KR20070060279A - Crest factor reduction apparatus to optimize the performance of the each frequency allocation in cdma system - Google Patents

Abstract

A CFR(Crest Factor Reductor) having a performance optimizing function at each FA(Frequency Allocation) in a CDMA mobile communication system and a method thereof are provided to diversely adjust the quality of signals according to FAs by adjusting the amount of clipping noise applied to a specific FA and to remarkably improve the quality of high speed data services by obtaining optimal crest factor reduction effects according to FAs. A CFR having a performance optimizing function at each FA in a CDMA mobile communication system comprises a clipper(201), the first and second subtracters(202,208), a down-converter(203), a noise shaping filter part(240), an up-converter(205), a combiner(206), and a delay(207). The clipper(201) limits the strength of signals if a signal outputted from the original combiner of a base transceiver station exceeds a preset threshold. The first subtracter(202) subtracts the output signal of the clipper(201) from the output signal of the original combiner. The down-converter(203) down-converts the output signal of the first subtracter(202) and outputs a baseband signal of each FA. The noise shaping filter part(240) applies filtering coefficient values, respectively different according to FAs, to the signals outputted from the down-converter(203) and adjusts spectrums of signals of each FA. The up-converter(205) up-converts the signals of each FA outputted from the noise shaping filter part(240). The combiner(206) combines and outputs the signals outputted from the up-converter(205). The delay(207) delays and outputs the output signal of the original combiner. The second subtracter(208) subtracts a clipping signal, or the output signal of the combiner(206), from the output signal of the delay(207).

Description

Crest factor reduction apparatus to optimize the performance of the each frequency allocation in CDMA system for frequency division performance optimization in code division multiple access mobile communication systems

1 is a block diagram of a base station transmitter of a mobile communication system having a crest factor reduction apparatus according to the prior art,

FIG. 2 is a block diagram of a crest factor reduction apparatus configured in the base station transmitter of FIG.

3 is a block diagram of a crest factor reduction apparatus according to an embodiment of the present invention,

Figure 4 is a flow chart showing the processing of the crest factor reduction method according to an embodiment of the present invention.

Description of the main symbols in the drawings

100, 200: Crest factor reduction device

101, 201: Clipper 102, 202: First Substractor

103, 203: Down converter

104, 240: Noise Shaping Filter Part

104a to 104d, 241a to 244a: first to fourth noise shaping filters

241b-244b: 1st-4th RAM

105, 205: Up converter

106, 206: Combiner 107, 207: Delay

108, 208: Second subtractor

The present invention relates to an apparatus for transmitting a base station of a code division multiple access mobile communication system, and more particularly, to a frequency of downlink (downlink) in a code division multiple access mobile communication system using multiple frequencies (FA). The present invention relates to a crest factor reduction apparatus having a performance optimization function for each frequency in a code division multiple access mobile communication system capable of controlling a crest factor for each frequency allocation (FA).

In general, when a base station of a CDMA mobile communication system uses multiple frequencies FA, a crest factor increases when multiple frequencies FA are combined by a combiner. As mentioned above, the increased crest factor requires that devices with nonlinear characteristics have high performance to maintain linearity.

Therefore, in order to solve this problem, the base station transmitter of the prior art is provided with a Crest Factor Reductor (CFR) to appropriately reduce the crest factor (Crest Factor).

FIG. 1 is a block diagram of a conventional base station transmitter equipped with a crest factor reduction apparatus as described above, and FIG. 2 is a block diagram of a crest factor reduction apparatus of FIG.

In the description of FIGS. 1 and 2, the base station has four frequencies (4FA).

As shown in FIG. 1, the conventional base station transmitter transmits CDMA baseband signals for I and Q channels by FA (OFA, 1FA, 2FA, and 3FA) for the first to fourth channel cards 11 to 14. ), First to fourth digital modulators 21 to 24 which are provided in one-to-one correspondence with the first to fourth channel cards 11 to 14, and modulate a signal for each FA; A combiner 30 for coupling the respective output signals of the fourth digital modulators 21 to 24, and a crest factor reduction device (CFR) 100 for reducing and outputting a crest factor with respect to the output signal of the combiner; It is configured to include an RF (RF) unit 40 for converting the output signal of the crest factor reduction apparatus 100 to an analog signal, and then outputting the frequency after adjusting the frequency up.

