Relay device and relay method

Abstract

To provide a relay device and a method for relaying which relay a multiple signal.SOLUTION: The relay device according to an embodiment includes a reception unit, a correction unit, a determination unit, and a sending unit. The reception unit receives a third signal including a first signal with a first power level and a second signal with a second power level lower than the first power level. The correction unit determines the estimated value of the frequency characteristics of a propagation path of the third signal on the basis of the third signal and corrects the frequency characteristics of the third signal according to the estimated value. The determination unit determines the value of the third signal with the frequency characteristics corrected by the correction unit. The transmission unit transmits the third signal of the value determined by the determination unit.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a radio signal relay device and relay method. [Background technology]

[0002] The relay device receives the signal transmitted from the transmitting device, processes the received signal, and transmits the processed signal to the receiving device.

[0003] In recent years, in order to improve frequency utilization efficiency, a Layered Division Multiplexing (LDM) method has been proposed, which transmits two different signals at the same time in the same band by transmitting a multiplexed signal in which two different signals are added together at different power levels.

[0004] Conventional repeaters do not take the LDM method into consideration, and therefore are unable to correctly determine multiplexed signals, resulting in performance degradation when relaying multiplexed signals. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-67123 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a relay device and a relay method for relaying a multiplexed signal. [Means for solving the problem]

[0007] A relay device according to an embodiment includes a receiving unit that receives a third signal including a first signal at a first power level and a second signal at a second power level lower than the first power level; a correction unit that calculates an estimate of the frequency characteristics of the propagation path of the third signal based on the third signal and corrects the frequency characteristics of the third signal according to the estimate; a determination unit that determines the value of the third signal whose frequency characteristics have been corrected by the correction unit; and a transmitting unit that transmits the third signal having the value determined by the determination unit. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram for explaining an example of a multiplexed signal of the LDM method according to the embodiment. [Figure 2] FIG. 1 is a diagram for explaining the concept of an LDM method according to an embodiment. [Figure 3] FIG. 4 is a diagram for explaining an injection level of the LDM method according to the embodiment. [Figure 4] FIG. 1 is a block circuit diagram illustrating an example of a transmission device according to an embodiment. [Figure 5] FIG. 2 is a diagram for explaining an example of mapping of a multiplexed signal in a transmission device according to an embodiment. [Figure 6] FIG. 10 is a diagram for explaining another example of mapping of a multiplexed signal in the transmitting device according to the embodiment. [Figure 7] FIG. 10 is a diagram for explaining yet another example of mapping of a multiplexed signal in the transmitting device according to the embodiment. [Figure 8] FIG. 10 is a diagram for explaining an example of the relationship between the injection level and the mapping candidate points in the LDM method according to the embodiment. [Figure 9] FIG. 10 is a diagram for explaining another example of the relationship between the injection level and the mapping candidate points in the LDM method according to the embodiment. [Figure 10] FIG. 10 is a diagram for explaining yet another example of the relationship between the injection level and the mapping candidate points in the LDM method according to the embodiment. [Figure 11] FIG. 2 is a diagram for explaining an example of an OFDM segment in the LDM method according to the embodiment. [Figure 12]FIG. 2 is a block circuit diagram illustrating an example of a relay device according to an embodiment. [Figure 13] FIG. 10 is a diagram for explaining an example of symbol determination in the relay device according to the embodiment. [Figure 14] FIG. 10 is a diagram for explaining another example of symbol determination in the relay device according to the embodiment. [Figure 15] FIG. 1 is a block circuit diagram illustrating an example of a receiving device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. The following description exemplifies devices and methods for embodying the technical concepts of the embodiments. The technical concepts of the embodiments are not limited to the structures, shapes, arrangements, materials, etc. of the components described below. Modifications that can be easily conceived by those skilled in the art are naturally included within the scope of the disclosure. For clarity of explanation, the drawings may schematically depict elements with different sizes, thicknesses, planar dimensions, shapes, etc., compared to the actual embodiment. Elements with different dimensional relationships or ratios may be included in multiple drawings. Corresponding elements may be designated by the same reference numerals in multiple drawings, and redundant description may be omitted. Some elements may be designated by multiple names, but these designations are merely examples and do not necessarily mean that these elements may be designated by other names. Furthermore, elements that do not have multiple names may also be designated by other names. In the following description, "connection" may include not only direct connection but also connection via other elements.

[0010] In the study of the next-generation standard for the current terrestrial digital television broadcasting, known as the Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) system, the use of the LDM system has been proposed to improve frequency utilization efficiency and enable coexistence with the current system. As an example, it is being considered to transmit a multiplexed signal in which signals conforming to the ISDB-T system (hereinafter referred to as ISDB-T signals) are used as high-power hierarchical layers and signals conforming to a next-generation terrestrial digital television broadcasting system (e.g., 4K / 8K system or Super Hi-Vision (SHV) system), which is an advanced version of the ISDB-T system (hereinafter referred to as SHV signals), are used as low-power hierarchical layers. This would enable the transmission of SHV signals without allocating new frequencies.

[0011] First, an example of the LDM method according to the embodiment will be described.

[0012] FIG. 1 is a diagram illustrating an example of a multiplexed signal in an LDM system according to an embodiment. In the LDM system, two different signals, a high-power layer (also referred to as an upper layer (UL)) signal and a low-power layer (also referred to as a lower layer (LL)) signal, modulated by the same or different methods, are added together to transmit a multiplexed signal. This allows two signals to be transmitted simultaneously in the same band. An example of the higher-layer signal may be an ISDB-T signal, and an example of the lower-layer signal may be an SHV signal. The power level of the higher-layer signal is higher than the power level of the lower-layer signal. The power ratio of the two layer signals is called an injection level. An example of the injection level is 23 dB or 15 dB.

[0013] Note that the transmission is not limited to a multiplexed signal of two different signals, but may also include a multiplexed signal of the same signal. For example, an SHV signal may be transmitted in an upper and lower layer without transmitting an ISDB-T signal. Furthermore, the transmission is not limited to signals in two layers, but may include signals in three or more layers. In the following, an LDM system will be described in which the number of layers is two, the upper layer signal is an ISDB-T signal, and the lower layer signal is an SHV signal.

[0014] 2 is a diagram illustrating the concept of the LDM method according to the embodiment. The LDM method includes a method in which multiple signals are normalized and then added, and a method in which multiple signals are added without normalization. FIG. 2 shows an example of the method in which multiple signals are normalized and then added.

