JP2016123100A - Transmitter and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for reducing power consumption at the time of transmitting a pilot signal, by calculating transmission path response at a high frequency.SOLUTION: A transmitter includes an OFDM modulation unit 13 including a pilot signal insertion unit 136 for inserting a significant pilot signal and a no-signal pilot signal into first and second transmission signals; inserting the significant pilot signal, a code-inverted pilot signal, and the no-signal pilot signal into third and fourth transmission signals; inserting the no-signal pilot signal into the first and third transmission signals at the same predetermined position; inserting the no-signal pilot signal into the second and fourth transmission signals at a position differing from the same predetermined position; and inserting the significant pilot signal and the code-inverted pilot signal into the third and fourth transmission signals so that the signals are arranged alternately with respect to time and frequencies.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a transmission apparatus and a reception apparatus in a transmission system that performs MIMO (Multi Input Multi Output) transmission using a plurality of OFDM (Orthogonal Frequency Division Multiplexing) signals in the same frequency band.

  Conventionally, when a transmission path response of one OFDM signal is estimated for a plurality of OFDM signals transmitted in the same frequency band, a transmission path response is estimated with no pilot signal of another OFDM signal being used. Is known (see, for example, Patent Document 1). In this specification, this method is referred to as a null pilot method. Further, there is known a method for estimating a transmission path response by inverting the sign of a pilot signal to make the pilot signal orthogonal (see, for example, Patent Document 2). In this specification, this method is referred to as a code-inverted pilot method.

  An example of an OFDM signal transmission system in which the number of transmission antennas of the transmission apparatus is two and the number of reception antennas of the reception apparatus is two or more and two OFDM signals are transmitted in the same frequency band is taken as an example. The pilot signal pattern of the method will be described with reference to FIGS. 18 to 21 show only the minimum unit of repetition of the pilot signal in the OFDM symbols, and non-pilot signals such as data signals are omitted. Pattern 1 shows a pilot signal pattern of an OFDM signal transmitted from one transmission antenna, and pattern 2 shows a pilot signal pattern of an OFDM signal transmitted from the other transmission antenna. In the OFDM symbol in the figure, the right direction is the carrier (frequency) direction, and the downward direction is the symbol (time) direction.

  FIG. 18 is a diagram illustrating a pilot signal pattern when a null pilot scheme is applied in a system that transmits two OFDM signals in the same frequency band. Squares in the figure indicate pilot signals having a certain significant value, and circles indicate non-signal pilot signals. In FIG. 19, the position of the transmission line response obtained directly (that is, not by interpolation) from the pilot signal of FIG. 18 is indicated by a hatched circle. In this specification, the pilot signal at symbol number s and carrier number c is represented as P (s, c). In the null pilot scheme, the transmission path response at the positions P (1,1) and P (2,2) is obtained in the pattern 1 in FIG. 18, and P (1,2), P (2,2) in the pattern 2 in FIG. The transmission line response at the position 1) is obtained. In the null pilot scheme, the power consumption used for transmission can be set to zero in a section in which the pilot signal is not a signal.

FIG. 20 is a diagram showing a pilot signal pattern of an OFDM signal in the code inversion pilot scheme. A square in the figure indicates a pilot signal having a certain significant value, a circle indicates a pilot signal without a signal, and 1 and −1 marked in the square mean that the pilot signal has an inverted sign. In FIG. 21, the position of the transmission line response directly obtained from the pilot signal of FIG. 20 is indicated by a hatched circle. In this specification, the received signal of the pilot signal P (s, c) is represented as Rx (s, c). In the sign inversion pilot method, for example, the transmission path response at the positions of points P1 and P2 in the figure is obtained by the following equation when the amplitude value of the pilot signal is 1.
P1: (Rx (1,1) + Rx (1,2)) / 2
P2: (Rx (1,1) -Rx (1,2)) / 2

  When two OFDM signals are transmitted in the same frequency band, in the null pilot system, 1/2 of the pilot signal becomes no signal, so the power consumption used for transmitting the pilot signal becomes 1/2, and transmission obtained directly The frequency of the road response is also halved. In the sign-inverted pilot scheme, since there is no pilot signal that becomes no signal, power consumption used for transmission of the pilot signal does not decrease, but a transmission path response can be obtained with high frequency.

JP 2004-96186 A Japanese Patent No. 4336281

  The problems of the null pilot scheme and the code-inverted pilot scheme when the number of OFDM signals transmitted in the same frequency band is greater than two will be described. Here, a case will be described in which the number of transmission antennas of the transmission device is four and the number of reception antennas of the reception device is four or more, and four OFDM signals are transmitted in the same frequency band.

  FIG. 22 is a diagram illustrating a pilot signal pattern when a null pilot scheme is applied in a system that transmits four OFDM signals in the same frequency band. 22A shows an example in which pilot signals having a significant value are arranged linearly in the symbol direction, and FIG. 22B shows an example in which pilot signals having a significant value are arranged linearly in the carrier direction. FIG. 22C shows an example in which pilot signals having significant values are arranged obliquely. In addition, the position of the transmission line response directly obtained from the pilot signal is indicated by a hatched circle. In FIG. 22A, pilot signals are inserted in different carriers of four OFDM signals, and other OFDM signals are non-signaled in a section in which one OFDM signal is transmitting a pilot signal. Therefore, the transmission line response can be obtained at the insertion position of the pilot signal having a significant value without performing any special calculation. Similarly, in FIGS. 22B and 22C, the transmission path response is obtained at the insertion position of the pilot signal having a significant value. In other words, in FIG. 22, four transmission path responses are directly obtained in a 4 symbol × 4 carrier section, and the power consumption used for pilot signal transmission is ¼.

