WO2014057924A1

WO2014057924A1 - Transmission apparatus, reception apparatus, transmission method, reception method and chips

Info

Publication number: WO2014057924A1
Application number: PCT/JP2013/077307
Authority: WO
Inventors: 慎悟朝倉; 研一村山; 誠田口; 拓也蔀; 澁谷　一彦
Original assignee: 日本放送協会
Priority date: 2012-10-11
Filing date: 2013-10-08
Publication date: 2014-04-17
Also published as: JP6228419B2; JP2014096790A

Abstract

A transmission apparatus (1) comprises: an output processing unit (16) that generates an OFDM signal; and a transmission timing adjusting unit (17) that adjusts the transmission timing of the OFDM signal. The OFDM symbol length of a first OFDM signal generated by the transmission apparatus (1), the arrangement of a pilot signal and the code sequence of this pilot signal are the same as the OFDM symbol length of a second OFDM signal generated by a transmission apparatus (2), the arrangement of a pilot signal and the code sequence of this pilot signal, respectively. The transmission timing adjusting unit (17) establishes a temporal difference between the transmission timing of the pilot signal included in the first OFDM signal and the transmission timing of the pilot signal included in the second OFDM signal such that the transmission timing of the pilot signal included in the first OFDM signal is not coincident with the transmission timing of the pilot signal included in the second OFDM signal.

Description

Transmitting device, receiving device, transmitting method, receiving method, and chip

The present invention relates to a transmission device, a reception device, a transmission method, a reception method, and a chip that transmit an OFDM (Orthogonal Frequency Division Multiplexing) signal.

In Japan, high-definition broadcasting (or multiple standard-definition broadcasting) for fixed receivers is realized by ISDB-T (Integrated Services Digital Broadcasting-Terrestrial), which is a terrestrial digital broadcasting system. In the next-generation terrestrial digital broadcasting system, it is required to provide services with a larger amount of information such as 3D high-definition broadcasting and super high-definition with 16 times the resolution of high-definition instead of conventional high-definition. Therefore, the required C / N reduction by the data capacity expansion and the error correction technique is a problem.

Therefore, as a technique for expanding the data transmission capacity by radio, 2 × 2 polarization MIMO transmission in which horizontal polarization and vertical polarization are simultaneously used for transmitting and receiving antennas has been proposed (for example, see Non-Patent Document 1). . MIMO (Multi Input Multi Output) transmission can be combined with an OFDM modulation method to realize large capacity transmission highly resistant to multipath.

Although it is possible to realize large-capacity transmission by MIMO transmission, when an interference wave of the same channel as the desired wave exists, the interference wave component cannot be removed by a filter or the like because it is the same channel. For example, the current terrestrial digital broadcasting uses the UHF band nationwide, and if the UHF band is used in broadcasting by other systems such as the next generation terrestrial digital broadcasting system, the same channel interference between both broadcasts is a problem. Become.

If pilot signals are inserted at the same frequency interval in an ISDB-T OFDM frame and another OFDM frame, the pilot signal continues to receive interference. When the pilot signal receives interference, the pilot signal of the interference wave is recognized as the pilot signal of the desired wave and is equalized as a false multipath, so that transmission characteristics such as bit error rate (BER) are deteriorated.

The first feature is that a mapping unit that generates a carrier modulation signal by mapping a transmission signal to an IQ plane according to a predetermined modulation scheme for each subcarrier, and insertion and reverse of a pilot signal with respect to the carrier modulation signal A transmission apparatus comprising: an output processing unit that generates an OFDM signal by performing a Fourier transform process and adding a guard interval; and a transmission timing adjustment unit that adjusts a transmission timing of the OFDM signal. The OFDM symbol length of the first OFDM signal, the arrangement of the pilot signal, and the code sequence of the pilot signal are the OFDM symbol length of the second OFDM signal generated by another transmitting apparatus different from the transmitting apparatus, the arrangement of the pilot signal, And the pilot signal code sequence, and the transmission timing And a transmission timing of the pilot signal included in the first OFDM signal so that a transmission timing of the pilot signal included in the first OFDM signal does not match a transmission timing of the pilot signal included in the second OFDM signal. The gist is to provide a time difference with the transmission timing of the pilot signal included in the second OFDM signal.

A second feature is a receiving apparatus configured to be able to receive an OFDM signal transmitted from a first transmitting apparatus or a second transmitting apparatus different from the first transmitting apparatus, and a guard interval for the OFDM signal , An orthogonal demodulation process and a Fourier transform process to extract a pilot signal and an input processing unit for extracting a pilot signal, the OFDM symbol length of the first OFDM signal generated by the first transmission device, the arrangement of the pilot signal, and the pilot signal Is the same as the OFDM symbol length of the second OFDM signal generated by the second transmitter, the arrangement of the pilot signal, and the code sequence of the pilot signal, and the transmission timing of the pilot signal included in the first OFDM signal Does not match the transmission timing of the pilot signal included in the second OFDM signal Sea urchin, and summarized in that a time difference is provided between the transmission timing of the pilot signal included in the first 2OFDM signal transmission timing of the pilot signals included in the 1OFDM signal.

