JP2009124301A - Communication device and method of estimating amount of phase rotation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new technique for accurately estimating the amount of phase rotation. <P>SOLUTION: A communication device, which uses an OFDM signal having a dispersedly disposed pilot signal to perform communications, includes a transmission path frequency response calculation section 162 for calculating a transmission path frequency response in the pilot signal included in the received OFDM signal; a correlation value calculation section 164 for calculating a correlation value of the transmission path frequency response between the pilot signals; and a phase rotation amount calculation section 166 for calculating the amount of phase rotation using a plurality of correlation values. The correlation value calculation section 164 calculates the plurality of correlation values having a different position relationship between pilot signals. The phase rotation amount calculation section calculates the amount of phase rotation using the plurality of correlation values having a different position relationship between pilot signals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a communication device and a phase rotation amount estimation method.

  In OFDM (including OFDMA, the same applies hereinafter) communication, it is important to synchronize signal timing and frequency between the transmission side and the reception side.

For example, when a reception delay occurs on the receiving side, if a CP (cyclic prefix) is added to the data, intersymbol interference does not occur if the delay is within the CP length, but the phase of the carrier (subcarrier) Rotation occurs, resulting in a phase error.
A technique for correcting the phase error due to such phase rotation is described in Patent Document 1, for example.

The conventional method for calculating the amount of phase rotation is as follows.
Here, in the two-dimensional subcarrier arrangement in the frequency axis direction (subcarrier direction) -time axis direction (symbol direction) as shown in FIG. 13, it is assumed that pilot subcarriers are arranged as shown.
Here, in order to calculate the timing offset, the transmission channel frequency response H (f, t) for the pilot subcarrier A of frequency f and time t is located away from the pilot subcarrier A in the frequency axis direction. Using the frequency f + Δf and the transmission channel frequency response H (f + Δf, t) for the pilot subcarrier B at time t, the phase rotation amount in the frequency direction is obtained.

First, let H ₀ be the transmission path frequency response for pilot subcarrier A at frequency f and time t when there is no timing offset / frequency offset.
At this time, if there is a timing offset T ₀ and a frequency offset F ₀ , the transmission channel frequency response H (f, t) of the pilot subcarrier A at the frequency f and time t is expressed by the following equation (1).

Further, the transmission path frequency response H (f + Δf, t) for the pilot subcarrier B at the frequency f + Δf and time t is expressed by the following equation (2).

The phase rotation amount θ between the two pilot subcarriers A and B arranged in the frequency axis direction is calculated as a correlation value between H (f, t) and H (f + Δf, t), and the angle of the correlation value is calculated. The following equation (3) is established by obtaining arg. In formula (3), “*” is a complex conjugate.

Therefore, the timing offset T ₀ can be calculated by the following equation (4). However, −1 / (2Δf) <T ₀ ≦ 1 / (2Δf).

The frequency offset F ₀ can be obtained in the same manner. Specifically, the correlation value between two pilot subcarriers arranged in the time axis direction is obtained, and the phase rotation amount θ in the time direction is calculated from the correlation value. The frequency offset F ₀ may be calculated from the phase rotation amount θ.
JP 2000-295195 A

In the conventional calculation of the phase rotation amount, the phase rotation amount in the time axis direction or the frequency axis direction is calculated using the correlation value of the channel frequency response between the subcarriers at a certain frequency interval Δf or between the subcarriers at a certain time interval Δt. Was estimated.
That is, conventionally, the amount of phase rotation is estimated using only the correlation value of one transmission path frequency response, the estimation error tends to increase, and there is room for improvement in estimation accuracy.

  Therefore, an object of the present invention is to provide a new technique for accurately estimating the amount of phase rotation.

  The present invention is a communication apparatus that performs communication using OFDM signals in which pilot signals used for calculation of a transmission channel frequency response are distributed in a two-dimensional arrangement in the time direction and the frequency direction, and are included in a received OFDM signal A transmission line frequency response calculation unit for calculating a transmission line frequency response in the pilot signal, and a correlation value of the transmission line frequency response between the pilot signals is calculated based on the transmission line frequency response calculated by the transmission line frequency response calculation unit. A correlation value calculation unit, and a phase rotation amount calculation unit that calculates a phase rotation amount using a plurality of correlation values calculated by the correlation value calculation unit, wherein the correlation value calculation unit The phase rotation amount calculation unit is configured to calculate a plurality of correlation values having different positional relationships, and the phase rotation amount calculating unit Using different plurality of correlation values, and calculates the phase rotation amount.

