JP2003046470A - OFDM receiver circuit - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide an OFDM receiving circuit capable of realizing both high-speed signal transmission and high frequency use efficiency. SOLUTION: A demultiplexer 11 for demultiplexing a received signal into a plurality of N sequences and N oscillators which output carrier signals having an interval which is an integral multiple of a subcarrier frequency interval of the received signal and which are frequency synchronized with each other. N quadrature detectors 12 and 13 for inputting each of the N-series OFDM signals and signals output from N oscillators 14 and 15 and a complex OFDM signal output from the quadrature detectors 12 and 13 Filters 16 to 19 for removing unnecessary wave components from the signal and N for converting a complex OFDM signal output from them into a digital signal.
A / D converters 20 to 23 and digital complex OFD
N for inputting M signal and outputting modulation signal for each subcarrier
Fourier transformers 24 and 25 and a subcarrier demodulator 26 for demodulating a modulation signal for each subcarrier are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM receiving circuit for receiving and demodulating an OFDM (Orthogonal Frequency Division Multiplexing) signal mainly used for wireless communication, and particularly realizing high speed signal transmission and high frequency utilization efficiency. The present invention relates to an OFDM receiving circuit.

[0002]

2. Description of the Related Art A conventional OFDM receiver circuit is constructed as shown in FIG. In the case of the OFDM receiving circuit shown in FIG. 4, the received OFDM signal is converted into a baseband complex OFDM signal by the carrier signal output from the oscillator 52 in the quadrature detector 51.

The baseband complex OFDM signal is converted into a digital signal by A / D converters 55 and 56 after removing unnecessary wave components by filters (LPF) 53 and 54. The digital baseband complex OFDM signals output from the A / D converters 55 and 56 are subjected to discrete Fourier transform by a Fourier transformer (FFT) 57 and separated into modulated signals for each subcarrier. The modulated signal for each subcarrier is demodulated by the subcarrier demodulator 58. The data transmitted by the transmitting side is obtained at the output of the subcarrier demodulator 58.

In the OFDM receiving circuit shown in FIG. 5,
The quadrature detection circuit is digitized. This OFD
In the case of the M receiving circuit, the received OFDM signal is frequency-converted in the frequency converter 71 using the local oscillation signal output from the oscillator 72, and converted into a carrier frequency for digital quadrature detection. The OFDM reception signal frequency-converted by the frequency converter 71 is filtered by the filter 73 to remove unnecessary wave components, and then converted into a digital signal by the A / D converter 74.

The digital OFDM received signal output from the A / D converter 74 is quadrature detected by the digital quadrature detector 75. A digital baseband complex OFDM signal is obtained at the output of the digital quadrature detector 75. This baseband complex OFDM signal is subjected to discrete Fourier transform by the Fourier transformer 76 and separated into modulated signals for each subcarrier. The modulated signal for each subcarrier is demodulated by the subcarrier demodulator 77.
The data transmitted by the transmission side is obtained at the output of the subcarrier demodulator 77.

[0006]

[Problems to be Solved by the Invention]
In the receiving circuit, a filter (LPF) for removing harmonics that are unnecessary waves is used before A / D conversion to avoid aliasing. Further, in the conventional general OFDM receiving circuit, it is assumed that harmonics are removed by using a filter having a steep filter characteristic as shown in FIG.

However, in reality, a filter having such a steep filter characteristic cannot be realized. Therefore, in practice, of the many subcarriers included in the OFDM signal, a specific carrier located outside is not used. As a result, the substantial frequency interval between the adjacent channel and the adjacent band can be widened,
The characteristics required for the filter are relaxed. However, frequency utilization efficiency is sacrificed because the specific carrier located outside cannot be used. It is difficult to achieve both high frequency utilization efficiency and steep filter feasibility.

On the other hand, by causing the A / D converter to perform an oversampling operation and taking a large number of Fourier transform (FFT) calculation points, it is possible to avoid interference due to aliasing of unnecessary waves. In that case,
The characteristics of the filter used to remove the unwanted wave are relaxed as shown in FIG. 6 (b). However, when transmitting a high-speed signal as an OFDM signal, it is necessary to use an A / D converter having a remarkably high operating speed in order to perform oversampling operation of the A / D converter, which increases power consumption and realizes it. There is a problem in terms of sex.

