Receiving device and receiving method

Abstract

To provide a receiver and a reception method capable of improving reception performance with high layer separation accuracy, while reducing reception processing in a Layered Division Multiplexing (LDM) system.SOLUTION: A receiver 20 in an LDM system of the invention includes: an orthogonal demodulation part 22 for extracting an LDM symbol by receiving an LDM signal and performing orthogonal demodulation for it; an LLR calculation part 23 for UL for calculating a Log-likelihood ratio (LLR) with assuming the received LDM symbol as UL; an error correction decoding part 24 for UL for performing decoding processing for a UL signal indicating the LLR; a reference point determination part 25R for narrowing down reference points indicating possible symbol positions which can be taken by symbols for LL within the received LDM symbols based on decoding results of the UL signals; an LLR calculation part 27R for LL for calculating an LLR for the received LDM symbol corresponding to the UL signal based only on the reference point determined by the reference point determination part 25R; and an error correction decoding part 28 for LL for performing decoding processing for an LL signal indicating the LLR.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transmission system using Layered Division Multiplexing (LDM) in satellite broadcasting or terrestrial broadcasting, and more particularly to an LDM receiving device and receiving method for receiving and processing an LDM signal in which two modulated signals, one for a higher layer (UL) and one for a lower layer (LL), are multiplexed with different powers and then orthogonally modulated in the same frequency band and transmitted. [Background technology]

[0002] One of the wireless transmission methods aimed at improving frequency utilization efficiency is the hierarchical division multiplexing (hereinafter referred to as the "LDM method"), which multiplexes two modulated signals with different power levels and transmits them in the same frequency band. The use of the LDM method is also being considered for terrestrial digital broadcasting, and a system that uses the LDM method to multiplex a new terrestrial broadcasting method with the current terrestrial broadcasting is being considered (see, for example, Non-Patent Documents 1 and 2).

[0003] The LDM method is a method of multiplexing two modulated signals in the same frequency band with a power difference between them. Generally, the higher power signal is called the UL (Upper Layer) and the lower power signal is called the LL (Lower Layer). The power ratio between the upper layer (UL) and the lower layer (LL) is defined by the IL (Injection Level), which represents the ratio of the average power of the UL to the average power of the LL.

[0004] Fig. 11 is a block diagram showing a schematic configuration of a typical LDM transmitter 10 in the prior art. Fig. 11 illustrates a schematic configuration of the LDM transmitter 10 using single-carrier transmission, but the LDM system can also be applied to multi-carrier OFDM transmission, and the configuration related to the LDM signal transmission itself is similar. The LDM transmitter 10 shown in Fig. 11 includes an error correction encoder 11 and a mapper 12 for UL, an error correction encoder 13 and a mapper 14 for LL, a power adjuster 15, a combiner 16, and an orthogonal modulator 17.

[0005] The error correction coding unit 11 inputs UL transmission information, which is information to be transmitted via UL in the LDM system, performs error correction coding processing (LDPC code, etc.) predetermined for UL, and outputs the result to the mapping unit 12.

[0006] The mapping unit 12 maps the data obtained from the error correction coding unit 11 after the error correction coding process using a modulation method (such as QPSK) predetermined for UL, generates a modulated signal having a symbol for UL as an IQ signal that can be represented on an IQ plane of an in-phase component I and a quadrature phase component Q, and outputs the modulated signal to the combining unit 16.

[0007] The error correction coding unit 13 inputs LL transmission information, which is information to be transmitted via LL in the LDM system, performs error correction coding processing (LDPC code, etc.) predetermined for LL, and outputs the result to the mapping unit 14. The error correction coding processing for UL and LL may use the same error correction coding method and coding rate, or may use different error correction coding methods and coding rates.

[0008] The mapping unit 14 maps the data after error correction coding processing obtained from the error correction coding unit 13 using a modulation method (such as QPSK) predetermined for LL, generates a modulated signal having LL symbols as an IQ signal, and outputs it to the power adjustment unit 15. The modulation methods for UL and LL may be the same or different, and may be π / 2 shift BPSK, 8PSK, 16APSK, etc., in addition to QPSK.

[0009] The power adjustment unit 15 adjusts the amplitude of the LL symbols obtained from the mapping unit 14 using a predetermined IL value (i.e., adjusts the power ratio between layers according to the IL), and outputs the amplitude-adjusted LL symbols to the combining unit 16. Note that, although an example configuration in which the power adjustment unit 15 adjusts the amplitude of the LL symbols is shown here, it is sufficient if the power adjustment unit 15 can adjust the power ratio between layers according to the IL, and such power adjustment unit 15 may adjust the amplitude of either or both of the UL and LL symbols.

[0010] The combiner 16 generates an LDM symbol by adding the power of each of the UL and LL symbols obtained from the mapper 12 and the power adjuster 15 , respectively, and outputs the LDM symbol to the orthogonal modulator 17 .

[0011] The orthogonal modulation unit 17 generates an LDM signal by orthogonally modulating the LDM symbol obtained from the combining unit 16 in the same frequency band according to a modulation method predetermined for UL, and transmits the signal from the transmitting antenna 18 to the receiving device (including via a terrestrial or satellite repeater) after a predetermined power amplification (not shown).

[0012] In a receiver that receives this LDM signal, the reception performance is greatly affected by the accuracy of UL and LL separation in the reception processing, so various UL and LL layer separation methods have been studied. The most common layer separation method is SIC (Successive Interference Cancellation), which generates replica signals and performs power subtraction processing (see, for example, Non-Patent Document 1).

[0013] Fig. 12 is a block diagram showing a schematic configuration of a typical SIC receiver 20S in the prior art. The SIC receiver 20S shown in Fig. 12 includes an orthogonal demodulator 22, a UL LLR calculator 23, an error correction decoder 24, a UL re-modulation replica signal generator 25, a subtractor 26, an LL LLR calculator 27, and an error correction decoder 28.

