radio frequency remote unit through the antenna. In some embodiments, the user terminal may also include: a power amplification unit, a frequency conversion unit, a channel equalization unit, a channel estimation unit and a channel decoding unit, wherein the channel equalization unit is used to perform electrical domain compensation for dispersion, nonlinearity and IQ imbalance in optical fiber transmission, and to preprocess the signal transmitted in the wireless space.

[0071] In the disclosed embodiment, at the transmitting end of the A-ROF system, the baseband signal adopts OFDM technology to perform carrier aggregation. At the receiving end of the A-ROF system, channel estimation (implemented by OFDM training sequence method) and signal equalization (implemented by least squares algorithm with lower computational complexity) are performed respectively, and LDPC (Low Density Parity Check Code) / Polar (polarization code) coding technology is combined to compensate for the electro-optical modulation process and the optical transmission process.

[0072] By adjusting the frequency of the driving RF signal of the second electro-optic modulator and designing the bandwidth of the microwave devices in the A-ROF system (including the driving circuit of the electro-optic modulator, the filter bandwidth, the optoelectronic conversion unit bandwidth, the antenna bandwidth, and the working bandwidth of the power amplifier unit), the frequency band covered by the A-ROF system includes Sub 6G and millimeter wave bands, and can be flexibly upgraded to high frequency bands (26G, 40G, 60G or any other frequency point), thereby realizing the continuous adjustment of the operating frequency of the A-ROF system and full coverage of the high and low frequency bands of 5G.

[0073] Combination Figure 4 and Figure 5 As shown in the figure, for C-RAN applications, the BBU of the A-ROF system includes a two-stage electro-optical modulator. The two-stage modulation adopts external modulation technology. The first and second electro-optical modulators use lithium niobate Mach-Zehnder modulators (MZM). In order to reduce costs, the first-stage electro-optical modulation (i.e., the first electro-optical modulator MZM1) can use a low-bandwidth MZM, using a double-sideband modulation method. The electrical signal input to the first electro-optical modulator is a baseband signal, and the output optical signal is a baseband optical carrier baseband signal. The RF signal input to the second-stage electro-optical modulation (i.e., the second electro-optical modulator MZM2) is used as a subcarrier. The frequency is usually high, up to tens of gigahertz. Therefore, a high-bandwidth MZM is selected, and a suppressed carrier double-sideband modulation method is adopted. The photoelectric conversion unit (PD) in the radio remote unit of the A-ROF system directly detects, and the frequency of the output signal is twice the frequency of the input RF signal of the second electro-optical modulator, thereby realizing millimeter wave modulation. When the subcarrier frequency changes, the corresponding output frequency also changes accordingly.

[0074] In another embodiment of the present disclosure, the first electro-optic modulator may adopt a directly modulated laser (DML), and the input to the first electro-optic modulator may be a baseband signal or a Sub 6G RF signal. The second electro-optic modulator may adopt external modulation technology, using a lithium niobate Mach-Zehnder modulator (MZM), and the input to the second electro-optic modulator is a RF signal, which is directly detected by the photoelectric conversion unit (PD) in the RRU of the A-ROF system, and the frequency of the output signal is twice the frequency of the input RF signal of the second electro-optic modulator, thereby realizing the access of any signal of the two frequency points of Sub 6G or millimeter wave. On the one hand, the A-ROF system of the embodiment of the present disclosure can be compatible with the existing 5G access network, and on the other hand, it can expand the existing Sub 6G frequency band range, and can be flexibly upgraded to high frequency bands (26G, 40G, 60G or any other frequency point).

[0075] like Figure 6 As shown, the A-ROF of the embodiment of the present disclosure can be applied to a bidirectional optical fiber direct transmission scenario, that is, a point-to-point bidirectional direct transmission scenario. Figure 6As shown, in this scenario, an optical circulator is used to realize parallel operation of bidirectional communication, and there is one optical circulator at each end of the interaction.

[0076] Two-stage analog electro-optical modulator, the first stage modulation realizes baseband modulation, which can adopt direct modulated laser (DML) or external modulation Hertzian modulator MZM, and the second stage modulation can adopt external modulation technology.

[0077] Using wavelength division multiplexing technology, a single optical fiber transmits multiple signals at the same time. The channel frequency of the optical wave multiplexer must match the laser to form a WDM A-ROF system. The optical wave multiplexer can be WDM, DWDM, CWDM or AWG.

[0078] Frequency division multiplexing technology is adopted, and OFDM technology is used in the baseband signal of the transmitting end to perform carrier aggregation; at the receiving end of the A-ROF system, channel estimation (implemented by the OFDM training sequence method) and signal equalization (implemented by the least squares algorithm with lower computational complexity) are performed respectively, and LDPC / Polar coding technology is combined to compensate for the electro-optical modulation process and the optical transmission process.