[0015] An ISDB-T signal Txi is input to a power adjustment unit 2. The power adjustment unit 2 adjusts the power level of the ISDB-T signal Txi based on a normalization coefficient β. An SHV signal Txs in the time domain is input to a power adjustment unit 4. The power adjustment unit 4 adjusts the power level of the SHV signal Txs based on the product of the normalization coefficient β and a scaling coefficient α. The outputs of the power adjustment units 2 and 4 are added in an adder 6 to generate a multiplexed signal Tx of the ISDB-T signal Txi and the SHV signal Txs. The multiplexed signal Tx is expressed by Equation 1A. Tx = βTxi + αβTxs Equation 1A The injection level is a value that represents the ratio of the average power of the ISDB-T signal Txi to the average power of the SHV signal Txs. The higher the injection level, the higher the power ratio of the ISDB-T signal Txi in the multiplexed signal, and the lower the injection level, the lower the power ratio of the ISDB-T signal Txi in the multiplexed signal. The normalization coefficient β and scaling coefficient α, which are coefficients for power adjustment, are determined according to the injection level.

[0016] 3 is a diagram for explaining the injection level of the LDM method according to the embodiment. The injection level is determined according to the normalization coefficient β and the scaling coefficient α.

[0017] In the case of the LDM method in which multiple signals are added without normalization, the multiplexed signal Tx1 is expressed by Equation 1B. Tx1=ATxi+BTxs Equation 1B A and B are arbitrary coefficients. By adjusting coefficients A and B, the amplitudes of the ISDB-T signal and the SHV signal can be changed arbitrarily and multiplexed.

[0018] 4 is a block diagram showing an example of a transmitting device according to the embodiment. An example of a signal modulation method according to the embodiment is Orthogonal Frequency Division Multiplexing (OFDM) modulation.

[0019] The transmitting device includes an upper layer (UL) information bit generator 12 and a lower layer (LL) information bit generator 42. The UL information bit generator 12 and the LL information bit generator 42 may be realized by devices in upper layers of the transmitting device. The UL information bit generator 12 generates an information bit sequence for the upper layer signal (ISDB-T signal), and the LL information bit generator 42 generates an information bit sequence for the lower layer signal (SHV signal).

[0020] First, the transmission process of the upper layer signal will be described. The information bit string of the ISDB-T signal is input to an encoder 14. The encoder 14 is also called an outer encoder. The encoder 14 can employ, for example, a Reed Solomon (RS) encoding method. Hereinafter, the encoder 14 will be called an RS encoder 14. The RS encoder 14 performs, for example, shortened RS encoding. The shortened RS encoding can correct random errors in up to 8 bytes out of 204 bytes.

[0021] The encoded bit string output from the RS encoding unit 14 is input to the energy dispersal unit 16. Energy dispersal is performed using a pseudo-random code sequence PRBS. The generating polynomial of the pseudo-random code sequence PRBS is shown in Equation 2. g1(x)=x 15 +x 14 +1 formula 2 That is, the pseudorandom code sequence PRBS generation circuit consists of 15 D-type flip-flops connected in series. The output x of the 14th flip-flop counting from the input side is 14 and the output of the 15th flip-flop, x 15 are added together and input to the first flip-flop.

[0022] The signal (excluding the synchronization byte) is subjected to a bit-wise exclusive OR operation with the PRBS sequence. The initial value of each flip-flop in the PRBS generation circuit is set to "100101010000000" from the input side and is initialized for each OFDM frame.

[0023] The output bit string of the energy dispersal unit 16 is input to the byte interleave (byte IL) unit 18. The byte IL unit 18 performs convolutional byte interleaving on the 204-byte signal. The interleaving depth is, for example, 12 bytes. The byte IL unit 18 has 12 paths. Path 0 has a delay of 0. The capacity of the FIFO shift register of path 1 is 17 bytes, the capacity of the FIFO shift register of path 2 is 17×2=34 bytes, and similarly, the capacity of the FIFO shift register of path 11 is 17×11=187 bytes. The input and output are switched cyclically for each byte, in the order of path 0, path 1, path 2, ... path 11, path 0, path 1, ...

[0024] The output bit string of the byte IL unit 18 is input to the convolutional coding unit 22. The convolutional coding unit 22 is also referred to as an inner coding unit. The convolutional coding unit 22 performs punctured convolutional coding, for example, with a high-speed length k=7 and a coding rate of 1 / 2 as the mother code. The generating polynomial of the mother code is G1=171 (decimal) for the X output and G2=133 (decimal) for the Y output. The convolutional coding unit 22 also performs error correction coding.

[0025] The encoded bit string output from the convolutional coding unit 22 is input to a bit interleave (bit IL) unit 24. The output of the bit IL unit 24 is input to a time-frequency interleave (time-frequency IL) unit 28. First, the time-frequency IL unit 28 performs intra-segment time interleave processing in modulation symbol units (I-axis, Q-axis units). Next, the time-frequency IL unit 28 performs intra-segment interleave processing by performing carrier rotation processing and carrier randomization processing.

[0026] The output of the time / frequency IL unit 28 is input to the mapping / LDM multiplexing unit 32 .

[0027] Next, a description will be given of the transmission process of the lower layer signal. The information bit string of the SHV signal is input to the energy dispersal unit 44. Similar to the energy dispersal unit 16, the energy dispersal unit 44 performs energy dispersal using a pseudo-random code sequence PRBS.

[0028] The output bit string of the energy dispersal unit 44 is input to the encoding unit. The encoding unit can employ convolutional encoding, BCH (Bose Chaudhuri Hocquenghem) encoding, BCC (Block Check Character) encoding, LDPC (Low Density Parity Check) encoding, or the like. Here, the BCH encoding and LDPC encoding are employed. The output bit string of the energy dispersal unit 44 is input to the BCH encoding unit 46. The output bit string of the BCH encoding unit 46 is input to the LDPC encoding unit 48. Both the BCH encoding unit 46 and the LDPC encoding unit 48 perform error correction encoding.

[0029] Although Figure 4 shows different coding methods for the upper and lower layers, the coding methods for the upper and lower layers may be the same. If the coding methods for the upper and lower layers are the same, the error correction capabilities and code lengths of the coding methods for the upper and lower layers may be the same or different.

