JP7289737B2 - Data transmission system and data transmission method - Google Patents

Description

The present invention relates to a data transmission system that transmits data using frames containing data symbols and pilot symbols.

Orthogonal Frequency Division Multiplexing (OFDM) is adopted as a radio transmission method in a radio transmission device (FPU: Field Pick-up Unit) for digital terrestrial broadcasting and broadcast program materials. In order for a receiver to demodulate a signal transmitted by the OFDM system, it is necessary to estimate the amplitude and phase characteristics of the transmission path, and demodulation (equalization) processing is performed based on the estimation results.

In order to estimate the channel characteristics, the transmitting side inserts a pilot signal with known amplitude and phase at predetermined intervals in each direction of frequency (carrier) and time (symbol), and the receiving side inserts the received pilot signal The signal is interpolated in each direction of frequency and time. This enables the receiving side to estimate the transmission path characteristics of the data carrier portion where no pilot carrier is arranged.

It is desirable to arrange the pilot signals according to the transmission path characteristics. In other words, in transmission paths with long-delay multipaths, the pilot spacing in the frequency direction is densely arranged, and in transmission paths with large temporal fluctuations, the pilot spacing in the time direction is densely arranged, resulting in high accuracy. transmission channel estimation becomes possible.

In recent years, eigenmode transmission using 4×4 MIMO (Multiple Input Multiple Output) has been studied (Non-Patent Document 1). Non-Patent Document 1 proposes configuring a frame with a pilot symbol, all of which are pilot carriers, and a data symbol, all of which are data carriers. In the 4×4 MIMO system of Non-Patent Document 1, it is necessary to provide orthogonal pilots for each of the four transmitting antennas in order to correctly estimate all transmission paths from each transmitting antenna on the receiving side.

In the pilot symbol of Non-Patent Document 1, a pilot signal is orthogonalized for each transmission antenna by assigning a pilot carrier to each transmission antenna at an interval of 1 out of 4 subcarriers. In this case, according to the sampling theorem, it is possible to accurately estimate the characteristics of the transmission path in which the delay wave up to the delay time corresponding to 1/4 of one symbol is mixed. Therefore, if 1/4 of the symbol length is provided as a guard interval, multipaths up to 1/4 of 1 symbol can be equalized (demodulated) accurately without significant deterioration.

Kazuhiko Mitsuyama, 3 others, "Wireless Transmission Technology for Realization of 1.2 GHz/2.3 GHz Band Super Hi-Vision FPU for Mobile Relay", NHK Giken R&D, No. 165, pp.54-67, September 2017 Standard ARIB STD-B57 Version 2.1 "Portable OFDM digital wireless transmission system for transmission of 1.2 GHz/2.3 GHz band television broadcast program material", Association of Radio Industries and Businesses, July 2016

In the conventional technique, as shown in FIG. 5A, since a guard interval corresponding to 1/4 of one symbol time is added to each symbol, there is a problem that transmission efficiency is lowered. To address this problem, Non-Patent Document 2 discloses increasing the transmission efficiency by lengthening the symbol length and reducing the guard interval ratio with the same guard interval time. For example, as shown in FIG. 5B, by doubling the symbol length, the guard interval ratio for having the same guard interval time becomes 1/8, and transmission efficiency can be improved. However, in the format of Non-Patent Document 1, if the intervals between pilot symbols are made constant in order to equalize the resistance to time fluctuations of the transmission path, the transmission efficiency is not improved as shown in FIG. 5B.

SUMMARY OF THE INVENTION The present invention has been made in view of the conventional circumstances as described above, and an object of the present invention is to propose a technique capable of realizing both improvement in multipath resistance and improvement in transmission efficiency.

In order to achieve the above objects, the present invention has a data transmission system configured as follows.
That is, in a data transmission system that transmits data using a frame containing data symbols and pilot symbols, the frame has a data symbol length greater than the pilot symbol length, and a pilot symbol guard interval ratio It is characterized by a format with a smaller guard interval ratio of data symbols.

