JP2001069112A - Ofdm transmitter, ofdm receiver, ofdm communication equipment using them and ofdm communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decode only the information sequence of a desired channel from the information sequences of many partial receiving channels, to which orthogonal frequency division multiplex(OFDM) modulation is applied, by transmitting the information sequences of many partial channels to a prescribed frequency band after OFDM modulation. SOLUTION: In an OFDM transmitter 10A, a mapping circuit 11A independently maps plural information sequences having a band width fBW and different central frequencies, a multiplexer 13A multiplexes the frequencies of plural mapping signals and a frequency converter 18 converts the frequency of an orthogonal modulation signal with a central frequency f3 as a reference among the central frequencies of plural information sequences. In an OFDM receiver 30A, a channel selector 39 sets the frequency of an information sequence to be set out of received channels and a frequency converter 32A converts the frequency of a signal having a frequency, for which an intermediate frequency fIF is added to a frequency fn selected by the channel selector 39, and the received signal. A frequency converter 38 performs frequency correction corresponding to the difference between the frequency f3 of a center among the central frequencies of plural information sequences and the frequency fn selected by the channel selector 39.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonal frequency division multiplexing system (O) transmitted by frequency-multiplexing a plurality of information.
FDM: Orthogonal Frequency Division Multiplexin
g) An OFDM communication apparatus for transmitting and receiving the signal modulated in the above. More specifically, the present invention provides an OFD capable of multiplexing a plurality of partial information sequences and transmitting the multiplexed information sequence as an OFDM signal.
M transmitting apparatus, an OFDM receiving apparatus capable of receiving only a desired partial information sequence from the transmitted OFDM signal, and an OFDM communication apparatus including the OFDM transmitting apparatus and the OFDM receiving apparatus, and Related to the communication method.

[0002]

2. Description of the Related Art A large number of orthogonal carriers are used as a terrestrial digital broadcasting system, for example, as a modulation system for terrestrial digital radio broadcasting and terrestrial digital television broadcasting.
Each carrier is phase modulated (PSK) or quadrature amplitude modulated (Q
AM) and OFDM (OF).
DM: Orthogonal Frequency Division Multiplexing)
Has been proposed. The reason is that the OFDM signal has the advantage of being less susceptible to multipath, for example,
This is because the terrestrial digital broadcasting system in an area where many multi-paths are likely to occur, such as an urban area, is advantageous in that the multi-path is less likely to be affected even when the receiver is a mobile receiver.

[0003] For example, in Europe, the Eureka 147 project has been the center of development, and a digital audio broadcasting DAB (Digital Audio Broadcasting) has been developed which can be received by mobile units using terrestrial waves and artificial satellites.
Subsequently, DVB (Digital Video Broadcasting) has been organized, and standardization of digital broadcasting has been promoted. DV
B employs OFDM as a modulation method in order to avoid the influence of multipath that causes a problem with terrestrial waves. DVB-T (DV
The B via terrestial method employs an OFDM method in order to avoid the influence of multipath, which is a problem in terrestrial broadcasting.

The terrestrial digital broadcasting in Japan is different from the terrestrial digital broadcasting in Europe described above.
The condition that it is difficult to secure a frequency is added, and attempts have been made to develop a method suitable for the frequency situation. As described above, it is desirable to adopt OFDM as a modulation method in order to avoid the effect of multipath, which causes a problem with terrestrial waves, in order to enable reception by a mobile object.

As transmission lines for digital broadcasting, terrestrial broadcasting waves, CATV, ISDN, and the like are considered, but since these transmission lines have different use conditions, bit rates, modulation methods, and the like are different. In order to realize such interconnection between different systems and a common receiver, it is desirable to consider a broadcast system by dividing the image and audio input / output to the transmission path into several layers. As such a hierarchical method, an integrated service digital broadcast (ISDB) incorporating MPEG-2 is used.
ing) Broadcast systems have been proposed.

FIGS. 5A and 5B show OFDM such as DVB and DVB-T which are implemented in Europe and the like.
FIG. 5 is a configuration diagram of an OFDM communication device that performs a communication method;
FIG. 5A is a configuration diagram of the OFDM transmission apparatus 10, and FIG.
(B) is an OFDM corresponding to the OFDM transmitting apparatus of FIG.
FIG. 2 is a configuration diagram of a DM receiving device 30. OFDM transmitter 1
0 and the OFDM receiver 30 are connected via a transmission path to form an OFDM communication device.

The OFDM transmitter (transmitter) 10 illustrated in FIG. 5A includes a main channel mapping circuit 11
A partial reception channel mapping circuit 12, a multiplexer (multiplexer) 13, and an inverse fast Fourier transform (IFFT) circuit 14.
And a guard interval adding circuit 15 and the quadrature modulator 1
6, a first local oscillator 17, a frequency converter 18,
It has a second local oscillator 19 and a transmitting antenna 20.

[0008] OFDM receiver 3 illustrated in FIG.
0 is the receiving antenna 31, the frequency converter 32, the third
Local oscillator 33 and intermediate frequency (IF) filter 34
, A quadrature demodulator 35, a second local oscillator 36, and a fast Fourier transform circuit (FFT) 37.

FIGS. 6A and 6B show an OFDM transmission apparatus 10 illustrated in FIG. 5A and an OFDM communication apparatus including an OFDM receiving apparatus 30 illustrated in FIG. 5B. FIG. 2 is a diagram illustrating an RF channel arrangement in a system. In DVB and DVB-T OFDM communication apparatuses implemented in Europe and the like, all subcarriers of OFDM are allocated to one channel, or only signals in a part of a central band are partially received and hierarchically. And transmitted. Here, the bandwidth of the partial reception channel is shown as f _BW . Shows the center frequency of the main channel as f _c.

