JP3553517B2 - Frequency offset estimation device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a frequency offset amount estimating apparatus that can be used in a wireless communication system such as a mobile phone, a car phone, and a private digital wireless communication phone.
[0002]
[Prior art]
Conventionally, a frequency offset amount estimating apparatus provided in a receiving apparatus in a wireless communication system is based on a complex correlation result with the same known pattern repeatedly received on the receiving side and a reception time difference between the repeatedly received known patterns. A phase difference per time is obtained to estimate a frequency offset amount. Hereinafter, a frequency offset detection method described in Japanese Patent Application Laid-Open No. 8-195778 will be described as a conventional example. FIG. 7 is an explanatory diagram showing a state of estimating a frequency offset amount in a TDMA receiver that receives burst data having a slot configuration transmitted periodically. As shown in FIGS. 7A and 7B, the first burst data b1 and the second burst data b2 are received in the same periodic slot, and a specific burst included in the first burst data b1 is received. A phase obtained from the known pattern is compared with a phase obtained from a specific known pattern included in the second burst data b2, and a frequency offset amount is estimated based on the phase difference calculated by the comparison. However, in the conventional example described here, FIG. 7C shows the result of correlation obtained by using the synchronization bit as a known pattern, and indicates that the correlation value peaks at the positions of t1 and t2. Θ1 and θ2 shown in FIG. 7D represent the complex correlation values at t1 and t2 on the IQ plane. .theta.1 'is such that the initial phases of .theta.1 and .theta.2 are equal, but if the phase rotating during the time t2-t1 shown in FIG. The frequency offset amount can be estimated.
[0003]
[Problems to be solved by the invention]
However, in the above-described conventional frequency offset amount estimating apparatus, although the number of repetitions and the pattern length depend on the target performance such as the communication channel condition and the bit error rate, it is necessary to insert a repetition pattern having a certain length. The repetition distance had to be designed according to the maximum possible frequency offset. In particular, in order to accurately estimate the frequency offset amount under multipath fading conditions with a large delay spread, the symbol length of the repetition pattern increases, and the amount of calculation and the detection time for estimating the frequency offset increase. Further, in the case of detecting a frequency offset using a UW (unique word) for acquiring timing synchronization, which is a known pattern, in a receiving apparatus using the TDMA method, it is desired to improve timing synchronization acquisition performance and to estimate frequency offset satisfactorily. We need to derive patterns that satisfy both things we can do. Furthermore, in a TDMA receiving system, when UW is used as information for identifying a frame before decoding, it is necessary to select a pattern in which a plurality of UWs reduce mutual correlation with each other. In order to satisfy these three conditions, the performance must be concessioned to each other, and there is a high possibility that the reception performance is totally deteriorated.
[0004]
The present invention has been made to solve the problem in the related art, and in a communication system in which a known pattern is inserted at a fixed length, even under a multipath fading condition in which intersymbol interference occurs, a small amount of computation is required. in an object to provide a frequency offset amount estimating apparatus capable of estimating the frequency offset, the mobile station radio apparatus capable of performing good frequency offset compensation, the base station radio equipment.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a frequency offset amount estimating apparatus according to the present invention includes a complex correlation calculating unit that calculates a complex correlation with known reception data, and a different correlation length set in advance in a calculation process of the complex correlation calculating unit. Complex correlation value acquiring means for acquiring a complex correlation value of the above, phase calculating means for calculating a phase difference between the acquired plurality of correlation values, and a frequency offset amount for estimating a frequency offset amount from a relationship between the correlation length and the phase difference. The phase of the complex correlation value with respect to each correlation length is always uniquely determined by the frequency offset component and the correlation length, regardless of the initial phase. Thus, the frequency offset amount can be estimated.
[0006]
Further, the frequency offset amount estimating apparatus of the present invention obtains a complex correlation calculating means for obtaining a complex correlation with known reception data, and obtains a complex correlation value with a different correlation length set in advance in the calculating process of the complex correlation calculating means. Complex correlation value acquiring means, a phase calculating means for calculating a phase difference between the acquired plurality of correlation values, a frequency offset amount estimating means for estimating a frequency offset amount from a relationship between the correlation length and the phase difference, and a propagation path. Delay profile obtaining means for obtaining a delay profile of the same, estimating the frequency offset amount for each timing of a plurality of arriving waves, and averaging these frequency offset amounts, thereby obtaining the accuracy of the finally obtained frequency offset amount. Can be improved.