A third feature is a transmission method applied to a transmission apparatus, wherein the carrier modulation signal is generated by mapping a transmission signal to an IQ plane according to a predetermined modulation method for each subcarrier, and the carrier modulation Step B for generating an OFDM signal by inserting a pilot signal, inverse Fourier transform processing, and addition of a guard interval to the signal, and Step C for adjusting the transmission timing of the OFDM signal, The OFDM symbol length of the first OFDM signal generated by the apparatus, the arrangement of the pilot signal, and the code sequence of the pilot signal are the OFDM symbol length of the second OFDM signal generated by another transmitting apparatus different from the transmitting apparatus, and the pilot signal And the code sequence of the pilot signal, The transmission timing of the pilot signal included in the first OFDM signal and the transmission timing of the pilot signal included in the second OFDM signal do not coincide with the transmission timing of the pilot signal included in the second OFDM signal. The gist is to include a step of providing a time difference with the transmission timing of the pilot signal included in the second OFDM signal.

A fourth feature is a reception method configured to be able to receive an OFDM signal transmitted from a first transmission device or a second transmission device different from the first transmission device, and a guard interval for the OFDM signal. , Quadrature demodulation processing, and Fourier transform processing to extract a pilot signal, and includes a step A for extracting the pilot signal, the OFDM symbol length of the first OFDM signal generated by the first transmission device, the arrangement of the pilot signal, and the pilot signal The code sequence is the same as the OFDM symbol length of the second OFDM signal generated by the second transmission device, the arrangement of the pilot signal, and the code sequence of the pilot signal, and the transmission timing of the pilot signal included in the first OFDM signal; The transmission timing of the pilot signal included in the second OFDM signal does not match Sea urchin, and summarized in that a time difference is provided between the transmission timing of the pilot signal included in the first 2OFDM signal transmission timing of the pilot signals included in the 1OFDM signal.

A fifth feature is a chip mounted on a receiving apparatus configured to be able to receive an OFDM signal transmitted from a first transmitting apparatus or a second transmitting apparatus different from the first transmitting apparatus, On the other hand, an input processing unit for extracting a pilot signal by performing guard interval removal, quadrature demodulation processing, and Fourier transform processing is provided, and the OFDM symbol length of the first OFDM signal generated by the first transmission device, the pilot signal The arrangement and the code sequence of the pilot signal are the same as the OFDM symbol length of the second OFDM signal generated by the second transmission device, the arrangement of the pilot signal, and the code sequence of the pilot signal, and are included in the first OFDM signal. Transmission timing of pilot signal and transmission timing of pilot signal included in the second OFDM signal As grayed and does not match, it is summarized in that a time difference between a transmission timing of the pilot signal included in the first 2OFDM signal and the transmission timing of the pilot signal included in the first 1OFDM signal is provided.

FIG. 1 is a block diagram showing a configuration of a transmission apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of a pilot pattern of an OFDM signal transmitted by the transmission apparatus 1 of FIG. FIG. 3 is a diagram illustrating an example of a pilot pattern of an OFDM signal transmitted by the transmission apparatus 2 of FIG. FIG. 4 is a block diagram illustrating a configuration of a receiving device corresponding to the transmitting device 1 of FIG. FIG. 5 is a diagram for explaining processing in the transmission path response calculation unit of the receiving apparatus. FIG. 6 is a diagram for explaining the operation of the transmission timing adjustment unit in the transmission apparatus according to the embodiment of the present invention. FIG. 7 is a diagram illustrating a simulation result by the transmission apparatus according to the embodiment of the present invention. FIG. 8 is a diagram illustrating a case where the transmission apparatus 2 of FIG. 1 transmits a signal obtained by time-division multiplexing OFDM signals of different modes.

The transmission apparatus according to the embodiment aims to suppress co-channel interference between a plurality of OFDM signals having the same symbol length, pilot signal arrangement, and pilot signal code sequence, and different data signals. Here, the first transmission device generates the first OFDM signal based on the first data signal, and the second transmission device different from the first transmission device is based on the second data signal different from the first data signal. Note that the second OFDM signal is generated. It should be noted that the receiving device is configured to receive an OFDM signal transmitted from the first transmitting device or the second transmitting device. The combination of the first OFDM signal and the second OFDM signal includes (1) OFDM signals transmitted by the ISDB-T system, (2) Next-generation digital terrestrial broadcasting system (hereinafter referred to as “next-generation system”) ), And (3) OFDM signals transmitted by the next generation method and OFDM signals transmitted by the ISDB-T method. In the present embodiment, (3) co-channel interference in the OFDM signal transmitted by the next generation method and the OFDM signal transmitted by the ISDB-T method will be described as an example.