  According to the present invention, since the phase rotation amount is calculated using a plurality of correlation values having different positional relationships between pilot signals, the number of samples for calculating the phase rotation amount is increased, and the phase rotation amount is accurately determined. Can be calculated.

  It is preferable that a phase rotation amount correction unit that corrects the phase rotation amount of the received signal using the phase rotation amount calculated by the phase rotation amount calculation unit is provided. In this case, the phase rotation amount of the received signal can be corrected.

  In addition, a window position correction unit that calculates a timing offset using the phase rotation amount calculated by the phase rotation amount calculation unit and corrects the FFT window timing of the received signal based on the calculated timing offset is provided. Is preferred. In this case, the FFT window timing is appropriately corrected with a precise timing offset.

  In addition, a frequency offset is calculated using the phase rotation amount calculated by the phase rotation amount calculation unit, and a reference frequency correction unit that corrects the reference frequency of reception based on the calculated frequency offset is provided. preferable. In this case, the reception reference frequency is appropriately corrected by a precise frequency offset.

  A transmission unit that calculates a timing offset and / or a frequency offset using the phase rotation amount calculated by the phase rotation amount calculation unit, and transmits the calculated timing offset and / or frequency offset to the signal transmission side. Is preferably provided. In this case, the transmission side of the signal can appropriately correct the transmission timing and the transmission reference frequency with a precise timing offset and / or frequency offset.

  Further, the present invention related to the phase rotation amount estimation method uses the pilot signal included in the OFDM signal in which pilot signals used for calculating the transmission channel frequency response are distributed in a two-dimensional arrangement in the time direction and the frequency direction. A method for estimating a phase rotation amount, the step of calculating a channel frequency response in a pilot signal included in a received OFDM signal, and a correlation value calculating step of calculating a correlation value of a channel frequency response between pilot signals A phase rotation amount calculation step for calculating a phase rotation amount using a plurality of correlation values calculated in the correlation value calculation step, wherein the correlation value calculation step includes a plurality of different positional relationships between pilot signals. The correlation value is calculated, and in the phase rotation amount calculation step, the positional relationship between the pilot signals differs. Using a plurality of correlation values, and calculates the phase rotation amount.

  According to the present invention, the amount of phase rotation can be calculated with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the present embodiment, WiMAX (Worldwide Interoperability for Microwave Access, IEEE 802.16) will be described as an example of a communication method.

  FIG. 1 shows an OFDM subcarrier arrangement employed in WiMAX. OFDM is a type of frequency multiplexing method, and is a communication method in which digital information is transmitted by applying QAM modulation to a large number of carriers (subcarriers) arranged so as to be orthogonal on the frequency axis.

There are three types of OFDM subcarriers: a data subcarrier (Data Sub-Carrier), a pilot subcarrier (Pilot Sub-Carrier), and a null subcarrier (Null Sub-Carrier).
The data subcarrier (data signal) is a subcarrier for transmitting data and a control message. The pilot subcarrier is a known signal (pilot signal) on the reception side and the transmission side, and is used for calculating a transmission channel frequency response.

  A null subcarrier is a subcarrier in which nothing is actually transmitted, and a guard subband (guard subcarrier) on the low frequency side, a guard subband (guard subcarrier) on the high frequency side, and a DC subcarrier ( Center frequency subcarrier).

FIG. 2 shows a two-dimensional arrangement of data subcarriers and pilot subcarriers excluding null subcarriers of WiMAX uplink PUSC. In FIG. 2, the horizontal axis is the frequency axis, and the vertical axis is the time axis.
1 (1-L) on the horizontal axis in FIG. 2 indicates the subcarrier number. The subcarrier number is a number in which the subcarriers excluding the null subcarrier are numbered in ascending order of frequency. When the number of all subcarriers including null subcarriers is 1024, the total number L of data subcarriers and pilot subcarriers is 840.
K on the vertical axis in FIG. 2 indicates a symbol number. The symbol number is a number assigned to symbols in order of arrival time.

