CN113709074A - Baseband signal processing method, baseband processing unit and base station - Google Patents
Baseband signal processing method, baseband processing unit and base station Download PDFInfo
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- H—ELECTRICITY
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Abstract
The invention provides a baseband signal processing method, a baseband processing unit and a base station. The baseband signal processing method comprises the following steps: carrying out peak clipping processing on a baseband signal to reduce the PAR (peak-to-average ratio) of the baseband signal; carrying out digital pre-distortion processing on the baseband signal subjected to peak clipping processing to obtain a pre-distortion baseband signal; amplifying the power of the predistortion baseband signal to obtain a downlink baseband signal; and transmitting the downlink baseband signal to a radio remote unit RRU. The invention can reduce the power consumption and the cost of the distributed base station under the condition of ensuring the signal transmission quality.
Description
Technical Field
The present disclosure relates to the field of communications technologies, and in particular, to a baseband signal processing method, a baseband processing unit, and a base station.
Background
The distributed base station system adopts a design of separating a Baseband processing Unit (BBU) and a Radio Remote Unit (RRU), the BBU integrates the functions of a Baseband, a master control, transmission, a clock and the like of a traditional macro base station, the installation position is flexible, for example, the BBU can be arranged in a machine room, the RRU integrates the Radio functions of a transceiver, a power amplifier and the like, and a Remote end close to an antenna is generally arranged. The BBU and the RRU are connected through optical fibers.
At present, distributed base station systems still have high costs.
Disclosure of Invention
To solve at least one aspect of the above problems in the prior art, the present disclosure provides a baseband signal processing method and a baseband processing unit performing the same.
In order to achieve the above object, as a first aspect of the present disclosure, there is provided a baseband signal processing method applied to a baseband processing unit BBU, including:
carrying out peak clipping processing on a baseband signal to reduce the PAR (peak-to-average ratio) of the baseband signal;
carrying out digital pre-distortion processing on the baseband signal subjected to peak clipping processing to obtain a pre-distortion baseband signal;
amplifying the power of the predistortion baseband signal to obtain a downlink baseband signal;
and transmitting the downlink baseband signal to a radio remote unit RRU.
Optionally, the step of performing digital predistortion on the baseband signal after the peak clipping processing to obtain a predistorted baseband signal includes:
sampling and quantizing the downlink baseband signal to obtain a feedback signal;
and carrying out digital pre-distortion processing on the baseband signal after the peak clipping processing according to the feedback signal to obtain the pre-distortion baseband signal.
Optionally, before the step of amplifying the power of the predistortion baseband signal to obtain the downlink baseband signal, the baseband signal processing method further includes:
converting the pre-distorted baseband signal into an analog signal.
Optionally, before the step of transmitting the downlink baseband signal to a radio remote unit RRU, the baseband signal processing method further includes:
sampling and quantizing the downlink baseband signal to obtain a digital baseband signal;
adjusting the time delay of the digital baseband signal according to the time delay generated when the baseband signal after the peak clipping processing is subjected to digital pre-distortion processing;
transmitting the downlink baseband signal to a Radio Remote Unit (RRU), so that the step of generating a radio frequency signal by the RRU according to the downlink baseband signal comprises
And filling the data in the digital baseband signal after the time delay is adjusted into a downlink frame of a common public radio interface (CPRI/eCPRI), so as to transmit the digital baseband signal after the time delay is adjusted to the RRU through the CPRI/eCPRI.
Optionally, the PAR of the baseband signal after the peak reduction processing is in a range of 6 to 8 dB.
Optionally, the error vector magnitude EVM of the downlink baseband signal is less than or equal to 3%.
As a second aspect of the present disclosure, there is provided a baseband processing unit BBU including:
the peak clipping processing module is used for carrying out peak clipping processing on the baseband signal so as to reduce the PAR (peak-to-average ratio) of the baseband signal;
the digital pre-distortion module is used for carrying out digital pre-distortion processing on the baseband signal after the peak clipping processing to obtain a pre-distortion baseband signal;
the power amplifier is used for amplifying the power of the predistortion baseband signal to obtain a downlink baseband signal;
and the signal transmission module is used for transmitting the downlink baseband signal to a Radio Remote Unit (RRU).
Optionally, the BBU further comprises:
the first analog-to-digital conversion module is used for sampling and quantizing the downlink baseband signal to obtain a feedback signal;
and the digital predistortion module performs digital predistortion processing on the baseband signal after the peak clipping processing according to the feedback signal to obtain the predistortion baseband signal.