[0030] The encoded bit string output from the LDPC encoding unit 48 is input to a bit interleave (bit IL) unit 52. The output of the bit IL unit 52 is input to a time-frequency IL unit 56. The time-frequency IL unit 56 performs the same processing as the time-frequency IL unit 28. Note that the interleave lengths of the upper and lower layers may be the same or different.

[0031] The output of the time / frequency IL unit 56 is input to the mapping / LDM multiplexing unit 32 .

[0032] Multiplexing will now be described.

[0033] The mapping and LDM multiplexing unit 32 performs multi-value mapping specified for each of the ISDB-T signal and the SHV signal in the frequency domain. Mapping methods include QPSK (Quadrature Phase Shift Keying), 16QAM (16 Quadrature Amplitude Modulation), and 64QAM. The transmitting device selects the type of mapping method for each of the ISDB-T signal and the SHV signal and performs mapping using the selected method.

[0034] QPSK method: The majority value is 2, and 2 bits of the input signal are treated as 1 symbol. The symbol is mapped to one of 4 mapping candidate points on the complex plane, and the complex coordinate information representing the mapped point is output as mapping data. The coordinates of the mapping candidate point are candidate values of the mapping data.

[0035] 16QAM method: The majority value is 4, and 4 bits of the input signal are considered to be 1 symbol. The symbol is mapped to one of 16 mapping candidate points on the complex plane, and complex coordinate information representing the mapped point is output as mapping data.

[0036] 64QAM method: The majority value is 6, and 6 bits of the input signal are considered to be 1 symbol. The symbol is mapped to one of 64 mapping candidate points on the complex plane, and complex coordinate information representing the mapped point is output as mapping data.

[0037] A specific example of mapping will be described later with reference to FIGS.

[0038] As shown in Figure 2, the mapping and LDM multiplexing unit 32 uses the carrier-modulated ISDB-T signal as the higher layer signal and the SHV signal as the lower layer signal, reduces the power level of the lower layer signal to be lower than the power level of the higher layer signal, and adds both signals with a power difference to generate a multiplexed signal.

[0039] The multiplexed signal output from the mapping and LDM multiplexing unit 32 is input to the pilot adding unit 34. The pilot adding unit 34 inserts a pilot signal into the OFDM segment. Details of the pilot signal insertion process by the pilot adding unit 34 will be described later with reference to FIG. 11. The pilot signal is a known signal. By inserting a pilot signal into the OFDM segment, the receiving device can estimate the frequency characteristics of the propagation path by comparing the received pilot signal with a known signal, and can compensate for degradation of the frequency characteristics of the propagation path by correcting the frequency characteristics of the propagation path according to the estimation result. Degradation of the frequency characteristics of the propagation path may result in errors in the transmitted data. Compensating for degradation of the frequency characteristics of the propagation path can reduce transmission errors.

[0040] Pilot signals include scattered pilot signals (also called SP signals) that are inserted in a dispersed manner in the frequency direction (carrier direction), and continual pilot signals (also called continuous pilot signals, or CP signals) that are inserted continuously in the time direction at frequencies within the transmission band other than the OFDM segment. Note that SP signals may also be inserted in a dispersed manner in the time direction (symbol direction).

[0041] The output of the pilot adding unit 34 is input to an inverse fast Fourier transform (IFFT) unit 38. The IFFT unit 38 performs IFFT processing on the OFDM segment to obtain a bit string in the time domain.

[0042] The output of the IFFT unit 38 may be input to a guard interval (GI) adding unit 40. The GI adding unit adds data of a specified time length (guard interval) directly to the front of the OFDM symbol from the temporally rear side of the output data after IFFT.

[0043] The output of the GI adding unit 40 is transmitted via a transmission circuit and a transmission antenna (not shown). The signal transmitted from the transmitting device is received by a receiving device (television receiver). If the distance between the transmitting device and the receiving device is long, a relay device is provided between the transmitting device and the receiving device, and the signal transmitted from the transmitting device is received by the receiving device via the relay device.

[0044] FIG. 5 is a diagram illustrating an example of modulation of a transmitting device according to an embodiment. FIG. 5 is a constellation map showing mapping candidate points of a signal expressed as a complex number. The I axis and Q axis represent the amplitude of two signal components that are 90 degrees out of phase with each other. FIG. 5 shows an example in which the mapping and LDM multiplexing unit 32 maps an ISDB-T signal using the QPSK method and an SHV signal using the QPSK method. The mapping and LDM multiplexing unit 32 maps the symbols of the ISDB-T signal to one of four mapping candidate points on the constellation map shown in FIG. 5(a). The mapping and LDM multiplexing unit 32 maps the symbols of the SHV signal to one of four mapping candidate points on the constellation map shown in FIG. 5(b).

[0045] In the LDM system, the mapping / LDM multiplexing unit 32 superimposes a constellation map of the lower layer signal (SHV signal), which includes four mapping candidate points, onto each of four mapping candidate points of the higher layer signal (ISDB-T signal), to generate a constellation map of the multiplexed signal including 16 mapping candidate points, which is the product of the four mapping candidate points of the ISDB-T signal and the four mapping candidate points of the SHV signal, as shown in FIG. 5(c). The mapping / LDM multiplexing unit 32 maps the symbols of a multiplexed signal of an ISDB-T signal mapped using QPSK and an SHV signal mapped using QPSK to one of the 16 mapping candidate points on the constellation map of the multiplexed signal. A multiplexed signal of an ISDB-T signal mapped using QPSK and an SHV signal mapped using QPSK is equivalent to a signal mapped using 16QAM.

[0046] For example, if the mapping point of the ISDB-T signal symbol is mapping candidate point 70 in the first quadrant of Figure 5(a) and the mapping point of the SHV signal symbol is mapping candidate point 72 in the third quadrant of Figure 5(b), the mapping point of the multiplexed signal symbol is mapping candidate point 74, the bottom left of the four mapping candidate points in the first quadrant of Figure 5(c).

[0047] Fig. 6 is a constellation map for explaining another example of mapping in the transmitting device according to the embodiment. Fig. 6 shows an example in which the mapping and LDM multiplexing unit 32 maps the ISDB-T signal using the QPSK method and the SHV signal using the 16QAM method. The mapping and LDM multiplexing unit 32 maps the symbols of the ISDB-T signal to one of four mapping candidate points on the constellation map shown in Fig. 6(a). The mapping and LDM multiplexing unit 32 maps the symbols of the SHV signal to one of 16 mapping candidate points on the constellation map shown in Fig. 6(b).