In FIG. 2, one tile structure is configured by a total of 12 subcarriers, 3 in the symbol direction (time axis direction) and 4 in the frequency axis direction. A tile is a minimum unit for user allocation.
Pilot subcarriers are arranged at the four corners of the tile, and the other subcarriers in the tile are data subcarriers.
As shown in FIG. 2, the tiles are regularly arranged in the time axis direction and the frequency axis direction. As a result, the pilot subcarriers are dispersedly arranged in the two-dimensional arrangement of FIG.

  FIG. 3 shows functional blocks of the communication device 1 according to the first embodiment. FIG. 3 mainly shows a reception function (function as an OFDM receiver) in the communication apparatus 1. The communication apparatus 1 includes an antenna element 11, an RF unit 12, a BB unit 13, an FFT unit 14, and a filter processing unit 15 as a basic configuration. Note that the communication device 1 here mainly assumes a base station that performs communication with a mobile terminal.

  The RF (Radio Frequency) unit 12 performs conversion from a received signal carrier frequency to a baseband frequency. The BB (Base Band) unit 13 performs removal of GI (Guard Interval) added on the transmission side, A / D conversion, and the like. The FFT unit performs signal serial / parallel conversion, discrete Fourier transform, and the like. The filter processing unit 15 combines the output signals from the FFT unit with appropriate weights, and extracts a desired signal in each subcarrier. This weight is calculated from the pilot subcarrier.

  The transmission path between the transmission side communication apparatus and the reception side communication apparatus 1 is a fading transmission path. When the subcarrier passes through the fading propagation path, its amplitude and phase change. The amount of change varies depending on the position of the subcarrier (time axis direction position and frequency axis direction position).

  In addition, the communication device 1 according to the first embodiment includes a phase rotation amount estimation unit 16 that estimates the phase rotation amount from the frequency domain signal output from the FFT unit (see FIG. 2), and the estimated phase rotation amount. And a phase rotation amount correction unit 17 for correcting the phase rotation amount of the signal. In the first embodiment, the receiving side communication device 1 corrects the phase rotation, so that it is possible to prevent phase rotation between symbols and phase rotation between subcarriers.

  The basic function of the phase rotation amount estimation unit 16 in the present embodiment is as follows. For example, consider obtaining the phase rotation amount in the subcarrier arrangement of FIG. 4 (WiMAX uplink PUSC as in FIG. 2). Here, the amount of phase rotation in the frequency axis direction that occurs every time one subcarrier advances in the frequency direction (horizontal axis direction in FIG. 4) is X, and the time axis that occurs every time one symbol advances in the time direction (vertical axis direction in FIG. 4). Let Y be the phase rotation amount in the direction.

First, an estimation method when the conventional phase rotation amount estimation is applied to the subcarrier arrangement of FIG. 4 will be described. In the conventional phase rotation amount estimation, the phase rotation amount is obtained between subcarriers at a constant frequency interval or between subcarriers (between symbols) at a constant time interval.
Therefore, when the phase rotation amount X in the frequency axis direction is obtained with the subcarrier arrangement of FIG. 4, the frequency interval corresponds to, for example, the frequency interval between the pilot subcarrier a and the pilot subcarrier b of FIG. The phase rotation amount X = Z1 / 3 for each subcarrier in the frequency axis direction is obtained from the phase rotation amount Z1 obtained by this frequency interval 3 × Δf.

  Similarly, when the phase rotation amount Y in the time axis direction is obtained by the conventional phase rotation amount estimation, the time interval is set to, for example, the time interval between the pilot subcarrier g and the pilot subcarrier h in FIG. A corresponding Δt is determined, and the phase rotation amount Y = Z4 for each symbol in the time axis direction is obtained from the phase rotation amount Z4 obtained at the time interval Δt.

The phase rotation amounts Z1 and Z4 are Z1 = 3X + N1 (N1: estimation error) and Z4 = Y + N4 (N4: estimation error), respectively.
Therefore,
Estimated value of X = Z1 / 3 = X + N1 / 3
Estimated value of Y = Z4 = Y + N4
It becomes.

  On the other hand, the phase rotation amount estimation unit 16 according to the present embodiment does not calculate the phase rotation amount only by one fixed frequency interval or time interval, but determines the phase rotation amount between pilot subcarriers. A plurality of positional relationships are used to improve the phase rotation amount estimation accuracy. This utilizes the fact that the subcarrier arrangement in FIG. 4 has various positional relationships with different frequency intervals, time intervals, and directions as the positional relationship between pilot subcarriers.

