JP3117412B2 - Diversity system and its transmitter and receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiving method, a transmitting apparatus and a diversity receiving apparatus employing a selection method used for receiving a radio transmission signal of broadcasting or communication, and more particularly to transmitting a digital signal by an OFDM method. The present invention relates to a diversity system, a transmitting device, and a diversity receiving device provided for a system.

[0002]

2. Description of the Related Art As a conventional spatial diversity receiver, for example, as disclosed in Japanese Patent Laid-Open No. 2-19042, signals received by a plurality of antennas are demodulated, and the number of errors in the demodulated data is demodulated. There is known a method of detecting using an error detection code included in data and selecting demodulated data having a small number of errors.

FIG. 8 shows a simplified version of FIG. 1 described in the above publication. In FIG. 8, signals received by a plurality of (two in FIG. 2) antennas 81a and 81b are demodulated by demodulators 82a and 82b, respectively.
a, 83b. These error detectors 83a,
83b detects the number of errors included in the demodulated data by using an error detection code for each of the input demodulated data. Demodulated data output from each of the error detectors 83a and 83b is supplied to a switching circuit 86, and information on the number of errors is supplied to an error number comparing circuit 84.

The error number comparison circuit 84 includes an error detection unit 83
The information on the number of errors from a and 83b is compared, and the comparison result is supplied to the switching control circuit 85. The switching control circuit 85 selects the demodulated data having the smaller number of errors from the comparison result of the error number comparing circuit 84 so as to select the demodulated data having the smaller number of errors.
6 is switched. As a result, the demodulated data having less error among the outputs of the error detectors 83a and 83b can be selectively extracted from the switching circuit 86 as output data.

[0005]

However, in the conventional spatial diversity receiver as described above, the first
The problem is that a plurality of demodulation units must be provided. In particular, when the OFDM scheme, which is one of the multi-carrier schemes, is used as the transmission scheme, the receiver has a plurality of demodulation units compared to the case where the single-carrier scheme is adopted. The increase is remarkable.

That is, in the OFDM system, FFT (Fast Fourier Transform) processing is required for demodulation, but when transmitting a video signal and an audio signal by the OFDM system, hundreds to thousands of carriers are required. For use, a large-scale FFT circuit of several hundred to several thousand points is required. Therefore, if the number of demodulation units is plural, the number of FFT circuits is also plural, and the overall circuit scale is greatly increased.

[0007] The second problem is that a plurality of error correction code decoding circuits and deinterleave circuits must be provided. In particular, in the case of terrestrial broadcasting, a large increase in circuit scale is required.

That is, in the case of terrestrial broadcasting, there are fading and multipath. In order to compensate for the deterioration in transmission quality by error correction, a method having a high error correction capability is required, and it is assumed that a concatenated code of a convolutional code and a Reed-Solomon code is adopted. in this case,
The receiver requires a Viterbi decoder and a Reed-Solomon decoder for error detection. Furthermore, since a deinterleave circuit is usually inserted between these correction code decoding circuits, a plurality of large-capacity memories are required for the deinterleave, and the overall circuit scale is greatly increased.

[0009] The present invention solves the above-mentioned problems and provides an OFD
It is an object of the present invention to provide a diversity system capable of diversity receiving a transmission signal by the M system with a relatively small configuration, and a transmitter and a receiver thereof.

[0010]

In order to achieve the above object, a diversity system according to the present invention is a system used for a system for wirelessly transmitting information by an OFDM (Orthogonal Frequency Division Multiplexing) system. Comprises a known digital signal sequence insertion means for allocating and inserting a known digital signal sequence to one or more specific carriers of an OFDM signal to be transmitted, wherein the receiving device includes OFDM signals transmitted from the transmitting device independently of each other. Receiving means, and extracting the specific carrier from each of the OFDM signals received by the plurality of receiving means, demodulating a known digital signal sequence, and calculating the number of errors contained in the digital signal sequence. The plurality of error number detecting means to be detected and the number of errors obtained by the plurality of error number detecting means are compared with each other to thereby minimize the number of errors. And a selection means for selecting have receiving means, OFDM reception means selected by said selection means
It is configured to demodulate information from the received signal.

