JP3800503B2 - Multi-carrier signal generation method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention is capable of supporting a wide range of transmission speeds by flexibly operating a communication bandwidth and performing multimedia communication with a good channel utilization rate.Multi-carrier signal generation methodIt is related.
[0002]
[Prior art]
Conventionally, multi-carrier signal transmission techniques such as OFDM (Orthogonal Frequency Division Multiplexing) have been put to practical use as a technique for realizing a high-speed wireless LAN (local area network) and a high-speed wireless access system.
[0003]
The radio access system in practical use uses a bandwidth of 100 MHz in the 5 GHz band, and arranges four channels with an interval of 20 MHz therein, and performs communication through each channel.
FIG. 11 shows a channel arrangement used in the radio access system.
[0004]
In the figure, each channel has a unit communication bandwidth of 20 MHz, and transmission of 20 MBps or more is possible. As a transmission method thereof, OFDM that is resistant to multipath interference caused by reflected waves from buildings, walls, etc., and has high frequency utilization efficiency. The method is used.
[0005]
FIG. 12 shows the arrangement of subcarrier frequencies for one channel in the 5 GHz band wireless access system.
The subcarriers in the figure have a carrier interval of 312.5 KHz, and when the center frequency is carrier # 0, there are 53 carriers from # −26 to # + 26, of which # 0 ( DC: DC) is not used with a carrier level of 0, and the four waves of carriers # -21, # -7, # 7, and # 21 are used as pilot carriers, so the information signal is transmitted to the remaining 48 carriers. Allocated as data to be transmitted.
[0006]
  FIG. 13 shows a configuration of a radio access system generation apparatus that transmits such a signal.
  In the figure, the supplied serial data is converted into parallel data by the serial / parallel conversion circuit 12, and the converted parallel data is assigned to each carrier constituting the OFDM by the carrier mapping circuit 13a, and the data allocation is performed. ThisTesaThe received signal is supplied to a 64-point IFFT (Inverse fast Fourier transform) circuit 14a.
[0007]
In the IFFT circuit 14a, inverse Fourier transform is performed based on each of the 64 real part data and imaginary part data supplied from the carrier mapping circuit 13a, and the supplied frequency domain data is converted into a time domain signal. The converted real part and imaginary part signals are supplied to the quadrature modulation circuit 15.
[0008]
An IFFT operation is generally used for the conversion from the frequency domain to the time domain signal.
FIG. 14 shows a state of a signal supplied to a terminal of a 64-point IFFT element used in the example of the 5 GHz band wireless access system.
[0009]
In the figure, the terminal shown on the left side shows the input state of a complex signal supplied when an OFDM signal is generated using an IFFT element. That is, since the carrier 0 (DC: direct current) constituting the OFDM signal is not used here, the level of the input signal is 0.
[0010]
The signal levels of the inputs 27 to 37 corresponding to the frequencies at both ends of the transmission frequency band are also set to 0 to suppress the frequency spectrum component at the boundary between adjacent frequency channels, thereby forming a guard band.
[0011]
In this way, OFDM signals having a spectrum with subcarrier frequency arrangements indicated as # -26 to # -1 and # 1 to # 26 as shown in FIG. 12 are generated as transmission signals.
[0012]
Among the transmission signals, subcarriers other than the pilot signal for transmitting the information signal are BPSK (bi-phase shift keying), QPSK (quadrature phase shift keying), 16QAM (16 Level Quadrature Amplitude Modulation), etc. is generated, and when the IFFT sampling clock frequency is 20 MHz, the modulation signal has an IQ modulation circuit output after IFFT operation processing, and each subcarrier frequency interval is It is generated as an OFDM signal that is 312.5 KHz.
[0013]
Here, the modulation by BPSK, QPSK, 16QAM, and the like has a difference in the number of bits assigned at the time of digital modulation to each subcarrier in the carrier mapping circuit 13a of the generation apparatus in FIG. 13, which is the case of BPSK. Assigns 1 bit for 1 subcarrier wave, 2 bits for QPSK, and 4 bits for 16QAM to generate a modulated wave.
[0014]
The subcarriers generated in this way are supplied to the quadrature modulation circuit 15, and the IQ (In-phase Quadrature) signal component supplied thereto is quadrature modulated as a signal in the intermediate frequency band and obtained by quadrature modulation. The OFDM signal is limited to a signal in a required band to be transmitted by the BPF 16, and the band-limited intermediate frequency signal is frequency-converted (U / C: up-converted) into a signal in the frequency band of 5 GHz by the frequency conversion circuit 17. The signal generated by frequency conversion is radiated from the antenna 19 to the spatial transmission path.
[0015]
Next, reception of the OFDM signal radiated to the spatial transmission path in this way will be described.
FIG. 15 shows the configuration of the OFDM decoding apparatus and its operation will be described.
[0016]
In the figure, the signal radiated to the spatial transmission line is obtained by the antenna 21, the obtained signal is down-converted (D / C) by the frequency conversion circuit 22, and the signal in the intermediate frequency band obtained by down-conversion is A signal in a frequency band necessary for demodulation is selectively extracted by the BPF 23, and the extracted signal is supplied to the orthogonal demodulation circuit 24.
[0017]
The orthogonal demodulation circuit 24 performs IQ demodulation of the supplied signal to obtain I and Q component signals, and the obtained signal is converted into a digital signal by an A / D converter (not shown), and the converted I , Q signals are supplied to a 64-point FFT circuit 25a.
[0018]
In the FFT circuit 25a, the supplied I and Q signals are converted from time domain to frequency domain signals, and demodulated outputs corresponding to digital modulation such as BPSK, QPSK, 16QAM, etc. which are made to each subcarrier signal constituting OFDM. A signal is obtained.