Optionally, the BBU further comprises:
the digital-to-analog conversion module is used for converting the predistortion baseband signal into an analog signal;
and the power amplifier amplifies the power of the analog signal to obtain the downlink baseband signal.
Optionally, the BBU further comprises:
the second analog-to-digital conversion module is used for sampling and quantizing the downlink baseband signal to obtain a digital baseband signal;
the time delay adjusting module is used for adjusting the time delay of the digital baseband signal according to the time delay generated by the digital predistortion module;
and the common public radio interface CPRI/eCPRI is used for filling data in the digital baseband signal after the time delay is adjusted into a downlink frame of the CPRI/eCPRI so as to transmit the digital baseband signal after the time delay is adjusted to the RRU through the CPRI/eCPRI.
Optionally, the PAR of the baseband signal after the peak reduction processing is in a range of 6 to 8 dB.
Optionally, the error vector magnitude EVM of the downlink baseband signal is less than or equal to 3%.
As a third aspect of the present disclosure, there is provided a base station comprising a BBU and an RRU, wherein the BBU is the BBU provided in the second aspect of the present disclosure.
According to the baseband signal processing method provided by the disclosure, the baseband signal is subjected to peak clipping and digital pre-distortion amplification processing on the BBU, so that the baseband signal transmitted to the RRU has a lower EVM and the distortion of the baseband signal is acceptable; meanwhile, the radio remote unit has smaller PAR, so that a power amplifier in the RRU works in a linear working area. The RRU can directly amplify and transmit the received downlink baseband signal without pre-distortion processing. Therefore, a DPD module in the RRU can be omitted, a large amount of DPD algorithm resources are saved, and the cost of the distributed base station system is reduced.
Drawings
Fig. 1 is an architecture diagram of a conventional distributed base station system;
FIG. 2 is a flow chart of one embodiment of a baseband signal processing method of the present disclosure;
FIG. 3 is a flow chart of another embodiment of a baseband signal processing method of the present disclosure;
fig. 4 is a flow chart of yet another embodiment of a baseband signal processing method in the present disclosure;
FIG. 5 is a block diagram of one embodiment of a baseband processing unit in accordance with the present disclosure;
FIG. 6 is a block diagram representation of another embodiment of a baseband processing unit in the present disclosure;
fig. 7 is an architecture diagram of one embodiment of a distributed base station system employing a baseband processing unit as provided by the present disclosure.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
In 4G and 5G, Orthogonal Frequency Division Multiplexing (OFDM) technology is used to implement multicarrier transmission. However, the multi-carrier transmission also brings a high Peak to Average ratio (PAR), so that the non-linear distortion of a Power Amplifier (PA) in the base station is more serious. Digital Pre-Distortion (DPD) techniques can eliminate nonlinear Distortion of the PA, thereby improving the efficiency of the PA.
As shown in fig. 1, in a conventional distributed base station system, one BBU can support and connect multiple RRUs. There is a power amplifier on each RRU. In the power amplifier design process: in order to obtain a larger output signal power, the input signal peak of the power amplifier is typically in the vicinity of the saturation point P1dB or even P3 dB. Thus, the nonlinear distortion of the power amplifier can generate new frequency components, such as second harmonic and double-tone beat frequency for second-order distortion and third harmonic and multi-tone beat frequency for third-order distortion. In order to solve the nonlinear distortion caused by the high peak-to-average ratio of the input signal, a Digital Predistortion (DPD) module is arranged on the RRU. However, each RRU performs digital predistortion amplification on the baseband signal, which requires a large amount of DPD algorithm resources to be added, so that the cost is increased.
The inventor of the present disclosure considers that if digital predistortion amplification can be performed on a baseband signal in a BBU, a DPD module in each RRU can be omitted, so that resources can be greatly saved and costs can be reduced.
In view of this, as a first aspect of the present disclosure, there is provided a baseband signal processing method applied to a baseband processing unit BBU, as shown in fig. 2, including:
in step S110, a peak clipping process is performed on a baseband signal to reduce a peak-to-average ratio PAR of the baseband signal;
in step S120, performing digital predistortion on the baseband signal after the peak clipping processing to obtain a predistortion baseband signal;
in step S130, amplifying the power of the predistortion baseband signal to obtain a downlink baseband signal;
in step S140, the downlink baseband signal is transmitted to a radio remote unit RRU.