[0079] Using code division multiplexing technology, we first design a sparse codebook matrix M, and then divide the OFDM subcarriers into several groups, each group contains K subcarriers, and each subcarrier corresponds to one row of the M matrix; after mapping by the matrix M, N virtual subcarrier frequency resources are output, which can support N users and realize the joint multiplexing of information in the frequency domain and code domain.

[0080] The A-ROF system of the disclosed embodiment adopts a multi-dimensional joint multiplexing method that combines code division multiplexing, orthogonal frequency division multiplexing and optical wavelength division multiplexing technologies. The signal processing complexity is controllable, which can solve the compatibility problem of the 5G system's wireless fronthaul solutions in the low-frequency and high-frequency bands, and increase the number of massive access users of the wireless access system, thereby improving frequency efficiency.

[0081] The present disclosure also provides a signal processing method, combining Figure 1 As shown, the method includes: performing at least two-stage modulation on the received signal, and the at least two-stage modulation on the received signal includes step a and step b. Step a, receiving the driving RF signal, and performing subcarrier modulation according to the driving RF signal. In this step, the second electro-optical modulator receives the driving RF signal, and performs subcarrier modulation according to the driving RF signal. Step b, modulating the received baseband signal. In this step, the first electro-optical modulator modulates the received baseband signal. It should be noted that step b can be performed before or after step a.

[0082] By adjusting the frequency range of the driving RF signal of the second electro-optical modulator, the operating frequency of the A-ROF system can be adjusted so that the operating signal of the A-ROF system can cover the millimeter wave band, thereby solving the compatibility problem of the analog wireless fronthaul system in the low-frequency and high-frequency bands, achieving full coverage of the 5G high and low frequency bands, and continuously adjustable operating frequency of the A-ROF system.

[0083] In some embodiments, the modulation mode of the second electro-optical modulator is suppressed carrier double sideband modulation.

[0084] In some embodiments, after performing at least two-stage modulation on the received signal, the following steps may also be included: performing optical wavelength division multiplexing on the two-stage modulated signal. In this step, the optical wavelength multiplexer in the BBU performs optical wavelength division multiplexing on the two-stage modulated signal and transmits the processed signal to the RRU via optical fiber.

[0085] In some embodiments, the interval between the channels of the optical wave multiplexer is at least greater than twice the RF frequency of the driving RF signal.

[0086] In some embodiments, the signal processing method may further include the following steps: before performing at least two-level modulation on the received signal, code division multiplexing is performed on multiple user code streams, and frequency division multiplexing is performed on each of the code division multiplexing user code streams. In this step, the code division multiplexing unit in the BBU performs code division multiplexing on multiple user code streams, and the frequency division multiplexing unit performs frequency division multiplexing on each of the code division multiplexing user code streams, thereby realizing joint multiplexing of information in the frequency domain and the code domain.

[0087] In some embodiments, the code division multiplexing unit is a codebook matrix, the number of rows of the codebook matrix is ​​the number of subcarriers in the frequency division multiplexing unit or the number of subcarriers after subcarrier grouping, and the number of columns of the codebook matrix is ​​the total number of user code streams, wherein the number of subcarriers is less than the total number of user code streams.

[0088] In some embodiments, the codebook matrix is ​​a sparse matrix.

[0089] In some embodiments, the frequency division multiplexing unit comprises an orthogonal frequency division multiplexing unit or an orthogonal frequency division multiplexing unit with sub-band filtering.

[0090] In some embodiments, the signal processing method further includes the following steps: transmitting the signal processed by optical wavelength division multiplexing to the radio remote unit via optical fiber, so that the radio remote unit demultiplexes the received signal and sends the demultiplexed signal to the user terminal via an antenna.

[0091] In some embodiments, the user terminal receives the signal sent by the radio remote unit using an antenna, the signal being the demultiplexed signal; and performs frequency division multiplexing demodulation processing and code division multiplexing decoding processing on the signal. The user terminal can perform channel estimation (implemented by OFDM training sequence method), signal equalization (implemented by least squares algorithm with lower computational complexity), and compensate for the electro-optical modulation process and the optical transmission process in combination with LDPC / Polar coding technology.

[0092] It will be appreciated by those skilled in the art that all or some of the steps in the method disclosed above, the functional modules / units in the device may be implemented as software, firmware, hardware, and appropriate combinations thereof. In hardware implementations, the division between the functional modules / units mentioned in the above description does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed by several physical components in cooperation. Some physical components or all physical components may be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software may be distributed on a computer-readable medium, which may include a computer storage medium (or non-transitory medium) and a communication medium (or temporary medium). As known to those skilled in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, it is well known to those of ordinary skill in the art that communication media typically contain computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism, and may include any information delivery media.