  As described above, when the null pilot scheme is applied, the power consumption used for transmission of the pilot signal is suppressed to ¼. However, there is a problem that the number of transmission line responses directly obtained in 4 symbols × 4 carrier sections for each OFDM signal is only four, and the estimation frequency of transmission line responses is low.

  FIG. 23 is a diagram illustrating a pilot signal pattern when a code-inverted pilot scheme is applied in a system that transmits four OFDM signals in the same frequency band. In the pilot signal shown in FIG. 23, the transmission line response is obtained by performing addition / subtraction of the pilot signal in the 4-symbol section for each carrier. The position of the transmission line response directly obtained from the pilot signal is indicated by a hatched circle.

FIG. 23A shows an example in which pilot signals with inverted codes are arranged linearly in the symbol direction, and FIG. 23B shows an example in which pilot signals with inverted codes are arranged linearly in the carrier direction. is there. In FIG. 23A, the transmission line responses at points P1 to P4 are obtained by the following equations.
P1: (Rx (1,1) + Rx (1,2) + Rx (1,3) + Rx (1,4)) / 4
P2: (Rx (1,1) + Rx (1,2) -Rx (1,3) -Rx (1,4)) / 4
P3: (Rx (1,1) -Rx (1,2) -Rx (1,3) + Rx (1,4)) / 4
P4: (Rx (1,1) -Rx (1,2) + Rx (1,3) -Rx (1,4)) / 4
In FIGS. 23 (a) and 23 (b), the number of transmission line responses directly obtained in 4 symbols × 4 carrier sections for each OFDM signal is eight.

  FIG. 23C is an example in which pilot signals with inverted signs are arranged in an oblique direction, and FIG. 23D is an example in which pilot signals with inverted signs are arranged in a vertical, horizontal, and diagonal direction. In FIGS. 23C and 23D, the number of transmission path responses directly obtained in 4 symbols × 4 carrier sections is 16 for each OFDM signal. As described above, when the code-inverted pilot method is applied, the number of transmission line responses directly obtained in 4 symbols × 4 carrier sections is 16 in the example of FIGS. 23C and 23D, and the transmission line responses are obtained with high frequency. However, there is a problem that power consumption used for transmission of pilot signals cannot be reduced.

  In order to solve the above problems, an object of the present invention is to provide an OFDM signal transmitting apparatus and receiving apparatus capable of obtaining a transmission path response at a high frequency and reducing power consumption used for transmitting a pilot signal. It is to provide.

  In order to solve the above problems, a transmission apparatus according to the present invention is a transmission apparatus that transmits four OFDM signals from four transmission antennas, and inserts pilot signals having different patterns into the four types of transmission signals. A pilot signal insertion unit that generates four types of OFDM symbols; and an OFDM signal generation unit that generates four patterns of OFDM signals by modulating each carrier of the four types of OFDM symbols, and the pilot signal insertion unit includes: Inserting a pilot signal having a significant value and a non-signal pilot signal with respect to the first and second transmission signals, and having a significant value with respect to the third and fourth transmission signals, Inserting a pilot signal obtained by inverting the sign of the pilot signal having a significant value and a non-signal pilot signal, the first and the third The no-signal pilot signal is inserted at the same predetermined position with respect to the transmission signal, and the no-signal pilot signal is inserted at a position different from the same predetermined position with respect to the second and fourth transmission signals. The pilot signal having the significant value and the pilot signal having the sign of the pilot signal having the significant value inverted with respect to the third and fourth transmission signals are temporally and frequency alternately. It is inserted so that it may be arrange | positioned.

  In order to solve the above-described problem, a receiving apparatus according to the present invention is a receiving apparatus that receives four OFDM signals transmitted from the above-described transmitting apparatus using four receiving antennas, and the received four OFDM signals. An OFDM demodulator is provided that demodulates the signal and estimates a baseband signal and transmission path response corresponding to each receiving antenna.

  According to the present invention, in a transmission system using a plurality of OFDM signals in the same frequency band, a transmission path response can be obtained with high frequency, and power consumption used for transmitting a pilot signal can be reduced. .

It is a block diagram which shows the structure of the transmitter which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the OFDM modulation part in the transmitter which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the receiver which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the OFDM demodulation part in the receiver which concerns on Example 1 of this invention. It is a figure which shows the 1st pilot signal pattern in the code inversion type | mold null pilot system which concerns on this invention. It is a figure which shows the 2nd pilot signal pattern in the code inversion type | mold null pilot system which concerns on this invention. It is a figure which shows the 3rd pilot signal pattern in the code inversion type | mold null pilot system which concerns on this invention. It is a figure which shows the 4th pilot signal pattern in the code inversion type | mold null pilot system which concerns on this invention. It is a figure which shows the 5th pilot signal pattern in the code inversion type | mold null pilot system which concerns on this invention. It is a figure which shows the 6th pilot signal pattern in the code inversion type | mold null pilot system which concerns on this invention. It is a figure which shows arrangement | positioning of the pilot signal of the code inversion type | mold null pilot system which concerns on this invention. It is a figure which shows arrangement | positioning of the pilot signal in terrestrial digital broadcasting. FIG. 12 is a diagram showing an example in which the pilot signal pattern shown in FIG. 9 is applied to the pilot signal arrangement shown in FIG. 11. It is a block diagram which shows the structure of the transmitter which concerns on Example 2 of this invention. It is a block diagram which shows the structure of the receiver which concerns on Example 2 of this invention. It is a block diagram which shows the structure of the OFDM demodulation part in the receiver which concerns on Example 2 of this invention. It is a block diagram which shows the structure of the receiver which concerns on Example 3 of this invention. It is a figure which shows the pilot signal pattern at the time of applying a null pilot system in the system which transmits two OFDM signals in the same frequency band. It is a figure which shows the position of the transmission line response calculated | required with the pilot signal of FIG. It is a figure which shows the pilot signal pattern at the time of applying a code inversion type pilot system in the system which transmits two OFDM signals in the same frequency band. It is a figure which shows the position of the transmission line response calculated | required with the pilot signal of FIG. It is a figure which shows the pilot signal pattern at the time of applying a null pilot system in the system which transmits four OFDM signals in the same frequency band. It is a figure which shows the pilot signal pattern at the time of applying an inverting pilot system in the system which transmits four OFDM signals in the same frequency band.