A plurality of OFs whose frequencies are shifted from each other
High-speed signal transmission becomes possible by using DM signals in parallel. However, in that case, it is necessary to provide a guard band as shown in FIG. 6C so that a plurality of OFDM signals do not interfere with each other. When the guard band is provided, it is inevitable that the utilization efficiency of the frequency is lowered. It is an object of the present invention to provide an OFDM receiver circuit capable of realizing both high speed signal transmission and high frequency utilization efficiency.

[0010]

According to a first aspect of the present invention, there is provided an OFDM receiving circuit, in which a demultiplexer for demultiplexing a received OFDM signal into a plurality of N sequences and an integer of frequency intervals of subcarriers included in the received OFDM signal. N oscillators that output carrier signals that have a frequency interval corresponding to twice the frequency synchronization with each other, N sequence OFDM signals that are output from the demultiplexer, and the N oscillators. N quadrature detectors that input the signals output from each and output a baseband complex OFDM signal, and N pairs of filters that remove unnecessary wave components from the complex OFDM signal output by the quadrature detector. , N pairs of A / D for converting the complex OFDM signal output from the filter into a digital signal
A converter, N Fourier transformers that input a digital complex OFDM signal output from the pair of A / D converters, perform a discrete Fourier transform, and output a modulated signal for each subcarrier; and the Fourier transform And a subcarrier demodulator for demodulating a modulated signal for each subcarrier output from the device.

According to the first aspect, the band of the OFDM signal to be received is divided and the signal is processed for each band. This allows
It is possible to prevent the operating speed of the A / D converter from becoming extremely high. However, only by band-dividing the OFDM signal on the transmitting side, it is necessary to provide a guard band so that a plurality of OFDM signals do not interfere with each other as described above (see FIG. 6C), and the frequency utilization efficiency can be improved. There is a problem that there is no.

[0012] Therefore, in claim 1, the OFD is divided and received.
The M signal interval is set to M times the subcarrier interval of the OFDM signal (M is a natural number) so that the OFDM signals do not overlap. Furthermore, a plurality of OFs that are divided
Frequency synchronization is established between a plurality of oscillators that generate a carrier for quadrature detection of a DM signal. As a result, the OFDM signal is divided into a plurality of signals, and it is as if one broadband O
The FDM signal can be processed as if demodulated. Therefore, it is not necessary to install a guard band, and high frequency utilization efficiency can be realized.

According to a second aspect of the present invention, there is provided an OFDM receiving circuit, wherein a demultiplexer for demultiplexing a received OFDM signal into a plurality of N sequences and a frequency interval corresponding to an integer multiple of a frequency interval of subcarriers included in the received OFDM signal. And N oscillators that output carrier signals whose frequency synchronization is established with each other,
N frequency converters for frequency-converting each of the N-series OFDM signals output from the demultiplexer using the signals output from each of the N oscillators, and output from the frequency converters. N filters for removing unnecessary wave components from the OFDM signal and the N A / N for converting the OFDM signal output from the filter into a digital signal.
A D converter and N digital quadrature detectors for inputting the digital OFDM signal output from the A / D converter to perform digital quadrature detection and outputting a baseband complex OFDM signal; N Fourier transformers that perform a discrete Fourier transform on the complex OFDM signal output from the quadrature detector to output a modulation signal for each subcarrier, and subcarriers that demodulate the modulation signal for each subcarrier output by the Fourier transformer And a demodulator.

In the second aspect, the band of the OFDM signal to be received is divided similarly to the first aspect, and the signal is processed for each band. This makes it possible to prevent the operating speed of the A / D converter from becoming extremely high. Also, the interval between the OFDM signals to be divided and received is set to M times (M is a natural number) the subcarrier interval of the OFDM signals so that the OFDM signals do not overlap.

Further, frequency synchronization is established between a plurality of oscillators that generate a local oscillation signal used for frequency conversion of a plurality of divided OFDM signals. As a result, the OFDM signal is divided into a plurality of signals, and it is as if one broadband O
The FDM signal can be processed as if demodulated. Therefore, it is not necessary to install a guard band, and high frequency utilization efficiency can be realized.