Specifically, the phase rotation amount estimation unit 16 of the present embodiment estimates not only the pilot subcarriers a and b (frequency interval 3Δf) but also a position different from this in order to estimate the phase rotation amount X in the frequency direction. The related pilot subcarriers c and d and pilot subcarriers e and f are used.
Here, the pilot subcarriers c and d have a positional relationship that is 2Δt apart in the time axis direction, and the pilot subcarriers e and f have a positional relationship that is 3Δf apart in the frequency axis direction and 2Δt apart in the time axis direction. Is.
The phase rotation amount Z3 between the pilot subcarriers e and f can be considered as the sum of the phase rotation amount in the case of the frequency interval 3Δf and the phase rotation amount in the case of the time interval 2Δt.

That is, by subtracting the phase rotation amount Z2 between the pilot subcarriers c and d from the phase rotation amount Z3 between the pilot subcarriers e and f, the phase rotation amount at the frequency interval 3Δf can be obtained.
Thus, the amount of phase rotation at a certain frequency interval (3Δf) is not only calculated (Z1) using pilot subcarriers having the frequency interval (3Δf) but also a positional relationship in terms of frequency and time. It can also be obtained using the one (Z3-Z2) calculated using other pilot subcarriers having different values.

Similarly, the phase rotation amount estimation unit 16 of the present embodiment estimates not only the pilot subcarriers g and h (time interval Δt) but also a different positional relationship in order to estimate the phase rotation amount X in the time direction. Some pilot subcarriers c and d are used.
Here, as described above, the pilot subcarriers c and d have a positional relationship of 2Δt apart in the time axis direction. Therefore, the phase rotation amount Z2 between the pilot subcarriers c and d can be considered to be twice the phase rotation amount in the case of the time interval Δt.

That is, if the phase rotation amount Z2 between the pilot subcarriers c and d is divided by 2, the phase rotation amount at the time interval Δt can be obtained.
Thus, the phase rotation amount at a certain time interval (Δt) is not only calculated (Z4) using pilot subcarriers having the frequency interval (Δt) but also the positional relationship in terms of frequency and time. It can also be obtained using the one (Z2 / 2) calculated using other pilot subcarriers having different values.

Therefore, the phase rotation amount estimation unit 16 of the present embodiment can obtain the phase rotation amount X in the frequency axis direction and the phase rotation amount Y in the time axis direction, for example, as follows.
Estimated value of X = (Z1 / 3 + (Z3−Z2) / 3) / 2 = X + (N1 + N3−N2) / 6
Estimated value of Y = (Z2 / 2 + Z4) / 2 = Y + N2 / 4 + N1 / 2

  The phase rotation amounts Z2 and Z3 are Z2 = 2Y + N2 (N2: estimation error) and Z3 = 3X + 2Y + N3 (N3: estimation error), respectively.

  In the phase rotation amount estimation unit 16 according to the present embodiment, the number of samples used for estimating the phase rotation amount becomes larger than that in the conventional case, and an estimation error can be suppressed and estimation accuracy can be improved.

  Now, the calculation method of the timing offset and the frequency offset will be organized here. In the case where the transmission path is a single path, the timing offset can be obtained as in the above formulas (1) to (4), and the same discussion can be made for the frequency offset.

Furthermore, when the transmission path is a multipath fading environment, consider that a timing offset and a frequency offset are taken. The timing offset in the nth path is Tn and the frequency offset is Fn. At this time, the frequency response H (f, t) at the frequency f and the time t is expressed by Expression (5).

As in the above equation (5), in a multipath environment, the transmission path frequency response has a complicated shape. Therefore, the timing offset T0 to TN and the frequency offset F0 to FN of each path are weighted and averaged according to the amplitude. Consider Tmean of (6) and Fmean of Equation (7) (see FIGS. 5A and 5B).

First, as preparation, equations (8) and (9) are defined, and equation (5) is replaced as equation (10).

At this time, when the average of Expression (11) is taken for frequency f and time t, the second term on the right side of Expression (11) disappears, and Expression (12) is obtained.

  Furthermore, assuming that equations (13) and (14) hold for any n, (TmeanΔf + FmeanΔt) can be obtained by calculating the phase of equation (12) as in equation (15).