In the present disclosure, in order to digitally pre-distort and amplify the baseband signal in the BBU, thereby eliminating the DPD module in each RRU, it is necessary to ensure that the baseband signal distortion transmitted by the BBU to the RRU is within an acceptable range. In the present disclosure, the baseband signal distortion is measured by Error Vector Magnitude (EVM). The EVM includes vectors of amplitude and phase, which are the vector differences between the ideal error-free reference signal and the actual transmitted signal at a given moment, and can comprehensively measure the amplitude error and the phase error of the modulated signal. EVM is specifically defined as the ratio of the root mean square value of the mean power of the error vector signal to the root mean square value of the mean power of the ideal signal, expressed in percentage terms. The smaller the EVM, the better the signal quality.
In the technical scheme provided by the disclosure, as the DPD module in the RRU is omitted, the linear range of the power amplifier in the RRU is reduced, and the EVM lossless operating point is reduced. Therefore, the baseband signal transmitted from the BBU to the RRU needs not only distortion within an acceptable range, but also has a proper peak-to-average ratio (PAR) so that the power amplifier on the RRU can operate in a linear operating area, thereby ensuring that the radio frequency signal amplified and transmitted by the RRU also has a small EVM.
It should be noted that PAR is the ratio of the peak power of the signal to the evaluation power. Since the wireless signal is observed from the time domain as a sine wave with a constantly changing amplitude, the average power and the peak power of the signal in different periods are different. The probability of different peak power values occurring is also different. The PAR is usually the ratio of the peak power with an occurrence probability of 0.01% to the total average power of the system. The PAR at this time is also called a CREST Factor (CF). When the PAR is large, the instantaneous power of the signal exceeds the linear range of the power amplifier, which will cause the nonlinear distortion of the signal, cause the signal distortion and the increase of the noise power in the frequency band and the diffusion of the out-of-band power, and will also cause the orthogonality destruction between the sub-channels, and generate the mutual interference.
In BBU, the processed baseband signal usually has a higher PAR, and in multi-carrier transmission, the peak-to-average ratio is theoretically doubled (3dB) every time a carrier is added. Therefore, in order to enable the power amplifier on the RRU to operate in the linear operating region, in step S110, the baseband signal is subjected to peak clipping. The baseband signal is peak clipped, i.e., Crest Factor Removed (CFR) is performed, to reduce the PAR of the baseband signal. The present disclosure does not specifically limit the specific manner of CFR. For example, the signal waveform can be directly changed through signal pre-distortion to achieve the purpose of peak suppression; high PAR symbols can also be removed by coding at the cost of redundancy; and the phase combination which can obtain the lowest PAPR can be found by optimizing the carrier phase of the subchannel, so that the transmission probability of the symbol with high PAPR is reduced.
CFR reduces the PAR of the baseband signal but introduces some frequency domain harmonic distortion of the original signal due to time domain signal changes at the cost of EVM corruption. For the power amplifier system and the DPD algorithm, the harmonic distortion introduced by the CFR is not different from the harmonic distortion of the baseband signal caused by the power amplifier, and therefore, the harmonic distortion may be processed by the DPD in step S120.
The DPD technique is cascaded through a predistortion component and a PA, and the predistortion component generates a predistortion with a phase opposite to that of the amplifier, which corresponds to the amount of distortion of the amplifier. Therefore, the predistortion element and the power amplifier element have highly linear and distortion-free characteristics as a whole. The DPD enlarges the range of the linear working area of the PA and improves the efficiency of the power amplifier.
In step S120, when the baseband signal after the peak clipping is subjected to the digital predistortion processing, the predistortion parameters include harmonic distortion caused by the power amplifier and harmonic distortion introduced by the CFR, so that the harmonic distortion caused by the power amplifier and the harmonic distortion introduced by the CFR can be compensated and corrected at the same time. After the power of the predistortion baseband signal is amplified in step S130, the harmonic distortion caused by the power amplifier and the harmonic distortion introduced by the CFR are simultaneously cancelled, and the obtained downlink baseband signal has a lower EVM.
DPD is based on generating a curve symmetrical to the PA curve and then superimposing the curve with the PA curve, which results in a linear result of the overall effect, thus allowing a wider linear range of PA to be obtained without using a powerful PA.
The downlink baseband signal transmitted to the RRU in step S140 not only has a lower EVM, but also ensures that the distortion of the downlink baseband signal is acceptable; meanwhile, the radio remote unit has smaller PAR, so that a power amplifier in the RRU works in a linear working area. The RRU can directly amplify and transmit the received downlink baseband signal without pre-distortion processing.
