JP7216521B2 - Transmitter, receiver, transmission method, and reception method - Google Patents

Description

The present invention relates to transmitters, receivers, transmission methods, and reception methods.

Multiplexing multiple signals into a composite signal to share a single medium is a common practice in data communications. Conventionally, various services that transmit data are multiplexed in time or frequency. It has also been shown that the superimposition of various services actually increases the capacity more than TDM (Time Division Multiplexing) or FDM (Frequency Division Multiplexing) (Non-Patent Documents 1-3).

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

EP-A-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）（デジタルビデオブロードキャスティング（ＤＶＢ）：第２世代地上デジタルテレビ放送システム(frame-structured channel coding and modulation for DVB-T2)”, version 1.4.1, February 2015. P. P. Bergmans and T. M. Cover, "Cooperative broadcasting," 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," IEEE Transactions on Broadcasting, Vol. 62, No. 1, March 2016, p. 233-243 E. Stare, J. J. Gimenez, P. Klenner, "WIB: a new system concept for digital terrestrial television (DTT)," IBC Conference 2016. DVB-TM-WiB Study Mission Input Document TM-WIB0088, "Suggested approach forward for optimized interference cancellation processing." ATSC Standard: Physical Layer Protocol (A/322), June 2017

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

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

A transmitter according to an aspect of the present invention has four signal points including at least two signal points with different amplitudes by QAM (Quadrature Amplitude Modulation), and the phases of adjacent signal points are different by 90 degrees. A modulation circuit that modulates by mapping a data string only to four signal points, and the data string mapped to the four signal points by modulation by the modulation circuit are subjected to OFDM (Orthogonal Frequency Division Multiplexing) mutually and a transmission circuit that allocates to different subcarriers and transmits by radio.

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

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

FIG. 1 is an explanatory diagram of a transmitter that performs constellation superimposition for two-layer LDM of ATSC 3.0 according to an embodiment. FIG. 2 is an explanatory diagram of a WiB transmission scenario according to the embodiment. FIG. 3 is an explanatory diagram of a superimposition modulation system model applicable to two-layer LDM and WiB according to the embodiment. FIG. 4 is an explanatory diagram of power distribution according to the embodiment. FIG. 5 is an illustration of non-Gray mapping aQAM for the first of the two transmitters according to the embodiment. FIG. 6 is an illustration of non-Gray mapping aQAM for the second of the 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 rate for two transmitters according to an embodiment. FIG. 10 is an explanatory diagram of aQAM for the first transmitter out of three transmitters according to the embodiment. FIG. 11 is an explanatory diagram of aQAM for the second transmitter of the three transmitters according to the embodiment. FIG. 12 is an explanatory diagram of aQAM for the third transmitter among the three transmitters according to the embodiment. FIG. 13 is an explanatory diagram of replacing the concept of power division according to the embodiment with QAM signals of two transmitters. FIG. 14 is an explanatory diagram of replacing the concept of power division according to the embodiment with QAM signals of three transmitters. FIG. 15 is an explanatory diagram of a parity check matrix from ATSC 3.0 for a coding rate of 8/15 according to an embodiment. FIG. 16 is an explanatory diagram of a variable node degree distribution for LDPC with a coding rate of 8/15 according to the embodiment. FIG. 17 is an explanatory diagram of superimposition modulation with two transmitters according to the embodiment. FIG. 18 is an explanatory diagram of a harmonic bit interleaver for power division QAM according to an embodiment. Solid vertical lines highlight which cell types are connected to which variable nodes. FIG. 19 is an explanatory diagram of bit interleaving with three transmitters according to the embodiment. FIG. 20 is an explanatory diagram of the receiver according to the embodiment. 21 is a block diagram showing a configuration of a transmitter according to a modification of the embodiment; FIG. FIG. 22 is a flowchart showing a transmission method executed by a transmitter according to the modification of the embodiment; 23 is a block diagram showing a configuration of a receiver according to a modification of the embodiment; FIG. FIG. 24 is a flowchart showing a receiving method executed by a receiver according to the modification of the embodiment;

(Knowledge on which the present invention is based)
The present invention relates to asymmetric QAM for superposition modulation and adaptive bit interleaving. The invention applies to the field of digital communications for broadcasting digital data, and in particular to novel transmission techniques for modern multiplexing schemes based on superimposition for simultaneous delivery of different service types to stationary and mobile users. be.

Multiplexing multiple signals into a composite signal to share a single medium is a common practice in data communications. Conventionally, various services that transmit data are multiplexed in time or frequency. These methods are called time division multiplexing (TDM) and frequency division multiplexing (FDM). Practical applications of TDM and FDM are described in DVB-T2 (Non-Patent Document 1) and the Japanese ISDB-T standard, which has an excellent 1seg system. In DVB-T2 [1], multiple so-called PLPs (physical layer pipes), each featuring its own modulation and time interleaver, share a frequency band in dedicated timeslots; The T standard allows energy-saving partial reception of individual segments by transmitting data in segmented segments that are strictly separated in the frequency domain.