[0014] The orthogonal demodulation unit 22 receives an LDM signal via the receiving antenna 21, in which two modulated signals are multiplexed at different power levels as a high layer (UL) and a low layer (LL), and then orthogonally modulated and transmitted in the same frequency band.The orthogonal demodulation unit 22 inputs the received LDM signal after undergoing power (amplitude) normalization processing using a predetermined gain adjustment (not shown) based on the average power or maximum power, performs symbol synchronization and carrier recovery, and performs orthogonal demodulation processing to extract the LDM symbol, which is then output to the LLR calculation unit 23 and subtraction unit 26 for the UL.

[0015] The LLR calculation unit 23 regards the LDM symbols obtained from the orthogonal demodulation unit 22 as symbols for UL, calculates log-likelihood ratios (LLRs) using reference points indicating all possible symbol positions of the LDM symbols (when UL is QPSK and LL is QPSK, 16-symbol reference points shown in FIG. 4, which will be described later), generates a UL signal indicating the log-likelihood ratios (LLRs), and outputs the UL signal to the error correction decoding unit 24. Note that the LLR calculation unit 23 may also regard the LDM symbols obtained from the orthogonal demodulation unit 22 as symbols for UL, calculates log-likelihood ratios (LLRs) using reference points indicating symbol positions according to a predetermined modulation scheme for UL (although not shown, when UL is QPSK, 4-symbol reference points corresponding to QPSK for UL, regardless of the LL modulation scheme), and generates a UL signal indicating the log-likelihood ratios (LLRs). In this case, the accuracy of the LLR decreases especially when the IL is small, but it is the same as the LLR calculation method related to general error correction decoding processing.

[0016] The error correction decoding unit 24 performs a decoding process on the UL signal obtained from the LLR calculation unit 23, corresponding to an error correction coding process (LDPC code, etc.) predetermined for the UL on the transmitting side, generates decoded bits of the UL signal indicating UL transmission information, outputs the decoded bits to the outside, and also outputs the decoded bits to the replica signal generation unit 25.

[0017] The replica signal generation unit 25 performs re-modulation processing by again applying error correction coding processing (LDPC code, etc.) predetermined for UL on the transmitting side to the decoded bits of the UL signal obtained from the error correction decoding unit 24, and further performs re-modulation processing by again applying orthogonal modulation processing according to a modulation method predetermined for UL, thereby generating a replica signal indicating a symbol for UL and outputting it to the subtraction unit 26.

[0018] The subtraction unit 26 performs delay adjustment on the LDM symbol obtained from the orthogonal demodulation unit 22 until the replica signal is generated by the replica signal generation unit 25, and then obtains a symbol for LL by power subtracting the replica signal indicating the symbol for UL from the LDM symbol, and outputs the symbol for LL to the LLR calculation unit 27.

[0019] The LLR calculation unit 27 calculates the log-likelihood ratio (LLR) for the LL symbol obtained from the subtraction unit 26 using a reference point indicating the symbol position according to a modulation method predetermined for LL, generates an LL signal indicating the log-likelihood ratio (LLR), and outputs it to the error correction decoding unit 28.

[0020] The error correction decoding unit 28 performs a decoding process on the LL signal obtained from the LLR calculation unit 27, corresponding to an error correction coding process (LDPC code, etc.) predetermined for LL on the transmitting side, and generates decoded bits of the LL signal indicating transmission information for LL, and outputs the decoded bits to the outside.

[0021] This SIC-based layer separation method has high separation accuracy and can achieve good reception performance. However, the reception processing using the above-mentioned replica signal generation and power subtraction process has the problem of significantly increasing costs compared to general receiving devices that do not rely on the LDM method.

[0022] Therefore, a method has been disclosed in which the generation of replica signals and power subtraction processing are omitted for LDM symbols obtained by performing orthogonal demodulation processing, and the UL and LL are decoded separately (hereinafter referred to as "collective demodulation") (see, for example, Patent Document 1).

[0023] Fig. 13 is a block diagram showing a schematic configuration of a typical batch demodulation receiving device 20B in the prior art. In Fig. 13, the same components as those shown in Fig. 12 are given the same reference numerals.

[0024] A batch demodulation type receiving device 20B shown in FIG. 13 includes an orthogonal demodulation unit 22, an LLR calculation unit 23 and an error correction decoding unit 24 for UL, and an LLR calculation unit 27B and an error correction decoding unit 28 for LL.

[0025] In the batch demodulation type receiving device 20B shown in FIG. 13, the orthogonal demodulation unit 22, the LLR calculation unit 23, the error correction decoding unit 24, and the error correction decoding unit 28 each function in the same way as those shown in FIG. 12, and the description thereof will be omitted, but the difference is that the LLR calculation unit 27B shown in FIG. 13 replaces the LLR calculation unit 27 shown in FIG. 12.

[0026] That is, the LLR calculation unit 27B shown in FIG. 13 regards the LDM symbols obtained from the orthogonal demodulation unit 22 as symbols for LL, calculates the log-likelihood ratio (LLR) using reference points indicating all symbol positions that the LDM symbols can take, generates an LL signal indicating the log-likelihood ratio (LLR), and outputs it to the error correction decoding unit 28.

[0027] The error correction decoding unit 28 shown in FIG. 13 performs decoding processing on the LL signal obtained from the LLR calculation unit 27B, corresponding to an error correction coding processing (LDPC code, etc.) predetermined for LL on the transmitting side.

[0028] However, while this hierarchical separation method using simultaneous demodulation can reduce the cost of reception processing compared to SIC, it has low noise tolerance and it is difficult to achieve high reception performance in environments with low reception C / N ratios. [Prior art documents] [Patent documents]

[0029] [Patent Document 1] Japanese Patent Application Publication No. 2019-87894 [Non-patent literature]

[0030] [Non-Patent Document 1] Akihiko Sato and 11 others, "A Study on the Application of LDM for Next-Generation Terrestrial Broadcasting," ITE Technical Report, vol. 41, no. 6, BCT2017-34, pp. 45-48, February 2017 [Non-patent document 2] Hiromasa Okada and six others, "A Study on Improving Various Issues When Applying LDM to Terrestrial Digital Broadcasting - Examination of New Broadcasting System Reception Area Expansion Methods and Synchronization Methods -", ​​ITE Technical Report, vol. 42, no. 28, BCT2018-76, pp. 13-16, September 2018. Summary of the Invention [Problem to be solved by the invention]

[0031] As described above, two types of layer separation techniques, "SIC" and "collective demodulation", are known as conventional techniques for receiving LDM signals.

