JPH1198102A - Ofdm receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the orthogonal frequency division multiplex OFDM receiver with a fast signal processing speed. SOLUTION: A threshold level calculation section 1 detects an amplitude change amount of each pilot signal stored in a pilot signal storage section 16, and a pitch of a scale of a symbol layout diagram used for a QAM decoder 2 is adjusted to compensate the amplitude change amount of each signal based on the detection result. The signal processing speed is increased by the processing time of multipliers in comparison with a conventional receiver where an amplitude equalization coefficient is multiplied with each signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM receiver, and more particularly to an OFDM receiver in which an original signal is encoded into a plurality of complex symbol signals including a plurality of pilot signals based on a symbol arrangement diagram on a complex plane, and transmitted by an OFDM method. OFD
The present invention relates to an OFDM receiver that receives an M signal and reproduces an original signal from the OFDM signal.

[0002]

2. Description of the Related Art In recent years, in a system for transmitting a video signal or an audio signal, as a digital modulation / demodulation system useful for high-quality transmission and improvement in frequency use efficiency,
An OFDM (Orthogonal Frequency Division Multiplexing) system has been proposed. The OFDM method uses 256 to 8 within one channel band.
This is a modulation method for setting up a large number of subcarriers of about 192.

In general, in the OFDM system, a pilot carrier for synchronizing a transmitting side and a receiving side is also transmitted. There are various types of pilot carrier transmission systems, but here, the European DVB-T standard (DVB-T
DOCUMENT A102: “FRAMING STRUCTURE, CHANNEL CODING
AND MODULATION FOR DIGITAL TERRESTRIAL TELEVISION
"See JUNE 1996).

In the DVB-T standard, as shown in FIG. 4 (a), a predetermined number of N subcarriers are used as pilot carriers, and the pilot carrier has a larger amplitude than a normal carrier. Is set. An original signal (for example, a digital TV signal) is encoded by, for example, a non-hierarchical 16QAM system, and
As shown in (b), each I-axis component (real number component)
And a 16-point complex symbol signal having a Q-axis component (imaginary component). The pilot signal has only an I-axis component and no Q-axis component. Each carrier is modulated by a corresponding complex symbol signal and transmitted to the receiving side.

As shown in FIG. 5, each carrier changes its amplitude and its phase under the influence of the frequency characteristics of the transmission path between the transmitting side and the receiving side. FIG. 5B shows a state in which the amplitude of the complex symbol signal is halved and the phase is advanced by θ (radian).

The original signal cannot be reproduced even if the signal whose amplitude and phase are changed is decoded as it is,
An equalizer for compensating the frequency characteristics of a transmission path is provided in an OFDM receiver.

FIG. 6 is a block diagram showing the configuration of such an OFDM receiver. Referring to FIG.
The DM receiver includes an antenna 10, a tuner 11, an FFT
(Fast Fourier Transform) unit 12, multipliers 13a, 13b,
14A and 14B, a QAM decoder 15, a pilot signal storage unit 16, a phase equalization coefficient calculation unit 17, and an amplitude equalization coefficient calculation unit 18.

[0008] The antenna 10 receives the OFDM signal group transmitted from the transmitting device. The tuner 11 selects an ODM of a desired program from the OFDM signal group received by the antenna 10.
The FDM signal is selected and given to the FFT unit 12. FFT section 12 demodulates the OFDM signal and generates N complex symbol signals. In FIG. 6, only one pilot signal and one normal signal are shown for simplicity of the drawing. Pilot signal storage section 16 stores a plurality of pilot signals output from FFT section 12.

A phase equalization coefficient calculation unit 17 detects a phase shift θ of each pilot signal stored in the pilot signal storage unit 16 with respect to the original pilot signal, and a phase equalization coefficient for compensating the phase shift θ. Calculate exp (−jθ). Further, the phase equalization coefficient calculation unit 17 calculates a phase equalization coefficient exp (-j for a normal signal between the two pilot signals.
θ ′) is obtained by interpolating the phase equalization coefficients of the two pilot signals. The multipliers 13a and 13b respectively provide phase equalization coefficients exp (−jθ ′) and exp (−j
θ) is multiplied by the normal signal and the pilot signal to compensate for the phase shift of each signal.

The amplitude equalization coefficient calculator 18 calculates an amplitude ratio 1 / K of the pilot signal stored in the pilot signal storage 16 to the original pilot signal (1/1 in FIG. 5B).
2) is detected, and an amplitude equalization coefficient K for compensating the amplitude ratio 1 / K is calculated. Further, the amplitude equalization coefficient calculation unit 18
The amplitude equalization coefficient K 'for a normal signal between two pilot signals is obtained by interpolating the phase equalization coefficient of the two pilot signals. The multipliers 14a and 14b multiply the normal signal and the pilot signal by the amplitude equalization coefficients K 'and K, respectively, to compensate the amplitude of each signal.