A transmitting apparatus according to the present invention is an apparatus for transmitting information by an OFDM (Orthogonal Frequency Division Multiplexing) method, and includes a known digital signal sequence generating means for generating a known digital signal sequence, and a generating means for generating the known digital signal sequence. And a known digital signal sequence inserting means for assigning and inserting the known digital signal sequence to one or more specific carriers of the transmitted OFDM signal .
Conster of one or more carriers for transmitting a digital signal sequence
Constellation of other carriers
That the minimum inter-code distance is smaller than
Features.

In particular, the known digital signal generation means includes:
It is characterized in that generation of a known digital signal sequence is performed in synchronization with a frame synchronization signal.

In particular, said known digital signal sequence inserting means
Is characterized in that the constellation arrangement of one or more carriers transmitting the known digital signal sequence has a smaller minimum inter-symbol distance by making the amplitude smaller than the constellation arrangement of other carriers. Alternatively, for the constellation arrangement of one or more carriers transmitting the known digital signal sequence, the minimum inter-symbol distance is reduced by increasing the multilevel levels of those constellations to be larger than the multilevel levels of other carriers. Features.

[0014]

Further, the receiving apparatus of the present invention modulates a known digital signal sequence on one or more specific carriers of an OFDM (Orthogonal Frequency Division Multiplexing) method and modulates the signal by radio.
A diversity-type apparatus for receiving an FDM signal, comprising: a carrier extracting unit that receives the wirelessly transmitted OFDM signal and extracts the specific one or more carrier components; Demodulating means for demodulating a known digital signal sequence; known digital signal sequence generating means for generating the known digital signal sequence;
Compare the known digital signal sequence obtained by this means and the known digital signal sequence demodulated by the demodulation means,
A plurality of receiving systems each including a comparing unit for detecting the number of errors included in the demodulated output, and comparing the number of errors obtained by the comparing units of the respective receiving systems, the receiving system having a small number of errors. And demodulates information to be transmitted.

In particular, the known digital signal sequence generating means generates a PN signal which is the same as the known digital signal sequence on the transmitting side, in synchronization with a frame synchronization signal.

Further, the switching for selecting a receiving system having a small number of errors is performed in frame units.

That is, in the diversity system of the present invention, a PN which is a digital signal sequence known in a transmitting apparatus is used.
It has means (1 and 3 in FIG. 1) for multiplexing the signal, and the receiving apparatus receives the PN received by the diversity reception.
It has means (19, 29 in FIG. 1) for comparing the signal sequence with the PN signal generated in the receiver, and means (31, 32 in FIG. 1) for selecting a reception system with less error from the comparison result.

In particular, in the diversity system of the present invention,
By demodulating the OFDM signal by the FFT of a small number of points or demodulating the OFDM signal by the single carrier method,
The occurrence frequency of errors in a plurality of receiving systems can be grasped. As a result, it is possible to simplify the circuit of the demodulation system of the diversity receiving apparatus of the system that selects the system according to the frequency of occurrence of errors in each reception system.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS.

FIGS. 1A and 1B respectively show an OFDM transmitting apparatus and OFD using a diversity system according to the present invention.
3 shows a configuration of an M receiving device.

In the OFDM transmitting apparatus shown in FIG. 1A, the mapping circuit 1 synchronizes with the output of the frame synchronizing signal generating circuit 2 together with the video and audio digital signals to generate a PN signal.
The PN signal generated by the signal generation circuit 3 is input and symbolized to correspond to one of a plurality of carriers. A plurality of signals output from the mapping circuit 1 and arranged in the frequency axis direction are converted into signals on the time axis by an IFFT (Inverse Fast Fourier Transform) circuit 4, and then output to an OFDM signal by a quadrature modulation circuit 5. Become. The OFDM signal output from the quadrature modulation circuit 5 is frequency-converted and power-amplified by the transmitter 6, and then transmitted to the space through the antenna 7.