FDM and TDM have long been known not to be the most spectrally efficient way to share a medium. These advantages are more related to ease of implementation. [2] shows that overlaying different services actually increases capacity over TDM or FDM. More recently, this form of multiplexing has become the current standard, namely ATSC 3.0, also called Layered Division Multiplexing (LDM) [3, 6].

Superimposition modulation is also a core component of a recently proposed new terrestrial broadcasting system called WiB, which is an abbreviation for Wideband transmission with a reuse factor of 1 (Non-Patent Document 4). In WiB, adjacent transmitters carry individual services. With an implicit reuse factor of 1, a receiver especially in the area of interference between transmitters receives the sum of all transmitted signals. However, from the receiver's point of view, this received signal looks like a signal resulting from hierarchical division multiplexing. Therefore, with a properly designed FEC coding and modulation scheme, the receiver can utilize Successive Interference Cancellation techniques to read out the data.

Intuitively, the advantage of superposition modulation over TDM/FDM in capacity is obtained by transmitting more than one service simultaneously without interruption in the time or frequency domain. A particular use case for superposition modulation, and one where its benefits are most pronounced, is in serving mobile and fixed receivers. Mobile and fixed reception are typically characterized by low and high SNR (signal-to-noise ratio), respectively. Here, mobile services are performed at data rates low enough to withstand the low SNR as well as the presence of fixed services. On the other hand, the fixed service receiver takes advantage of the relatively high SNR to detect the robust mobile layer first, then subtract its data, and then find the data that is actually desired for the fixed service. You can proceed with the process.

Regarding WiB, [5] speculated that a power splitting approach would be beneficial 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 repeatedly suggested for receiver implementations to operate at near maximum capacity. However, the discussion was made using an ideal Gaussian signal.

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 an aspect of the present invention uses Quadrature Amplitude Modulation (QAM) to generate four signal points including at least two signal points with different amplitudes, and the phases of adjacent signal points are 90° apart. a modulation circuit that modulates by mapping a data string only to four signal points with different degrees; different subcarriers from each other and transmit by radio.

According to the above aspect, even when there is another transmitter whose transmittable area is at least partly overlapping and the other transmitter transmits a signal in the same subcarrier, QAM demodulation can succeed. Since the amplitudes of at least two of the four signal points used for QAM modulation are different from each other, the signal points used for QAM modulation by the transmitter and the signal points used for QAM modulation by other transmitters This is because they can be arranged so as not to overlap each other. Therefore, the transmitter according to one aspect of the present invention can transmit signals using a more suitable transmission method in an actual environment. Such QAM is also called asymmetric QAM.

For example, among the four signal points, two signal points having phases different from each other by 180 degrees are at equal distances from the origin on the IQ plane, and among the four signal points, the two signal points , may have the same distance from the origin on the IQ plane.

According to the above aspects, the transmitter can more easily transmit data sequences with QAM modulation.

For example, the data string includes first data and second data preceding or following the first data, and the modulation circuit modulates the first data by mapping it to signal points based on a gray arrangement. and modulates the second data by mapping to signal points based on a non-Gray constellation, and the transmission circuit transmits the modulated first data and the modulated second data in a time division manner. may

According to the above aspect, by time-divisionally using both the gray allocation and the non-gray allocation, which are two signal point allocations having different error resilience, the error resilience can be improved more than when either one is used. can be done.

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 signal points based on a gray arrangement. and modulates the fourth data by mapping to signal points based on a non-Gray allocation, the transmitting circuit assigns the modulated third data to subcarriers to be transmitted in a first frequency band, and transmits the third data; The modulated fourth data may be transmitted by being assigned to subcarriers transmitted in a second frequency band different from the first frequency band.

According to the above aspect, by using both the gray arrangement and the non-gray arrangement, which are arrangements of two signal points having different error resilience, in frequency division, the error resilience can be improved more than when either one is used. can be done.

For example, the data string includes fifth data and sixth data preceding or succeeding the fifth data, and the modulation circuit modulates the fifth data by QAM and modulates the sixth data by QPSK. (Quadrature Phase Shift Keying), the transmission circuit assigns the modulated fifth data to a subcarrier to be transmitted at the first power, transmits the modulated sixth data from the first power It may be transmitted by assigning it to a subcarrier transmitted with a small second power.

According to the above aspect, it is possible to improve the error resilience of signals of subcarriers transmitted with high power in LDM by asymmetric QAM, and to transmit signals even with subcarriers transmitted with low power.