Here, as one configuration example, both the guard interval length of the data symbol and the guard interval length of the pilot symbol are set to be equal to or greater than the presumed maximum multipath delay time, and the symbol length of the data symbol is set to one symbol time. The length may be set such that the time variation of the transmission path characteristics is substantially constant, and the symbol length of the pilot symbol may be set to a value equal to or greater than the maximum delay time multiplied by the number of transmission antennas.

It should be noted that the device on the transmission side in the above system can be realized by various configurations.
For example, the device on the transmitting side includes a first IFFT unit that performs IFFT processing with the number of points corresponding to the guard interval length of the data symbol, and a first guard interval that performs guard interval addition processing with the guard interval ratio of the data symbol. an addition unit, a second IFFT unit that performs IFFT processing with the number of points corresponding to the guard interval length of the pilot symbol, and a second guard interval addition unit that performs guard interval addition processing with the guard interval ratio of the pilot symbol. and generating data symbols using the first IFFT section and the first guard interval adding section, and generating pilot symbols using the second IFFT section and the second guard interval adding section. can be

Alternatively, a device on the transmitting side can perform IFFT processing by switching between the number of points corresponding to the guard interval length of the data symbol and the number of points corresponding to the guard interval length of the pilot symbol; a guard interval addition unit capable of performing guard interval addition processing by switching between the guard interval ratio and the guard interval ratio of the pilot symbol, and sharing the IFFT unit and the guard interval addition unit for data symbols and pilot symbols It may be configured to generate a symbol.

Also, the device on the receiving side in the above system can be realized by various configurations.
For example, a device on the receiving side includes a transmission channel estimator for estimating transmission channel characteristics for the same number of subcarriers as data symbols, based on pilot symbols included in a received signal, and the transmission channel estimator receives input a first interpolation unit that performs symbol-direction interpolation on the pilot symbols obtained from the input signal; and a second interpolation unit that performs interpolation in the frequency direction on the result of the upsampling unit, and outputs the result of the second interpolation unit as an estimated value of transmission path characteristics. can be

According to the present invention, it is possible to achieve both improvement in multipath resistance and improvement in transmission efficiency.

1 is a diagram showing a configuration example of a transmitting device in a data transmission system according to an embodiment of the present invention; FIG. 2 is a diagram showing a configuration example of a receiving device corresponding to the transmitting device in FIG. 1; FIG. 3 is a diagram showing a configuration example of a transmission path estimator in the receiving-side apparatus of FIG. 2; FIG. FIG. 4 is a diagram showing an output example of a symbol direction primary interpolation unit of the channel estimation unit in FIG. 3; FIG. 4 is a diagram showing an output example of a 0-inserted up-sampling unit of the channel estimation unit in FIG. 3; FIG. 4 is a diagram showing an output example of a frequency interpolation filter unit of the channel estimation unit in FIG. 3; FIG. 4 is a diagram for explaining the transmission efficiency of a conventional frame format; FIG. 4 is a diagram for explaining the transmission efficiency of a conventional frame format; FIG. 4 is a diagram for explaining the transmission efficiency of the frame format of the system of the present invention;

A data transmission system according to an embodiment of the present invention will be described with reference to the drawings.
Here, before describing the specific configuration of the data transmission system of this example, the frame format of the system of the present invention will be described.

As described above, when pilot carriers are arranged at an interval of one for every four subcarriers, even if the symbol length of the pilot symbols remains 1, the delay time is up to 1/4 of the symbol length. can estimate the channel characteristics correctly. Therefore, for example, as shown in FIG. 5C, pilot symbols have a symbol length of 1 and a guard interval ratio of 1/4, and data symbols have a symbol length of 2 and a guard interval ratio of 1/8. By doing so, it is possible to achieve both an improvement in multipath resistance and an improvement in transmission efficiency.

In the following, frame format optimization is generally expressed using mathematical formulas.
First, determine the maximum multipath delay time _Tdelay that the system can handle, and the data symbol length _TDS that allows the time variation of the transmission path characteristics for one symbol time to be considered constant.

