CN107104659B - Digital filtering method and device for LTE carrier - Google Patents
Digital filtering method and device for LTE carrier Download PDFInfo
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- H—ELECTRICITY
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- H03H17/00—Networks using digital techniques
- H03H17/02—Frequency selective networks
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- H03H17/0416—Recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing
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- H03H17/0444—Recursive filters with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing characterized by the ratio between the input-sampling and output-delivery frequencies the ratio being integer where the output-delivery frequency is higher than the input sampling frequency, i.e. interpolation
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- H—ELECTRICITY
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Abstract
The invention discloses a digital filtering method and a digital filtering device for an LTE carrier, wherein the method comprises the following steps: adjusting the sampling rate of the input signal and/or the output signal to adapt to the system requirement; according to the signal bandwidth, dividing signals with the bandwidth not greater than 5MHz into a group, and processing the group by a filtering module A; dividing the signals with the bandwidth of more than 5MHz into another group, and processing the other group by a filtering module B; the signal processed by the filtering module B is further processed by a time delay adjusting module, so that the consistency of time delay of two paths of signals of the filtering module A and the filtering module B is ensured; the control module completes the steps of analyzing the carrier bandwidth, controlling the switching of the filtering module A and the filtering module B and controlling the time delay adjusting module. The invention can solve the problem that certain specific LTE receiver equipment needs to switch the filtering of multiple bandwidth carriers in real time, and reasonably reduces the design complexity of a filtering system.
Description
Technical Field
The invention belongs to the technical field of filtering of wireless communication systems, and particularly relates to a digital filtering method and device for an LTE carrier.
Background
The lte (long Term evolution) project is an evolution of 3G, which improves and enhances the over-the-air access technology of 3G. OFDM and MIMO are adopted as the only standards for their wireless network evolution. The main performance goals of 3GPP LTE include: the peak rate of 100Mbps downlink and 50Mbps uplink can be provided in the 20MHz frequency spectrum bandwidth; improving the performance of cell edge users; the cell capacity is improved; reducing system delay; paired or unpaired frequency spectrums are supported, and six bandwidths can be flexibly configured, which are respectively: 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz, 20 MHz.
Fir (finite Impulse response) filters, finite single-bit Impulse response filters, also called non-recursive filters, are the most basic units in digital signal processing systems. Its advantages are high amplitude-frequency characteristics and high linear phase-frequency characteristics. This type of filter is a stable system because its unit-sample response is finite in length. FIR filters are widely used in the fields of communication, image processing, pattern recognition, etc.
The FPGA (Field Programmable Gate Array) is widely used in a communication hardware device system to complete functions such as board-level logic control, interface conversion, data transmission, algorithm processing and the like by virtue of parallel operation of internal logics, a high-speed working clock, abundant input/output pin resources, an integrated high-speed serial transceiver module, IP-Core (Intellectual Property Core) resources of a specific interface protocol and the like.
In order to adapt to various network bandwidth configuration situations of LTE and meet the requirements of post-stage signal processing, a method needs to be designed to realize a filtering function of switching six bandwidths in real time for LTE signals, so that the optimal effects of two aspects of processing speed and resource occupation of an FPGA are achieved, and the design complexity of a filtering system is reasonably reduced.
Disclosure of Invention
The invention mainly aims to overcome the defects of the prior art, provides a digital filtering method for LTE (Long term evolution) carrier waves, can solve the problem that filtering of carrier waves with various bandwidths needs to be switched in real time in certain specific LTE receiver equipment, realizes the optimal effects of the FPGA on both the processing speed and the occupied resources, and reasonably reduces the design complexity of a filtering system.
Another objective of the present invention is to overcome the disadvantages and shortcomings of the prior art, and provide a digital filtering apparatus for LTE carriers, which can solve the problem that filtering of multiple bandwidth carriers needs to be switched in real time in some specific LTE receiver devices, achieve the optimal effects of both processing speed and resource occupation of an FPGA, and reasonably reduce the design complexity of a filtering system.