The operation of the OFDM transmission device 10 will be described. A main channel information sequence (bit stream) S _M is applied to the main channel mapping circuit 11. Mapping circuit 11, the information sequence S _M a QPSK or QAM in the main channel, for example, is modulated by a modulation scheme such as 16QAM, I-axis and Q axis (mapped) assigned to the modulation point in the coordinate system perpendicular. In the mapping circuit 11, interleaving, error correction, and the like may be performed. The partial reception channel mapping circuit 12 includes:
FIG 6 (B) to illustrate the partial reception channel bandwidth f partial reception channel information sequence represented by _BW (bit stream) S _P is applied. Mapping circuit 12, the information sequence of the partial reception channel S _P a QPSK or QAM, for example, is modulated by a modulation scheme such as 16QAM,
Assignment (mapping) to modulation points in a coordinate system where the I axis and the Q axis are orthogonal. The interleaving and error correction processing in the mapping circuit 12 may be the same as or different from the interleaving and error correction processing in the mapping circuit 11.

The multiplexer 13 receives the mapping output of the main channel mapping circuit 11 and the mapping output of the partial reception channel mapping circuit 12 and performs frequency multiplexing. That is, the multiplexer 13 multiplexes the mapping output of the mapping circuit 11 and the mapping output of the mapping circuit 12 on the frequency axis. FIG. 7 shows a multiplexer 1
OFDM frequency-multiplexed into subcarriers in subcarrier 3
It is the figure which illustrated the signal. The multiplexer 13, the partial information sequence S _P output reception channel is frequency-multiplexed in the center of the band.

[0012] IFFT circuit 14, are frequency-multiplexed in the multiplexer 13, the mapped main channel information sequence S _M and mapped together with the information sequence S _P output partial reception channel inverse fast Fourier transform Then, the frequency-multiplexed mapping symbols are converted into real space signals.

The guard interval adding circuit 15 has an IFF
A guard interval is added to the T-converted signal to generate a baseband time signal.

The local oscillator 17 oscillates a signal having an intermediate frequency _fIF . Quadrature modulator 16, and the intermediate frequency f _IF of the signal output from the local oscillator 17, and orthogonal transformation and the time signal of the baseband outputted from the guard interval adding circuit 15, the coordinate system of the I and Q axes generating a deployed intermediate frequency f _IF of the intermediate frequency signal IF to.

The local oscillator 19 oscillates a signal having the sum of the intermediate frequency f _IF and the center frequency f _c the frequency (f _c + f _IF). Frequency converter 18, an intermediate frequency signal IF which has been orthogonally converted by the orthogonal modulator 16, and a signal of the output frequency from the local oscillator 19 (f _c + f _IF) and a frequency conversion (multiplication with) the center frequency It generates a signal f _c. The center frequency f _c is a radio frequency RF that can be transmitted in the transmitting antenna 20.

The transmitting antenna 20 includes a frequency converter 18
An RF signal, which is an output signal of the above, is transmitted.

The operation of the OFDM receiver 30 will be described. The reception antenna 31 receives the RF signal transmitted from the transmission antenna 20 of the OFDM transmission device 10. The local oscillator 33 oscillates a signal having the sum of the intermediate frequency f _IF and the center frequency f _c the frequency (f _c + f _IF). The frequency converter 32 outputs the frequency (f _c) output from the local oscillator 33.
+ F _IF ) and the RF signal received by the receiving antenna 31 are frequency-converted (multiplied) to generate an intermediate frequency signal IF having an intermediate frequency f _IF .

An intermediate frequency (IF) filter 34 selectively outputs only a signal in a predetermined frequency band from the intermediate frequency signal IF output from the frequency converter 32. FIG. 8 is a characteristic diagram illustrating the frequency selection characteristic of the IF filter 34. That, IF filter 34, to extract the partial reception channel signal bandwidth f _BW, before and after the intermediate frequency f _IF as the center frequency having a band cut-off frequency of ± f _BW / 2, the band-pass filter is there.

The local oscillator 36 is an oscillator which oscillates intermediate frequency f _IF of the signal as a carrier signal. The quadrature demodulator 35 sets the center frequency extracted by the IF filter 34 to f _IF
To orthogonally transform the signal of the bandwidth f _{BW and} the signal of the intermediate frequency f _IF output from the local oscillator 36 to generate a quadrature demodulated signal.

The fast Fourier transform circuit (FFT) 37
The signal orthogonally modulated by the orthogonal transformer 35 is subjected to fast Fourier transform to generate a signal in a frequency space, that is, an OFDM demodulated signal.

[0021]

In the communication system described above, as illustrated in FIG. 6B, the information sequence SP of the partial reception channel to be received is replaced with the information sequence _SP of the main channel.
It is located at the center of _M. Therefore, the reception of the OFDM receiver 30 is fixed and has a simple configuration. Therefore, it is advantageous when one program, for example, a digital radio broadcast and / or a digital television broadcast from one broadcasting station is received by a plurality of receiving devices with the same contents. However, such a communication form is not a broadcast form intended for terrestrial digital broadcasting. In terrestrial digital broadcasting, it is intended to transmit various programs to various receiving devices. In such a case, only the information sequence of one partial channel can be transmitted and received using only the frequency band illustrated in FIG. 6B, and the information sequence of a plurality of partial reception channels cannot be transmitted and received. If information sequences of a plurality of partial reception channels are to be transmitted and received, it is necessary to prepare a plurality of main channels having the frequency bands of the main channels illustrated in FIG. 6 (B) and make their center frequencies different. Then, a frequency band of the frequency band of the main channel × n (n is the number of a plurality of main channels) is required. Such a method is difficult to realize when there is a restriction on the use of frequency such as in Japan. In countries other than Japan, terrestrial digital broadcasting occupies a wide range of frequencies, which is not preferable.

[0022] In the communication system described above must be provided a large number of multiple parts when the information sequence S _P output received channel is present, a pair of main channel mapping circuit 11 and the partial reception channel mapping circuit 12, OFDM
The configuration of the transmission device 10 becomes complicated.