[0019]
The demodulated output signal of each subcarrier obtained by the FFT circuit 25a is supplied to the carrier demapping circuit 26a and obtained by decoding the modulated signal digitally modulated for each subcarrier.
[0020]
The parallel data for each carrier obtained by decoding is supplied to the parallel-serial conversion circuit 27 and converted into serial data. The converted serial data is output as a decoded output signal from the information signal output terminal 29 of the OFDM signal decoding device 20a. Supplied.
[0021]
As described above, the OFDM signal radiated from the OFDM signal generation device 10a to the spatial transmission path is received and decoded by the OFDM signal decoding device 20a. The operation for decoding is performed in synchronization with the IFFT 14a. This is performed based on the demodulated output of the FFT 25a.
That is, the synchronization of the FFT 25a is performed based on the pilot signal shown in FIG. 12 described above, such as clock signal synchronization of the FFT circuit of the decoding device 20a and symbol synchronization related to the window time synchronization of the FFT circuit. Thus, the digital demodulation and decoding circuit performs demodulation and decoding operations of the supplied OFDM signal.
[0022]
In addition to the synchronization between the generation device and the decoding device, the synchronization of the information signal to be transmitted and the generation device is also performed.
The transfer rate of the information signal supplied to the generation device may be the same as the transfer rate transmitted by the generation device, but usually both transfer rates have different values.
[0023]
In particular, in recent years, in addition to video and audio information, many types of information such as character codes called multimedia information, still image information, graphics information, and instrument control information have been transmitted.
[0024]
Due to various contents in multimedia communication for transmitting such multimedia information, there is a large difference in the transfer rate of data treated as information. However, the OFDM signal generation device and the decoding device have such a difference in data rate. It is necessary to generate and decode an OFDM signal without disturbing synchronization even for a large information signal.
[0025]
As a conventional method for transmitting content with different transmission rates, there is a TDM (time division multiplex system) or TDMA (time division multiple access) method.
[0026]
In these transmission methods, a method of assigning the number of assigned slots according to a communication partner that requires speed is used, and the assigned slots are also changed by changing the modulation method to BPSK, QPSK, 16QAM, 64QAM, etc. In the method of performing digital modulation of the value, the transmission distance is shortened, but the rate of the information signal transmitted varies depending on the transmission parameter such as a larger transmission rate.
[0027]
In a general wireless transmission system, the number of transmission channels required for a given frequency bandwidth is determined, and content information is transmitted by assigning the number of channels to be used according to the information to be transmitted. There are many cases.
[0028]
[Problems to be solved by the invention]
By the way, in the information-oriented society in recent years, the demand for multimedia communication that transmits various contents such as images and sounds will continue to increase in the future, and further, higher definition of video signals and higher quality of sound signals will advance. For high-quality information signal transmission, the communication path is increased in speed and capacity.
[0029]
In order to increase the speed of the communication channel, it is necessary to allocate a wide frequency bandwidth for each transmission channel. However, if the bandwidth per channel is increased, the number of channels that can be operated within the frequency band allocated to the entire communication system is increased. It is not possible to increase both the number of channels and the transmission rate per channel, such as decreasing.
[0030]
Further, for multimedia communication, it is required to construct a wireless transmission / reception system that can efficiently transmit content information even for content of various transmission rates.
[0031]
In order to obtain a high transmission rate, the modulation scheme needs to be multi-valued. However, since a high C / N is required for transmission of a multi-value modulated signal, the maximum reachable distance becomes small. .
[0032]
In this way, in order to obtain a higher transmission rate in a limited bandwidth, it is important to increase the bandwidth that can be practically used while eliminating waste in use of a given frequency band. .
[0033]
Therefore, for example, there is a method of flexibly operating by switching the bandwidth according to the communication speed, but in order to change the bandwidth, it is necessary to prepare and switch a plurality of filters in a plurality of passbands, and the apparatus is complicated. There is a problem to become.
[0034]
In addition, there is a method of communicating by mixing a wide bandwidth channel and a narrow channel, but there is a bandwidth available according to the channel usage situation, and it is difficult to divert the narrow bandwidth channel to a broadband signal transmission channel. Even in these cases, the bandwidth use efficiency is lowered.
[0035]
And there is a method for distributing and transmitting data to a plurality of channels only when communication at a high transmission rate is necessary. Although a high transmission rate can be obtained thereby, a plurality of individual modulation / demodulation devices are still available in this case. And transmission / reception means such as a filter are required, which causes problems such as a complicated apparatus and high price.
[0036]
  Therefore, the present invention has been made in view of the above points, and enables a high-speed, large-capacity transmission, can flexibly and efficiently cope with a wide range of transmission speeds, and has a high channel utilization rate and high frequency utilization efficiency. To realizeMulti-carrier signal generation methodThe purpose is to provide.
[0037]
[Means for Solving the Problems]
  In order to solve the above problems, the present invention provides the following 1) to2).
  That is,
[0038]
1)After assigning information signals corresponding to subcarriers of a plurality of bands used for communication, IFFT conversion is performed by a predetermined method to generate an OFDM signal,
Next, an error correction signal for error correction of subcarriers in two unit communication bands adjacent to each other is inserted into the guard band existing between the plurality of bands.A method of generating a multi-carrier signal.
[0039]
2)After assigning subcarriers of a plurality of bands used for communication to the information signal, IFFT conversion is performed by a predetermined method to generate an OFDM signal,
Next, the two unit communication bands adjacent to each other are packed in a central portion so that the guard bands existing between the plurality of bands are filled, and the plurality of subcarriers are continuous. Do not place subcarriers in the band corresponding to the guard bandA method of generating a multi-carrier signal.
