CN100375401C - Narrowband interference eliminating method and apparatus in spread-spectrum system - Google Patents
Narrowband interference eliminating method and apparatus in spread-spectrum system Download PDFInfo
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Abstract
The present invention relates to a method and a device for eliminating narrowband interference in a spread spectrum system. The device comprises a data storage unit, an FFT conversion unit, an interference elimination unit, an IFFT conversion unit, a selection unit and an interference elimination controlling unit, wherein the interference elimination controlling unit comprises N energy calculating units, N accumulating units, an accumulation counting and controlling unit, a minimum value evaluating unit, a time averaging unit, a multiplier, a comparing unit and a position storing unit which are decided by minimum distinguishable interference bandwidth. In the method, narrowband interference signals are eliminated in the device. In the present invention, a signal is converted to a frequency domain, and a plurality of periodograms are averaged in a period of time so as to estimate a power spectrum; subsequently, the multiple of the minimum value of the obtained power spectrum serves as a narrowband interference judging threshold, and various conditions can be satisfied in a self-adaptive way so as to prevent erroneous judgment. Meanwhile, a calculated amount is obviously reduced so as to reduce the real-time calculation amount of hardware.
Description
Technical Field
The present invention relates to a method and an apparatus for eliminating narrowband interference in a wireless communication system, and more particularly, to a method and an apparatus for eliminating narrowband interference in a spread spectrum communication system.
Background
Spread spectrum communication systems are becoming more prevalent in today's world. Spread spectrum or pseudo-random code (PN) modulation may reduce interference to other users as well as wireless signals. When the interference is a narrowband signal, the interference signal may spread over the entire frequency band during the cross-correlation of the received signal and the PN sequence to reduce the effect of the interference. The spread spectrum signal can attenuate the narrowband interference to some extent.
A typical spectrum of a spread spectrum signal (e.g., spread by a PN sequence) is buried in noise, as shown in fig. 1. The ideal signal refers to the signal energy actually transmitted by the mobile station and the noise refers to those additive interferences. It is apparent that the ideal signal energy for spreading is generally less than the noise energy. "strong interference" generally refers to blocking signals or signals emitted by a television, wireless station, or nearby communication device, and "typical interference" refers to those emitted by low power sources, such as amateur radio. The processing gain represents the level of interference signals that the mobile station spread signal can tolerate. The spread signal can also be recovered when it is affected by typical interference, but the signal can no longer be recovered at all when strong interference occurs. And even with typical interference, system performance may degrade while the signal may be recovered.
Before the CDMA communication system is adopted, the frequency band is swept to protect the CDMA signal from the interference of the narrowband signal, but some burst signals are not easily completely forbidden due to their burst characteristics. The narrowband interference will exhibit disorder and randomness. Narrowband interference can increase the congestion and drop rates of Code Division Multiple Access (CDMA) systems, overload radio frequency power control systems, increase mobile station power consumption, and reduce base station coverage. In extreme cases, the high power interference may even block the entire cell, making normal communication impossible. Therefore, a good solution is needed to eliminate the influence of the narrowband interference signal on the cdma signal so as to ensure the communication quality.
Methods for dealing with narrowband interference can be generally classified into two categories:
one is to pass the signal (usually analog) through a narrow band trap or trap set. This method is generally implemented by acoustic surface-like techniques. Some estimates are made of the frequency of the interfering signal, and based on the estimates, a narrow band notch is placed where the interfering signal is present. (phase locked loops may also be used to track interfering signals.) but analog techniques have their limitations and are often inflexible.
Another type is frequency domain cancellation, which is typically implemented through digital processing. The signal is transformed to the frequency domain through Fourier transform after being digitized, and the data is transformed to the time domain for output through inverse Fourier transform after being processed in the frequency domain. The method for processing the interference signal in the frequency domain can be classified into two methods, one is to use a filter on the frequency domain data to filter the influence of the interference. This method is applicable to situations where the interference bandwidth and location are known. When the position of the interference in the frequency domain, the interference bandwidth and the number cannot be determined clearly, the method has certain limitations. Since designing a filter that is fully adaptive to changes has certain difficulties. The other is to calculate the signal amplitude at each frequency and then compare it to a threshold to set the signal above the threshold to 0 or to a noise level. The method can adaptively process a plurality of interferences and different interference bandwidths and interference frequency changes. However, how to set the threshold well in this method is a problem, and the performance of the threshold setting will be directly affected. In addition, the above methods have certain difficulties in real-time implementation of hardware, because each data sample is processed and operated during processing. The spectrum estimation is required to be carried out continuously, the power spectrum is limited within a certain range, and the requirement on the calculation amount is large for the data of the broadband system with high speed.