An object of the present invention is to provide an information sequence (bit stream) of a number of partial reception channels within a predetermined frequency band.
To provide an OFDM communication apparatus capable of multiplexing and transmitting frequency division, selecting information sequences of a plurality of partial reception channels, and arbitrarily receiving the information sequences. Another object of the present invention is to provide the OF
An object of the present invention is to provide an OFDM transmission device constituting a DM communication device. Still another object of the present invention is to provide an OFDM receiving apparatus constituting the above-mentioned OFDM communication apparatus and a method therefor.

[0024]

According to a first aspect of the present invention, a mapping means for independently mapping a plurality of information sequences each having a fixed bandwidth and a different center frequency, respectively, Frequency multiplexing means for frequency multiplexing the plurality of mapping symbols, orthogonal transform means for orthogonally transforming the frequency-multiplexed symbols, and orthogonal modulation means for orthogonally modulating the orthogonally modulated signal at an intermediate frequency, Frequency conversion means for frequency-converting the quadrature modulated signal with reference to a center frequency among the center frequencies of the plurality of information sequences.

The above-mentioned mapping means includes QAM, QPSK
For example, the plurality of information sequences can be mapped to symbols in the rectangular coordinate system. These mapping methods are determined according to the amount of information to be mapped, the characteristics of the transmission path, and the like. For example, a case where the information sequence is only a voice signal and a case where the information sequence is a video signal is exemplified by a mapping method suitable for the information amount of each information sequence.

The orthogonal transform means (14) may include fast Fourier inverse transform means or discrete cosine inverse transform means. The orthogonal transformation method in the orthogonal transformation means is determined according to the information amount of the information sequence to be orthogonally transformed and the signal characteristics. For example, if the information sequence is only audio, an inverse fast Fourier transform is applied, and if the information sequence is a video signal, an inverse discrete cosine transform is applied.

Preferably, a guard interval adding means for adding a guard interval to the orthogonal transform result is provided between the orthogonal transform means and the orthogonal modulation means.

According to a second aspect of the present invention, a plurality of information sequences each having a fixed bandwidth and different center frequencies are independently mapped, frequency-multiplexed, orthogonally transformed, and guard interval Receiving means for receiving a signal which is orthogonally modulated at an intermediate frequency, and which is obtained by frequency-converting the orthogonally modulated signal with reference to a center frequency among center frequencies of the plurality of information sequences; and Channel selection means for setting a frequency of an information sequence to be selected, oscillation means for oscillating a signal having a frequency obtained by adding an intermediate frequency to the frequency selected by the channel selection means, and a signal received by the reception means. Frequency converting means for converting the frequency with an oscillation signal from the oscillating means, and having a band-pass characteristic equal to the predetermined bandwidth, A band-pass filter for passing the signal frequency-converted by the conversion means with the above-mentioned band-pass characteristic, an orthogonal demodulation means for orthogonally demodulating an output signal of the band-pass filter with an intermediate frequency signal, and an orthogonal transform of the orthogonally demodulated signal Orthogonal transform means, and frequency correction for performing a frequency correction according to a difference between a center frequency among the center frequencies of the plurality of information sequences and a frequency selected by the channel selecting means for the orthogonally transformed signal. Means are provided.

The frequency correction means determines a phase shift angle from a frequency corresponding to a difference between a center frequency of the plurality of information sequences and a frequency selected by the channel selection means, and a guard interval length. Phase shift angle generating means for calculating, and accumulating means for resetting the calculated phase shift angle to 0 (radian) when it exceeds 2π (radian), and performing cumulative addition to calculate a cumulative phase shift angle And phase shifting means for shifting the signal orthogonally transformed by the orthogonal transforming means at the cumulative addition phase shift angle.

The phase shift angle generating means calculates the phase shift angle θ based on the following equation (1), and the phase shift means shifts the phase of the signal orthogonally transformed by the orthogonal transform means based on the following equation (2).

[0031]

(Equation 2)

The orthogonal transform means may include fast Fourier transform means or discrete cosine transform means. The orthogonal transformation method in the orthogonal transformation means is determined according to the information amount of the information sequence to be orthogonally transformed and the signal characteristics. For example, if the information sequence is only audio, a fast Fourier transform is applied, and if the information sequence is a video signal, a discrete cosine transform is applied.

According to the present invention, the OFDM transmitting apparatus and the OFDM receiving apparatus are connected to each other via a transmission path.
An FDM communication device is provided.

According to the present invention, there is provided a method in the above-mentioned OFDM communication apparatus. The OFDM communication method has the following steps, i.e., independently maps a plurality of information sequences each having a fixed bandwidth and a different center frequency, frequency-multiplexes the mapped symbols, and The frequency-multiplexed symbols are orthogonally transformed, the orthogonally-modulated signal is orthogonally modulated at an intermediate frequency, and the orthogonally-modulated signal is frequency-divided with reference to a center frequency among center frequencies of the plurality of information sequences. The frequency is obtained by converting the frequency-converted signal, receiving the transmitted signal, setting the frequency of the information sequence to be selected among the received signals, and adding an intermediate frequency to the selected frequency. Frequency-converted between the oscillated signal and the received signal, and converts the frequency-converted signal into the certain band component. Only, the bandpass signal is orthogonally demodulated with an intermediate frequency signal, the orthogonally demodulated signal is orthogonally transformed, and the orthogonally transformed signal is the center of the center frequencies of the plurality of information sequences. There are various steps for performing frequency correction according to the difference between the frequency and the frequency selected by the channel selection means.

The OFDM transmitting apparatus modulates the information sequences of the plurality of partial reception channels with reference to the center frequency in the information sequences of the plurality of partial reception channels. As a result, the information sequence of n partial reception channels is divided into OFDM using a frequency band of n times (n is the number of information sequences of a plurality of partial reception channels) the band of the information sequence of the partial reception channel.
It can be transmitted as a signal.