[0032] However, while SIC can achieve high accuracy in separating UL and LL layers and achieve good reception performance, it has the problem of increasing costs related to reception processing.

[0033] Furthermore, while batch demodulation reduces the cost of reception processing, it has the problem that it is difficult to achieve high reception performance.

[0034] Therefore, in view of the above-mentioned problems, an object of the present invention is to provide a receiving device and a receiving method that reduce the receiving processing of the layer division multiplexing (LDM) method while improving receiving performance with high layer separation accuracy. [Means for solving the problem]

[0035] The receiving device of the present invention is a layer division multiplexing (LDM) receiving device, and includes an orthogonal demodulation unit that receives an LDM signal in which two modulated signals as a high layer (UL) and a low layer (LL) are multiplexed with different powers and orthogonally modulated in the same frequency band and transmitted, and performs orthogonal demodulation processing to extract an LDM symbol, an UL LLR calculation unit that regards the LDM symbol as a UL symbol, calculates a log-likelihood ratio using all symbol positions that the LDM symbol can take or a reference point indicating a symbol position according to a modulation method predetermined for UL, and generates a UL signal indicating the log-likelihood ratio, an UL error correction decoding unit that performs error correction decoding processing predetermined for UL on the UL signal, and generates decoded bits of the UL signal, and The system is characterized by comprising: a reference point determination unit that determines a reference point to be used in calculating a log-likelihood ratio for LL decoding according to the decoded bits of the UL signal by narrowing down reference points that indicate symbol positions that LL symbols in the received LDM symbols can take from among reference points that indicate all symbol positions that LDM symbols can take, based on the decoded bits of the UL signal; an LLR calculation unit for LL that calculates a log-likelihood ratio for the received LDM symbol corresponding to the UL signal based only on the reference points determined by the reference point determination unit, and generates an LL signal that indicates the log-likelihood ratio; and an error correction decoding unit for LL that performs error correction decoding processing predetermined for LL on the LL signal, and generates decoded bits of the LL signal.

[0036] In addition, in the receiving device of the present invention, the error correction decoding unit for UL is characterized in that it attaches identification information that enables the reference point determination unit to identify the LDM symbol corresponding to the UL signal, and feeds back the decoding result indicating the decoded bits of the UL signal to the reference point determination unit.

[0037] In addition, in the receiving device of the present invention, the LLR calculation unit for LL is characterized in that, in order to generate an LL signal corresponding to the UL signal, it performs delay adjustment on the received LDM symbol variably based on the identification information, and then calculates a log-likelihood ratio for the received LDM symbol corresponding to the UL signal using only the reference point determined by the reference point determination unit, and generates an LL signal indicating the log-likelihood ratio.

[0038] In addition, in the receiving device of the present invention, the LLR calculation unit for LL performs delay adjustment on the received LDM symbol for a fixed time period for generating an LL signal corresponding to the UL signal, and then calculates a log-likelihood ratio for the received LDM symbol corresponding to the UL signal using only the reference point determined by the reference point determination unit, and generates an LL signal indicating the log-likelihood ratio.

[0039] Furthermore, in the receiving device of the present invention, the UL LLR calculation unit calculates the log-likelihood ratio using reference points indicating all possible symbol positions of the LDM symbol, and further includes a Euclidean distance accumulation unit that temporarily accumulates, while updating, information on the Euclidean distance to each reference point for each received LDM symbol used in calculating the log-likelihood ratio indicated as the UL signal for a predetermined number of symbols, and the reference point determination unit has a Euclidean distance selection unit that selects, for each LDM symbol decoded for the UL signal by the UL error correction decoding unit, the Euclidean distance of a reference point to be used for decoding the LL signal from the Euclidean distances of each reference point accumulated in the Euclidean distance accumulation unit based on the decoded bits of the UL signal, and the LL LLR calculation unit calculates the log-likelihood ratio for the received LDM symbol corresponding to the UL signal using only the Euclidean distance selected for decoding the LL signal by the Euclidean distance selection unit, and generates an LL signal indicating the log-likelihood ratio.

[0040] Furthermore, a receiving method of the present invention is a receiving method for a layer division multiplexing (LDM) system, comprising the steps of receiving an LDM signal in which two modulated signals, one for a high layer (UL) and one for a low layer (LL), are multiplexed with different powers and orthogonally modulated in the same frequency band and transmitted, and performing orthogonal demodulation processing to extract an LDM symbol; regarding the LDM symbol as a symbol for UL, calculating a log-likelihood ratio using all symbol positions that the LDM symbol can take or a reference point indicating a symbol position according to a modulation method predetermined for UL, and generating a UL signal indicating the log-likelihood ratio; and performing error correction decoding processing predetermined for UL on the UL signal, and generating decoded bits of the UL signal. a step of determining a reference point to be used for calculating a log-likelihood ratio for LL decoding in accordance with the decoded bits of the UL signal by narrowing down reference points indicating symbol positions that the LL symbol in the received LDM symbol can take from among reference points indicating all symbol positions that the LDM symbol can take, based on the decoded bits of the UL signal; a step of calculating a log-likelihood ratio for the received LDM symbol corresponding to the UL signal based only on the reference point determined in the step, and generating an LL signal indicating the log-likelihood ratio; and a step of performing a predetermined error correction decoding process for LL on the LL signal, and generating decoded bits of the LL signal. [Effects of the Invention]

[0041] According to the present invention, it is possible to achieve good reception performance with high noise resistance equivalent to or greater than that of SIC as reception processing for a layer division multiplexing (LDM) system, and furthermore, it is possible to significantly reduce the cost associated with reception processing compared to SIC. [Brief explanation of the drawings]