A third aspect of the present invention is the OF of the first or second aspect.
In the DM receiving circuit, a reference signal oscillator for providing a common reference signal to the N oscillators is further provided. By commonly using one reference signal output from the reference signal oscillator among the N oscillators, the frequencies of the signals output from the N oscillators can be synchronized with each other. Also, for example, PLL (Phase-Locked Loop)
By configuring each oscillator by using a circuit, it is possible to output signals having different frequencies and constant frequency intervals from the N oscillators.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) O of the present invention
One embodiment of the FDM receiver circuit will be described with reference to FIGS. 1 and 3. This form corresponds to claims 1 and 3. FIG. 1 is a block diagram showing an OFDM receiving circuit of this form. FIG. 3 is a spectrum diagram showing the spectrum arrangement of a signal of this form.

In this embodiment, the demultiplexer, the oscillator, the quadrature detector, the filter, the A / D (analog / digital) converter, the Fourier transformer, and the subcarrier demodulator of claim 1 are the demultiplexer 11, respectively. Oscillator (14, 15), quadrature detector (12, 13), low-pass filter (16 to 1)
9), A / D converters (20 to 23), Fourier transformers (24, 25) and subcarrier demodulator 26. The reference signal oscillator of claim 3 is a reference oscillator 27.
Corresponding to.

Referring to FIG. 1, this OFDM receiving circuit includes a demultiplexer 11, quadrature detectors 12 and 13, oscillators 14 and 1.
5, low-pass filter 16-19, A / D converter 20-
23, Fourier transformers 24 and 25, a subcarrier demodulator 26, and a reference oscillator 27. In this form,
It is assumed that the received OFDM signal is divided into two systems and the two systems process the signals respectively. That is, as in regions RL and RU shown by hatching in FIGS. 3A and 3B, the band of the received signal is divided into upper and lower regions, and the signal is processed for each band.

The demultiplexer 11 divides the received OFDM signal into 2
Then, the OFDM signals are output to the two signal processing systems. That is, one OFDM signal is input to the quadrature detector 12, and the other OFDM signal is input to the quadrature detector 13. The quadrature detectors 12 and 13 use the carrier signals output from the oscillators 14 and 15, respectively, for OF.
Quadrature detection of the DM signal is performed. By this quadrature detection, a baseband complex OFDM signal is obtained. That is, the OFDM signals composed of the real number component (I signal) and the imaginary number component (Q signal) are output from the quadrature detectors 12 and 13, respectively.

There is a predetermined frequency difference Δfd between the carrier signal output from the oscillator 14 and the carrier signal output from the oscillator 15. This frequency difference Δfd
Is an integer multiple of the subcarrier spacing in the received OFDM signal. Further, the frequency difference Δfd is set so that the divided signals in the respective bands do not overlap each other.

Further, frequency synchronization of the carrier signal is established between the two oscillators 14 and 15 so that the frequency difference Δfd does not change. In this example, the oscillators 14 and 15
Is formed of a PLL circuit, and the reference signal output from the reference oscillator 27 is applied to the two oscillators 14 and 15 as a common reference signal. The baseband complex OFDM signal output from the quadrature detector 12 is an unnecessary wave component (harmonic).
Is input to the low-pass filters 16 and 17 in order to remove. Similarly, the baseband complex OFDM signal output from the quadrature detector 13 is input to the low-pass filters 18 and 19 in order to remove unnecessary wave components.

The complex OFDM signals output from the low-pass filters 16 and 17 are converted into digital signals by the A / D converters 20 and 21, and the low-pass filters 18 and 1 are supplied.
The complex OFDM signal output from 9 is the A / D converter 2
At 2, 23, it is converted into a digital signal. Furthermore, A / D
Digital complex OF output from the converters 20 and 21
The DM signal is Fourier-transformed by the Fourier transformer 24 and separated into a modulation signal for each subcarrier. Similarly, A / D
Digital complex OF output from the converters 22 and 23
The DM signal is Fourier-transformed by the Fourier transformer 25 and separated into a modulation signal for each subcarrier.

The modulated signal output from the Fourier transformer 24 is a component of each subcarrier included in the half region RL shown in FIG. 3 in the received OFDM signal, and the modulated signal output from the Fourier transformer 25. Signal is received OFDM
It is a component of each subcarrier included in the half region RU shown in FIG. 3 in the signal. Fourier transformer 24, 25
The subcarrier demodulator 26 demodulates the modulated signal of each subcarrier output from the subcarrier demodulator 26 and is output from the subcarrier demodulator 26 as output data.

