JP2015065501A - Transmitter and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise estimation accuracy of a transmission path response in transmission of a plurality of OFDM signals.SOLUTION: A transmitter comprises: a pilot signal insertion part 136 which generates n OFDM symbols by inserting pilot signals with mutually different patterns into the same position of n (n≥2) transmission signals; and an OFDM signal generation part 137 which generates n OFDM signals by modulating the respective carriers of the n OFDM symbols. The pilot signal insertion part 136 inserts at least one of only a signal having a significant value, the signal having the significant value and a non-signal, and the signal with the significant value and a signal obtained by inverting a symbol of the signal having the significant value, and the signal having the significant value, the signal obtained by inverting the symbol of the signal having the significant value, and the non-signal as the pilot signals with the different patterns, and further inserts the non-signal into a position adjacent to a carrier direction of the inserted signal.

Description

  The present invention relates to a transmission apparatus and a reception apparatus in a transmission system that transmits a plurality of OFDM signals 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 “sign-inversion pilot method”.

  With reference to FIGS. 13 to 16, pilot signal patterns of the null pilot scheme and the code-inverted pilot scheme will be described by taking as an example an OFDM signal transmission system that transmits two OFDM signals from two transmitting antennas in the same frequency band. . 13 to 16, only the minimum unit for repeating the pilot signal in the OFDM symbol is shown, and the non-pilot signal such as the data signal is omitted. Pattern 1 shows a pilot signal pattern of the OFDM signal transmitted from the first transmission antenna, and pattern 2 shows a pilot signal pattern of the OFDM signal transmitted from the second 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. 13 is a diagram showing 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. FIG. 14 is a diagram showing the position of the transmission line response obtained directly (that is, not based on interpolation) from the pilot signal of FIG. 13 with 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 of FIG. The position transmission line response 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. 15 is a diagram showing a pilot signal pattern to which a code inversion pilot scheme is applied in a system that transmits two OFDM signals in the same frequency band. A square in the figure indicates a pilot signal having a certain significant value, and 1 and −1 marked in the square mean a pilot signal with a sign inverted. FIG. 16 is a diagram showing the position of the transmission line response directly obtained from the pilot signal of FIG. 15 by hatched circles. In this specification, the received signal at the position 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 (2,1)) / 2
P2: (Rx (1,1) -Rx (2,1)) / 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 code-inverted pilot scheme, since there is no pilot signal that becomes no signal, power consumption used for transmission of the pilot signal is not reduced, but a transmission path response can be obtained more frequently than in the null pilot scheme.

  On the other hand, consider an environment in which an OFDM signal is transmitted while both or one of the transmitter and the receiver physically move. In a mobile transmission environment, Doppler shift occurs, and in OFDM transmission, transmission is performed by a plurality of carriers. Therefore, inter-carrier interference occurs in which a carrier symbol of a specific frequency interferes with an adjacent carrier symbol. In general, the narrower the carrier interval in OFDM transmission, the more susceptible to inter-carrier interference.

  FIG. 17 is a diagram illustrating an image of inter-carrier interference. When the carrier interval is wide as shown in FIG. 17B, if a Doppler shift occurs in a carrier symbol having a certain carrier number, the interference power for the carrier symbol having an adjacent carrier number becomes relatively small. On the other hand, when the carrier interval is narrow as shown in FIG. 17A, if a Doppler shift occurs in a carrier symbol having a certain carrier number, the interference power leaking into the carrier symbol having an adjacent carrier number increases. Consider a case where a pilot signal for estimating a channel response is transmitted by carrier number # 1 and a data signal is transmitted by carrier number # 2. When the carrier interval is narrow, the interference power from carrier number # 2 to carrier number # 1 increases, making it difficult to obtain an accurate transmission path response using the pilot signal transmitted by carrier number # 1.

  Therefore, in SISO (single-input single-output) transmission, in order to observe the inter-carrier interference power and estimate the transmission path response of the inter-carrier interference component, the carrier symbols adjacent to the left and right in the carrier direction of a pilot signal are not signaled A method for observing inter-carrier interference components has been studied (see Non-Patent Document 1). In this specification, inserting a non-signaled pilot signal into carrier symbol positions adjacent to the left and right in the carrier direction of the pilot signal is referred to as “clustering” of the pilot signal, and the clustered pilot signal is referred to as “cluster”. This is referred to as a “pilot signal”.

