JP2019106700A - Transmitter, receiver, transmission method, and reception method - Google Patents

Abstract

To provide a transmitter capable of transmitting signals with a transmission method suitable for actual environment.SOLUTION: A transmitter 10A includes: a modulation circuit 11A that is configured to modulate signals by performing mapping of a data string only to four signal points each of which has the phase different by 90 degrees from the neighboring signal points, which are four signal points including at least two signal points in which the amplitudes are different from each other by means of QAM (Quadrature Amplitude Modulation); and a transmission circuit 18A that is configured to allot the data strings which are mapped to the four signal points by means of modulation by the modulation circuit 11A to subcarriers OFDM (Orthogonal Frequency Division Multiplexing) of which are different from each other and transmit the same via radio.SELECTED DRAWING: Figure 21

Description

  The present invention relates to a transmitter, a receiver, a transmission method, and a reception method.

  Multiplexing multiple signals into a composite signal to share a single medium is a common method in data communication. Conventionally, the various services that transmit data are time or frequency multiplexed. Also, it has been shown that the superposition of various services actually increases the capacity compared to Time Division Multiplexing (TDM) or Frequency Division Multiplexing (FDM) (Non-Patent Documents 1 to 3).

  Superimposed modulation is also a core element of a recently proposed new terrestrial broadcast system called Wideband transmission (WiB) having a reuse factor of 1 (Non-Patent Document 4). In WiB, adjacent transmitters transmit individual services. For WiB, in [5], it was speculated that the power partitioning method would be useful in a broadcast environment. Non-Patent Document 5 proposes using a non-uniform power distribution rather than using a uniform power distribution from each transmitter over the available bandwidth as a receiver implementation that can operate at near maximum capacity ing.

European Patent Application Publication No. 3334075

ETSI EN 302 755, "Digital Video Broadcasting (DVB); Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2) (Digital Video Broadcasting (DVB): second-generation digital terrestrial television broadcasting system Frame structure channel coding and modulation for (DVB-T2) ”, version 1.4.1, February 2015 P. P. Bergmans and T.W. M. Cover, "Cooperative broadcasting (broadcast cooperation system)", IEEE Trans. Inf. Theory, Vol. 20, No. 3, May 1974, p. 317-324 S. I. Park et al., "Low Complexity Layered Division for ATSC 3.0 (Low Complexity Layer Division in ATSC 3.0)", IEEE Transactions on Broadcasting, Vol. 62, No. 1, March 2016, p. 233-243 E. Stare, J.M. J. Gimenez, P .; Klenner, "WIB: a new system concept for digital terrestrial television (DTT) (WIB: new system concept in digital terrestrial television (DTT))", IBC Conference 2016 DVB-TM-WiB Study Mission Input Document TM-WIB 0088, "Suggested approach forward for optimized interference cancellation processing (proposed method for optimized interference cancellation processing)" ATSC Standard: Physical Layer Protocol (A / 322), June 2017

  However, in Non-Patent Document 5, an argument is made using an ideal Gaussian signal. Therefore, there is room for improvement in applying the power division method to the actual environment.

  Thus, the present invention provides a transmitter or the like that transmits a signal by a transmission method more suitable for the actual environment.

  A transmitter according to one aspect of the present invention is four signal points including at least two signal points having different amplitudes from each other by QAM (Quadrature Amplitude Modulation), and the phase is different by 90 degrees from adjacent signal points. A modulation circuit that modulates data strings by mapping only to four signal points, and the data strings mapped to the four signal points by modulation by the modulation circuit are mutually different in OFDM (Orthogonal Frequency Division Multiplexing) And a transmitting circuit that allocates to different subcarriers and transmits by radio.

  These general or specific aspects may be realized by a system, a method, an integrated circuit, a computer program, or a recording medium such as a computer readable CD-ROM, and the system, the method, the integrated circuit, the computer program And any combination of recording media.

  The transmitter of the present invention can transmit signals in a transmission manner that is more suitable for the actual environment.

