JP2003188846A - Communication apparatus and frequency deviation estimation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication apparatus capable of reducing the effect of multi-path and inter-code interference and estimating a frequency offset value of a local oscillation signal even when preceding and succeeding transmission pilot symbols differ from each other. <P>SOLUTION: The communication apparatus of this invention provided with a cross-correlation value calculation means (complex multiplexers 4, 5, 6, and integrator 7) that calculates cross-correlation value of a received pilot symbol and at least one transmission pilot symbol already known at a receiver side, and a frequency deviation estimate means (phase rotary angle estimation unit 8 and frequency deviation estimate unit 9) for estimating the frequency offset value of the local oscillation signal on the basis of the cross-correlation value, is characterized in that the communication apparatus makes the frequency of the local oscillation signal follow the frequency of a carrier used for the modulation on the basis of the frequency offset value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to OFDM (Orthog
onal frequency division multiplexing) relates to a communication device that employs a modulation / demodulation method, and in particular, uses a known pilot symbol on the receiving side to estimate the frequency deviation based on the difference between the oscillation frequency of the transmitter and the oscillation frequency of the receiver. The present invention relates to a communication device and a frequency deviation estimation method.

[0002]

2. Description of the Related Art A conventional communication device will be described below. FIG. 3 is a diagram showing a configuration of a conventional communication device (receiver). In FIG. 3, 101 is an analog / digital converter (A / D), 102 and 111 are delay devices, 103 is a complex multiplier, 104 is an integrator, and 105 is a peak value detector. Yes, 106 is a phase rotation angle estimator, 107 is a frequency deviation estimator, 1
Reference numeral 08 is a complex multiplier, 109 is a serial / parallel converter (S / P), and 110 is an FFT.

FIG. 4 shows an OFDM (Orthogonal Fre
FIG. 15 is a diagram showing a burst configuration in a quency division multiplexing (VDM) modulation / demodulation system, in which 151 is a guard interval (GI) and 152 is data (Data).

The frequency of the local oscillation wave generated by the communication device (receiver) must exactly match the frequency of the carrier wave used for modulation of the transmitter because of the product of the synchronous detection. If the frequency of the oscillation signal shifts by Δf,
The output of the synchronous detector fluctuates gently at the frequency Δf.

Therefore, as shown in FIG. 3, in the receiver, A
An autocorrelation value (for m samples) between the received signal after the / D conversion and the signal delayed by n samples is calculated. In this case, in the OFDM modulation method, since the last part of the data (Data) for n samples and the guard interval (GI) for m samples are the same, the autocorrelation value peaks when the sample point matches GI. Becomes Therefore,
The local oscillation signal is obtained by searching the integrated value to find the peak value, and estimating the frequency offset value Δf from the phase rotation amount generated based on the deviation between the oscillation frequency of the transmitter and the oscillation frequency of the peak value. The frequency of is followed by the frequency of the carrier wave used for modulation. (Refer to the document "OFDM Modulation Technology" Trikeps p110-111)

In the above conventional communication device, first, the A / D 1
01 converts the received signal from an analog value to a digital value. The delay device 102 delays the digital signal output from the A / D 101 by n samples. In the complex multiplier 103,
Complex multiplication is performed using the m-sample digital signal from the A / D 101 and the m-sample delay signal from the delay unit 102. The integrator 104 integrates the complex multiplication results. The peak value detector 105 detects a peak value from the integration result. In the phase rotation angle estimator 106,
From the peak value, the phase rotation angle based on the difference between the oscillation frequency of the transmitter and the oscillation frequency of the receiver is calculated. The frequency deviation estimator 107 estimates the frequency deviation from the phase rotation angle and calculates the phase correction vector. In the delay device 111, the A / D 101 is operated until the phase correction vector information from the frequency deviation estimator 107 is input to the complex multiplier 108.
Delay the output signal. The complex multiplier 108 corrects the phase rotation due to the frequency offset by complexly multiplying the digital signal output from the delay device 111 by the phase correction vector. In S / P109, the complex multiplier 10
The 8-output serial signal is converted into a parallel signal. FF
At T110, the parallel signal is converted into a frequency component signal.

Further, as a frequency tracking method using pilot symbols, a burst structure shown in FIG. 5 (“small power data communication system broadband mobile access system (HiSWA
Na) Standard (draft), version 0.3 ", Japan Radio Industry Association, 2000 1
There is a method using (October 12). In FIG. 5, 20
1, 202 are pilot symbols, and 203, 20
4, 205 and 206 are data symbols, and the pilot symbols P (1) and P (2) at the time of transmission are the same.
The transmitter outputs a transmission signal in the burst structure shown in FIG.

FIG. 6 is a diagram showing the structure of a receiver for receiving the transmission signal shown in FIG. The same components as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted.