  FIG. 18 is a diagram illustrating a first example of a cluster pilot signal. Here, an example is shown in which one pilot signal adjacent to the left and right of a pilot signal having a significant value is set as no signal, and a pilot signal having a significant value is transmitted by a carrier of carrier number 2 and is adjacent. Carriers with carrier numbers 1 and 3 are set to no signal. When inter-carrier interference occurs, a component leaking from the carrier of carrier number 2 to the adjacent carriers of carrier numbers 1 and 3, that is, the transmission path response of the inter-carrier interference component can be observed.

  FIG. 19 is a diagram illustrating a second example of the cluster pilot signal. Here, an example is shown in which two pilot signals adjacent to the left and right of the pilot signal having a significant value are set as no signals, and the pilot signal having a significant value is transmitted by the carrier of the carrier number 3 and is adjacent. Carriers with carrier numbers 1, 2, 4, and 5 are set to no signal. When inter-carrier interference occurs, components leaking from the carrier of carrier number 3 to the adjacent carriers of carrier numbers 1, 2, 4 and 5 can be observed, and a wider range of inter-carrier interference can be observed. it can. However, as no signal increases, the number of carrier symbols that can be used for data transmission decreases, and the data transmission efficiency decreases.

JP 2004-96186 A Japanese Patent No. 4336281

“Novel pilot structures for BEM channel estimation and ICI compensation in high-mobility DVB”, IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), 2011

  However, there has been no example in which the above-described cluster pilot signal is used when a plurality of OFDM signals are transmitted from a plurality of transmission antennas. By clustering pilot signals of the above-described null pilot scheme, code-inverted pilot scheme, or a combination of both, it is possible to further improve the estimation accuracy of the transmission path response.

  In order to solve the above problem, an object of the present invention is to provide a transmission device and a reception device capable of improving the estimation accuracy of a transmission path response when transmitting a plurality of OFDM signals.

  In order to solve the above-described problem, a transmitting apparatus according to the present invention is a transmitting apparatus that transmits a plurality of OFDM signals, and inserts pilot signals having different patterns at the same position of n (n ≧ 2) transmission signals. A pilot signal insertion unit that generates n OFDM symbols, and an OFDM signal generation unit that generates n OFDM signals by modulating each carrier of the n OFDM symbols, the pilot signal insertion A signal having a significant value only, a signal having a significant value and no signal, and a signal having a significant value and a signal having the significant value inverted as pilot signals of different patterns And at least one of a signal having a significant value, a signal obtained by inverting the sign of the signal having a significant value, and no signal, and further inserting a key of the inserted signal. Characterized by inserting a no-signal to a position adjacent to the rear direction.

  Furthermore, in the transmission apparatus according to the present invention, the n is 2, and the pilot signal insertion unit includes a signal having a significant value in the first and second transmission signals as the pilot signal having the different pattern. It is characterized by inserting a signal.

  Furthermore, in the transmission apparatus according to the present invention, the n is 2, and the pilot signal insertion unit inserts only a signal having a significant value in the first transmission signal as the pilot signal of the different pattern, A signal having a significant value and a signal obtained by inverting the sign of the signal having the significant value are inserted into the two transmission signals.

  Furthermore, in the transmission device according to the present invention, the n is 4, and the pilot signal insertion unit includes a signal having a significant value in the first to fourth transmission signals as the pilot signal having the different pattern. It is characterized by inserting a signal.

  Furthermore, in the transmission apparatus according to the present invention, the n is 4, and the pilot signal insertion unit inserts only a signal having a significant value in the first transmission signal as the pilot signal of the different pattern, The second to fourth transmission signals are characterized by inserting a signal having a significant value and a signal obtained by inverting the sign of the signal having the significant value.

  Further, in the transmission apparatus according to the present invention, the n is 4, and the pilot signal insertion unit includes a signal having a significant value in the first and second transmission signals and no signal as the pilot signals of the different patterns. And a signal having a significant value in the third and fourth transmission signals, a signal obtained by inverting the sign of the signal having the significant value, and a no signal are inserted.