FIG. 1 is an explanatory diagram of a transmitter that performs constellation superposition on a two-layer LDM of ATSC 3.0 according to the embodiment. FIG. 2 is an explanatory diagram of a transmission scenario of WiB according to the embodiment. FIG. 3 is an explanatory diagram of a system model of superposition modulation applicable to the two-layer LDM and WiB according to the embodiment. FIG. 4 is an explanatory view of a power distribution according to the embodiment. FIG. 5 is an explanatory diagram of non-gray mapping aQAM for the first transmitter of the two transmitters according to the embodiment. FIG. 6 is an explanatory diagram of non-gray mapping aQAM for a second transmitter of two transmitters according to the embodiment. FIG. 7 is an explanatory diagram of gray mapping aQAM for the first transmitter of the two transmitters according to the embodiment. FIG. 8 is an explanatory diagram of gray mapping aQAM for the second transmitter of the two transmitters according to the embodiment. FIG. 9 is an illustration of joint demapping, various C / I and C / N conditions, and 1 bit / s / Hz rates for two transmitters according to an embodiment. FIG. 10 is an explanatory diagram of aQAM for a first transmitter among three transmitters according to the embodiment. FIG. 11 is an explanatory diagram of aQAM to a second transmitter of three transmitters according to the embodiment. FIG. 12 is an explanatory diagram of aQAM for the third transmitter of the three transmitters according to the embodiment. FIG. 13 is an explanatory diagram of one in which the concept of power division according to the embodiment is replaced with QAM signals of two transmitters. FIG. 14 is an explanatory diagram of one in which the concept of power division according to the embodiment is replaced with QAM signals of three transmitters. FIG. 15 is an explanatory diagram of a parity check matrix from ATSC 3.0 with respect to a coding rate 8/15 according to the embodiment. FIG. 16 is an explanatory diagram of variable node degree distribution for LDPC with a coding rate of 8/15 according to the embodiment. FIG. 17 is an explanatory diagram of two superposition modulation in which the transmitter according to the embodiment is two. FIG. 18 is an explanatory diagram of a harmonic bit interleaver to power division QAM according to the embodiment. Vertical solid lines indicate highlights of which cell type is connected to which variable node. FIG. 19 is an explanatory diagram of a transmitter according to an embodiment of three bit interleaving. FIG. 20 is an explanatory diagram of a receiver according to the embodiment. FIG. 21 is a block diagram showing a configuration of a transmitter according to a modification of the embodiment. FIG. 22 is a flowchart showing a transmission method performed by a transmitter according to a modification of the embodiment. FIG. 23 is a block diagram showing a configuration of a receiver according to a modification of the embodiment. FIG. 24 is a flowchart showing a reception method performed by a receiver according to a modification of the embodiment.

(Findings that formed the basis of the present invention)
The present invention relates to asymmetric QAM for superposition modulation and adaptive bit interleaving. The invention applies to the field of digital communications that broadcast digital data, and in particular to superposition-based modern multiplexing-oriented new transmission techniques for simultaneously delivering various service types to stationary and mobile users. Ru.

  Multiplexing multiple signals into a composite signal to share a single medium is a common method in data communication. Conventionally, the various services that transmit data are time or frequency multiplexed. These methods are called time division multiplexing (TDM) and frequency division multiplexing (FDM). The practical application of TDM and FDM is described in DVB-T2 (Non-Patent Document 1), and the Japanese ISDB-T standard with an excellent One-Seg system. In DVB-T2 (Non-Patent Document 1), a plurality of so-called PLPs (Physical Layer Pipes), each characterized by its own modulation and time interleaver, share a certain frequency band in a dedicated time slot, ISDB- According to the T standard, energy saving partial reception of individual segments is enabled by transmitting data in strictly divided divided segments in the frequency domain.

  FDM and TDM will be known for a long time as they are not the most spectrally efficient way to share media. These advantages are more related to ease of implementation. Non-Patent Document 2 shows that superposition of various services actually increases capacity over TDM or FDM. Recently, this type of multiplexing is the current standard, that is, ATSC 3.0, and is also called Layered Division Multiplexing (LDM) (Non-Patent Documents 3 and 6).

  In addition, superposition modulation is also a core element of a recently proposed new terrestrial broadcast system called WiB, which is an abbreviation of Wideband transmission with a reuse factor of 1 (Non-Patent Document 4). In WiB, adjacent transmitters transmit individual services. With an implicit reuse factor of 1, the receiver, especially in the interference region between transmitters, receives the sum signal of all transmitted signals. However, from the perspective of a receiver, this received signal looks like a signal obtained from layer division multiplexing. Thus, with a correctly designed FEC encoding and modulation scheme, the receiver can read data using Successive Interference Cancellation techniques.

  Intuitively, the strength of superposition modulation via TDM / FDM in capacity is obtained by transmitting more than one service simultaneously without interruption in the time domain or frequency domain. A separate use case of superposition modulation, and the use case in which the advantages are most striking, is the provision of services to mobile and fixed receivers. Usually, mobile reception and fixed reception are characterized by low SNR (signal to noise ratio) and high SNR, respectively. Here, mobile services are performed at a data rate sufficiently low to withstand low SNR as well as the presence of fixed services. On the other hand, fixed-point service receivers make good use of relatively high SNRs to first detect a robust mobile-oriented layer and then subtract that data, and to detect data that is actually desirable for fixed-point services You can proceed with the process.

  For WiB, it was speculated in [5] that power partitioning techniques would be useful in a broadcast environment. Rather than using a uniform power distribution from each transmitter over the available bandwidth, a non-uniform power distribution has been suggested for iterative receiver implementations to operate at near maximum capacity. However, discussions have been made using ideal Gaussian signals.

  As described above, there is room for improvement in applying the power division method described in Non-Patent Document 5 to an actual environment.

  Therefore, a transmitter according to one aspect of the present invention is a signal point including 90 signal points and 90 adjacent signal points including at least two signal points having different amplitudes according to QAM (Quadrature Amplitude Modulation). A modulation circuit that modulates by mapping a data sequence to only four different signal points, and a data sequence mapped to the four signal points by modulation by the modulation circuit are represented by OFDM (Orthogonal Frequency Division Multiplexing) And a transmitter circuit for wireless transmission by assigning to different subcarriers.