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

  In the first embodiment, a system that performs 4 × 4 MIMO transmission will be described. The transmission apparatus in this system transmits an OFDM signal to one transmission station, and performs MIMO transmission by SDM from four transmission antennas at one transmission station. The receiving device in this system performs SDM MIMO reception using four receiving antennas.

[OFDM Signal Transmitting Apparatus According to Embodiment 1]
An OFDM signal transmission apparatus according to the first embodiment will be described. FIG. 1 is a block diagram illustrating a configuration of an OFDM signal transmission apparatus according to the first embodiment. As illustrated in FIG. 1, the transmission device 1a includes an error correction encoding unit 10 (10-1 to 10-4), a carrier modulation unit 11 (11-1 to 11-4), and an OFDM modulation unit 13. Prepare. The input signal to the transmission device 1a is assumed to be four systems of TS (Transport Stream) signals (TS1 to TS4). Note that a TS dividing device or the like may be arranged before the input of the transmission device 1a, and a TS signal after dividing one system TS into four systems may be input to the transmission device 1a. The transmission device 1 a outputs four OFDM signals in four systems, and the four OFDM signals are sent to one transmission station 14.

  The transmitting station 14 performs MIMO transmission by SDM from the antennas AT-tx1 to AT-tx4.

  The error correction coding unit 10 performs error correction coding on the TS signal and outputs it to the carrier modulation unit 11. For error correction, for example, a BCH code is used as an outer code, and an LDPC (Low Density Parity Check) code is used as an inner code.

  The carrier modulation unit 11 performs mapping on the IQ plane according to a predetermined modulation method for each subcarrier, and outputs the result to the OFDM modulation unit 13.

  The OFDM modulation unit 13 generates four systems of four OFDM signals from the four types of transmission signals (a 1, a 2, b 1, b 2) input from the carrier modulation unit 11 and transmits them to the transmitting station 14. FIG. 2 is a block diagram illustrating a configuration of the OFDM modulation unit 13. As shown in FIG. 2, the OFDM modulation unit 13 includes a pilot signal insertion unit 136 and an OFDM signal generation unit 137.

  The pilot signal insertion unit 136 inserts pilot signals having different patterns into the four types of transmission signals (a1, b1, a2, b2) input from the carrier modulation unit 11 to generate four types of OFDM symbols. Pilot signal insertion section 136 includes pilot signal generation section 130 and OFDM symbol configuration section 131 (131-1 to 131-4).

  Pilot signal generation section 130 generates a pilot signal and outputs it to OFDM symbol configuration section 131 in order to insert a pilot signal having a predetermined amplitude and phase at a predetermined position.

  OFDM symbol configuration section 131 inserts and arranges pilot signals input from pilot signal generation section 130 with respect to the four types of transmission signals (a1, b1, a2, b2) input from carrier modulation section 11. As a result, an OFDM symbol is generated and output to the IFFT unit 132.

[Pilot signal pattern and arrangement]
Here, the pattern and arrangement of pilot signals inserted by the pilot signal insertion unit 136 will be described. In this specification, the pilot signal transmission method according to the present invention is referred to as a code-inverted null pilot method. 5 to 10 are diagrams showing examples of pilot signal patterns in the code-inverted null pilot scheme according to the present invention. 5 to 10, the non-pilot signal such as a data signal is omitted, only the minimum unit of the pilot signal repetition is shown, and the position of the transmission line response directly obtained from the pilot signal is indicated by a hatched circle. Patterns 1 to 4 show the arrangement of pilot signals of OFDM signals transmitted from different transmission antennas among the transmission antennas AT-t1 to AT-t4. In the figure, a pilot signal indicated by a square means a signal having a certain significant value, and a pilot signal indicated by a circle means no signal. Further, the pilot signal indicated by 1 and the pilot signal indicated by -1 mean that the signals are inverted in sign. In the OFDM symbol in the figure, the right direction is the carrier (frequency) direction, and the downward direction is the symbol (time) direction. 5 to 7 show examples in which no signal pilot signals are arranged in the symbol direction, and FIGS. 8 and 9 show examples in which no signal pilot signals are arranged obliquely. FIG. 10 shows an example in which the pattern of the pilot signal of the first symbol is changed with respect to the pilot signal pattern of FIG. 5, and patterns 2 and 4 can estimate a transmission path response denser in the carrier direction than patterns 1 and 3.

  Although not shown, pilot signal generation section 130 may arrange a no-signal pilot signal in the carrier direction. The pilot signal pattern in this case is a pattern obtained by inverting the symbol direction and the carrier direction with respect to the patterns shown in FIGS.