  In order to solve the above problem, a receiving apparatus according to the present invention is a receiving apparatus that receives a plurality of OFDM signals transmitted from a transmitting apparatus, and demodulates the received OFDM signals to generate a baseband signal. An FFT unit, a pilot signal generation unit that generates a pilot signal, a channel response estimation unit that estimates a channel response using the pilot signal, and a transmission signal that is detected using the baseband signal and the channel response A transmission signal detection unit that performs the pilot signal generation unit, as the pilot signal, only a signal having a significant value, a signal having a significant value, no signal, a signal having a significant value, and the significant signal Of the signal obtained by inverting the sign of a signal having a value, and the signal having a significant value and the signal having the sign of the significant value inverted and no signal Also generate one further and generates no signal at the position adjacent to the carrier direction of the generated signal.

  In a conventional pilot signal, in a transmission environment where inter-carrier interference occurs, adjacent carrier symbols interfere with the pilot signal for estimating the transmission path response, and it is difficult to accurately estimate the transmission path response. However, according to the present invention, the transmission path response can be accurately estimated even in a transmission environment in which inter-carrier interference occurs.

It is a block diagram which shows the structure of the transmitter which concerns on this invention. It is a block diagram which shows the structure of the OFDM modulation part in the transmitter which concerns on this invention. It is a block diagram which shows the structure of the receiver which concerns on this invention. It is a block diagram which shows the structure of the OFDM demodulation part in the receiver which concerns on this invention. It is a figure which shows the example which clustered the pilot signal of the null pilot system in the case of transmitting two OFDM signals with the same frequency. It is a figure which shows the example which clustered the pilot signal of the code inversion type pilot system in the case of transmitting two OFDM signals with the same frequency. It is a figure which shows the example which clustered the pilot signal of the null pilot system in the case of transmitting four OFDM signals at the same frequency. It is a figure which shows the example which clustered the pilot signal of the code inversion type pilot system in the case of transmitting four OFDM signals at the same frequency. It is a figure which shows the example which clustered the pilot signal of the code inversion type | mold null pilot system in the case of transmitting four OFDM signals at the same frequency. It is a figure which shows arrangement | positioning of the scattered pilot signal in ISDB-T. FIG. 11 is a diagram illustrating an example in which the code-inverted null pilot scheme clustering illustrated in FIG. 9 is applied to the pilot signal arrangement illustrated in FIG. 10. It is a figure which shows the example which clustered the pilot signal continuous in a symbol direction. It is a figure which shows the pilot signal pattern to which the conventional null pilot system is applied. It is a figure which shows the position of the transmission line response directly calculated | required by the pilot signal of FIG. It is a figure which shows the pilot signal pattern to which the conventional code inversion type pilot system is applied. It is a figure which shows the position of the transmission-line response directly calculated | required by the pilot signal of FIG. It is a figure which shows the image of the interference between carriers. It is a figure which shows the 1st example of a cluster pilot signal. It is a figure which shows the 2nd example of a cluster pilot signal.

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

[Transmitter]
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 1 includes an error correction encoding unit 10, a carrier modulation unit 11, a distribution unit 12, and an OFDM modulation unit 13. The transmission apparatus 1 outputs four OFDM signals, and the four OFDM signals are sent to one transmission station 14. The transmission apparatus 1 transmits an OFDM signal to one transmission station, and transmits an OFDM signal by space division multiplexing (SDM) from four transmission antennas at one transmission station. Although FIG. 1 shows a case where there are four transmission antennas, the transmission apparatus according to the present invention only needs to have a plurality of transmission antennas and is not limited to four. The transmission apparatus 1 can also transmit an OFDM signal to two or more transmission stations, and can transmit a part (or all) of the OFDM signal from each transmission station.

  The transmitting station 14 transmits an OFDM signal by SDM from the antennas AT-tx1 to AT-tx4.

  The error correction coding unit 10 performs error correction coding on an input signal such as a TS (Transport Stream) 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 to the IQ plane according to a predetermined modulation method for each subcarrier, and outputs the result to the distribution unit 12.

  The distribution unit 12 distributes the signal input from the carrier modulation unit 11 into four streams and outputs the four streams to the OFDM modulation unit 13.

  The OFDM modulation unit 13 generates four OFDM signals from the four transmission signals (s 1, s 2, s 3, s 4) input from the distribution unit 12 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 transmission signals (s1, s2, s3, s4) input from the distribution unit 12 to generate four 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. The pilot signal generation unit 130 performs the following (1) to (4) as pilot signals of different patterns.
(1) Only signals with significant values (signals other than no signals)
(2) A signal having a significant value and no signal,
(3) a signal having a significant value and a signal obtained by inverting the sign of the signal having the significant value;
(4) Generate at least one of a signal having a significant value, a signal obtained by inverting the sign of the signal having the significant value, and no signal, and further, at a position adjacent to the carrier direction of the generated signal. Generate no signal.

