JP4108699B2 - Frequency offset estimation device - Google Patents

Description

  The present invention relates to a signal processing technique, and more particularly to a frequency offset estimation apparatus in wireless communication.

In a wireless communication system, when a receiving apparatus receives a signal transmitted from a transmitting apparatus, a frequency offset occurs due to instability of a signal oscillated from a crystal or the like used in the transmitting apparatus and the receiving apparatus. Generally, the frequency offset is estimated and corrected using the received signal. Furthermore, in an environment where frequency selective fading occurs, the frequency component of the signal is locally reduced, making it difficult to accurately estimate the frequency offset even when using a received signal that is a time domain signal. . Conventionally, with respect to such a problem, the signal is converted into a plurality of frequency domain signals using Fast Fourier Transform (FFT), and the frequency corresponding to the maximum value of the signal amplitude in the frequency domain is converted to It was detected as an offset (see, for example, Patent Document 1). Moreover, the frequency offset was estimated using the known signal contained in the signal of a frequency domain (for example, refer patent document 2).
Japanese Patent Laid-Open No. 3-171954 (FIG. 1) Japanese Patent Laid-Open No. 2003-018116 (FIG. 3)

  Under such circumstances, the present inventor has come to recognize the following problems. That is, there is a problem that the detection accuracy of the frequency offset is lowered under an unfavorable condition where there is no known signal and there is a lot of noise.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a frequency offset capable of accurately detecting a frequency offset even under adverse conditions where there is no known signal and there is a lot of noise. It is to provide an estimation device.

  In order to solve the above-described problem, a frequency offset estimation device according to an aspect of the present invention includes an input unit that sequentially inputs signals, and at least a part of a frequency band of the signal input to the input unit. At least one of a dividing unit that divides the signal into a plurality of signals, an integrating unit that integrates signals of a plurality of partial bands divided by the dividing unit for each partial band, and an integrated value for each partial band integrated by the integrating unit A frequency offset output unit that detects one integrated value and outputs a partial band corresponding to the detected integrated value as a value of a frequency offset included in the input signal.

  Here, “at least a part of the frequency band of the input signal” includes a frequency band to which at least a part of the frequency components among all the frequency components included in the input signal belongs. The “plurality of partial bands” includes a band included in at least a part of the frequency band of the input signal, and the bandwidth of each partial band may not be constant. Further, “dividing into signals of a plurality of partial bands” means, for example, at least a part of an input signal using a discrete Fourier transform (DFT), a fast Fourier transform (FFT), a wavelet transform, or the like. Dividing the frequency band into a plurality of partial bands. “Detecting at least one integrated value” includes detecting some integrated values of the integrated values, for example, detecting the top three integrated values.

  According to this aspect, since the frequency offset is estimated based on the integrated result, the influence of noise and the like can be reduced, and the frequency offset can be detected with high accuracy.

  The frequency offset output unit includes a search unit that searches for an integrated value having the largest value among the integrated values for each partial band integrated by the integrating unit, the integrated value searched by the search unit, and a predetermined threshold value. When the integrated value is larger as a result of comparison in the comparing unit and the comparing unit, the integration in the integrating unit is stopped, and the output control unit that outputs the partial band corresponding to the integrated value as a frequency offset, May be included.

  Here, “the partial band corresponding to the integrated value” corresponds to a partial band that is an object of integration in order to obtain the integrated value. “As a frequency offset included in the input signal as a partial band” includes, for example, setting any one of the frequency bands included in the partial band as a frequency offset. For example, the center of the frequency band included in the partial band Including frequency. “Frequency offset” is referred to as frequency error, frequency shift, phase rotation, or the like.

  According to this aspect, since the integrated value having the largest value is used as a reference for frequency offset detection, the reliability of frequency offset detection can be improved.

  The output control unit may extend the integration in the integration unit when the predetermined threshold is larger as a result of the comparison in the comparison unit. According to this aspect, as a result of the comparison in the comparison unit, when the predetermined threshold value is larger, that is, when the searched integrated value is smaller than the threshold value, it can be determined that the influence of noise or the like is large. The integration in the integration unit is extended to improve the reliability of frequency offset detection.

  You may further provide the signal strength measurement part which measures the signal strength of the input signal. The integration unit may perform integration while weighting a plurality of partial bands in accordance with the signal intensity measured by the signal intensity measurement unit.

  According to this aspect, the estimation time can be shortened by performing integration processing after weighting a signal having high signal strength and high reliability with a larger weighting factor.

  The frequency offset output unit may weight the predetermined threshold according to the signal strength measured by the signal strength measurement unit.