[0042] [Figure 1] 1 is a block diagram showing a schematic configuration of an LDM receiving device according to a first embodiment of the present invention; [Figure 2] 1 is an IQ plane diagram showing an example of allocation of bits constituting symbols of an LDM signal in an LDM receiving device according to a first embodiment of the present invention; [Figure 3] 4 is a flowchart showing a receiving process in the LDM receiving device according to the first embodiment of the present invention. [Figure 4] FIG. 2 is an IQ plane diagram for explaining the processing of the UL LLR calculation unit in the LDM receiving device according to the first embodiment of the present invention. [Figure 5] 1 is a diagram for explaining the processing of a reference signal determination unit and an LLR calculation unit for LL in an LDM receiving device according to a first embodiment of the present invention. FIG. [Figure 6] 1 is a diagram showing C / N versus BER characteristics under white noise, comparing the LDM receiving device of the first embodiment of the present invention with the prior art. FIG. [Figure 7] FIG. 2 is a diagram showing the required C / N ratio for a receiving device using the LDM method according to the first embodiment of the present invention compared with the prior art. [Figure 8] FIG. 10 is a block diagram showing a schematic configuration of an LDM receiving device according to a second embodiment of the present invention. [Figure 9] 10 is a flowchart showing a receiving process in an LDM receiving device according to a second embodiment of the present invention. [Figure 10] 10A and 10B are diagrams illustrating processing performed by a Euclidean distance storage unit in an LDM receiving device according to a second embodiment of the present invention. [Figure 11] FIG. 1 is a block diagram showing a schematic configuration of a typical LDM transmitter 10 in the prior art. [Figure 12] FIG. 1 is a block diagram showing a schematic configuration of a typical SIC type receiving device 20S in the prior art. [Figure 13] FIG. 1 is a block diagram showing a schematic configuration of a typical batch demodulation receiving device 20B in the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0043] Hereinafter, an LDM receiving device 20 and a receiving method thereof according to each embodiment of the present invention will be described with reference to the drawings.

[0044] [Receiving device of embodiment 1] FIG. 1 is a block diagram showing a schematic configuration of an LDM receiving device 20 according to a first embodiment of the present invention. The LDM receiving device 20 according to the first embodiment of the present invention shown in FIG. 1 receives and demodulates an LDM signal transmitted from an LDM transmitting device 10 using single-carrier transmission as shown in FIG. 11, separates the LDM signal into a higher layer (UL) and a lower layer (LL), and decodes the signal. The LDM receiving device 20 includes an orthogonal demodulator 22, a UL LLR calculator 23, an error correction decoder 24, a reference point determiner 25R, an LL LLR calculator 27R, and an error correction decoder 28. Note that in FIG. 1, the same components as those shown in FIG. 12 are denoted by the same reference numerals. Although FIG. 1 illustrates the schematic configuration of the LDM receiving device 20 using single-carrier transmission, the device may be configured similarly when receiving and demodulating an LDM signal transmitted using multi-carrier OFDM transmission, and separating the LDM signal into a higher layer (UL) and a lower layer (LL) and decoding the signal.

[0045] That is, the LDM type receiving device 20 of the first embodiment according to the present invention shown in FIG. 1 is similar to the SIC type receiving device 20S shown in FIG. 12 in that it includes an orthogonal demodulation unit 22, an LLR calculation unit 23 for UL and an error correction decoding unit 24, and an error correction decoding unit 28 for LL, but differs in that it includes a "reference point determination unit 25R" instead of the SIC type "replica signal generation unit 25 by UL re-modulation and subtraction unit 26", and further includes an "LL LLR calculation unit 27R" according to the present invention that performs LLR calculation using only the reference point determined by the "reference point determination unit 25R" instead of the SIC type "LLR calculation unit 27".

[0046] The configuration of the LDM receiving device 20 according to the first embodiment of the present invention shown in FIG. 1 will be described below in more detail.

[0047] Orthogonal demodulation unit 22 receives an LDM signal via receiving antenna 21, in which two modulated signals, one for a higher layer (UL) and one for a lower layer (LL), are multiplexed at different powers and orthogonally modulated in the same frequency band and transmitted, and then performs power (amplitude) normalization processing on the received LDM signal using predetermined gain adjustment (not shown) based on average power or maximum power before inputting it, performing symbol synchronization and carrier recovery, and performing orthogonal demodulation processing to extract LDM symbols, which are then output to UL LLR calculation unit 23 and LL LLR calculation unit 27R. Here, the LDM signal received via receiving antenna 21 is a signal transmitted from LDM-based transmission device 10 shown in FIG.

[0048] The LLR calculation unit 23 regards the LDM symbols obtained from the orthogonal demodulation unit 22 as symbols for UL, calculates log-likelihood ratios (LLRs) using all possible symbol positions of the LDM symbols or reference points indicating symbol positions according to a modulation method predetermined for UL, generates a UL signal indicating the log-likelihood ratios (LLRs), and outputs it to the error correction decoding unit 24.

[0049] The error correction decoding unit 24 performs a decoding process on the UL signal obtained from the LLR calculation unit 23, corresponding to an error correction coding process (LDPC code, etc.) predetermined for the UL on the transmitting side, generates decoded bits of the UL signal indicating the UL transmission information, outputs the decoded bits to the outside, and also feeds back the decoded bits to the reference point determination unit 25R.

[0050] Based on the decoded bits of the UL signal obtained from the error correction decoding unit 24, the reference point determination unit 25R narrows down the reference points indicating the symbol positions that the LL symbols in the received LDM symbols can take from among the reference points indicating all the symbol positions that the LDM symbols can take, thereby determining the reference points to be used for calculating the log-likelihood ratio (LLR) for LL decoding according to the decoded bits of the UL signal, and outputs the reference points to the LLR calculation unit 27R.