Disclosure of Invention
The technical problem to be solved by the present invention is to improve the second scheme in the existing frequency domain elimination technology, optimize the generation process of the threshold, so that the threshold can maintain certain stability and can adapt to the corresponding change according to the change of the channel environment, overcome the problem that the hardware in the prior art is not easy to realize in real time, and reduce the calculation amount and the complexity of the hardware.
The method comprises the following steps:
1.1 taking Fourier transform (FFT) length of the received sampling signal to store in a data storage unit, and carrying out N-point Fourier transform determined by minimum distinguishable interference bandwidth on the received signal.
1.2, the output data after Fourier transform is input into an energy calculating unit to calculate the square of the modulus of the data after N-point Fourier transform, namely the energy of the data.
1.3, outputting N-point energy data from the energy calculating unit to N accumulating units for accumulating the energy data;
1.4 when the accumulation times of the accumulation unit exceed a certain accumulation count determined by the response capability performance of the system to interference, outputting the result of the accumulation unit, and sending the result to a minimum value calculating unit to obtain a minimum value; the accumulation count is determined by an accumulation time, a number of points N of the Fourier transform, and a data sampling interval, the accumulation count being equal to the accumulation time divided by a product of the number of points and the data sampling interval. The accumulation time is generally 60 to 120ms.
1.5 the result of the accumulation unit is input into the comparison unit, and compared with the judgment threshold obtained by multiplying the minimum value output by the minimum value obtaining unit by a multiple, if the accumulation result is larger than the judgment threshold, the corresponding position information of the accumulation result in the accumulation unit is recorded, and the value of the position register unit is updated; if the accumulated result is not larger than the judgment threshold, recording the position corresponding to the accumulated result, and resetting the value of the position register unit; the multiple ranges from 2.0 to 4.0.
1.6 if the position register unit has no non-zero position record, starting the selection unit to select the signal output data stored in the data storage unit; if the position register unit has non-zero position record, the data output after the current Fourier transform adjusts the energy amplitude of the data output after the corresponding position Fourier transform according to the non-zero position information in the position register unit, and adjusts the energy to be the time average value of the minimum value output by the minimum value calculating unit.
1.7 inverse Fourier transform (IFFT) is carried out on the adjusted data and the data is output to a selection unit.
The device comprises a data storage unit, an FFT (fast Fourier transform) unit, an interference elimination unit, an IFFT (inverse fast Fourier transform) unit, a selection unit and an interference elimination control unit, wherein the FFT unit, the interference elimination unit, the IFFT unit and the selection unit are sequentially connected; the data storage unit stores the input data and transmits the input data to the selection unit; the FFT conversion unit is used for carrying out FFT conversion on the received signal and outputting the signal to the interference elimination control unit and the interference elimination unit; the interference elimination control unit calculates the energy of the input signal and carries out multiple accumulation, a certain multiple of the minimum value of the input signal is taken as a judgment threshold, and the obtained energy is compared with the threshold to obtain the position information of the estimated narrow-band interference; and outputting control information to the selection unit according to the existence of the position information, if the position information record which is not zero does not exist, the current output data is the output of the data storage unit, otherwise, the current output data is the output data of the IFFT conversion unit; the interference elimination unit modifies the result output by the FFT conversion unit by using the non-zero position information output by the interference elimination control unit and the minimum value after time averaging, and outputs the result to the IFFT conversion unit; the IFFT transforming unit IFFT-transforms the input data and outputs the result to the selecting unit.