  According to the above aspect, it is possible to demodulate QAM even when there is another transmitter in which at least a part of the transmittable area overlaps, and another transmitter transmits a signal on the same subcarrier. Can be successful. Since the amplitudes of at least two of the four signal points used for QAM modulation are different from each other, the signal point used by the transmitter for QAM modulation and the signal point used by other transmitters for QAM modulation And can be arranged so as not to overlap each other. Thus, the transmitter according to an aspect of the present invention can transmit signals in a more suitable transmission method in an actual environment. Note that such QAM is also referred to as asymmetric QAM.

  For example, among the four signal points, two signal points whose phases are different from each other by 180 degrees have equal distances from the origin in the IQ plane, and the two signal points among the four signal points are the two signal points. The two signal points other than may have equal distances from the origin in the IQ plane.

  According to the above aspect, the transmitter can more easily transmit the data sequence by QAM modulation.

  For example, the data string includes a first data and a second data before or after the first data, and the modulation circuit modulates the first data by mapping the first data to a signal point based on gray arrangement. Modulation by mapping the second data to signal points based on a non-gray arrangement, and the transmitting circuit transmits the modulated first data and the modulated second data in a time division manner. May be

  According to the above aspect, by using both the gray arrangement and the non-gray arrangement in time division, which is an arrangement of two signal points having different error resistances, it is possible to make the error resistance higher than when either one is used. Can.

  For example, the data string includes third data and fourth data preceding or following the third data, and the modulation circuit modulates the third data by mapping it to a signal point based on gray arrangement. Modulation by mapping the fourth data to a signal point based on a non-gray arrangement, and the transmission circuit allocates and transmits the modulated third data to subcarriers to be transmitted in a first frequency band, The modulated fourth data may be allocated to subcarriers for transmission in a second frequency band different from the first frequency band for transmission.

  According to the above aspect, by using both of the gray arrangement and the non-gray arrangement in frequency division, which is an arrangement of two signal points having different error resistances, it is possible to make the error resistance higher than when either one is used. Can.

  For example, the data string includes fifth data and sixth data preceding or following the fifth data, the modulation circuit modulates the fifth data by the QAM, and QPSK the sixth data. Modulating according to (Quadrature Phase Shift Keying), the transmission circuit assigns the modulated fifth data to a subcarrier for transmission with the first power and transmits the subcarrier, and the modulated sixth data is transmitted from the first power. It may be allocated and transmitted to a subcarrier that transmits with a small second power.

  According to the above aspect, it is possible to increase the error resistance of the signal of the subcarrier transmitted with high power in the LDM by asymmetric QAM, and to transmit the signal even with the subcarrier transmitted with low power.

  For example, the data string includes an LDPC (Low-Density Parity-Check) code, and the transmitter is further configured to convert data modulated by the modulation circuit as the fifth data from a predetermined order of the LDPC code. The bit interleaver may be configured to rearrange bits in the data train to be a high node, and the modulation circuit may modulate the data train after the bit interleaver performs the rearrangement.

  According to the above aspect, it is possible to cause the receiver to more reliably receive a node of a relatively high degree of the LDPC code, that is, a bit with a relatively high correction capability in decoding of a data string. This can increase the probability that the entire data string can be decoded.

  For example, the modulation circuit modulates using the four new signal points obtained by rotating the four signal points on the IQ plane by a predetermined angle around the origin as the four signal points. It is also good.

  According to the above aspect, it is possible to avoid that the original four signal points and the new four signal points overlap on the IQ plane (that is, the complex plane). Thus, when there are other transmitters in which at least a part of the transmittable area overlaps, signal points overlap even when the other transmitters transmit signals on the same subcarrier. By avoiding, QAM can be successfully demodulated.

  For example, the transmitter is one transmitter out of a plurality of transmitters in which at least a part of a transmittable area overlaps, and the predetermined angle is 180 degrees by the number of the plurality of transmitters. It may be a divided angle.

  According to the above aspect, this makes it possible to separate the positions of the signal points on the IQ plane as much as possible when there are other transmitters in which at least a part of the transmittable area overlaps. This can reduce the probability that a reception error will occur.

  In the receiver according to one aspect of the present invention, four signal points including two signal points having different amplitudes from each other according to QAM (Quadrature Amplitude Modulation) are 90 degrees in phase with an adjacent signal point. A receiver circuit which is modulated by being mapped to only four different signal points and which is allocated to different subcarriers of orthogonal frequency division multiplexing (OFDM) to receive a wirelessly transmitted signal, and the receiver circuit receives the signal. And a demodulation circuit that demodulates the signal by mapping data sequences to the four signal points by the QAM.

  According to the above aspect, the receiver is able to receive the signal transmitted by radio by modulating the data string by the above-mentioned transmitter with asymmetric QAM, and restore the original data string. A receiver according to an aspect of the present invention may receive a signal transmitted by a transmitter in a more suitable transmission manner in a practical environment.

  Further, in the transmission method according to one aspect of the present invention, the modulation circuit includes four signal points including two signal points having different amplitudes according to QAM (Quadrature Amplitude Modulation), and the adjacent signal points The data sequence is modulated by mapping the data sequence to only four signal points that are 90 degrees out of phase, and the transmitting circuit is configured to transmit the data sequence mapped to the four signal points by modulation by the modulation circuit as OFDM (Orthogonal). Allocate to different sub-carriers of Frequency Division Multiplexing) and transmit by radio.

  According to the above aspect, the same effect as that of the above transmission apparatus can be obtained.