  It is also possible to obtain (TmeanΔf + FmeanΔt) by calculating the phase at the time of equation (11) and taking the average over frequency f and time t.

And about two patterns (Δf1, Δt1), (Δf2), Δt2),
TmeanΔf1 + FmeanΔt1
TmeanΔf2 + FmeanΔt2
Tmean and Fmean can be derived by solving the simultaneous equations obtained from the above two patterns. Note that Δf1Δf2 ≠ Δf2Δf1.

  According to the offset calculation method as described above, Tmean Δf and Fmean Δf are respectively obtained, and information on various patterns (Δfk, Δfk) (k = 1 to K) is integrated as compared with the case where Tmean and Fmean are derived. Since the offsets Tmean and Fmean are estimated, highly accurate estimation is possible.

  Hereinafter, the details of the phase rotation amount estimation unit 16 having the above basic function will be described. As illustrated in FIG. 6, the phase rotation amount estimation unit 16 includes a first buffer unit 161 that sequentially stores the frequency domain received signals output from the FFT unit 14. In the phase rotation amount estimation in the present embodiment, a pilot subcarrier that is temporally previous may be used. Therefore, the received signal is accumulated in the first buffer unit 161 so that an arbitrary pilot subcarrier can be used.

  Further, the phase rotation amount estimation unit 16 includes a transmission line frequency response calculation unit 162 that calculates a transmission line frequency response using the received signal (pilot subcarrier) accumulated in the first buffer 161. The transmission channel frequency response calculation unit 162 calculates a transmission channel frequency response H for each pilot subcarrier using the reference signal (known signal) generated by the reference signal generation unit 162a. The transmission line frequency response H calculated by the transmission line frequency response calculation unit 162 is accumulated in the second buffer unit 163.

Further, the phase rotation amount estimation unit 16 includes a correlation calculation unit 164 that calculates a correlation value (H ^* H) of transmission path frequency responses of arbitrary two pilot subcarriers. The correlation value calculated by the correlation calculation unit 164 is stored in the correlation value storage unit 165.
Furthermore, the phase rotation estimation unit 16 includes a phase rotation amount calculation unit 166 that calculates the phase rotation amount by obtaining the declination arg of the correlation value (complex number) calculated by the correlation calculation unit 164. Here, the phase rotation amount calculation unit 166 can further calculate a timing offset and / or a frequency offset from the calculated declination arg.

Specifically, the correlation value calculation unit 164 performs the first correlation value S (3Δf, 0), the second correlation value S (0, 2Δt), and the third correlation value S according to the following equations (16) to (19). (3Δf, 2Δt) and the fourth correlation value (3Δf, −2Δt) are calculated.

The calculations of the above formulas (16) to (19) by the correlation value calculation unit 164 are based on the received tile (minimum of user allocation) in the uplink PUSC subcarrier arrangement of WiMAX (mobile WiMAX) as shown in FIGS. It is performed every unit; see FIG. By performing calculation for each minimum unit of user allocation, it is possible to perform calculation with high accuracy regardless of what user allocation is performed.
In other words, if two arbitrary pilot subcarriers are used for the calculation, the calculation is performed using the pilot in the burst region allocated to one user and the pilot in the burst region allocated to another user. There is a possibility of going.
Different users have different transmission path frequency responses, which reduces the accuracy of the calculation. However, by using the combination of pilot subcarriers within the minimum unit of user allocation for the calculation, it is possible to improve the accuracy without being affected by the user allocation. Arithmetic can be performed.

  In FIG. 7, the frequency of pilot subcarrier P1 at the upper left corner of the tile is f, and the time is t. Therefore, the frequency of the pilot subcarrier P2 in the upper right corner of the tile is f + Δf, and the time is t. The frequency of the pilot subcarrier P3 at the lower left corner of the tile is f and the time is 2Δt. The frequency of the pilot subcarrier P4 at the lower right corner of the tile is f + 3Δf, and the time is 2Δt.

  Correlation values S (nΔf, mΔt) shown in the equations (16) to (19) are expressed as “correlation values Sprev (nΔf, mΔt determined previously) shown in the first term on the right side of the equations (16) to (19). ) "Is updated by the second term on the right side of each equation (16) to equation (19).