[0044]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the method of generating the multicarrier signal of the present inventionTo the lawWith a preferred embodiment.
  FIG. 1 shows the configuration of the multicarrier signal generation apparatus, FIG. 2 shows the configuration of the multicarrier signal decoding apparatus, and the operation of these apparatuses will be described.
[0045]
1 includes an information signal input terminal 11, a serial-parallel conversion circuit 12, a carrier mapping circuit 13, an IFFT circuit 14, an orthogonal modulation circuit 15, a BPF (band pass filter) 16, and an up-converter. (U / C) 17, the transmission signal of this generation device is supplied to the antenna 19 and radiated from the antenna to the spatial transmission path.
[0046]
The transmission signal supplied to the spatial transmission path is received by the antenna 21 and supplied to the multicarrier signal decoding apparatus to perform decoding operation. The multicarrier signal decoding apparatus 20 includes a down converter (D / C) 22. , BPF 23, orthogonal demodulation circuit 24, FFT (Fast Fourier Transform) 25, carrier demapping circuit 26, parallel / serial conversion circuit 27, and information signal output terminal 29.
[0047]
Next, operations of the multicarrier signal generation device 10 and the multicarrier signal decoding device 20 configured as described above will be described.
First, an information signal in a serial format related to the content to be transmitted is supplied to the serial / parallel conversion circuit 12 via the information signal input terminal 11.
[0048]
In the serial-parallel conversion circuit 12, the serial-format information signal is converted into a parallel-format signal divided into a plurality of blocks described later, and the converted signal is supplied to the carrier mapping circuit 13.
[0049]
In the carrier mapping circuit 13, the real axis (I) and the imaginary axis (I) and the imaginary axis (I) and the imaginary axis (I) depend on whether the digital modulation method for the subcarriers of a plurality of blocks constituting the multicarrier signal is BPSK, QPSK, 16QAM, 64QAM, or the like. Each voltage value corresponding to the signal point in the two-dimensional plane defined by Q) is selected and supplied.
[0050]
That is, a voltage value of a signal point defined for each signal in a parallel format for each subcarrier is generated by the serial / parallel conversion circuit 12, and the voltage value is supplied to the IFFT circuit 14.
[0051]
In this way, the IFFT circuit 14 performs inverse Fourier transform on the frequency domain information related to the signal point position for each subcarrier supplied for each of the plurality of operation blocks, and is obtained as time domain information in each IFFT circuit block. The obtained I (In-phase) signal and Q (Quadrature) signal are supplied to the quadrature modulation circuit 15.
[0052]
In the quadrature modulation circuit 15, an intermediate frequency signal is supplied and obtained as a digitally modulated multicarrier signal that is a positive and negative frequency with respect to the intermediate frequency, and the obtained signal is supplied to the BPF 16. The frequency component necessary for transmission is obtained by passing.
[0053]
The signal that has passed through the BPF 16 is supplied to the up-converter 17, where the multi-carrier signal in the intermediate frequency band is converted into a signal of the transmission frequency supplied to the spatial transmission path, is amplified in power, and is supplied to the antenna 19, The supplied multicarrier signal is radiated from the antenna to the spatial transmission path.
[0054]
As described above, the content information is modulated as a multi-carrier signal of a plurality of blocks and radiated to the spatial transmission path. The radiated signal is received by the multi-carrier signal decoding apparatus, and the content information is decoded.
[0055]
That is, the multi-carrier signals of a plurality of blocks supplied to the spatial transmission path are received by the antenna 21, and the received signals are supplied to the down converter (D / C) 22, where they are converted into intermediate frequency signals.
[0056]
The signal converted to the intermediate frequency is supplied to the BPF 23, where only the signal necessary for reception is passed, and the passed signal is supplied to the quadrature demodulation circuit 24, where quadrature demodulation is performed, and a plurality of blocks are received. I and Q signals are obtained, and the obtained signals are supplied to the FFT 25.
[0057]
In the FFT 25, the I and Q signals, which are the time domain signals of a plurality of blocks, are time-frequency converted and obtained as demodulated signals related to the respective multicarrier signals that are frequency domain signals. The demodulated signal is supplied to the carrier demapping circuit 26.
[0058]
In the carrier demapping circuit 26, a digital data value obtained as a demodulated signal point on the I and Q planes of each subcarrier and supplied near the demodulated signal point is supplied as decoded data. It is made like.
[0059]
In this way, data supplied in a plurality of parallel signal formats obtained by decoding a multicarrier signal composed of a plurality of transmitted subcarriers is supplied to a serial-to-parallel conversion circuit 27, where the serial signal The data is converted into format data, and the converted data is supplied to the information signal output terminal 29.
[0060]
In this way, a multicarrier signal composed of a plurality of blocks of subcarrier signals is simultaneously demodulated by the FFT 25, and the demodulated signals of a plurality of blocks obtained by demodulation are simultaneously decoded and obtained by the carrier mapping circuit 26. The decoded signal of a plurality of blocks is converted into a serial data format signal by the parallel-serial conversion circuit 27, and the signal obtained by the conversion is supplied to the information signal output terminal 29.
[0061]
As described above, the multicarrier signal generation device 10 and the multicarrier signal decoding device 20 generate multicarrier signals for simultaneous transmission using a plurality of communication bands, transmit the signals, and are transmitted. The multi-carrier signal can be generated and decoded so that multi-carrier signals in a plurality of communication bands can be collectively received.