The QAM decoder 15 converts the N complex symbol signals supplied from the FFT unit 12 via multipliers 13a and 13b; 14a and 14b into serial signals, and converts each complex symbol signal into a serial signal as shown in FIG. The decoding is performed based on the constellation diagram (the symbol arrangement section on the complex plane) shown in FIG.

Next, the operation of the OFDM receiver will be briefly described. The OFDM signal transmitted from the transmitting device is received by antenna 10 and tuner 11 and provided to FFT section 12.

The OFDM signal provided to FFT section 12 is converted into N complex symbol signals. A pilot signal of the N complex symbol signals is stored in a pilot signal storage unit 16, and a phase equalization coefficient exp by a phase equalization coefficient calculation unit 17 and an amplitude equalization coefficient calculation unit 18 based on the stored pilot signals. (-Jθ '), ex
p (−jθ) and amplitude equalization coefficients K ′, K are calculated. These coefficients exp (−jθ ′), exp (−j
θ), K ', and K are multipliers 13a, 13b, 14a, and 14
Each signal is multiplied by b, and the frequency characteristic of the transmission path is compensated.

Each of the complex symbol signals whose phases and amplitudes have been compensated is converted into a serial signal by the QAM decoder 15 and then decoded to obtain an original signal (digital TV signal).
Will be played.

[0015]

However, the conventional OFD
In the M receiving apparatus, each complex symbol signal has a phase equalization coefficient e
Since xp (−jθ) and exp (−jθ ′) and the amplitude equalization coefficients K and K ′ are multiplied, there is a problem that the signal processing speed is low. In particular, since the change in the amplitude of the signal in the transmission path is large, the multipliers 14a and 14b for multiplying the amplitude equalization coefficients K and K 'are large, and the signal processing speed is low.

Therefore, a main object of the present invention is to provide an OFDM receiver having a high signal processing speed.

[0017]

The invention according to claim 1 is
An original signal is encoded into a plurality of complex symbol signals including a plurality of pilot signals based on a symbol arrangement diagram on a complex plane, an OFDM signal transmitted by the OFDM method is received, and the original signal is reproduced from the OFDM signal. An OFDM receiving apparatus includes a demodulation unit, a decoding unit, a first calculation unit, and an adjustment unit. The demodulation means demodulates the OFDM signal to generate a plurality of complex symbol signals. The decoding unit decodes each of the plurality of complex symbol signals generated by the demodulation unit based on a symbol arrangement diagram on a complex plane, and reproduces an original signal. The first calculating means detects a change amount of the amplitude of each pilot signal generated by the demodulation means in the transmission path of the OFDM signal, and based on the detection result, detects the amount of change in the amplitude of each complex symbol signal in the transmission path of the OFDM signal. Calculate the amount of change. The adjusting means adjusts the size of the scale of the symbol arrangement diagram on the complex plane used by the decoding means so as to compensate for the amount of change in the amplitude of each complex symbol signal calculated by the first calculating means.

According to the second aspect of the present invention, the second aspect of the present invention further comprises a second arithmetic means and a multiplying means. The second calculating means detects a phase shift of each pilot signal generated by the demodulating means in the transmission path of the OFDM signal, and based on a result of the detection, detects a phase shift of each complex symbol signal.
A phase equalization coefficient for compensating for a phase shift in the transmission path of the FDM signal is calculated. The multiplication means is provided between the demodulation means and the decoding means for each complex symbol signal, and multiplies the corresponding complex symbol signal by the corresponding phase equalization coefficient calculated by the calculation means.

[0019]

FIG. 1 is a block diagram showing a configuration of an OFDM receiving apparatus according to an embodiment of the present invention, which is compared with FIG.

Referring to FIG. 1, this OFDM receiver differs from the OFDM receiver of FIG. 6 in that amplitude equalizing coefficient calculator 18, multipliers 14a and 14b, and QAM decoder 15 include threshold calculator 1 and QAM Decoder 2
Is replaced by Outputs of the multipliers 13a and 13b are directly input to the QAM decoder 2.

The threshold calculator 1 calculates an amplitude ratio 1 / K of each pilot signal stored in the pilot signal storage 16 to the original pilot signal. The threshold calculator 1 calculates the amplitude ratio 1 / K 'of the normal signal amount between the two pilot signals by interpolation of the amplitude ratio of the two pilot signals.

