JP2000269930A - Synchronization system for multi-carrier receiver, synchronizing circuit for multi-carrier receiver, and multi-carrier receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately decide a position of an FFT window for fast Fourier transform in a multi-carrier receiver adopting a phase modulation system having a provision for insertion of a guard interval(GI). SOLUTION: A window circuit 220 extracts a component corresponding to one effective symbol length Ts from outputs I, Q of an orthogonal demodulation circuit 210, a serial parallel conversion circuit (S/P) 230 applies serial parallel conversion to the extracted component, a fast Fourier transform device (FFT) 240 applies fast Fourier transform to an output of the S/P 230, and a parallel serial converter (P/S) 250 provides an output of one signal stream. A carrier level measurement circuit 110 measures the power level of each carrier that is an output of the FFT 240, and a flatness measurement circuit 120 obtains a variance of the power levels to discriminate whether or not the window circuit 220 correctly extracts one effective symbol. Since a window timing is completely synchronized when an output from the flatness measurement circuit 120 takes a minimum value, a PLL 130 applies feedback control to the window circuit 220.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a synchronization circuit of a multi-carrier receiver. The present invention is particularly effective as a synchronization circuit in a receiving apparatus of a digital transmission system for transmitting digital data by orthogonal frequency division multiplex modulation.

[0002]

2. Description of the Related Art In recent years, a multiplex communication system using a large number of carriers has been actively developed. Among them,
Orthogonal Frequency Division Multiplex
Multiplexing) has attracted attention as a digital transmission system for high-speed and high-density signals. This OFDM system is considered to be promising as a means for transmitting audio signals and video signals particularly suitable for mobile reception in automobiles and the like because of its high quality and strong resistance to interference.

The OFDM system can reduce the data rate of each carrier to hundreds or thousands by using hundreds or thousands of carriers orthogonal to each other. This can reduce so-called multipath interference. Further, by repeatedly transmitting a substantial signal (effective symbol) and a signal (guard interval, GI) transmitted on the premise that the signal is removed on the receiving side, it is possible to further reduce multipath interference. Have been done.

In the method of transmitting a signal including a guard interval (GI), it is necessary for a receiving apparatus to discriminate and remove the guard interval (GI) during demodulation. As means for achieving the synchronization (accurately measuring the timing of the guard interval), for example, an OFDM reception synchronization circuit 9 described in JP-A-7-99486 shown in FIG.
00 is known. The received signal is subjected to quadrature demodulation, so that in-phase components (Inphase, Inphase,
The signals are demodulated into two streams of an I component) and a quadrature component (Quadrature, Q component). OFDM reception synchronization circuit 900
For one of the in-phase component (I component) and the quadrature component (Q component), a multiplication circuit 92 multiplies the delayed signal delayed by the delay circuit 91 and the original signal that has not been delayed.
The synchronization signal is obtained by taking the correlation value at.

The operation of the OFDM reception synchronization circuit 900 is as follows. FIG. 2 shows a conceptual diagram of a signal obtained by orthogonally demodulating a received signal. A signal obtained by orthogonally demodulating the received signal is input to the OFDM reception synchronization circuit 900 through analog / digital conversion (A / D conversion). For simplicity, FIG. 2 shows a signal in an analog state. . The signal input to the OFDM reception synchronization circuit 900 is a digital signal to the last.

FIG. 2 shows one effective symbol and a guard interval (GI) corresponding thereto. The guard interval (GI) is formed by copying a certain period at the end of the corresponding (subsequent) effective symbol. When the signal Sa obtained by orthogonally demodulating the received signal is input to the OFDM reception synchronization circuit 900 shown in FIG. 7, the signal is input to the delay circuit 91 and the multiplication circuit 92. Delay circuit 91
, The signal Sb delayed by the effective symbol period is output to the multiplication circuit 92.