The OFDM receiver receives the OFDM signal transmitted from the OFDM transmitter and selects only the information sequence of the desired partial reception channel. When the information sequence of the selected partial reception channel is transmitted by the OFDM transmitting apparatus, the original center frequency of the information sequence of the selected partial reception channel is shifted from the center frequency in the modulation, so that the frequency correction according to the frequency difference is performed. I do.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B show an OFDM communication system, an OFDM transmission device, and an OFDM reception device according to an embodiment of the present invention. 1A is a configuration diagram of an OFDM transmission device, and FIG. 1B is a configuration diagram of an OFDM reception device corresponding to the OFDM transmission device of FIG. is there. As the OFDM communication apparatus of the present embodiment, for example, one OFDM
It can be composed of a transmitting device 10A and a plurality of OFDM receiving devices 30A. Examples of such an OFDM receiver 30A include a plurality of mobile receivers, a plurality of fixed receivers, and the like. However, in order to simplify the illustration, FIG. 1B illustrates one typical OFDM receiver 30A.

FIG. 2 is a diagram illustrating an OFDM baseband signal frequency-multiplexed on an OFDM subcarrier by a multiplexer 13A in the OFDM transmitting apparatus 10A illustrated in FIG. 1A.

The OFDM transmitter 1 illustrated in FIG.
0A is a mapping circuit 11A, a multiplexer (multiplexer) 13A, and a fast Fourier inverse transform circuit (IFFF).
T) 14A, a guard interval adding circuit 15, a quadrature modulator 16, a first local oscillator 17, a frequency converter 18, a second local oscillator 19A, and a transmitting antenna 20. The mapping circuit 11A has first to fifth mapping circuits 111 to 115. As illustrated in FIG. 2, these mapping circuits 111 to 115 have a center frequency of f _{1 to} f ₅ and a 5-channel information sequence (bit stream) having a constant bandwidth f _BW , respectively.
Is applied. In the present embodiment, the information sequence of these five channels is transmitted simultaneously from OFDM transmitting device 10A, and the information sequence of any channel can be selected in OFDM receiving device 30A.

The example illustrated in FIG. 2 is a channel configuration in which each band is the above-mentioned partial reception channel bandwidth f _BW, and each center frequency is multiplexed with five channels f _{1 to} f _{5 in} the frequency axis direction. Is shown. Of course, the number of channels to be multiplexed is not limited to five, but may be any number. In the following, the case of five channels will be described.

The OFDM transmitter 1 illustrated in FIG.
0A has a configuration similar to that of the OFDM transmission device 10 illustrated in FIG. 5A, but has a configuration difference described below.

The main channel mapping circuit 11 and the partial reception channel mapping circuit 12 illustrated in FIG.
1A, the OFDM transmitting apparatus 10A of FIG.
To a fifth mapping circuit 111 to 115. That is, the OF of FIG.
In DM transmitter 10, in the main channel mapping circuit 11 and the partial reception channel mapping circuit 12 and mapped information sequence S _M and a pair of information sequence with the information sequence S _P output portion receiving channel of the main channel However, the mapping circuit 11A of FIG. 1A maps a partial information sequence of five channels. Although the multiplexer 13 illustrated in FIG. 5A frequency-multiplexes the mapping signals (mapping symbols) of two channels, the multiplexer 13A of FIG. 1A maps the information sequence of the partial channels of five channels. The obtained signal (mapping symbol) is frequency-multiplexed.

The local oscillator 19 in FIG. 5 (A), the sum of the intermediate frequency f _IF and the center frequency f _c the frequency (f _c + f _IF)
1A, the local oscillator 19 shown in FIG.
A oscillates a signal having a frequency (f ₃ + f _IF ) which is the sum of the center frequency f ₃ of the third channel at the center of the five channels and the intermediate frequency f _IF . Of course, any center frequency among the center frequencies of the five channels can be selected in place of the center frequency f _3. However, if a center frequency located at the center of all the channels is used, the frequency difference is small, so OFDM
Since frequency correction value in the frequency converter 38 of the receiving apparatus 30A is reduced as a whole, as the local oscillator 19A employs a center frequency f _3. IF in FIG. 1 (A)
The FT 14A can be smaller than the IFFT 14 in FIG. The details will be described later.

The OFDM receiver 3 illustrated in FIG.
The configuration of 0A will be described. The OFDM receiver 30A includes a receiving antenna 31, a frequency converter 32A, a third local oscillator 33A, a channel selector 39, and an intermediate frequency (I
F) a filter 34, a quadrature demodulator 35, a third local oscillator 36, a fast Fourier transform circuit (FFT) 37,
And a frequency converter 38.

The OFDM receiver 3 illustrated in FIG.
0A is similar to the OFDM receiver 30 illustrated in FIG. 5B, but has the following configuration differences.

The OFDM receiver 30A shown in FIG. 1B is provided with a frequency converter 38 as frequency correction means and a channel selector 39 as channel selection means. Details of the frequency converter 38 and the channel selector 39 will be described later.

The local oscillator 33A shown in FIG.
As local oscillator 33 (B), the center frequency f _c and the intermediate frequency f instead of oscillating a signal of a frequency of the sum of the _{IF (f c + f IF)} , the frequency f which is selected by the channel selector 39 _n and the intermediate frequency f _IF (f _n +
f _IF ). The reason is that the OFDM receiver 30A selects only the partial information sequence of the desired channel.

