JP2003032314A - Phase error correction method and apparatus - Google Patents

Abstract

(57) [Problem] To correct the orthogonality of an I channel component and a Q channel component of a received signal. SOLUTION: An I-channel component and a Q-channel component of a received preamble signal are respectively integrated for a certain period of time, and the integrated values are squared and added. By comparing the value obtained by squaring the integrated value and adding the values, the orthogonality of the I-channel component and the Q-channel component of the reception preamble signal is estimated, and the transmission device and the reception device are obtained by taking the autocorrelation of the reception preamble signal. And estimating a local frequency error between the received preamble signal and the phase of the I-channel component and the Q-channel component of the received preamble signal based on the result of the local frequency error estimation and the result of the orthogonality estimation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase error correction method and apparatus for a radio received signal such as OFDM, and more particularly to a phase error in a quadrature demodulator in a receiver and a local frequency error between a transmitter and a receiver. The present invention relates to a technique for preventing deterioration of communication quality due to a phase error.

[0002]

2. Description of the Related Art As shown in FIG. 3, an OFDM receiver down-converts an OFDM signal received by an antenna 1 into an IF signal by a local frequency signal in a high frequency section 2 or performs only band limitation, and an orthogonal demodulator (orthogonal demodulator) is used. The detector 3 distributes the I-channel component (in-phase component) and the Q-channel component (quadrature component), and further converts both channel components into digital signals by the A / D converter 4, and then the demodulator 5 disperses them. This is to demodulate data by extracting subcarriers by Fourier transform and demapping.

[0003]

However, in such an OFDM receiver, the quadrature demodulator 3 has a high degree of orthogonality between the I-channel component and the Q-channel component (the ensuring property of the phase difference of 90 degrees). It can be guaranteed by using,
Since the OFDM signal has a wide band, it has been difficult to realize a quadrature demodulator that obtains an I channel component and a Q channel component having a phase difference of 90 degrees with respect to all frequencies in the band. Therefore, by moving the A / D converter 4 from the rear stage to the front stage of the quadrature demodulator 3, the A / D converter 4 uses the clock of four times or more of the OFDM signal band to perform OF.
Although it is possible to sample a DM signal and allocate the sampled signal to the I channel and the Q channel alternately by the quadrature demodulator 3, it is possible to carry out quadrature demodulation without error. Since it has a wide band, it is difficult to realize an A / D converter that can operate with a clock that is four times the band or more. Thus, even if the quadrature demodulator 3 is inserted immediately after the high frequency unit 2 or the A / D converter 4 is inserted immediately after the high frequency unit 2, it is difficult to eliminate the quadrature error.

Further, a local frequency error between the transmitter and the receiver (frequency error between the local oscillators for frequency conversion in the high frequency section 2 of the transmitter and the receiver, and a quadrature modulator of the transmitter and the receiver). The frequency error between the local oscillators of the quadrature demodulator can be estimated and corrected by using the received preamble signal, but the phase difference between the I channel component and the Q channel component is 90 as described above. If the deviation is out of degrees, the frequency error could not be corrected correctly.

The present invention has been made in view of the above points, and an object thereof is to accurately correct a phase error of a signal including a phase error and a local frequency error by a quadrature demodulator. To provide a phase error correction method and device.

[0006]

According to a first aspect of the present invention, an I-channel component and a Q-channel component of a received preamble signal are integrated for a certain period of time and the integrated value is squared and added, and an I of a normal preamble signal. The channel component and the Q channel component are each integrated for a certain period of time, and the integrated value is squared and added to compare the values, and the orthogonality between the I channel component and the Q channel component of the received preamble signal is estimated, and the estimated result is obtained. Based on this, the phase error correction method is characterized in that the phases of the I channel component and the Q channel component of the received preamble signal are adjusted.

According to a second aspect of the present invention, the I channel component and the Q channel component of the received preamble signal are integrated for a certain period of time, the integrated value is squared and added, and the I channel component and the Q channel component of the normal preamble signal. And estimating the orthogonality of the I-channel component and the Q-channel component of the received preamble signal by comparing with a value obtained by squaring the added value and adding the integrated values for a certain period, and obtaining the autocorrelation of the received preamble signal. Estimating a local frequency error between the transmitter and the receiver, and adjusting the phases of the I channel component and the Q channel component of the received preamble signal based on the result of the local frequency error estimation and the result of the orthogonality estimation. The phase error correction method is characterized by

According to a third aspect of the present invention, in the first or second aspect of the invention, the I channel component and the Q channel component of the phase-adjusted received preamble signal are fed back to estimate the orthogonality again and the phase adjustment is performed. The phase error correction method is characterized in that

According to a fourth aspect of the present invention, the I channel component and the Q channel component of the received preamble signal are integrated for a certain period of time, the integrated value is squared and added, and the I channel component and the Q channel component of the normal preamble signal. And a orthogonality estimator that estimates the orthogonality of the I-channel component and the Q-channel component of the received preamble signal by comparing the values obtained by integrating the Based on the estimated value obtained by the estimation unit,
The phase error correction device is provided with a phase rotation unit that adjusts the phases of the I channel component and the Q channel component of the reception preamble signal.