The interference elimination control unit in the device comprises N energy calculation units, N accumulation units, an accumulation count control unit, a minimum value calculation unit, a time averaging unit, a multiplier, a comparison unit and a position register unit, wherein the N energy calculation units, the N accumulation units, the accumulation count control unit, the minimum value calculation unit, the time averaging unit, the multiplier, the comparison unit and the position register unit are determined by the minimum distinguishable interference bandwidth; the N point signals after Fourier transformation pass through the N energy calculating units to output the energy of the N point signals, the energy is sent to the N accumulating units, and then the energy is accumulated with the previous energy; the accumulation count control unit determines whether the current accumulation number reaches an accumulation count determined by a response capability of the system to the interference, wherein the accumulation count corresponds to an accumulation time. If the accumulated count is reached, outputting the result to the minimum value calculating unit to calculate the minimum value, and sending the results of the N accumulation units to the comparison unit and the minimum value unit to be compared through a judgment threshold obtained by a certain multiple of the minimum value output by the multiplier; if the result of the accumulation unit is larger than the judgment threshold, recording the corresponding position information of the value in the accumulation unit, and updating the value of the position register unit; if the result of the accumulation unit is not greater than the judgment threshold, finding the position corresponding to the value, and clearing the value of the corresponding position register unit; if the accumulated count is not reached, the position register unit is not updated, and other units process according to the result recorded by the original position register unit; the position register unit records all positions where the values are larger than the judgment threshold value, and if the values are not larger than the judgment threshold value, the values of the corresponding position register units are cleared; the time averaging unit performs an averaging operation on the output of the minimum value solving unit on the accumulated count determined by the reaction capability of the system to the interference and inputs the result into the interference elimination unit for use.
Aiming at the elimination of the narrow-band interference in a spread spectrum communication system, the invention transforms a signal to a frequency domain, estimates a power spectrum by averaging a plurality of periodograms in a period of time, and then utilizes the multiple of the minimum value of the obtained power spectrum as a judgment threshold of the narrow-band interference. The obtained threshold is very stable and can be self-adaptively met in various conditions to prevent misjudgment. Meanwhile, narrow-band interference judgment is carried out by utilizing the power spectrum estimated in a period of time, the position where the narrow-band interference occurs is recorded, the real-time data processing is only limited to the data on the position where the narrow-band interference is obtained according to the previous period of time, and the calculated amount is obviously reduced. And the minimum value calculation and the comparison operation are performed at intervals, and each section of data is not required to be operated, so that the requirement of hardware on real-time processing is greatly reduced. Compared with the prior art, the method can obtain satisfactory performance and greatly reduce the real-time calculation amount of hardware as long as the selection of the accumulation time length is correct. The invention also designs a selection unit, and can shield the execution of a module with larger calculation amount, such as an IFFT transformation unit, when no narrow-band interference exists, thereby further reducing the occupation of hardware resources. In a word, the method is simple in calculation, has obvious effect of inhibiting the narrow-band interference, can be realized by hardware in real time, and reduces the requirement on the hardware.
Drawings
Fig. 1 is a diagram of the spectral energy of a typical spread spectrum signal.
Fig. 2 is a schematic diagram of the operation of the apparatus of the present invention.
Fig. 3 is a schematic diagram of an interference cancellation control unit in fig. 2.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples.
Fig. 1 is a diagram illustrating spectrum energy of a general spread spectrum signal, which has been described in detail in the background art and is not described herein again.
FIG. 2 is a schematic diagram of the operation of the apparatus of the present invention, wherein the apparatus parts of the present invention are enclosed. Fig. 3 is a schematic diagram of the interference cancellation control unit 180 in fig. 2. The invention is described below in connection with fig. 2 and 3.