  In the reception method according to one aspect of the present invention, the reception circuit is four signal points including two signal points having different amplitudes according to QAM (Quadrature Amplitude Modulation), and the adjacent signal points The modulation is performed by mapping only to four signal points different in phase by 90 degrees, and allocated to different subcarriers of orthogonal frequency division multiplexing (OFDM) to receive a signal transmitted by radio, and a demodulation circuit The signal received by the receiving circuit is demodulated by mapping the four signal points by the QAM.

  According to the above aspect, the same effect as that of the above receiving apparatus can be obtained.

  These general or specific aspects may be realized by a system, a method, an integrated circuit, a computer program, or a recording medium such as a computer readable CD-ROM, and the system, the method, the integrated circuit, the computer program Or it may be realized by any combination of recording media.

  Embodiments will be specifically described below with reference to the drawings.

  The embodiments described below are all inclusive or specific examples. Numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, order of steps, and the like shown in the following embodiments are merely examples, and the present invention is not limited thereto. Further, among the components in the following embodiments, components not described in the independent claim indicating the highest concept are described as arbitrary components.

Embodiment
In this embodiment, a transmitter which transmits a signal by a transmission method more suitable for an actual environment will be described.

  First, an outline of a transmitter according to the present embodiment will be described.

  The author in the present disclosure proposes two specific means to realize the concept.

  The first means is asymmetric QAM. In its simplest form, it may be based on a QPSK signal in which the two diametrically opposite symbols across the origin on the IQ plane are given greater amplitude at the expense of the other two symbols. It is believed that the bit mapping in such a case is preferably selected in a non-gray manner such that two adjacent symbols differ by one bit. If the second transmitter uses the same asymmetric QAM but rotated 90 degrees, then the symbols with higher amplitude from the first transmitter overlap with the symbols with lower amplitude and the SINR of the mixture of these symbols is more It has the effect of becoming larger. This concept can be extended to higher order QAM by skewing or shearing a regular rectangular constellation accordingly.

  The second means is a bit interleaver which is different for each transmitter, in particular adapted for the purpose of power splitting effect. By way of background here, all LDPC-FEC codes expanded in the field have variable node distribution which is not uniform. Broadly speaking, there are high-order, middle-order, low-order variable nodes. The order determines the number of connections to other adjacent nodes that one node has. Therefore, it is important to provide reliable input from the demapper output to high-order variable nodes. Matching of variable nodes to the demapper output is accomplished by a bit interleaver. In a simple design, the same bit interleaver would be used for all transmitters. The proposal here is to adopt a bit interleaver tailored to the power split ratio of the transmitter so that higher order variable nodes match the high power frequency band part.

  A receiver based on "Iterative demapping for superposition modulation" according to the patent document 1 would be ideally created to detect signals from two or more transmitters.

  The present invention comprises asymmetric QAM (abbreviated as "aQAM") for the purpose of realizing power division, and a bit interleaver for suitably adapting variable nodes of an LDPC code to power distribution on a channel.

  Hereinafter, the transmitter according to the present embodiment will be specifically described.

(1) Hierarchical division multiplexing (LDM)
FIG. 1 is an explanatory diagram of a transmitter 10 that performs constellation superposition on a two-layer LDM of ATSC 3.0.

  The basic concept of LDM is described in the case of two layers in FIG. Depending on the context, these layers are referred to as upper and lower layers, or mobile-oriented and fixed-oriented or stationary-oriented layers. In ATSC 3.0, the upper layer is called a core layer, and the lower layer is called an enhanced layer. Otherwise, hierarchical division multiplexing is defined as shown in FIG.

  In principle, of course, more than two layers are also conceivable. Either layer can carry one or more PLPs. The upper layer transmits the low-speed service xU for mobile reception, and the lower layer transmits the high-speed service xL for stationary reception.

  The transmitter 10 performs BICM (Bit-Interleaved Coded Modulation) modulation of upper layer information bits to be input and outputs the low-speed service xU by BICM modulating the upper layer information bits and lower layer information bits to be input. And a lower layer BICM modulator 12 for outputting a high-speed service xL.

  The LDM synthesizer 13 includes a level control unit 14 (also referred to as an injection level controller) and a normalization unit 15.

  After giving a positive magnification α ≦ 1 for reducing the power of the lower layer, the level controller 14 superposes the two layers to generate an unnormalized signal xU + αxL. Subsequently, the normalization unit 15 normalizes the synthesized signal into a unit output with an appropriate magnification β. Thereafter, the combined signal is added here for the sake of completeness, the time interleaver 16 (TI: Time Interleaver), the frequency interleaver 17 (FI: Frequency Interleaver), and an OFDM modulator 18 and a framer Pass through).

  Here, the upper and lower BICM modulation units respectively correspond to modulation circuits. Also, the OFDM modulation unit 18 and the framing unit correspond to a transmission circuit.

  In general, the operation of the receiver corresponding to the transmitter 10 is understood as a mobile receiver that is only interested in the upper layer will also detect only the upper layer. Stationary receivers of interest to the lower layer need to perform successive interference cancellation, ie, first to detect the upper layer. The receiver then remodulates the detected upper layer, assuming that the upper layer was successfully detected, subtracts the remodulated cell from the received cell, and then detects the lower layer.