[0051] The LLR calculation unit 27R performs a predetermined delay adjustment for the LDM symbol obtained from the orthogonal demodulation unit 22 to generate an LL signal corresponding to the UL signal, and then, using only the reference point determined by the reference point determination unit 25R, calculates the log-likelihood ratio (LLR) for the received LDM symbol corresponding to the UL signal related to the determination of the reference point, generates an LL signal indicating this log-likelihood ratio (LLR), and outputs it to the error correction decoding unit 28.

[0052] The error correction decoding unit 28 performs a decoding process on the LL signal obtained from the LLR calculation unit 27R, corresponding to an error correction coding process (LDPC code, etc.) predetermined for LL on the transmitting side, and generates decoded bits of the LL signal indicating transmission information for LL, and outputs the decoded bits to the outside.

[0053] As described above, in the receiving device 20 shown in FIG. 1, the UL decoding process itself is the same as the conventional SIC method, but instead of being equipped with the SIC-type "replica signal generating unit 25 by UL remodulation and subtraction unit 26," it is equipped with a "reference point determining unit 25R," and is configured to be equipped with an "LL LLR calculation unit 27R" that performs LLR calculation for LL using only the reference point determined by the "reference point determining unit 25R," so it is possible to significantly reduce the cost associated with the LL receiving process.

[0054] [Reception process in embodiment 1] The reception process in the receiving device 20 shown in FIG. 1 will be described below with more specific examples.

[0055] First, in the receiving device 20 shown in Figure 1, the LDM signal received via the receiving antenna 21 is a signal transmitted from the LDM transmitting device 10 shown in Figure 11, and the bits constituting the LDM symbol in this embodiment are configured so that the bits constituting the UL symbol are arranged on the upper side and the bits constituting the LL symbol are arranged on the lower side.

[0056] For example, Fig. 2 shows an IQ plane diagram centered on the origin O when the modulation method for UL and LL is QPSK and the bit allocation to the QPSK symbols is Gray code mapped, as an example of the allocation of bits that make up the symbols of an LDM signal (LDM symbols). In this case, the LDM symbols are configured as 16 symbols in total, and the bits allocated to these 16 symbols are, as shown in Fig. 2 (for convenience of explanation, illustrated as 16QAM), with the most significant 2 bits being UL and the least significant 2 bits being LL. However, the allocation of UL and LL bits in the LDM symbols does not need to be limited to that shown in Fig. 2, as long as the UL and LL bits can be distinguished on the LDM symbol.

[0057] Therefore, as a representative example, an example will be described in which the modulation scheme for UL and LL is QPSK, and the orthogonal demodulation unit 22 shown in Fig. 1 receives and processes LDM symbols according to the Gray code mapping shown in Fig. 2. Note that the present invention is similar to the case where set partitioning mapping is used instead of Gray code mapping.

[0058] FIG. 3 is a flowchart showing the reception process in the LDM receiving device 20 according to the first embodiment of the present invention.

[0059] First, in receiving device 20, orthogonal demodulation unit 22 extracts, as a "received symbol," an LDM symbol obtained by orthogonal demodulation processing of an LDM signal received via receiving antenna 21 (step S1). Here, the LDM symbol output by orthogonal demodulation unit 22 is output as received symbol #n with a symbol number assigned so as to be identifiable for subsequent processing. Furthermore, receiving device 20, using LLR calculation unit 23, regards the LDM symbol obtained from orthogonal demodulation unit 22 (i.e., the received symbol) as a UL symbol, and calculates a log-likelihood ratio (LLR) using all symbol positions that the LDM symbol can take or a reference point indicating a symbol position according to a modulation method predetermined for UL.

[0060] 4 is an IQ plane diagram for explaining the processing of the UL LLR calculation unit 23 in the LDM receiving device 20 of the first embodiment according to the present invention. As shown in Fig. 4, the reference points of 16 symbols determined by QPSK as the modulation method for UL and LL and IL are all symbol positions that the LDM symbol can take. Therefore, when calculating the log-likelihood ratio (LLR) for the received symbol #1 (indicated by "△" in Fig. 4) as the LDM symbol, the UL LLR calculation unit 23 calculates the log-likelihood ratio (LLR) of each bit in the error correction code block used in the error correction decoding unit 24 from the Euclidean distance between the received symbol #1 and each reference point of the 16 symbols.

[0061] Then, the receiving device 20 performs a decoding process corresponding to an error correction coding process (LDPC code, etc.) predetermined for the UL on the transmitting side on the UL signal indicated by the log-likelihood ratio (LLR) obtained from the LLR calculation unit 23, by the error correction decoding unit 24, and generates decoded bits of the UL signal as the decoding result and outputs them to the outside.

[0062] Furthermore, receiving device 20 causes error correction decoder 24 to feedback output decoded bits of the UL signal generated as a decoding result to reference point determiner 25R (step S2). Here, we consider received symbol #1 as an LDM symbol, but in actual processing, error correction decoder 24 sequentially feeds back the decoded results of the UL signal for each received symbol #n to reference point determiner 25R. Preferably, error correction decoder 24 sequentially feeds back the decoded results of the UL signal for each received symbol #n to reference point determiner 25R, with identification information (e.g., symbol number) attached that enables identification of the LDM symbol corresponding to the UL signal.

[0063] Next, the receiving device 20 determines the reference point to be used for calculating the log-likelihood ratio (LLR) for LL decoding according to the decoded bits of the UL signal by using the reference point determination unit 25R to narrow down the reference points indicating the symbol positions that the LL symbol can take in the received LDM symbol (i.e., the received symbol) from among the reference points indicating all symbol positions that the LDM symbol can take (16 symbols in this example) based on the decoded bits of the UL signal (step S3).