The signal is received by the rf converter 100, then sampled by the digital quantizer 110 to become a digital signal, and input to the interference cancellation device 120 of the present invention. The interference cancellation apparatus 120 of the present invention includes a data storage unit 130, an FFT transformation unit 140, an interference cancellation unit 150, an IFFT transformation unit 160, a selection unit 170, and an interference cancellation control unit 180. The received digital signal takes N points at a time and enters the interference cancellation device 120 for FFT operation. The number of points N taken is related to the minimum distinguishable narrowband interference bandwidth. In one embodiment of the invention, the bandwidth of the spread spectrum signal is 1.2288MHz, the data sampling rate is 2 × 1.2288MHz, and in order to distinguish the narrowband interference of 30kHz, at least 2 × 1.2288 × 10^ 6/(30 × 10^ 3) =81.92 points, namely 128-point FFT is adopted. Obviously, the more the number of points of the FFT is, the stronger the resolution capability of the FFT is on the narrow-band interference, and the larger the calculation amount of hardware realization is, the N value can be actually selected according to the identification precision of the own system and the requirement on the narrow-band interference. N =256 was adopted in the above embodiment. The FFT unit 140 performs N-point FFT operation, and the data storage unit 130 stores N-point data before entering the FFT unit 140. The N point data from the FFT conversion unit 140 is input to the interference cancellation unit 150 and the interference cancellation control unit 180. If the location register 188 in the interference elimination unit 180 does not indicate any location information, the selection unit 170 directly outputs the data stored in the data storage unit 130 without performing the operations of the interference elimination unit 150 and the IFFT transformation unit 160, thereby reducing the operations of hardware and saving the hardware overhead. If the location registering unit 188 indicates location information, the interference canceling unit 150 processes the N-point FFT result using the location information output from the location registering unit 188 and the output information of the minimum value time averaging unit 189, and adjusts the energy value of the location data corresponding to the location registering unit 188 to the minimum value after time averaging. And outputs the result to the IFFT transforming unit 160 for IFFT transformation. And then output by the selection unit 170 to a subsequent processing unit (e.g., despreading, etc., shown last in the figure). The interference cancellation control unit 180 completes updating the contents of the position register unit 188 and the minimum value 184 at intervals.
The interference cancellation control unit 180 includes N energy calculating units 181, N accumulating units 182, an accumulation count control output 183, a minimum unit 184, a multiplier 185, a comparing unit 187, a position registering unit 188, and a time averaging unit 189. The output of the FFT unit 140 is a complex signal, and the energy calculating unit 181 calculates the square of the modulus of the complex signal. N energy calculating units are metersThe result of the square of the modulus of the N FFT output signals is calculated. It is obvious that the above calculation results in a periodogram for the data segment. The periodogram is an estimate of the power spectrum in which a normal wideband signal is buried in noise, while a narrowband interferer is powerful because the energy is concentrated at some frequency points. For better power spectrum estimation, the accumulation unit 182 performs accumulation of the periodogram results over a period of time. The accumulation allows the estimation result to better approximate the actual power spectrum and thus reflect more realistic data characteristics. In order to enable the power spectrum estimation result to reflect the change of the narrowband interference on the spread spectrum signal in time, the accumulation time is not easy to be too long, generally, the duration of the narrowband interference is in the order of seconds, therefore, the accumulation time can be 60-120 ms, and the value does not cause great influence on the response capability of the system to the narrowband interference. In one embodiment of the present invention, about 106.7ms is selected as the accumulated time length, and the simulation result shows that the selection of the length does not affect the capability of the system to eliminate the narrow-band interference and can obtain a relatively stable power spectrum estimation result. The accumulated count being in correspondence with an accumulation time, accumulatedThe count will vary depending on the accumulation time selected and the number of points N of the FFT. In one embodiment of the present invention, the number of FFT points is 256, the data sampling rate is 2 × 1.2288MHz, and the duration of each sample point is 256
The accumulated count is