The OFDM transmitting apparatus 1 illustrated in FIG.
The basic operation of each unit of 0A will be described. Mapping circuit 11A
The first to fifth mapping circuits 111 to 115 constituting
Are applied with information channels of five channels each having a center frequency of f _{1 to} f ₅ and a bandwidth f _BW of a partial reception channel. Each of the first to fifth mapping circuits 111 to 115 modulates the applied information sequence by a modulation method such as QPSK or QAM, for example, 16QAM,
Assignment (mapping) to modulation points (symbols) in a coordinate system (I-Q coordinate system) where the I axis and the Q axis are orthogonal. Such modulation methods include transmission capacity of data to be transmitted,
Select an appropriate modulation method in consideration of noise resistance characteristics and the like.
For example, if the information sequence is audio data, QPS
K and 16QAM are applied, and when the information sequence is a video signal, 64QAM and 128QAM are applied. The first to fifth mapping circuits 111 to 115 perform interleaving, error correction processing, and the like as necessary. For interleaving, error correction, and the like, a known appropriate method is selected according to the characteristics of the information sequence.

The multiplexer 13A multiplexes (frequency multiplexes) the five mapping outputs from the first to fifth mapping circuits 111 to 115 on the frequency axis. FIG. 3 is a diagram illustrating an OFDM baseband signal frequency-multiplexed on an OFDM subcarrier by the multiplexer 13A. The center frequency of the first channel OFDM baseband signal is (f ₁ −f ₃ ), and the second channel OFDM base band signal is
The center frequency of the baseband signal is (f ₂ −f ₃ ), the center frequency of the third channel OFDM baseband signal is 0, and the center frequency of the fourth channel OFDM baseband signal is (f ₄ −f 3). ₃ ), and the center frequency of the fifth channel OFDM baseband signal is (f ₅ −
f ₃ ). Multiplexer 13A in this way, with reference to the center frequency f ₃ of the third channel of the center of the 5-channel, and frequency multiplexing, the whole of frequency multiplexed OFD
The center frequency of the M baseband signal is set to 0.

As described above, partial information sequences of a plurality of channels are converted into OFDM signals by the mapping circuit 11 and the multiplexer 13A. In the example illustrated in FIG. 6B, the information sequence S of one partial reception channel is used for the main channel.
_Although only _P is frequency-multiplexed, in the present embodiment, each of the five channels shown in FIG. 2 has a fixed bandwidth f _BW and has a center frequency f _{1 to} f _5. As illustrated in FIG. 3, all information sequences of five channels are frequency-multiplexed.

High-speed Fourier inverse transform circuit (IFFT circuit)
14A collectively performs inverse fast Fourier transform on the multiplexed 5-channel OFDM baseband signals into real-space signals. The IFFT 14 may perform inverse fast Fourier transform only on the 5-channel partial information sequence. That is, unlike the IFFT 14 illustrated in FIG. 5A, it is not necessary to perform the inverse fast Fourier transform on the signals in the entire frequency band of the main channel, so that the IFFT 14A may have a circuit configuration corresponding to the number of channels of the partial information sequence. it can.

The guard interval adding circuit 15 has an IFF
A guard interval is added to the signal output from T14A to generate a baseband time signal.

The local oscillator 17 oscillates a signal having the intermediate frequency _fIF . Quadrature modulator 16, an intermediate frequency f and _{the IF} signal, an intermediate frequency f _IF orthogonal modulation the intermediate frequency of the orthogonal transform and the time signal of the baseband outputted from the guard interval adding circuit 15 output from the local oscillator 17 Signal I
Generate F.

The local oscillator 19A oscillates a signal having a frequency (f ₃ + f _IF ) which is the sum of the intermediate frequency f ₃ and the intermediate frequency f _IF of the third channel at the center of the five channels. The frequency converter 18 frequency-converts (multiplies) the intermediate frequency signal IF quadrature-modulated by the quadrature modulator 16 and a signal of the frequency (f ₃ + f _IF ) output from the local oscillator 19.
Generating a signal having a center frequency f _3.

The transmitting antenna 20 is connected to the frequency converter 18.
Is transmitted to the transmission path.

According to the OFDM transmission apparatus 10A, each has a constant bandwidth f _BW and each of the center frequencies f ₁ to f ₁ .
5 channel information sequence f ₅ (each information sequence partial reception channels) are frequency multiplexed, are OFDM modulated, is orthogonally modulated, 5 all channels are transmitted to a transmission line. Therefore, if the OFDM transmission apparatus 10A is used, five information sequences can be transmitted using one frequency band (in this example, a bandwidth of f _BW × 5 channels) through one transmission path. . Therefore, even when there is no room for using the frequency, it is possible to transmit information sequences of a large number of partial reception channels using a limited frequency band.
In other words, it is possible to transmit information sequences of many partial reception channels even in a narrow frequency band. Since the signal transmitted from the OFDM transmitting apparatus 10A is an OFDM signal, it is hardly affected by a failure such as multipath.

The OFDM receiver 3 illustrated in FIG.
The operation at 0A will be described. The OFDM receiver 30A may be, for example, a mobile receiver. The receiving antenna 31
The RF signal illustrated in FIG. 3 transmitted from the transmitting antenna 20 of the OFDM transmitting apparatus 10A illustrated in FIG. 1A is received.

The user of the OFDM receiving apparatus 30A designates one channel to be received from the above-mentioned five-channel information sequence to the channel selector 39. Channel selector 39 outputs the frequency obtained by adding the intermediate frequency _{f IF (f c + f IF} ) to the local oscillator 33A into the corresponding frequency f _n of the designated channel. The local oscillator 33A is, for example,
A channel selector 3 composed of a phase locked loop (PLL)
And it outputs a signal of specified frequency (f _c + f _IF) 9.

The frequency converter 32A includes a local oscillator 33A
A signal frequency (f _c + f _IF) output from, and frequency conversion of an RF signal received by the receiving antenna 31 (multiplied with) to produce the intermediate frequency f _IF intermediate frequency signal IF.