For example, the data string includes an LDPC (Low-Density Parity-Check) code, and the transmitter further controls the data modulated as the fifth data by the modulation circuit so that the order of the LDPC code is higher than a predetermined order. A bit interleaver may be provided for rearranging bits in the data string so as to become higher nodes, and the modulation circuit may modulate the data string after the rearrangement by the bit interleaver.

According to the above aspect, it is possible to allow the receiver to more reliably receive nodes of the LDPC code having a relatively high degree, that is, bits having a relatively high correction capability in decoding the data string. This makes it possible to increase the probability that the entire data string can be decoded.

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

According to the above aspect, it is possible to avoid overlapping of the original four signal points and the new four signal points on the IQ plane (that is, the complex plane). This prevents overlapping of signal points even when there are other transmitters whose transmittable areas overlap at least partly and the other transmitters transmit signals in the same subcarriers. Avoidance may allow successful demodulation of QAM.

For example, the transmitter is one of a plurality of transmitters whose transmittable areas at least partially overlap, and the predetermined angle is 180 degrees, which is the number of the plurality of transmitters. It may be a divided angle.

According to the above aspect, when there are other transmitters whose transmittable areas are at least partly overlapping, the positions of the signal points on the IQ plane can be separated as much as possible. As a result, the probability of reception errors occurring can be reduced.

Further, a receiver according to an aspect of the present invention uses quadrature amplitude modulation (QAM) to generate four signal points including two signal points having different amplitudes, and the phases of adjacent signal points are 90 degrees. a receiving circuit for receiving a signal that is modulated by being mapped to only four different signal points, is assigned to mutually different subcarriers of OFDM (Orthogonal Frequency Division Multiplexing), and is transmitted wirelessly; a demodulation circuit that demodulates the signal by mapping a data string to the four signal points by the QAM;

According to the above aspect, the receiver can receive the signal that the transmitter modulates the data sequence with asymmetric QAM and wirelessly transmits the signal, and restores the original data sequence. A receiver according to an aspect of the present invention can receive a signal transmitted by a transmitter using a more suitable transmission method in an actual environment.

Further, in the transmission method according to one aspect of the present invention, the modulation circuit uses Quadrature Amplitude Modulation (QAM) to generate four signal points including two signal points having different amplitudes, and the adjacent signal points and A data string is modulated by mapping it only to four signal points whose phases differ by 90 degrees, and a transmission circuit converts the data string mapped to the four signal points by modulation by the modulation circuit into OFDM (Orthogonal (Frequency Division Multiplexing) are assigned to mutually different subcarriers and transmitted by radio.

According to the aspect described above, the same effects as those of the transmitting apparatus described above can be obtained.

Further, in a receiving method according to an aspect of the present invention, the receiving circuit uses Quadrature Amplitude Modulation (QAM) to generate four signal points including two signal points having different amplitudes, and the adjacent signal points and Receives signals that are modulated by being mapped to only four signal points whose phases differ by 90 degrees, are assigned to mutually different subcarriers of OFDM (Orthogonal Frequency Division Multiplexing), and are wirelessly transmitted, and the demodulation circuit The signal received by the receiving circuit is demodulated by mapping to the four signal points by the QAM.

According to the aspect described above, the same effects as those of the receiving apparatus described above can be obtained.
Also, for the above transmitter, the four signal points are located in the first quadrant and have a first amplitude in the IQ plane, and a second symbol located in the second quadrant and having a second amplitude. a third symbol located in a third quadrant and having said first amplitude; and a fourth symbol located in a fourth quadrant and having said second amplitude, wherein said first amplitude is equal to said second amplitude. It may be different from the amplitude.
Also, for the above receiver, the four signal points are located in the first quadrant and have a first amplitude in the IQ plane, and a second symbol located in the second quadrant and having a second amplitude. a third symbol located in a third quadrant and having said first amplitude; and a fourth symbol located in a fourth quadrant and having said second amplitude, wherein said first amplitude is equal to said second amplitude. It may be different from the amplitude.
Further, with respect to the above transmission method, the four signal points are located in the first quadrant and have a first amplitude in the IQ plane, and a second symbol located in the second quadrant and having a second amplitude. a third symbol located in a third quadrant and having said first amplitude; and a fourth symbol located in a fourth quadrant and having said second amplitude, wherein said first amplitude is equal to said second amplitude. It may be different from the amplitude.
Further, in the above reception method, the four signal points are located in the first quadrant and have a first amplitude in the IQ plane, and a second symbol located in the second quadrant and having a second amplitude. a third symbol located in a third quadrant and having said first amplitude; and a fourth symbol located in a fourth quadrant and having said second amplitude, wherein said first amplitude is equal to said second amplitude. It may be different from the amplitude.

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

Hereinafter, embodiments will be specifically described with reference to the drawings.