In this example, the number of operation points (FFT window) in the Fourier transformers 24 and 25 is made larger than the bands of the divided regions RL and RU. Therefore, the low-pass filters 16 to 19 that remove unnecessary waves
The filter characteristics required for the above may be gentle characteristics as shown in FIG. The OFDM receiving circuit of FIG. 1 is a wideband OFDM combining the two regions RL and RU shown in FIG.
A signal can be received. Moreover, two regions R
Since it is not necessary to provide a guard band between L and RU,
High frequency utilization efficiency is realized.

Of course, it is also possible to divide the band of the received OFDM signal into three or more regions and process the signal for each region. (Second Embodiment) Another embodiment of the OFDM receiving circuit of the present invention will be described with reference to FIG.
This form corresponds to claims 2 and 3.

FIG. 2 is a block diagram showing an OFDM receiving circuit of this form. This form is a modification of the first embodiment, and the configuration is changed so that the quadrature detection is performed by a digital circuit. In this form, the demultiplexer, the oscillator, the frequency converter, the filter, the A / D converter, the digital quadrature detector, the Fourier transformer, and the subcarrier demodulator of claim 2 are respectively a demultiplexer 31 and an oscillator (34). ，
35), frequency converter (32, 33), low-pass filter (36, 37), A / D converter (38, 39), digital quadrature detector (40, 41), Fourier transformer (4
2, 43) and the subcarrier demodulator 44. The reference signal oscillator of claim 3 corresponds to the reference oscillator 45.

Referring to FIG. 2, the OFDM receiving circuit includes a demultiplexer 31, frequency converters 32 and 33, an oscillator 34,
35, low-pass filters 36 and 37, A / D converter 3
8, 39, digital quadrature detectors 40, 41, Fourier transformers 42, 43, subcarrier demodulator 44 and reference oscillator 45. In this mode, it is assumed that the received OFDM signal is divided into two systems and the signals are processed by the two systems as in the first embodiment. That is, as in regions RL and RU shown by hatching in FIGS. 3A and 3B, the band of the received signal is divided into upper and lower regions, and the signal is processed for each band.

The demultiplexer 31 converts the received OFDM signal into 2
Then, the OFDM signals are output to the two signal processing systems. That is, one OFDM signal is input to the frequency converter 32, and the other OFDM signal is input to the frequency converter 33. The frequency converters 32 and 33 convert the frequency of the OFDM signal into a carrier frequency used for digital quadrature detection by using the carrier signals output from the oscillators 34 and 35, respectively.

There is a predetermined frequency difference Δfd between the carrier signal output from the oscillator 34 and the carrier signal output from the oscillator 35. This frequency difference Δfd
Is an integer multiple of the subcarrier spacing in the received OFDM signal. Further, the frequency difference Δfd is set so that the divided signals in the respective bands do not overlap each other.

Further, frequency synchronization of the carrier signal is established between the two oscillators 34 and 35 so that the frequency difference Δfd does not change. In this example, the oscillators 34, 35
Is constituted by a PLL circuit, and the reference signal output from the reference oscillator 45 is given to the two oscillators 34 and 35 as a common reference signal. The OFDM signal frequency-converted by the frequency converter 32 is removed of unnecessary wave components by the low-pass filter 36, and then converted into a digital signal by the A / D converter 38. Similarly, the OFDM signal frequency-converted by the frequency converter 33 is removed of unnecessary wave components by the low-pass filter 37, and then converted into a digital signal by the A / D converter 39.

The digital OFDM signal output from the A / D converter 38 is quadrature-detected by the digital quadrature detector 40 to obtain a digital baseband complex OFDM signal.
Become a signal. The digital OFDM signal output from the A / D converter 39 is quadrature-detected by the digital quadrature detector 41 and becomes a digital baseband complex OFDM signal.

Further, the digital complex OFDM signal output from the digital quadrature detector 40 is Fourier transformed by the Fourier transformer 42 and separated into modulated signals for each subcarrier. Similarly, the digital complex OFDM signal output from the digital quadrature detector 41 is Fourier-transformed by the Fourier transformer 43 to be separated into modulation signals for each subcarrier.