In the receiver, first, the A / D 101 converts the received signal from an analog value to a digital value. The delay device 102 delays the pilot symbol P (1) in the digital signal by one symbol. In the complex multiplier 103, the pilot symbol P in the digital signal
Complex multiplication is performed using (2) and the delayed pilot symbol P (1). The integrator 104 integrates the complex multiplication results. The phase rotation angle estimator 106 calculates the phase rotation angle from the integration result. The subsequent processing is the same as in the case of FIG.

[0010]

However, the above
In the conventional communication device shown in FIG. 3, since the processing is performed using the autocorrelation value of the received signal, there is a problem that the frequency deviation estimation result deteriorates due to the effects of multipath and intersymbol interference. It was Further, in the conventional communication device shown in FIG. 6, when the transmission pilot symbols P (1) and P (2) are different, the frequency offset value of the local oscillation signal cannot be estimated by autocorrelation. there were.

The present invention has been made in view of the above, and it is possible to reduce the effects of multipath and intersymbol interference, and further, in the case where the transmission pilot symbols P (1) and P (2) are different. Another object is to obtain a communication device capable of estimating the frequency offset value of the local oscillation signal, and a frequency deviation estimation method.

[0012]

[Means for Solving the Problems]
In order to achieve the object, in the communication device according to the present invention, a cross-correlation value calculating means for calculating a cross-correlation value between the reception pilot symbol and at least one transmission pilot symbol known on the receiving side, Frequency deviation estimating means for estimating the frequency offset value of the local oscillation signal based on the cross-correlation value, and based on the frequency offset value, the frequency of the local oscillation signal to the frequency of the carrier used for modulation It is characterized by following.

In the communication device according to the next invention, the frequency deviation estimating means calculates a phase rotation angle from the cross-correlation value, estimates a frequency offset value from the phase rotation angle, and calculates a phase rotation angle. Then, a sample having a correlation lower than a predetermined value defined in advance is excluded from the calculation.

In the frequency deviation estimating method according to the next invention, a cross-correlation value calculating step of calculating a cross-correlation value between the reception pilot symbol and at least one transmission pilot symbol known on the receiving side, A frequency deviation estimating step of estimating a frequency offset value of the local oscillation signal based on the cross-correlation value.

In the frequency deviation estimating method according to the next invention, in the frequency deviation estimating step, the phase rotation angle is calculated from the cross-correlation value, the frequency offset value is estimated from the phase rotation angle, and the phase rotation is calculated. It is characterized in that, in the step of calculating the angle, a sample having a correlation lower than a predetermined value defined in advance is excluded from the calculation.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a communication device and a frequency deviation estimating method according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1. FIG. 1 is a diagram showing a configuration of a communication device (receiver) according to the present invention. In FIG. 1, 1 is an analog / digital converter (A / D), 2 is a known pilot symbol: P (1), 3
Is a known pilot symbol: P (2), 4, 5,
Reference numerals 6 and 10 are complex multipliers, 7 is an integrator, 8 is a phase rotation angle estimator, 9 is a frequency deviation estimator, and 11 is a serial / parallel converter (S / P). , 12 are FFTs (Fast Fourier Transforms), 13
Is a delay device. Note that FIG. 5 described above is used as the frame structure of the transmission signal. Further, transmission pilot symbols P (1) and P (2) are known symbols.

FIG. 2 is a diagram showing a received frame structure when the transmission signal shown in FIG. 5 is received.
2 is a received pilot symbol and is 23, 24, 2
Reference numerals 5 and 26 are received data symbols.

In the above communication device, first, the A / D 1 converts the received signal from an analog value to a digital value. The complex multiplier 4 receives the received pilot symbol P of the A / D1 output.
(1) r and known pilot symbol 2 (P (1) in FIG. 5)
(Corresponding to 201) is used to calculate a channel response hp1 (n). Here, n is an arbitrary value and represents the nth sample. Similarly, the complex multiplier 5 similarly receives the received pilot symbol P of the A / D1 output.
(2) r and known pilot symbol 3 (P (2) in FIG. 5)
(Corresponding to 202) and the channel response hp2 (n) is calculated.

In the complex multiplier 6, the complex multipliers 4 and 5 are used.
A complex operation is further performed using the output operation result. The integrator 7 integrates the complex multiplication results of the complex multiplier 6. The phase rotation angle estimator 8 calculates the phase rotation angle δ from the integrated value. The processing in the complex multiplier 6, the integrator 7, and the phase rotation angle estimator 8 can be expressed by equation (1).

[0021]

[Equation 1]

The frequency deviation estimator 9 estimates the frequency deviation from the phase rotation angle δ and calculates the phase correction vector as in the conventional method. The delay unit 13 delays the signal output from the A / D 1 until the phase correction vector information from the frequency deviation estimator 9 is input to the complex multiplier 10. The complex multiplier 10 corrects the phase rotation due to the frequency offset by complexly multiplying the received signal output from the delay device 13 by the phase correction vector. In S / P11, the serial signal output from the complex multiplier 10 is converted into a parallel signal. The FFT 12 converts the parallel signal (signal on the time axis) into a frequency component signal.