It should be noted that the embodiments described below are all comprehensive 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 examples and are not intended to limit the present invention. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in independent claims representing the highest concept will be described as arbitrary constituent elements.

(Embodiment)
In this embodiment, a transmitter and the like that transmit signals by a transmission method more suitable for the actual environment will be described.

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

The authors in this disclosure propose two specific means of implementing the concept.

The first means is asymmetric QAM. In its simplest form, it may be based on a QPSK signal in which two symbols diametrically opposite each other on the IQ plane are given greater amplitude at the expense of the other two symbols. The bit mapping for such cases would preferably be chosen in a non-Gray fashion such that two adjacent symbols differ by one bit. If the second transmitter uses the same asymmetric QAM but rotated by 90 degrees, the higher amplitude symbols from the first transmitter overlap with the lower amplitude symbols, and the SINR of the mixture of these symbols is higher. It has the effect of making it bigger. This concept can be extended to higher order QAM by correspondingly skewing or shearing the regular rectangular constellation.

A second means is a bit interleaver specifically adapted for the purpose of the power splitting effect, which differs from transmitter to transmitter. As background here, all LDPC-FEC codes deployed in the field have non-uniform variable node distributions. Broadly speaking, there are high-, medium-, and low-order variable nodes. The degree determines how many connections a node has to other neighboring nodes. Therefore, it is important that higher-order variable nodes are also given reliable inputs from the demapper output. Matching of variable nodes to demapper outputs is accomplished by a bit interleaver. A simple design would use the same bit interleaver for all transmitters. The proposal here is to employ a bit interleaver tailored to the power split ratio of the transmitter so that the higher order variable nodes match the high power frequency band parts.

A receiver based on "Repeated Demapping for Superimposed Modulation" according to US Pat.

The present invention comprises an asymmetric QAM (abbreviated "aQAM") aimed at achieving power splitting and a bit interleaver that better adapts the variable nodes of the LDPC code to the power distribution on the channel.

Hereinafter, the transmitter and the like according to this embodiment will be specifically described.

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

The basic concept of LDM is illustrated in FIG. 1 for the case of two layers. Depending on the context, these layers are called upper and lower layers, or mobile and stationary or stationary 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 carries the low speed service xU intended for mobile reception and the lower layer carries the high speed service xL intended for stationary reception.

The transmitter 10 performs BICM (Bit-Interleaved Coded Modulation) modulation on the input upper layer information bits and outputs a low-speed service xU. and a lower layer BICM modulation unit 12 for outputting the high-speed service xL.

The LDM combiner 13 includes a level controller 14 (also called an injection level controller) and a normalizer 15 .

The level control unit 14 applies a positive scaling factor α≦1 that reduces the power of the lower layer, and then superimposes the two layers to generate a non-normalized signal xU+αxL. Subsequently, the normalization unit 15 normalizes the combined signal to unit output with an appropriate scaling factor β. The composite signal is then processed by a Time Interleaver 16 (TI), a Frequency Interleaver 17 (FI), and an OFDM Modulator 18 and a Framer (which are added here for completeness). shown).

Here, the upper and lower BICM modulation units correspond to modulation circuits, respectively. 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 such that a mobile receiver that is only interested in the upper layers will also detect only the upper layers. A stationary receiver that is interested in the lower layers must perform Successive Interference Cancellation, ie detect the upper layers first. The receiver then considers the upper layer to be successfully detected, remodulates the detected upper layer, subtracts the remodulated cells from the received cells, and then detects the lower layer.

(1.1) Wideband transmission (WiB)
Non-Patent Document 4 describes a next-generation DTT system in which a transmitter can explicitly tolerate interference using a frequency reuse factor of one. A further aspect of WiB is the use of very large bandwidths (e.g., the entire remainder of the UHF band currently used for conventional DTT, which is around 220 MHz) and highly robust transmission modes to combat interference, The goal is to significantly reduce transmission power over conventional transmission concepts.

FIG. 2 illustrates the WiB concept in which two transmitters S0 and S1 emit signals x0 and x1 in the same frequency band, respectively. The ellipse in the figure represents the coverage area of the transmitter. A receiver within the interference region 21 observes the combined signal of the transmissions of both transmitters S0 and S1.

As noted above, LDM and WiB are each separate cases of superposition modulation (SM). In LDM, the transmitter explicitly sums the transmitted signals. In addition, in WiB, the use of the same frequency band results in implicit addition of transmission signals from different transmitters at the receiver.