  The previously obtained correlation value Sprev (nΔf, mΔt) is the correlation value S (nΔf, mΔt) updated immediately before based on another tile, and is stored in the correlation value storage unit 165. The correlation calculation unit 164 acquires the previously obtained correlation value Sprev from the correlation value storage unit 165 and stores the updated correlation value S in the correlation value storage unit 165.

When updating the correlation value S (nΔf, mΔt), the first term on the right side of each equation (16) to equation (19) is multiplied by the weighting factors α _{1 to} α ₄ , and the second term is ( 1-α ₁ ) to (1-α ₄ ). In order to suppress the influence of the noise when the noise in the transmission line is large, the weighting factors α _{1 to} α ₄ are increased to reduce (1-α ₁ ) to (1-α ₄ ), and the noise in the transmission line is reduced. When it is small, it is preferable to reduce the weighting factors α _{1 to} α _{4 in} order to improve the follow-up performance to the transmission line fluctuation.

Now, the first correlation value S (3Δf, 0) shown in Equation (16) represents the transmission channel frequency response correlation value when the frequency interval between pilot subcarriers is 3Δf and the time interval is zero. In order to update the first correlation value S (3Δf, 0), in equation (16), the transmission channel frequency response correlation value H (f, t) ^* between the pilot subcarrier P1 and the pilot subcarrier P2 H (f + 3Δf, t) and a transmission channel frequency response correlation value H (f, t + 2Δt) ^* H (f + 3Δf, t + 2Δt) between pilot subcarrier P3 and pilot subcarrier P4 are used.

The second correlation value S (0, 2Δt) shown in Expression (17) represents the transmission channel frequency response correlation value when the frequency interval between pilot subcarriers is 0 and the time interval is 2Δt. In order to update the second correlation value S (0, 2Δt), in equation (17), the transmission channel frequency response correlation value H (f, t) ^* between the pilot subcarrier P1 and the pilot subcarrier P3 ^. H (f, t + 2Δt) and a transmission channel frequency response correlation value H (f + 3Δf, t) ^* H (f + 3Δf, t + 2Δt) between pilot subcarrier P2 and pilot subcarrier P4 are used.

The third correlation value S (3Δf, 2Δt) shown in Expression (18) represents the transmission channel frequency response correlation value when the frequency interval between pilot subcarriers is 3Δf and the time interval is 2Δt. In order to update the third correlation value S (3Δf, 2Δt), the transmission channel frequency response correlation value (f, t) ^* H between the pilot subcarrier P1 and the pilot subcarrier P4 is expressed in equation (18). (F + 3Δf, t + 2Δt) is used.

The fourth correlation value S (3Δf, −2Δt) shown in Expression (19) represents a transmission path frequency response correlation value when the frequency interval between pilot subcarriers is 3Δf and the time interval is −2Δt. In order to update the fourth correlation value S (3Δf, −2Δt), in equation (7), the transmission channel frequency response correlation value (f, t + 2Δt) between the pilot subcarrier P3 and the pilot subcarrier P2 is expressed by ^: H (f + 3Δf, t) is used.

  Then, the phase rotation amount calculation unit 166 calculates the argument arg for each of the first correlation value to the fourth correlation value. Further, the phase rotation amount calculation unit 166 calculates a timing offset T ^ mean and a frequency offset F ^ mean from the argument arg.

The timing offset T ^ mean is calculated by adding each weight with an appropriate weight β _{1 to} β ₄ and dividing by 2πΔf as shown in the following equation (20).

The frequency offset F ^ mean is calculated by adding appropriate weights [gamma] _{1 to} [gamma] ₄ to each deflection angle and dividing by 2 [pi] [Delta] t as shown in the following equation (21).

The weights β _{1 to} β ₄ and the weights γ _{1 to} γ ₄ are preferably set so as to satisfy the following formulas (22) to (25). In addition, it is desirable to assign large weights β and γ to the correlation value having a small subcarrier interval and updated many times.
In Expression (20) and Expression (21), the weighted calculation is performed after calculating the declination of the correlation value, but the declination may be calculated after performing the weighted calculation of the correlation value.

  As described above, in the first embodiment, the phase rotation amount correction unit 17 compensates for the phase rotation after the FFT using the estimated offset. First, the correction of the timing offset uses the estimated average value Tmean of the timing offset to compensate for the phase rotation corresponding to the subcarrier.

