JP2002290364A - OFDM transmission / reception method and apparatus - Google Patents

Abstract

(57) [Summary] [Problem] To significantly improve frequency use efficiency and reduce costs. SOLUTION: In an OFDM transmission / reception method using a plurality of channels, each center frequency of the plurality of channels is set to a frequency satisfying an orthogonal relationship with each other, and based on a reference frequency signal transmitted from a specific OFDM transmission / reception apparatus, another Of the channel setting of the OFDM transmission / reception apparatus of FIG.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM transmission / reception method and apparatus with improved frequency use efficiency.

[0002]

2. Description of the Related Art Wireless LAN using OFDM transmission system
In the system, as shown in FIG. 3, a plurality of mobile terminal transmitting / receiving apparatuses 2
00, and the access point transmitting / receiving apparatus 100 and the mobile terminal transmitting / receiving apparatus 200 or the mobile terminal transmitting / receiving apparatus 2 are used in one channel selected from a plurality of channels.
00 are performed.

[0003] The transmission section 1 of such an OFDM transmission / reception apparatus
0 is configured as shown in FIG. The binary input data is sequentially loaded by the mapping unit 11 on a plurality of carrier waves (subcarriers) having mutually orthogonal frequencies. That is, the amplitude and phase of each subcarrier are modulated by the input data. For example, if the input data is QPSK
When modulation is performed, binary data is assigned to two subcarriers in pairs of I and Q. Data mapped to a plurality of subcarriers is IFFT
After a high-speed inverse Fourier transform is performed by the unit 12 and converted into one time axis data (OFDM signal) to become an OFDM baseband signal, a guard interval is added by the guard interval adding unit 13, and the orthogonal modulation is performed by the orthogonal modulation unit 14. After being modulated and further converted into an analog signal by the D / A converter 15, the signal is converted into a frequency of a specific channel by the up-converter 16 and radiated from the antenna 17 in the air.

[0004] Further, a receiving unit 20 of an OFDM transmitting / receiving apparatus is provided.
Is configured as shown in FIG. Antenna 21
The signal of the specific channel received by (shared with the antenna 17) is frequency-converted by the down-converter 22,
The signal is converted into a digital signal by the / D conversion unit 23, orthogonally demodulated by the orthogonal demodulation unit 24 to become a baseband OFDM signal, and then subjected to fast Fourier transform by the FFT unit 25 to convert time axis data to data of a plurality of subcarriers Then, the data signal is extracted by the demapping unit 26.

[0005]

By the way, in the OFDM transmission system, each subcarrier in the OFDM signal needs to satisfy an orthogonal relationship with each other. However, when an OFDM signal is transmitted and received using a plurality of channels, In general, subcarriers of an OFDM signal of a certain channel and subcarriers of an OFDM signal of another channel are not orthogonal.

Therefore, in the case of adjacent CH1 having a center frequency of f1 'and center frequency of f2'CH2, for example, as shown in FIG. It is necessary to provide a guard band (null channel: an unused sub-channel area) between channels, and there is a problem that the frequency use efficiency is reduced. In some cases, a filter having a steep attenuation characteristic is provided in order to cut an adjacent channel signal. In this case, the cost is increased.

An object of the present invention is to eliminate the need to provide a filter having a guard band or a steep attenuation characteristic, to greatly improve the frequency use efficiency and to reduce the cost.

[0008]

According to a first aspect of the present invention, there is provided an OFD using a plurality of channels.
In the M transmitting / receiving method, each center frequency of the plurality of channels is set to a frequency that satisfies an orthogonal relationship with each other, and based on a reference frequency signal transmitted from a specific OFDM transmitting / receiving device, a channel for another OFDM transmitting / receiving device is set. It was configured to calibrate the frequency.

According to a second aspect of the present invention, in the first aspect, OFDM signals for at least two adjacent channels among the plurality of channels are simultaneously transmitted from a transmission side, and the OFDM signal is demodulated on a reception side. Later desired one
It is configured to extract data for one channel.

According to a third aspect of the present invention, in the first aspect of the present invention, for two adjacent channels, the frequency interval between the lowest frequency subcarrier of one channel and the highest frequency subcarrier of the other channel is determined. ,
The frequency is set to the subcarrier frequency pitch of one or the other channel.