  According to this aspect, the threshold value is weighted with a small weighting factor for a highly reliable signal, and the weighted threshold value is used as a comparison target, thereby reducing the frequency offset estimation criterion and shortening the estimation time. . On the other hand, when the reliability of multiple partial bands is low, the threshold is weighted with a large weighting factor, and the weighted threshold is used as a comparison target, thereby raising the frequency offset estimation criteria and improving the estimation accuracy. Improve.

  As a result of comparison in the frequency offset output unit, the division unit targets a band that is different from some of the already divided frequency bands of the input signal when there is no integrated value greater than the threshold value. As an alternative, the division of the signals of a plurality of partial bands may be performed.

  Here, “when it does not exist” includes a case where any of the integrated values calculated over a predetermined number of times is smaller than a threshold value. The “integrated value” includes, for example, adding a frequency band at a certain time and a signal of a frequency band at another time for each partial band in the input signal. The “integrated value calculated over a predetermined number of times” includes sequentially increasing the number of signals in the frequency band to be integrated. The integrated value calculated over a predetermined number of times may be a value obtained by moving average processing or the like. As the number of calculations increases, the time required for integration processing increases, while the influence of noise and the like is averaged, and the estimation accuracy can be improved.

  According to this aspect, when there is no integrated value greater than the threshold value, it is determined that there is no frequency offset in the first place, and a band different from a part of the already divided bands is targeted. Thus, the frequency offset detection time can be reduced.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, a frequency offset can be detected with high accuracy.

  Before describing the present invention in detail, an outline will be described. An embodiment of the present invention relates to a frequency offset estimation apparatus that estimates a frequency offset in a wireless communication terminal that receives a continuous signal, for example. The frequency offset estimation apparatus according to the present embodiment analyzes the received signal in the frequency domain and estimates the frequency offset. That is, the frequency band of the received signal is divided into a plurality of partial bands, and the partial band having the maximum strength among the signal strengths included in the plurality of partial bands is estimated as a frequency offset. In addition, the received signal is sequentially divided while shifting the time, and a plurality of partial bands obtained are averaged to remove the influence of noise and the like as much as possible. Details will be described later.

  First, a configuration example of a frequency offset estimation apparatus according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram illustrating a configuration example of a wireless communication terminal device according to an embodiment of the present invention. FIG. 1 shows only the configuration related to the radio signal reception process. The wireless communication terminal device includes an antenna 10, an RF (Radio Frequency) processing unit 11, an A / D (Analog to Digital) conversion unit 12, a frequency correction unit 16, and a demodulation unit 18. The antenna 10 receives a radio signal transmitted from a counterpart device communicating with the radio communication terminal device. The RF processing unit 11 down-converts the radio signal received by the antenna 10 to a baseband and outputs the signal to the A / D conversion unit 12. The A / D converter 12 converts the signal processed by the RF processor 11 into a digital signal. The frequency correction unit 16 includes a frequency offset estimation device to be described later, and estimates the frequency offset using the digital signal output from the A / D conversion unit 12. The digital signal output from the A / D conversion unit 12 is corrected using the estimated frequency offset. The demodulator 18 performs processing such as deinterleaving, demodulation processing, and error correction decoding on the signal whose frequency offset has been corrected by the frequency correction unit 16.

  FIG. 2 is a diagram illustrating a configuration example of the frequency correction unit 16 of FIG. The frequency correction unit 16 includes a frequency offset estimation unit 100 indicated by a broken line, an oscillator control unit 26, a local (Local) oscillator 28, a frequency mixer 30, and an LPF 14 (Low Pass Filter). The frequency offset estimation unit 100 includes an FFT 20, an integration unit 22, and a frequency offset output unit 24. In FIG. 2, the frequency offset is corrected by feedback control using the input of the frequency offset estimation unit 100 as the subsequent stage of the frequency mixer 30. However, the present invention is not limited to this, and the input of the frequency offset estimator 100 may be the previous stage of the frequency mixer 30 and the frequency offset may be corrected by feedforward control.

  The LPF 14 limits the band of the signal output from the frequency mixer 30 described later. Note that carrier regeneration may be performed by providing a multiplier and a unit circulator after the LPF 14.

  The FFT 20 divides at least a part of the frequency band of the signal output from the LPF 14 into a plurality of partial band signals. In the following description, the number of partial bands divided by the FFT 20 is assumed to be M. M is a positive integer. The “partial band” is called “FFT point” or “bin”. In the following description, “partial band” is referred to as “FFT point”.