Therefore, in principle, it is irrelevant to the receiver front-end in which way the superposition occurred. A system model applicable to both LDM and WiB is shown in FIG. 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 core concept from Non-Patent Document 5 is shown in FIG. The x-axis should be understood as useful bandwidth and the y-axis as power. Let two transmitters share this bandwidth divided by two. The first transmitter S0 uses a higher power P1a in the first subband and a lower power P1b in the second subband. The second transmitter S1 operates in reverse to the first transmitter S0. That is, the second transmitter S1 uses a higher power P2b in the second subband and a lower power P2a in the first subband.

(3) Asymmetric QAM (aQAM)
A modulation circuit (that is, a modulation section) uses QAM to transmit data to four signal points including two signal points having mutually different amplitudes and having a phase different from that of an adjacent signal point by 90 degrees. Modulate by mapping columns. Further, the transmission circuit allocates the data string mapped to the four signal points by modulation by the modulation circuit to different subcarriers of OFDM and transmits the same by radio. The above QAM modulation method is also called aQAM.

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

aQAM is 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) carrying bit label 00. The diametrically opposite and closest constellation point is given the bit label 01, which makes the bit mapping totally non-Gray mapping. Note that non-Gray mapping refers to mapping based on signal points based on a non-Gray arrangement.

A constellation for non-Gray-mapping asymmetric QAM with four signal points can be expressed as the following (equation 1).

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.

It can be said that the constellations shown in FIGS. 5 and 6 correspond to QPSK constellations with increased amplitudes at the signal points of bit labels 11 and 10 .

In addition, a constellation for asymmetric QAM with four signal points and Gray mapping can be expressed by the following (Equation 2). An example is shown in FIG. Note that gray mapping refers to mapping based on signal points based on gray allocation.

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

It can be said that the constellations shown in FIGS. 7 and 8 correspond to QPSK constellations with increased amplitudes of signal points of bit labels 01 and 10. FIG.

To appreciate the performance gain, Figure 9 shows the 1 bit/s/Hz curves of asymmetric QAM versus dB conditions for various C/I and C/N in an AWGN (Additive White Gaussian Noise) channel. .

In particular, for a C/I of 0 dB, transmission with conventional QPSK requires a very high SNR, since certain symbol combinations disappear completely when receiving two transmitted signals with similar power. Among the three modulation schemes shown in FIG. 9, non-Gray mapping aQAM shows the best performance when C/I is 0 dB.

On the other hand, if the C/I is too large or too small, asymmetric QAM will produce loss. where aQAM is a non-Gray mapping in the form of QPSK. Therefore, in one embodiment of the present invention, we assume a combination of Gray-mapped asymmetric QAM with FEC blocks and non-Gray-mapped asymmetric QAM.

For example, Gray-mapping asymmetric QAM and non-Gray-mapping asymmetric QAM are combined in time division. Specifically, when the data string includes first data and second data preceding or following the first data, the modulation circuit maps the first data to signal points based on the Gray allocation. and modulate by mapping the second data stream to signal points based on the non-Gray constellation. 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 in frequency division. Specifically, when the data string includes third data and fourth data preceding or succeeding the third data, the modulation circuit maps the third data to signal points based on the gray allocation to modulate the data. and modulate by mapping the fourth data to signal points based on the non-Gray constellation. Then, the transmission circuit allocates the modulated third data to subcarriers to be transmitted in the first frequency band and transmits the modulated fourth data in a second frequency band different from the first frequency band. Allocate to a subcarrier and transmit.

In the above description, when there are two transmitters, the constellation of signal points transmitted by one of the transmitters is rotated by 90 degrees. More generally, the modulation circuit rotates the four signal points by a predetermined angle around the origin on the IQ plane, and uses four new signal points as the four signal points. may be modulated by Then, when there are a plurality of transmitters whose transmittable areas at least partially overlap, the constellation is formed around the origin on the IQ plane by an angle obtained by dividing 180 degrees by the number of the plurality of transmitters. You can rotate it.

Specifically, if there are three transmitters, rotate the constellation by 60 degrees. In this way, a constellation can always be created that will never result in symbol erasure. Individual examples for the three transmitters are shown in FIGS. 10, 11 and 12. FIG.

(3.1) Power Splitting and Asymmetric QAM
FIG. 13 shows the concept of power division transposed to QAM signals. Asymmetric QAM is used for high power signals and conventional low power QPSK signals are used for low power signals.

Specifically, when the data string includes fifth data and sixth data preceding or succeeding the fifth data, the modulation circuit modulates the fifth data by asymmetric QAM and modulates the sixth data by QPSK. (Quadrature Phase Shift Keying). Then, the transmission circuit allocates and transmits the fifth modulated data to subcarriers transmitted with the first power, and allocates the sixth modulated data to subcarriers transmitted with a second power lower than the first power. Send. It should be noted that the range of power values used for transmitting the high-power signal may be characterized by being larger than the range of power values used for transmitting 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 range of power values.