[0062]
Here, generation and decoding of a multi-carrier signal having a plurality of bands configured as described above will be described in detail.
First, the number of unit communication bands (hereinafter referred to as “bands” for short) for transmitting OFDM signals is M = 4, all four consecutive bands are empty channels, and multicarrier signals are transmitted using all four bands. The operation when doing this is described.
[0063]
The data rate handled by the multicarrier signal generation apparatus that generates a transmission signal for transmission using all four bands is four times the data rate as compared to the generation apparatus that generates a transmission signal of only one band. be able to.
[0064]
That is, when the subcarrier modulation schemes in the four bands are the same, an input signal having a quadruple rate is supplied to the serial-parallel conversion circuit 12, and a signal having four times the number of parallel data is transmitted from there. The data is supplied to the mapping circuit 13 where the data allocation corresponding to the subcarriers of the four communication bands is performed, and the signal with the data allocation is supplied to the IFFT 14.
[0065]
The IFFT 14 performs IFFT signal processing using an IFFT arithmetic circuit having a number of points that is four times the number of points of IFFT arithmetic for generating a transmission signal of one communication band.
[0066]
FIG. 3 shows a state of conversion from the frequency domain to the time domain of a 256-point IFFT computing unit that simultaneously performs four 64-point IFFT computations.
In the same figure, the numbers shown on the left side of the IFFT arithmetic element indicated by a square indicate the input side terminals, the right side indicates the output side terminals, and 0 to 255 of the input side terminals indicate the input terminal numbers in the frequency domain. .
[0067]
The sixth to 58th input terminals are supplied with signals for performing digital modulation on the subcarriers whose channel 3 numbers are -26 to + 26th, and similarly, the input terminals 70th to 58th. The 122th, 134th to 186th, and 198th to 250th signals are supplied with signals for performing digital modulation on the subcarriers of channel 4, channel 1, and channel 2, respectively. It shows that the voltage 0 (Null) for setting the output signal to 0 is supplied.
[0068]
As a result of supplying such a signal and performing an IFFT calculation, an output signal in the time domain is obtained at 0 to 255 of the output side terminal, but the signal thus obtained is applied to the input terminals 6 to 58. In the same way, frequency domain signals for Bi + 2, 70 to 122 for Bi + 3, 134 to 186 for Bi, and 198 to 250 for Bi + 1 are supplied. As a signal converted into a time domain signal, an output signal in time order is obtained at the terminal shown on the right side of the figure.
[0069]
Next, the frequency distribution of the signal obtained as a result of supplying the output signal thus obtained to the quadrature modulation circuit 15 will be described.
FIG. 4 shows the frequency band and the position of the subcarrier frequency in the band.
[0070]
In the figure, the horizontal axis represents the frequency, and the vertical axis represents the signal spectrum level.
That is, the frequency bands are in the order of Bi, Bi + 1, Bi + 2, and Bi + 3 from the left side, and there are negative 26th carrier to positive 26th carrier on the left side of each frequency band.
[0071]
In this way, modulated signals of four bands Bi to Bi + 3 are generated simultaneously by the IFFT shown in FIG.
Note that the sampling clock frequency for operating the IFFT at this time needs to be calculated at a higher speed than the IFFT that generates a modulation signal of one band, and the output of the time domain (region) in the last stage The circuit unit that generates the signal operates the output circuit that sequentially reads out the signal on the IFFT output terminal side with a quadruple frequency clock.
[0072]
The operation in the case of obtaining a modulated signal of four consecutive bands with one IFFT has been described above. Next, three of the four bands are reserved as vacant channels, and communication is performed using the three bands. The operation of the case will be described.
[0073]
FIG. 5 shows an example in which communication is performed using a band of an empty channel excluding a band during communication.
In the figure, the horizontal axis is the frequency axis, and the frequency band that has already been communicated on the frequency axis is indicated as a), and the band for performing communication using an empty channel is indicated as b).
[0074]
That is, B3 shown as a) in the communication band among B1 to B8 is already used by user A, B6 and B7 are already used by user B, and user C is the remaining B1, B2, B4, B5, and B8. In this case, communication is performed by setting three bands.
[0075]
Here, since three consecutive bands are not usable, in the conventional case, the communication was suspended until the three consecutive bands were freed. Although not shown, a multicarrier signal for communication can be generated using B1, B2, and B4 as shown in b).
[0076]
Such a multicarrier signal using a discontinuous band is generated by using the IFFT element shown in FIG. 3 to generate output signals in the band of Bi to Bi + 3 corresponding to B1 to B4. The output signal of the Bi + 2 channel is set to the carrier level 0 of the band by setting the signal level supplied to 3 # -26 to 3 # 26 to 0.
[0077]
In this way, a multicarrier signal using bands B1, B2, and B4 for communication by user C is generated by the multicarrier signal generation apparatus shown in FIG.
[0078]
And the bit rate of the information signal which can be transmitted with the multicarrier signal which used three bands as the communication band can be obtained three times as much as the case of transmitting one band.
[0079]
Therefore, when the multicarrier signal generation apparatus 10 uses the same modulation method for the multicarrier signal, the transmission rate of the information signal supplied to the input terminal 11 is set to three times the rate when one band is used. The parallel output signal of the parallel conversion circuit 12 is supplied to the carrier mapping circuit 13 as parallel data having a data amount three times the symbol time.
[0080]
In the carrier mapping circuit 13, data allocation for performing digital modulation is performed on each of the subcarriers for the three communication bands, and the subcarriers in the band B3 that are not used because the user A is using them. Does not allocate data.