[0048] The mapping and LDM multiplexing unit 32 generates the constellation map of the multiplexed signal shown in FIG. 6(c) by convolving the constellation map of the lower layer signal (SHV signal), which includes 16 mapping candidate points, on each of the four mapping candidate points of the higher layer signal (ISDB-T signal). FIG. 6(c) shows a constellation map of the multiplexed signal, which includes 64 mapping candidate points, which is the product of the four mapping candidate points of the ISDB-T signal and the 16 mapping candidate points of the SHV signal. The mapping and LDM multiplexing unit 32 maps the symbols of a multiplexed signal of an ISDB-T signal mapped using QPSK and an SHV signal mapped using 16QAM to one of the 64 mapping candidate points on the constellation map of the multiplexed signal. A multiplexed signal of an ISDB-T signal mapped using QPSK and an SHV signal mapped using 16QAM is equivalent to a signal mapped using 64QAM.

[0049] For example, if the mapping point of the ISDB-T signal symbol is mapping candidate point 76 in the third quadrant of Figure 6(a) and the mapping point of the SHV signal is the top left mapping candidate point 78 among the four mapping candidate points in the first quadrant of Figure 6(b), the mapping point of the multiplexed signal symbol is the second mapping candidate point from the right in the top row among the 16 mapping candidate points in the third quadrant of Figure 6(c).

[0050] Fig. 7 is a constellation map for explaining yet another example of mapping in the transmitting device according to the embodiment. Fig. 7 shows an example in which the mapping and LDM multiplexing unit 32 maps the ISDB-T signal using the 16QAM method and the SHV signal using the 64QAM method. The mapping and LDM multiplexing unit 32 maps the symbols of the ISDB-T signal to one of 16 mapping candidate points on the constellation map shown in Fig. 7(a). The mapping and LDM multiplexing unit 32 maps the symbols of the SHV signal to one of 64 mapping candidate points on the constellation map shown in Fig. 7(b).

[0051] The mapping / LDM multiplexing unit 32 generates the constellation map of the multiplexed signal shown in FIG. 7(c) by convolving the constellation map of the lower layer signal (SHV signal), which includes 64 mapping candidate points, on each of the 16 mapping candidate points of the higher layer signal (ISDB-T signal). FIG. 7(c) shows the constellation map of the multiplexed signal, which includes 1,024 mapping candidate points, which is the product of the 16 mapping candidate points of the ISDB-T signal and the 64 mapping candidate points of the SHV signal. The mapping / LDM multiplexing unit 32 maps the symbols of the multiplexed signal, which includes the ISDB-T signal mapped using the QPSK method and the SHV signal mapped using the QPSK method, to one of the 1,024 mapping candidate points on the constellation map of the multiplexed signal. A multiplexed signal of an ISDB-T signal mapped using the 16QAM method and an SHV signal mapped using the 64QAM method is equivalent to a signal mapped using the 1024QAM method.

[0052] For example, if the mapping point of the ISDB-T signal symbol is the bottom left mapping candidate point 82 among the four mapping candidate points in the first quadrant of Figure 7(a), and the mapping point of the SHV signal symbol is the top left mapping candidate point 84 among the 16 mapping candidate points in the second quadrant of Figure 7(b), the mapping point of the multiplexed signal symbol is the eighth mapping candidate point 86 from the top in the leftmost column among the 256 mapping candidate points in the first quadrant of Figure 7(c).

[0053] 8, 9, and 10 are diagrams illustrating an example of the arrangement relationship between injection levels and mapping candidate points in the LDM system according to the embodiment. FIGS. 8, 9, and 10 show constellation maps for different injection levels. In FIGS. 8, 9, and 10, the mapping system for ISDB-T signals is the 16QAM system, and the mapping system for SHV signals is the 64QAM system. FIG. 8 shows a constellation map for an injection level of 12 dB. FIG. 9 shows a constellation map for an injection level of 16 dB. FIG. 10 shows a constellation map for an injection level of 20 dB.

[0054] As shown in Figures 8, 9, and 10, as the injection level is increased, the mapping candidate points of the multiplexed signal are grouped into groups for each mapping candidate point of the ISDB-T (UL) signal, the spacing between mapping candidate point groups (inter-constellation distance) increases, and the intra-constellation distance decreases.

[0055] The distance within the constellation of the mapping candidate points for the SHV(LL) signal and the distance between the constellations of the mapping candidate points for the SHV signal change depending on the injection level. The smaller the injection level, the larger the distance within the constellation of the mapping candidate points for the SHV signal and the smaller the distance between the constellations of the mapping candidate points for the SHV signal. The higher the injection level, the smaller the distance within the constellation of the mapping candidate points for the SHV signal and the larger the distance between the constellations of the mapping candidate points for the SHV signal. In other words, when the injection level is high, the ISDB-T signal has fewer errors and the SHV signal has more errors.

[0056] An example of SP signal insertion by the pilot adding unit 34 will be described with reference to Fig. 11. Fig. 11 is a diagram for explaining an example of one OFDM segment in the LDM method according to the embodiment. In the example of Fig. 11, one OFDM segment includes 431 carriers. The number of carriers in an OFDM segment is not limited to this example, and the OFDM segment may include 108 or 216 carriers. 431 carrier symbols are collectively referred to as a symbol group. 13 OFDM segments are referred to as one OFDM symbol. 204 OFDM symbols are referred to as an OFDM frame. 13 OFDM segments are referred to as one OFDM symbol. In other words, one OFDM symbol is 5616 (= 13 x 432) symbols. When a CP signal is inserted, one OFDM symbol is 5617 symbols. S i,j (i=0 to 383, j=0 to 203) represents the carrier symbols after interleaving.

[0057] The pilot adding unit 34 inserts one SP signal into the OFDM segment every 12 carrier symbols in the frequency (carrier number) direction. The insertion period of the SP signals in the frequency direction is the first period (12 carriers). The pilot adding unit 34 inserts one SP signal every four carrier symbols in the time (symbol number) direction. The insertion period of the SP signals in the time direction is the second period (4 carrier symbols).