In the above (1), in order to reduce the influence of noise, samples having 1 / a or less of the peak values of the channel responses hp1 (n) and hp2 (n) may be excluded from the calculation. However, the above a is arbitrary within a range in which a desired frequency offset value estimation accuracy is obtained. Although the number of pilot symbols has been described as two, the number of pilot symbols is arbitrary.

As described above, according to the present invention, the processing is performed without using the autocorrelation value of the received signal, that is, the cross-correlation value of the received signal and the known pilot symbol that does not include multipath or noise is used. Since the processing is performed in this manner, the effects of multipath and intersymbol interference can be reduced. Also, since the frequency offset value of the local oscillation signal is estimated based on the cross-correlation value between the received signal and each known pilot symbol, the frequency of the local oscillation signal is modulated even when the pilot symbols before and after are different. The frequency of the carrier wave used for can be made to follow. In addition, in the calculation of the equation (1), the channel response hp1
It is possible to improve the frequency offset value estimation accuracy by excluding the samples of 1 / a or less of the peak values of (n) and hp2 (n) from the calculation.

[0025]

As described above, according to the present invention, the processing is performed without using the autocorrelation value of the received signal, that is, the received signal containing no multipath or noise and the known pilot symbol are included. Since the processing is performed using the cross-correlation value, it is possible to reduce the influence of multipath and intersymbol interference. Further, since the frequency offset value of the local oscillation signal is estimated based on the cross-correlation value between the received signal and each known pilot symbol, even if the pilot symbols before and after are different, the frequency of the local oscillation signal is It is possible to follow the frequency of the carrier wave used for modulation.

According to the next invention, for example, the configuration is such that the sample of the channel response less than or equal to the predetermined value is excluded from the calculation, so that it is possible to obtain the communication device capable of greatly improving the frequency offset value estimation accuracy. There is an effect that it can.

According to the next invention, since the processing is performed without using the autocorrelation value of the received signal, that is, the processing is performed using the cross-correlation value of the received signal and the known pilot symbol, The effect of reducing the influence of paths and intersymbol interference can be achieved. Since the frequency offset value of the local oscillation signal is estimated based on the cross-correlation value between the received signal and each known pilot symbol, even if the pilot symbols before and after are different, the frequency of the local oscillation signal is It is possible to follow the frequency of the carrier wave used for modulation.

According to the next invention, for example, the sample of the channel response equal to or less than the predetermined value is excluded from the calculation, so that the frequency offset value estimation accuracy can be greatly improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a communication device (receiver) according to the present invention.

FIG. 2 is a diagram showing a received frame structure when the transmission signal shown in FIG. 5 is received.

FIG. 3 is a diagram showing a configuration of a conventional communication device.

FIG. 4 is a diagram showing a burst structure in the OFDM modulation / demodulation system.

FIG. 5 is a diagram showing a frequency tracking method using pilot symbols.

6 is a diagram showing a configuration of a receiver for receiving the transmission signal shown in FIG.

[Explanation of symbols]

1 analog / digital converter (A / D), 2, 3
Known pilot symbols, 4, 5, 6, 10 complex multiplier, 7 integrator, 8 phase rotation angle estimator, 9 frequency deviation estimator, 11 serial / parallel converter (S / P),
12 FFT (Fast Fourier Transform), 13 delay device.

Claims (4)

[Claims] 1. A cross-correlation value calculating means for calculating a cross-correlation value between a reception pilot symbol and at least one transmission pilot symbol known on the receiving side, and a frequency offset of a local oscillation signal based on the cross-correlation value. A frequency deviation estimating means for estimating a value, and making the frequency of the local oscillation signal follow the frequency of the carrier wave used for modulation based on the frequency offset value. 2. The frequency deviation estimating means calculates a phase rotation angle from the cross-correlation value, estimates a frequency offset value from the phase rotation angle, and calculates a phase rotation angle. The communication device according to claim 1, wherein a sample having a correlation lower than a predetermined value is excluded from the calculation. 3. A cross-correlation value calculating step of calculating a cross-correlation value between a received pilot symbol and at least one transmission pilot symbol known on the receiving side, and a frequency offset of a local oscillation signal based on the cross-correlation value. A frequency deviation estimation method comprising: a frequency deviation estimation step of estimating a value; 4. The frequency deviation estimating step calculates a phase rotation angle from the cross-correlation value, estimates a frequency offset value from the phase rotation angle, and calculates a phase rotation angle in advance. The frequency deviation estimation method according to claim 3, wherein a sample having a correlation lower than a predetermined value is excluded from the calculation.