  In this way, the pilot signal insertion unit 136 inserts a pilot signal having a significant value and a non-signal pilot signal with respect to the first transmission signal and the second transmission signal, and the third transmission signal and For the fourth transmission signal, a pilot signal having a significant value, a pilot signal obtained by inverting the sign of the pilot signal having the significant value, and a non-signal pilot signal are inserted. For the first transmission signal and the third transmission signal, a no-signal pilot signal is inserted at the same position, and for the second transmission signal and the fourth transmission signal, the first transmission signal is transmitted. A no-signal pilot signal is inserted at a position different from the position where the no-signal pilot signal is inserted into the signal and the third transmission signal.

  The first to fourth transmission signals are any of the four types of transmission signals (a1, b1, a2, b2) input from the carrier modulation unit 11. 5 to 10, the pilot signal insertion pattern for the first transmission signal is shown as pattern 1, the pilot signal insertion pattern for the second transmission signal is shown as pattern 2, and the pilot signal insertion for the third transmission signal is shown. The pattern is shown as pattern 3, and the pilot signal insertion pattern for the fourth transmission signal is shown as pattern 4.

  As shown in FIGS. 5 to 9, the pilot signal insertion unit 136 further sets half of the pilot signals to be inserted as non-signal pilot signals for the four types of transmission signals, When a pilot signal is inserted so that the number of pilot signals having a significant value and the number of pilot signals obtained by inverting the sign of the pilot signal having a significant value with respect to the fourth transmission signal are equal, The positions at which are directly obtained are uniform and suitable. In addition, as shown in FIG. 9, the pilot signal having a significant value and the pilot signal obtained by inverting the sign of the pilot signal having a significant value with respect to the third transmission signal and the fourth transmission signal. May be inserted alternately in time and frequency.

  FIG. 11 is a diagram illustrating an arrangement of pilot signals of the code-inverted null pilot scheme. The hatched portion in the figure indicates the pilot signal arrangement position, and the white portion indicates the non-pilot signal arrangement position. The non-pilot signal may be only a data signal, or may include a TMCC signal indicating control information and an AC signal indicating additional information in addition to the data signal. The pilot signals are arranged in a grid pattern as shown in FIG. 11 (a), arranged in a staggered pattern as shown in FIG. 11 (b), or arranged obliquely as shown in FIG. 11 (c). Is preferred. FIG. 11 shows a case where the arrangement interval of pilot signals in the symbol direction / carrier direction is narrow. As the arrangement interval of the pilot signal in the symbol direction / carrier direction becomes wider, the ratio of the pilot signal to the entire signal can be reduced (the transmission efficiency of the data signal can be increased), but the position where the transmission path response is directly obtained decreases. On the other hand, as the interval between the pilot signals in the symbol direction and the carrier direction becomes narrower, the ratio of the pilot signal to the whole signal increases (the transmission efficiency of the data signal decreases), but the position where the transmission line response is directly obtained may be increased. it can.

  In terrestrial digital broadcasting, a scattered pilot (SP) signal is used as a pilot signal. FIG. 12 is a diagram showing the arrangement of SP signals in terrestrial digital broadcasting. FIG. 12 is an example of an example in which the pilot signals illustrated in FIG. 11C are arranged obliquely, and pilot signals are inserted once in 12 carriers and once in 4 symbols. FIG. 13 is a diagram showing an example in which the pilot signal pattern shown in FIG. 9 is applied to the pilot signal arrangement shown in FIG.

  The OFDM signal generation unit 137 generates four OFDM signals by modulating each carrier of the OFDM symbol input by the pilot signal insertion unit 136, and transmits four transmission antennas AT-Tx 1 to AT− via the transmission station 14. Output to Tx4. The OFDM signal generation unit 137 includes an IFFT unit 132 (132-1 to 132-4), a GI addition unit 133 (133-1 to 133-4), and an orthogonal modulation unit 134 (134-1 to 134-4). , D / A converter 135 (135-1 to 135-4). In order to synchronize the four OFDM signals, the OFDM signal generation unit 137 supplies a clock with the same frequency to each block.

  The IFFT unit 132 performs an IFFT (Inverse Fast Fourier Transform) process on the OFDM symbol input from the OFDM symbol configuration unit 131 to generate a time-domain effective symbol signal, and a GI addition unit 133 Output to.

  The GI adding unit 133 inserts a guard interval obtained by copying the second half of the effective symbol signal at the head of the effective symbol signal input from the IFFT unit 132 and outputs the guard interval to the quadrature modulation unit 134. The guard interval is inserted in order to reduce intersymbol interference when receiving an OFDM signal, and is set so that the delay time of the multipath delay wave does not exceed the guard interval length.

  The orthogonal modulation unit 134 performs orthogonal modulation processing on the baseband signal input from the GI addition unit 133 to generate an OFDM signal, and outputs the OFDM signal to the D / A conversion unit 135.

  The D / A conversion unit 135 converts the OFDM signal input from the quadrature modulation unit 134 into an analog signal.