[0058] For example, the pilot adding unit 34 inserts SP signals into the carrier symbols with carrier numbers 0, 12, . . . in the symbol group with symbol number 0. The pilot adding unit 34 inserts SP signals into the carrier symbols with carrier numbers 3, 15, . . . in the symbol group with symbol number 1. Similarly, for each symbol group, the pilot adding unit 34 inserts an SP signal into a carrier symbol having a carrier number different from that of an adjacent symbol group. The carrier numbers of the carrier symbols into which the SP signals are inserted may be the same for every several symbol groups. For example, for the symbol group with symbol number 4, the pilot adding unit 34 inserts the SP signals into the carrier symbols with carrier numbers 0, 12, ..., just as in the symbol group with symbol number 0.

[0059] The SP signal is a BPSK (Binary Phase Shift Keying) signal associated with the output bit string Wi of the PRBS generator circuit, which corresponds to the carrier number i of the OFDM segment. The generator polynomial of the PRBS generator circuit that generates the bit string g2(x) is shown in Equation 3. g2(x)=x 11 +x 9 +1 formula 3 That is, the PRBS generator consists of 11 D-type flip-flops connected in series. The output of the ninth flip-flop, x 9 and the output of the 11th flip-flop x 11 (=Wi) is added and input to the first flip-flop. The initial value of the PRBS generator is determined for each OFDM segment.

[0060] The pilot adding unit 34 also inserts a TMCC (Transmission and Multiplexing Configuration Control) signal and an AC (Auxiliary Channel) signal into the OFDM segment.

[0061] TMCC signals are signals used to transmit control information. Control signals are information that assists the receiving device in making decisions and performing decoding operations, such as the hierarchical structure and transmission parameters of OFDM segments. Control information includes system identification, a transmission parameter switching indicator, a start control signal (start flag for emergency alert broadcasting), current information, next information, etc. Current information indicates the current transmission parameters of each hierarchical signal, and next information indicates the transmission parameters of each hierarchical signal after switching. Next information can be set or changed at any time before the countdown for switching, but cannot be changed during the countdown.

[0062] The transmission parameter information of each layer signal included in the current / next information indicates the type of mapping method. For example, transmission parameter information "001" indicates the QPSK method, transmission parameter information "010" indicates the 16QAM method, transmission parameter information "011" indicates the 64QAM method, and transmission parameter information "111" indicates that the corresponding layer is unused or that no next information exists. The transmitting device may transmit the transmission parameter information to the relay device by including it in a signal other than the TMCC signal, such as an AC signal, or by including it in any control information other than the pilot signal for channel estimation.

[0063] The AC signal is an extension signal for transmitting additional information related to broadcasting. The additional information is additional information related to transmission control or earthquake warning information. A transmitting device in an area where a relay device according to the embodiment is installed transmits not only multiplexed signals but also ISDB-T signals alone. The relay device performs different relay processing when receiving a multiplexed signal and when receiving a non-multiplexed signal (ISDB-T signal). For this reason, the pilot adding unit 34 includes a multiplex flag in the AC signal, indicating whether the signal to be transmitted is a multiplexed signal or an ISDB-T signal. The transmitting device may include the multiplex flag in a signal other than the AC signal, for example, a TMCC signal, and transmit it to the relay device, or may include the flag in any control information other than the pilot signal for channel estimation and transmit it.

[0064] The carriers of the TMCC signal and AC signal are randomly arranged in the frequency direction to reduce the effects of periodic dips in the propagation path characteristics due to multipath.

[0065] The multiplexed signal transmitted from the transmitter shown in Figure 4 is received by television receivers in each home. In places where direct waves from the broadcasting station cannot reach easily, the signal transmitted from the transmitter is received by the television receiver via a relay device.

[0066] FIG. 12 is a block circuit diagram illustrating an example of a relay device according to an embodiment. The relay device may have the functions of a receiving device and a transmitting device. The functions of the receiving device may include a function of correcting frequency characteristics to compensate for degradation of the frequency characteristics of the propagation path, a function of calculating a log-likelihood ratio (LLR), a function of deinterleaving a signal interleaved on the transmitting side, a function of decoding a signal coded on the transmitting side, and a function of despreading a signal energy-dispersed on the transmitting side. The functions of the transmitting device may include a coding function, a function of dispersing signal energy, a function of interleaving a signal, a symbol mapping function, and a function of adding a pilot signal. If the relay device has the same functions as the receiving device and performs the processes of frequency characteristic correction, LLR calculation, deinterleaving, decoding, and energy despreading in the same way as the receiving device, and transmits the processed signal, the error rate in the receiving device will be lowest. However, if the relay device performs the same processes as the receiving device, relaying will take time, resulting in delays. The relay device of the embodiment performs frequency characteristic correction and symbol determination processing, but does not perform deinterleaving, decoding, and energy despreading processing, thereby reducing the error rate in the receiving device and shortening the time required for relaying.

[0067] The relay device includes a GI removal unit 112. A multiplexed signal received by an antenna and a receiving circuit (not shown) is input to the GI removal unit 112. The GI removal unit 112 removes GIs between OFDM symbols from the multiplexed signal.

[0068] The output of the GI removal unit 112 is input to a fast Fourier transform (FFT) unit 114. The FFT unit 114 performs FFT processing on the input signal at an FFT size to obtain a signal in the frequency domain.

[0069] Let H be the propagation path characteristic in the frequency domain for the transmission signal Txi in the frequency domain of the multiplexed signal. The received signal Rx after FFT is expressed as shown in Equation 4. Here, noise will be ignored in the explanation.

[0070] Rx=HTxi Equation 4 The output of the FFT unit 114 is input to a frequency equalization unit 116 and a propagation path estimation unit 118 .

[0071] The channel estimation unit 118 extracts a pilot signal from the input frequency domain signal, and estimates the channel characteristics (frequency characteristics) H of the frequency domain multiplexed signal from the received signal Rx after FFT, using the extracted pilot signal as a transmission signal Txi. The output of the channel estimation unit 118 is input to the frequency equalization unit 116.

[0072] The frequency equalization unit 116 performs frequency equalization processing on the multiplexed signal in accordance with the estimation result of the propagation path estimation unit 118, thereby obtaining a multiplexed signal in which degradation of the frequency characteristics of the propagation path has been compensated for. The frequency equalization processing is a correction of the frequency characteristics of the propagation path. Specifically, the frequency equalization unit 116 divides the received signal Rx after FFT by the frequency characteristic H of the propagation path, as shown in Equation 5, to obtain a frequency equalized signal Req. Req=Rx / H Equation 5 The output Req of the frequency equalizer 116 is input to the selector 122 and the LDM determiner 124. The LDM determiner 124 extracts the AC signal from the output of the frequency equalizer 116 and extracts the multiplex flag from the AC signal. The LDM determiner 124 switches the selector 122 based on the multiplex flag.