This will be described using an example. Assume that a series of input signals input to the FFT 20 is S (j). j is a positive integer of 1 to N × M. N is a positive integer and may be the number of memories 34 to be described later. The FFT 20 processes S (j) every M pieces, and outputs the processed signal as M FFT point signals D (t, k). Here, t is a positive integer of 1 or more and N or less, and is a value that increases every time the FFT 20 performs FFT processing. K is a positive integer of 1 to M. Then, the output by the FFT 20 can be expressed as follows. Here, FFT () is a function indicating the dividing process in the FFT 20.
D (t, k) = FFT (S (t × M + k))) Equation (1)

  The accumulating unit 22 accumulates signals of a plurality of FFT points divided by the FFT 20 for each FFT point. Here, “integrating signals of a plurality of FFT points for each FFT point” includes adding each FFT point every time a signal in the frequency band is output from the FFT 20. For example, in the first “integration”, only a signal for each FFT point first output from the FFT 20 is output. Details will be described later.

  The frequency offset output unit 24 detects at least one integrated value among the integrated values for each FFT point integrated by the integrating unit 22, and the frequency offset included in the input signal includes the FFT point corresponding to the detected integrated value. Output as. Here, the “FFT point corresponding to the integrated value” includes the FFT point from which the integrated value is obtained. “As an FFT point as a frequency offset included in the input signal” includes, for example, setting any one of the frequency bands of the FFT point as a frequency offset. For example, the center of the frequency band of the FFT point Including frequency. “Frequency offset” is referred to as frequency error, frequency shift, phase rotation, or the like. Details will be described later.

  The oscillator control unit 26 controls the local oscillator 28 using the frequency offset output from the frequency offset output unit 24 of the frequency offset estimation unit 100. Specifically, the local oscillator 28 is caused to generate a frequency signal so that the received signal is frequency-shifted by a frequency mixer 30 described later by the frequency offset output from the frequency offset output unit 24. The oscillator control unit 26 may instruct the local oscillator 28 together with the generation timing of the frequency signal.

  The local oscillator 28 generates a frequency signal at a desired timing in accordance with an instruction from the oscillator control unit 26 and outputs the frequency signal to the frequency mixer 30.

  The frequency mixer 30 superimposes the frequency signal output from the local oscillator 28 and the signal output from the A / D converter 12 and outputs the result to the demodulator 18 and the frequency offset estimator 100. As a result, the signal output from the A / D converter 12 is frequency shifted by an amount corresponding to the frequency of the frequency signal output from the local oscillator 28.

  Here, a configuration example of the integrating unit 22 will be described in detail with reference to FIG. FIG. 3 is a diagram illustrating a configuration example of the integrating unit 22 of FIG. The accumulating unit 22 includes an intensity deriving unit 32A, an intensity deriving unit 32B, an intensity deriving unit 32M, which are collectively referred to as an intensity deriving unit 32, a memory 34A, a memory 34B, a memory 34N, and an accumulation control unit 36. including.

Since the intensity deriving unit 32 is a block that receives signals of M FFT points that are outputs of the FFT 20, the integrating unit 22 includes M intensity deriving units 32. The intensity deriving unit 32 processes the FFT point signals D (t, k) output from the FFT 20 as follows, and outputs the signals as Dout (t, k), respectively. Here, ω represents an angular frequency.
Dout (t, k) = | Itk | + | Qtk | (2)
Itk = D (t, k) cos (ωk) (3)
Qtk = D (t, k) sin (ωk) (4)

The strength deriving unit 32 may derive the strength using the following equation (5) instead of the equation (2).
Dout (t, k) = | Itk | ² + | Qtk | ² Expression (5)

  Each of the memories 34 stores M FFT point signals output from the intensity deriving unit 32. The signals of M FFT points stored in the memories 34 are adjacent each time the value of t increases, that is, whenever the next M FFT point signals are output from the intensity deriving unit 32. To the memory 34. For example, it is assumed that Dout (1, k) and k = 1 to M are stored in the memory 34A at t = 1. Next, at t = 2, Dout (1, k) is moved from the memory 34A to the memory 34B, and Dout (2, k) is output from the intensity deriving unit 32 and stored in the memory 34A. In other words, the memory 34 can be said to be a FIFO buffer that sequentially shifts the signal for each FFT point. Note that it is assumed that t = 0, that is, 0 is stored in all memories 34 in the initial state.

The integration control unit 36 reads Dout (t, k) stored in each memory 34 and performs integration processing according to the following equation (6).
^{_{Y T (k) = Σ T}} t = 1 Dout (t, k) ··· (6)
Here, T is a value of t at the time when the integration process is performed. For example, at t = 1, Y ₁ (k) = Dout (1, k), and at t = 2, Y ₂ (k) = Dout (1, k) + Dout (2, k). . That is, as the value of t increases, the objects to be added also increase. In other words, the noise components included in Dout (t, k) are averaged, and the influence is reduced.

  The integration control unit 36 stops the integration process according to an instruction from the frequency offset output unit 24 described later. At this time, all values stored in the memory 34 may be initialized to zero.