The purpose of the invention is realized by the following technical scheme:
a digital filtering method for an LTE carrier, comprising the steps of:
1. adjusting the sampling rate of the input signal and/or the output signal to adapt to the system requirement;
2. according to the signal bandwidth, dividing signals with the bandwidth not greater than 5MHz into a group, processing the group by a filtering module A, and filtering at a certain sampling rate; dividing the signals with the bandwidth of more than 5MHz into another group, processing the other group by a filtering module B, and filtering at a certain sampling rate;
3. the signal processed by the filtering module B is further processed by a time delay adjusting module, so that the consistency of time delay of two paths of signals of the filtering module A and the filtering module B is ensured;
4. the control module completes the steps of analyzing the carrier bandwidth, controlling the switching of the filtering module A and the filtering module B and controlling the time delay adjusting module.
Preferably, the step of adjusting the sampling rate of the input signal and/or the output signal comprises: selecting a reasonable sampling rate for filtering, and performing 2 times of extraction operation for a plurality of times when the sampling rate is higher than the filtering requirement, so as to reduce the sampling rate to a certain value; when the sampling rate is lower than the filtering requirement, carrying out 2 times of interpolation operation for a plurality of times, and increasing the sampling rate to a certain value; and adjusting the filtered sampling rate to the same sampling rate.
Further, filtering the signal with the bandwidth not more than 5MHz at a sampling rate of 7.68 Msps; signals with bandwidths greater than 5MHz are filtered at a sample rate of 30.72 Msps.
Preferably, the method further comprises the steps of: and analyzing the filtering processes of the filtering module A and the filtering module B to obtain the time delay difference of the two modules, and writing the time delay difference into the time delay adjusting module as a parameter.
Further, when the filter coefficient of the filtering module a or the filtering module B is changed, the delay difference between the two paths needs to be analyzed again and updated to the delay adjusting module.
Preferably, the FIR coefficient reloading function is applied to the signals of different bandwidths to filter the signals in real time according to the selected filtering bandwidth: the coefficient overloading module selects different filter coefficients according to the carrier bandwidth value sent by the control module, loads the selected filter coefficients to the coefficient overloading FIR filter according to a specific time sequence, and the coefficient overloading FIR filter completes the corresponding filtering function.
Preferably, the signal with the bandwidth not greater than 5MHz comprises three cases of 1.4MHz, 3MHz and 5MHz, and the signal with the bandwidth greater than 5MHz comprises three cases of 10MHz, 15MHz and 20 MHz.
A digital filtering device for LTE carrier waves comprises a filtering module A, a filtering module B, a time delay adjusting module and a control module;
the filtering module A comprises two stages of 2-time extraction half-band filters, a first coefficient heavy-load FIR filter and two stages of 2-time interpolation half-band filters which are connected in sequence;
the filtering module B comprises a second coefficient heavy-load FIR filter, and is connected with the time delay adjusting module;
the input signal is divided into two paths according to the bandwidth, the signal with the bandwidth not more than 5MHz is processed by the filtering module A and then output, and the signal with the bandwidth more than 5MHz is processed by the filtering module B and the time delay adjusting module and then output; the control module analyzes the carrier bandwidth, controls the switching of the filtering module A and the filtering module B and controls the function of the delay adjusting module.
Preferably, the coefficient reloading FIR filter is connected with the coefficient reloading module, and the coefficient reloading module stores filter coefficients with different bandwidths.
Preferably, the delay adjusting module is implemented based on a dual-port RAM.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the invention, the six configurable bandwidths of the LTE network protocol are divided into two groups, and reasonable sampling rate is selected for filtering, so that better filtering effect can be achieved, the complexity of filtering processing is reduced, and resources such as a multiplier of an FPGA (field programmable gate array) and the like are effectively saved.
2. The invention can filter the signal in real time according to the selected filtering bandwidth by applying the FIR coefficient reloading function.
3. The invention ensures the consistent time delay of the two groups of filtering processing branches by using the time delay adjusting module.