The accumulation control output 183 completes control of the accumulation time, and determines whether the current accumulation number reaches the accumulation count number by the control of the accumulation time. The accumulated count or accumulated time is determined according to the performance requirements that the system is expected to achieve, for example, if the system is expected to be stable, the accumulated count or accumulated time is higher, and if the system is expected to react faster to the external interference, the accumulated count or accumulated time is lower. When the accumulated count does not reach the designated time, the minimum value unit 184 and the position register sheet are not performedAn update of element 188; when the count of accumulation reaches a predetermined time, the minimum value section 184 and the position register section 188 are updated and the accumulation section 182 is cleared. Minimum unit 184 finds the minimum of the N accumulation units. The minimum value is not taken as the average value, because the power spectrum is stable at this time, and the value is not too low. The mean value is greatly affected by the variation of the number and intensity of the narrow-band interference. In addition, the minimum value is required only by some comparison operations, and the calculation amount is small. The multiplier 185 multiplies the minimum value by a multiple to serve as a judgment threshold of the narrowband interference. In order to prevent useful signals from being influenced by interference, the performance of a final system is influenced by selecting the multiple, and through simulation, the value range of the multiple can be 2.0-4.0 generally. After the threshold is determined, the N accumulated energies output by the accumulated numerical control unit 183 are compared in the comparing unit 187, and finally, the position where the energy value greater than the threshold is located is placed in the position registering unit 188, and if the energy value is not greater than the threshold, the value of the corresponding position registering unit is cleared. The position register unit 188 and the minimum value unit 184 are updated at regular intervals, so that the self-adaptive change along with the change of the surrounding situation can be realized, and a better effect is achieved. The interference cancellation unit 150 requires the output result of the minimum unit 184, because the operations after the accumulation output are all comparison operations, and it is not useful to perform averaging, but the interference cancellation unit 150 requires a single set of data processing, and therefore, a time averaging unit 189 is required. The value obtained by the time averaging unit 189 is input to the interference canceling unit 150, and the interference canceling operation is completed.
The invention has been realized in the CDMA-20001 x reverse link simulation, and the simulation proves that the invention can effectively weaken the influence of a plurality of narrow-band interferences on the system at different time and different frequency band positions, so that the CDMA congestion rate and the call drop rate are obviously reduced, and the power consumption of the mobile station is reduced.
Claims (6)
1. A method for narrowband interference cancellation in a spread spectrum system, comprising the steps of:
1.1 taking Fourier transform length from received sampling signal to store in data storage unit, and carrying out N-point Fourier transform determined by minimum distinguishable interference bandwidth on received signal;
1.2, inputting the output data after Fourier transform into an energy calculating unit to obtain the energy of the data after N-point Fourier transform;
1.3 outputting N-point energy from the energy calculating unit to N accumulating units for energy accumulation;
1.4 when the accumulation times of the accumulation unit exceed the accumulation count determined by the response capability of the system to the interference, outputting the result of the accumulation unit, and sending the result to a minimum value solving unit to obtain a minimum value;
1.5 the result of the accumulation unit is input into the comparison unit, and compared with the judgment threshold obtained by multiplying the minimum value output by the minimum value obtaining unit by a multiple, if the accumulation result is larger than the judgment threshold, the corresponding position information of the accumulation result in the accumulation unit is recorded, and the value of the position register unit is updated; if the accumulated result is not larger than the judgment threshold, recording the position corresponding to the accumulated result, and resetting the value in the position register unit;
1.6 if the position register unit does not have any non-zero position record, starting the selection unit to select the signal output data stored in the data storage unit; if the position register unit has non-zero position record, the data output after the current Fourier transform adjusts the output data after the corresponding position Fourier transform according to the non-zero position information in the position register unit, and adjusts the energy of the output data to be the time average value of the minimum value output by the minimum value calculating unit;
1.7, the adjusted data is output to a selection unit through inverse Fourier transformation.
2. The method of claim 1 wherein the multiple of step 1.5 is in a range of 2.0 to 4.0.
3. A method for narrowband interference cancellation in a spread spectrum system as claimed in claim 1, characterised in that the accumulation count in step 1.4 is determined by the accumulation time, the number N of fourier transforms and the data sampling interval, the accumulation count being equal to the accumulation time divided by the product of the number N of samples and the data sampling interval.
4. A method for narrowband interference cancellation in a spread spectrum system according to claim 3, characterised in that the accumulation time is 60-120 ms.