(1.1) Broadband transmission (WiB)
Non-Patent Document 4 describes a next-generation DTT system in which a transmitter can explicitly tolerate interference by using a frequency reuse factor of one. A further aspect of WiB uses a very large bandwidth (e.g. the whole of the rest of the UHF band currently used for conventional DTT to be about 220 MHz) and a highly robust transmission mode to address interference. It is a significant reduction of transmission power over conventional transmission concepts.

  FIG. 2 shows the concept of WiB in which two transmitters S0 and S1 emit signals x0 and x1 in the same frequency band, respectively. The oval in the figure represents the coverage area of the transmitter. The receiver in the interference area 21 observes the combined signal of the two transmitters S0 and S1.

  As mentioned above, LDM and WiB are each individual cases of superposition modulation (SM). In LDM, the transmitter explicitly adds the transmitted signals. In WiB, transmission signals from different transmitters are implicitly added by the receiver by using the same frequency band.

  Thus, in principle, it does not matter to the receiver front end how the superposition occurs. A system model applicable to both LDM and WiB is shown in FIG. The coefficients h0 and h1 may function as scaling factors or channel coefficients. In the former case, the system model represents LDM and in the latter case WiB.

(2) Power Division The concept of the core from Non-Patent Document 5 is shown in FIG. The x-axis should be understood as useful bandwidth and the y-axis as power. Two transmitters share this bandwidth divided by two. The first transmitter S0 uses a higher power P1a in the first sub-band and a lower power P1b in the second sub-band. The second transmitter S1 operates in reverse to the first transmitter S0. That is, the second transmitter S1 uses higher power P2b in the second subband and lower power P2a in the first subband.

(3) Asymmetric QAM (aQAM: asymmetric QAM)
The modulation circuit (that is, the modulation section) is data based on QAM in four signal points including two signal points whose amplitudes are different from each other, and only in four signal points whose phases are different by 90 degrees from the adjacent signal points. Modulate by mapping columns. Also, the transmission circuit assigns the data strings mapped to the four signal points by the modulation by the modulation circuit to different subcarriers of OFDM and transmits them by radio. The above QAM modulation method is also called a QAM.

  Specifically, among the four signal points, two signal points having phases different from each other by 180 degrees have equal distances from the origin in the IQ plane, and the two signal points among the four signal points The two signal points other than the signal point are equal in distance from the origin in the IQ plane.

  The aQAM will be described in more detail below.

  FIG. 5 shows an example of asymmetric QAM signal points in the IQ plane. The scalar "a" represents the amplitude of the first signal point (symbol) transmitting the bit label 00. The opposite and closest signal point is given a bit label 01, which makes the bit mapping as a whole non gray mapping. In addition, non-gray mapping means mapping based on signal points based on non-gray arrangement.

  The constellation for asymmetric QAM with four constellation points and non-gray mapping can be expressed as (Equation 1) below.

  In this case, for the second transmitter, the constellation is rotated 90 degrees counterclockwise around the origin in the IQ plane. An example is shown in FIG.

  The constellations shown in FIG. 5 and FIG. 6 can be said to correspond to those in which the amplitudes of the signal points of the bit labels 11 and 10 are enlarged based on the constellation of QPSK.

  Also, the constellation for asymmetric QAM with four signal points and gray mapping can be expressed as (Equation 2) below. An example is shown in FIG. Gray mapping refers to mapping based on signal points based on gray arrangement.

  In this case, as in the case of non-gray mapping, for the second transmitter, the constellation is rotated 90 degrees counterclockwise around the origin in the IQ plane. An example is shown in FIG.

  The constellations shown in FIGS. 7 and 8 can be said to correspond to those in which the amplitudes of the signal points of the bit labels 01 and 10 are increased based on the constellation of QPSK.

  FIG. 9 shows a 1 bit / s / Hz curve of asymmetric QAM for dB conditions for various C / I and C / N in Additive White Gaussian Noise (AWGN) channel so that the performance gain can be understood correctly. .

  In particular, when C / I is 0 dB, when two transmission signals are received with similar power, a combination of symbols disappears completely, so that the conventional QPSK transmission requires a very high SNR. Among the three modulation schemes shown in FIG. 9, a non-Gray mapped aQAM shows the best performance when C / I is 0 dB.

  On the other hand, asymmetric QAM causes losses if C / I is very large or very small. Here, aQAM is a non-gray mapping in the form of QPSK. Thus, in one embodiment of the present invention, a combination of gray mapped asymmetric QAM with FEC block and non gray mapped asymmetric QAM is assumed.

  For example, gray mapping asymmetric QAM and non-gray mapping asymmetric QAM are combined in time division. Specifically, when the data string includes the first data and the second data preceding or following the first data, the modulation circuit maps the first data to the signal points based on the gray arrangement. Modulate and modulate by mapping the second data sequence to signal points based on the non-gray arrangement. Then, the transmission circuit transmits the modulated first data and the modulated second data in a time division manner.

  Also, for example, gray mapping asymmetric QAM and non-gray mapping asymmetric QAM are combined by frequency division. Specifically, when the data string includes the third data and the fourth data preceding or following the third data, the modulation circuit modulates the third data by mapping the signal points based on the gray arrangement. And modulation by mapping the fourth data to signal points based on the non-gray arrangement. Then, the transmission circuit assigns the modulated third data to the subcarrier for transmission in the first frequency band and transmits it, and transmits the modulated fourth data in the second frequency band different from the first frequency band. Allocate to subcarriers and transmit.