[0073] A first output terminal of the selector 122 is connected to a symbol decision unit 132 for the higher layer signal. A second output terminal of the selector 122 is connected to a symbol decision unit 142 for the multiplexed signal. The LDM decision unit 124 extracts the AC signal from the input signal and extracts the multiplex flag from the AC signal. If the multiplex flag indicates that the transmission signal is a multiplexed signal, the LDM decision unit 124 causes the selector 122 to output the input signal from its second output terminal. If the multiplex flag indicates that the transmission signal is an ISDB-T signal, the LDM decision unit 124 causes the selector 122 to output the input signal from its first output terminal.

[0074] The symbol decision units 132 and 142 extract the TMCC signal from the input signal and extract transmission parameter information from the TMCC signal. The symbol decision units 132 and 142 determine the position of the mapping point of the symbol of the input signal based on the mapping candidate point on the symbol constellation map according to the mapping method represented by the transmission parameter information (symbol decision). The symbol decision includes hard decision and soft decision. Details of the symbol decision will be described later with reference to FIGS. 13 and 14.

[0075] When the input signal is an ISDB-T signal, the selector 122 outputs the input signal to the symbol decision unit 132. When the mapping method of the ISDB-T signal is, for example, the 16QAM method, the symbol decision unit 132 determines the position of the mapping point of the symbol of the input signal based on 16 mapping candidate points of the 16QAM method.

[0076] The output of the symbol decision unit 132 is input to the IFFT unit 134. The IFFT unit 134 performs IFFT processing on the OFDM segments of the ISDB-T signal to obtain a bit string in the time domain.

[0077] The output of the IFFT unit 134 is input to the GI adding unit 136. The GI adding unit 136 adds data (GI) of a specified time length directly to the front of the OFDM symbol from the temporally rear side of the output data after IFFT.

[0078] The output of the GI adding unit 136 is transmitted as an ISDB-T signal via a transmitting circuit, a transmitting antenna, etc. (not shown).

[0079] When the input signal is a multiplexed signal, the selector 122 outputs the input signal to the symbol decision unit 142. When the mapping method for the ISDB-T signal is, for example, the QPSK method and the mapping method for the SHV signal is, for example, the 16QAM method, the symbol decision unit 142 determines the position of the mapping point for the symbol of the input signal based on 64 mapping candidate points of the 64QAM method.

[0080] The output of the symbol decision unit 142 is input to the IFFT unit 144. The IFFT unit 144 performs IFFT processing on the OFDM segments of the multiplexed signal to obtain a bit string in the time domain.

[0081] The output of the IFFT unit 144 is input to the GI adding unit 146. The GI adding unit 146 adds data of a specified time length (GI) directly to the front of the OFDM symbol from the temporally rear side of the output data after IFFT.

[0082] The output of the GI adding unit 146 is transmitted as a multiplexed signal via a transmission circuit, a transmission antenna, etc. (not shown).

[0083] A specific example of symbol determination by the symbol determining units 132 and 142 will be described.

[0084] FIG. 13 is a diagram illustrating an example of the operation of the symbol decision unit 142 of the relay device according to the embodiment. FIG. 13 illustrates an example of hard decision by the symbol decision unit 142 when the transmitting device transmits a multiplexed signal in which the ISDB-T signal is mapped using the QPSK method and the SHV signal is mapped using the 16QAM method. The symbol decision unit 142 detects the mapping method for the ISDB-T signal and the SHV signal from the transmission parameter information. The constellation map illustrated in FIG. 13 corresponds to the constellation map illustrated in FIG. 6(c). The mapping point of the symbol of the multiplexed signal transmitted by the transmitting device is one of 64 mapping candidate points illustrated in FIG. 13. The propagation path from the transmitting device to the relay device is affected by noise and interference. In this case, the point 170 on the constellation map of the symbol input to the symbol decision unit 142 (hereinafter referred to as the input symbol point) may deviate from the 64 mapping candidate points, as illustrated in FIG. 13.

[0085] The symbol decision unit 142 decides the input symbol point by hard decision or soft decision processing. By deciding the input symbol point, the symbol decision unit 142 can reduce distortion of the symbol on the propagation path from the transmitting device to the relay device.

[0086] 13, in the case of hard decision, the symbol decision unit 142 calculates the distance between the input symbol point 170 and each of the 64 mapping candidate points on the constellation map of the multiplexed signal, and detects the mapping candidate point 172 that is closest to the input symbol point 170. The symbol decision unit 142 outputs the coordinates of the detected mapping candidate point 172 as the coordinates (I coordinate, Q coordinate) of the mapping point of the symbol of the multiplexed signal transmitted by the transmitting device, i.e., as a decision value.

[0087] In the case of soft decision, the symbol decision unit 142 performs soft decision calculations on 64 mapping candidate points on the constellation map of the multiplexed signal and the input symbol point 170 to find the position of the soft replica.

[0088] The soft decision calculation includes LLR calculation, bit likelihood calculation, symbol probability calculation, and soft replica calculation.

[0089] Assuming that one symbol transmits multiple bits of data, the symbol decision unit 142 calculates the LLR of the k-th bit of one symbol using Equation 6.

[0090]

number

[0091] where y I , y Q indicates the I and Q components of the k-th bit of the input symbol point 170. j,I , y j,Q indicates the I and Q components of the j-th symbol among the mapping candidate points of the multiplexed signal. 2 is the noise variance estimated at the relay device. k,0 is a set of symbols whose k-th bit is 0 among the mapping candidate points of the multiplexed signal. k,1 is a set of symbols whose k-th bit is 1 among the mapping candidate points of the multiplexed signal.

[0092] k-th bit likelihood P k (0) and P k (1) is P k (0)+P k (1)=1. The symbol decision unit 142 calculates the k-th bit likelihood P k (0), P k (1) is calculated using LLRk according to Equations 7 and 8.