According to the baseband signal processing method provided by the disclosure, the baseband signal is subjected to peak clipping and predistortion amplification processing on the BBU, so that the baseband signal transmitted to the RRU has a lower EVM and the distortion of the baseband signal is acceptable; meanwhile, the radio remote unit has smaller PAR, so that a power amplifier in the RRU works in a linear working area. The RRU can directly amplify and transmit the received downlink baseband signal without pre-distortion processing. Therefore, a DPD module in the RRU can be omitted, a large amount of DPD algorithm resources are saved, and the cost of the distributed base station system is reduced.
It should be noted that the power amplifier has a linear dynamic range, i.e. a linear operation region, and whether the PA operates in the linear region or the non-linear region depends on the input signal level. In the linear region, the output power of the PA increases linearly with the input power; when the PA enters the non-linear region, its output power no longer increases linearly with increasing input power, that is, its output power is lower than ideal for linear amplification. The output power level at which the gain of the PA drops to 1dB below the ideal linear gain is typically defined as the 1dB compression point of the output power, denoted by P1 dB. In this disclosure, in order to enable the power amplifier on the RRU to operate in the linear region, as an optional implementation manner, after performing peak clipping processing on the baseband signal, the PAR of the baseband signal is reduced to 6 to 8 dB. As another alternative, after the peak clipping process, the PAR of the baseband signal is reduced to 7.5 dB.
In addition, in order to ensure that the distortion of the baseband signal transmitted from the BBU to the RRU is within an acceptable range, as an optional real-time mode, in the present disclosure, after performing digital pre-distortion processing on the baseband signal after peak clipping processing and further performing power amplification, the EVM of the obtained downlink baseband signal is less than or equal to 3%.
In this disclosure, when performing digital predistortion processing on the baseband signal after peak clipping processing, a feedback signal is obtained from an output end of the PA to set predistortion parameters, and as described above, the feedback signal obtained from the output signal of the PA includes harmonic distortion introduced by the CFR and harmonic distortion of the baseband signal caused by the power amplifier, so that the harmonic distortion introduced by the CFR and the harmonic distortion of the baseband signal caused by the power amplifier can be compensated and corrected at the same time. Because the signal amplified by the PA is an analog signal, and the DPD processes a digital signal, when acquiring the feedback signal, it is necessary to sample and quantize the output signal of the PA first, and convert the analog signal into a digital signal. Correspondingly, step S120 specifically includes:
in step S121, sampling and quantizing the downlink baseband signal to obtain a feedback signal;
in step S122, the baseband signal after the peak clipping processing is subjected to digital predistortion processing according to the feedback signal, so as to obtain the predistortion baseband signal.
Since the PA can only amplify the power of the analog signal, the pre-distorted baseband signal needs to be converted to an analog signal before it is amplified. Accordingly, the baseband signal processing method provided by the present disclosure, in addition to the steps S110 to S140, as shown in fig. 4, further includes:
in step S150, the pre-distorted baseband signal is converted into an analog signal.
In a distributed base station system, a BBU and an RRU are connected via a Common Public Radio Interface (CPRI) or an evolved Common Radio Interface (eccri). The CPRI/eccri transmits baseband signals in a digital manner, defines an interface relationship between a base station data processing control unit rec (radio Equipment control) and a base station transceiver unit re (radio Equipment), and can perform multiplex transmission on information streams such as user platform data, control and management platform data, and synchronous platform data, and supports an electrical interface and an optical interface on a physical layer and mobility and scalability on a data link layer. In addition, a direction from the BBU to the RRU is referred to as a downlink direction, and a direction from the RRU to the BBU is referred to as an uplink direction. In the present disclosure, the BBU and the RRU are connected by an optical fiber, and the CPRI/eccri is specifically an optical interface. Accordingly, the baseband signal processing method provided by the present disclosure, in addition to the above steps S110 to S140, as shown in fig. 4, before step S140, further includes:
in step S160, sampling and quantizing the downlink baseband signal to obtain a digital baseband signal;
in step S170, the time delay of the digital baseband signal is adjusted according to the time delay generated when the digital pre-distortion processing is performed on the baseband signal after the peak clipping processing.