  Here, the “position adjacent to the carrier direction of the generated signal” may be one each on the left and right of the generated signal, two on each of the left and right, or different on the left and right. It may be a number. In addition, the “position adjacent to the carrier direction of the generated signal” is set to two on the left and right sides of the generated signal for the partial receivers that want to increase resistance to inter-carrier interference in the OFDM segment, and the other segments. May be different depending on the tolerance of inter-carrier interference required for the system, such as one on each side of the generated signal. Specific examples of the pilot signal pattern and arrangement will be described later.

  OFDM symbol configuration section 131 inserts the pilot signal input from pilot signal generation section 130 into the four transmission signals (s 1, s 2, s 3, s 4) input from distribution section 12, and enters IFFT section 132. Output.

  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.

[Receiver]
Next, an OFDM signal receiving apparatus according to the present invention 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 2 includes an OFDM demodulator 20, a transmission signal detector 21, a carrier demodulator 22 (22-1 to 22-4), and an error correction decoder 23 (23. -1 to 23-4). The receiving device 2 receives the four systems of OFDM signals transmitted from the transmitting device 1 with the four receiving antennas AT-rx1 to AT-rx4. Although FIG. 3 shows a case where there are four receiving antennas, the receiving apparatus according to the present invention may have one or more receiving antennas, and is not limited to four.

  The OFDM demodulator 20 demodulates the four received OFDM signals to generate four types of baseband signals (c1, c2, c3, c4), and the pilot signal inserted by the pilot signal insertion unit 136 of the transmission apparatus. And 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 20. As shown in FIG. 4, the OFDM demodulator 20 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 an FFT (Fast Fourier Transform) process on the effective symbol signal input from the GI removal unit 202 to generate complex baseband signals c1, c2, c3, and c4. The signal is output to the signal extraction unit 205.

The pilot signal generation unit 204 generates a pilot signal having the same amplitude and phase as the pilot signal inserted by the pilot signal generation unit 130 of the transmission apparatus 1, and uses the pilot signal position information inserted by the transmission apparatus 1 as a pilot signal. It outputs to the extraction part 205, and outputs the amplitude value and phase value of a pilot signal to the transmission line response estimation part 206. That is, the pilot signal generation unit 204 uses the following (1) to (4) as pilot signals.
(1) Only signals with significant values (signals other than no signals)
(2) A signal having a significant value and no signal,
(3) a signal having a significant value and a signal obtained by inverting the sign of the signal having the significant value;
(4) Generate at least one of a signal having a significant value, a signal obtained by inverting the sign of the signal having the significant value, and no signal, and further, at a position adjacent to the carrier direction of the generated signal. Generate no signal.

  The pilot signal extraction unit 205 extracts a pilot signal from the complex baseband signals c1, c2, c3, and c4 input from the FFT unit 203 based on the position information input from the pilot signal generation unit 204, and transmits the channel response. It outputs to the estimation part 206.

  Transmission path response estimation section 206 calculates a transmission path response using the pilot signal generated by pilot signal generation section 204 and the pilot signal extracted by pilot signal extraction section 205.

  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 transmission signal detection unit 21 detects a MISO signal or a MIMO signal using the baseband signal c and the transmission path response h input from the OFDM demodulation unit 20. For this detection, known techniques 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 demodulation unit 22 demodulates the signal input from the transmission signal detection unit 21 for each subcarrier, and outputs a signal such as a bit LLR (Log Likelihood Ratio) 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 1.

[Pilot signal pattern and arrangement]
Next, the pattern and arrangement of pilot signals inserted by pilot signal generation section 130 will be described. In FIG. 5 to FIG. 9, non-pilot signals such as data signals are omitted, and only the minimum unit of pilot signal repetition is shown. 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. The position of the transmission line response obtained from the pilot signal is indicated by a hatched circle, and the position of the transmission line response of the inter-carrier interference component that can be observed is indicated by an arrow. In FIG. 5, an arrow is attached to a non-signal adjacent to a signal having a significant value, and the transmission line response of the inter-carrier interference component can be observed at the position of this signal. 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. 5 is a diagram showing an example in which null pilot pilot signals are clustered when two OFDM signals are transmitted at the same frequency, and pattern 1 shows a pilot signal insertion pattern for the first transmission signal. Pattern 2 shows a pilot signal insertion pattern for the second transmission signal. In this example, the number of transmission antennas is two, and the pilot signal insertion unit 136 inserts a signal having a significant value as a pilot signal and no signal, and further, no signal at a position adjacent to the carrier direction of the inserted signal. Insert.