  As described above, the transmission apparatus 1a according to the first embodiment uses the pilot signal insertion unit 136, as shown in FIGS. 5 to 10, to have a pilot value having a significant value with respect to the first and second transmission signals. A pilot signal having a significant value, a pilot signal obtained by inverting the sign of the pilot signal having the significant value, and no signal. A pilot signal of a signal is inserted, a pilot signal of no signal is inserted at the same predetermined position with respect to the first and third transmission signals, and the same predetermined position with respect to the second and fourth transmission signals. A no-signal pilot signal is inserted at a different position. For this reason, in the 4 symbol × 4 carrier section, the transmission path response can be obtained at a high frequency, and the power consumption used for transmitting the pilot signal can be reduced. For example, for four types of transmission signals, half of the pilot signals to be inserted are non-signal pilot signals, and for the third and fourth transmission signals, the pilot signals having the significant values, and When inserting pilot signals so that the number of pilot signals with the sign of a significant pilot signal inverted is the same, 16 channel transmission line responses can be obtained directly (without interpolation). The power consumption used for pilot signal transmission can be halved.

  In addition, the pilot signal having the significant value and the pilot signal obtained by inverting the sign of the pilot signal having the significant value alternately with respect to the third and fourth transmission signals in terms of time and frequency. By inserting the signals so that they are arranged, the receiver uses only the pilot signal included in the single frequency (carrier) or the estimation of the channel response using only the pilot signal included in the single time (symbol). The transmission path response can be estimated, and the transmission path response according to the reception environment can be estimated. For example, in a mobile reception environment, since the transmission path response varies in the time direction, it is possible to estimate the transmission path with high accuracy by estimating the transmission path response using only the pilot signal included in a single time. In a non-moving reception environment, it is considered that there is little time variation of the transmission line response. For example, paying attention to a single frequency, the transmission line response is estimated using two pilot signals separated in the time direction. Thus, transmission path estimation with high accuracy is possible.

[OFDM Signal Receiving Device According to Embodiment 1]
Next, an OFDM signal receiving apparatus according to the first embodiment will be described. FIG. 3 is a block diagram illustrating the configuration of the OFDM signal receiving apparatus according to the first embodiment. As shown in FIG. 3, the OFDM signal receiver 2a includes an OFDM demodulator 20a, a MIMO detector 25, a carrier demodulator 22 (22-1 to 22-4), and an error correction decoder 23 (23- 1-23-4). The receiving device 2a receives four systems of four OFDM signals transmitted from the transmitting device 1a by four receiving antennas AT-rx1 to AT-rx4.

  The OFDM demodulator 20a demodulates four received OFDM signals to generate four types of baseband signals (c1, c2, c3, c4), and uses four types of transmission path responses (h1, h2, h3, h4) are estimated. FIG. 4 is a block diagram showing a configuration of the OFDM demodulator 20a. As shown in FIG. 4, the OFDM demodulator 20a includes an A / D converter 200 (200-1 to 200-4), an orthogonal demodulator 201 (201-1 to 201-4), and a GI remover 202 ( 202-1 to 202-4), FFT section 203 (203-1 to 203-4), pilot signal generation section 204, pilot signal extraction section 205 (205-1 to 205-4), and transmission path response An estimation unit 206 (206-1 to 206-4) and a transmission path response interpolation unit 207 (207-1 to 207-4) are provided.

  The A / D conversion unit 200 converts an analog reception signal input from the antenna AT-rx into a digital signal and outputs the digital signal to the quadrature demodulation unit 201.

  The orthogonal demodulation unit 201 generates a baseband signal for the signal input from the A / D conversion unit 200 and outputs the baseband signal to the GI removal unit 202.

  GI removal section 202 removes the guard interval from the signal input from quadrature demodulation section 201, extracts an effective symbol signal, and outputs it to FFT section 203.

  The FFT unit 203 performs FFT (Fast Fourier Transform) processing on the effective symbol signal input from the GI removal unit 202 to generate complex baseband signals c1 and c2, and a pilot signal extraction unit 205 Output to.

  Pilot signal generating section 204 generates a pilot signal having the same amplitude and phase as the pilot signal inserted by transmitting apparatus 1a, and outputs the position information of the pilot signal inserted by transmitting apparatus 1a to pilot signal extracting section 205. The amplitude value and phase value of the pilot signal are output to the transmission path response estimation unit 206.

  The pilot signal extraction unit 205 extracts a pilot signal from the complex baseband signals c1 and c2 input from the FFT unit 203 based on the position information input from the pilot signal generation unit 204, and sends it to the transmission path response estimation unit 206. Output.

Transmission path response estimation section 206 calculates a transmission path response using the pilot signal extracted by pilot signal extraction section 205. For example, the transmission path response at the positions of points P1 to P4 in FIG. 8 can be obtained by the following equation when the amplitude value of the pilot signal is 1.
P1: h1 = (Rx (1,1) + Rx (2,2)) / 2
P2: h2 = (Rx (1,2) + Rx (2,1)) / 2
P3: h3 = (Rx (1,1) −Rx (2,2)) / 2
P4: h4 = (Rx (1,2) −Rx (2,1)) / 2
Further, the transmission line response at the positions of points P1 to P4 in FIG. 9 is obtained by the following equation when the amplitude value of the pilot signal is 1.
P1: h1 = (Rx (1,1) + Rx (2,2)) / 2
P2: h2 = (Rx (2,1) + Rx (2,3)) / 2
P3: h3 = (Rx (1,1) −Rx (2,2)) / 2
P4: h4 = (Rx (2,1) −Rx (2,3)) / 2

  Transmission path response interpolation section 207 performs transmission path response interpolation processing based on part or all of the transmission path response calculated by transmission path response estimation section 206, and calculates transmission path responses for all subcarriers. .

  The MIMO detection unit 25 detects a MIMO signal using the baseband signal c and the transmission path response h input from the OFDM demodulation unit 20a. For detection of MIMO, known methods such as ZF (Zero Forcing), MMSE (Minimum Mean Squared Error), BLAST (Bell Laboratories Layered Space-Time), and MLD (Maximum Likelihood Detection) can be applied.