It should be noted that, in this disclosure, after the sampling quantization is performed on the downlink baseband signal, the delay generated by the DPD module is adjusted by re-adapting the sampling rate and the DPD delay, so that the DPD delay is aligned with the system synchronization and the CPRI frame. It should be noted that, in the RRU, there is also DPD delay, so that no extra delay is generated in the base station system. In the present disclosure, each RRU has a delay adjustment function, and can be aligned with an air interface (air interface) of the farthest RRU. Accordingly, as an optional implementation manner, in step S170, the DPD delay is processed on the BBU side, and only the transmission of the frame header of the uplink and downlink carrier frequencies (TRX) and the alignment of the actual TRX data need to be ensured. Therefore, only the actual delay of the CFR + DPD module needs to be measured and compensated on the TRX frame header signal. In addition, as another optional embodiment, if the DPD delay is the group delay of the RRU, the modulation of the time delay may be incorporated into the delay adjustment of the RRU, and no compensation is performed at the BBU end.
Because a delay occurs when the DPD processing is performed on the baseband signal, and the CPRI/eccri transmission signal needs to be encapsulated into a signal conforming to the CPRI/eccri frame format through the common public radio interface, as shown in fig. 4, step S140 specifically includes:
in step S141, the data in the digital baseband signal with the time delay adjusted is filled into a downlink frame of the CPRI/eccri, so as to transmit the digital baseband signal with the time delay adjusted to the RRU through the CPRI/eccri.
As a second aspect of the present disclosure, there is provided a baseband processing unit BBU, as shown in fig. 5, including:
a peak clipping processing module 110, configured to perform peak clipping processing on a baseband signal to reduce a peak-to-average ratio PAR of the baseband signal;
the digital predistortion module 120 is configured to perform digital predistortion on the baseband signal after the peak clipping processing to obtain a predistortion baseband signal;
the power amplifier 130 is configured to amplify the power of the predistortion baseband signal to obtain a downlink baseband signal;
a signal transmission module 140, configured to transmit the downlink baseband signal to a radio remote unit RRU.
As shown in fig. 7, the distributed base station system constructed by using the BBU provided by the present disclosure can omit a DPD module on the RRU without reducing the quality of radio frequency signals and affecting the performance of the base station.
According to the baseband processing unit BBU provided by the disclosure, peak clipping and pre-distortion amplification processing are performed on a baseband signal on the BBU, so that the baseband signal transmitted to the RRU has a lower EVM and the distortion of the baseband signal is acceptable; meanwhile, the radio remote unit has smaller PAR, so that a power amplifier in the RRU works in a linear working area. The RRU can directly amplify and transmit the received downlink baseband signal without pre-distortion processing. Therefore, a DPD module in the RRU can be omitted, a large amount of DPD algorithm resources are saved, and the cost of the distributed base station system is reduced.
Optionally, as shown in fig. 6, the BBU further includes:
the first analog-to-digital conversion module 150 is configured to perform sampling quantization on the downlink baseband signal to obtain a feedback signal;
the digital predistortion module 120 performs digital predistortion on the baseband signal after the peak clipping processing according to the feedback signal to obtain the predistortion baseband signal.
Optionally, as shown in fig. 6, the BBU further includes:
a digital-to-analog conversion module 160, configured to convert the pre-distorted baseband signal into an analog signal;
the power amplifier 130 amplifies the power of the analog signal to obtain the downlink baseband signal.
Optionally, as shown in fig. 6, the BBU further includes:
the second analog-to-digital conversion module 170 is configured to perform sampling quantization on the downlink baseband signal to obtain a digital baseband signal;
a delay adjusting module 180, configured to adjust a time delay of the digital baseband signal according to a delay generated by the digital predistortion module;
the signal transmission module 140 includes:
a common public radio interface (CPRI/eccri) 141, configured to stuff data in the digital baseband signal with the adjusted time delay into a downlink frame of the common public radio interface 141, so as to transmit the digital baseband signal with the adjusted time delay to the RRU through the common public radio interface 141.
Optionally, the PAR of the baseband signal after the peak reduction processing is in a range of 6 to 8 dB.
Optionally, the error vector magnitude EVM of the downlink baseband signal is less than or equal to 3%.
As a third aspect of the present disclosure, as shown in fig. 7, there is provided a base station comprising a BBU and an RRU, wherein the BBU is the BBU provided in the second aspect of the present disclosure.
As shown in fig. 7, the DPD module is omitted in the RRU. As an alternative implementation, the power amplifier in the RRU may employ a class AB power amplifier with power back-off.
The BBU in the base station provided by the third aspect of the present disclosure executes the baseband signal processing method provided by the first aspect of the present disclosure, and the principle and the beneficial effects of the baseband signal processing method have been described in detail above, and are not repeated herein.