  In FIG. 5, in pattern 1, pilot signals having significant values are inserted into P (1,2) and P (2,5), and carrier symbols adjacent to the left and right are set to be no signal, so that intercarrier interference occurs. Even in the transmission environment, the inter-carrier interference component received by the pilot signals P (1,2) and P (2,5) is reduced, and the transmission path response can be accurately estimated. Furthermore, the inter-carrier interference component given by P (1,2) can be observed at the positions P (1,1) and P (1,3), and P (2,4), P (2,6 ), The inter-carrier interference component given by P (2,5) can be observed. The same applies to pattern 2.

  FIG. 6 is a diagram showing an example of clustering pilot-inverted pilot signals in the case where two OFDM signals are transmitted at the same frequency, and pattern 1 is a pilot signal insertion pattern for the first transmission signal. Pattern 2 shows a pilot signal insertion pattern for the second transmission signal. In this example, the number of transmission antennas is 2, and the pilot signal insertion unit 136 inserts only a signal having a significant value in the first transmission signal as a pilot signal, and assigns a significant value to the second transmission signal. And a signal obtained by inverting the sign of the signal having the significant value and the signal having the significant value, and further inserting no signal at a position adjacent to the carrier direction of the inserted signal.

  In FIG. 6, in pattern 1, pilot signals having significant values are inserted into P (1,2), P (1,5), P (2,2), and P (2,5), and are adjacent to the left and right. Since no carrier symbol is used, pilot signals of P (1,2), P (1,5), P (2,2), and P (2,5) are used even in a transmission environment in which intercarrier interference occurs. The inter-carrier interference component received by the receiver becomes small, and the transmission path response can be accurately estimated. Furthermore, an inter-carrier interference component can be observed at the position of the arrow. The same applies to pattern 2.

  Next, consider a case where four OFDM signals are transmitted at the same frequency. FIG. 7 is a diagram illustrating an example in which null pilot pilot signals are clustered when four OFDM signals are transmitted at the same frequency. Patterns 1 to 4 correspond to first to fourth transmission signals, respectively. An insertion pattern of a pilot signal is shown. In this example, pilot signals having significant values are arranged linearly in the symbol direction, the number of transmission antennas is 4, and the pilot signal insertion unit 136 uses the first to fourth transmission signals as pilot signals. In addition, a signal having a significant value and a no signal are inserted, and a no signal is further inserted at a position adjacent to the carrier direction of the inserted signal.

  In FIG. 7, pilot signals are inserted in different carriers of four OFDM signals, and in a section where one OFDM signal is transmitting a pilot signal, other OFDM signals are no signal, The transmission line response can be obtained without performing a complicated calculation. The pilot signal having a significant value can be arranged linearly in the carrier direction or can be arranged in an oblique direction. Since the carrier symbols adjacent to both sides of the pilot signal having a significant value are set as no signal, the transmission path response can be accurately estimated even in a transmission environment in which inter-carrier interference occurs.

  FIG. 8 is a diagram illustrating an example of clustering pilot-inverted pilot signals in the case where four OFDM signals are transmitted at the same frequency, and pilot signal insertion patterns for the first to fourth transmission signals Are shown as pattern 1 to pattern 4, respectively. In this example, the number of transmission antennas is four, and the pilot signal insertion unit 136 inserts only a signal having a significant value in the first transmission signal as a pilot signal, and significant in the second to fourth transmission signals. A signal having a positive value and a signal obtained by inverting the sign of the signal having a significant value are inserted, and a non-signal is inserted at a position adjacent to the carrier direction of the inserted signal.