  Here, a configuration example of the frequency offset output unit 24 will be described in detail with reference to FIG. FIG. 4 is a diagram illustrating a configuration example of the frequency offset output unit 24 of FIG. The frequency offset output unit 24 includes a search unit 40, a comparison unit 42, and an output control unit 44.

The search unit 40 searches for the integrated value MAX (Y _T (k)) having the largest value among the integrated values Y _T (k) for each FFT point integrated by the integrating unit 22.

The comparison unit 42 compares the integrated value MAX (Y _T (k)) searched by the search unit 40 with a predetermined threshold value.

When the integrated value MAX (Y _T (k)) is larger as a result of the comparison by the comparing unit 42, the output control unit 44 stops the integration in the integrating unit 22, and the integrated value MAX (Y _T (k)). The FFT point corresponding to is output to the oscillator control unit 26 as a frequency offset.

  Here, “cancel” means to stop the integration process, etc., and the integration process may be initialized. In addition, the dividing process in the dividing unit may be stopped along with the stop of the process integration process.

  As a result of comparison in the comparison unit 42, the output control unit 44 extends the integration in the integration unit 22 when the predetermined threshold value is larger. That is, the value of t is increased, the number of integration targets is increased, and a more reliable integrated value is generated.

  By adopting the configuration as described above, the frequency offset is obtained based on the integrated result, so that the influence of noise and the like can be reduced, and the frequency offset can be detected with high accuracy.

  Next, the operation of the frequency correction unit 16 in FIG. 2 will be described with reference to FIGS. 5A to 5E, FIG. 6, and FIG.

  First, operations of the integrating unit 22 and the frequency offset output unit 24 of FIG. 2 according to the embodiment of the present invention will be described in detail with reference to FIGS. 5 (a) to 5 (e). FIG. 5A to FIG. 5E are diagrams showing examples of input / output signals of the integrating unit 22 in FIG. 2 at t = 1-3. FIG. 5A to FIG. 5E are diagrams showing frequency distributions with the vertical axis representing frequency and the horizontal axis representing intensity. Here, the number M of FFT points is set to 10 and indicated by f0 to f9 in the figure.

FIG. 5A is a diagram illustrating the input signal Dout (1, k) of the integrating unit 22 of FIG. 2 at t = 1. FIG. 5A is also a diagram showing signals stored in the memory 34A at t = 1. FIG. 5A is also a diagram illustrating a result Y ₁ (k) obtained by integrating each FFT point by the integration control unit 36 in FIG. 3 at t = 1. This is because, at t = 1, the other memories except the memory 34A are in the initial state, and Dout (1, k) becomes the integration result as it is. FIG. 5A is also a diagram showing signals stored in the memory 34B of FIG. 2 at t = 2. This is because the signal stored in the memory 34 is transferred in order each time t increases. Similarly, FIG. 5A is a diagram showing signals stored in a memory 34C (not shown) at t = 3.

FIG. 5B is a diagram illustrating the input signal Dout (2, k) of the integrating unit 22 in FIG. 2 at t = 2. FIG. 5B is also a diagram illustrating signals stored in the memory 34A at t = 2. FIG. 5B is a diagram showing signals stored in the memory 34B at t = 3. FIG. 5C is a diagram illustrating a result Y ₂ (k) obtained by integrating each FFT point by the integration control unit 36 in FIG. 2 at t = 2. That is, FIG. 5C shows the result of integrating the signals Dout (t, k) of t = 1 to 2 for each FFT point in FIGS. 5A and 5B.

FIG. 5D is a diagram showing the input signal Dout (3, k) of the integrating unit 22 in FIG. 2 at t = 3. FIG. 5D is also a diagram illustrating signals stored in the memory 34A at t = 3. FIG. 5E is a diagram showing a result Y ₃ (k) obtained by integrating each FFT point by the integration control unit 36 in FIG. 3 at t = 3. That is, FIG. 5 (e) shows the result of integrating the signals Dout (t, k) of t = 1 to 3 for each FFT point in FIGS. 5 (a), 5 (b), and 5 (d). ing.

Here, the search unit 40 in FIG. 4 when the input signals of the integration unit 22 in FIG. 2 at t = 1 to 3 are respectively FIG. 5 (a), FIG. 5 (b), and FIG. 5 (d). The operation of the comparison unit 42 will be described in detail. First, at t = 1, D (1, k) is input to the accumulating unit 22 and processed by the intensity deriving unit 32. Then, Dout (1, k), that is, 10 pieces of 10 shown in FIG. The FFT point signal is stored in the memory 34A. Since there is no other D (t, k) at t = 1, the integration control unit 36 outputs Dout (1, k) as Y ₁ (k) to the frequency offset output unit 24. Search unit _{40, Y} 1 obtains a maximum value MAX _(Y 1 _(k)) of the (k), and outputs to the comparison unit 42. That is, f3 having the maximum amplitude in FIG. 5A, that is, Y ₁ (4) is output. Further, the comparison unit 42 compares the amplitude applied to f3 with a threshold value. As illustrated in FIG. 5A, since Y ₁ (4) is smaller than the threshold value, the output control unit 44 extends the integration in the integration unit 22. That is, the integration unit 22 repeats the integration process with t = 2.