In the OFDM receiving apparatus shown in FIG. 1B, the antennas 11 and 21 receive signals transmitted from the OFDM transmitting apparatus. The signal is amplified and frequency-converted by 22 to produce an intermediate-frequency OFDM signal, which is then distributed to three systems. The signals of each of the two systems are band-pass filters 13, 14, 23, 24, respectively.
And the signals of the other systems are supplied to the quadrature demodulation circuits 20 and 30.
Supplied to

The band-pass filters 13, 14, 23,
Numeral 24 is for passing the frequency band on which the PN signal is placed on the OFDM transmitter side. Each filter output is subjected to quadrature demodulation by the quadrature demodulation circuits 15, 16, 25 and 26, and then the FFT 17 of a small number of points. , 18, 27,
At 28, it is converted to data on the frequency axis by FFT processing.

PN obtained from outputs of FFTs 17 and 18
The signal is compared with a PN signal generated internally by the comparison circuit 19, and the number of errors is detected. This error number detection result is supplied to the error comparison circuit 31. Similarly, FFT
The PN signal obtained from the outputs of 27 and 28 is
Is compared with the internally generated PN signal, and the number of errors is detected. This error number detection result is output to the error comparison circuit 3
1 is supplied. The error comparison circuit 31 compares the error number detection results of both systems and controls the switching of the switching circuit 32 so as to select the system with the smaller number of errors.

The quadrature demodulation circuits 20 and 30 perform quadrature demodulation of the received signals from the high frequency receiving circuits 12 and 22, respectively. The demodulated signals are selectively derived by a switching circuit 32, and a frame synchronization circuit 33 and an FFT 35 Supplied to

The frame synchronization circuit 33 detects and synchronizes the frame synchronization signal of the demodulated signal, and sends the synchronization timing to a PN signal generation circuit 34. The PN signal generation circuit 34 generates the same PN signal as that on the transmission side in accordance with the timing signal from the frame synchronization circuit 33, and sends it to the above-described comparison circuits 19 and 29.

The FFT 35 converts the orthogonally demodulated OFDM signal into data on the frequency axis by performing a fast Fourier transform. The output of the FFT 35 is demodulated by a demodulation circuit 36 to become a video or audio digital signal. Is output.

In order to simplify the explanation, FIG.
In (B), the description of circuits relating to error correction and interleaving is omitted.

Next, the operation of the embodiment of the present invention will be described.
This will be described in detail with reference to FIGS.

FIG. 2 shows an arrangement of carriers of an OFDM signal. FIG. 2A shows a case where two carriers each transmitting a PN signal indicated by a broken line are arranged at two positions, that is, an upper frequency portion and a lower frequency portion in the band, and FIG. And a case where a carrier for transmitting a PN signal indicated by a broken line is arranged in each of three places, that is, a center part and a lower part. Here, the embodiment shown in FIGS. 1A and 1B corresponds to the carrier arrangement shown in FIG. 2A.

The PN signal generating circuit 3 in FIG. 1A is a PN signal transmitted by a carrier indicated by a broken line in FIG.
A signal is generated, and data transmitted on a carrier indicated by a solid line in FIG. 2 is data in which video and audio digital data are allocated to each carrier by the mapping circuit 1 in FIG. The PN signal transmitted on the carrier indicated by the broken line in FIG. 2 is a known code sequence, and the receiving device compares the received PN signal with the PN signal generated by the receiving device, thereby obtaining the received PN signal. Used to know the number of errors contained in the signal.

In FIG. 1A, a frame synchronization signal generation circuit 2 generates a frame synchronization signal. When performing OFDM transmission, a frame configuration is generally adopted for synchronization on the receiving side. A frame is composed of a plurality of data symbols and synchronization symbols. The data symbol is one in which digital data to be transmitted is arranged, and a null signal (no signal) or a chirp signal (frequency sweep signal) is used for the synchronization symbol. The receiving device detects a null signal or a chirp signal and establishes frame synchronization. The OF explained above in FIG.
1 shows a frame configuration of a DM system.

In FIG. 1A, a PN signal generation circuit 3
Generates a PN signal based on the frame synchronization signal generated by the frame synchronization signal generation circuit 2. The PN signal output from the PN signal generating circuit 3 is allocated to a plurality of carriers indicated by broken lines in FIG. On the other hand, the video to be transmitted,
The audio digital signal is input to the mapping circuit 1,
Similarly, allocation is made to a plurality of carriers indicated by solid lines in FIG.