When the amplitude value of the pilot signal is 1, the transmission path response estimation unit 206 can obtain the transmission path response at positions P1 to P4 in FIG.
P1: (Rx (1,2) + Rx (2,2) + Rx (3,2) + Rx (4,2)) / 4
P2: (Rx (1,2) + Rx (2,2) -Rx (3,2) -Rx (4,2)) / 4
P3: (Rx (1,2) -Rx (2,2) -Rx (3,2) + Rx (4,2)) / 4
P4: (Rx (1,2) -Rx (2,2) + Rx (3,2) -Rx (4,2)) / 4
Also in this case, since the carrier symbols adjacent to the left and right of the pilot signal having a significant value are set as no signals, the transmission path response can be accurately estimated even in a transmission environment in which inter-carrier interference occurs.

  FIG. 9 shows a clustering of pilot signals of a combination of a null pilot scheme and a code-inverted pilot scheme (hereinafter referred to as “code-inverted null pilot scheme”) when four OFDM signals are transmitted at the same frequency. FIG. In this example, the pilot signal insertion unit 136 inserts a signal having a significant value and a no-signal into the first and second transmission signals as a pilot signal, and assigns a significant value to the third and fourth transmission signals. A signal obtained by inverting the sign of a signal having a significant value and a signal having a significant value and a non-signal are inserted, and a non-signal is inserted at a position adjacent to the carrier direction of the inserted signal. In addition, the no-signal pilot signal is inserted at different positions in the patterns 1 and 3 and the patterns 2 and 4.

  In the sign-inverted null pilot scheme, the pilot signal insertion unit 136 makes no signal half of the pilot signals to be inserted for the four transmission signals, and for the third transmission signal and the fourth transmission signal. If the pilot signals are inserted so that the number of signals having a significant value and the number of signals obtained by inverting the sign of the signal having a significant value are the same, the positions where the transmission line responses are directly obtained are preferably equalized.

When the amplitude value of the pilot signal is 1, the transmission path response estimation unit 206 can obtain the transmission path response at the positions P1 to P4 in FIG.
P1: (Rx (1,2) + Rx (3,2)) / 2
P2: (Rx (2,2) + Rx (4,2)) / 2
P3: (Rx (1,2) -Rx (3,2)) / 2
P4: (Rx (2,2) -Rx (4,2)) / 2
Also in this case, since the carrier symbols adjacent to the left and right of the pilot signal having a significant value are set as no signals, the transmission path response can be accurately estimated even in a transmission environment in which inter-carrier interference occurs. It is also possible to observe the inter-carrier interference component given by the pilot signal.

  FIG. 10 is a diagram showing the arrangement of scattered pilot (SP) signals in the transmission system ISDB-T of Japanese terrestrial digital broadcasting. The pilot signal is inserted once every 12 carriers and once every 4 symbols. The arrangement position of the pilot signal is not limited to this position, and the pilot signal may be arranged in a lattice shape or a zigzag shape. 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.

  11 is a diagram showing an example in which the clustering of the code-inverted null pilot scheme shown in FIG. 9 is applied to the pilot signal arrangement shown in FIG. Here, one pilot signal is inserted into each of the left and right adjacent to the pilot signal for clustering, but two or more pilot signals may be inserted into the left and right adjacent to the pilot signal for clustering. Further, clustering of pilot signals of the null pilot scheme (FIG. 7) and clustering of pilot signals of the sign inversion pilot scheme (FIG. 8) can be similarly applied to the pilot signal arrangement shown in FIG. it can.

  In ISDB-T, a continuous pilot (CP) is used in the leftmost carrier of a segment in a differential modulation unit. In CP, pilot signals are continuously inserted in the symbol (time) direction. Such pilot signals may be clustered.

  FIG. 12 is a diagram illustrating an example in which pilot signals continuous in the symbol direction are clustered when two OFDM signals are transmitted at the same frequency. Here, an example of clustering of null pilot CP signals in 2 × 2 MIMO transmission is shown, and pilot signals are arranged and clustered at intervals of 12 carriers. Note that the number of non-signal pilot signals adjacent to the null pilot CP signal is not limited to two each on the left and right. Also, code-inverted pilot scheme and code-inverted null pilot scheme CP signals can be clustered by the same method.

  As described above, the pilot signal insertion unit 136 includes (1) only a signal having a significant value, (2) a signal having a significant value and no signal, and (3) a signal having a significant value as the pilot signal. A signal obtained by inverting the sign of a signal having a significant value; and (4) at least one of a signal having a significant value and a signal obtained by inverting the sign of the signal having a significant value and no signal. Further, no signal is inserted at a position adjacent to the inserted signal in the carrier direction. In addition, the receiving device 2 generates the same pilot signal as that of the transmitting device 1. For this reason, according to the present invention, it is possible to accurately estimate the transmission path response even in a transmission environment in which inter-carrier interference occurs.