In this case, in order to avoid inter-symbol interference between data symbols and pilot symbols, the data symbol guard interval length T _{DS_GI} and the pilot symbol guard interval length T _{PS_GI} are set as shown in the following (Equation 1) and (Equation 2). and T _delay or longer.
T _{DS_GI} ≧T _delay (Formula 1)
T _{PS_GI} ≧T _delay (Formula 2)

Therefore, the guard interval ratio _{RDS_GI} of data symbols is as shown in (Equation 3) below.
R _{DS_GI} =T _{DS_GI} /T _DS (Formula 3)

Next, as shown in (Equation 4) below, by setting the pilot symbol length T _PS to T _delay or more, it is possible to accurately estimate channel fluctuations due to multipath delay times of T _delay or less. Become.
In addition, in a system using a plurality of transmission antennas, it is necessary to provide orthogonal pilot signals for each of the transmission antennas. Therefore, when subcarriers are used to separate pilot signals, if the number of antennas is N, as shown in the following (Equation 5), by setting the pilot symbol length T _PS to N times or more of T _delay , the same can be estimated to

[Single antenna]
T _PS ≧T _delay (Formula 4)
[Multiple antennas]
T _PS ≧N×T _delay (Formula 5)

Therefore, the pilot symbol guard interval ratio R _{PS_GI} is as shown in (Equation 6) below.
R _{PS_GI} =T _{PS_GI} /T _PS (Formula 6)

A frame format with high transmission efficiency can be obtained by determining the symbol length and guard interval length of each of the pilot symbols and data symbols according to the above equations.

For example, by setting the pilot symbol length to 1024 samples, the data symbol length to 2048 samples, the pilot symbol guard interval ratio to 1/4, and the data symbol guard interval ratio to 1/8, the delay wave corresponding to 256 samples can be obtained. Correct demodulation becomes possible. As a result, the frame format of FIG. 5C (the method of the present invention) has the same long-delay multipath resistance as the frame format of FIG. 5B (the conventional method), while improving the transmission efficiency by about 12%.

Next, a specific configuration of the data transmission system of this example will be described.
FIG. 1 shows a configuration example of a transmitting device (transmitting wireless transmission device) in a data transmission system according to an embodiment of the present invention, and FIG. (wireless transmission device) is shown.

The transmitting side device shown in FIG. , IFFT section 106 , guard interval adding section 107 , signal selection section 108 , frame timing generation section 109 , frequency conversion section 110 and transmission antenna 111 .

First, generation of data symbols will be described.
In the transmission side apparatus, the transmission code generator 101 performs processing such as error correction coding on the information bits input from the outside to generate a transmission code sequence. The generated transmission code sequence is input to mapping section 102 , mapped onto the complex plane by a modulation method such as 64QAM (Quadrature Amplitude Modulation) or 1024QAM, and input to IFFT section 103 .

The IFFT section 103 performs IFFT processing on the input frequency domain signal to convert it into a time domain signal, and inputs it to the guard interval adding section 104 . The number of points used for IFFT is the number of points that can obtain the data symbol length T _DS described above. The guard interval adding section 104 cyclically adds the latter half of the input time domain signal to the front side and inputs it to the signal selecting section 108 . The ratio of signals to be cyclically added is assumed to be the guard interval ratio R _{DS_GI} described above. The above processing is processing related to the generation of data symbols.

Next, generation of pilot symbols will be described.
Pilot symbols are generated by pilot symbol generation section 105 using a complex signal with known amplitude and phase as a carrier. The generated pilot signal is input to IFFT section 106, where IFFT processing is performed to transform the signal in the frequency domain into a signal in the time domain. The number of points to be used for IFFT is the number of points from which the previously described pilot symbol length T _PS can be obtained. Guard interval addition section 107 cyclically adds the latter half of the input time domain signal to the front side, and inputs it to signal selection section 108 . The ratio of signals to be cyclically added is assumed to be the guard interval ratio R _{PS_GI} described above. The above processing is processing related to the generation of pilot symbols.