  In addition, in the above, when two transmitters exist, it demonstrated that the constellation of the signal point which one transmitter transmits transmits 90 degree | times. That is, more generally, the modulation circuit uses four new signal points obtained by rotating four signal points by a predetermined angle around the origin on the IQ plane as the four signal points. May be modulated. Then, in the case where there are a plurality of transmitters in which at least a part of the transmittable area is overlapped, a constellation is divided around the origin on the IQ plane by an angle obtained by dividing 180 degrees by the number of the plurality of transmitters. You may rotate it.

  Specifically, in the case of three transmitters, the constellation is rotated 60 degrees. In this way, it is possible to create a constellation that will never be symbol erasure. An individual example for three transmitters is shown in FIG. 10, FIG. 11 and FIG.

(3.1) Power Division and Asymmetric QAM
What replaced the concept of power division with a QAM signal is shown in FIG. For high power signals, asymmetric QAM is used, and for low power signals, conventional low power QPSK signals are used.

  Specifically, when the data string includes fifth data and sixth data preceding or following the fifth data, the modulation circuit modulates the fifth data by asymmetric QAM and QPSK the sixth data. Modulate by (Quadrature Phase Shift Keying). Then, the transmission circuit assigns the modulated fifth data to the subcarrier for transmission with the first power and transmits it, and assigns the modulated sixth data to the subcarrier for transmission with the second power smaller than the first power. Send. The width of the power value used for transmission of the high power signal may have a feature that it is larger than the width of power used for transmission of the low power signal. In this way, there is an advantage that asymmetric QAM can be used using a high power signal with a relatively wide power value.

  If one considers more than two receivers, NPL 5 proposes a further power split into three partitions. This concept is illustrated in FIG. High power signals are carried in asymmetric QAM, and low power signals are carried in low power QPSK signals.

  Note that the relative power levels depend on the network design and can be assigned when the network is deployed. Furthermore, these levels are assumed to be conveyed in L1 signaling and are known to the receiver at the time of data detection.

(4) Non-regular LDPC Code A typical parity check matrix from ATSC 3.0 for a long LDPC code with a coding rate of 8/15 is shown in FIG. It can be clearly seen that the check nodes are more dense forward in the parity check matrix.

  Then, by summing all the values of the parity check matrix for each column, it is possible to explicitly plot the distribution of edge orders. The results are shown in FIG. In this case, the largest part of the variable nodes has orders 2 and 3. There is also a relatively large group of variable nodes with degree 19 which is the largest degree. This relatively large group is the high-order variable node group focused on in the present invention.

(5) Power Division and Harmonic Bit Interleaver FIG. 17 is a diagram of superposition modulation when there are two transmitters. Bit interleavers π0 and π1 are components that connect the FEC encoding unit and the mapping unit.

  For convenience of explanation, the bit interleaver π0 is a sequence from 0 to FEC code word length-1 (FEC code word length minus 1), ie, neutral with respect to bit interleaving, and the bit interleaver π1 is an inverse sequence thereof, ie, The FEC code word length can be a sequence from -1 to 0. In other words, the bit interleaver π0 outputs the input bit string as it is, and the bit interleaver π1 reverses the order of the input bit string and outputs it.

  FIG. 18 shows the net effect. Here, the cell transmitted with high power P1a is connected to the high-order variable node of the first LDPC code by the bit interleaver π0. Also, the cell transmitted with high power P2b is connected to the high-order variable node of the second LDPC code by the bit interleaver π1.

  As described above, when the data string includes an LDPC (Low-Density Parity-Check) code, the transmitter further determines that the modulation circuit transmits fifth data (that is, data to be allocated to subcarriers transmitting at high power). The data interleaver includes a bit interleaver that rearranges bits in a data string such that data to be modulated is a node whose order is higher than a predetermined one of LDPC codes. Then, the modulation circuit modulates the data sequence after being rearranged by the bit interleaver. Note that a node whose order is higher than a predetermined level is, for example, a node whose order is higher than 1⁄2 of the maximum order, and in FIG. 18, for example, the order is higher than 10.5 which is 1⁄2 of 19 which is the maximum order. It is a node. By doing this, it is possible to cause the receiver to receive bits with relatively high error correction ability with high probability, improve the error correction rates of other bits, and as a result, the error correction rate of the entire data string. It can be improved.

  Defining a bit interleaver to move high-order variable nodes to any desired area is straightforward. Therefore, it is easy to define an interleaver that moves high-order variable nodes to the center side of the FEC block for the third transmitter. For example, FIG. 19 shows a bit string rearranged by the bit interleaver of the first transmitter S0, the second transmitter S1, and the third transmitter S2. By such rearrangement, it is possible to assign a node higher in order than a predetermined number to a subcarrier transmitting with high power.

(6) Receiver FIG. 20 is an explanatory diagram of the receiver 50. As shown in FIG. The receiver 50 shown in FIG. 20 is a receiver that receives a signal that the transmitter 10 shown in FIG. 1 transmits wirelessly.