[Transmitter]
FIG. 1 is a block diagram showing a configuration of a transmission apparatus according to the first embodiment of the present invention, in which a transmission apparatus 1 that transmits an OFDM signal by a next generation method and a transmission that transmits an OFDM signal by an ISDB-T system Device 2 is shown. Although an example in which the transmission device 1 and the transmission device 2 use the same transmission station 3 is shown, when the

transmission devices

1 and 2 transmit from different locations, different transmission stations are used. Further, FIG. 1 shows a transmission apparatus 1 that performs polarization MIMO transmission, which is assumed as one mode of the next generation method, but the transmission method of the next generation method is not limited to this.

As shown in FIG. 1, the transmission apparatus 1 includes an error correction coding unit 11, a bit interleaving unit 12, a mapping unit 13, a time interleaving unit 14, a frequency interleaving unit 15, and an output processing unit 16 (16- 1 and 16-2), a transmission timing adjustment unit 17 (17-1 and 17-2), and a transmission antenna 18 (18-1 and 18-2). In this configuration example, the bit interleaving unit 12, the time interleaving unit 14, and the frequency interleaving unit 15 are provided in order to perform the interleaving process, but these are not essential, and only one or two of them are included. The structure provided may be sufficient. The transmission device 1 transmits an OFDM signal via a plurality of transmission antennas 18. In the present embodiment, the number of transmission antennas is two.

In the present embodiment, only the transmission device 1 has the transmission timing adjustment unit 17, but only the transmission device 2 may have the transmission timing adjustment unit, and the transmission device 1 and the transmission device 2 each have a transmission timing. It is good also as a structure which has an adjustment part.

The error correction encoding unit 11 generates an error correction code by encoding an input transmission signal using a predetermined error correction method so that a transmission error can be corrected on the receiving side, and outputs the error correction code to the bit interleaving unit 12 . The error correction code is, for example, a BCH code or an LDPC code.

The bit interleaving unit 12 rearranges each bit of the error correction code generated by the error correction encoding unit 11 and outputs it to the mapping unit 13.

The mapping unit 13 performs mapping on the IQ plane of the data rearranged by the bit interleaving unit 12 as m bits / symbol, and generates a carrier modulation signal (carrier symbol) that has been subjected to carrier modulation in accordance with the multilevel modulation scheme. Generate and output to the time interleave unit 14.

The time interleaving unit 14 rearranges the order of the carrier modulation signals generated by the mapping unit 13 in the time direction and outputs the rearranged signals to the frequency interleaving unit 15.

The frequency interleaving unit 15 rearranges the order of the carrier modulation signals interleaved in the time direction by the time interleaving unit 14 between the frequency direction and the transmission antennas, and generates interleaved data for each transmission antenna 18 for output. The data is output to the processing unit 16. When the number of transmission antennas 18 is two, the frequency interleaving unit 15 generates two systems of signals for the output processing units 16-1 and 16-2. The transmission apparatus 1 includes two frequency interleaving units 15, one frequency interleaving unit 15 generates a signal for the output processing unit 16-1, and the other frequency interleaving unit 15 is used for the output processing unit 16-2. A signal may be generated.

The output processing unit 16 generates an OFDM signal obtained by adding a guard interval to a signal obtained by inserting a pilot signal or the like into the signal generated by the frequency interleaving unit 15 and performing inverse Fourier transform. As shown in FIG. 1, the output processing unit 16 includes an OFDM frame configuration unit 161 (161-1 and 161-2), an IFFT (Inverse Fast Fourier Transform) unit 162 (162-1 and 162-2). 2) and a GI (Guard interval) adding unit 163 (163-1 and 163-2).

The OFDM frame configuration unit 161 inserts a pilot signal (SP signal, CP signal), a TMCC signal indicating control information, and an AC signal indicating additional information into the signal generated by the frequency interleaving unit 15, and sets all carriers to 1 OFDM. As a symbol, an OFDM frame is composed of a predetermined number of OFDM symbol blocks, and is output to IFFT section 162.

The IFFT unit 162 performs an IFFT process on the OFDM symbol generated by the OFDM frame configuration unit 161 to generate a time-domain effective symbol signal, and outputs it to the GI adding unit 163.

GI adding section 163 inserts a guard interval obtained by copying the latter half of the effective symbol signal at the beginning of the effective symbol signal generated by IFFT section 162, and generates an OFDM signal subjected to orthogonal modulation processing and D / A conversion To do. A guard interval ratio (GIR) representing a ratio of the guard interval length to the effective symbol length is set to 1/8, for example.

The transmission timing adjustment unit 17 adjusts the transmission timing of the OFDM signal generated by the GI addition unit 163 and transmits it to the transmission station 3. Details of the transmission timing adjustment unit 17 will be described later.