The multiplying circuit 92 correlates the delayed signal Sb from the delay circuit 91 with the original signal Sa which has not been delayed, and outputs a correlation value R. At this time, in the undelayed signal shown in Sa, “..., a fixed period at the end of the effective symbol k−1, a fixed period at the end of the effective symbol k, a fixed period at the end of the effective symbol k + 1,. .., GI _k−1 , GI _k , GI _{k + 1} ,... Of the delayed signal shown, the correlation value R is the end of each effective symbol (“Sa”) of the undelayed signal shown in Sa. A peak is shown at the end of each GI of the delayed signal shown in Sb). In this manner, a synchronization signal for guard interval (GI) removal,
That is, a synchronizing signal for determining a period for performing fast Fourier transform (FFT) is obtained.

[0008]

However, the correlation value of the OFDM reception synchronization circuit 900 does not generally become a waveform having a constant peak as shown by R in FIG. In general, a certain period at the end of the effective symbol k of the undelayed signal,
Correlation values other than GI _k of the delayed signal can be expected to take 0 as an average value in terms of probability. However, the correlation value is
It depends on the waveform in the card interval, and the waveform in this section changes according to the effective symbol. Therefore, the correlation value changes in accordance with the transmitted effective symbol, and the effective symbol greatly changes with time, so that the correlation value greatly changes with time. Therefore, it is not always possible to always obtain a peak signal having a predetermined (above a threshold) magnitude at each end of the effective symbol of the original signal. That is, there is a problem that a synchronization signal cannot be reliably obtained for each symbol.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to propose a synchronization method of a multi-carrier receiving apparatus which determines an effective symbol extraction timing. Another object of the present invention is to provide a synchronization circuit for a multicarrier receiving apparatus using the method, and further to provide a multicarrier receiving apparatus having the synchronization circuit.

[0010]

According to a first aspect of the present invention, there is provided an information processing apparatus comprising: an effective symbol;
A signal having an effective symbol length is extracted from a signal consisting of a guard interval obtained by copying a part of the signal, and in a synchronization method of a multicarrier receiving apparatus that determines a time window for performing a discrete Fourier transform, a reception signal modulated by a phase modulation method is used. Quadrature demodulation, extracting a signal of an effective symbol length at a certain timing from the demodulated signal, performing a discrete Fourier transform for each of the extracted signals of the effective symbol length,
The magnitude of the complex vector of a carrier having a different frequency, which is the result of the discrete Fourier transform, is compared, and the feedback control of the effective symbol extraction timing is performed so that the variance of the magnitude of the complex vector of the carrier becomes a minimum value. I do.

According to the second aspect of the present invention, a time window for extracting a signal having an effective symbol length from a signal including an effective symbol and a guard interval obtained by copying a part of the effective symbol and performing a discrete Fourier transform is provided. A synchronization circuit of a multicarrier receiving apparatus for determining a timing of extracting a signal of an effective symbol length for a demodulated signal obtained by orthogonally demodulating a received signal modulated by a phase modulation method; And a carrier amplitude comparing means for comparing the magnitudes of complex vectors of carriers having different frequencies which are outputs of the discrete Fourier transform calculating means, and an output of the carrier amplitude comparing means. Timing to adjust effective symbol extraction timing Is composed of a unit, the size of the dispersion of the complex vector of the carrier and wherein the feedback control of the effective symbol extraction timing to be the minimum value.

According to a third aspect of the present invention, in the synchronous circuit for a multicarrier receiving apparatus according to the second aspect, the timing adjusting means is a phase locked loop.

According to a fourth aspect of the present invention, there is provided a multicarrier receiving apparatus including the synchronous circuit for a multicarrier receiving apparatus according to the second or third aspect.