Drawings
FIG. 1 is a schematic diagram of a processing module of an embodiment;
fig. 2 is a schematic diagram of the multi-stage filtering of the embodiment.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
The six bandwidths of the LTE network are: 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz, and 20 MHz. Dividing three conditions of 1.4MHz, 3MHz and 5MHz into a group according to the bandwidth size, and filtering at a lower sampling rate of 7.68 Msps; the three cases with the bandwidths of 10MHz, 15MHz and 20MHz are divided into another group, and filtering is carried out on the higher sampling rate of 30.72 Msps. As shown in fig. 1, the filtering module a processes the carrier with a low sampling rate, and the filtering module B processes the carrier with a high sampling rate. The filtering module A completes signal filtering with the bandwidth less than 5 MHz; and the filtering module B completes signal filtering with the bandwidth of more than 5 MHz. Because one path of filtering processing with the bandwidth less than 5MHz uses FIR filtering more than one path of filtering processing with the bandwidth more than 5MHz and filters at a lower sampling rate, the time delay of one path of signal with the bandwidth less than 5MHz is larger. In order to ensure the consistency of the time delay of the two paths of signals, a time delay adjusting module is added after the signal with the bandwidth larger than 5MHz is processed. The control module completes the functions of analyzing the carrier bandwidth, controlling the selector switch and controlling the delay adjusting module.
Specifically, the input is set to zero intermediate frequency I or Q data with a sampling rate of 122.88Msps, and the output is set to zero intermediate frequency data with a sampling rate of 30.72Msps, as shown in fig. 2.
The data to be processed is broadband zero intermediate frequency I or Q data with a sampling rate of 122.88Msps, and the broadband signal is filtered according to six bandwidths of LTE according to the system requirement; the filtered zero intermediate frequency I or Q data needs to be transmitted to the following modules at a sampling rate of 30.72 Msps. Because the sampling rate of the input signal is 122.88Msps, two times of extraction is needed, and the sampling rate is reduced to 30.72Msps so as to meet the signal filtering requirements of 10MHz, 15MHz and 20MHz bandwidths. And performing 2-time extraction on the signal with the sampling rate of 30.72Msps twice, and reducing the sampling rate to 7.68Msps so as to meet the signal filtering requirements of 1.4MHz, 3MHz and 5MHz bandwidths. Because the system requires the output signal sampling rate of the module to be 30.72Msps, a group of signals with the sampling rate of 7.68Msps needs to be subjected to two times of interpolation operation, and data with the sampling rate of 30.72Msps is obtained.
Here, a half-band filter is used to perform a 2-fold decimation or 2-fold interpolation operation and filtering. The signal with a sample rate of 122.88Msps is first passed through a two-stage 2-fold decimated half-band filter, reducing the sample rate to 30.72 Msps. Here divided into two branches. The branch B processes signals with the bandwidths of 10MHz, 15MHz and 20MHz, and performs filtering processing when the sampling rate is reduced to 30.72Msps, so that the condition of the bandwidth of 20MHz can be considered. Branch A needs to pass through a two-stage half-band filter with 2 times of extraction, and the sampling rate is reduced to 7.68 Msps. And on the basis of the sampling rate of 7.68Msps, the signals with the bandwidths of 1.4MHz, 3MHz and 5MHz are subjected to filtering processing, so that the condition of the bandwidth of 5MHz can be considered. And the sampling rate of the branch A is increased to 30.72Msps through a two-stage half-band filter with 2 times of interpolation, and the sampling rate is the same as that of the branch B, so that the subsequent processing is facilitated.
The two processing branches respectively use FIR filters with the function of coefficient reloading, the coefficient reloading module selects different filter coefficients according to the bandwidth value of a carrier wave issued by the control module, the selected filter coefficients are loaded to the coefficient reloading FIR according to a specific time sequence, and the coefficient reloading FIR completes the corresponding filter function. As shown in fig. 2, the FIR filters of the two sets of signals respectively correspond to a coefficient reloading module a and a coefficient reloading module B. The coefficient reloading module A stores filter coefficients with the bandwidths of 1.4MHz, 3MHz and 5MHz, the coefficient reloading module B stores filter coefficients with the bandwidths of 10MHz, 15MHz and 20MHz, and the two coefficient reloading modules complete the function of loading the coefficients to the corresponding coefficients.
And the time delay adjusting module is realized based on a double-port RAM and is used for adjusting the time delay consistency of the branch A and the branch B. Since the processing of branch a is complex and the filtering operation is done at a lower sampling rate, the delay introduced by branch a is larger than that introduced by branch B. In order to ensure the consistent time delay of the processing of the two branches, a time delay adjusting module is added in the branch B. And obtaining the time delay difference of the two branches according to the filtering process of the analysis branch A and the filtering process of the analysis branch B, and writing the time delay difference into a time delay adjusting module as a parameter. When the filter coefficient of branch a or branch B changes, the delay difference between the two paths needs to be analyzed again and updated to the delay adjustment module.