In the configuration of FIG. 1, the crest factor reduction apparatus 100, as illustrated in FIG. 2, provides a clipper 101 for suggesting the magnitude of the signal when the output signal of the combiner 30 exceeds a predetermined threshold. Wow; A first subtractor (102) for subtracting the output signal of the clipper (101) from the output signal of the combiner (30); A down converter (103) for adjusting the output signal of the first subtractor (102) to frequency down and outputting the baseband signal for each frequency (FA); A noise shaping filter part 104 for performing low pass filtering for each signal FA for the signal output from the down converter 103 to adjust the spectrum of the output signal; An up converter 105 for adjusting the frequency up to the original signal for each frequency FA output from the noise shaping filter unit 104; A combiner 106 for synthesizing and outputting a signal for each frequency Fa output from the upconverter 105; A second subtractor (108) for subtracting the output signal (Clipping Signal) of the combiner (106) from the output signal of the combiner (30); Of the combiner 30 input to the second subtractor 108 to compensate for the time delay of the output signal of the combiner 30 and the output signal of the combiner 106 to the second subtractor 108. And a delay 107 for delaying an output signal and outputting the delayed signal to the second subtractor 108. In the above configuration, the down converter 103 and the up converter 105 are configured as many as the number of frequencies FA.

In the crest factor reduction apparatus 100 of FIG. 2 having the above-described configuration, the output signal of the combiner 30 is first divided into three first to third paths P1, P2, and P3. Among these, the signal of the third path P3 is input to the clipper 101, and a threshold value is outputted to a signal having an input signal exceeding a given threshold value, and if it does not exceed the threshold value, the original signal is output as it is. The signal separated from the second path P2 is input to the first subtractor 102. The signal output from the clipper 101 is input to the first subtractor 102 through the fourth path P4, and a subtraction operation is performed with the signal input through the second path P2. Accordingly, the output signal of the first subtractor 102 is a difference signal between the output signal of the combiner 30 and the signal clipped by the clipper 101. At this time, since the output signal of the first subtractor 102 is a signal that is forcibly clipped to a signal exceeding a given threshold, the frequency spectrum is broken.

Accordingly, the signal output through the first subtractor 102 is input to the down converter 103 through the fifth path P5. The signal input through the fifth path P5 is frequency-shifted to each base frequency signal to a base-band signal using four down-converters 103. A signal for each frequency FA that becomes a base-band signal is passed through a noise shaping filter 104 for each frequency FA to restore a broken spectrum. The frequency shifted by the up-converter (Up Converter) in order to convert each frequency (FA) signal thus restored into four frequency (FA) signals, combined with a combiner (Combiner) and then the second through the sixth path (P6) Output to subtractor 108.

The signal input through the first path P1 is input to a delay 107 for compensating for a time delay according to a signal processing process for the input signals of the second and third paths P2 and P2. After synchronization with the output signal of the combiner (106) is input to the second subtractor (108).

Thereafter, the second subtractor 108 subtracts the output signal of the combiner 106 from the output signal of the delayed combiner 30 input through the seventh path P7 and clipping to a given threshold value. By outputting the signal, it becomes a signal having a smaller Peak to Average Power Ratio (PAPR) than the output signal of the original combiner 30.

The prior art reduces the crest factor of the base station transmitter using the multi-frequency FA by the operation of the crest factor reduction apparatus 100 as described above, thereby reducing the linearity of elements having nonlinear characteristics according to the crest factor increase. To solve the problem of having a high performance to maintain.

In the case of the crest factor reduction apparatus 100 of the related art as described above, a noise shaping filter becomes an important factor in determining the performance of the crest factor reduction apparatus 100. That is, the performance of the CFR is determined by how low the peak to average power ratio (PAPR) is by adding a low power noise while maintaining the shape of the frequency spectrum.

However, in the crest factor reduction apparatus 100 of the prior art as described above, the noise shaping filter is optimized according to the number and location of the base station assigned frequencies FA. Therefore, since the noise shaping filter 104 is fixed to a specific coefficient value in the prior art crest factor reduction apparatus 100 has a problem that does not exhibit a proper function in all situations.

This problem makes it impossible to adjust the PAPR and EVM for each frequency FA even if the PAPR and EVM required for each frequency FA assigned to the base station are different. Therefore, when a system provides various services such as data and video as well as voice in one base station, an optimal crest factor reduction effect cannot be obtained for each frequency FA.