[0014]

[Functions and Effects of the Invention] BPSK (Binary Phase Shift)
Keying), QPSK (Quadrature Phase Shift Keyin)
In the phase modulation method such as g), the amplitude of the modulated wave is constant. Therefore, if these phase modulation methods are adopted in the multi-carrier transmission method, the amplitudes of carriers having different frequencies are constant. When this transmission wave is received and demodulated by discrete Fourier transform from a received signal composed of an effective symbol and a guard interval obtained by copying a part of the effective symbol, one symbol interval (a guard interval and a subsequent effective symbol corresponding thereto) If a signal having one effective symbol length is correctly extracted from the data and subjected to discrete Fourier transform, the amplitude of each carrier as an output result is all equal. However, 2
When a signal of one effective symbol length is extracted over a symbol section (a guard interval and a subsequent effective symbol corresponding thereto, and a further succeeding guard interval and a subsequent effective symbol corresponding thereto), the output result of the discrete Fourier transform is The interference of each carrier causes a difference in carrier amplitude. Using this principle, 1
The carrier amplitude is compared from the result of the discrete Fourier transform using the time window of the effective symbol length, the time window is swept over time, and if the timing at which the variance of the amplitude of the carrier takes a minimum value is found, the correct time window is obtained. It's timing.

The use of a phase locked loop is effective in a circuit employing the above-described synchronization method. A multi-carrier receiving apparatus using such a synchronization circuit can achieve reliable synchronization. When there is no interference wave (interference wave due to delay) with respect to the transmission wave, the timing of the start of the time window has an allowable width from the start to the end of the guard interval. The above-described synchronization method, synchronization circuit, and receiver are, for example, O
This is particularly effective in the FDM system.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the present invention will be described below with reference to the drawings. In the following embodiment, QP
An example using the SK-OFDM method will be described, but the present invention is not limited to the following examples.

First, the application of the principle of the present invention to the QPSK-OFDM system will be described. The OFDM signal is
Inverse Descrete Fourier Transform
form) or Inverse Fast Fouri
er Transform), the digital signal x (n) subjected to quadrature demodulation and analog / digital (A / D) conversion can be placed as follows. Here, X (h) is a complex symbol on the frequency axis of each carrier forming the baseband signal to be transmitted, and j is an imaginary unit. It is assumed that 0 ≦ n, h ≦ N−1, that is, an inverse discrete Fourier transform at N points.

(Equation 1)

The signal is quadrature-demodulated on the receiving side, and is subjected to signal processing by a discrete Fourier transform (Descrete Fourier Transform) or a fast Fourier transform (Fast Fourier Transform).
(h) is obtained as follows.

(Equation 2)

However, since the guard interval (GI) is inserted, it is necessary to rewrite the digital signal x (n) as follows. That is, the guard interval length is m digital signals (0 <m <N), and the k-th guard interval (GI) digital signal is x _Gk (n) (0
.Ltoreq.n.ltoreq.m-1) and the digital signal of the succeeding k-th effective symbol is _xSk (n) (0.ltoreq.n.ltoreq.N-1).

(Equation 3)

Now, assume that 0 <p <m and the FFT window timing is shifted by p digital signal lengths as shown in FIGS. 6A and 6B.
FIG. 6A shows a case where the FFT window timing extends over the k-th guard interval (GI) and the succeeding k-th effective symbol, and FIG. Subsequent k +
This is the case where it extends over the first guard interval (GI).

[Case of FIG. 6 (a)] FFT result X '
(h) is as follows.

(Equation 4)

That is, the amplitude (absolute value of the complex symbol) | X '(h) | of each carrier is the same as the amplitude | X (h) | when the FFT window timing matches the effective symbol.

[Case (b) of FIG. 6] FFT result X ″
(h) is as follows.

(Equation 5)

The second term (braces) in equation (5) is not always 0. Therefore, the amplitude | X ″ (h) | of each carrier is | X
(h) |

FIG. 1 is a block diagram of an OFDM receiving apparatus synchronizing circuit 100 according to a specific embodiment of the present invention.
FIG. 3 is a block diagram shown together with peripheral circuits (210 to 250) inside the M receiving apparatus. The OFDM receiver synchronization circuit 100 includes a carrier level measurement circuit 110, a flatness measurement circuit 120, and a phase locked loop 130.