[0007]
Further, the frequency offset amount estimating apparatus of the present invention obtains a complex correlation calculating means for obtaining a complex correlation with known reception data, and obtains a complex correlation value with a different correlation length set in advance in the calculating process of the complex correlation calculating means. Complex correlation value acquiring means, a phase calculating means for calculating a phase difference between the acquired plurality of correlation values, a frequency offset amount estimating means for estimating a frequency offset amount from a relationship between the correlation length and the phase difference, and a propagation path. A delay profile obtaining means for obtaining a delay profile of a plurality of arriving waves, estimating a frequency offset amount for each timing of a plurality of arriving waves, and performing a weighted average of these frequency offset amounts according to the arriving wave level to obtain a final It is possible to improve the accuracy of the frequency offset amount obtained in the above.
[0008]
Further, the frequency offset amount estimating apparatus of the present invention performs the frequency offset amount estimation a plurality of times by the above-described frequency offset amount estimating apparatus, averages the frequency offset amount estimation results of the plurality of times, and sets this as the final offset amount. The averaging can improve the accuracy of estimation of the final frequency offset amount.
[0009]
Further, the frequency offset amount estimating apparatus of the present invention performs a plurality of times of the frequency offset amount estimation by the means for detecting the reception level of the received data and the frequency offset amount estimating apparatus described above, It is characterized by performing weighted averaging according to the reception level at the time of each estimation, and using this as a final offset amount, thereby improving the estimation accuracy of the final frequency offset amount.
[0010]
Further, the mobile station radio apparatus of the present invention includes the above-described frequency offset amount estimating apparatus, and means for correcting the frequency offset based on the estimated frequency offset amount, and based on the frequency offset estimated value. By controlling the oscillation frequency to correct the frequency offset, or by performing phase rotation on the received data based on the estimated value of the frequency offset to correct the frequency offset, the known frequency included in the received data included in the received data by the frequency offset amount estimating apparatus. Regardless of the pattern, it is possible to estimate the frequency offset amount, correct the frequency offset by the above means, and secure good reception characteristics.
[0011]
Further, the base station radio apparatus of the present invention includes the above-described frequency offset amount estimating apparatus, and means for correcting the frequency offset based on the estimated frequency offset amount, and based on the frequency offset estimated value. By controlling the oscillation frequency to correct the frequency offset, or by performing phase rotation on the received data based on the estimated value of the frequency offset to correct the frequency offset, the known frequency included in the received data included in the received data by the frequency offset amount estimating apparatus. Regardless of the pattern, it is possible to estimate the frequency offset amount, correct the frequency offset by the above means, and secure good reception characteristics.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 shows a configuration of a transmitting unit of a mobile station radio apparatus or a base station radio apparatus including a frequency offset amount estimating apparatus according to an embodiment of the present invention. In FIG. 1, a received signal received from an antenna 101 is input to a mixer unit 102 and down-converted. The down-converted signal is input to the quadrature demodulator 103, and the quadrature demodulated signal is output. This signal is input to the AD converter 104 and is converted from an analog signal to a sampled digital signal. This signal is input to the timing synchronization section 105, and a signal at the timing of arrival of a known symbol is output. This signal is input to the frequency offset amount estimating device 106, and the frequency offset amount is estimated. This estimated amount of frequency offset is input to the transmission frequency conversion unit 107, and the oscillation frequency of the oscillator 108 is converted to correct the frequency offset, or the estimated amount of frequency offset is input to the phase rotation unit 109, and is subjected to AD conversion. The output signal of the unit 104 is subjected to phase rotation for correcting a frequency offset.
[0014]
FIG. 2 shows the configuration of the frequency offset amount estimating apparatus 106 described above. A complex correlation calculating means 201 for obtaining a complex correlation with known reception data, and a different correlation length set in advance in the calculation process of the complex correlation calculating means 201. A complex correlation value acquiring means 202 for acquiring a complex correlation value in the above, a phase calculating means 203 for calculating a phase difference between the acquired plurality of correlation values, and a frequency offset for estimating a frequency offset amount from a relationship between the correlation length and the phase difference. And an amount estimating means 204.