[0081]
In this way, by setting all the input signal levels of the subcarriers to the terminals for the band B3 in the IFFT 14 to be 0, the time domain signal obtained from the IFFT 14 is the communication band B1, as shown in FIG. It is generated as a multicarrier transmission signal having a subcarrier signal spectrum only in the three bands B2 and B4.
[0082]
The multicarrier signal supplied from the multicarrier signal generation device 10 to the spatial transmission path via the antenna 19 is received and decoded by the multicarrier signal decoding device 20, and then received by the multicarrier signal decoding device 20. The operation will be described.
[0083]
The FFT 25 in the above-described multicarrier signal decoding apparatus 20 has 256 time domain input terminals corresponding to the IFFT shown in FIG. 3 described above, or a serial signal input terminal for sequentially inputting 256 time domain signals. A 256-point FFT operation for generating an output signal in 256 frequency domains by performing an FFT operation on the signal supplied to the terminal.
[0084]
A decoding device that receives a normal one-channel OFDM signal can be realized using a 64-point FFT, but the multi-carrier signal decoding device 20 having the 256-point FFT has four channels supplied as signals in the same symbol period. Multi-carrier signals can be simultaneously demodulated and the demodulated data can be decoded simultaneously.
[0085]
In addition, a signal of an arbitrary channel among four consecutive channels can be received. For example, the signal shown as b) in FIG. 5 described above can also be received.
[0086]
FIG. 6 illustrates a received signal frequency spectrum when the signal is received. In the figure, the horizontal axis is the frequency axis, and the vertical axis represents the spectrum of the received signal.
[0087]
Of the received signal spectrum, the three bands B1, B2, and B4 indicate the spectrum obtained by receiving the received signal in the synchronized state at the same symbol time, and B3 is a signal that is not in the synchronized state. Is shown as a round signal.
[0088]
That is, in the decoding of a signal having such a spectrum distribution, the signal obtained from the antenna 21 is supplied to the down converter 22 and converted to an intermediate frequency, and the converted signal is supplied to the BPF 23 and necessary for demodulation. The signal components in the frequency band are obtained by frequency selection, and the signals for the obtained four communication bandwidths are A / D converted by an A / D converter (not shown) and then supplied to the FFT 25. Yes.
[0089]
In the FFT 25, the four band signals B1 to B4 are converted from the time domain signal to the frequency domain signal, but the user C in the three bands B1, B2, and B4, which are synchronized in the symbol time, etc. The data of user A in the B3 band is asynchronously communicated with the user C, so the asynchronous B3 signal is computed and supplied by the FFT 25 as an unnecessary noise signal component. The Rukoto.
[0090]
Accordingly, the signal supplied from the FFT 25 to the carrier demapping circuit 26 is selected as a signal corresponding to the three bands B1, B2, and B4 used by the user C for communication, and is mapped to the subcarrier. The transmitted received data is supplied to the carrier demapping circuit 26.
[0091]
In the carrier demapping circuit 26, digital data is decoded from the supplied data by a method corresponding to carrier mapping, and the data obtained by decoding is supplied to the parallel-serial conversion circuit 27, where it is obtained for each subcarrier. The parallel data is converted into serial data by a method corresponding to the multi-carrier signal generator and supplied to the information signal output terminal 29.
[0092]
In this way, a signal transmitted using a plurality of bands is received at the same time, and a decoded signal is obtained. Channel allocation information related to the allocation of the plurality of bands used at that time is For example, channel information may be transmitted at the beginning of a transmission signal, and a plurality of channel information assigned thereto may be transmitted to a decoding device.
[0093]
The channel assignment information includes a synchronization signal acquisition preamble signal that is transmitted prior to transmitting the modulated subcarrier, a modulation scheme related to multi-level modulation of transmission data, or information on transmission parameters of a data frame such as a coding rate, etc. In addition, a method of transmitting allocation information of a plurality of channels may be used.
[0094]
Furthermore, the information may be transmitted in all communication bands to be used, or a specific frequency band, for example, a band arranged at a position where the lowest frequency is designated as a transmission parameter transmission band, You may make it transmit including a transmission parameter in a zone | band.
[0095]
The case where an information signal is transmitted using a plurality of bands has been described above. However, the transmission channel changes the transmission characteristics of the band according to the use state of the band or the adjacent band, and the information is transmitted according to the band. Thus, a method of transmitting a multi-value number of digital modulation or changing a coding rate of digital modulation is used.
[0096]
Even in such a case, information signals can be generated and decoded even when different transmission rates are set for each band as long as the symbol periods are the same, that is, the window periods of IFFT 14 and FFT 25 are the same. is there.
[0097]
The communication parameters are set by, for example, digital modulation of transmitted subcarriers by a multi-value number of modulation such as BPSK (bi-phase shift keying), QPSK (quadrature phase shift keying), 16QAM (16-level Quadrature Amplitude Modulation), etc. Change.
[0098]
In addition, transmission of an information signal is performed even when means for transmitting an error correction code such as a convolutional code or a Reed-Solomon code (Forward Error Correction; FEC) is used to perform error correction of data to be transmitted. The rate changes.
[0099]
When such an FEC circuit is used, the FEC circuit is inserted before the serial-parallel conversion circuit shown in FIG. 1 on the generation side, and the parallel-serial conversion circuit 27 shown in FIG. By inserting an FEC circuit after the error data, error data generated during data transmission can be corrected.
[0100]
Next, an example of transmission parameters when such multilevel modulation and FEC circuit are used will be described.
The first parameter example is a case where FEC coding rate R = 3/4, each subcarrier is modulated by QPSK, and multimedia contents are transmitted at a transmission rate of 72 Mbps using four frequency bands.