The transmitting station 3 performs MIMO transmission by space division multiplexing (SDM) via the transmitting antennas 18-1 and 18-2.

For example, in the case of polarization MIMO using orthogonality between polarizations, the transmission antenna 18 is a horizontally polarized antenna and a vertically polarized antenna, or a right-handed circularly polarized antenna and a left-handed circularly polarized antenna. is there.

FIG. 2 is a diagram illustrating an example of a pilot pattern of an OFDM signal transmitted by the transmission apparatus 1. In the OFDM signal in the figure, the right direction is the frequency direction (carrier direction), and the downward direction is the time direction (symbol direction). A circle with x means a null pilot signal with no signal, and a double circle means a pilot signal. Others mean non-pilot signals such as data signals and control signals. The transmission apparatus 1 transmits an OFDM signal having a pilot pattern shown in FIG. 2A via one transmission antenna 18 and transmits an OFDM signal having a pilot pattern shown in FIG. 2B via the other transmission antenna 18. Send.

Referring to FIG. 1 again, the transmission apparatus 2 includes an error correction encoding unit 21, a bit interleaving unit 22, a mapping unit 23, a time interleaving unit 24, a frequency interleaving unit 25, an output processing unit 26, A transmission antenna 27. Similarly to the transmission apparatus 1, the bit interleaving unit 22, the time interleaving unit 24, and the frequency interleaving unit 25 are not essential, and may be configured to include only one or two of them.

The transmission device 2 is different from the transmission device 1 in that it has only one output system, and therefore includes only one output processing unit 26 and a transmission antenna 27 and does not include a transmission timing adjustment unit. Since other points are the same as those of the transmission device 1, the description thereof is omitted.

FIG. 3 is a diagram illustrating an example of a pilot pattern of an OFDM signal transmitted by the transmission apparatus 2. A double circle signifies a pilot signal, and the other signifies a non-pilot signal such as a data signal or a control signal. In the ISDB-T system, as shown in FIG. 3, pilot signals are inserted once every 12 carriers in the frequency direction (carrier direction) and once every 4 symbols in the time direction (symbol direction). The insertion interval in the frequency direction when the pilot signal is interpolated in the time direction is 3 carriers.

[Receiver]
Next, in order to help understanding of the transmission apparatus according to the present invention, an embodiment of a reception apparatus corresponding to the transmission apparatus 1 will be described.

FIG. 4 is a block diagram illustrating a configuration of a receiving device corresponding to the transmitting device 1. As shown in FIG. 4, the receiving device 4 includes a receiving antenna 41 (41-1 and 41-2), an input processing unit 42 (42-1 and 42-2), a transmission path response calculating unit 43, a MIMO A detection unit (transmission signal estimation unit) 44, a first frequency deinterleave unit 45, a noise variance calculation unit 46, a second frequency deinterleave unit 47, a likelihood ratio calculation unit 48, a time deinterleave unit 49, A bit deinterleaving unit 50 and an error correction code decoding unit 51. The receiving device 4 does not need to include the bit deinterleaving unit 50 when the transmitting device 1 does not include the bit interleaving unit 12, and the time deinterleaving unit when the transmitting device 1 does not include the time interleaving unit 14. 49 does not need to be provided, and when the transmission apparatus 1 does not include the frequency interleave unit 15, it is not necessary to include the first frequency deinterleave unit 45 and the second frequency deinterleave unit 47.

The input processing unit 42 (42-1 and 42-2) receives the OFDM signal transmitted from the transmission device 1 corresponding to the reception device 4 via the reception antenna 41 (41-1 and 41-2), The received OFDM signal is subjected to orthogonal demodulation processing and Fourier transform processing to generate a complex baseband signal. The input processing unit 42 includes a GI removal unit 421 (421-1 and 421-2), a Fourier transform unit 422 (4222-1 and 422-2), and a pilot signal extraction unit 423 (423-1 and 423-2). And comprising.

The GI removal unit 421 generates a baseband signal by performing orthogonal demodulation processing on the received OFDM signal, and generates a digital signal by A / D conversion. Subsequently, the GI removal unit 421 extracts the effective symbol signal by removing the guard interval. Then, the effective symbol signal is output to Fourier transform section 422.

The Fourier transform unit 422 performs FFT (Fast Fourier Transform) processing on the effective symbol signal extracted by the GI removal unit 421 to generate complex baseband signals y _i1 and y _{i2 in the} frequency domain. Then, complex baseband signals y _i1 and y _i2 are output to pilot signal extraction section 423 and MIMO detection section 44. In other words, the Fourier transform unit 422-1 generates the complex baseband signal y _i1 by performing an FFT process on the OFDM signal received from the reception antenna 41-1, and outputs the complex baseband signal y _i1 to the pilot signal extraction unit 423-1 and the MIMO detection unit 44. To do. The Fourier transform unit 422-2 performs an FFT process on the OFDM signal received from the reception antenna 41-2 to generate a complex baseband signal y _i2 and outputs the complex baseband signal y _i2 to the pilot signal extraction unit 423-2 and the MIMO detection unit 44.