If more than two receivers are considered, [5] proposes a further power division into three partitions. This concept is illustrated in FIG. High power signals are carried by asymmetric QAM and low power signals are carried by 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) Irregular LDPC Codes A typical parity check matrix from ATSC 3.0 for a long LDPC code with rate 8/15 is shown in FIG. It can clearly be seen that there is a higher density of check nodes earlier in the parity check matrix.

The edge degree distribution can then be explicitly plotted by summing all the values of the parity check matrix column by column. The results are shown in FIG. In this case, the largest part of the variable nodes have degrees 2 and 3. There is also a relatively large group of variable nodes with degree 19, which is the highest 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 for 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 the sequence from 0 to the FEC codeword length−1 (the FEC codeword length minus 1), i.e. neutral with respect to bit interleaving, and the bit interleaver π1 is the inverse sequence, i.e. FEC codeword length - can be a sequence of numbers from 1 to 0; In other words, the bit interleaver π0 outputs the input bit string as it is, and the bit interleaver π1 outputs the input bit string in reverse order.

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

In this way, when the data string contains an LDPC (Low-Density Parity-Check) code, the transmitter further uses the modulation circuit as the fifth data (that is, data assigned to subcarriers transmitted at high power) A bit interleaver is provided for rearranging the bits in the data string so that the data to be modulated becomes a node whose degree is higher than a predetermined degree in the LDPC code. Then, the modulation circuit modulates the data sequence rearranged by the bit interleaver. Note that a node whose degree is higher than a predetermined degree is, for example, a node whose degree is higher than 1/2 of the maximum degree. For example, in FIG. is a node. By doing so, it is possible to cause the receiver to receive bits with relatively high error correction capability with high probability, improve the error correction rate of other bits, and as a result improve the error correction rate of the entire data string. can be improved.

It is a simple matter to define a bit interleaver that moves high-order variable nodes to any desired area. Therefore, for the third transmitter, it is easy to define an interleaver that moves the high-order variable nodes toward the center of the FEC block. For example, FIG. 19 shows bit sequences rearranged by the bit interleavers of the first transmitter S0, the second transmitter S1 and the third transmitter S2. By such rearrangement, nodes with a higher order than a predetermined number can be assigned to subcarriers that transmit with high power.

(6) Receiver FIG. 20 is an explanatory diagram of the receiver 50 . A receiver 50 shown in FIG. 20 is a receiver that receives a signal wirelessly transmitted by the transmitter 10 shown in FIG.

A signal received by the receiver 50 is demodulated by an OFDM demodulator 51 and passes through a frequency deinterleaver 52 and a time deinterleaver 53 . Note that the OFDM demodulator 51 corresponds to a receiving circuit.

The upper-layer BICM demodulator 54 generates upper-layer information bits by demodulating the BICM-modulated signal. 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 BICM modulation unit 55 modulates the generated upper-layer information bits, and the modulated signal is subtracted from the signal output by the time deinterleaver 53 . The lower-layer BICM demodulator 56 demodulates the signal after the subtraction to generate lower-layer information bits. The upper-layer and lower-layer BICM demodulators respectively correspond to demodulator circuits.

Thus, the receiver is mapped by QAM to only 4 signal points, including 2 signal points with different amplitudes, and 90 degrees out of phase with adjacent signal points. a receiving circuit that receives signals that have been modulated by and wirelessly transmitted by assigning them to OFDM subcarriers that are different from each other; and a demodulation circuit.

This allows the receiver to receive signals transmitted by transmitters that are more suitable for the actual environment.

(7) Conclusion An asymmetric power distribution is effective for superposition modulation in the broadcast field. In this disclosure, we propose to use asymmetric QAM to achieve such power distribution. Asymmetric QAM is used for the high power portion of the signal in a combination of Gray-mapped and non-Gray-mapped cells. Low power cells are transmitted as symmetrical QPSK signals. In addition, we propose harmonic bit interleaving to fit high-order variable nodes to asymmetric QAM cells transmitted at high power. This is useful for convergence of iterative FEC decoding.

(Modification)
In this modified example, a modified example of the transmitter, transmission method, receiver, and reception method according to the above embodiments will be described.

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

As shown in FIG. 21, the transmitter 10A uses QAM to generate four signal points including at least two signal points with mutually different amplitudes, and four signals whose phases are different from adjacent signal points by 90 degrees. A modulation circuit 11A that modulates by mapping data strings only to points, and a transmission that assigns the data strings mapped to four signal points by modulation by the modulation circuit 11A to OFDM subcarriers that are different from each other and transmits them wirelessly. and circuit 18A.

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

As shown in FIG. 22, in step S101, the modulation circuit 11A modulates four signal points including two signal points with different amplitudes by QAM, the phases of which are different from adjacent signal points by 90 degrees. Modulation is performed by mapping data strings to only four signal points.