The phase locked loop 130 includes a voltage controlled oscillator, a phase discriminator, and a low-pass filter.

As shown in FIG. 1, a received signal phase-modulated by the QPSK method is input to a quadrature demodulation circuit 210. As shown in FIG. 2, the OFDM signal includes an effective symbol and a guard interval (GI) obtained by copying a fixed period at the end of the effective symbol. OFDM of FIG.
The signal is a composite signal of carriers having frequencies that are orthogonal to each other, and the amplitude of each carrier is constant.

FIG. 3 shows the phase modulation by the QPSK method. The original data is π of the same frequency in a set of 2 bits each.
The transmission is performed using I-phase and Q-phase carriers having different phases.
That is, one effective symbol is 2 bits. As shown in FIG. 3, the original data (00) (10) (11) (01) are compared with the I-phase and Q-phase (1, 1) (-1, 1) (-1, 1).
1) (1, -1) corresponds. These are orthogonally modulated as one carrier and transmitted. This signal is received as shown in FIG. 1 and is quadrature-modulated by the quadrature demodulation circuit 210, so that the I-phase and Q-phase (1, 1) (-1, 1) (-1, 1,-)
1) (1, -1) is demodulated.

The outputs I and Q of the quadrature demodulation circuit 210 of FIG.
Are a guard interval (GI) and a signal sequence of effective symbols, respectively, as shown in FIG. This is as shown in FIG. Here, the window circuit 220 extracts one effective symbol length Ts at the timing indicated by FFT-Wa in FIG.
/ P) 220 to perform a fast-Fourier transform (F
If fast Fourier transform is performed at (FT) 240, synchronous demodulation is performed correctly. This is output as one signal train by a parallel / serial converter (P / S) 250.

However, when only one effective symbol length Ts is extracted at the timing indicated by FFT-Wb in FIG.
The frequency spectrum output from the FFT 240 does not have the same carrier power level as shown in FIG. 5A, but does not have the same carrier power level as shown in FIG. 5B. Therefore, as shown in FIG.
The signal is input to the FDM receiver synchronization circuit 100, and the window timing of the window circuit 220 is feedback-controlled.

The feedback control by the OFDM receiver synchronization circuit 100 is as follows. The power level of each carrier, which is the output of the FFT 240, is measured by the carrier level measurement circuit 110. Since the output of the FFT 240 is a complex vector of the information of each carrier, the operation of the carrier level measuring circuit 110 determines the magnitude of the complex vector of the information. If the number of carriers is N, the output of the N-point FFT 240 is 2N (N pairs), and the output of the carrier level measuring circuit 110 is N.

The variance of the N outputs of the carrier level measuring circuit 110 is determined by the flatness measuring circuit 120. The N outputs of the carrier level measuring circuit 110 are a _i (1 ≦ i ≦ N)
Then, the average value M and the variance V are such that the sum symbol is 1 ≦
Assuming that the sum is obtained when i ≦ N is as follows. M = Σa _i / N (6) NV = Σ (M-a _i ) ² (7)

In this manner, the variance V or the amount NV which is N times the variance is obtained, and its time derivative or time proportional integral is calculated and output to a phase locked loop (Phase Locked Loop) 130. Variance V
Since the time derivative is 0 at the minimum value of the (or N times the amount NV), the phase locked loop 130 outputs a signal synchronized with the time of the minimum value of the variance V (or the N times the amount NV). be able to.

As described above, the phase locked loop 130 feedback-controls the window timing of the window circuit 220 based on the output of the flatness measuring circuit 120. Thus, when the output from the flatness measuring circuit 120 takes the minimum value, the window timing in the window circuit 220 is completely synchronized.