The intermediate frequency (IF) filter 34 has the band-pass characteristic illustrated in FIG.
From the intermediate frequency signal IF output from the controller, only a signal having a bandwidth f _BW is passed. IF filter 34 for extracting a partial reception channel signal bandwidth f _BW that illustrated in FIG. 8, f _BW before and after the intermediate frequency f _IF as the center frequency
This is a bandpass filter having a cutoff frequency of a band of / 2.

[0061] The local oscillator 36 is an oscillator which oscillates intermediate frequency f _IF of the signal as a carrier signal. The quadrature demodulator 35 sets the center frequency extracted by the IF filter 34 to f _IF
To orthogonally transform the signal of the bandwidth f _{BW and} the signal of the intermediate frequency f _IF output from the local oscillator 36 to generate a quadrature demodulated signal.

The fast Fourier transform circuit (FFT) 37
A signal orthogonally modulated by the orthogonal demodulator 35 is subjected to a fast Fourier transform to generate an OFDM demodulated signal. IF filter 34
Is subjected to FFT processing in the FFT 37 for a signal subjected to quadrature demodulation by the quadrature demodulator 35, that is, for a signal whose band is limited, the bandwidth f _BW
The circuit scale of the FFT 37 that processes the signal of (1) can be reduced.

The role of the frequency converter 38 as the frequency correcting means of the present invention will be described. OFD illustrated in FIG. 1 (A)
M transmitting apparatus 10A is frequency multiplexed in the center frequency f ₃ of the third channel of the center of the 5 channels, OFDM
Has a the demodulation processing with respect to the third channel frequency f ₃ of the center of the 5-channel also in the receiving apparatus 30A. Therefore, information sequences of channels other than the third channel include:
There is a frequency shift. Therefore, the frequency converter 38
The OFDM demodulated signal output from the FFT 37 is frequency-converted to adjust the frequency shift, in other words, to adjust the phase.

FIG. 4 is a circuit diagram of an embodiment of the frequency converter 38. The frequency converter 38 includes a phase shifter 381
And a phase shift angle generation circuit 382 and a cumulative adder 383. The first input terminal T1 has a fast Fourier transform circuit (F
The OFDM demodulated signal from the FT 37 is applied and input to the phase shifter 381. The frequency shift amount Δf is applied to the second input terminal T2. The frequency shift amount Δf is defined as Δf = f _n −f ₃ where the frequency of the channel selected by the channel selector 39 is f _n . This frequency shift amount Δf can be set, for example, by the channel selector 39. OFD is connected to the third input terminal T3.
The guard interval length ΔT added by the guard interval adding circuit 15 in the M transmitting device 10A is applied. The phase shift angle generation circuit 382 receives the frequency shift amount Δf and the guard interval length ΔT, and generates a signal of the phase angle θ. The phase angle θ is represented by the following equation.

[0065]

(Equation 3)

The phase angle θ generated by the phase shift angle generation circuit 382
Are cumulatively added for each OFDM in the accumulator 383 to calculate the phase shift amount. The phase shift amount calculated by the accumulator 383 is 0 to 2π, for example, 0 to 102
3, but the phase shift amount is 2π
Is exceeded, the value is reset to 0, and thereafter, cyclic addition is performed.

The phase shifter 381 outputs the signal from the fast Fourier transform circuit (FFT) 37 applied to the first input terminal T1.
The FDM demodulated signal (mapping point signal) is added to the accumulator 38.
The phase is adjusted with the phase shift amount calculated in step 3. The phase adjustment in the phase shifter 381 performs the following calculation.

[0068]

(Equation 4)

By performing the above-described frequency correction by the frequency converter 38, the OFDM transmitting apparatus 10A receives the OFDM-modulated signal based on the center frequency f ₃ in the OFDM receiving apparatus 30A, and receives the signal of the desired partial reception channel. even in the case of receiving the information sequence, a center frequency f _3, without being dependent on the frequency difference between the frequency f _n of the selected channel can be decoded signals of a desired channel accurately. Since the received signal of the OFDM receiving apparatus 30A of the present embodiment is an OFDM signal, it is hardly affected by multipath, and the OFDM receiving apparatus 30A is a mobile receiving apparatus or the like and easily affected by multipath caused by buildings or the like. Even when receiving in an environment, it can be received without being affected by multipath.

The frequency converter 38, which performs the above-described operation and includes the phase shifter 381, the phase shift angle generating circuit 382, and the accumulator 383, can be integrally formed by, for example, a digital signal processor (DSP).

More preferably, the fast Fourier transform circuit (FFT) 37 and the frequency converter 38 can be integrally formed using a DSP. That is, using a high-speed Fourier transform circuit (FFT) 3
When the arithmetic processing of No. 7 and the arithmetic processing of the frequency converter 38 are realized, the device configuration is simplified.

The OFDM communication apparatus according to the present embodiment
At least one OFDM transmitting apparatus 10A illustrated in FIG. 1A and the OFDM receiving apparatus 30A illustrated in FIG.
Are combined with one unit or a plurality of units.
In such an OFDM communication apparatus, when an information sequence of, for example, 5 channels is transmitted from the OFDM transmission apparatus 10A, the plurality of OFDM reception apparatuses 30A receive desired channels among 1 to 5 channels, respectively. Demodulation becomes possible. That is, an information sequence for 5 channels can be communicated using a frequency band for a bandwidth _fBW × 5 channels. In terrestrial digital broadcasting and the like, it is expected that a very large number of broadcasts will be performed. According to the present embodiment, an excessive frequency is not required even in such a use form. Therefore, the OFDM communication apparatus according to the present embodiment is advantageous, for example, when there is a restriction on the use of frequency.