The input of the IFFT 4 is the output of the mapping circuit 1 corresponding to each carrier, and these signals are converted by the IFFT 4 from signals arranged on the frequency axis to signals arranged on the time axis. The signal converted to a signal on the time axis by the IFFT 4 is quadrature-modulated by the quadrature modulation circuit 5, frequency-converted and amplified by the transmitter 6, and transmitted by the antenna 7.

On the other hand, in the receiving device, the signals are received by a plurality of antennas 11 and 21 and received by high-frequency circuits 12 and 22.
After the signals are amplified and frequency-converted into intermediate frequency signals, the band-pass filters 13, 14, 23, and 24 and the quadrature demodulation circuits 20, 3 for demodulating signals of all bands to be received.
Output to 0. Outputs of the quadrature demodulation circuits 20 and 30 are input to a switching circuit 32 for selecting a receiving system.

On the other hand, the band-pass filters 13 and 14 are filters for passing signals in different frequency bands, and pass signals corresponding to two frequency bands for transmitting the PN signal shown in FIG. Let it. The same applies to the band-pass filters 23 and 24.
3 passes signals in the same frequency band. The same applies to the band-pass filters 14 and 24.

Each band-pass filter 13, 14, 23, 2
The output of No. 4 is input to FFTs 17, 18, 27 and 28 of a small number of points, for example, 4 points after quadrature demodulation, and is converted into a signal on a frequency axis corresponding to each carrier. FFT
The outputs of 17 and 18 are compared in a comparison circuit 19 with the output signal of a PN signal generation circuit 34. FFT 27, 28
Is also the same, and the comparison circuit 29 compares the output signal with the output signal of the PN signal generation circuit 34.

The PN signal generation circuit 34 generates the same PN signal sequence as the PN generation circuit 3 in the above-described transmission device, based on the output signal of the frame synchronization circuit 33. Therefore, the number of errors included in the received PN signal sequence can be detected in the comparison circuit 18, and the number of errors is output to the error comparison circuit 31. At this time, the comparison circuits 19 and 29 output, for example, the number of errors that occurred in one frame.

In the error comparison circuit 31 to which the outputs of the comparison circuits 19 and 29 are input, the number of errors obtained by the comparison circuits 19 and 29 is compared. Select the frame synchronization circuit 33
And outputs it to the FFT 35.

The frame synchronization circuit 33 detects a frame synchronization signal, and a PN signal generation circuit 34 generates a predetermined PN signal based on the synchronization signal. On the other hand, FFT3
Reference numeral 5 performs OFDM demodulation by fast Fourier transforming the output of the switching circuit 32 to convert a signal on the time axis into a signal on the frequency axis. The output is demodulated by the demodulation circuit 36 based on the determination based on the threshold value, and digital signals of video and audio are obtained.

FIG. 4 is a block diagram showing a second embodiment of the present invention. In FIG. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will not be repeated.

The difference between the second embodiment shown in FIG. 4 and the first embodiment shown in FIG. 1 is that in the first embodiment,
While the PN signal is demodulated by FFT with a small number of points, the second embodiment is that demodulation is performed by a single-carrier demodulation circuit. Note that the transmitting device used in the second embodiment has the same block configuration as the transmitting device used in the first embodiment, so that its display is omitted in FIG.

The second embodiment shown in FIG.
This corresponds to a case where carriers for transmitting PN signals are arranged at three places in the band shown in FIG. Similarly to the first embodiment, the outputs of the reception high-frequency circuits 12 and 22 are output from the band-pass filters 41, 42 and 43 or the band-pass filters 51 and 5,
2 and 53 and the quadrature demodulation circuits 20 and 30
Is output to

Each of the band-pass filters 41, 42, and 43 is a filter that allows signals in different frequency bands to pass therethrough. The band-pass filters 41, 42, and 43 pass signals corresponding to the three frequency bands in which the PN signal shown in FIG. Let it pass. The band-pass filters 41 and 51, the band-pass filters 42 and 52, and the band-pass filters 43
And the band-pass filter 53 pass signals in the same frequency band.

These band-pass filters 41, 42, 4
Carriers through which the PN signals selected by 3, 51, 52, 53 are transmitted are demodulation circuits 44, 45, 46, 54,
A single carrier is demodulated by 55 and 56, and a PN signal is output. These outputs are input to the comparison circuits 47 and 57 as in the first embodiment, where the number of errors contained in the received PN signal sequence is detected.