[0093] P k (0)=exp(LLR k ) / (1+exp(LLR k )) Equation 7 P k (1)=1 / ((1+exp(LLR k )) Equation 8 The symbol decision unit 142 calculates the symbol probability according to the bit sequence represented by the symbol using Equation 9.

[0094]

number

[0095] where v is the number of bits that one symbol represents, and b j (k) is an arbitrary mapping candidate point x j indicates the kth bit of the bit sequence represented by

[0096] The symbol decision unit 142 calculates the position (I coordinate, Q coordinate) of the soft replica according to Equations 10 and 11 using the symbol probability Q(xj).

[0097]

number

[0098] The symbol decision unit 142 outputs the position of the soft replica as the coordinates of the mapping point of the symbol of the multiplexed signal transmitted by the transmitting device, that is, as a decision value.

[0099] As described above, the symbol decision unit 142 decides the position of the input symbol point of the multiplexed signal by hard decision or soft decision using mapping candidate points on the constellation map of the multiplexed signal.

[0100] The operation of the symbol decision unit 132 is substantially the same as that of the symbol decision unit 142. The only difference between the operation of the symbol decision unit 132 and the operation of the symbol decision unit 142 is that the input signal is an ISDB-T signal rather than a multiplexed signal. The symbol decision unit 132 determines the position of the input symbol point by hard decision or soft decision depending on the distance between the input symbol point and a mapping candidate point on a constellation map in accordance with the mapping method of the ISDB-T signal.

[0101] The soft decision calculations shown in Equations 6 to 11 include LLR calculations for all mapping candidate points of the modulated signal. If the mapping method for the ISDB-T signal is QPSK and the mapping method for the SHV signal is 16QAM, there are 64 mapping candidate points for the multiplexed signal, as shown in FIG. 13. As the number of modulation bits for the multiplexed signal increases and the number of mapping candidate points also increases, the amount of calculation required for the soft replica increases. For example, if the mapping method for the ISDB-T signal is 64QAM and the mapping method for the SHV signal is 64QAM, there are 4096 mapping candidate points for the multiplexed signal, which requires a significant amount of time for LLR calculation. If the calculation time for the soft replica is long, delays in relaying may occur.

[0102] Another example of a soft decision method that can reduce the calculation time of a soft replica will now be described.

[0103] In the LDM system, when the injection level is high, it is expected that there will be few transmission errors for ISDB-T signals and many transmission errors for SHV signals. In the LDM system, it is expected that the injection level will be high.

[0104] In another example of the soft decision method, it is assumed that no errors occur in the symbols of the ISDB-T signal during transmission. First, the symbol decision unit 142 determines which quadrant of the ISDB-T signal constellation map the symbol point of the input signal falls in. Next, the symbol decision unit 142 calculates a soft decision value from only the mapping candidate points that fall in that quadrant.

[0105] Fig. 14 is a diagram for explaining another example of the operation of the symbol determination unit 142 of the relay device according to the embodiment. Fig. 14 shows an example in which a transmitting device transmits a multiplexed signal in which ISDB-T signals are mapped in the QPSK format and SHV signals are mapped in the 16QAM format. Fig. 14(a) shows a constellation map of the ISDB-T signal, and Fig. 14(b) shows a constellation map of the multiplexed signal.

[0106] First, the symbol decision unit 142 calculates the distance between the input symbol point 180 and each of the four mapping candidate points on the constellation map of the ISDB-T signal shown in Fig. 14(a), and detects the mapping candidate point 182 that is closest to the input symbol point 180. The symbol decision unit 142 detects that the mapping candidate point 182 that is closest to the input symbol point 180 is located in the third quadrant.

[0107] Next, the symbol decision unit 142 performs soft decision calculations on 16 mapping candidate points 184 located in the third quadrant among the 64 mapping candidate points on the constellation map of the multiplexed signal shown in Figure 14(b) and the input symbol point 180, to determine the position of the soft replica.

[0108] In this way, symbol decisions are made on the upper layer signals, and the number of mapping candidate points that are the subject of soft decision calculations for the multiplexed signal is reduced to one-fourth, thereby reducing the calculation time for the soft replica.

[0109] Since the SP signal is known, the symbol decision units 132 and 142 may omit symbol decision for symbols into which the SP signal is inserted. For symbols into which the SP signal is inserted, the symbol decision units 132 and 142 may insert the known SP signal instead of inserting the decision result.

[0110] 15 is a block circuit diagram showing an example of a receiving device according to an embodiment. The receiving device is obtained by adding multiple processing units to the relay device shown in FIG. 12. The receiving device includes a GI removal unit 212, an FFT unit 214, a frequency equalization unit 216, a channel estimation unit 218, a selector 222, an LDM determination unit 224, an LLR calculation unit 232, and an LLR calculation unit 252. The GI removal unit 212, the FFT unit 214, the frequency equalization unit 216, the channel estimation unit 218, the selector 222, and the LDM determination unit 224 are equivalent to the GI removal unit 112, the FFT unit 114, the frequency equalization unit 116, the channel estimation unit 118, the selector 122, and the LDM determination unit 124 of the relay device, respectively. The LLR calculation unit 232 calculates the LLR of the symbol point of the input signal using the mapping candidate points of the ISDB-T signal, and outputs the LLR to a time-frequency De-IL unit 234.

[0111] The time-frequency De-IL unit 234 performs deinterleaving on the LLR, which is the inverse of the interleaving performed by the time-frequency IL unit 28 of the transmitting device shown in Figure 4, to obtain an input to the time-frequency IL unit 28, i.e., a signal equivalent to the output of the bit IL unit 24.

[0112] The output of the time / frequency De-IL unit 234 is supplied to a bit De-IL unit 236. The bit De-IL unit 236 performs deinterleaving processing corresponding to the inverse processing of the interleaving processing performed by the bit IL unit 24 of the transmitting device, and obtains the input to the bit IL unit 24, i.e., a signal equivalent to the output of the convolutional coding unit 22. The output of the bit De-IL unit 236 is input to a Viterbi decoding unit 238.

[0113] The Viterbi decoder 238 performs error correction decoding processing that corresponds to the inverse processing of the encoding processing by the convolutional encoder 22 of the transmitting device, and obtains a signal that corresponds to the input of the convolutional encoder 22, i.e., the output of the byte IL unit 18. The output of the Viterbi decoder 238 is input to a byte deinterleave (De-IL) unit 240.