The above embodiment is an exemplification. For example, the fast Fourier inverse transform circuit (IFFT) shown in FIG.
Reference numeral 14 denotes an example of an orthogonal transform circuit suitable when the information sequence is audio (radio broadcast information) or the like. When the information sequence is a video signal or the like, the orthogonal transform circuit is an example of a discrete cosine inverse. Conversion (IDCT: Invers
A circuit that performs eDiscrete Cosine Transform) can be used. Similarly, the fast Fourier transform circuit (FFT) 37 in FIG. 1B can be replaced with another orthogonal transform circuit such as a circuit performing a discrete cosine transform (DCT). In the above-described embodiment, the description has been made of the "upper local" in which the local oscillation frequency is higher than the frequency of the RF signal, but the present invention can also be applied to the opposite "lower local".

Although the above-described embodiment has been described with reference to an embodiment suitable for digital terrestrial broadcasting, a CA
When a cable such as a TV is used, the transmitting antenna 20 of FIG. 1A is deleted, and the receiving antenna 31 of FIG.
Can be deleted. Of course, when CATV is used, there is no need to perform the above-mentioned OFDM processing because the influence of multipath is less.

[0075]

According to the OFDM transmission apparatus of the present invention, information sequences of a plurality of channels (each of which is a partial reception channel) each having a fixed bandwidth and a center frequency are frequency-multiplexed, and OFDM transmission is performed. The signals are modulated and quadrature-modulated, and all of the plurality of channels are transmitted to the transmission path. That is, if the OFDM transmitting apparatus of the present invention is used,
Using one frequency band (bandwidth × frequency band for a plurality of channels in this example) via one transmission line,
Multiple information sequences can be sent. As a result, even when there is no room for using the frequency, it is possible to transmit information sequences of a large number of partial reception channels using a limited frequency band. In other words, it is possible to transmit information sequences of many partial reception channels even in a narrow frequency band.

Since the signal transmitted from the OFDM transmitting apparatus of the present invention is an OFDM signal, it is hardly affected by a failure such as multipath.

In the OFDM receiving apparatus of the present invention, the frequency conversion means corrects the frequency so that the OFDM transmitting apparatus receives the OFDM-modulated signal based on the center frequency in the OFDM transmitting apparatus, and obtains information on a desired partial reception channel. Even when a sequence is received, a signal of a desired channel can be accurately decoded without depending on a frequency difference between a center frequency and a frequency of a selected channel.

The received signal of the OFDM receiver of the present invention is
Because it is an FDM signal, it is less susceptible to multipath. Therefore, even when the OFDM receiving apparatus is a mobile receiving apparatus or the like and receives in an environment susceptible to multipath due to a building or the like, it is possible to receive without being affected by multipath.

The OFDM transmitting apparatus of the present invention and the OF
The OFDM communication apparatus according to the present invention, which is combined with a DM receiving apparatus, can simultaneously communicate information sequences of a plurality of channels using a bandwidth × frequency band of a plurality of channels. In terrestrial digital broadcasting and the like, it is expected that a very large number of broadcasts will be performed. According to the OFDM communication apparatus of the present invention, an excessive frequency is not required even in such a use form. Therefore, the OFDM communication apparatus of the present invention is advantageous, for example, when the use of frequency is limited.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an OFDM communication device according to a first embodiment of the present invention; FIG. 1A is a configuration diagram of an OFDM transmission device according to an embodiment of the present invention; FIG. 2B is a configuration diagram of the OFDM receiver according to the first embodiment of the present invention.

FIG. 2 is a diagram illustrating an OFDM baseband signal frequency-multiplexed on an OFDM subcarrier by a multiplexer illustrated in FIG. 1 (A).

FIG. 3 is a diagram showing OFD signals obtained by the multiplexer shown in FIG.
FIG. 3 is a diagram illustrating an OFDM baseband signal frequency-multiplexed on M subcarriers.

FIG. 4 shows one of the frequency converters illustrated in FIG. 1 (B).
FIG. 2 is a circuit configuration diagram of the embodiment.

FIGS. 5A and 5B are configuration diagrams of an OFDM communication apparatus that performs an OFDM communication method, and FIG.
FIG. 5B is a configuration diagram of an M transmission device, and FIG. 5B is a configuration diagram of an OFDM reception device corresponding to the OFDM transmission device of FIG.

6 (A) and 6 (B) are an OFDM transmitting apparatus illustrated in FIG. 5 (A) and an OFDM transmitting apparatus illustrated in FIG. 5 (B).
FIG. 2 is a diagram illustrating an RF channel arrangement in an OFDM system performed by an OFDM communication device including a receiving device.

FIG. 7 is a diagram illustrating an OFDM signal frequency-multiplexed on subcarriers in the multiplexer of FIG. 5 (A).

FIG. 8 is a characteristic diagram illustrating a frequency selection characteristic of an intermediate frequency (IF) filter.

[Explanation of symbols]

 10, 10A OFDM transmitter (transmitter) 11 Main channel mapping circuit 12 Partial reception channel mapping circuit 11A Mapping circuit 111-115 First to fifth mapping circuit 13, 13A ··· Multiplexer (multiplexer) 14, 14A ··· Fast Fourier inverse transform circuit (IFFT) 15 ··· Guard interval addition circuit 16 ··· Quadrature modulator 17 ··· First local oscillator 18 ··· Frequency converter 19 , 19A second local oscillator 20 transmission antenna 30, 30A OFDM receiver (receiver) 31, receiving antenna 32, 32A frequency converter 33, 33A third local oscillator 34 Intermediate frequency (IF) filter 35 Quadrature demodulator 36 Third local oscillator 37 Fast Fourier transform circuit ( FT) 38 ... frequency converter 381 · phase shifter 382 · phase angle generator 383 · accumulator 39 · channel selector

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C063 AB03 AB06 AB20 CA23 CA31 CA40 5K022 DD00 DD13 DD17 DD19 DD22 DD23 DD32 DD33 5K041 AA00 BB10 CC04 HH09 HH10 JJ11

Claims (12)