FIG. 5 is a block diagram showing a third embodiment of the present invention. In FIG. 5, the same parts as those in FIG. 4 are denoted by the same reference numerals, and duplicate description will be omitted.

The difference between the third embodiment shown in FIG. 5 and the second embodiment shown in FIG. 4 is that a specific carrier is extracted by a band-pass filter in the second embodiment. In the third embodiment, a specific carrier is extracted by a low-pass filter. For this reason, the frequency conversion circuits are used by the number of low-pass filters. In addition, an embodiment in which the number of the quadrature demodulation circuits is reduced by providing the switching circuit 32 in front of the quadrature demodulation circuit 20 is shown.

Since the transmitting device used in the third embodiment has the same block diagram as the transmitting device used in the first embodiment, the display in FIG. 5 is omitted.

In the third embodiment shown in FIG. 5, similarly to the second embodiment shown in FIG. 4, carriers for transmitting PN signals are arranged at three places in the band shown in FIG. 2B. If you do. The reception signals converted into the intermediate frequency signals by the reception high-frequency circuits 12 and 22 are respectively converted into frequency conversion circuits 4
8, 49, 50, frequency conversion circuits 58, 59, 60 and the switching circuit 32.

The frequency conversion circuits 48, 49, 50, 58,
At 59 and 60, the center frequency of the desired carrier is converted into a direct current signal (DC). Here, the desired carrier is a carrier of three frequencies at which the PN signal shown in FIG. 2B is transmitted.

The frequency conversion circuits 48, 49, 50, 58,
The outputs of 59 and 60 are low-pass filters 61 and 6 respectively.
Unnecessary carrier components are removed by 2, 63, 71, 72, 73, and demodulation circuits 44, 45, 46, 54, 5
Single carrier demodulation is performed by 5, 56, whereby a PN signal is obtained. The PN signals are input to comparison circuits 47 and 57, respectively, where the number of errors included in the received PN signal sequence is detected.

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the carriers shown as data in FIGS. 2A and 2B, digital data of audio and video is transmitted, and the modulation format of each carrier is QP.
SK, multi-level QAM and the like are adopted. These modulation formats are determined in consideration of the transmission speed, C / N required for reception, and the like. Further, although it depends on the strength of the error correction code, the practical error rate before error correction is about 10 −2 to 10 −3.

Therefore, when transmitting a PN signal in the same modulation format as that of a carrier for transmitting data, a PN signal of at least about 1000 bits is required. However, since this PN signal does not contribute to the transmission of information, it is not efficient to transmit a large number of PN signals.

Since the PN signal is used only for judging the reception quality (error rate) of a plurality of reception systems, the received PN signal is in a range where the reception quality (error rate) can be compared. It is desirable that the reception quality (error rate) is poor.
The means for increasing the error rate of the carrier transmitting the PN signal will be specifically described below.

FIG. 6 shows an example in which QPSK is used for data transmission. FIG. 6A shows a constellation of this QPSK. (B) to (D) show constellations for transmitting a PN signal.

FIG. 6B shows a case where the constellation for transmitting the PN signal is smaller than the constellation for transmitting the data, and FIG.
Multi-level constellation for signal transmission (16QA
M), and (D) shows a case where the constellation for transmitting the PN signal is distorted.

FIGS. 6B to 6D show a method of reducing the minimum inter-code distance. FIG. 6 (B)-
C / N required for reception that results in a constant error rate of modulation shown in (D)
Is larger than the C / N required for reception, which is a constant error rate of the modulation shown in FIG. Therefore, the data and PN
When a signal and a signal are received at the same C / N, the error rate of the PN signal increases, and it is possible to determine the quality of the reception (error rate) with a small number of bits.

FIG. 6 shows a case where QPSK is used for data transmission, but multi-valued QAM or DAPS is used for data transmission.
Even when K is used, the error rate of the PN signal can be increased by the same method.

In addition to the above, the transmission of the PN signal can be performed depending on the presence or absence of a carrier. For example, when the PN signal is "1", a carrier is set up, and when the PN signal is "0", no carrier is transmitted. In this case, the receiving device determines the presence or absence of the carrier by comparing the level of the signal of the specific frequency using a certain threshold value,
The PN signal can be demodulated. Similarly, it is also possible to transmit a PN signal according to the magnitude of the amplitude.