[0114] The byte De-IL unit 240 performs deinterleaving, which is the inverse of the interleaving performed by the byte IL unit 18 of the transmitting device, to obtain the input to the byte IL unit 18, i.e., a signal equivalent to the output of the energy dispersal unit 16. The output of the byte De-IL unit 240 is input to the energy despreading unit 242.

[0115] The energy despreading unit 242 performs energy despreading processing that corresponds to the inverse of the energy dispersal processing performed by the energy dispersal unit 16 of the transmitting device, and obtains a signal that corresponds to the input to the energy dispersal unit 16, i.e., the output of the RS encoding unit 14. The output of the energy despreading unit 242 is input to the RS decoding unit 244.

[0116] The RS decoder 244 performs error correction RS decoding processing corresponding to the inverse processing of the encoding processing by the RS encoder 14 of the transmitting device, and obtains the input of the RS encoder 14, that is, the information bit string of the higher layer ISDB-T signal.

[0117] The LLR calculation unit 252 calculates the LLR of the symbol point of the input signal using the mapping candidate points of the multiplexed signal, and outputs the LLR to the time-frequency De-IL unit 254 .

[0118] The time / frequency De-IL unit 254 performs deinterleaving on the LLR, which corresponds to the inverse of the interleaving performed by the time / frequency IL unit 56 of the transmitting device shown in Figure 4, and obtains an input to the time / frequency IL unit 56, i.e., a signal equivalent to the output of the bit IL unit 52.

[0119] The output of the time / frequency De-IL unit 254 is input to a bit De-IL unit 256 .

[0120] The bit De-IL unit 256 performs deinterleaving processing that corresponds to the inverse of the interleaving processing performed by the bit IL unit 52 of the transmitting device, and obtains a signal that corresponds to the input of the bit IL unit 52, i.e., the output of the LDPC encoding unit 48. The output of the bit De-IL unit 256 is input to the LDPC decoding unit 258.

[0121] The LDPC decoding unit 258 performs error correction decoding processing that corresponds to the inverse processing of the encoding processing by the LDPC encoding unit 48 of the transmitting device, and obtains the input to the LDPC encoding unit 48, i.e., a signal that corresponds to the output of the BCH encoding unit 46. The output of the LDPC decoding unit 258 is input to the BCH decoding unit 260.

[0122] The BCH decoding unit 260 performs error correction decoding processing that corresponds to the inverse processing of the encoding processing by the BCH encoding unit 46 of the transmitting device, and obtains the input to the BCH encoding unit 46, i.e., a signal that corresponds to the output of the energy dispersal unit 44. The output of the BCH decoding unit 260 is input to the energy despreading unit 262.

[0123] The energy dispersal unit 262 performs energy dispersal processing corresponding to the inverse of the energy dispersal processing of the energy dispersal unit 44 of the transmitting device, and obtains the input of the energy dispersal unit 44, that is, the information bit string of the SHV signal of the lower layer.

[0124] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0125] 112...GI removal unit, 114...FFT unit, 116...frequency equalization unit, 118...propagation path estimation unit, 122...selector, 124...LDM determination unit, 132...symbol determination unit, 134...IFFT unit, 136...GI addition unit, 142...symbol determination unit, 144...IFFT unit, 146...GI addition unit

Claims

1. a receiver for receiving a third signal including a first signal at a first power level and a second signal at a second power level lower than the first power level; a correction unit that obtains an estimate of a frequency characteristic of a propagation path of the third signal based on the third signal, and corrects the frequency characteristic of the third signal in accordance with the estimate; a determination unit that determines a value of the third signal whose frequency characteristics have been corrected by the correction unit; a transmitter that transmits a third signal having the value determined by the determiner; A relay device comprising:

2. the first signal includes a first signal point that is one of a plurality of first candidate points included in a first constellation map according to a first mapping scheme; the second signal includes a second signal point that is one of a plurality of second candidate points included in a second constellation map according to a second mapping scheme; the second mapping scheme is the same as or different from the first mapping scheme, the third signal includes a third signal point that is one of a plurality of third candidate points included in a third constellation map generated by convolving the second constellation map on each of the plurality of first candidate points; The relay device according to claim 1 , wherein the determining unit determines the value of the third signal point based on the plurality of third candidate points.

3. The relay device according to claim 2 , wherein the decision unit decides the value of the third signal point by soft decision or hard decision.

4. The relay device according to claim 2 , wherein the determination unit determines the value of the third signal based on a third candidate point that is closest to the third signal point among the plurality of third candidate points.

5. The relay device according to claim 2 , wherein the determining unit determines the value of the third signal based on a log-likelihood ratio between each of the plurality of third candidate points and the third signal point.

6. The determination unit Detecting a quadrant in which a first candidate point closest to the third signal point is located among the plurality of first candidate points included in the first constellation map; 3. The relay device according to claim 2, wherein the value of the third signal is determined based on a log-likelihood ratio between each of a plurality of third candidate points included in the quadrant of the third constellation map among the plurality of third candidate points and the third signal point.

7. the receiving unit receives first identification information indicating the first mapping method and second identification information indicating the second mapping method; The relay device according to claim 2 , wherein the determining unit generates the first constellation map based on the first identification information and generates the second constellation map based on the second identification information.

8. the receiving unit receives the first signal or the third signal, When the receiving unit receives the first signal, the correcting unit obtains a second estimate of a frequency characteristic of a propagation path of the first signal based on the first signal, and corrects the frequency characteristic of the first signal in accordance with the second estimate; When the receiving unit receives the first signal, the determining unit determines a value of the first signal from the first signal whose frequency characteristics have been corrected by the correcting unit; The relay device according to claim 2 , wherein when the receiving unit receives the first signal, the transmitting unit transmits a first signal having the value determined by the determining unit.

9. the first mapping scheme is a QPSK (Quadrature Phase Shift Keying) scheme, a 16QAM (16 Quadrature Amplitude Modulation) scheme, or a 64QAM scheme; 9. The relay device according to claim 2, wherein the second mapping method is a QPSK method, a 16QAM method, or a 64QAM method.

10. receiving a third signal including a first signal at a first power level and a second signal at a second power level lower than the first power level; determining an estimate of frequency characteristics of a propagation path of the third signal based on the third signal; correcting the frequency characteristic of the third signal in accordance with the estimated value; determining a value of the third signal after the frequency characteristic has been corrected; transmitting a third signal of the determined value.

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