  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.

  For example, the pilot signal may be inserted so that the transmission line response can be calculated, and is not limited to the pattern and arrangement described above. Alternatively, the transmitter 1 may perform space-time encoding and then perform OFDM modulation, and the receiver 2 may perform OFDM demodulation and space-time decoding. Also, the number of reception antennas may be made larger than the number of transmission antennas, and the reception apparatus 2 may perform diversity reception.

  Thus, according to the present invention, it is possible to improve the estimation accuracy of the transmission path response, which is useful for any application that transmits a plurality of OFDM signals.

DESCRIPTION OF SYMBOLS 1 Transmission apparatus 2 Reception apparatus 10 Error correction encoding part 11 Carrier modulation part 12 Distribution part 13 OFDM modulation part 14 Transmitting station 20 OFDM demodulation part 21 Transmission signal detection part 22 Carrier demodulation part 23 Error correction decoding part 130 Pilot signal generation part 131 OFDM symbol configuration section 132 IFFT section 133 GI addition section 134 Orthogonal modulation section 135 D / A conversion section 136 Pilot signal insertion section 137 OFDM signal generation section 200 A / D conversion section 201 Orthogonal demodulation section 202 GI removal section 203 FFT section 204 Pilot Signal generation section 205 Pilot signal extraction section 206 Transmission path response estimation section 207 Transmission path response interpolation section

Claims (7)

A transmission device that transmits a plurality of OFDM signals,
a pilot signal insertion unit that inserts pilot signals of different patterns at the same position of n (n ≧ 2) transmission signals to generate n OFDM symbols;
An OFDM signal generator that modulates each carrier of the n OFDM symbols to generate n OFDM signals, and
The pilot signal insertion unit, as the pilot signal of the different pattern,
Only signals with significant values,
Signals with significant values and no signals,
A signal having a significant value and a signal obtained by inverting the sign of the signal having the significant value, and
A signal having a significant value, a signal obtained by inverting the sign of the signal having the significant value, and no signal,
Insert at least one of
Further, a non-signal is inserted at a position adjacent to the inserted signal in the carrier direction. N is 2;
The transmission according to claim 1, wherein the pilot signal insertion unit inserts a signal having a significant value and a no-signal into the first and second transmission signals as the pilot signals having different patterns. apparatus. N is 2;
The pilot signal insertion unit inserts only a signal having a significant value in the first transmission signal as the pilot signal having the different pattern, and a signal having a significant value in the second transmission signal and the significant value. The transmission apparatus according to claim 1, wherein a signal obtained by inverting the sign of the signal is inserted. N is 4;
The transmission according to claim 1, wherein the pilot signal insertion unit inserts a signal having a significant value and a no-signal into the first to fourth transmission signals as the pilot signals of different patterns. apparatus. N is 4;
The pilot signal insertion unit inserts only a signal having a significant value in the first transmission signal as the pilot signal of the different pattern, and a signal having a significant value in the second to fourth transmission signals and the significant signal The transmission apparatus according to claim 1, wherein a signal obtained by inverting a sign of a signal having a different value is inserted. N is 4;
The pilot signal insertion unit inserts a signal having a significant value and a no-signal into the first and second transmission signals as the different pattern pilot signals, and assigns a significant value to the third and fourth transmission signals. The transmitting apparatus according to claim 1, wherein a signal having no sign and a signal having a sign of the significant signal and the signal having a significant value are inserted. A receiving device that receives a plurality of OFDM signals transmitted from a transmitting device,
An FFT unit that demodulates the received OFDM signal to generate a baseband signal;
A pilot signal generator for generating a pilot signal;
A channel response estimation unit that estimates a channel response using the pilot signal;
A transmission signal detection unit that detects a transmission signal using the baseband signal and the transmission path response, and
The pilot signal generation unit, as the pilot signal,
Only signals with significant values,
Signals with significant values and no signals,
A signal having a significant value and a signal obtained by inverting the sign of the signal having the significant value, and
A signal having a significant value, a signal obtained by inverting the sign of the signal having the significant value, and no signal,
Generate at least one of
Furthermore, a non-signal is generated at a position adjacent to the generated signal in the carrier direction.

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