At t = 2, first, D (1, k) stored in the memory 34A is transferred to the memory 34B. After that, as in the case of t = 1, D (2, k) is input to the accumulating unit 22 and processed by the intensity deriving unit 32. Then, Dout (2, k), that is, FIG. The 10 FFT point signals shown are stored in the memory 34A. Here, the integration control unit 36 integrates D (2, k) stored in the memory 34A and D (1, k) stored in the memory 34B for each FFT point, and FIG. A signal Y ₂ (k) as shown in (c) is output. Searching unit 40 _obtains the maximum value MAX _(Y 2 _(k)) of _Y 2 (k), and outputs to the comparison unit 42. That is, f3 having the maximum amplitude in FIG. 5C, that is, Y ₂ (4) is output. Further, the comparison unit 42 compares the amplitude applied to f3 with a threshold value. As illustrated in FIG. 5C, since Y ₂ (4) is smaller than the threshold value, the output control unit 44 extends the integration in the integration unit 22. That is, the integration unit 22 repeats the integration process with t = 3.

At t = 3, first, D (1, k) stored in the memory 34B is transferred to the memory 34C (not shown). In addition, D (2, k) stored in the memory 34A is transferred to the memory 34B. Thereafter, as in the case of t = 2, D (3, k) is input to the accumulating unit 22 and processed by the intensity deriving unit 32. Then, Dout (3, k), that is, FIG. The 10 FFT point signals shown are stored in the memory 34A. Here, the integration control unit 36 has D (3, k) stored in the memory 34A, D (2, k) stored in the memory 34B, and D (1, k) stored in the memory 34C. k) is integrated for each FFT point to output a signal Y ₃ (k) as shown in FIG. Search unit _{40, Y} 3 obtains a maximum value MAX of the _{(k) (Y 3 (k} )), and outputs to the comparison unit 42. That is, f3 having the maximum amplitude in FIG. 5E, that is, Y ₃ (4) is output. Further, the comparison unit 42 compares the amplitude applied to f3 with a threshold value. As shown in FIG. 5E, since Y ₃ (4) is larger than the threshold value, the integration in the integration unit 22 is stopped, and the FFT point corresponding to the integration value Y ₃ (4), that is, The frequency offset f3 is output to the oscillator control unit 26.

FIG. 6 is a diagram illustrating an example of control by the oscillator control unit 26 of FIG. FIG. 6 is also a diagram illustrating an example of frequency components of a signal output from the A / D conversion unit 12. (1) to (5) shown in FIG. 6 are frequency bands of signals input to the FFT 20 of FIG. The input of the FFT 20 is cut out by the LPF 14 with the band from f ₋ to f ₊ centered around the frequency f = 0. 2 repeats the integration process a predetermined number of times, for example, N times, and MAX (Y _t (k)) exceeding the threshold does not exist, the frequency offset output unit 24 of FIG. If determined, the local oscillator 28 is controlled to change the band to be divided in the FFT 20. That is, the oscillator control unit 26 controls the local oscillator 28 so that the center frequency of any one of the bands (1) to (5) becomes f = 0. Note that the predetermined number of times may be larger than the number N of memories 34. Specifically, when t is larger than N, for example, data used for integration when t = N + 1 is Dout (N + 1, k), Dout (N, k),..., Dout (2 , K). Here, Dout (1, k) stored in the memory 34N when t = N is discarded. That is, the memory 34 sequentially discards old data like a FIFO buffer. Therefore, the accumulation is always the latest N pieces of data.

  Here, it is assumed that the FFT 20 is divided into M FFT points for the band (1) illustrated in FIG. 6 at t = 1 to N−1. When the predetermined number of times is N, that is, when t = N, the local oscillator 28 is controlled so that the frequency band targeted for the FFT 20 is the frequency band (2) shown in FIG. In other words, for FFT points that could not exceed the threshold even if the integration was performed for a predetermined number of times, there is a possibility that it will take time even if the integration is continued further. Integration processing and the like are performed for the frequency band. If the threshold value cannot be exceeded even if the integration process is repeated a predetermined number of times in the frequency band (2), the division process and the integration process are performed for the frequency band (3). Thereafter, in the same manner, trials are performed in the order of the frequency bands of (4) and (5) in order of the left and right alternating frequency bands centering on (1).