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

This allows the transmitter 10A to transmit signals using a transmission method that is more suitable for the actual environment.

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

As shown in FIG. 23, the receiver 50A uses QAM to generate four signal points including two signal points with mutually different amplitudes and four signal points whose phases are different from adjacent signal points by 90 degrees. A receiving circuit 51A that receives signals that are modulated by being mapped to only one, are assigned to OFDM subcarriers that are different from each other, and are transmitted wirelessly; and a demodulation circuit 54A that performs demodulation by mapping to .

FIG. 24 is a flow diagram showing a receiving method executed by the receiver 50A according to this modification.

As shown in FIG. 24, in step S201, the receiving circuit 51A receives four signal points including two signal points having different amplitudes by QAM, and the phases of the adjacent signal points are different from each other by 90 degrees. It receives signals that are modulated by being mapped to only four signal points and that are wirelessly transmitted by assigning different subcarriers of OFDM.

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

This allows the receiver 50A to receive the signal transmitted by the transmitter in a more suitable transmission method in the actual environment.

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

That is, this program instructs the computer that the modulation circuit uses QAM (Quadrature Amplitude Modulation) to convert 4 signal points including 2 signal points having different amplitudes, which are 90 degrees out of phase with adjacent signal points. A data string is modulated by mapping only to four different signal points, and a transmission circuit performs OFDM (Orthogonal Frequency Division Multiplexing) on the data string mapped to the four signal points by modulation by the modulation circuit. are assigned to subcarriers different from each other and transmitted by radio.

In addition, this program instructs the computer that the receiving circuit uses QAM (Quadrature Amplitude Modulation) to convert four signal points including two signal points having mutually different amplitudes, which are 90 degrees out of phase with adjacent signal points. Receive signals that are modulated by being mapped to only four different signal points, are assigned to mutually different subcarriers of OFDM (Orthogonal Frequency Division Multiplexing), and are wirelessly transmitted, and a demodulation circuit receives the signals. The received signal is demodulated by mapping a data string to the four signal points by the QAM.

Although the transmitter and the like according to one or more aspects have been described above based on the embodiments, the present invention is not limited to these embodiments. As long as it does not deviate from the spirit of the present invention, the scope of one or more embodiments includes various modifications that can be made by those skilled in the art, and configurations constructed by combining the components of different embodiments. may be included within

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

10, 10A, S0, S1, S2 transmitter 11, 12, 55 BICM modulator 11A modulator circuit 13 LDM combiner 14 level controller 15 normalizer 16 time interleaver 17 frequency interleaver 18 OFDM modulator 18A transmitter circuit 21 interference region 50, 50A receiver 51 OFDM demodulator 51A receiver circuit 52 frequency deinterleaver 53 time deinterleaver 54, 56 BICM demodulator 54A demodulator

Claims (14)