In addition to data symbols and pilot symbols, signal selection section 108 receives a timing signal for selecting data symbols or pilot symbols from frame timing generation section 109 . Signal selection section 108 selects a data symbol or pilot symbol signal according to the timing signal, and outputs it to frequency conversion section 110 .

Here, in the above description, two types of IFFT units 103 and 106 using different numbers of points and two types of guard interval adding units 104 and 107 using different guard interval ratios are provided. is switched by the signal selection unit 108, the present invention is not limited to this. That is, for example, an IFFT unit having a function of switching the number of points and a guard interval addition unit having a function of switching the guard interval ratio are provided, and the number of points and the guard interval ratio are provided according to whether data symbol generation or pilot symbol generation is performed. may be configured to switch between

The OFDM signal generated by the above processing is converted to an RF (Radio Frequency) band frequency by the frequency conversion unit 110, and is sent to space from the transmission antenna 111 as radio waves.

The receiving device shown in FIG. 2 includes a receiving antenna 201, a frequency inverse transform unit 202, a frame timing detection unit 203, a signal selection unit 204, an FFT (Fast Fourier Transform) unit 205, and a delay unit. 206 , FFT section 207 , transmission path estimation section 208 , equalization section 209 and decoding section 210 .

In the receiving device, the signal received by the receiving antenna 201 is converted from an analog signal to a digital signal via frequency inverse conversion section 202 that converts the RF frequency to a low frequency. The received digital signal thus obtained is input to frame timing detection section 203 and signal selection section 204 .

Frame timing detection section 203 detects frame timing using cross-correlation, auto-correlation, or the like, and signal selection section 204 outputs a timing signal indicating the symbol type of the current received signal (whether it is a data symbol or a pilot symbol). Output to Signal selection section 204 outputs the received signal input from frequency conversion section 202 to an output destination according to the symbol type according to the timing signal indicating the symbol type input from frame timing detection section 203 . In addition, FFT time windows are provided at appropriate time positions for output so that inter-symbol interference does not occur.

The data symbols are output from signal selection section 204 to FFT section 205, and subjected to FFT processing in FFT section 205 with the same number of points as the IFFT processing points of IFFT section 103. is converted to The converted signal is delayed by delay section 206 so as to have the same timing as the pilot symbol delay time by FFT section 207 and transmission path estimation section 208 , which will be described later, and is output to equalization section 209 .

On the other hand, the pilot symbols are output from signal selection section 204 to FFT section 207, and subjected to FFT processing in FFT section 207 with the same number of points as the IFFT processing points of IFFT section 106. is output to the transmission path estimation section 208 after being converted into a signal of . Although the details of the transmission path estimation unit 208 will be described later, the signal input from the FFT unit 207 is interpolated in the frequency direction and the time direction to estimate the transmission path, and the result of the transmission path estimation is sent to the equalization unit 209. to output

Equalization section 209 performs demodulation (equalization) processing on the received signal based on the result of channel estimation, and outputs the resulting signal to decoding section 210 . The decoding unit 210 performs decoding processing on the input signal and outputs the decoding result.

Next, the internal configuration of transmission path estimation section 208 will be described with reference to FIG. As shown in FIG. 3 , transmission path estimation section 208 has symbol direction primary interpolation section 301 , 0-insertion up-sampling section 302 , and frequency interpolation filter section 303 .

A pilot symbol is input from FFT section 207 to symbol direction primary interpolation section 301 . Symbol direction primary interpolation section 301 performs inter-symbol primary interpolation on input pilot symbols. FIG. 4A shows an output example (interpolation result in the symbol direction) of the symbol direction primary interpolation unit 301 . Although linear interpolation is used here, it is not limited to this, and interpolation in the symbol direction may be performed by other methods.