The pilot signal extraction unit 423 extracts a known pilot signal included in the complex baseband signals y _i1 and y _i2 generated by the Fourier transform unit 422. Then, the pilot signal is output to the transmission path response calculation unit 43.

The transmission path response calculation unit 43 calculates the transmission path response H _i for each carrier from the delay profile of the pilot signal extracted by the pilot signal extraction unit 423, and outputs it to the MIMO detection unit 44.

FIG. 5 is a diagram for explaining the processing in the transmission path response calculation unit 43 of the reception device 4. FIG. 5A shows a pilot signal for every three carriers obtained by accumulating OFDM signals for 8 symbols and linearly interpolating the amplitude response of the pilot signal in the time direction. In order to interpolate the pilot signal, the transmission path response calculation unit 43 first performs inverse Fourier transform on the pilot signal for every three carriers to calculate a time-domain pilot signal. When the pilot signal for every n carriers is subjected to inverse Fourier transform, the data between the pilot signals is interpolated to 0, so that aliasing occurs, and the same waveform repeatedly appears n times within one OFDM symbol length. Since n = 3 in this embodiment, the same waveform repeatedly appears three times within one OFDM symbol length in the time domain (delay profile) of the pilot signal as shown in FIG. 5B.

Next, the transmission path response calculation unit 43 arranges the interpolation filter F as shown in FIG. 5B, and extracts only the real signal that is not the return signal. Time width _F w of the interpolation filter F is represented by the effective symbol length T and the product of the guard interval ratio GIR of OFDM signals. If the delay time of the delay wave is smaller than F _w it may be to equalize the multipath components. And the transmission line response calculation part 43 acquires the transmission line response for every carrier as shown in FIG.5 (c) by carrying out the Fourier transform again of the pilot signal extracted by the filter process. White circles represent interpolated transmission line responses.

The channel response H _i of 2 × 2 MIMO transmission is

It can be expressed as. Each element h _i11 , h _i12 , h _i21 , h _i22 of the transmission line response H is a complex number. h _i11 represents the state of the transmission path from the transmission antenna 18-1 to the reception antenna 41-1, h _i12 represents the state of the transmission path from the transmission antenna 18-2 to the reception antenna 41-1, and h _i21 represents transmission. The state of the transmission path from the antenna 18-1 to the reception antenna 41-2 is represented, and h _i22 represents the state of the transmission path from the transmission antenna 18-2 to the reception antenna 41-2. Here, h _i11 and h _i22 are parallel transmission path components, and h _i12 and h _i21 are interference components.

The MIMO detection unit 44 uses the complex baseband signals y _i1 and y _i2 generated by the Fourier transform unit 422 and the transmission path response H _i calculated by the transmission path response calculation unit 43 to perform ZF (Zero Forcing), By using a known method such as MMSE (Minimum Mean Squared Error), the data streams received by the plurality of receiving antennas 41 are separated to generate the estimated values x ^ _i1 and x ^ _i2 of the transmission signals. Then, the estimated values x ^ _i1 and x ^ _i2 of the transmission signal are output to the first frequency deinterleave unit 45 and the noise variance calculation unit 46.

The first frequency deinterleaving unit 45 performs deinterleaving processing in the frequency direction on the estimated values x ^ _i1 and x ^ _{i2 of} the transmission signals generated by the MIMO detection unit 44. Then, estimated values x ^ _i1 and x ^ _i2 of the deinterleaved transmission signal are output to likelihood ratio calculation section 48. The deinterleaving process in the frequency direction is a process for returning the data rearranged in the frequency direction by the frequency interleaving unit 15 of the transmission device 1 to the original order.

The noise variance calculation unit 46 calculates the noise variances σ _i1 ² and σ _i2 ² of the received OFDM signal using the estimated values x ^ _i1 and x ^ _i2 of the transmission signal generated by the MIMO detection unit 44. Then, the noise variances σ _i1 ² and σ _i2 ² are output to the second frequency deinterleave unit 47.

The second frequency deinterleaving unit 47 performs deinterleaving processing on the noise variances σ _i1 ² and σ _i2 ² calculated by the noise variance calculating unit 46. The deinterleaved noise variances σ _i1 ² and σ _i2 ² are output to the likelihood ratio calculation unit 48.

The likelihood ratio calculation unit 48 estimates the transmission signals x ^ _i1 and x ^ _i2 deinterleaved by the first frequency deinterleaver 45 and the noise variance _σi1 input from the second frequency deinterleaver 47. ² and σ _i2 ² are used to calculate the likelihood ratio λ of the received signal. Then, the likelihood ratio λ is output to the time deinterleave unit 49. The likelihood ratio λ is calculated for each bit of the error correction code and represents the probabilistic reliability information of the received signal.