And finally, judging which branch of output data is selected according to the carrier bandwidth value of the control module. The design scheme fully considers the problems of saving resources and reducing design complexity, can meet the requirement of switching the filtering bandwidth in real time in the LTE signal processing process, optimizes the complexity of a filtering system and ensures the consistency of system time delay.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (10)
1. A digital filtering method for LTE carrier, characterized by comprising the following steps:
s1, adjusting the sampling rate of the input signal and/or the output signal to adapt to the system requirement;
s2, dividing the signals with the bandwidth not more than 5MHz into a group according to the signal bandwidth, processing the group by a filtering module A, and filtering at a certain sampling rate; dividing the signals with the bandwidth of more than 5MHz into another group, processing the other group by a filtering module B, and filtering at a certain sampling rate;
s3, the signals processed by the filtering module B are further processed by a time delay adjusting module, so that the consistency of time delay of the two paths of signals of the filtering module A and the filtering module B is ensured;
and S4, the control module completes the steps of analyzing the carrier bandwidth, controlling the switching of the filtering module A and the filtering module B and controlling the time delay adjusting module.
2. The digital filtering method for the LTE carrier according to claim 1, wherein step S1 comprises: selecting a reasonable sampling rate for filtering, and performing 2 times of extraction operation for a plurality of times when the sampling rate is higher than the filtering requirement, so as to reduce the sampling rate to a certain value; when the sampling rate is lower than the filtering requirement, carrying out 2 times of interpolation operation for a plurality of times, and increasing the sampling rate to a certain value; and adjusting the filtered sampling rate to the same sampling rate.
3. The digital filtering method for the LTE carrier according to claim 1, wherein the signal with the bandwidth not greater than 5MHz is filtered at a sampling rate of 7.68Msps in step S2; signals with bandwidths greater than 5MHz are filtered at a sample rate of 30.72 Msps.
4. The digital filtering method for the LTE carrier according to claim 1, wherein the step S3 further comprises the steps of: and analyzing the filtering processes of the filtering module A and the filtering module B to obtain the time delay difference of the two modules, and writing the time delay difference into the time delay adjusting module as a parameter.
5. The digital filtering method for the LTE carrier of claim 4, wherein when the filter coefficient of the filtering module A or the filtering module B is changed, the delay difference of the two paths is analyzed again and updated to the delay adjustment module.
6. The digital filtering method for the LTE carrier according to claim 1, wherein the FIR coefficient reloading function is applied to the signals with different bandwidths in step S2 to filter the signals according to the selected filtering bandwidth in real time: the coefficient overloading module selects different filter coefficients according to the carrier bandwidth value sent by the control module, loads the selected filter coefficients to the coefficient overloading FIR filter according to a specific time sequence, and the coefficient overloading FIR filter completes the corresponding filtering function.
7. The digital filtering method for the LTE carrier according to claim 1, wherein the signal with the bandwidth not greater than 5MHz includes three cases of 1.4MHz, 3MHz and 5MHz, and the signal with the bandwidth greater than 5MHz includes three cases of 10MHz, 15MHz and 20 MHz.
8. A digital filtering device aiming at LTE carrier wave based on the method of claim 1 is characterized by comprising a filtering module A, a filtering module B, a time delay adjusting module and a control module;
the filtering module A comprises two stages of 2-time extraction half-band filters, a first coefficient heavy-load FIR filter and two stages of 2-time interpolation half-band filters which are connected in sequence;
the filtering module B comprises a second coefficient heavy-load FIR filter, and is connected with the time delay adjusting module;
the input signal is divided into two paths according to the bandwidth, the signal with the bandwidth not more than 5MHz is processed by the filtering module A and then output, and the signal with the bandwidth more than 5MHz is processed by the filtering module B and the time delay adjusting module and then output; the control module analyzes the carrier bandwidth, controls the switching of the filtering module A and the filtering module B and controls the function of the delay adjusting module.
9. The digital filtering device for the LTE carrier according to claim 8, wherein the coefficient reloading FIR filter is connected to the coefficient reloading module, and the coefficient reloading module stores filter coefficients with different bandwidths.
10. The digital filtering device for the LTE carrier according to claim 8, wherein the delay adjustment module is implemented based on a dual port RAM.
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