  Here, as a result of the comparison in the frequency offset output unit 24, if the integrated value greater than the threshold value does not exist, the FFT 20 selects a band that is different from the already divided part of the frequency band of the input signal. As a target, division of signals at a plurality of FFT points is executed. Here, “when it does not exist” includes a case where any of the integrated values is smaller than the threshold as a result of comparing the threshold value with the integrated value obtained a predetermined number of times. “Integrated value” includes, for example, adding a frequency band at a certain time and a signal of a frequency band at another time among the input signals for each FFT point. The “integrated value obtained a predetermined number of times” includes the number of signals in the frequency band to be added, and the number of signals in the target wave number band and the target time increase as the number increases.

  FIG. 7 is a flowchart showing an operation example of the frequency correction unit 16 of FIG. First, the FFT 20 divides at least a part of the frequency band of the input signal into a plurality of FFT point signals (S20). Next, the integrating unit 22 performs symbol processing on the signal output from the FFT 20 for each FFT point, and stores it in the memory 34 (S34). Next, the integrating unit 22 integrates for each FFT point (S36). Next, the frequency offset output unit 24 searches for the integrated value having the largest value among the integrated values for each FFT point integrated by the integrating unit 22 (S40). Further, the frequency offset output unit 24 compares the searched integrated value with a predetermined threshold value (S40). When the integrated value is larger as a result of comparison by the comparing unit 42 (Y in S42), the output control unit 44 stops the integration in the integrating unit 22, and outputs the FFT point corresponding to the integrated value as a frequency offset. (S44). Furthermore, the oscillator control unit 26 controls the local oscillator 28 using the frequency offset output from the output control unit 44, and corrects the frequency of the signal output from the A / D conversion unit 12 (S46).

  On the other hand, as a result of the comparison in the comparison unit 42, the output control unit 44 extends the integration in the integration unit 22 when the predetermined threshold value is larger (N in S42). Here, if the number of times of extension exceeds the predetermined number of times (Y of S48), the FFT 20 is compared in the frequency offset output unit 24. As a result, if there is no integrated value larger than the threshold value, Of the frequency bands, division of signals of a plurality of FFT points is executed for a band different from some of the already divided bands (S50), and the process returns to S20. On the other hand, if the extended number does not exceed the predetermined number (N in S48), the process returns to S20 to repeat the integration process.

  Next, a modification of the embodiment of the present invention will be shown. In addition, the same code | symbol is attached | subjected about the part which is common in the Example mentioned above, and description is simplified.

  FIG. 8 is a diagram illustrating a modification of the configuration of the integrating unit 22 of FIG. The integrating unit 22 shown in FIG. 8 includes an intensity deriving unit 32A, an intensity deriving unit 32B, an intensity deriving unit 32M, a memory 34, an integrating control unit 36, and a signal intensity measuring unit 50. Including. As described above, the intensity deriving unit 32 performs symbol processing on the signal for each FFT point output from the FFT 20 and outputs the signal to the memory 34A. The memory 34 stores the signal output from the intensity deriving unit 32. The signal for each FFT point in the memory 34 is sequentially transferred to the memory 34B, the memory 34C,..., The memory 34N each time the signal is output from the intensity deriving unit 32.

The signal strength measurement unit 50 measures the signal strength of the signal output from the LPF 14 and outputs the signal strength to the integration control unit 36. Here, the “signal strength” includes, for example, reception power, a power-to-noise ratio (Signal per Noise Ratio), a power interference ratio (Signal Per Interference Ratio), and the like. Furthermore, the integration controller 36 weights and integrates a plurality of FFT points according to the signal intensity measured by the signal intensity measuring unit 50. Here, when the weight at t = 1 is α ₁ and the weight at t = 2 is α ₂ , the outputs Y ₁ (k) and Y ₂ (k) of the integration control unit 36 at t = 1 and t = 2. ) Is shown as follows.
Y ₁ (k) = α ₁ × Dout (1, k) (7)
Y ₂ (k) = α ₁ × Dout (1, k) + α ₂ × Dout (2, k)
... Formula (8)

For example, it is assumed that the signal intensity measured by the signal intensity measurement unit 50 at t = 1 is weak and α ₁ = 0.7 is set. Further, it is assumed that the signal intensity measured by the signal intensity measuring unit 50 at t = 2 is strong and α ₂ = 1.3 is set. In this case, Y ₂ (k) is calculated as 0.7 × Dout (1, k) + 1.3 × Dout (2, k). As described above, Dout (2, k) at t = 2 where the signal strength is strong is emphasized, while Dout (1, k) where the signal strength is weak is reduced.

  By taking such an aspect, when the signal strength is high, that is, when it can be determined that the influence of noise or the like is small, the reliability of the signal at the FFT point corresponding to the input signal having the signal strength is high. Therefore, the accuracy of frequency offset detection can be improved by performing weighting and integration. When the signal strength is low, the integration may be performed after multiplying by a smaller weight coefficient than when the signal strength is high. The small weighting factor is, for example, a value less than 1, and is determined so that the influence of the input signal is small on the integration result.