[0015]
Next, a method of estimating a frequency offset in the frequency offset amount estimating apparatus 106 will be described with reference to FIG. Vn shown in FIG. 3B is a complex correlation value obtained as a result of performing a complex correlation operation from a portion including the known pattern of the received data to the correlation length N from the beginning of the known pattern shown in FIG. Vm shown in FIG. 3B is a complex correlation value obtained as a result of performing a complex correlation operation from a portion including the known pattern of the received data to the correlation length M from the beginning of the known pattern shown in FIG. That is, the complex correlation value Vn is an intermediate result when calculating the complex correlation value Vm. The complex correlation operation is to cumulatively add the complex conjugate product by the correlation length. The phase of the complex conjugate product at each sample point is determined by the frequency offset, noise, and interference due to multipath. However, by performing cumulative addition for a fixed correlation length, the influence on the phase due to noise and multipath interference is averaged, and only the influence on the phase due to the frequency offset remains. Further, the phase difference between the complex correlation values compared at different time points of the correlation length uniquely determines the phase difference with respect to the frequency offset amount due to the difference in the correlation length. Conversely, the frequency offset amount per unit time can be estimated from the difference between the correlation lengths and the phase difference between the complex correlation values.
[0016]
(Embodiment 2)
Next, a second embodiment of the present invention will be described. As shown in FIG. 4, the frequency offset amount estimating apparatus according to the second embodiment is obtained by adding delay profile acquisition means 205 for acquiring a propagation path delay profile to the configuration of FIG. Based on this, it is intended to improve the accuracy of estimating the frequency offset amount.
[0017]
Hereinafter, the operation of the second embodiment will be described. FIG. 5 shows an example in which the delay profile estimating means 205 uses a correlation with a known pattern. The horizontal axis indicates time, and the vertical axis indicates a correlation value. Since the correlation value S1 and the correlation value S2 are larger than the correlation values at other times, it indicates that the components of the known pattern included in the reception data at that time were relatively large. Therefore, it can be estimated that there is an incoming wave at the time points S1 and S2 shown in FIG. As described above, in a multipath environment, components of a known pattern are dispersed. In the second embodiment, means for positively absorbing the known pattern components dispersed by the multipath is provided, and the frequency offset estimation amount obtained by the frequency offset amount estimation means 204 described in the first embodiment is averaged. Or weighted average.
[0018]
As described above, in the second embodiment, at the time of the correlation value S1 and the correlation value S2 shown in FIG. 5, the frequency offset amount is estimated at each time by the frequency offset amount estimating means 204 described in the first embodiment. By averaging the frequency offset estimation amounts, the final frequency offset amount is estimated. Further, at the time of the correlation value S1 and the correlation value S2 shown in FIG. 5, the frequency offset amount is estimated by the frequency offset amount estimating means 204 described in the first embodiment at each time, and the frequency offset estimation amount is determined by the correlation value A final frequency offset amount is estimated by performing addition in proportion to the magnitudes of S1 and the correlation value S2.
[0019]
(Embodiment 3)
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 6 shows that the reception data includes a plurality of known patterns. The third embodiment uses the frequency offset estimation amount obtained by the means described in the first and second embodiments. A frequency offset estimation amount is obtained from the reception data shown in FIG. 6 using a known pattern, and the frequency offset estimation amount is held. Since the received data shown in FIG. 6 includes a plurality of known patterns, a frequency offset estimation amount is obtained for each of them, and the frequency offset estimation amount is held. Next, the final frequency offset amount is estimated by averaging the frequency offset estimation amounts obtained at the time of arrival of each known pattern. Further, a means for detecting a reception level at the time of reception of each known pattern is provided, and a weighted average in proportion to the reception level is applied to the frequency offset estimator obtained at the time of arrival of each known pattern, thereby obtaining a final frequency. Estimate the offset amount.