According to a fourth aspect of the present invention, in the OFDM transmitting / receiving apparatus using a plurality of channels, the center frequencies of the plurality of channels are set to frequencies satisfying an orthogonal relationship with each other, and the channel is set based on a received reference frequency signal. Frequency calibration means for calibrating the frequency for use.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the frequency calibrating means includes a filter for extracting the reference frequency signal from a received signal received by a receiving unit, and a filter for extracting the reference frequency signal from the signal extracted by the filter. A reference frequency signal detection circuit that detects a reference frequency signal; a repetition signal generation circuit that captures and temporarily stores the reference frequency signal detected by the reference frequency signal detection circuit to generate a repetition frequency signal of the reference frequency signal; PL that takes in a continuous frequency signal obtained by a repetitive signal generation circuit as a reference signal
And an output frequency signal of the PLL circuit for the channel setting.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In this embodiment, a wireless LAN access point transmitting / receiving apparatus 100 and a terminal transmitting / receiving apparatus 20 are described.
The center frequencies of a plurality of channels commonly used by the transmission unit 10 and the reception unit 20 of 0 are determined so as to satisfy an orthogonal relationship with each other. For example, when using two channels, CH1 and CH2, as shown in FIG.
And the center frequencies f1 and f2 of CH2 satisfy the orthogonal relationship. As a result, the frequencies of the subcarriers included in all the channels satisfy the orthogonal relationship with each other.

The access point transmitting / receiving apparatus 100
, A reference frequency signal having a frequency fo is transmitted periodically at a predetermined time interval, and the plurality of terminal transmitting / receiving apparatuses 200 receive the reference frequency signal and adjust the local frequencies of the internal up-converter 16 and down-converter 22. Calibrate so as to have a specific relationship with the reference frequency signal.

For example, when two channels are used as described above, as shown in FIG. 1, the center frequency f1 of CH1 has a frequency difference Δf1 with respect to the reference frequency fo.
The center frequency f2 of CH2 is Δf with respect to the reference frequency fo.
The local frequency is calibrated so as to have a frequency difference of 2. This prevents the orthogonal relationship between the subcarriers of each channel from being unsatisfied due to the local frequency shift of the mobile terminal transmitting / receiving apparatus 200 using each channel. Note that the reference frequency signal of frequency fo is C
It is not necessary to have an orthogonal relationship with the center frequencies f1 and f2 of H1 and CH2.

FIG. 2 shows the receiving section 20 of the terminal transmitting / receiving apparatus 200.
Is a block diagram showing a part of the down converter 22 of FIG.
In FIG. 2, reference numeral 221 denotes an RF amplifier for amplifying a signal received by the antenna 21; 222, a voltage controlled oscillator (VCO) for oscillating a local frequency signal; and 223, an antenna 21 based on the local frequency signal oscillated by the voltage controlled oscillator 222. And 224 are band-pass filters for extracting an intermediate frequency signal, which is a frequency common to each channel, from the signal output from the multiplier 223. Reference numeral 225 denotes a programmable frequency divider for dividing the oscillation output signal frequency of the voltage controlled oscillator 222 by a frequency division ratio according to the channel selection signal, 226 a phase comparator, and 227 a phase comparator 22
6 is a low-pass filter that extracts a DC component from the signal output from the control signal generator 6 and inputs the DC component to the voltage-controlled oscillator 222 as a control voltage.

Reference numeral 228 denotes a narrow-band bandpass filter whose center frequency is set to the frequency fo of the reference frequency signal. Reference numeral 229 denotes a reference frequency signal detection for detecting a reference frequency signal from output signals of the bandpass filter 228. A circuit 230 is a repetition signal generation circuit that temporarily stores the detected reference frequency signal and repeatedly generates a signal of the frequency fo based on the reference frequency signal. The repetition signal serves as a reference signal of the phase comparator 226.

As described above, in each mobile terminal transmitting / receiving apparatus 200, the reference frequency signal of the frequency fo periodically transmitted from the access point transmitting apparatus 100 is transmitted to the RF amplifier 221.
, And is detected by the reference frequency signal detection circuit 229, and is input to the signal generation circuit 230 repeatedly. The repetitive signal generating circuit 230 temporarily stores the frequency fo of the input reference frequency signal, generates a repetitive signal (for example, a sine wave) based on the frequency fo, and generates a repetitive signal as a reference signal having a continuous frequency fo. Output to the comparator 226.

As a result, the local frequency f oscillated by the voltage-controlled oscillator 22 by the PLL circuit including the phase comparator 226, the low-pass filter 227, the voltage-controlled oscillator 222, and the programmable frequency-divider 225 If the frequency division ratio is N, then f
= N × fo, and this frequency signal f is input to the multiplier 223 for frequency conversion.

The upconverter 16 of the transmitting section 10 of each mobile terminal transmitting / receiving apparatus 200 may also be provided with a frequency calibrating section for calibrating with the reference frequency signal of the frequency fo. Are not performed at the same time, the voltage-controlled oscillator 22 of FIG.
2 can be used as a local signal. At this time, the frequency division ratio of the programmable frequency divider 225 is set to a value according to the channel selection signal of the transmission channel.

As described above, the P which generates the local frequency of the transmitting unit 10 and the receiving unit 20 of the mobile terminal transmitting / receiving apparatus 200
Since the reference signal input to the phase comparator of the LL circuit is periodically calibrated to an accurate frequency, it is possible to prevent the orthogonality between the center frequencies and the subcarriers of each channel from being lost due to the frequency shift.