5. A device for eliminating narrow-band interference in a spread spectrum system comprises a data storage unit, a Fourier transform unit, an interference elimination unit, an inverse Fourier transform unit, a selection unit and an interference elimination control unit, wherein the Fourier transform unit, the interference elimination unit, the inverse Fourier transform unit and the selection unit are sequentially connected;
the data storage unit stores the input data and transmits the input data to the selection unit; the Fourier transformation unit performs Fourier transformation on the received signal and outputs the signal to the interference elimination control unit and the interference elimination unit; the interference elimination control unit calculates the energy of the input signal and carries out multiple accumulation, a certain multiple of the minimum value of the input signal is taken as a judgment threshold, and the obtained energy is compared with the threshold to obtain the position information of the estimated narrow-band interference; and outputting control information to the selection unit according to the existence of the position information, if the non-zero position information record does not exist, the current output data is the output of the data storage unit, otherwise, the current output data is the output data of the inverse Fourier transform unit; the interference elimination unit modifies the result output by the Fourier transformation unit by using the non-zero position information output by the interference elimination control unit and the minimum value after time averaging, and outputs the result to the inverse Fourier transformation unit; the inverse Fourier transform unit performs inverse Fourier transform on the input data and outputs the result to the selection unit.
6. The apparatus for narrowband interference cancellation in a spread spectrum system of claim 5,
the interference elimination control unit comprises N energy calculation units, N accumulation units, an accumulation count control unit, a minimum value solving unit, a time averaging unit, a multiplier, a comparison unit and a position register unit, wherein the N energy calculation units, the N accumulation units, the accumulation count control unit, the minimum value solving unit, the time averaging unit, the multiplier, the comparison unit and the position register unit are determined by the minimum distinguishable interference bandwidth; the N point signals after Fourier transformation pass through the N energy calculation units to output the energy of the N point signals, the energy is sent to the N accumulation units, and then the energy is accumulated with the previous energy; the accumulation count control unit determines whether the current accumulation number of times reaches an accumulation count determined by a response capability of the system to interference:
if the accumulated count is reached, outputting the result to the minimum value calculating unit to calculate the minimum value, and sending the results of the N accumulated units to the comparing unit to be compared with a judgment threshold obtained by the minimum value unit through a certain multiple of the minimum value output by the multiplier; if the result of the accumulation unit is larger than the judgment threshold, recording the corresponding position information of the value in the accumulation unit, and updating the value of the position register unit; if the result of the accumulation unit is not larger than the judgment threshold, finding the position corresponding to the value, and clearing the value in the corresponding position register unit;
if the accumulated count is not reached, the position register unit is not updated, and other units process according to the result recorded by the original position register unit;
the position registering unit records all positions where the positions are larger than the judgment threshold, and clears the rest positions; the time averaging unit performs an averaging operation on the output of the minimum value calculating unit on the accumulation count determined by the system performance and inputs the output to the interference cancellation unit for use.
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| CN101136654B (en) * | 2007-06-06 | 2010-09-08 | 中兴通讯股份有限公司 | Method and device for eliminating narrow-band interference in communication system |
| CN101902426B (en) * | 2009-05-27 | 2012-12-19 | 中兴通讯股份有限公司 | Method and device for realizing decimal frequency deviation estimation |
| CN101604985B (en) * | 2009-07-20 | 2013-04-24 | 重庆大学 | Method and device for eliminating time-domain narrowband interference of direct sequence spread spectrum communication system |
| CN111752527A (en) * | 2019-03-29 | 2020-10-09 | 刘启庆 | Accumulation management device and accumulation management system |
| CN115622581B (en) * | 2022-12-19 | 2023-03-10 | 长沙先度科技有限公司 | Frequency domain anti-interference method for non-cooperative communication signals under non-ideal channel |
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| CN1341306A (en) * | 1999-12-28 | 2002-03-20 | 松下电器产业株式会社 | Interfering signal removing device and interfering signal removing method |
| WO2004109961A2 (en) * | 2003-05-22 | 2004-12-16 | Canada Interworld Telecommunications Inc. | Method and apparatus for transceivers in wireless communications using ofdm spread spectrum |
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| CN1341306A (en) * | 1999-12-28 | 2002-03-20 | 松下电器产业株式会社 | Interfering signal removing device and interfering signal removing method |
| WO2004109961A2 (en) * | 2003-05-22 | 2004-12-16 | Canada Interworld Telecommunications Inc. | Method and apparatus for transceivers in wireless communications using ofdm spread spectrum |
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