The time deinterleaving unit 49 performs a deinterleaving process in the time direction on the likelihood ratio λ calculated by the likelihood ratio calculating unit 48. Then, the likelihood ratio λ that has been subjected to the deinterleaving process is output to the bit deinterleaving unit 50. The deinterleaving process in the time direction is a process for returning the data rearranged in the time direction by the time interleaving unit 14 of the transmission apparatus 1 to the original order.

The bit deinterleaving unit 50 performs a deinterleaving process in the bit direction on the likelihood ratio λ calculated by the time deinterleaving unit 49. Then, the likelihood ratio λ subjected to the deinterleaving process is output to the error correction code decoding unit 51. The deinterleaving process in the bit direction is a process for returning the data rearranged in the bit direction by the bit interleaving unit 12 of the transmission device 1 to the original order.

The error correction code decoding unit 51 decodes the error correction code using the likelihood ratio λ deinterleaved by the bit deinterleaving unit 50, and outputs an estimated value of the bit transmitted from the transmission device 1.

[Transmission timing adjustment unit]
Next, the operation of the transmission timing adjustment unit 17 of the transmission device 1 will be described in detail.

When there is an OFDM signal having the same desired signal and symbol length, pilot signal arrangement, and pilot signal code sequence (for example, PN code sequence) as an interference wave, the desired signal and the pilot signal of the interference signal are completely The signals are equal. In this case, even if the data signal is different, the transmission line response calculation unit 43 of the receiving device 4 regards the interference wave as a delayed wave of the same signal as the desired wave and performs equalization processing. For this reason, the transmission line response calculation unit 43 cannot accurately obtain the transmission line response, and transmission characteristics deteriorate. Therefore, the transmission timing adjustment unit 17 sets the delay difference from the interference wave so that the interference wave is located outside the interpolation filter, thereby suppressing the influence of the interference wave and improving the transmission characteristics.

FIG. 6 is a diagram for explaining the operation of the transmission timing adjustment unit 17 of the transmission device 1. As illustrated in FIG. 6A, the transmission apparatus 1 uses the transmission timing adjustment unit 17 so that the OFDM signal transmitted from the transmission apparatus 1 does not match the timing of the pilot signal with the OFDM signal transmitted from the transmission apparatus 2. , Adjust the transmission timing. By adjusting the time difference (delay difference) between the OFDM signal (desired wave) transmitted from the transmission apparatus 1 and the OFDM signal (interference wave) transmitted from the transmission apparatus 2, an interference wave is generated in the delay profile of the pilot signal. Can be adjusted.

FIG. 6B shows a delay profile in the pilot signal when the time difference between the OFDM signal (desired wave) transmitted from the transmission apparatus 1 and the OFDM signal (interference wave) transmitted from the transmission apparatus 2 is τ. Show. Thus, when the interference wave is arranged outside the interpolation filter F, the receiving device 4 can calculate the transmission path response with high accuracy by the transmission path response calculation unit 43.

A time domain t in which the interpolation filter F is arranged within one OFDM symbol length is expressed by the following equation (1). Here, n is a period in the frequency direction when the pilot signal is interpolated in the time direction, and k is an integer from 1 to n-1. Also, the time width _{F w} of the interpolation filter F, as shown in the following equation (2) is expressed by the product of the guard interval ratio GIR of the effective symbol length T and OFDM signal of the OFDM signal.

Therefore, in order to place the interference wave outside the interpolation filter F, it is necessary to set the time difference τ within the range shown in the following equation (3).

If the correlation between pilot signals is sufficiently low, such as when the initial value of the code sequence of the pilot signal is different or the generation polynomial of the code sequence is different, the data carrier of the desired wave is the pilot of the interference wave regardless of the time τ. It is affected by the signal. Since the pilot signal has periodicity in the time direction, the time difference τ also has periodicity in the time direction.

In order to obtain the best BER characteristics, it is particularly preferable to set the time difference τ within the range when k = 1 in the equation (3). The time difference τ at this time is expressed by the following equation (4).

The reason why k = 1 is preferable is shown below. When the time difference τ is gradually increased from 0, the interference wave is first located outside the interpolation filter when k = 1. At this time, most of the energy components of the pilot signal of the interference wave collide with the pilot signal of the desired wave. When the time difference τ is further increased, the interference wave is again located outside the interpolation filter when k = 2. However, the energy component of the pilot signal of the interference wave is higher than that of the desired wave when k = 1. Does not hit the pilot signal. In general, in OFDM, a pilot signal has a higher power than a data signal (for example, boosted 4/3 times in the ISDB-T system), so how much energy of the pilot signal of the interference wave becomes the pilot signal of the desired wave. The BER characteristic changes depending on whether the collision occurs. When the energy of the pilot signal of as many interference waves as possible collides with the pilot signal of the desired wave, the influence on the data signal of the desired wave is reduced. Therefore, the BER characteristic is the best when k = 1.