Since the first-order interpolated signal has a smaller number of subcarriers than data symbols, 0 insertion is performed by 0 insertion up-sampling section 302 in order to make the number of subcarriers for pilot symbols the same as the number of subcarriers for data symbols. Perform upsampling by FIG. 4B shows an output example (result of 0-insertion upsampling) of the 0-insertion upsampling section 302 .

After that, the up-sampled signal is interpolated in the frequency direction by the frequency interpolation filter section 303 to obtain the transmission channel estimation results for the same number of subcarriers as the data symbols. FIG. 4C shows an output example of the frequency interpolation filter unit 303 (interpolation result in the frequency direction). The transmission path estimation result thus obtained is output to equalization section 209 .

Through the above processing, transmission path characteristics for the same number of subcarriers as data symbols can be estimated. Therefore, by demodulating (equalizing) the received signal based on this transmission path characteristic, it is possible to appropriately restore the transmission data from the transmission side apparatus.

As described above, in this example, as a frame format used for data transmission, the symbol length (T _DS ) of the data symbol is longer than the symbol length (T _PS ) of the pilot symbol, and the guard of the pilot symbol It is characterized by using a format in which the data symbol guard interval ratio (R _{DS_GI} ) is smaller than the interval ratio (R _{PS_GI} ).

More specifically, the data symbol guard interval length (T _{DS_GI} ) and the pilot symbol guard interval length (T _{PS_GI} ) are both equal to or greater than the presumed multipath maximum delay time (T _delay ), and the data The symbol length (T _DS ) of the symbol is set to a length at which the time variation of the transmission path characteristics for one symbol time can be regarded as substantially constant, and the symbol length (T _PS ) of the pilot symbol is set to the maximum delay time (T _delay ) of the transmission antenna. It is equal to or greater than the value multiplied by the number (N).

In this way, by performing transmission using a frame having a format in which pilot symbols and data symbols have different symbol lengths, it is possible to improve both multipath resistance and transmission efficiency.

In the above embodiment (FIG. 1), the transmitting device includes IFFT section 103 that performs IFFT processing with the number of points (for example, 2048 samples) corresponding to the guard interval length of the data symbol, and the guard interval ratio of the data symbol. (e.g., 1/8), guard interval addition section 104 performs guard interval addition processing, IFFT section 106 performs IFFT processing with the number of points corresponding to the guard interval length of the pilot symbol (e.g., 1024 samples), and pilot A guard interval addition section 107 is provided for performing guard interval addition processing at a symbol guard interval ratio (for example, 1/4). IFFT section 103 and guard interval adding section 104 are used to generate data symbols, and IFFT section 106 and guard interval adding section 107 are used to generate pilot symbols. Note that this configuration is merely an example, and the transmitting device may be implemented with other configurations.

For example, an IFFT unit capable of performing IFFT processing by switching the number of points corresponding to the guard interval length of the data symbol and the number of points corresponding to the guard interval length of the pilot symbol, and the guard of the data symbol. and a guard interval addition unit capable of performing guard interval addition processing by switching between the interval ratio and the guard interval ratio of the pilot symbol. Then, the IFFT section and the guard interval adding section may be configured to be shared for data symbol generation and pilot symbol generation.

Further, in the above-described embodiments (FIGS. 2 and 3), the receiving apparatus has a transmission path estimation unit that estimates the transmission path characteristics for the same number of subcarriers as the data symbols, based on the pilot symbols included in the received signal. 208. Then, transmission path estimation section 208 performs symbol-direction interpolation on the input pilot symbols, and performs symbol-direction primary interpolation section 301 on the result so that the number of subcarriers is the same as that of data symbols. 0-insertion up-sampling section 302 for up-sampling, and frequency interpolation filter section 303 for performing interpolation on the result in the frequency direction. It is configured to output as It should be noted that this configuration is merely an example, and the receiving-side device may be realized with another configuration.