[0101]
In this case, when the number of subcarriers for data transmission used in one band is 48 waves, the symbol period length is 4 μs, and the digital modulation of the carrier is QPSK, 2 bits per carrier wave can be transmitted in the symbol period. Since the conversion rate R is 3/4, the total transmission rate when transmitting using all four bands is
2 bits x 48 waves x 1 / (4 x 10^-6Second) × (3/4) × 4 = 72 Mbps
It becomes.
[0102]
The second parameter example is a parameter for transmitting this 72 Mbps information signal using three of the four bands, and 16QAM, which can transmit 4 bits of digital modulation of the subcarrier at that time, is encoded. When the rate R is set to 1/2 by enhancing the correction capability, the transmission rate of the three bands is
4 bits x 48 waves x 1 / (4 x 10^-6Second) × (1/2) × 3 = 72 Mbps
It becomes.
[0103]
In the second parameter example, since the modulation is changed from QPSK to 16 QAM as compared with the first parameter example, it is considered that the required C / N (carrier to noise ratio) is increased and the code error rate is increased. By reducing the length from / 4 to 1/2, the error signal correction capability is increased to reduce the increase in data code errors, and 72 Mbps, which is the same as 4 bands, is transmitted in 3 bands.
[0104]
In addition, when using the three bands, the positions of the respective bands may be three consecutive bands, and other users use the three bands as shown in FIG. 5b). There may be three bands in which a certain band exists.
[0105]
The example of parameters when transmitting a 72 Mbps information signal using 3 bands and 4 bands has been described above. Next, an example of transmitting a 96 Mbps information signal will be described.
[0106]
The third parameter example is a case where the 96 Mbps multimedia content signal is transmitted using four bands, FEC coding rate R = 1/2, and each subcarrier is digitally modulated by 16QAM.
[0107]
In this case, the transmission rate when transmitting using 4 bands is
4 bits x 48 waves x 1 / (4 x 10^-6Second) × (1/2) × 4 = 96 Mbps
It becomes.
[0108]
An example of the fourth parameter is a case where the 96-Mbps information signal is performed using three bands that can be used for transmission in four bands. In this case, the carrier digital modulation is 16QAM, and the coding rate R is 3 / 4, the transmission speed is
4 bits x 48 waves x 1 / (4 x 10^-6Second) × (3/4) × 3 = 108 Mbps
It becomes.
[0109]
In this fourth example, since the coding rate 1/2 is increased to 3/4, the correction capability is reduced and the maximum transmission distance is reduced. Therefore, the data of 12 Mbps, which is the difference between 108 Mbps and 96 Mbps, is, for example, Reed-Solomon Transmission quality deterioration is improved by adding an error correction signal such as.
[0110]
An example of the fifth parameter is a case where the 96 Mbps signal is used in three usable bands. In this case, assuming that the digital modulation of the carrier is 16QAM and the coding rate R is 2/3, the transmission rate is
4 bits x 48 waves x 1 / (4 x 10^-6Second) × (2/3) × 3 = 96 Mbps
It becomes.
[0111]
In this fifth example, the coding rate is changed from 1/2 to 2/3 compared to the third example, but it is possible to transmit 96 Mbps content data using three bands. .
[0112]
In the above, five parameter examples in the case where digital data is transmitted by a multicarrier signal using the bands 3 to 4 have been shown. The subcarriers transmitted in these bands are not continuously arranged even when transmitting in adjacent bands, and a guard band is provided between these bands.
[0113]
This is because the guard band is transmitted by inserting 53-wave carriers in a band where 64-wave carriers can be arranged, and this is because Null data is generated when subcarriers are generated using IFFT. Is assigned.
[0114]
FIG. 7 shows a terminal diagram of an IFFT element for explaining a 64-point IFFT used for communication in a conventional single band.
The 64-point IFFT in the figure prevents the components of subcarriers # −32 to # −27 and # + 27 to # + 31 on the frequency axis from being generated by setting the input values of the input terminals 27 to 37 to 0. The spectral components at both ends of the band are reduced.
[0115]
The same applies to the IFFT shown in FIG. 3 described above. For example, a subcarrier signal for transmission in the band Bi + 2 is supplied to terminals 6 to 58, and Nulls are supplied to terminals 0 to 5 and 59 to 63. This is because the subcarrier arrangement according to the conventional communication method for preventing signal interference between adjacent bands is performed.
[0116]
By providing such a guard band region, it is possible to perform communication with reduced interference between adjacent bands, which is necessary for a plurality of users to communicate using one band independently. Is.
[0117]
However, as shown in the above-described example, when communication is performed using a plurality of bands, it is not necessary to provide such a guard band when the bands exist continuously. This is because OFDM signals in a plurality of bands generated by one IFFT are orthogonal to each other, and they do not interfere with each other.
[0118]
Even if the OFDM signals that are orthogonal between the multiple bands are generated using a plurality of IFFTs, if the IFFTs are operated in synchronization in the same symbol period, for example, each subcarrier has an orthogonal relationship. Therefore, the guard band can be omitted.
[0119]
Therefore, in the communication of multicarrier signals performed using a plurality of continuous bands, it is not necessary to suppress the signal component of the guard band portion existing between the continuous bands, and therefore there is a subcarrier signal in synchronization therewith. To be placed.
[0120]
FIG. 8 shows a state in which subcarriers that are continuously present in a continuously used band are arranged.
In the figure, the horizontal axis is the frequency axis, and the vertical axis indicates the spectrum of the multicarrier signal.
[0121]
The signal spectrum shown in c) is a case where signals are transmitted using three bands B1, B2, and B4, but a continuous multicarrier signal is arranged between adjacent bands B1 and B2. .