By QAM (Quadrature Amplitude Modulation), only four signal points including at least two signal points with mutually different amplitudes, and four signal points with phases different from adjacent signal points by 90 degrees, are added to the data string . a modulation circuit that modulates by mapping the contained fifth data ;
a transmission circuit that allocates the fifth data modulated by being mapped to the four signal points by modulation by the modulation circuit to mutually different subcarriers of OFDM (Orthogonal Frequency Division Multiplexing) and wirelessly transmits the data; prepared ,
The modulation circuit further
Modulating the sixth data contained in the data string, which is ahead or behind the fifth data, by QPSK (Quadrature Phase Shift Keying),
The transmission circuit is
assigning the modulated fifth data to subcarriers transmitted with the first power and transmitting the data;
transmitting the modulated sixth data by allocating it to a subcarrier transmitted with a second power lower than the first power;
Transmitter. two of the four signal points having phases different from each other by 180 degrees have the same distance from the origin on the IQ plane,
2. The transmitter according to claim 1, wherein, among the four signal points, two signal points other than the two signal points have the same distance from the origin on the IQ plane. The data string includes first data and second data preceding or following the first data,
The modulation circuit is
modulate by mapping the first data to signal points based on a gray constellation;
modulating the second data by mapping to signal points based on a non-Gray constellation;
The transmission circuit is
3. The transmitter according to claim 1, wherein the modulated first data and the modulated second data are transmitted in a time division manner. The data string includes third data and fourth data preceding or following the third data,
The modulation circuit is
modulate by mapping the third data to signal points based on the Gray constellation;
modulating the fourth data by mapping to signal points based on a non-Gray constellation;
The transmission circuit is
assigning the modulated third data to subcarriers to be transmitted in the first frequency band and transmitting;
The transmitter according to any one of claims 1 to 3, wherein the modulated fourth data is assigned to subcarriers transmitted in a second frequency band different from the first frequency band and transmitted. The data string includes an LDPC (Low-Density Parity-Check) code,
The transmitter further
a bit interleaver that rearranges the bits in the data string so that the data modulated by the modulation circuit as the fifth data is a node whose degree is higher than a predetermined degree in the LDPC code;
The modulation circuit is
The transmitter according to any one of claims 1 to 4, wherein the bit interleaver modulates the data sequence after the rearrangement. The modulation circuit is
Instead of modulating the data string using the four signal points, only four new signal points are obtained by rotating the four signal points around the origin on the IQ plane by a predetermined angle. 6. The transmitter according to any one of claims 1 to 5 , wherein the data sequence is modulated using the transmitter is one of a plurality of transmitters having at least a portion of overlapping transmittable areas;
The transmitter according to Claim 6 , 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 with different amplitudes are mapped only to four signal points whose phases are different from adjacent signal points by 90 degrees. a receiving circuit for receiving a signal transmitted wirelessly by allocating the fifth data contained in the modulated data sequence to subcarriers transmitted with mutually different first powers in OFDM (Orthogonal Frequency Division Multiplexing);
a demodulation circuit that demodulates the fifth data by mapping the signal received by the reception circuit to only the four signal points by the QAM ;
The receiving circuit further comprises:
Sixth data contained in the data sequence modulated by QPSK (Quadrature Phase Shift Keying), wherein the sixth data preceding or following the fifth data are OFDM subcarriers different from each other, receiving signals transmitted wirelessly assigned to subcarriers transmitted at a second power less than one power;
The demodulation circuit further
demodulate the sixth data with the QPSK
Receiving machine. The modulation circuit uses QAM (Quadrature Amplitude Modulation) to four signal points including two signal points having mutually different amplitudes, and four signal points having phases different from adjacent signal points by 90 degrees , modulating by mapping the fifth data contained in the data string;
A transmission circuit wirelessly transmits the fifth data modulated by being mapped to the four signal points by the modulation circuit by assigning the fifth data to mutually different subcarriers of OFDM (Orthogonal Frequency Division Multiplexing). ,
The modulation circuit further
Modulating the sixth data contained in the data string, which is ahead or behind the fifth data, by QPSK (Quadrature Phase Shift Keying),
The transmission circuit is
assigning the modulated fifth data to subcarriers transmitted with the first power and transmitting the data;
transmitting the modulated sixth data by allocating it to a subcarrier transmitted with a second power lower than the first power;
Send method. A receiving circuit maps only four signal points, including two signal points with different amplitudes, which are different in phase from adjacent signal points by 90 degrees, by QAM (Quadrature Amplitude Modulation). receiving a signal transmitted wirelessly by assigning the fifth data contained in the data sequence, which is modulated by being modulated, to subcarriers transmitted with mutually different first powers in OFDM (Orthogonal Frequency Division Multiplexing);
a demodulator circuit demodulating the fifth data by mapping the signal received by the receiver circuit to only the four signal points by the QAM ;
The receiving circuit further comprises:
Sixth data contained in the data sequence modulated by QPSK (Quadrature Phase Shift Keying), wherein the sixth data preceding or following the fifth data are OFDM subcarriers different from each other, receiving signals transmitted wirelessly assigned to subcarriers transmitted at a second power less than one power;
The demodulation circuit further
demodulate the sixth data with the QPSK
receiving method. The four signal points are, in the IQ plane,
a first symbol located in the first quadrant and having a first amplitude;
a second symbol located in the second quadrant and having a second amplitude;
a third symbol located in the third quadrant and having the first amplitude;
a fourth symbol located in the fourth quadrant and having the second amplitude;
2. The transmitter of claim 1, wherein said first amplitude is different than said second amplitude. The four signal points are, in the IQ plane,
a first symbol located in the first quadrant and having a first amplitude;
a second symbol located in the second quadrant and having a second amplitude;
a third symbol located in the third quadrant and having the first amplitude;
a fourth symbol located in the fourth quadrant and having the second amplitude;
9. The receiver of claim 8 , wherein said first amplitude is different than said second amplitude. The four signal points are, in the IQ plane,
a first symbol located in the first quadrant and having a first amplitude;
a second symbol located in the second quadrant and having a second amplitude;
a third symbol located in the third quadrant and having the first amplitude;
a fourth symbol located in the fourth quadrant and having the second amplitude;
10. The transmission method of Claim 9 , wherein the first amplitude is different from the second amplitude. The four signal points are, in the IQ plane,
a first symbol located in the first quadrant and having a first amplitude;
a second symbol located in the second quadrant and having a second amplitude;
a third symbol located in the third quadrant and having the first amplitude;
a fourth symbol located in the fourth quadrant and having the second amplitude;
11. The receiving method according to claim 10 , wherein said first amplitude is different from said second amplitude.

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