It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.
Claims (13)
1. A baseband signal processing method is applied to a baseband processing unit (BBU) and comprises the following steps:
carrying out peak clipping processing on a baseband signal to reduce the PAR (peak-to-average ratio) of the baseband signal;
carrying out digital pre-distortion processing on the baseband signal subjected to peak clipping processing to obtain a pre-distortion baseband signal;
amplifying the power of the predistortion baseband signal to obtain a downlink baseband signal;
and transmitting the downlink baseband signal to a radio remote unit RRU.
2. The baseband signal processing method according to claim 1, wherein the step of performing digital predistortion on the baseband signal after the peak clipping to obtain a predistorted baseband signal comprises:
sampling and quantizing the downlink baseband signal to obtain a feedback signal;
and carrying out digital pre-distortion processing on the baseband signal after the peak clipping processing according to the feedback signal to obtain the pre-distortion baseband signal.
3. The baseband signal processing method according to claim 1 or 2, wherein before the step of amplifying the power of the pre-distorted baseband signal to obtain the downlink baseband signal, the baseband signal processing method further comprises:
converting the pre-distorted baseband signal into an analog signal.
4. The baseband signal processing method according to claim 1 or 2, wherein, before the step of transmitting the downlink baseband signal to a radio remote unit, RRU, the baseband signal processing method further comprises:
sampling and quantizing the downlink baseband signal to obtain a digital baseband signal;
adjusting the time delay of the digital baseband signal according to the time delay generated when the baseband signal after the peak clipping processing is subjected to digital pre-distortion processing;
transmitting the downlink baseband signal to a Radio Remote Unit (RRU), so that the step of generating a radio frequency signal by the RRU according to the downlink baseband signal comprises
And filling the data in the digital baseband signal after the time delay is adjusted into a downlink frame of a common public radio interface (CPRI/eCPRI), so as to transmit the digital baseband signal after the time delay is adjusted to the RRU through the CPRI/eCPRI.
5. The baseband signal processing method according to claim 1 or 2, wherein,
the PAR of the baseband signal after the peak reduction process ranges from 6 to 8 dB.
6. The baseband signal processing method according to claim 1 or 2, wherein,
the error vector magnitude EVM of the downlink baseband signal is less than or equal to 3%.
7. A baseband processing unit, BBU, comprising:
the peak clipping processing module is used for carrying out peak clipping processing on the baseband signal so as to reduce the PAR (peak-to-average ratio) of the baseband signal;
the digital pre-distortion module is used for carrying out digital pre-distortion processing on the baseband signal after the peak clipping processing to obtain a pre-distortion baseband signal;
the power amplifier is used for amplifying the power of the predistortion baseband signal to obtain a downlink baseband signal;
and the signal transmission module is used for transmitting the downlink baseband signal to a Radio Remote Unit (RRU).
8. The BBU of claim 7, wherein said BBU further comprises:
the first analog-to-digital conversion module is used for sampling and quantizing the downlink baseband signal to obtain a feedback signal;
and the digital predistortion module performs digital predistortion processing on the baseband signal after the peak clipping processing according to the feedback signal to obtain the predistortion baseband signal.
9. The BBU of claim 7 or 8, wherein said BBU further comprises:
the digital-to-analog conversion module is used for converting the predistortion baseband signal into an analog signal;
and the power amplifier amplifies the power of the analog signal to obtain the downlink baseband signal.
10. The BBU of claim 7 or 8, wherein said BBU further comprises:
the second analog-to-digital conversion module is used for sampling and quantizing the downlink baseband signal to obtain a digital baseband signal;
the time delay adjusting module is used for adjusting the time delay of the digital baseband signal according to the time delay generated by the digital predistortion module;
the signal transmission module comprises a common public radio interface (CPRI/eCPRI) for filling data in the digital baseband signal after the time delay is adjusted into a downlink frame of the CPRI/eCPRI, so as to transmit the digital baseband signal after the time delay is adjusted to the RRU through the CPRI/eCPRI.
11. The BBU of claim 7 or 8, wherein,
the PAR of the baseband signal after the peak reduction process ranges from 6 to 8 dB.
12. The BBU of claim 7 or 8, wherein,
the error vector magnitude EVM of the downlink baseband signal is less than or equal to 3%.
13. A base station comprising a BBU and an RRU, wherein the BBU is the BBU of any one of claims 7 to 12.
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