The modulated signal output from the Fourier transformer 42 is a component of each subcarrier included in the half region RL shown in FIG. 3 in the received OFDM signal, and the modulated signal output from the Fourier transformer 43. Signal is received OFDM
It is a component of each subcarrier included in the half region RU shown in FIG. 3 in the signal. Fourier transformers 42, 43
The subcarrier demodulator 44 demodulates the modulated signal of each subcarrier output from the subcarrier demodulator and is output from the subcarrier demodulator 44 as output data.

In this example, the number of operation points (FFT window) in the Fourier transformers 42 and 43 is made larger than the bands of the divided regions RL and RU. Therefore, the low-pass filters 36 and 37 that remove unnecessary waves
The filter characteristics required for the above may be gentle characteristics as shown in FIG.

The OFDM receiver circuit shown in FIG. 2 has the same structure as that shown in FIG.
It is possible to receive a wideband OFDM signal in which the two regions RL and RU are combined. Moreover, the two regions RL and RU
Since it is not necessary to provide a guard band between them, high frequency utilization efficiency is realized.

[0037]

As described above, the OFDM of the present invention
According to the receiving circuit, high-speed signal transmission and high frequency utilization efficiency can be realized without significantly increasing the operating speed of the A / D converter.

[Brief description of drawings]

FIG. 1 is a block diagram showing an OFDM receiving circuit of a first embodiment.

FIG. 2 is a block diagram showing an OFDM receiving circuit according to a second embodiment.

FIG. 3 is a spectrum diagram showing a spectrum arrangement of signals according to the first embodiment.

FIG. 4 is a block diagram showing a conventional OFDM receiving circuit.

FIG. 5 is a block diagram showing a conventional OFDM receiving circuit.

FIG. 6 is a spectrum diagram showing a spectrum arrangement of signals of a conventional example.

[Explanation of symbols]

11 duplexer 12, 13 Quadrature detector 14,15 oscillator 16, 17, 18, 19 Low-pass filter 20, 21, 22, 23 A / D converter 24,25 Fourier transformer 26 subcarrier demodulator 27 Reference oscillator 31 duplexer 32, 33 frequency converter 34,35 oscillator 36,37 Low-pass filter 38,39 A / D converter 40,41 Digital quadrature detector 42,43 Fourier Transform 44 subcarrier demodulator 45 Reference oscillator

Continued front page    (72) Inventor Masahiro Morikura             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F-term (reference) 5K022 DD01 DD33

Claims (3)

[Claims] 1. A demultiplexer for demultiplexing a received OFDM signal into a plurality of N sequences and a frequency interval corresponding to an integer multiple of a frequency interval of subcarriers included in the received OFDM signal, and frequency-synchronized with each other. Of the N-sequence OFDM signals output from the demultiplexer and the signals output from each of the N oscillators are input to the baseband. N quadrature detectors that output the complex OFDM signal, N pairs of filters that remove unnecessary wave components from the complex OFDM signal output by the quadrature detector, and the complex OFDM signal output by the filter into a digital signal. N pairs of A / D converters for converting, and a digital complex OF output from the pair of A / D converters
N Fourier transformers for inputting a DM signal, performing a discrete Fourier transform, and outputting a modulated signal for each subcarrier, and a subcarrier demodulator for demodulating the modulated signal for each subcarrier output by the Fourier transformer An OFDM receiver circuit characterized by being provided. 2. A demultiplexer for demultiplexing a received OFDM signal into a plurality of N sequences, and a frequency interval corresponding to an integer multiple of a frequency interval of subcarriers included in the received OFDM signal, and frequency-synchronized with each other. N oscillators that output the carrier signals established by the above, and N-sequence OFDM signals that are output from the demultiplexer are frequency-converted using the signals output from each of the N oscillators. Frequency converters, N filters for removing unnecessary wave components from the OFDM signals output from the frequency converters, and N A / D conversions for converting the OFDM signals output by the filters into digital signals And a digital OFDM output from the A / D converter
N digital quadrature detectors that input signals to perform digital quadrature detection and output baseband complex OFDM signals, and perform a complex Fourier transform on the complex OFDM signals output from the digital quadrature detectors for each subcarrier The OFDM receiving circuit is provided with N Fourier transformers for outputting the modulated signals of 1. and a subcarrier demodulator for demodulating the modulated signals for each subcarrier output by the Fourier transformers. 3. The OFD receiving circuit according to claim 1 or 2, further comprising a reference signal oscillator for providing a common reference signal to the N oscillators.
M receiver circuit.