[0020]
As described above, according to each of the above-described embodiments, a complex correlation operation is performed between received data including a known pattern and a previously prepared known pattern, and a different correlation length set in advance in the calculation process is used. The frequency offset amount is estimated by calculating multiple complex correlation values and calculating the phase difference per unit time from the complex correlation value for the correlation length based on the difference between each correlation length, so it is necessary to include a repetitive pattern in the known pattern. In addition, it is possible to cope with the allowable estimation range of the maximum frequency offset amount by setting the correlation length difference so that the phase difference of the complex correlation value for each correlation length does not exceed 180 degrees. it can.
[0021]
【The invention's effect】
As described above, according to the frequency offset amount estimating apparatus of the present invention, the complex correlation value at a different time point of the correlation length in the operation process of the complex correlation operation is obtained only by the fact that the known pattern of a certain length is included in the received data. Since the frequency offset amount can be estimated from the phase difference of the above, the frequency offset amount can be estimated even if the known pattern is any pattern. The frequency offset estimation amount can be averaged and weighted according to the level of the known pattern component included in the received data and the reception level at the time of reception of the known pattern. This has the effect that the accuracy can be improved.
[0022]
Further, according to the present invention, restrictions on known patterns for solving the problem of performance degradation due to frequency offset are reduced, and constraints on system construction are relaxed, thereby facilitating the design of a wireless communication system. For example, since the frequency offset amount can be estimated using a known pattern used for obtaining timing synchronization as it is, the ratio of the known pattern included in the received data can be reduced. Known patterns have a low degree of freedom and therefore have little value as information. Therefore, it is possible to reduce the ratio of known patterns included in received data, thereby facilitating system construction.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a transmission unit of a mobile station radio apparatus or a base station radio apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of a frequency offset amount estimating apparatus according to Embodiment 1 of the present invention. FIG. 3 is an explanatory diagram of a frequency offset amount estimating method according to the first embodiment of the present invention; FIG. 4 is a block diagram of a frequency offset amount estimating device according to the second embodiment of the present invention; FIG. FIG. 6 is a state diagram in which a delay profile is estimated by a correlation result of a known pattern in FIG. 6 FIG. 6 is a state diagram in which a plurality of known patterns are included in received data in Embodiment 3 of the present invention FIG. Explanatory diagram of estimation method [Explanation of reference numerals]
Reference Signs List 101 Receiving antenna 102 Mixer unit 103 Quadrature demodulation unit 104 A / D conversion unit 105 Timing synchronization unit 106 Frequency offset amount estimation device 107 Oscillation frequency conversion unit 108 Oscillator 109 Phase rotation unit 201 Complex correlation operation unit 202 Complex correlation value acquisition unit 203 Phase calculation unit 204 Frequency offset amount estimation means 205 Delay profile acquisition means

Claims (7)

Complex correlation calculating means for obtaining a complex correlation with known reception data; complex correlation value obtaining means for obtaining complex correlation values at different correlation lengths set in advance in the calculation process of the complex correlation calculating means; And a frequency offset amount estimating unit for estimating a frequency offset amount from the relationship between the correlation length and the phase difference. Providing a delay profile acquisition unit for acquiring a delay profile of a propagation path, estimating a frequency offset amount for each timing of a plurality of arriving waves, averaging these frequency offset amounts, and determining a final frequency offset amount. The frequency offset amount estimating apparatus according to claim 1, wherein A delay profile acquisition means for acquiring a delay profile of a propagation path, estimating a frequency offset amount for each timing of a plurality of arriving waves, performing a weighted average of these frequency offset amounts according to the arriving wave level, and The frequency offset amount estimating apparatus according to claim 1, wherein the frequency offset amount is determined. The frequency offset according to any one of claims 1 to 3, wherein the frequency offset amount is estimated a plurality of times, and the results of the frequency offset amount estimation are averaged and the final frequency offset amount is obtained. Quantity estimation device. A means for detecting the reception level of the reception data is provided, the frequency offset amount is estimated a plurality of times, and the frequency offset amount estimation results are weighted and averaged according to the reception level at the time of each estimation. 4. The frequency offset amount estimating device according to claim 1, wherein the frequency offset amount is used. 6. A mobile station radio apparatus comprising: the frequency offset amount estimating apparatus according to claim 1; and means for correcting a frequency offset based on the estimated frequency offset amount. A base station radio apparatus comprising: the frequency offset amount estimating apparatus according to claim 1; and a unit that corrects a frequency offset based on the estimated frequency offset amount.

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