FIG. 7 is a diagram showing a BER characteristic by simulation when the transmission timing is adjusted by the transmission device 1. The horizontal axis represents the time difference τ between the OFDM signal (desired wave) transmitted from the transmission apparatus 1 and the OFDM signal (interference wave, ISDB-T mode 3) transmitted from the transmission apparatus 2, and the vertical axis represents BER. Here, the time difference τ is indicated by the number of FFT samples. In this simulation example, the FFT size is 8K (8192 samples), that is, the effective symbol length T of the OFDM signal is 8192 samples. The GI ratio is 1/8, the desired wave carrier modulation scheme is 1024 QAM, the interference wave carrier modulation scheme is 64 QAM, the D / U ratio is 26.0 dB, and the C / N ratio is 29.0 dB.

The pattern shown in FIG. 2 was used as the pilot pattern of the desired wave, and the pattern shown in FIG. 3 was used as the pilot pattern of the interference wave. In the pilot patterns of FIGS. 2 and 3, the insertion interval n in the frequency direction when the pilot signal is interpolated in the time direction is 3 carriers. Under this condition, the range of the delay time τ satisfying the equation (3) is expressed by the following equation (5).

When the effective symbol length T of the OFDM signal is 8192, the range of the time difference τ satisfying the equation (5) is 504 <τ <2227 (k = 1), 3235 <τ <4957 (k = 2), 5965 <τ <. 7688 (k = 3). The simulation results also show that the delay time τ is in this range, and particularly when k = 1, the BER is lowered and the transmission characteristics are improved.

FIG. 8 shows a case where the OFDM signal (interference wave) transmitted from the transmission apparatus 2 is a signal obtained by time division multiplexing of OFDM signals of different modes (mode 2 and mode 3) in the ISDB-T system. . As shown in FIG. 8A, when the time difference τ = 0, the OFDM symbol length is the same in mode 3, so that co-channel interference occurs. Therefore, even when the symbol lengths of only a part of the OFDM signal match in this way, by appropriately setting the time difference τ as shown in FIG. 8B, the deterioration of transmission characteristics due to co-channel interference is suppressed. can do.

As described above, in the transmission apparatus 1 according to the present embodiment, the transmission timing adjustment unit 17 uses the pilot length and the pilot signal arrangement, the pilot signal code sequences, and other OFDM signals having different data signals and the pilot signal. Since adjustment is performed so that the signal transmission timings do not coincide with each other, it is possible to suppress deterioration in transmission characteristics due to co-channel interference.

In the embodiment described above, co-channel interference between the next-generation OFDM signal transmitted by the transmission apparatus 1 and the ISDB-T OFDM signal transmitted by the transmission apparatus 2 has been described. Similarly, with respect to co-channel interference between OFDM signals of the system, similarly, by adjusting the time difference between the OFDM signals by the transmission timing adjustment unit provided in the transmission apparatus 1, it is possible to suppress deterioration in transmission characteristics due to co-channel interference. Similarly, for the same channel interference between ISDB-T OFDM signals transmitted by the transmission apparatus 2, the transmission timing adjustment unit provided in the transmission apparatus 2 adjusts the time difference between the OFDM signals, thereby causing the same channel interference. Deterioration of transmission characteristics can be suppressed.

Note that a computer can be suitably used to function as a transmission device, and such a computer stores a program describing processing contents for realizing each function of the transmission device in a storage unit of the computer. It can be realized by reading and executing this program by the CPU of the computer.

Although not particularly mentioned in the embodiment, a program for causing a computer to execute each process performed by the transmission device 1 and the reception device 4 may be provided. The program may be recorded on a computer readable medium. If a computer-readable medium is used, a program can be installed in the computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or a DVD-ROM.

Alternatively, a chip configured by a memory that stores a program for executing each process performed by the transmission device 1 and the reception device 4 and a processor that executes the program stored in the memory may be provided.

Note that the entire content of Japanese Patent Application No. 2012-226248 (filed on Oct. 11, 2012) is incorporated herein by reference.

Thus, according to the present invention, deterioration of transmission characteristics due to co-channel interference can be suppressed, which is useful for any application for transmitting OFDM signals.