[0064] For example, in the example of bit allocation in the LDM symbol shown in Fig. 2, it can be divided into regions R1 to R4 of the first to fourth quadrants, with the most significant two bits being UL and the least significant two bits being LL. Therefore, when the UL decoding result is 00, the reference point determination unit 25R determines the reference point of four symbols in region R1 of the first quadrant as the reference point used to calculate the log-likelihood ratio (LLR) for LL decoding (step S4). Also, when the UL decoding result is 10, the reference point determination unit 25R determines the reference point of four symbols in region R2 of the second quadrant as the reference point used to calculate the log-likelihood ratio (LLR) for LL decoding (step S5). Also, when the UL decoding result is 11, the reference point determination unit 25R determines the reference point of four symbols in region R3 of the third quadrant as the reference point used to calculate the log-likelihood ratio (LLR) for LL decoding (step S6). Furthermore, when the UL decoding result is 01, the reference point determination unit 25R determines the reference points of four symbols in the fourth quadrant R4 area as the reference points to be used for calculating the log-likelihood ratio (LLR) for LL decoding (step S7). By feeding back the UL decoding result to the reference point determination unit 25R in this way, it becomes possible to narrow down the reference points to be used for LL decoding.

[0065] Next, the receiving device 20 performs a predetermined delay adjustment using the LLR calculation unit 27R to generate an LL signal corresponding to the UL signal for the LDM symbol obtained from the orthogonal demodulation unit 22, and then calculates the log-likelihood ratio (LLR) for the received LDM symbol corresponding to the UL signal related to the determination of the reference point using only the reference point determined by the reference point determination unit 25R (step S8).

[0066] FIG. 5 is a diagram for explaining the processing of the reference signal determination unit 25R and the LLR calculation unit 27R for LL in the LDM receiving device 20 according to the first embodiment of the present invention.

[0067] As shown in Fig. 5, the UL error correction decoder 24 feeds back the UL decoding result to the reference point determiner 25R. Preferably, the error correction decoder 24 sequentially feeds back the UL signal decoding result for each received symbol #n to the reference point determiner 25R, with identification information (e.g., symbol number) that enables identification of the LDM symbol corresponding to the UL signal. The reference point determiner 25R can then narrow down the reference points that indicate the symbol positions that the LL symbol in the received LDM symbol (i.e., received symbol #1) can take from among the reference points that indicate all symbol positions that the LDM symbol can take (16 symbols in this example). In the example shown in Fig. 5, when the UL decoding result is 00, the reference point of four symbols in the R1 region of the first quadrant is determined as the reference point to be used for calculating the log-likelihood ratio (LLR) for LL decoding, and preferably notifies the LLR calculation unit 27R of this together with the identification number (e.g., symbol number).

[0068] Then, the LLR calculation unit 27R for LL calculates the Euclidean distance between each reference point (R1 in the example shown in Figure 5) of the four symbols notified by the reference point determination unit 25R and the received symbol #1, and converts the Euclidean distance into a probability to obtain the log-likelihood ratio (LLR) of each bit in the error correction code (LDPC, etc.) block in the error correction decoding unit 28 for LL, generates an LL signal indicating this log-likelihood ratio (LLR), and outputs it to the error correction decoding unit 28.

[0069] Here, when the error correction decoder 24 feeds back and notifies the LLR calculator 27R of the decoded result of the UL signal via the reference point determiner 25R, it is preferable to attach identification information (e.g., a symbol number) to the decoded result of the UL signal. In this case, the LLR calculator 27R can variably and accurately adjust the delay of the received LDM symbol based on the identification information in order to generate an LL signal corresponding to the UL signal. After performing this delay adjustment, the LLR calculator 27R calculates a log-likelihood ratio (LLR) for the received LDM symbol corresponding to the UL signal using only the reference point determined by the reference point determiner 25R, and generates an LL signal indicating the log-likelihood ratio (LLR). However, if the LLR calculator 23 and the error correction decoder 24 are configured to perform the LLR calculation process and error correction decoding process for the UL signal in a fixed time, such identification information (e.g., a symbol number) can be omitted. In this case, the LLR calculator 27R can perform a delay adjustment for a fixed time period in order to generate an LL signal corresponding to the UL signal.

[0070] Next, the receiving device 20 performs a decoding process on the UL signal obtained from the LLR calculation unit 27R using the error correction decoding unit 28, which corresponds to an error correction coding process (such as an LDPC code) predetermined for the LL on the transmitting side, and generates decoded bits of the LL signal as the decoding result, which are output to the outside.

[0071] In the receiving device 20 according to the present invention configured as described above, it is possible to narrow down the reference points for calculating the LLR for LL decoding by feeding back the UL decoding result to the reference point determination unit 25R, thereby making it possible to significantly reduce the cost of receiving processing compared to the SIC type illustrated in Fig. 12. Furthermore, by narrowing down the reference points as in the receiving device 20 according to the present invention, it is possible to improve the LL decoding performance, and it is possible to achieve better receiving performance compared to the batch demodulation type illustrated in Fig. 13.

[0072] (simulation) Next, a description will be given of the results of a simulation comparing the LDM type receiving device 20 of the first embodiment of the present invention with the prior art ("SIC" and "collective modulation").

[0073] First, as a simulation condition, a single-carrier LDM transmission is assumed using the transmitting device 10 illustrated in Fig. 11, and information bits constituting UL and LL transmission information are error-correction coded at coding rates of 3 / 5 and 4 / 5, respectively, using a parity check matrix of an LDPC code conforming to ISDB-S3. Furthermore, the LDPC block (44,880 bits) after error-correction coding is QPSK-modulated (22,440 symbols) for both UL and LL, and the power of UL and LL is adjusted to IL = 3 dB. It is assumed that an LDM signal is generated by quadrature-modulating an LDM symbol obtained by combining UL and LL symbols from the transmitting device 10 illustrated in Fig. 11, and transmitted to the LDM receiving device 20 of the first embodiment of the present invention, simulating a white noise transmission channel.

[0074] Fig. 6 is a diagram showing the C / N vs. BER characteristics under white noise, comparing the LDM receiver 20 of the first embodiment of the present invention with the conventional techniques ("SIC" and "batch modulation"). Fig. 7 is a diagram showing the required C / N, comparing the LDM receiver 20 of the first embodiment of the present invention with the conventional techniques ("SIC" and "batch modulation"). A pseudo-error-free state is defined as a bit error rate (BER) of 1E-11, and the C / N at this point is defined as the required C / N. Since the C / N at which both UL and LL are pseudo-error-free is defined as the required C / N, the BER of LL, which has low noise tolerance, was evaluated.