Accordingly, the present invention is to solve the above-mentioned problems in the prior art, by frequency of downlink (downlink) in a code division multiple access (CDMA) two-communication system using a frequency frequency allocation (FA) Frequency assigned to the mobile communication system by reducing the Crest Factor in adjusting the Average to Peak Power Ratio (PAPR) and Error Vector Magnitude (EVM) values with Frequency Allocation (FA) It is an object of the present invention to provide an apparatus and method for reducing crest factor having a performance optimization function for each frequency in a code division multiple access mobile communication system each having an optimal performance.

In the code division multiple access mobile communication system of the present invention for achieving the above object, the crest factor reduction apparatus having a frequency-specific performance optimization function, when the output signal of the original combiner of the base station transmission apparatus exceeds a predetermined threshold value of the signal size A proposed clipper; A first subtractor subtracting the output signal of the clipper from the output signal of the combiner; A down converter outputting a baseband signal for each frequency FA by down-regulating the output signal of the first subtractor; A noise shaping filter unit adjusting the spectrum of the signal for each frequency FA by applying different filtering coefficient values for each frequency FA with respect to the signal output from the down converter; An up-converter for adjusting the frequency up by each frequency FA output from the noise shaping filter unit; A combiner for combining and outputting a signal for each frequency FA output from the upconverter; A delay unit for delaying and outputting the output signal of the original coupler; And a second subtractor subtracting an output signal of the combiner from the output signal of the combiner inputted from the delayer.

In the above-described configuration, the noise shaping filter unit reads and writes at least one memory for storing the specified noise shaping filtering coefficient value according to the number of taps of the noise filter for each frequency in order to perform filtering by applying different filtering coefficient values for each frequency. Wow; And at least one noise shaping filter for performing low pass filtering by selecting the noise shaping filtering coefficients stored in the memory for each frequency.

The memory of the noise shaping filter unit may store as many coefficient values as the number of taps of the noise shaping filter.

In the code division multiple access mobile communication system of the present invention for achieving the above object, a crest factor reduction method having a performance optimization function for each frequency is provided by combining the combiner output signals of the base station transmission apparatus with three first through third paths P1 and P2. Clipping the signal of the third path P3 after dividing into P3; A first subtraction process of subtracting the signal clipped in the clipping process from the second path signal; A downverting process of outputting the signal subtracted by the first subtraction process as a base-band signal for each frequency by performing frequency down adjustment for each frequency FA; A noise shaping filtering process for applying noise shaping filtering to each baseband signal output in the down-converting process by applying a coefficient value for each frequency; Upconverting the frequency shaping of the noise shaping filtered respective frequency (FA) signals; A combine process of combining signals for each frequency FA adjusted in the up-converting process; And a second subtraction step of subtracting the combined signal by the combine process from the delayed signal after delaying the first path signal.

The delay of the first path signal of the second subtraction process may be a delay for compensating for a time delay caused by a signal processing process for input signals of the second and third paths P2 and P2.

The noise shaping filtering process may include: a filtering coefficient setting process of storing, in memory, a frequency-specific filtering coefficient having a number of taps of the noise shaping filter for the noise shaping filtering; A filtering coefficient setting step of selecting a coefficient set by the filtering coefficient setting step; And a filtering step of performing noise shaping filtering by applying the filtering coefficients.

The coefficient of the filter for each frequency is characterized in that the controllable by the user.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

Hereinafter, in the description of FIGS. 3 and 4, it is assumed that the base station transmitter has the same configuration as the base station transmitter of FIG. 1 except for the crest factor reduction apparatus 200.

3 is a block diagram of a crest factor reduction apparatus 200 according to an embodiment of the present invention.

As shown in FIG. 3, the crest factor reduction apparatus 200 includes a clipper 201 for limiting the magnitude of the signal when the output signal of the original coupler 30 of FIG. 1 exceeds a predetermined threshold value; A first subtractor (202) for subtracting the output signal of the clipper (201) from the output signal of the combiner (30); A down converter (203) for outputting a base band signal for each frequency by performing frequency down-adjustment for each frequency (FA) signal output from the first subtractor for each frequency; A noise shaping filter unit 240 for adjusting the spectrum of the signal for each frequency FA by applying different filtering coefficient values for each frequency FA with respect to the signal output from the down converter 203; An up-converter (205) for frequency-adjusting and outputting a signal for each frequency output from the noise shaping filter unit (240); A combiner 206 for synthesizing and outputting a signal for each frequency Fa output from the upconverter 205; A delay (207) for delaying and outputting the output signal of the original combiner;

A second subtractor (208) for subtracting the output signal (Clipping Signal) of the combiner (206) from the output signal of the original combiner (30) delayed by the delay (107); It is configured to include. At this time, the delay unit 207 compensates for the time delay between the output signal of the original coupler 30 and the output signal of the combiner 206 input to the second subtractor 208. Is a delay time according to a signal processing process for input signals of the second and third paths P2 and P2.