  The signal received by the receiver 50 is demodulated by the OFDM demodulation unit 51 and passes through a frequency deinterleaver 52 (Frequency Deinterleaver) and a time deinterleaver 53 (Time Deinterleaver). The OFDM demodulation unit 51 corresponds to a reception circuit.

  The upper layer BICM demodulation unit 54 demodulates the BICM modulated signal to generate upper layer information bits. The processing performed by the BICM demodulation unit 54 is demodulation processing corresponding to the modulation processing performed by the BICM modulation unit 11 of the transmitter 10.

  Next, the upper layer information bit generated is modulated by the upper layer BICM modulation unit 55, and the modulated signal is subtracted from the signal output from the time deinterleaver 53. The lower layer BICM demodulation unit 56 demodulates the signal after subtraction to generate lower layer information bits. The upper and lower BICM demodulation units correspond to demodulation circuits, respectively.

  Thus, the receiver is mapped by QAM to only four signal points including two signal points having different amplitudes from each other and having a phase difference of 90 degrees with respect to the adjacent signal points. Reception circuit that is modulated by modulation and assigned to different subcarriers of OFDM and receives a signal transmitted wirelessly, and demodulation is performed by mapping the signal received by the reception circuit to four signal points by the QAM. And a demodulation circuit.

  This allows the receiver to receive the signal transmitted by the transmitter that is better suited to the actual environment.

(7) Summary Asymmetrical power distribution is effective for superposition modulation in the broadcast field. The present disclosure proposes to use asymmetric QAM to realize such power distribution. Asymmetric QAM is used for the high power part of the signal in the combination of gray and non gray mapping cells. The low power cells are transmitted as symmetric QPSK signals. Furthermore, harmonic bit interleaving is proposed to align higher order variable nodes with asymmetric QAM cells transmitted at high power. This is useful for the convergence of iterative FEC decoding.

(Modification)
In this modification, modifications of the transmitter, the transmission method, the receiver, and the reception method according to the above embodiment will be described.

  FIG. 21 is a block diagram showing a configuration of a transmitter 10A according to the present modification.

  As shown in FIG. 21, the transmitter 10A is four signal points including at least two signal points having different amplitudes according to QAM, and four signals having a phase difference of 90 degrees with the adjacent signal points. A modulation circuit 11A that modulates by mapping a data string only to a point, and a data string mapped to four signal points by modulation by the modulation circuit 11A are allocated to different subcarriers of OFDM and transmitted by radio And a circuit 18A.

  FIG. 22 is a flowchart showing a transmission method performed by the transmitter 10A according to the present modification.

  As shown in FIG. 22, in step S101, the modulation circuit 11A is four signal points including two signal points having mutually different amplitudes by QAM, and the phase is different by 90 degrees from the adjacent signal points. Modulate by mapping the data sequence to only 4 signal points.

  In step S102, the transmission circuit 18A assigns the data sequences mapped to four signal points by modulation by the modulation circuit 11A to different subcarriers of OFDM and transmits them by radio.

  Thereby, the transmitter 10A can transmit a signal by a transmission method more suitable for the actual environment.

  FIG. 23 is a block diagram showing a configuration of a receiver 50A according to the present modification.

  As shown in FIG. 23, the receiver 50A is four signal points including two signal points having different amplitudes according to QAM, and four signal points having a phase difference of 90 degrees with respect to the adjacent signal points. The receiver circuit 51A that is modulated by mapping only to different OFDM allocated to different sub-carriers and receives the signal transmitted by radio, and the signal received by the receiver circuit 51A are the four signal points according to the QAM. And a demodulation circuit 54A for performing demodulation by mapping to

  FIG. 24 is a flowchart showing the reception method performed by the receiver 50A according to the present modification.

  As shown in FIG. 24, in step S201, the reception circuit 51A is four signal points including two signal points having different amplitudes by QAM, and the phase is different by 90 degrees from the adjacent signal points. It is modulated by being mapped to only 4 signal points and allocated to different subcarriers of OFDM to receive a wirelessly transmitted signal.

  In step S202, the demodulation circuit 54A demodulates the signal received by the reception circuit 51A by mapping the signal to four signal points by the QAM.

  Thus, the receiver 50A may receive the signal transmitted by the transmitter in a more suitable transmission method in the actual environment.

  In the above embodiment, each component may be configured by dedicated hardware or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or a processor reading and executing a software program recorded in a recording medium such as a hard disk or a semiconductor memory. Here, the software for realizing the transmitter and the like of the above embodiment is a program as follows.

  That is, in this program, the modulation circuit is four signal points including two signal points having different amplitudes according to QAM (Quadrature Amplitude Modulation) in the computer, and the phase is 90 degrees with the adjacent signal points. Orthogonal Frequency Division Multiplexing (OFDM) modulation is performed by mapping a data string to only four different signal points, and a transmitter circuit maps the data string mapped to the four signal points by modulation by the modulation circuit. Are assigned to different sub-carriers from each other and are transmitted by radio.

  In addition, in this program, in the computer, the receiving circuit is four signal points including two signal points different in amplitude according to QAM (Quadrature Amplitude Modulation), and the phase is 90 degrees with the adjacent signal points. Modulated by mapping only to 4 different signal points, assign to different subcarriers of OFDM (Orthogonal Frequency Division Multiplexing) and receive a wirelessly transmitted signal, and the demodulation circuit receives the signal received by the reception circuit The received signal is demodulated by mapping data sequences to the four signal points by the QAM.