FIG. 7 shows an example of a PN signal generation circuit used in the receiving apparatus of the above-described embodiment. FIG. 7A shows an example using a delay element, and FIG. 7B shows a memory element. Here is an example using.

The PN signal generation circuit shown in FIG. 7A has a plurality of (six in the figure) delay elements (D) 91 to 96 connected in series, and any two delay elements (94 and 96 in the figure) are connected. )
Is input to an exclusive-OR (EX-OR) gate 97, and its operation output is input to a first-stage delay element 91 to obtain a PN signal from the output of the last-stage delay element 96. It is.

In the case of using this delay element, an initial value is given to each delay element by a data set signal synchronized with the frame synchronization signal. At this time, if the same initial value is given in transmission and reception, the same PN signal synchronized with the frame synchronization signal can be obtained in transmission and reception. Note that a flip-flop can be used as the delay element, which can cause a delay of a clock cycle.

The PN signal generating circuit shown in FIG. 7B is provided with a ROM (read only memory) 98 in which a PN signal sequence is recorded in advance, and obtains a PN signal by reading data sequentially by an address counter 99. Things.

In the case of using this memory element, an address counter is reset by a reset signal synchronized with a frame synchronization signal, and a PN signal output from a memory (ROM) in which a PN signal sequence is recorded in advance is transmitted and received. They can be the same.

In the diversity receiving apparatus according to the present invention, switching for selecting a plurality of receiving means is desirably performed in frame units. The reason for this is that the reference signal for synchronous detection is generally transmitted in frame units, and the differential conversion for delay detection is performed in frame units, so that switching in frame units can reduce the circuit scale. That's why. Further, when switching is performed on a frame basis, the receiving apparatus can use a frame synchronization signal to determine a period for integrating the number of errors.

In the above description, the case where the PN signal is allocated to a plurality of carriers and transmitted is described as an example.
In a plurality of carriers, the same P
It is also possible to transmit N signals.

When the phasing of the transmission path is not frequency selective, the known P
It is clear that the receiving system can be selected by transmitting and receiving N signals and comparing the number of errors included in the received signal.

A first effect of the present invention is that the circuit scale of the receiving device can be reduced.

The reason is that a demodulation circuit using a small number of FFTs or a single-carrier demodulation circuit can be used to detect the reception quality, and it does not have a plurality of error correction code decoding circuits and a deinterleave circuit. It is also good.

A second effect of the present invention is that the information amount of a PN signal to be transmitted for detecting reception quality can be reduced.

The reason is that a modulation format having a high C / N required for reception can be adopted for the PN signal transmitted for discrimination of the reception quality, and the reception quality is compared with a small number of bits.

[0074]

As described above, according to the present invention, OFDM
It is possible to provide a diversity system capable of diversity receiving a transmission signal by the system with a relatively small configuration, and a transmission device and a reception device thereof.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a diversity system and apparatus according to the present invention.

FIG. 2 is a diagram showing a carrier arrangement of the diversity system of the present invention.

FIG. 3 is a diagram illustrating an example of an OFDM frame configuration.

FIG. 4 is a block diagram showing a second embodiment of the diversity receiver according to the present invention.

FIG. 5 is a block diagram showing a third embodiment of the diversity receiver according to the present invention.

FIG. 6 is a diagram showing an example of a constellation.

FIG. 7 is a diagram illustrating an example of a PN signal generation circuit.

FIG. 8 is a block diagram showing a conventional technique.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 mapping circuit 2 frame synchronization signal generation circuit 3 PN signal generation circuit 4 IFFT 5 orthogonal modulation circuit 6 transmitter 7 antenna 11, 21 antenna 12, 22 reception high-frequency circuits 13, 14, 23, 24 band-pass filter 15, 16, 25, 26 quadrature demodulation circuit 17, 18, 27, 28 FFT 19, 29 comparison circuit 20, 30 quadrature demodulation circuit 31 error comparison circuit 32 switching circuit 33 frame Synchronization circuit 34 PN signal generation circuit 35 FFT 36 Demodulation circuit 41, 42, 43, 51, 52, 53 Bandpass filter 44, 45, 46, 54, 55, 56 Demodulation circuit 47, 57 Comparison circuit 48, 49, 50, 58, 59, 60 frequency conversion circuits 61, 62, 63, 71, 72, 73 low-pass filters 91 to 96 delay elements 7 ... EX-OR gate 98 ... PN signal sequence storing ROM 99 ... address counter