  The carrier demodulator 22 demodulates the signal input from the OFDM demodulator 20 a for each subcarrier and outputs the demodulated signal to the error correction decoder 23.

  The error correction decoding unit 23 performs error correction on the signal input from the carrier demodulation unit 22 and decodes the signal transmitted from the transmission device 1a.

  As described above, according to the receiving device 2a according to the first embodiment, the OFDM signal transmitted from the transmitting device 1a can be received by the four receiving antennas, and the received OFDM signal can be decoded.

  In current terrestrial digital television broadcasting, SFN (Single Frequency Network) is being constructed from the viewpoint of effective use of frequency, but the D / U (Desired to Undesired signal ratio) of SFN desired wave and SFN interference wave In the SFN interference area close to 0 dB, the transmission characteristics are deteriorated. In an OFDM signal transmission system using space-time coding (STC), transmission characteristics are improved in an SFN interference area where the D / U is near 0 dB, and the frequency can be effectively used. In the second embodiment, an OFDM signal transmission apparatus and reception apparatus using STC will be described. In the second embodiment, a system that performs 4 × 2 MIMO transmission will be described. The transmission apparatus in this system transmits OFDM signals to two transmission stations, and performs MIMO transmission by SDM from two transmission antennas at one transmission station. The receiving apparatus in this system performs SDM MIMO reception using two receiving antennas.

[OFDM Signal Transmitting Apparatus According to Second Embodiment]
An OFDM signal transmission apparatus according to the second embodiment will be described. FIG. 14 is a block diagram illustrating a configuration of an OFDM signal transmission apparatus according to the second embodiment. In addition, the same reference number is attached | subjected to the same component as the transmitter 1a of Example 1, and description is abbreviate | omitted suitably. As illustrated in FIG. 14, the transmission device 1b includes an error correction encoding unit 10 (10-1 and 10-2), a carrier modulation unit 11 (11-1 and 11-2), and a space-time encoding unit 12. (12-1 and 12-2) and an OFDM modulation unit 13. The input signal to the transmission device 1b is assumed to be two systems of TS signals (TS1, TS2). Note that a TS dividing device or the like may be arranged before the input of the transmission device 1b, and a TS signal after dividing one system TS into two systems may be input to the transmission device 1b. The transmitting apparatus 1b outputs four OFDM signals in two systems, the two OFDM signals are sent to the transmitting station 14-1, and the remaining two OFDM signals are sent to the transmitting station 14-2.

  The transmitting station 14-1 performs MIMO transmission by SDM from the antennas AT-tx1 and AT-tx2. The transmitting station 14-2 performs MIMO transmission by SDM from the antennas AT-tx3 and AT-tx4.

  Similar to the transmission apparatus 1a according to the first embodiment, the error correction coding unit 10 performs error correction coding on the TS signal, and the carrier modulation unit 11 performs mapping on the IQ plane according to a predetermined modulation method for each subcarrier. I do.

The space-time coding unit 12 performs space-time coding on the two systems of signals (a, b) input from the carrier modulation unit 11 and performs four types of space-time coding signals (a1, a2, b1, b2) is generated and output to the OFDM modulator 13. When Alamouti STBC (Space-Time Block Coding) is applied as space-time coding, the space-time coding unit 12-1 space-time codes (STBC coding) the complex baseband signal a to be transmitted, and a1 , A2, and the space-time encoding unit 12-2 performs space-time encoding (STBC encoding) on the complex baseband signal b to be transmitted, and outputs it as b1, b2. The value of the complex baseband signal to be transmitted is x1, x2, x3, x4 (where x ₁ = a (m), x ₂ = a (m + 1), x ₃ = b (m), x ₄ = b (m + 1) )), A1, a2, b1, b2 have the following values by STBC encoding.
a ₁ (m) = x ₁
a ₁ (m + 1) = − x ^* ₂
a ₂ (m) = x ₂
a ₂ (m + 1) = x ^* ₁
b ₁ (m) = x ₃
b ₁ (m + 1) = − x ^* ₄
b ₂ (m) = x ₄
b ₂ (m + 1) = x ^* ₃
Here, m represents a certain discrete time, and ^* represents a complex conjugate.

  The OFDM modulator 13 generates two systems of four OFDM signals from the four types of space-time encoded signals (a1, a2, b1, b2) input from the space-time encoder 12, 14-2. The transmitting stations 14-1 and 14-2 transmit MIMO-OFDM signals by SDM in the same frequency band. The configuration of the OFDM modulation unit 13 is as shown in FIG.

  As described above, the transmission apparatus 1b according to the second embodiment performs space-time coding on the two systems of signals, respectively, and generates a space-time coding unit 12 that generates four types of space-time coded signals. Is further provided. For this reason, it is possible to improve transmission characteristics in an SFN interference area where D / U is near 0 dB.

[OFDM Signal Receiving Device According to Second Embodiment]
Next, an OFDM signal receiving apparatus according to the second embodiment will be described. FIG. 15 is a block diagram illustrating a configuration of an OFDM signal receiving apparatus according to the second embodiment. In addition, the same reference number is attached | subjected to the same component as the receiver 2a of Example 1, and description is abbreviate | omitted suitably. As shown in FIG. 15, the OFDM signal receiver 2b includes an OFDM demodulator 20b, a space-time decoder 21, a carrier demodulator 22 (22-1 and 22-2), and an error correction decoder 23 (23 -1 and 23-2). The receiving device 2b receives two systems of four OFDM signals transmitted from the transmitting device 1b with two receiving antennas AT-rx1 and AT-rx2.