From the above, it is not necessary to provide a guard band between adjacent subcarriers of two adjacent channels, and the center frequency of the two adjacent channels is set to the extent that the subcarriers do not overlap, for example, as shown in FIG. As shown in (2), the proximity can be achieved, so that the frequency use efficiency is improved. Further, it is not necessary to use a filter having a steep attenuation characteristic.

In this embodiment, since all subcarriers satisfy orthogonality over two or more channels, it is possible to perform transmission and reception over a wide band by simultaneously using two or more channels in one transmitting / receiving apparatus. It becomes possible.
For example, in order to configure a transmitting / receiving apparatus so that transmission / reception for two adjacent channels can be performed, the IFFT unit 12 or the FFT unit 2
5 is set to be capable of processing twice as many subcarriers as a single channel (for example, if the number of subcarriers is 64 in a single channel, the number of subcarriers is 128 in two channels), and a band-pass filter for an intermediate frequency signal is used. Can be switched for two adjacent channels.
However, since the center frequency at this time is an intermediate frequency between the center frequencies of the adjacent two channels, the up converter 16 and the down converter 22 correspond to these frequencies.
It is necessary to set the local frequency. In this case, since the data of two channels is received and demodulated in the receiving unit, an output selecting unit for extracting only the data of the necessary channel may be provided.

[0030]

As described above, according to the present invention, there is no need to provide a guard band or a filter having a steep attenuation characteristic.
The frequency utilization efficiency can be greatly improved, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of subcarrier frequencies of two adjacent channels in an OFDM transmitting / receiving apparatus according to one embodiment of the present invention.

FIG. 2 is a block diagram of a downconverter part of a receiving unit according to one embodiment of the present invention.

FIG. 3 is an explanatory diagram of a general wireless LAN.

FIG. 4 is a block diagram of a transmission unit of the OFDM transmission / reception device.

FIG. 5 is a block diagram of a receiving unit of the OFDM transmitting / receiving apparatus.

FIG. 6 is an explanatory diagram of subcarrier frequencies of two adjacent channels in a conventional OFDM transmitting / receiving apparatus.

[Explanation of symbols]

100: access point transceiver, 200: mobile terminal transceiver 10: transmitter, 11: mapping unit, 12: IFFT
(High-speed inverse Fourier transform) section, 13: guard interval addition section, 14: quadrature modulation section, 15: D / A conversion section, 1
6: Up converter, 17: Antenna 20: Receiver, 21: Antenna, 22: Down converter, 23: A / D converter, 24: Quadrature demodulator, 25: F
FT (Fast Fourier Transform) unit, 26: Demapping unit 221: RF amplifier (RFAMP), 222: Voltage controlled oscillator (VCO), 223: Multiplier, 224: Bandpass filter (BPF), 225: Programmable frequency divider (P.DEV), 226: Phase comparator (PC), 22
7: low-pass filter (LPF), 228: band-pass filter (BPF), 229: reference frequency signal detection unit (fo detection), 230: repetitive signal generation circuit.

Claims (5)

[Claims] 1. An OFDM transmission / reception method using a plurality of channels, wherein each center frequency of the plurality of channels is set to a frequency satisfying an orthogonal relationship with each other, and based on a reference frequency signal transmitted from a specific OFDM transmission / reception apparatus. An OFDM transmission / reception method, wherein a frequency for setting a channel of another OFDM transmission / reception device is calibrated. 2. The OFDM according to claim 1, wherein at least two adjacent channels among the plurality of channels are provided.
The signal is transmitted from the transmitting side at the same time, and the OFDM
An OFDM transmission / reception method, wherein data of one desired channel is extracted after demodulating a signal. 3. The method according to claim 1, wherein, for two adjacent channels, the frequency interval between the lowest frequency sub-carrier of one channel and the highest frequency sub-carrier of the other channel is determined. An OFDM transmission / reception method, wherein a frequency pitch of a subcarrier is set. 4. An OFDM transmitting / receiving apparatus using a plurality of channels, wherein center frequencies of the plurality of channels are set to frequencies satisfying an orthogonal relationship with each other, and a frequency for channel setting is calibrated based on a received reference frequency signal. An OFDM transmission / reception apparatus characterized in that a frequency calibration means is provided. 5. A filter according to claim 4, wherein said frequency calibrating means comprises a filter for extracting said reference frequency signal from a received signal received by a receiving section, and a reference for detecting said reference frequency signal from a signal extracted by said filter. A frequency signal detection circuit, a repetition signal generation circuit that captures and temporarily stores the reference frequency signal detected by the reference frequency signal detection circuit and generates a repetition frequency signal of the reference frequency signal, and a repetition signal generation circuit. And a PLL circuit that takes in the continuous frequency signal as a reference signal.
An OFDM transmitting / receiving apparatus, wherein an output frequency signal of the PLL circuit is used for the channel setting.