The QAM decoder 2, as shown in FIG.
The scale of the I axis and Q axis of the constellation diagram
The signal is reduced to K, 1 / K ', and each complex symbol signal is decoded to reproduce the original signal. Other configurations and operations are the same as those of the OFDM receiver of FIG. 6, and therefore, description thereof will not be repeated.

In this embodiment, since the threshold value of the constellation diagram of QAM decoder 2 is changed according to the frequency characteristics of the transmission line, multipliers 14a and 14b for multiplying each complex symbol signal by an amplitude equalization coefficient are provided. Thus, the signal processing speed can be increased.

In this embodiment, a pilot signal is transmitted for each complex symbol group. However, a complex symbol group in which only a pilot signal exists may be transmitted for each of a plurality of complex symbol groups.

Further, in this embodiment, the frequency of the pilot signal carrier is fixed, but the frequency of the pilot signal carrier may be changed at a predetermined symbol period (for example, 4 symbol periods) for each symbol group. Good. In this case, the frequency characteristics of the transmission path can be detected with higher accuracy. However, the burden on the pilot signal storage unit 16 and the like increases.

In this embodiment, the phase and the scale of the constellation diagram are compensated for both the normal signal and the pilot signal. However, it is not necessary to compensate for only the normal signal and not for the pilot signal.

Further, since the phase shift due to the transmission path is extremely small, as shown in FIG.
The multipliers 13a and 13b may be omitted.

[0028]

As described above, according to the first aspect of the present invention, the amount of change in amplitude of each pilot signal in the transmission path is detected, and the amount of change in amplitude of each complex symbol signal is calculated based on the detection result. Then, the size of the scale of the symbol arrangement diagram of the decoding means is adjusted so as to compensate for the change in the amplitude of each complex symbol signal. Therefore, the signal processing speed can be increased by the amount of the multiplier, as compared with the related art in which each complex symbol signal is multiplied by an amplitude equalization coefficient to compensate for the amount of change in amplitude.

According to a second aspect of the present invention, in addition to the first aspect, a phase shift of each pilot signal in a transmission path is detected, and a phase shift of each complex symbol signal is compensated based on the detection result. Calculate the phase equalization coefficient of
Each complex symbol signal is multiplied by a phase equalization coefficient. In this case, signal processing can be performed accurately.

[Brief description of the drawings]

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

FIG. 2 is a constellation diagram used in the QAM decoder shown in FIG.

FIG. 3 is a block diagram showing an improved example of the OFDM receiver shown in FIG.

FIG. 4 is an OFDM transmitted from the transmission side of the OFDM scheme.
It is a figure for explaining a signal.

FIG. 5 is a diagram for explaining an OFDM signal reaching a receiving side of the OFDM scheme.

FIG. 6 is a block diagram showing a configuration of a conventional OFDM receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Threshold calculation part 2, 15 QAM decoder 10 Antenna 11 Tuner 12 FFT part 13a, 13b, 14a, 14b Multiplier 16 Pilot signal storage part 17 Phase equalization coefficient calculation part 18 Amplitude equalization coefficient calculation part

Claims (2)

[Claims] 1. An OFD system in which an original signal is encoded into a plurality of complex symbol signals including a plurality of pilot signals based on a symbol arrangement diagram on a complex plane and transmitted by an OFDM method.
An OFDM receiving apparatus that receives an M signal and reproduces the original signal from the OFDM signal, a demodulating unit that demodulates the OFDM signal to generate the plurality of complex symbol signals, Decoding means for decoding each of the plurality of complex symbol signals based on a symbol arrangement diagram on a complex plane to reproduce the original signal; and a change in the amplitude of each pilot signal generated by the demodulation means in the transmission path of the OFDM signal. And based on the detection result, the O value of the amplitude of each complex symbol signal is determined.
First calculating means for calculating the amount of change in the transmission path of the FDM signal, and the complex means used by the decoding means to compensate for the amount of change in the amplitude of each complex symbol signal calculated by the first calculating means. An OFDM receiver including an adjusting unit that adjusts the size of a scale of a symbol arrangement diagram on a plane. 2. A phase shift of each pilot signal generated by the demodulation means in a transmission path of the OFDM signal, and a phase shift of each complex symbol signal in a transmission path of the OFDM signal is detected based on a detection result. Second calculating means for calculating a phase equalization coefficient for compensating for the deviation;
And a multiplying means provided between the demodulating means and the decoding means for each complex symbol signal, and multiplying the corresponding complex symbol signal by a corresponding phase equalization coefficient calculated by the calculating means. Item 2. The OFDM receiver according to item 1.