  The OFDM demodulator 20b demodulates the received two systems of four OFDM signals to generate two types of baseband signals (c1, c2), and uses two types of transmission path responses (h1, h2) using pilot signals. Is estimated. FIG. 16 is a block diagram showing a configuration of the OFDM demodulator 20b. As shown in FIG. 16, the OFDM demodulator 20b includes an A / D converter 200 (200-1 and 200-2), an orthogonal demodulator 201 (201-1 and 201-2), and a GI remover 202 ( 202-1 and 202-2), FFT section 203 (203-1 and 203-2), pilot signal generation section 204, pilot signal extraction section 205 (205-1 and 205-2), and transmission path response An estimation unit 206 (206-1 and 206-2) and a transmission path response interpolation unit 207 (207-1 and 207-2) are provided. The OFDM demodulator 20a according to the first embodiment demodulates four OFDM signals, whereas the OFDM demodulator 20b according to the second embodiment demodulates two OFDM signals. Since the processing contents of each processing block are the same as those of the OFDM demodulator 20a of the first embodiment, description thereof is omitted.

  The space-time decoding unit 21 includes complex baseband signals c1 and c2, input channel responses h11, h12, h13, and h14 (denoted as h1 in FIG. 15) and transmission channel responses h21 and h22 input from the OFDM demodulator 20b. , H23, h24 (denoted as h2 in FIG. 15), space-time decoding is performed to generate a space-time decoded signal. Hereinafter, a method for calculating the space-time decoded signal will be described.

である伝送路を通過し、ノイズｚ１，ｚ２が付加されたものと考えられる。よって、複素ベースバンド信号ｃ１，ｃ２は次式（１）で表される。 The complex baseband signals c1 and c2 that are input to the space-time decoding unit 21 are complex baseband signals a1, a2, b1, and b2 transmitted from the transmission device 1b, and have a transmission path response.

It is considered that noises z1 and z2 are added through the transmission line. Therefore, the complex baseband signals c1 and c2 are expressed by the following equation (1).

時刻ｍ＋１において伝送路応答が変化しないとすると、時刻ｍ＋１における入力c１，c２は次式（２）で表され、式(２)の両辺の複素共役をとると、次式（３）が導出される。

If the transmission line response does not change at time m + 1, the inputs c1 and c2 at time m + 1 are expressed by the following equation (2), and the following equation (3) is derived by taking the complex conjugate of both sides of equation (2). The

式(１)，(３)より、ＳＴＢＣの復号は、次式（４）を解いてｘ１，ｘ２，ｘ３，ｘ４を求めることに相当する。

From equations (1) and (3), STBC decoding is equivalent to finding x1, x2, x3, and x4 by solving the following equation (4).

  To solve equation (4), ZF (Zero Forcing), MMSE (Minimum Mean Squared Error), MLD (Maximum Likelihood Detection), etc. can be applied. When ZF is applied to the separation of four streams, the procedure is as follows. In Expression (4), the weight matrix W is defined by the following Expression (5).

式(５)の両辺に、左からウェイト行列Ｗを乗算すると、次式（６）が導出される。

When both sides of the equation (5) are multiplied by the weight matrix W from the left, the following equation (6) is derived.

式(６)の雑音成分を無視すると、ｘ１，ｘ２，ｘ３，ｘ４は次式（７）により求められる。

If the noise component of equation (6) is ignored, x1, x2, x3, and x4 are obtained by the following equation (7).

As described above, the space-time decoding unit 21 receives the complex baseband signals c1 and c2, the transmission path responses h11, h12, h13, and h14 and the transmission path responses h21, h22, h23, and h24 that are input from the OFDM demodulation unit 20b. Then, the space-time decoded signals x ₁ , x ₂ , x ₃ , x ₄ (that is, a (m), a (m + 1), b (m), b (m + 1)) are calculated by Equation (7).

  Note that, when SFBC (Space-Frequency Block Coding) is applied as space-time coding, encoding and decoding can be performed in the same procedure as STBC. In the description of STBC, m represents a certain discrete time, but SFBC can be applied by replacing m as representing a certain subcarrier number.

  The carrier demodulation unit 22 demodulates the signal input from the space-time decoding unit 21 for each subcarrier and outputs the demodulated signal to the error correction decoding unit 23.

  The error correction decoding unit 23 performs error correction on the signal input from the carrier demodulation unit 22, and decodes the signal transmitted from the transmission device 1b.

  Thus, according to the receiving device 2b, the OFDM signal transmitted from the transmitting device 1b is received by the two receiving antennas, the received OFDM signal is demodulated by the OFDM demodulating unit 20b, and the time-space decoding unit 21 Spatial decoding can be performed.

  Next, as a third embodiment, an OFDM signal transmission apparatus and reception apparatus constituting a 4 × 4 MIMO transmission system will be described. In this third embodiment, the transmitting apparatus is the same as that of the second embodiment, and the number of transmitting stations is two, and MIMO transmission by SDM is performed from two transmitting antennas at one transmitting station. The receiving apparatus performs SDM MIMO reception using four receiving antennas.