Although the present invention has been described in detail above, it is needless to say that the present invention is not limited to the above embodiments, and can be widely applied to applications other than those described above.
Further, the present invention can also be provided as, for example, a method or system for executing the above processes, a program for realizing such a method or system, a storage medium for storing the program, or the like.

INDUSTRIAL APPLICABILITY The present invention can be used in data transmission systems that transmit data using frames containing data symbols and pilot symbols.

101: Transmission code generation unit 102: Mapping unit 103: IFFT unit 104: Guard interval addition unit 105: Pilot symbol generation unit 106: IFFT unit 106 107: Guard interval addition unit 108: Signal selection unit 109: Frame timing generator 110: Frequency converter 111: Transmitting antenna
201: Receiving antenna 202: Inverse frequency converter 203: Frame timing detector 204: Signal selector 205: FFT unit 206: Delay unit 207: FFT unit 208: Transmission channel estimator 209: etc. decryption unit, 210: decryption unit,
301: symbol-direction first-order interpolation unit, 302: 0-insertion up-sampling unit, 303: frequency interpolation filter unit

Claims (5)

In a data transmission system that transmits data using frames containing data symbols and pilot symbols,
The frame has a format in which the symbol length of the data symbol is longer than the symbol length of the pilot symbol and the guard interval ratio of the data symbol is smaller than the guard interval ratio of the pilot symbol ,
Both the guard interval length of the data symbol and the guard interval length of the pilot symbol are equal to or greater than the presumed maximum multipath delay time,
The symbol length of the data symbol is a length that can be regarded as a substantially constant time variation of the transmission path characteristics for one symbol time,
A data transmission system , wherein a symbol length of a pilot symbol is equal to or greater than a value obtained by multiplying the maximum delay time by the number of transmission antennas . The data transmission system according to claim 1 ,
A device on the transmitting side includes a first IFFT section that performs IFFT processing with the number of points corresponding to the guard interval length of the data symbol, and a first guard interval addition section that performs guard interval addition processing with the guard interval ratio of the data symbol. and a second IFFT unit that performs IFFT processing with the number of points corresponding to the guard interval length of the pilot symbol, and a second guard interval addition unit that performs guard interval addition processing with the guard interval ratio of the pilot symbol, Data symbols are generated using the first IFFT section and the first guard interval adding section, and pilot symbols are generated using the second IFFT section and the second guard interval adding section. data transmission system. The data transmission system according to claim 1 ,
An IFFT unit that enables a transmitting device to perform IFFT processing by switching between the number of points corresponding to the guard interval length of data symbols and the number of points corresponding to the guard interval length of pilot symbols, and the guard interval of data symbols. and a guard interval addition unit capable of performing guard interval addition processing by switching between the ratio and the guard interval ratio of the pilot symbol, and sharing the IFFT unit and the guard interval addition unit to add data symbols and pilot symbols. A data transmission system characterized by generating In the data transmission system according to any one of claims 1 to 3 ,
A device on the receiving side comprises a transmission channel estimator for estimating transmission channel characteristics for the same number of subcarriers as data symbols, based on pilot symbols contained in the received signal,
The transmission path estimation unit includes: a first interpolation unit that performs symbol-direction interpolation on the input pilot symbols; and a second interpolation unit for performing interpolation in the frequency direction on the result of the upsampling unit, and transmitting the result of the second interpolation unit. A data transmission system characterized by outputting estimated values of path characteristics. In a data transmission method for transmitting data using frames containing data symbols and pilot symbols,
The frame has a format in which the symbol length of the data symbol is longer than the symbol length of the pilot symbol and the guard interval ratio of the data symbol is smaller than the guard interval ratio of the pilot symbol ,
Both the guard interval length of the data symbol and the guard interval length of the pilot symbol are equal to or greater than the presumed maximum multipath delay time,
The symbol length of the data symbol is a length that can be regarded as a substantially constant time variation of the transmission path characteristics for one symbol time,
A data transmission method , wherein a symbol length of a pilot symbol is equal to or greater than a value obtained by multiplying the maximum delay time by the number of transmission antennas .

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