[0075] From Figures 6 and 7, it can be seen that the receiving performance of the receiving device 20 according to the present invention is almost equivalent to that of the conventional SIC method, and can significantly improve the receiving performance compared to batch demodulation.

[0076] Analyzing the results of Figures 6 and 7, since the batch demodulation method cannot narrow down the reference points, all 16 symbols shown in Figure 5 are used as reference points, and the Euclidean distance is calculated between received symbol #1 and all reference points to find the LLR. In this case, the Euclidean distance between the reference point in the R2 region shown in Figure 5 (the point corresponding to UL=10, LL=01) and received symbol #1 is the smallest, so in the batch demodulation method, the probability that the LL bit assigned to received symbol #1 is 01 is high, which is thought to be a cause of error correction decoding failure due to incorrect decision.

[0077] Therefore, according to the receiving device 20 of the first embodiment of the present invention, by narrowing down the reference point for LL decoding from the UL decoding result as a receiving process of the layer division multiplexing (LDM) method, it is possible to achieve good receiving performance with high noise resistance equivalent to or greater than that of SIC, and also to significantly reduce the cost of receiving processing compared to SIC.

[0078] [Receiving device of embodiment 2] Fig. 8 is a block diagram showing a schematic configuration of an LDM receiving device 20 according to a second embodiment of the present invention. The LDM receiving device 20 according to the second embodiment of the present invention shown in Fig. 8 receives and demodulates an LDM signal transmitted from an LDM transmitting device 10 using single-carrier transmission shown in Fig. 11, and performs layer separation into a higher layer (UL) and a lower layer (LL) in the LDM signal for decoding, and includes an orthogonal demodulation unit 22, an LLR calculation unit 23 for UL, an error correction decoding unit 24, a Euclidean distance accumulation unit 25E, a reference point determination unit 25R having a Euclidean distance selection unit 26E, an LLR calculation unit 27E for LL, and an error correction decoding unit 28. Note that in Fig. 8, the same reference numerals are used to designate components similar to those shown in Fig. 1. Furthermore, while Figure 1 illustrates the schematic configuration of a receiving device 20 using an LDM system with single-carrier transmission, the device can also be configured in a similar manner when receiving and demodulating an LDM signal transmitted by multi-carrier OFDM transmission, and separating the LDM signal into a higher layer (UL) and a lower layer (LL) to decode it.

[0079] That is, the LDM type receiving device 20 of the second embodiment according to the present invention shown in FIG. 8 is similar to the first embodiment shown in FIG. 1 in that it includes an orthogonal demodulation unit 22, an LLR calculation unit 23 and an error correction decoding unit 24 for UL, and an error correction decoding unit 28 for LL, but differs in that it includes a "Euclidean distance accumulation unit 25E," that the reference point determination unit 25R shown in FIG. 1 has a "Euclidean distance selection unit 26E," and that it includes an "LLR calculation unit 27E" that performs LLR calculation using only the Euclidean distance for the reference point selected by the "Euclidean distance selection unit 26E" from among the Euclidean distances for each reference point that have already been calculated at the time of UL decoding, instead of the "LLR calculation unit 27R" shown in FIG. 1.

[0080] The configuration of the LDM receiving device 20 according to the second embodiment of the present invention shown in FIG. 8 will be described below in more detail.

[0081] As in the first embodiment, the orthogonal demodulation unit 22 according to the second embodiment receives an LDM signal via the receiving antenna 21, in which two modulated signals are multiplexed at different powers as a high layer (UL) and a low layer (LL), and then orthogonally modulated and transmitted in the same frequency band. The orthogonal demodulation unit 22 then inputs the received LDM signal after power (amplitude) normalization processing using a predetermined gain adjustment (not shown) based on average power or maximum power, performs symbol synchronization and carrier recovery, and performs orthogonal demodulation processing to extract LDM symbols, and outputs the extracted LDM symbols to the LLR calculation unit 23 for UL.

[0082] However, it should be noted that the orthogonal demodulation unit 22 according to the second embodiment is not configured to output the received symbol (received LDM symbol) to the LLR calculation unit for LL 27E, unlike the first embodiment shown in Fig. 1. Here, the LDM signal received via the receiving antenna 21 is a signal transmitted from the LDM transmitting device 10 shown in Fig. 11.

[0083] Similarly to the first embodiment, the LLR calculation unit 23 according to the second embodiment regards the received symbol (received LDM symbol) obtained from the orthogonal demodulation unit 22 as a symbol for UL, calculates a log likelihood ratio (LLR) using reference points indicating all symbol positions that the LDM symbol can take, generates a UL signal indicating the log likelihood ratio (LLR), and outputs the UL signal to the error correction decoding unit 24. Note that the second embodiment does not assume a configuration in which the LLR calculation unit 23 may calculate the log likelihood ratio (LLR) using "reference points indicating symbol positions according to a modulation method predetermined for UL" as in the first embodiment, but calculates the log likelihood ratio (LLR) using "reference points indicating all symbol positions that the LDM symbol can take."

[0084] However, unlike in the first embodiment shown in FIG. 1, the LLR calculation unit 23 according to the second embodiment outputs information on the Euclidean distance for each reference point used when calculating the log-likelihood ratio (LLR) for the UL signal to the Euclidean distance accumulation unit 25E for each received symbol (received LDM symbol).

[0085] As in the first embodiment, the error correction decoding unit 24 according to the second embodiment performs a decoding process corresponding to an error correction coding process (such as an LDPC code) predetermined for UL on the transmitting side on the UL signal obtained from the LLR calculation unit 23, generates decoded bits of the UL signal indicating transmission information for UL, and outputs the decoded bits to the outside.

[0086] However, unlike the first embodiment shown in FIG. 1, the error correction decoder 24 according to the second embodiment outputs information on the decoded bits (decoding result) of the UL signal to a reference point determiner 25R having a Euclidean distance selector 26E.