According to a fifth aspect of the invention, in the fourth aspect of the invention, a correction value memory storing a correction value for setting the amount of phase adjustment in the phase rotation section based on the estimated value obtained by the orthogonality estimation section. The phase error correction device is characterized by comprising:

According to a sixth aspect of the present invention, the invention according to the fourth aspect further comprises a frequency error estimating section for estimating a local frequency error between the transmitter and the receiver by taking an autocorrelation of the received preamble signal, The phase rotation unit adjusts the phases of the I channel component and the Q channel component of the received preamble signal based on the estimated value obtained by the orthogonality estimation unit and the estimated value obtained by the frequency error estimation unit. The phase error correction device is characterized by the above.

According to a seventh aspect of the invention, in the invention of the sixth aspect, phase adjustment in the phase rotation section is performed based on the estimated value obtained by the orthogonality estimation section and the estimated value obtained by the frequency error estimation section. The phase error correction apparatus is provided with a correction memory that stores a correction value for setting the amount.

According to an eighth aspect of the present invention, in the invention according to any one of the fourth to seventh aspects, the I channel component and the Q channel component of the received preamble signal whose phase is adjusted by the phase rotation unit are used for the orthogonality estimation unit. The phase error correction apparatus is provided with a feedback means for re-inputting the signal to the terminal and performing the orthogonality estimation and the phase adjustment again.

[0014]

1 is a block diagram of an OFDM receiver according to one embodiment of the present invention. In FIG.
Reference numeral 1 is an antenna, 2 is a high frequency unit that down-converts a received signal into an IF signal by a local frequency signal or band-limits, 3 is a quadrature demodulator (quadrature detector) that divides the received signal into I channel components and Q channel components, Reference numeral 4 is an A / D converter that converts an analog signal of the I channel component and the Q channel component into a digital signal. Reference numeral 5 is data that is obtained by extracting the subcarrier from the OFDM reception signal by the discrete Fourier transform and further mounting it on the subcarrier by demapping. Is a demodulation unit for taking out the signal, and the above is the same as that shown in FIG.

In addition to these, the present embodiment is further provided with an orthogonality estimator for estimating the degree of orthogonality between the I channel component and the Q channel component (how much the phase difference between both channel components deviates from 90 degrees). 6, a frequency error estimator 7 that estimates a local frequency error between the transmitter and the receiver, and a phase rotation unit 8 that adjusts the phases of the I channel component and the Q channel component based on the obtained correction value. 9 is a preamble memory such as a ROM storing a regular preamble, 10
Is a correction value memory such as a ROM that stores the phase correction values obtained by simulation.

Since the subcarriers of the OFDM signal are QAM- or PSK-modulated, FIG. 2 shows a signal point constellation diagram of 64QAM as an example.
In FIG. 2, the black dots indicate the normal signal point arrangement, and the white dots on the dotted line indicate the signal point arrangement including the initial phase error of 0.05 [rad] of the local frequency and the phase error of 0.05 [rad] of the quadrature demodulator 3. . Further, when there is a local frequency error fc between the transmitter and the receiver, if the sampling period in the A / D converter 4 is Ts [sec], the phase shifts by 2πfcTs [rad].

The I channel component and the Q channel component are
It is converted into a digital signal by the A / D converter 4 and taken into the orthogonal estimation unit 6. The orthogonal estimator 6 integrates the I channel component and the Q channel component of the received preamble signal for a certain period of time, squares the respective integrated values, and adds the value, and the I channel component of the normal preamble signal read from the preamble memory 9. And the Q channel component are respectively integrated, and the respective integrated values are squared and compared with the added value to obtain a first estimated value D1 described later.

The frequency error estimator 7 estimates the phase error due to the frequency error by obtaining the autocorrelation using the continuity of the received preamble signal, and obtains the second estimated value D2 described later. For autocorrelation, the received preamble signal is 1
It is obtained by detecting the correlation between the signal delayed by the symbol and the subsequent received preamble signal. The second estimated value D2 includes not only the phase error due to the local frequency error but also the phase error due to the quadrature demodulator 3.

The correction value memory 10 has a correction value P whose addresses are the estimated values D1 and D2 obtained as described above.
1 and P2 are stored in advance according to the result of simulating the phase adjustment amount based on the estimated values D1 and D2. Therefore, the phase rotation unit 8 adjusts the phase by the correction values P1 and P2 so that the axes of the I channel component and the Q channel component of the received preamble signal input thereto are orthogonal, and the adjustment amount thereof Is retained.

The I channel component and the Q channel component whose phases have been adjusted here are fed back to the orthogonality estimation unit 6. That is, the orthogonality estimation unit 6 initially estimates the orthogonality of the received preamble signal and the normal preamble read from the preamble memory 9 to obtain the estimated value D1, but thereafter, the preamble signal fed back from the phase rotation unit 8 is obtained. And the normal preamble read from the preamble memory 9 to estimate orthogonality and estimate D1
It switches to the action of getting. The same applies to the frequency error estimation unit 7.