[0093] Example embodiments have been disclosed herein, and although specific terms are employed, they are used and should be interpreted only in a general illustrative sense and not for limiting purposes. In some instances, it will be apparent to those skilled in the art that, unless otherwise expressly stated, features, characteristics, and / or elements described in conjunction with a particular embodiment may be used alone or in combination with features, characteristics, and / or elements described in conjunction with other embodiments. Therefore, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A baseband processing unit, comprising a first electro-optical modulator for modulating a baseband signal, a frequency division multiplexing unit and a code division multiplexing unit, the baseband processing unit further comprising a second electro-optical modulator, the second electro-optical modulator being coupled to an input end of the first electro-optical modulator or an output end of the first electro-optical modulator, the second electro-optical modulator being used to receive a driving radio frequency signal and perform subcarrier modulation according to the driving radio frequency signal; The code division multiplexing unit is used to perform code division multiplexing processing on multiple user code streams; The frequency division multiplexing unit is coupled to the code division multiplexing unit and is used to perform frequency division multiplexing on each channel of user code stream that has undergone code division multiplexing.

2. The baseband processing unit according to claim 1, wherein: The modulation mode of the second electro-optical modulator is suppressed carrier double sideband modulation.

3. The baseband processing unit according to claim 1 or 2, wherein: It also includes an optical wave multiplexer, wherein the interval between each channel of the optical wave multiplexer is at least greater than twice the radio frequency frequency of the driving radio frequency signal.

4. The baseband processing unit according to claim 1, wherein: The code division multiplexing unit includes a codebook matrix, the number of rows of the codebook matrix is ​​the number of subcarriers in the frequency division multiplexing unit or the number of subcarriers after subcarrier grouping, and the number of columns of the codebook matrix is ​​the total number of user code streams, wherein the number of subcarriers is less than the total number of user code streams.

5. The baseband processing unit according to claim 4, wherein: The codebook matrix is ​​a sparse matrix.

6. The baseband processing unit according to claim 1, wherein: The frequency division multiplexing unit is an orthogonal frequency division multiplexing unit or an orthogonal frequency division multiplexing unit for sub-band filtering.

7. An analog wireless fronthaul system, comprising a baseband processing unit as claimed in any one of claims 1 to 6.

8. The analog wireless fronthaul system according to claim 7, wherein: The baseband processing unit is the baseband processing unit as described in any one of claims 3-6; the analog wireless fronthaul system also includes a radio frequency remote unit, the radio frequency remote unit includes an optical wave demultiplexer, and the optical wave demultiplexer is connected to the optical wave multiplexer of the baseband processing unit through optical fiber coupling.

9. The analog wireless fronthaul system according to claim 8, wherein: The optical fiber includes a single-mode optical fiber and a dispersion-compensating optical fiber for performing dispersion compensation on the single-mode optical fiber.

10. The analog wireless fronthaul system according to claim 8, wherein: Also included is a user terminal, the user terminal includes a code division multiplexing decoding unit and a frequency division multiplexing demodulation unit, the frequency division multiplexing demodulation unit is used to demodulate the frequency division multiplexing signal received from the radio remote unit; The code division multiplexing decoding unit is coupled to the frequency division multiplexing demodulation unit and is used to perform code division multiplexing decoding processing on the demodulated signal.

11. A signal processing method, comprising: Performing at least two-level modulation on the received signal; The step of performing at least two-level modulation on the received signal comprises: receiving a driving radio frequency signal, and performing subcarrier modulation according to the driving radio frequency signal; Modulating the received baseband signal; Before performing at least two-level modulation on the received signal, the method further comprises: Carry out code division multiplexing processing on multiple user code streams; The user code streams that have been subjected to code division multiplexing processing are subjected to frequency division multiplexing processing.

12. The method of claim 11, wherein: The performing subcarrier modulation according to the driving radio frequency signal comprises: Subcarrier modulation is performed according to the driving RF signal so that the frequency of the output signal is twice the frequency of the driving RF signal.

13. The method according to claim 11 or 12, wherein: After performing at least two-level modulation on the received signal, the method further comprises: The signals after two-stage modulation are subjected to optical wavelength division multiplexing processing.

14. The method of claim 13, wherein: Also includes: The signal processed by optical wavelength division multiplexing is transmitted to the radio remote unit through optical fiber, so that the radio remote unit demultiplexes the received signal and sends the demultiplexed signal to the user terminal through the antenna.

Images