In the above-described configuration, the noise shaping filter unit 240 may read-write the noise shaping filtering coefficient value specified according to the number of taps of the noise filter for each frequency in order to perform filtering by applying different filtering coefficient values for each frequency. To fourth memories 241b to 244b; And first to fourth noise shaping filters 241a to 244a which select the noise shaping filtering coefficients of the first to fourth memories to perform low pass filtering for each frequency FA. .

In the above-described configuration, the down converter 203 and the up converter 205 are configured by the number of frequencies FA. The number of coefficients stored in each of the first to fourth memories 241b to 244b of the noise shaping filter 240 is as many as the number of taps of the first to fourth noise shaping filters 241a to 244a. Store the coefficient value of.

Figure 4 is a flow chart showing the processing of the crest factor reduction method according to an embodiment of the present invention.

Referring to FIG. 4, the operation of the crest factor reduction apparatus 200 of FIG. 3 will be described.

First, the number of filtering coefficient values corresponding to the number of taps of the noise shaping filter is stored in a read-write memory such as a RAM (S1).

The output signal of the combiner 30 of FIG. 1 is first divided into three first to third paths P1, P2, and P3. Among these, the signal of the third path P3 is input to the clipper 201, and a threshold value is output to a signal having an input signal exceeding a given threshold value, and if it does not exceed the threshold value, the original signal is output as it is. The signal separated from the second path P2 is input to the first subtractor 202 (S2).

The signal output from the clipper 201 is input to the first subtractor 202 through the fourth path P4, and a subtraction operation is performed with the signal input through the second path P2. Accordingly, the output signal of the first subtractor 202 becomes a difference signal between the output signal of the combiner 30 and the signal clipped by the clipper 201. At this time, the output signal of the first subtractor 202 is a signal that is forcibly clipped by a signal exceeding a given threshold value, and thus the frequency spectrum is broken (S3).

Therefore, in order to restore the signal clipped by the first subtractor, frequency down-adjustment is performed by the down converter for each frequency (FA) signal, and then separated into four baseband frequency (FA) signals and outputted ( S4). (Downconversion Process)

Then, the noise shaping filter unit 240 having the first to fourth noise shaping filters 241a to 244a for each frequency FA, which is a base-band signal, for each frequency FA. In step S5, the spectrum is restored according to the characteristics of each frequency FA by performing the filtering by applying the optimum coefficient value for each frequency stored in the first to fourth memories (S5). )

Each of the four frequency (FA) signals on which the noise shaping filtering process has been performed is further adjusted upward using an up converter (205) (S6).

Each frequency FA signal adjusted up in the up-converting process is combined by a combiner and output to the second subtractor 208 through a sixth path P6 (S7).

The signal input through the first path P1 is input to a delay 207 for compensating for a time delay according to a signal processing process for input signals of the second and third paths P2 and P2. After synchronization with the output signal of the combiner (206) is input to the second subtractor 208 (S8).

Thereafter, the second subtractor 208 subtracts the output signal of the combiner 206 from the output signal of the delayed combiner 30 input through the seventh path P7 and clipping to a given threshold value. By outputting the signal, the signal becomes a signal having a smaller Peak to Average Power Ratio (PAPR) than the output signal of the original combiner 30 (S9).

The crest factor reduction apparatus 200 of FIG. 3 having the above-described configuration may control data from outside, such as a RAM, using coefficients of a noise shaping filter as compared to the crest factor reduction apparatus 100 of the related art. It is characterized by implementing a filter by storing it in a memory.

That is, the above-described crest factor reduction apparatus of the present invention stores the coefficients of each noise shaping filter in an external writable memory such as RAM, and the noise shaping filter uses the coefficients as the frequency. Since the characteristics of the noise shaping filter can be arbitrarily adjusted to filter for optimal crest factor reduction by (FA), not only the PAPR and EVM characteristics but also the spectral characteristics can be adjusted. Therefore, it is possible to obtain desired characteristics for each FA simply by storing coefficients of the noise shaping filter in RAM within the allowable noise shaping filter structure and the number of taps according to the desired characteristics. .