Therefore, when this feedback operation is repeated, the phase rotator 8 is gradually corrected to have accurate orthogonality, and the phase rotator 8 finally normalizes the I channel component and the Q channel component of the reception preamble. It is set to the amount of phase adjustment with the orthogonality of. The above operation may be performed even during reception of the preamble symbol,
At this time, the input data is temporarily saved in a memory or the like (not shown). Then, by the finally set phase adjustment amount, the phases of the I channel component and the Q channel component of the subsequent data are adjusted to have orthogonality, and the data is sent to the next demodulation unit 5.

The estimated values D1 and D2 are obtained by the following equations (1) and (2), and the signals Ai (nTs) after the phase adjustment of the I channel component and the Q channel component by the correction values P1 and P2 are performed.
Aq (nTs) is obtained from equation (3). In these equations (1) to (3), n: integer Ts: sampling period in A / D converter 4 Tp: preamble period Np: number of preamble signals Si (nTs): I channel component Sq (nTs) of received preamble signal ): Q channel component I (nTs) of received preamble signal: I channel component Q (nTs) of preamble signal stored in the memory 10: Q channel component of preamble signal stored in the memory 10

[0023]

[Equation 1]

In the above, the case of handling an ODFM signal in which the effect of the present invention is particularly remarkable has been described. However, a receiving apparatus having a quadrature demodulator and having a local frequency error between the transmitting apparatus and the receiving apparatus is described. Then, it is needless to say that the same can be applied to other receiving devices.

[0025]

As described above, according to the present invention, it becomes possible to accurately correct a phase error in a signal including a phase error due to a quadrature demodulator and further a local frequency error. It is suitable for a device that handles a wide band.

[Brief description of drawings]

FIG. 1 is a block diagram of an OFDM receiver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a signal point arrangement of 64QAM.

FIG. 3 is a block diagram of a conventional OFDM receiver.

[Explanation of symbols]

1: Antenna, 2: High frequency part, 3: Quadrature demodulator, 4: A
/ D converter, 5: demodulation unit, 6: orthogonality estimation unit, 7: frequency error estimation unit, 8: phase rotation unit, 9: preamble memory, 10: correction value memory

Claims (8)

[Claims] 1. A value obtained by integrating the I channel component and the Q channel component of a received preamble signal for a certain period and squaring the integrated values and adding them, and the I channel component and the Q channel component of a normal preamble signal are each integrated for a certain period. Then, the integrated value is squared and added, and the orthogonality between the I channel component and the Q channel component of the received preamble signal is estimated by comparing the calculated value with the I channel component of the received preamble signal based on the estimation result. A phase error correction method characterized by adjusting the phase of a Q channel component. 2. A value obtained by integrating the I channel component and the Q channel component of a received preamble signal for a certain period and squaring the integrated values and adding them, and an I channel component and a Q channel component of a normal preamble signal, respectively, for a certain period. Then, the integrated value is squared and added to be compared to estimate the orthogonality of the I channel component and the Q channel component of the received preamble signal, and the transmitter and the receiver are obtained by taking the autocorrelation of the received preamble signal. A phase characterized by estimating a local frequency error between devices and adjusting the phases of the I channel component and the Q channel component of the received preamble signal based on the result of the local frequency error estimation and the result of the orthogonality estimation. Error correction method. 3. The phase adjustment according to claim 1 or 2, wherein the I channel component and the Q channel component of the phase-adjusted received preamble signal are fed back to estimate the orthogonality again. Phase error correction method. 4. A value obtained by integrating the I channel component and the Q channel component of a received preamble signal for a certain period and squaring the integrated values and adding them, and the I channel component and the Q channel component of a normal preamble signal are each integrated for a certain period. Then, an orthogonality estimator that estimates the orthogonality of the I channel component and the Q channel component of the received preamble signal by comparing the sum of the squared values and the added value, and the orthogonality estimator A phase error correction device comprising: a phase rotation unit that adjusts the phases of the I channel component and the Q channel component of the received preamble signal based on the estimated value. 5. The correction value memory according to claim 4, further comprising a correction value memory that stores a correction value for setting the amount of phase adjustment in the phase rotation unit based on the estimated value obtained by the orthogonality estimation unit. Phase error correction device. 6. The frequency error estimation unit according to claim 4, wherein the frequency rotation estimation unit estimates a local frequency error between the transmission device and the reception device by taking an autocorrelation of the reception preamble signal. Based on the estimated value obtained by the frequency estimation section and the estimated value obtained by the frequency error estimation section,
A phase error correction apparatus for adjusting the phases of the I channel component and the Q channel component of the received preamble signal. 7. The correction value for setting the amount of phase adjustment in the phase rotation unit based on the estimation value obtained by the orthogonality estimation unit and the estimation value obtained by the frequency error estimation unit according to claim 6. A phase error correction device comprising a stored correction memory. 8. The I channel component and the Q channel component of the received preamble signal, the phase of which has been adjusted by the phase rotation unit, according to any one of claims 4 to 7, and input again to the orthogonality estimation unit and re-inputted. A phase error correction device comprising a feedback means for performing orthogonality estimation and the phase adjustment.