  As mentioned above, although the transmitter which concerns on one or several aspect etc. was demonstrated based on embodiment, this invention is not limited to this embodiment. Without departing from the spirit of the present invention, various modifications that can be conceived by those skilled in the art may be applied to the present embodiment, and modes configured by combining components in different embodiments may also be in the scope of one or more aspects. May be included within.

  The present invention is applicable to a transmitter that transmits a signal wirelessly to a receiver. For example, the present invention can be applied to a transmitter that transmits a digital broadcast signal to a television receiver as a receiver.

10, 10A, S0, S1, S2 Transmitters 11, 12, 55 BICM Modulator 11A Modulator 13 LDM Synthesizer 14 Level Controller 15 Normalizer 16 Temporal Interleaver 17 Frequency Interleaver 18 OFDM Modulator 18A Transmitter 21 Interference Region 50, 50A Receiver 51 OFDM demodulator 51A receiver 52 Frequency deinterleaver 53 Time deinterleaver 54, 56 BICM demodulator 54A demodulator

Claims (11)

By QAM (Quadrature Amplitude Modulation), the data sequence is mapped to only four signal points including at least two signal points having different amplitudes, which are 90 degrees different in phase from adjacent signal points. A modulation circuit that modulates by
A transmitter comprising: the data sequences mapped to the four signal points by the modulation by the modulation circuit are allocated to different subcarriers of orthogonal frequency division multiplexing (OFDM) and wirelessly transmitted. Of the four signal points, two signal points whose phases are different by 180 degrees have equal distances from the origin in the IQ plane,
The transmitter according to claim 1, wherein among the four signal points, two signal points excluding the two signal points have equal distances from an origin in an IQ plane. The data string includes first data and second data forward or backward from the first data,
The modulation circuit is
Modulate by mapping the first data to signal points based on gray arrangement,
Modulate by mapping the second data to signal points based on a non-gray arrangement,
The transmitter circuit is
The transmitter according to claim 1 or 2, wherein the modulated first data and the modulated second data are transmitted by time division. The data string includes third data and fourth data preceding or following the third data,
The modulation circuit is
Modulate the third data by mapping to signal points based on gray arrangement,
Modulate by mapping the fourth data to signal points based on the non-gray arrangement,
The transmitter circuit is
Assigning the modulated third data to subcarriers for transmission in a first frequency band for transmission;
The transmitter according to any one of claims 1 to 3, wherein the modulated fourth data is allocated to subcarriers to be transmitted in a second frequency band different from the first frequency band for transmission. The data string includes fifth data and sixth data preceding or following the fifth data,
The modulation circuit is
The fifth data is modulated by the QAM,
The sixth data is modulated by QPSK (Quadrature Phase Shift Keying),
The transmitter circuit is
Assigning the modulated fifth data to a subcarrier to be transmitted at a first power for transmission;
The transmitter according to any one of claims 1 to 4, wherein the modulated sixth data is allocated to a subcarrier that transmits with a second power smaller than the first power and transmitted. The data string includes an LDPC (Low-Density Parity-Check) code, and
The transmitter further comprises
The bit interleaver reorders bits in the data string such that data modulated by the modulation circuit as the fifth data is a node having a degree higher than a predetermined order in the LDPC code,
The modulation circuit is
The transmitter according to claim 5, wherein the bit interleaver modulates the data sequence after the reordering. The modulation circuit is
The new four signal points obtained by rotating the four signal points on the IQ plane by a predetermined angle around the origin are modulated as the four signal points. The transmitter according to item 1. The transmitter is one of a plurality of transmitters in which at least a part of a transmittable area is overlapped,
The transmitter according to claim 7, wherein the predetermined angle is an angle obtained by dividing 180 degrees by the number of the plurality of transmitters. By QAM (Quadrature Amplitude Modulation), four signal points including two signal points having different amplitudes are mapped to only four signal points that are 90 degrees out of phase with adjacent signal points. A reception circuit that is modulated and assigned to different subcarriers of orthogonal frequency division multiplexing (OFDM) to receive a wirelessly transmitted signal;
A demodulation circuit that demodulates the signal received by the reception circuit by mapping the signal to the four signal points using the QAM. A modulation circuit is data only at four signal points including two signal points having different amplitudes according to QAM (Quadrature Amplitude Modulation) and which are 90 degrees different in phase from adjacent signal points. Modulate by mapping the columns,
A transmission method, wherein a transmission circuit assigns the data strings mapped to the four signal points by modulation by the modulation circuit to different subcarriers of Orthogonal Frequency Division Multiplexing (OFDM) and transmits them by radio. The receiving circuit maps four signal points including two signal points having different amplitudes according to QAM (Quadrature Amplitude Modulation) to only four signal points having a phase difference of 90 degrees with the adjacent signal points. Modulated by being modulated and assigned to different subcarriers of Orthogonal Frequency Division Multiplexing (OFDM) to receive signals transmitted by radio,
And a demodulation circuit that demodulates the signal received by the reception circuit by mapping the signal to the four signal points using the QAM.

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