  The transmission apparatus according to the third embodiment is the same as the transmission apparatus 1b that performs 4 × 2 MIMO transmission illustrated in FIG. FIG. 17 is a block diagram illustrating the configuration of the receiving device 2c according to the third embodiment. Note that the same components as those of the receiving device 2b according to the second embodiment are denoted by the same reference numerals, and description thereof is omitted as appropriate. The receiving device 2c according to the third embodiment includes an OFDM demodulator 20a, a space-time decoder 21, a carrier demodulator 22, an error correction decoder 23, and a combiner 24. The receiving device 2c receives the four OFDM signals transmitted from the transmitting device 1b with the four receiving antennas AT-rx1 to AT-rx4. The receiving device 2c according to the third embodiment is different from the receiving device 2b according to the second embodiment in that the OFDM demodulator 20a estimates four types of transmission line responses corresponding to four receiving antennas, and a combining unit. 24 is different.

  The OFDM demodulator 20a is the same as that described with reference to FIG.

  The space-time decoding unit 21-1 includes complex baseband signals c1 and c2, input channel responses h11, h12, h13, and h14 (shown as h1 in FIG. 17) and a transmission channel response h21 input from the OFDM demodulator 20a. , H22, h23, and h24 (denoted as h2 in FIG. 17), space-time decoding is performed according to Equation (7) to generate space-time decoded signals x1, x2, x3, and x4. Similarly, the space-time decoding unit 21-2 includes complex baseband signals c3 and c4 input from the OFDM demodulation unit 20a, transmission path responses h31, h32, h33, and h34 (indicated as h3 in FIG. 17) and transmission. Using the path responses h41, h42, h43, and h44 (denoted as h4 in FIG. 17), space-time decoding is performed to generate space-time decoded signals x1, x2, x3, and x4.

  Since the synthesizing unit 24 obtains decoding results from the space-time decoding units 21-1 and 21-2, respectively, a known selective synthesis is performed on the space-time decoded signals x1, x2, x3, and x4 obtained two by two. Diversity synthesis is performed by applying a method, an in-phase synthesis method, a maximum ratio synthesis method, and the like, and finally one x1, x2, x3, and x4 are obtained.

  Note that even when SFBC is applied as STC, encoding and decoding can be performed in the same procedure as STBC. In the description of the STBC of the first embodiment, m represents a certain discrete time. However, if the first embodiment is replaced with m representing a certain subcarrier number, SFBC can be applied, and the received signals c1, c2 to x1, x2 can be applied. , X3, x4 can be obtained. Similarly, x1, x2, x3, and x4 are obtained from the received signals c3 and c4. Diversity combining is performed on x1, x2, x3, and x4 obtained two by two, and the final x1, x2, x3, and x4 are estimated, so that a diversity gain is obtained for 4 × 2 MIMO.

  As described above, the receiving device 2c according to the third embodiment receives the OFDM signal transmitted from the transmitting device 1b by the four receiving antennas, demodulates the received OFDM signal by the OFDM demodulating unit 20a, and the space-time decoding unit. After the space-time decoding by 21, the combining unit 24 diversity-combines the space-time decoded signal. For this reason, a diversity gain can be obtained with respect to 4 × 2 MIMO of the second embodiment. Note that the diversity gain can be improved by further increasing the number of reception antennas.

  Although the above embodiments have been described as representative examples, it will be apparent to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims.

  As described above, according to the present invention, the transmission path response can be obtained with high frequency and the power consumption used for transmitting the pilot signal can be reduced. Therefore, the present invention is useful for any application that performs MIMO transmission. .

1a, 1b Transmitting device 2a, 2b, 2c Receiving device 10 Error correction coding unit 11 Carrier modulation unit 12 Space-time coding unit 13 OFDM modulation unit 14 Transmitting station 20a, 20b OFDM demodulation unit 21 Space-time decoding unit 22 Carrier demodulation unit DESCRIPTION OF SYMBOLS 23 Error correction decoding part 24 Synthesis | combination part 25 MIMO detection part 130 Pilot signal generation part 131 OFDM symbol structure part 132 IFFT part 133 GI addition part 134 Orthogonal modulation part 135 D / A conversion part 136 Pilot signal insertion part 137 OFDM signal generation part 200 A / D conversion unit 201 Orthogonal demodulation unit 202 GI removal unit 203 FFT unit 204 Pilot signal generation unit 205 Pilot signal extraction unit 206 Transmission channel response estimation unit 207 Transmission channel response interpolation unit

Claims (2)

A transmission apparatus that transmits four OFDM signals from four transmission antennas,
A pilot signal insertion unit that generates four types of OFDM symbols by inserting pilot signals of different patterns into the four types of transmission signals;
An OFDM signal generator that modulates each carrier of the four types of OFDM symbols to generate four OFDM signals,
The pilot signal insertion unit is
A pilot signal having a significant value and a non-signal pilot signal are inserted into the first and second transmission signals, and a pilot signal having a significant value is inserted into the third and fourth transmission signals; Insert a pilot signal in which the sign of the pilot signal having a significant value is inverted and a non-signal pilot signal,
The no-signal pilot signal is inserted at the same predetermined position with respect to the first and third transmission signals, and at a position different from the same predetermined position with respect to the second and fourth transmission signals. Inserting the no-signal pilot signal;
The pilot signal having the significant value and the pilot signal obtained by inverting the sign of the pilot signal having the significant value are alternately arranged in time and frequency with respect to the third and fourth transmission signals. A transmission device characterized by being inserted as described above. A receiving apparatus that receives four OFDM signals transmitted from the transmitting apparatus according to claim 1, using four receiving antennas,
A receiving apparatus comprising: an OFDM demodulator that demodulates the four received OFDM signals and estimates a baseband signal and a transmission path response corresponding to each receiving antenna.

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