Claims

A transmitting device,
A mapping unit that maps a transmission signal to an IQ plane according to a predetermined modulation scheme for each subcarrier to generate a carrier modulation signal;
An output processing unit for generating an OFDM signal by performing pilot signal insertion, inverse Fourier transform processing and guard interval addition to the carrier modulation signal;
A transmission timing adjustment unit for adjusting the transmission timing of the OFDM signal,
The OFDM symbol length of the first OFDM signal generated by the transmitting apparatus, the arrangement of pilot signals, and the code sequence of the pilot signal are the OFDM symbol length of the second OFDM signal generated by another transmitting apparatus different from the transmitting apparatus, It is the same as the pilot signal arrangement and the pilot signal code sequence,
The transmission timing adjustment unit transmits the pilot signal included in the first OFDM signal so that the transmission timing of the pilot signal included in the first OFDM signal does not match the transmission timing of the pilot signal included in the second OFDM signal. A transmission apparatus characterized in that a time difference is provided between a timing and a transmission timing of a pilot signal included in the second OFDM signal.
The transmission timing adjustment unit is configured such that the effective symbol length of the OFDM signal is T, the period of the frequency direction when the pilot signal is interpolated in the time direction is n, the guard interval ratio of the OFDM signal is GIR, 1 to the n− When the integer up to 1 is k, the time difference τ is expressed by the following equation:

The transmission device according to claim 1, wherein the transmission device is set so as to satisfy.
3. The transmission apparatus according to claim 2, wherein the value of k is 1.
A receiving apparatus configured to be able to receive an OFDM signal transmitted from a first transmitting apparatus or a second transmitting apparatus different from the first transmitting apparatus,
The OFDM signal includes an input processing unit that extracts a pilot signal by performing guard interval removal, orthogonal demodulation processing, and Fourier transform processing,
The OFDM symbol length of the first OFDM signal generated by the first transmission device, the arrangement of pilot signals, and the code sequence of the pilot signal are the OFDM symbol length of the second OFDM signal generated by the second transmission device, and the pilot signal The same as the arrangement and the code sequence of the pilot signal,
The transmission timing of the pilot signal included in the first OFDM signal and the transmission timing of the pilot signal included in the second OFDM signal so that the transmission timing of the pilot signal included in the first OFDM signal does not match the transmission timing of the pilot signal included in the second OFDM signal. A receiving apparatus, wherein a time difference is provided between transmission timings of included pilot signals.
A transmission method applied to a transmission device,
Mapping the transmission signal to the IQ plane according to a predetermined modulation scheme for each subcarrier to generate a carrier modulation signal; and
Step B for generating an OFDM signal by performing insertion of a pilot signal, inverse Fourier transform processing and addition of a guard interval to the carrier modulation signal;
Adjusting the transmission timing of the OFDM signal,
The OFDM symbol length of the first OFDM signal generated by the transmitting apparatus, the arrangement of pilot signals, and the code sequence of the pilot signal are the OFDM symbol length of the second OFDM signal generated by another transmitting apparatus different from the transmitting apparatus, It is the same as the pilot signal arrangement and the pilot signal code sequence,
The step C includes a transmission timing of a pilot signal included in the first OFDM signal so that a transmission timing of a pilot signal included in the first OFDM signal does not match a transmission timing of a pilot signal included in the second OFDM signal. A transmission method comprising a step of providing a time difference with a transmission timing of a pilot signal included in the second OFDM signal.
A receiving method applied to a receiving apparatus configured to be able to receive an OFDM signal transmitted from a first transmitting apparatus or a second transmitting apparatus different from the first transmitting apparatus,
Step A for extracting a pilot signal by performing guard interval removal, orthogonal demodulation processing and Fourier transform processing on the OFDM signal,
The OFDM symbol length of the first OFDM signal generated by the first transmission apparatus, the pilot signal arrangement, and the pilot signal code sequence are the OFDM symbol length of the second OFDM signal, the pilot signal arrangement, and the pilot signal code sequence. Is the same as
The transmission timing of the pilot signal included in the first OFDM signal and the transmission timing of the pilot signal included in the second OFDM signal so that the transmission timing of the pilot signal included in the first OFDM signal does not match the transmission timing of the pilot signal included in the second OFDM signal. A reception method, wherein a time difference is provided between transmission timings of included pilot signals.
A chip mounted on a receiver configured to be able to receive an OFDM signal transmitted from a first transmitter or a second transmitter different from the first transmitter;
An OFDM signal is provided with an input processing unit that extracts a pilot signal by performing guard interval removal, orthogonal demodulation processing, and Fourier transform processing,
The OFDM symbol length of the first OFDM signal generated by the first transmission device, the arrangement of pilot signals, and the code sequence of the pilot signal are the OFDM symbol length of the second OFDM signal generated by the second transmission device, and the pilot signal The same as the arrangement and the code sequence of the pilot signal,
The transmission timing of the pilot signal included in the first OFDM signal and the transmission timing of the pilot signal included in the second OFDM signal so that the transmission timing of the pilot signal included in the first OFDM signal does not match the transmission timing of the pilot signal included in the second OFDM signal. A chip characterized in that a time difference is provided between transmission timings of included pilot signals.