[Claims] A mapping means for independently mapping a plurality of information sequences each having a constant bandwidth and a different center frequency; a frequency multiplexing means for frequency-multiplexing the plurality of mapped symbols; Orthogonal transformation means for orthogonally transforming a plurality of frequency-multiplexed symbols; orthogonal modulation means for orthogonally modulating the orthogonally-modulated signal at an intermediate frequency; center of the orthogonally-modulated signal in a center frequency of the plurality of information sequences Frequency conversion means for performing frequency conversion on the basis of the frequency of the OFDM transmitter. 2. The mapping means according to claim 1, wherein said mapping means comprises QAM, QPSK.
2. The OFDM transmitting apparatus according to claim 1, wherein the plurality of information sequences are mapped to symbols in an orthogonal coordinate system by using the method. 3. The OFDM transmitting apparatus according to claim 2, wherein said orthogonal transform means has a fast Fourier inverse transform means. 4. The OFDM transmitting apparatus according to claim 2, wherein said orthogonal transform means has a discrete cosine inverse transform means. 5. The OFDM transmission apparatus according to claim 1, further comprising a guard interval adding means for adding a guard interval to the orthogonal transform result between the orthogonal transform means and the orthogonal modulation means. 6. A plurality of information sequences each having a fixed bandwidth and a different center frequency are independently mapped, frequency-multiplexed, orthogonally transformed, a guard interval is added, and orthogonally modulated at an intermediate frequency. Receiving means for receiving a signal obtained by converting the quadrature-modulated signal into a frequency with reference to a center frequency among the center frequencies of the plurality of information sequences; and a frequency of an information sequence to be selected among the received signals. Channel selecting means for setting the frequency, an oscillating means for oscillating a signal having a frequency obtained by adding an intermediate frequency to the frequency selected by the channel selecting means, and a signal received by the receiving means being oscillated by the oscillation signal from the oscillating means. Frequency converting means for converting, and a signal having a band-pass characteristic equal to the fixed bandwidth, A band-pass filter that passes with the band-pass characteristic; an orthogonal demodulation unit that orthogonally demodulates an output signal of the band-pass filter with an intermediate frequency signal; an orthogonal transformation unit that orthogonally transforms the orthogonally demodulated signal; An OFDM receiving apparatus comprising: a frequency correction unit that performs a frequency correction on a converted signal in accordance with a difference between a center frequency among the center frequencies of the plurality of information sequences and a frequency selected by the channel selection unit. . 7. A phase shifter comprising: a frequency corresponding to a difference between a center frequency among the center frequencies of the plurality of information sequences and a frequency selected by the channel selector; and a guard interval length. A phase shift angle generating means for calculating an angle; and a cumulative addition for calculating the cumulative phase shift angle by resetting the calculated phase shift angle to 0 (radian) when it exceeds 2π (radian) and performing cumulative addition. 7. The method according to claim 6, further comprising: a phase shifter that shifts the signal orthogonally transformed by the orthogonal transformer by the cumulative addition phase shift angle.
FDM receiver. 8. The phase shift angle generating means calculates a phase shift angle θ based on the following equation (1), and the phase shift means shifts the phase of the orthogonally transformed signal based on the following equation (2). 8. The OFDM receiver according to 7. (Equation 1) 9. The OFDM receiver according to claim 6, wherein said orthogonal transform means has a fast Fourier transform means. 10. The OFDM receiver according to claim 6, wherein said orthogonal transform means has a discrete cosine transform means. 11. An OFDM communication device in which an OFDM transmission device and an OFDM reception device are connected via a transmission line, wherein the OFDM transmission device has a plurality of fixed bandwidths and different center frequencies. Mapping means for independently mapping the information sequences of the above, frequency multiplexing means for frequency-multiplexing the mapped symbols, orthogonal transform means for orthogonally transforming the frequency-multiplexed symbols, Orthogonal modulation means for orthogonally modulating the modulated signal at an intermediate frequency; frequency conversion means for converting the orthogonal modulation signal based on a center frequency among the center frequencies of the plurality of information sequences; Signal transmitting means for transmitting a signal whose frequency has been converted by the means. Receiving means for receiving a signal transmitted from the transmitting antenna of the OFDM transmitting apparatus; channel selecting means for setting a frequency of an information sequence to be selected among the received signals; An oscillating means for oscillating a signal having a frequency obtained by adding an intermediate frequency to a frequency; a frequency converting means for frequency-converting a signal received by the receiving means with an oscillating signal from the oscillating means; and a band-pass equal to the fixed bandwidth. A band-pass filter having characteristics and passing the signal frequency-converted by the frequency conversion means with the band-pass characteristic; an orthogonal demodulation means for orthogonally demodulating an output signal of the band-pass filter with an intermediate frequency signal; Orthogonal transform means for orthogonally transforming the demodulated signal; and a center frequency of the plurality of information sequences for the orthogonally transformed signal. Center frequency, OFDM communication apparatus and a frequency correction means for performing a frequency correction according to the difference between the frequency selected by the channel selecting means among. 12. A plurality of information sequences each having a fixed bandwidth and a different center frequency are independently mapped, a plurality of mapped symbols are frequency-multiplexed, and a plurality of frequency-multiplexed symbols are mapped. The orthogonally modulated signal is orthogonally modulated at the intermediate frequency, the orthogonally modulated signal is frequency-converted with reference to a center frequency among the center frequencies of the plurality of information sequences, and the frequency-converted signal is obtained. Transmitting the received signal, setting the frequency of the information sequence to be selected among the received signals, and oscillating a signal having a frequency obtained by adding an intermediate frequency to the selected frequency and the signal Frequency-converted with the received signal, passing the frequency-converted signal only through the certain band component, Quadrature demodulation with an intermediate frequency signal, quadrature transformation of the quadrature demodulated signal, and selection of the orthogonally transformed signal by the channel selection means with a center frequency among center frequencies of the plurality of information sequences. OFDM communication method for performing frequency correction according to a difference from a set frequency.