For example, if there is a timing offset Tmean as shown in equation (26) before correction, the phase rotation amount can be reduced to 0 by correcting with Tmean as shown in equation (27) ( (See FIG. 8). The correction is performed with reference to a certain subcarrier. In the case of OFDMA, it is preferable to perform estimation / correction within an area to which each user is assigned.

  By performing the phase rotation correction after the FFT as described above, the amount of change in the transmission path frequency response characteristic between adjacent subcarriers can be reduced. In addition, it is easy to estimate the transmission line frequency response characteristics.

  In the first embodiment, the frequency offset may be corrected by correcting the frequency of the frequency domain signal after the FFT by the estimated Fmean.

  By correcting the phase rotation on the receiving side as in the first embodiment, phase rotation between symbols and phase rotation between subcarriers can be prevented.

  FIG. 9 shows a communication apparatus according to the second embodiment. In the second embodiment, the phase rotation amount estimation unit 16 is provided as in the first embodiment, but the phase rotation correction is not performed after the FFT as in the first embodiment, but according to the timing offset. A window position correction unit 18 that corrects the FFT window timing is provided.

The FFT window refers to the range to be subjected to FFT in the signal with the cyclic prefix CP added to the beginning of the data. If the delay is within the CP length, the FFT window starts within the CP, and therefore, between symbols. Interference can be prevented.
In the second embodiment, as shown in FIG. 10, the window position correction unit 18 considers delay dispersion, and the arrival timings of the data portions of all delay signals fall within the CP length from the top of the FFT window. Adjust the window timing as follows.
This correction of the window timing is preferably performed when the timing offset becomes a certain threshold value or more. When the window timing is adjusted, the correlation value S is preferably corrected by the adjusted amount. Furthermore, when there are a plurality of users, it is desirable to perform the transmission timing of each user so that the weighted average phase rotation amount of each user is aligned.

  As described above, by correcting the window timing on the receiving side, inter-symbol interference, inter-carrier interference, inter-symbol phase rotation / sub-carrier phase rotation can be prevented.

  The communication device according to the second embodiment further includes a reference frequency correction unit 19. The reference frequency correction unit 19 corrects the reception reference frequency in the RF unit 12 according to the estimated frequency offset.

  FIG. 11 shows a communication apparatus according to the third embodiment. The third embodiment includes the phase rotation amount estimation unit 16 as in the first embodiment, but includes a transmission unit 20 that transmits the estimated timing offset and frequency offset to the transmission side. The transmission-side communication device that has received the timing offset can adjust the signal transmission timing to obtain the same effect as that obtained by correcting the window timing in the second embodiment. In addition, the transmission-side communication apparatus that has received the frequency offset can correct the frequency (carrier frequency) that is a reference for transmission.

  FIG. 12 shows a communication device according to the fourth embodiment. In the fourth embodiment, the communication device has a plurality of receiving antenna elements 11a and 11b. In general, since the offset amount (phase rotation amount) differs between a plurality of receiving antenna elements, when there are a plurality of antenna elements 11a and 11b, the phase rotation amount estimating unit 16 and the phase are respectively provided for each system of the antenna elements 11a and 11b. A rotation amount correction unit 17 is preferably provided.

  On the other hand, in the fourth embodiment, the phase rotation amount estimation unit 16 common to the plurality of antenna elements 11a and 11b is provided. Using the phase rotation amount estimated by the phase rotation amount estimation unit 16, the phase rotation amount correction units 17a and 17b provided in the respective systems of the antenna elements 11a and 11b perform phase rotation amount correction.

  As described above, the offset amounts are different between the plurality of antenna elements 11a and 11b. However, if the antenna elements 11a and 11b are arranged close to each other, the distribution of delay waves and Doppler waves becomes close, and the offset value is also close. Value. Therefore, when the distance between the plurality of antenna elements 11a and 11b is short, when the noise in the transmission path is large, or when the number of signals that can be used for estimation of the offset (phase rotation amount) is small, the phase rotation amount estimation unit 16 can average the offset estimated values (phase rotation amount estimated values) of the antenna elements 11a and 11b, thereby improving the estimation accuracy.

  Specifically, the phase rotation amount estimation unit 16 obtains a correlation value S in the system of the antennas 11a and 11b and obtains an average value of the correlation values S. Then, the phase rotation amount estimation unit 16 derives the timing offset T ^ mean and the frequency offset F ^ mean from the average value of the correlation values S.