  Next, another modification of the embodiment of the present invention will be shown. In addition, the same code | symbol is attached | subjected about the part which is common in the Example mentioned above, and description is simplified.

FIG. 9 is a diagram illustrating a modification of the configuration of the frequency offset output unit 24 of FIG. The frequency offset output unit 24 illustrated in FIG. 9 includes a search unit 40, a comparison unit 42, an output control unit 44, and a signal strength measurement unit 50. As described above, the search unit 40 searches for MAX (Y _T (k)) having the maximum amplitude among the signals Y _T (k) output from the integration unit 22 for each FFT point. The signal strength measurement unit 50 measures the signal strength of the signal output from the LPF 14 and outputs the signal strength to the comparison unit 42. The comparison unit 42 weights a predetermined threshold according to the signal strength measured by the signal strength measurement unit 50. Specifically, when the signal strength is good, a small weighting factor is used. Conversely, when the signal strength is bad, a large weighting factor is used. Further, the comparison unit 42 compares the weighted threshold value with MAX (Y _T (k)). The output control unit 44 controls the output of the frequency offset, the stop of the integration process, or the extension of the integration process by using the result compared by the comparison unit 42.

  By taking such an aspect, when the signal strength is high, that is, when it can be determined that the influence of noise or the like is small, the reliability of the signal at the FFT point corresponding to the input signal having the signal strength is high. I can say that. Therefore, the frequency offset detection time can be reduced by using a threshold weighted by a small weighting factor. The small weighting factor is a value less than 1, for example.

  Next, still another modification of the embodiment of the present invention will be shown. In the embodiment of the present invention, the frequency offset is estimated and corrected in the subsequent stage of the A / D converter 12. However, in this modification, the frequency offset is estimated in the subsequent stage of the A / D conversion unit 12 and the frequency offset is corrected in the previous stage of the A / D conversion unit 12 using the estimation result. In addition, the same code | symbol is attached | subjected about the part which is common in the Example mentioned above, and description is abbreviate | omitted.

  FIG. 10 is a diagram illustrating a configuration example of a wireless communication terminal device according to still another modification of the embodiment of the present invention. 10 includes an antenna 10, an RF processing unit 11, a quadrature detection unit 64, an LPF 14, an A / D conversion unit 12, a demodulation unit 18, and a frequency correction unit 66. The frequency correction unit 66 estimates the frequency offset using the signal converted into the digital signal by the A / D conversion unit 12. In addition, a frequency signal related to the estimated frequency offset is sent to the quadrature detection unit 64. The quadrature detection unit 64 performs quadrature detection on the signal output from the RF processing unit 11. Further, the frequency is corrected by inputting the frequency signal related to the frequency offset sent from the frequency correction unit 66 to one of the mixers (not shown).

  FIG. 11 is a diagram illustrating a configuration example of the frequency correction unit 66 of FIG. The frequency correction unit 66 includes a frequency offset estimation unit 100, an oscillator control unit 26, and a frequency transmitter 28. According to the operation described in the embodiment of the present invention, the frequency offset estimation unit 100 estimates the frequency offset. Further, the oscillator control unit 26 controls the frequency transmitter 28 using the frequency offset estimated by the frequency offset estimation unit 100. The frequency transmitter 28 sends a frequency signal to the quadrature detector 64 according to the control of the frequency transmitter 28. By adopting such a configuration, the frequency offset can be corrected even when the sampling rate of the A / D converter 12 is low.

  According to the present embodiment and the modification, since the frequency offset is obtained based on the result of integration, the influence of noise and the like can be reduced, and the frequency offset can be detected with high accuracy. Further, since the integrated value having the largest value is used as a reference for frequency offset detection, the reliability of frequency offset detection can be improved. Further, on the condition that the retrieved integrated value exceeds the threshold value, the integrated value is used as a reference for frequency offset detection. On the other hand, when the integrated value is below the threshold value, that is, when the signals of a plurality of partial bands are at a low level due to the influence of noise or the like, the integrated value is not a reference for frequency offset detection. Therefore, the reliability of frequency offset detection can be improved. Further, if the retrieved integrated value exceeds the threshold value, the frequency offset can be detected, so that it is not necessary to calculate the integrated value any more. Therefore, in such a case, power consumption can be reduced by stopping the integration process in the integration unit. Further, the estimation time of the frequency offset can be shortened.