[0122]
In the case of d), multi-carrier signals are continuously arranged between the continuous bands B3 and B4. In the case of e), the bands B1 to B3 are continuously used, so that the bands B1 to B3 are continuous. Multicarrier signals are arranged.
[0123]
When multicarrier signals are continuously arranged in this way, the number of multicarriers can be increased as compared with the case where guard bands are provided, and the transmission rate is increased accordingly.
[0124]
In the IFFT shown in FIG. 3, the input values of the input terminals 187 to 197 are set to 0. However, in the case of c), the subcarrier signal inserted between the bands B1 and B2 is generated. Data allocation for generating 10-wave subcarriers can be performed on 10 input terminals except for the input terminal 192 among the terminals 187 to 197.
[0125]
In this case, the increase in the transmission rate accompanying the increase in the subcarrier can add 10 subcarriers in the guard band to the carrier of 48 waves × 3 bands = 144 waves, and the increase rate is about 7 %.
[0126]
Then, when three consecutive bands B1, B2, and B3 are usable as shown in e), there are 10 subcarriers between B1 and B2 and between B2 and B3, for a total of 20 subcarriers. Data can be allocated, increasing the transmission rate by about 14%.
[0127]
Furthermore, when communication is performed using four consecutive bands, data can be allocated to a total of 30 subcarriers, in which case the transmission rate increases by about 16% (30/192).
[0128]
FIG. 9 shows a carrier arrangement in the case where such subcarriers are added.
In the figure, f) is a conventional arrangement of subcarriers having a guard band, and g) is a diagram in the case where subcarriers are continuously arranged in a continuous band.
[0129]
Then, additional information can be transmitted using the increase in subcarriers obtained in this way, and for example, an error correction code can be added as the additional information. If the coding rate is set to a large value, the transmission rate can be increased as a result by correcting the error signal generated thereby.
[0130]
The subcarrier signal that is additionally used for increasing the transmission rate has some data when it is decoded by a multicarrier signal decoding apparatus that does not have a function of decoding the subcarrier in the guard band. Although the error rate increases, the information signal transmitted within the normal band can be decoded, so that there is no drawback such as a large loss of transmitted information.
[0131]
In this way, the area of the guard band can be effectively utilized. Next, another utilization method will be described.
FIG. 10 shows how to use the guard band to narrow the transmission band.
In the figure, f) shows a spectrum when data is transmitted using two bands B1 and B2 which are the same as f) in FIG. 9, and h) is a guard band between the bands. Shows the spectrum when subcarriers are arranged.
[0132]
That is, in the spectrum shown in h), the number of data carriers is increased by assigning subcarrier data to the guard band between the continuous bands B1 and B2, and the number of assigned subcarriers on both sides of the increased band is shown. Less.
[0133]
Thus, since the subcarriers on the left side of the band B1 and the right side of B2 are reduced, the spread of the spectrum in each band can be suppressed, and interference with adjacent channels can be further reduced.
[0134]
This can reduce the influence of interference on adjacent stations, especially when weak electric field communication is performed near this generator. During communication of adjacent stations, the own station assigns adjacent channels. In the case of a multicarrier signal generation device that can be set in advance with less interference to adjacent stations when determining whether to perform communication, set the adjacent channel as an empty channel, perform channel assignment, and start communication Is something that can be done.
[0135]
That is, in order for the multicarrier signal generation device and the decoding device to set a communication channel, an empty channel search is performed using a means such as carrier sense (not shown) for a communication channel that is permitted to be transmitted. It is possible to easily set the communication channel.
[0136]
In the above, an example in which communication is performed by assigning a plurality of communication channels using an IFFT capable of generating OFDM signals for four bands has been described. For example, 8 IF using a 512-point IFFT obtained by multiplying the degree 64 by eight. This method can be expanded such as a method for generating multi-carrier signals for one band, and a method for generating multi-carrier signals for 16 bands using 16 times 1024-point IFFT.
[0137]
In these cases, it is necessary to increase the IFFT operation speed by increasing the multiple. In that case, for example, communication can be performed using any three free channels of 16 channels. This makes it easy to set the channel used.
[0138]
Then, the reception of a plurality of OFDM signals transmitted in separate bands as described above can be performed by a decoding device using an FFT of the order of 8 times or 16 times, similar to the generation device.
[0139]
As described above in detail, according to the embodiment shown here, a multicarrier signal generation device and a decoding device that perform generation processing and decoding processing of a signal to be transmitted in a communication band corresponding to a plurality of times the unit communication bandwidth Therefore, it is possible to perform multimedia communication that can support transmission speeds from medium-speed communication using one unit communication band to high-speed communication using a plurality of unit communication bandwidths.
[0140]
In an environment where a large number of individual users (transmitting stations) coexist under the rules such as carrier sense without using a base station or a control station, unit communication bands that are vacant channels are continuous. It is possible to perform high-speed communication using a plurality of unit communication bands even if not, and communication using the empty channels can be performed even if the unit communication bands of the empty channels are not continuous. Therefore, the channel usage rate can be increased.
[0141]
Furthermore, when communicating using a plurality of continuous unit communication bands, the method of using the guard band between these unit communication bands also increases the frequency utilization efficiency and further increases the transmission speed of the information signal. Can be increased.
[0142]
Also, when communicating using a plurality of continuous unit communication bands, the guard band between these unit communication bands is also used to reduce the multi-carrier signals on both the low and high band sides of the continuous unit communication band. By doing so, it is possible to perform communication while suppressing the spread of the spectrum and reducing the interference with the adjacent channel.