Instead of the phase rotation amount correction units 17a and 17b of the fourth embodiment, the window position correction unit 18 and the reference frequency correction unit 19 of the second embodiment are provided in each system of the plurality of antenna elements 11a and 11b, respectively. May be.
Moreover, instead of the phase rotation amount correction units 17a and 17b of the fourth embodiment, the transmission unit 20 of the third embodiment may be provided.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

It is a figure which shows the subcarrier structure of OFDM. It is a frequency-time two-dimensional array of subcarriers. It is a block diagram of the communication apparatus which concerns on 1st Embodiment. It is a basic concept explanatory drawing of phase rotation amount estimation. (A) is explanatory drawing of the weighted average of timing offset, (b) is explanatory drawing of the weighted average of frequency offset. It is a block diagram of a phase rotation amount estimation part. It is explanatory drawing for the timing offset for every tile, and the example of a frequency offset calculation. It is explanatory drawing of phase rotation correction | amendment. It is a block diagram of the communication apparatus which concerns on 2nd Embodiment. It is explanatory drawing of FFT window timing correction. It is a block diagram of the communication apparatus which concerns on 3rd Embodiment. It is a block diagram of the communication apparatus which concerns on 4th Embodiment. It is explanatory drawing of the conventional phase rotation amount estimation method.

Explanation of symbols

1: communication device, 11: antenna element, 12: RF unit, 13: BB unit, 14: FFT unit, 15: filter processing unit, 16: phase rotation amount estimation unit, 17: phase rotation amount correction unit, 161: buffer 162: transmission path frequency response calculation unit, 163: buffer, 164: correlation calculation unit, 165: correlation value storage unit, 166: phase rotation amount calculation unit 18: window position correction unit, 19: reference frequency correction unit, 20: Transmitter

Claims (6)

A communication apparatus that performs communication using OFDM signals in which pilot signals used for calculation of a transmission channel frequency response are distributed in a two-dimensional arrangement in a time direction and a frequency direction,
A transmission line frequency response calculation unit for calculating a transmission line frequency response in a pilot signal included in the received OFDM signal;
A correlation value calculating unit that calculates a correlation value of a channel frequency response between pilot signals based on the channel frequency response calculated by the channel frequency response calculating unit;
A phase rotation amount calculation unit that calculates a phase rotation amount using a plurality of correlation values calculated by the correlation value calculation unit;
With
The correlation value calculation unit is configured to calculate a plurality of correlation values having different positional relationships between pilot signals,
The phase rotation amount calculation unit calculates a phase rotation amount using a plurality of correlation values having different positional relationships between pilot signals.
A communication device.   The communication apparatus according to claim 1, further comprising: a phase rotation amount correction unit that corrects the phase rotation amount of the received signal using the phase rotation amount calculated by the phase rotation amount calculation unit.   2. A window position correction unit that calculates a timing offset using the phase rotation amount calculated by the phase rotation amount calculation unit and corrects the FFT window timing of the received signal based on the calculated timing offset. Or the communication apparatus of 2.   2. A reference frequency correction unit that calculates a frequency offset using the phase rotation amount calculated by the phase rotation amount calculation unit, and corrects a reception reference frequency based on the calculated frequency offset. 4. The communication device according to any one of items 3.   A transmission unit that calculates a timing offset and / or a frequency offset using the phase rotation amount calculated by the phase rotation amount calculation unit, and transmits the calculated timing offset and / or frequency offset to a signal transmission side. The communication apparatus according to any one of claims 1 to 4. A method of estimating a phase rotation amount using the pilot signal included in an OFDM signal in which pilot signals used for calculation of a transmission channel frequency response are distributed in a two-dimensional arrangement in a time direction and a frequency direction,
Calculating a channel frequency response in a pilot signal included in the received OFDM signal;
A correlation value calculating step for calculating a correlation value of a channel frequency response between pilot signals;
A phase rotation amount calculation step for calculating a phase rotation amount using a plurality of correlation values calculated in the correlation value calculation step;
Including
In the correlation value calculating step, a plurality of correlation values having different positional relationships between pilot signals are calculated,
In the phase rotation amount calculation step, the phase rotation amount is calculated using a plurality of correlation values having different positional relationships between pilot signals.
A method for estimating the amount of phase rotation.

Images