  Further, as a result of comparison in the comparison unit, when the predetermined threshold value is larger, that is, when the retrieved integrated value is smaller than the threshold value, it can be determined that the influence of noise or the like is large, so in the integration unit The integration can be extended and the reliability of frequency offset detection can be improved. When the signal strength is high, that is, when it can be determined that the influence of noise or the like is small, it can be said that the reliability of the partial band corresponding to the input signal having the signal strength is high. By weighting and integrating, the frequency offset estimation time can be shortened. Similarly, when the signal strength is high, that is, when it can be determined that the influence of noise or the like is small, it can be said that the reliability of the partial band corresponding to the input signal having the signal strength is high. By comparing with a threshold value weighted by the weighting factor, the frequency offset detection criterion can be lowered. Thereby, the estimation time of frequency offset detection can be shortened. Also, if there is no integrated value greater than the threshold value, it is determined that there is no frequency offset in the first place, and by targeting a band that is different from some of the already divided bands, Offset detection time can be reduced. It is possible to provide a frequency offset estimation device that can detect a frequency offset with high accuracy even under adverse conditions where there is no known signal and there is a lot of noise.

  In the present embodiment, its modified example, and another modified example, the signal intensity measuring unit 50 has been described as being mounted inside the integrating unit 22 or the frequency offset output unit 24. However, the signal strength measurement unit 50 may be mounted inside the frequency correction unit 16 without being limited thereto. Moreover, you may mount in the inside of the communication apparatus of FIG. The signal intensity measuring unit 50 can obtain the same effects as described above, regardless of the mounting location. In yet another modification of the present embodiment, the description has been made assuming that the frequency is corrected in the quadrature detection unit 64 using the frequency offset estimated by the frequency correction unit 66. However, the present invention is not limited to this, and the RF processing unit 11 may correct the frequency in a so-called direct conversion method in which an RF signal is directly converted into a baseband signal. That is, the present invention can also be applied to the direct conversion method.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

It is a figure which shows the structural example of the radio | wireless communication terminal device concerning the Example of this invention. It is a figure which shows the structural example of the frequency correction part of FIG. It is a figure which shows the structural example of the integrating | accumulating part of FIG. It is a figure which shows the structural example of the frequency offset output part of FIG. FIGS. 5A to 5E are diagrams illustrating examples of input / output signals of the integrating unit in FIG. 2 at t = 1 to 3. FIG. It is a figure which shows the example of control of the oscillator control part of FIG. It is a flowchart which shows the operation example of the frequency correction part of FIG. It is a figure which shows the modification of a structure of the integrating | accumulating part of FIG. It is a figure which shows the modification of a structure of the frequency offset output part of FIG. It is a figure which shows the structural example of the radio | wireless communication terminal device concerning another modification of the Example of this invention. It is a figure which shows the structural example of the frequency correction part of FIG.

Explanation of symbols

  10 antenna, 11 RF processing unit, 12 A / D conversion unit, 14 LPF, 16 frequency correction unit, 18 demodulating unit, 20 FFT, 22 integrating unit, 24 frequency offset output unit, 26 oscillator control unit, 28 local oscillator, 30 Frequency mixer, 32 intensity derivation unit, 34 memory, 36 integration control unit, 40 search unit, 42 comparison unit, 44 output control unit, 50 signal intensity measurement unit, 100 frequency offset estimation unit.

Claims (4)

An input unit for sequentially inputting signals;
A division unit that divides at least a part of a frequency band of a signal input from the input unit into a plurality of partial band signals on a frequency axis;
For each partial band divided by the dividing unit, on the time axis, an integrating unit that integrates amplitude values ;
At least one integrated value is detected from the integrated values for each partial band integrated by the integrating unit, and a partial band corresponding to the detected integrated value is output as a frequency offset value included in the input signal. A frequency offset output unit,
With
The frequency offset output unit
A search unit for searching for an integrated value having the largest value among the integrated values for each partial band integrated by the integrating unit;
A comparison unit that compares the integrated value searched by the search unit with a predetermined threshold;
As a result of the comparison in the comparison unit, when the integrated value is larger, the output control unit that stops the integration in the integration unit and outputs a partial band corresponding to the integration value as a frequency offset;
The frequency offset estimation apparatus characterized by including. The output control section as a result of the comparison at the comparison unit, if more predetermined threshold is larger, the frequency offset estimation apparatus according to claim 1, characterized in that to extend the integration in the integration unit. A signal strength measuring unit for measuring the signal strength of the input signal;
The integration unit, in response to the signal intensity measured by the signal intensity measuring unit, a frequency offset estimating apparatus according to claim 1 or 2, characterized in that integrated with weights the plurality of partial bands. As a result of comparison in the frequency offset output unit, the dividing unit is different from some of the already divided frequency bands of the input signal when there is no integrated value larger than the threshold value. The frequency offset estimation apparatus according to any one of claims 1 to 3 , wherein division of a signal of a plurality of partial bands is executed for a band.

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