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroo Takeda 1-10 Nisshinmachi, Fuchu-shi, Tokyo Inside the Fuchu Works of NEC Corporation (56) References JP-A-7-321176 (JP, A) JP-A Heisei 8-32546 (JP, A) JP-A-3-220934 (JP, A) JP-A-63-51737 (JP, A) JP-A-4-10723 (JP, A) JP-A-10-210000 (JP, A) A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B 7/00 H04B ⁷ /02-7/12 H04J 1/00-1/20 H04J 4/00-15/00 H04L 1/02 -1/06 H04L 5/00-5/12

Claims (8)

(57) [Claims] A diversity system provided for a system for wirelessly transmitting information by an OFDM (Orthogonal Frequency Division Multiplexing) system, wherein a transmitting apparatus transmits a known digital signal sequence to an OFDM-transmitted OFDM system.
A known digital signal sequence inserting means for allocating and inserting the digital signal sequence to one or more specific carriers of the signal; a receiving device receiving a plurality of OFDM signals transmitted from the transmitting device independently of each other; A plurality of error number detecting means for extracting the specific carrier from each of the OFDM signals received by the receiving means, demodulating a known digital signal sequence, and detecting the number of errors included in the digital signal sequence; Selecting means for selecting a receiving means having the smallest number of errors by comparing the numbers of errors obtained by the plurality of error number detecting means with each other, wherein information from the OFDM reception signal of the receiving means selected by the selecting means is provided. A diversity method characterized by demodulating the signal. 2. A transmitting apparatus for transmitting information by an OFDM (Orthogonal Frequency Division Multiplexing) method, comprising: a known digital signal sequence generating means for generating a known digital signal sequence; and a known digital signal generated by the means. Send column O
Known digital signal sequence insertion means for allocating and inserting to one or more specific carriers of an FDM signal , wherein the known digital signal sequence insertion means comprises the known digital signal sequence.
Constellation of one or more carriers transmitting a signal sequence
Installation arrangements of other carriers
A transmission apparatus characterized in that the minimum inter-symbol distance is smaller than that of a transmitter. 3. The transmitting apparatus according to claim 2, wherein said known digital signal generation means generates a known digital signal sequence in synchronization with a frame synchronization signal. 4. The known digital signal sequence inserting means according to claim 1, wherein a constellation arrangement of one or more carriers transmitting said known digital signal sequence has a smaller amplitude than a constellation arrangement of other carriers. 3. The transmission device according to claim 2, wherein the distance is reduced. 5. The method according to claim 1, wherein the known digital signal sequence insertion means sets the multilevel level of the constellation arrangement of one or more carriers transmitting the known digital signal sequence to be higher than the multilevel levels of other carriers. The minimum inter-code distance is reduced by performing
2. The transmitting device according to 2 . 6. A diversity receiver for receiving a known digital signal sequence on one or more specific carriers of an orthogonal frequency division multiplexing (OFDM) system and receiving an OFDM signal wirelessly transmitted together with information to be transmitted. Carrier extracting means for receiving the wirelessly transmitted OFDM signal and extracting the specific one or more carrier components; demodulating means for demodulating the known digital signal sequence from the carrier components extracted by the means; A known digital signal sequence generating means for generating the known digital signal sequence, and comparing the known digital signal sequence obtained by this means with the known digital signal sequence demodulated by the demodulation means,
A plurality of receiving systems each including a comparing unit that detects the number of errors included in the demodulated output; comparing the number of errors obtained by the comparing unit of each receiving system, And demodulating information to be transmitted. 7. The receiving apparatus according to claim 6, wherein said known digital signal sequence generating means generates the same known digital signal sequence as that of the transmitting side in synchronization with a frame synchronization signal. 8. The receiving apparatus according to claim 6 , wherein switching for selecting a receiving system having a small number of errors is performed on a frame basis.