[0143]
Further, the generation device and the decoding device have only one system of IFFT or FFT and a filter having a number of points corresponding to a plurality of times of the unit communication bandwidth, and a generation device for transmitting or receiving a signal of a plurality of unit communication bands And a decoding device.
[0144]
Accordingly, in a wireless transmission system in which a communication band is composed of N unit communication bands having a predetermined bandwidth (N is a positive integer), M unit communication (M is a positive integer equal to or less than N). A multi-carrier signal generating apparatus having a bandwidth transmission means, wherein a plurality of (M) band transmittable unit communication bands detected by means such as carrier sense among the plurality (M) of unit communication bands are used. A carrier for a unit communication band that enables high-speed transmission, generates data by assigning data only to subcarriers corresponding to the transmittable unit communication band, and refrains from transmission detected by means such as carrier sense. Can be realized.
[0145]
In addition, in the multicarrier signal decoding apparatus that receives the signal generated and transmitted by the generation apparatus, the multicarrier signal decoding apparatus having reception means for M (≦ N) continuous unit communication bandwidths is configured. Of the decoded data obtained by demodulating the multi-carrier signals of the M unit communication bands, the received data is transmitted so as to be extracted from the decoded data corresponding to the unit communication band used by the generation device. A multi-carrier signal decoding apparatus that decodes the received information signal.
[0146]
At this time, the generating device transmits in which unit communication band combination is used for transmission using a predetermined unit communication band, notifies the decoding device at the head of the transmission signal, and the decoding device starts from all necessary reception channels. The obtained signal is decoded.
[0147]
By these means, high-speed transmission is possible, and a multi-carrier signal that can cope with a wide transmission rate from low speed to high speed by one kind of generation device and decoding device that collectively process M unit communication bandwidths. A generation device and a decoding device can be configured.
[0148]
Further, when communicating using a plurality of unit communication bands, communication can be performed even if these unit communication bands are not continuous, so that the channel utilization efficiency can be improved.
[0149]
In addition, even when vacant channels that can be transmitted are adjacent to each other, it is possible to interfere with adjacent stations by assigning data to multicarrier signals located in the guard band band provided between normal unit communication bands. Therefore, a higher transmission speed can be realized.
[0150]
【The invention's effect】
  ContractAccording to the invention described in claim 1,Since the error correction signal is inserted in the guard band, even when the multi-level number of digital modulation is increased or the coding rate is set to a large value, errors in subcarriers in two adjacent bands are detected. Since the rate can be kept low, the transmission rate can be increased..
[0151]
  According to the invention of claim 2,Since two bands adjacent to each other are packed in the center so that the guard band is buried, a plurality of subcarriers are continuous, and subcarriers of the band corresponding to the guard band are not disposed at both ends of the plurality of bands. Interference can be reduced because the distance between the continuously existing subcarriers and the adjacent subbands of other bands is increased..
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of a multicarrier signal generation apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic block diagram of a multicarrier signal decoding apparatus according to an embodiment of the present invention.
FIG. 3 is a 256-point IFFT calculator that performs four-system 64-point IFFT calculations according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating a communication band and positions of subcarrier frequencies to be arranged according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating a state of communication performed using an unused channel band according to an embodiment of the present invention.
FIG. 6 is a diagram illustrating a received signal frequency spectrum when communication is performed using a plurality of bands according to the embodiment of the present invention.
FIG. 7 is a diagram showing the relationship between signals and terminals of a 64-point IFFT used when communication is performed in a single band.
FIG. 8 is a diagram in which consecutive subcarriers are arranged in consecutive bands according to an embodiment of the present invention.
FIG. 9 is a diagram for explaining a continuous arrangement of subcarriers according to an embodiment of the present invention.
FIG. 10 is a diagram illustrating an arrangement in which subcarriers are continuously arranged according to an embodiment of the present invention and a bandwidth is reduced.
FIG. 11 is a diagram showing a channel arrangement used in a conventional radio access system.
FIG. 12 is a diagram illustrating an arrangement of subcarrier frequencies for one channel in a conventional 5 GHz band wireless access system.
FIG. 13 is a diagram illustrating a configuration of a conventional wireless access system generation device.
FIG. 14 is a diagram showing a relationship between a 64-point IFFT terminal and a supply signal in a conventional wireless access system.
FIG. 15 is a diagram illustrating a configuration of a conventional OFDM signal decoding apparatus.
[Explanation of symbols]
10, 10a Multicarrier signal generator
11 Information signal input terminal
12 Series-parallel conversion circuit
13, 13a Carrier mapping circuit
14, 14a IFFT circuit
15 Quadrature modulation circuit
16 BPF
17 Upconverter
19 Antenna
20, 20a Multicarrier signal decoding apparatus
22 Downconverter
23 BPF
24 Quadrature demodulation circuit
25, 25a FFT
26, 26a Carrier demapping circuit
27 Parallel to serial converter
29 Information signal output terminal

Claims (2)

After assigning information signals corresponding to subcarriers of a plurality of bands used for communication, IFFT conversion is performed by a predetermined method to generate an OFDM signal,
Next, an error correction signal for performing error correction of subcarriers in two unit communication bands adjacent to each other is inserted into a guard band existing between the plurality of bands . After assigning subcarriers of a plurality of bands used for communication to the information signal, IFFT conversion is performed by a predetermined method to generate an OFDM signal,
Next, the two unit communication bands adjacent to each other are packed in a central portion so that a guard band existing between the plurality of bands is filled, and the plurality of subcarriers are continuous, and both ends of the plurality of bands are A method of generating a multicarrier signal, wherein subcarriers in a band corresponding to the guard band are not arranged .

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