In the above embodiment, the modulation scheme of the received signal is QP
Although shown as being SK, the present invention is not limited to this. BPSK, 8-phase PSK, or any other phase modulation method may be used. Also, OFDM is used as a multicarrier transmission method
Although the system is shown, the present invention can be applied to other multicarrier transmission systems.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a synchronization circuit 100 for an OFDM receiver according to a specific embodiment of the present invention.

FIG. 2 is a conceptual diagram showing an effective symbol and a guard interval (GI) of an OFDM signal received by an OFDM receiving apparatus according to a specific embodiment of the present invention.

FIG. 3 is a conceptual diagram of a QPSK modulation method.

FIG. 4 is a conceptual diagram showing a relationship between a demodulated signal and an FFT window.

5A is a diagram showing an FFT output by a window shown in FFT-Wa in FIG. 4, and FIG. 5B is a diagram showing an FFT output in FIG.
The figure which shows the FFT output by the window shown by -Wb.

FIG. 6 (a) shows that the FFT window timing is k
(B) when the FFT window timing is over the k-th effective symbol and the subsequent k +
The figure which shows the case where it straddles the 1st guard interval (GI).

FIG. 7 is a block diagram showing a conventional OFDM reception synchronization circuit 900.

FIG. 8 is a conceptual diagram showing a signal of an in-phase component (I component), a delay signal thereof, and a correlation value thereof, showing the operation of the conventional OFDM reception synchronization circuit 900.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 synchronization circuit for OFDM receiving apparatus 110 carrier level measurement circuit 120 flatness measurement circuit 130 phase locked loop 91 delay circuit 92 multiplication circuit 210 to 250 peripheral circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hideaki Ito 41-1, Oku-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture F-term in Toyota Central R & D Laboratories Co., Ltd. 5K022 DD13 DD17 DD19 DD33 DD42 5K047 AA05 BB01 CC01 CC08 DD01 DD02 EE02 EE04 HH01 HH11 HH55 MM12 MM13 MM62

Claims (4)

[Claims] 1. A method of synchronizing a multi-carrier receiving apparatus for extracting a signal having an effective symbol length from a signal including an effective symbol and a guard interval obtained by copying a part of the effective symbol and determining a time window for performing a discrete Fourier transform. A quadrature demodulation of the received signal modulated by the phase modulation method, an effective symbol length signal is extracted from the demodulated signal at a certain timing, and a discrete Fourier transform is performed for each extracted effective symbol length signal. The magnitude of a complex vector of a carrier having a different frequency, which is the result of the above, is compared, and the effective symbol extraction timing is feedback-controlled so that the dispersion-related value of the magnitude of the complex vector of the carrier becomes a minimum value. Carrier receiver synchronization method. 2. A synchronous circuit of a multicarrier receiving apparatus for extracting a signal having an effective symbol length from a signal including an effective symbol and a guard interval obtained by copying a part of the effective symbol and determining a time window for performing a discrete Fourier transform. A timing generating means for determining a timing for extracting a signal having an effective symbol length from a demodulated signal obtained by orthogonally demodulating a received signal modulated by the phase modulation method; and a discrete Fourier transform for performing a discrete Fourier transform for each signal having the extracted effective symbol length. A conversion calculating means for comparing the magnitudes of complex vectors of carriers having different frequencies, which are outputs of the discrete Fourier transform calculating means; and a carrier amplitude comparing means; and adjusting an effective symbol extraction timing by an output of the carrier amplitude comparing means. And timing adjustment means. A synchronous circuit for a multi-carrier receiving apparatus, wherein feedback control of effective symbol extraction timing is performed so that a dispersion-related value of a magnitude of a complex vector of a carrier becomes a minimum value. 3. The synchronization circuit according to claim 2, wherein said timing adjustment means is a phase locked loop. 4. A multicarrier receiving apparatus comprising the synchronization circuit for a multicarrier receiving apparatus according to claim 2 or 3.