Accordingly, the crest factor reduction apparatus 200 of FIG. 3 may optimize the characteristics of a noise shaping filter for each frequency FA, and may also reduce noise according to signal characteristics required for each frequency FA. By changing the coefficients of the noise shaping filter, the optimum crest factor reduction effect can be obtained.

If a high-speed data service, such as WCDMA's HSDPA, is required at a particular frequency, this frequency requires a low error vector magnitude (EVM). However, if you apply the general CFR, all FA's EVM will be bad. However, in the present invention, it is possible to lower only the EVM of a specific frequency (FA).

The present invention described above allows the base station to which a plurality of frequencies FA are allocated to obtain optimized performance according to the situation of a crest factor reduction device (CFR) for reducing PAPR for each frequency (FA) signal.

In addition, according to the present invention described above, it is possible to adjust the amount of clipping noise applied to a specific frequency FA, so that the quality of a signal can be adjusted differently for each frequency unit FA. In case of a high speed data service providing various services such as data and video as well as voice, this effect may reduce the optimal crest factor for each frequency if a different frequency is assigned to each high speed data service. This provides the effect of remarkably improving the quality of high-speed data services such as voice and video.

Claims (6)

A clipper for limiting the magnitude of the signal when the output signal of the original combiner of the base station transmitter exceeds a predetermined threshold; A first subtractor subtracting the output signal of the clipper from the output signal of the combiner; A down converter outputting a baseband signal for each frequency FA by down-regulating the output signal of the first subtractor; A noise shaping filter unit adjusting the spectrum of the signal for each frequency FA by applying different filtering coefficient values for each frequency FA with respect to the signal output from the down converter; An up-converter for adjusting the frequency up by each frequency FA output from the noise shaping filter unit; A combiner for combining and outputting a signal for each frequency FA output from the upconverter; A delay unit for delaying and outputting the output signal of the original coupler; And a second subtractor subtracting an output signal of the combiner from an output signal of the original combiner inputted from the delayer, for each frequency in a code division multiple access mobile communication system. Crest factor reduction device with performance optimization. The method of claim 1, wherein the noise shaping filter unit, At least one memory capable of storing noise shaping filtering coefficient values designated according to the number of taps of the noise filter for each frequency to perform filtering by applying different filtering coefficient values for each frequency; At least one noise shaping filter for performing low pass filtering by selecting the noise shaping filtering coefficients stored in the memory for each frequency; frequency in a code division multiple access mobile communication system Crest factor reduction device with star performance optimization. 3. The crest factor of claim 2, wherein the memory of the noise shaping filter unit stores coefficient values as many as the number of taps of the noise shaping filter. Reduction device. A clipping process of dividing a combiner output signal of the base station transmitter into three first to third paths (P1, P2, P3) and clipping the signal of the third path (P3); A first subtraction process of subtracting the signal clipped in the clipping process from the second path signal; A downverting process of outputting the signal subtracted by the first subtraction process as a base-band signal for each frequency by performing frequency down adjustment for each frequency FA; A noise shaping filtering process for applying noise shaping filtering to each baseband signal output in the down-converting process by applying a coefficient value for each frequency; Upconverting the frequency shaping of the noise shaping filtered respective frequency (FA) signals; A combine process of combining a signal for each frequency FA adjusted in the up-converting process; A second subtraction step of subtracting the combined signal by the combine process from the delayed signal after delaying the first path signal; and performing a frequency-specific performance optimization function in a code division multiple access mobile communication system. Eggplant crest reduction method. 5. The method of claim 4, wherein the delay of the first path signal of the second subtraction process is a delay for compensating a time delay caused by the signal processing of the input signals of the second and third paths P2 and P2. Crest factor reduction method having a frequency-specific performance optimization function in a code division multiple access mobile communication system. The method of claim 4, wherein the noise shaping filtering process A filtering coefficient setting step of storing a frequency-specific filtering coefficient having a number of taps of the noise shaping filter for the noise shaping filtering in a memory; A filtering coefficient setting step of selecting a coefficient set by the filtering coefficient setting step; And a filtering step of performing noise shaping filtering by applying the filtering coefficients. A crest factor reduction method having a performance optimization function for each frequency in a code division multiple access mobile communication system, comprising:

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