[0087] The Euclidean distance accumulation unit 25E inputs information on the Euclidean distance (r1 to r16) for each reference point of the received symbols used in the LLR calculation from the LLR calculation unit 23 for UL, and temporarily accumulates, while updating, information on the Euclidean distance (r1 to r16) for each reference point of each received symbol used in the calculation of the log-likelihood ratio (LLR) for UL decoding for a predetermined number of received symbols (received LDM symbols).

[0088] The reference point determination unit 25R of the second embodiment, like the first embodiment, narrows down the reference points used to calculate the log-likelihood ratio (LLR) for LL decoding for each received symbol based on the UL decoded bits, but differs from the first embodiment in that it has the function of a Euclidean distance selection unit 26E inside.

[0089] The Euclidean distance selection unit 26E selects and reads out, for each received symbol (received LDM symbol) decoded for the UL signal by the error correction decoding unit 24, the Euclidean distance of the reference point to be used for LL decoding from the Euclidean distances of each reference point stored in the Euclidean distance storage unit 25E based on the UL decoding bit, and outputs it to the LLR calculation unit 27E for LL.

[0090] As a series of operations from the decoding of the UL signal in the error correction decoding unit 24, the LLR calculation unit 27E calculates, for each received symbol, a log-likelihood ratio (LLR) for the corresponding received symbol (received LDM symbol) using only the Euclidean distance selected for LL decoding by the Euclidean distance selection unit 26E, generates an LL signal indicating this log-likelihood ratio (LLR), and outputs it to the error correction decoding unit 28.

[0091] The error correction decoding unit 28 performs a decoding process on the LL signal obtained from the LLR calculation unit 27E, corresponding to an error correction coding process (LDPC code, etc.) predetermined for LL on the transmitting side, and generates decoded bits of the LL signal indicating transmission information for LL, and outputs the decoded bits to the outside.

[0092] 8, the UL decoding process itself is the same as the conventional SIC method, but instead of having the SIC-type "replica signal generation unit 25 by UL re-modulation and subtraction unit 26," the receiver 20 is configured to have a "Euclidean distance accumulation unit 25E" and a "reference point determination unit 25R having a Euclidean distance selection unit 26E," and to have an "LLR calculation unit 27E for LL" that calculates the log-likelihood ratio (LLR) for LL using only the Euclidean distance selected by the "Euclidean distance selection unit 26E." This reduces at least the calculation process of the Euclidean distance, making it possible to significantly reduce the cost related to the LL reception process.

[0093] [Reception process in embodiment 2] Hereinafter, the reception process in the receiving device 20 shown in FIG. 8 will be described with more specific examples.

[0094] First, in the receiving device 20 shown in Figure 8, the LDM signal received via the receiving antenna 21 is a signal transmitted from the transmitting device 10 of the LDM system shown in Figure 11, and the bits constituting the LDM symbol of Example 2 are configured in the same way as in Example 1, with the bits constituting the UL symbol on the upper side and the bits constituting the LL symbol on the lower side.

[0095] For example, Figure 10(a) shows an IQ plane diagram centered on the origin O when the modulation method for UL and LL is QPSK and the bit allocation to the QPSK symbols is Gray code mapped, as an example of the allocation of bits that make up the symbols of an LDM signal (LDM symbols). In this case, the LDM symbols are made up of a total of 16 symbols, and the bits allocated to these 16 symbols are UL for the most significant 2 bits and LL for the least significant 2 bits, as shown in Figure 10(a).

[0096] 10(a), for the convenience of explaining the operation of the second embodiment, the bits constituting the LDM symbol are represented as [a1 a2 a3 a4], where a1 indicates the first bit (UL), a2 indicates the second bit (UL), a3 indicates the third bit (LL), and a4 indicates the fourth bit (LL), and r1 to r16 indicate the Euclidean distance from a certain received symbol (here, received symbol #1) to each reference point. However, the allocation of UL and LL bits in the LDM symbol does not need to be limited to that shown in FIG. 10(a), and it is sufficient if the UL and LL bits can be identified on the LDM symbol.

[0097] Therefore, as a representative example, an example will be described in which the modulation scheme for UL and LL is QPSK, and the orthogonal demodulation unit 22 shown in Fig. 8 receives and processes LDM symbols according to the Gray code mapping shown in Fig. 10(a). Note that the present invention is similar even when set partitioning mapping is used instead of Gray code mapping.

[0098] FIG. 9 is a flowchart showing the reception process in the LDM receiving device 20 according to the second embodiment of the present invention.

[0099] First, in the receiving device 20 according to the second embodiment, as in the first embodiment, the orthogonal demodulation unit 22 extracts an LDM symbol obtained by orthogonally demodulating an LDM signal received via the receiving antenna 21 as a "received symbol" (step S11). Here, the LDM symbol output by the orthogonal demodulation unit 22 is output as a received symbol #n with a symbol number assigned thereto so as to be identifiable for subsequent processing. Furthermore, the receiving device 20 uses the LLR calculation unit 23 to regard the LDM symbol obtained from the orthogonal demodulation unit 22 (i.e., the received symbol) as a symbol for UL, and calculates a log-likelihood ratio (LLR) using reference points indicating all symbol positions that the LDM symbol can take.

[0100] As shown in Fig. 10(a), the reference points of 16 symbols determined by the IL and QPSK modulation scheme for UL and LL are all symbol positions that the LDM symbol can take. Therefore, when calculating the log-likelihood ratio (LLR) for received symbol #1 ("△" shown in Fig. 10(a)) as the LDM symbol, the LLR calculation unit 23 for UL calculates the log-likelihood ratio (LLR) of each bit in the error correction code block used in the error correction decoding unit 24 from the Euclidean distance (r1 to r16) between the received symbol #1 and each reference point of the 16 symbols.

[0101] Here, the receiving device 20 according to the second embodiment is different from the receiving device 20 according to the first embodiment in that it includes a Euclidean distance storage unit 25E. The Euclidean distance storage unit 25E receives information on the Euclidean distances (r1 to r16) of received symbols used in calculating the log-likelihood ratios (LLRs) from the UL LLR calculation unit 23, and temporarily stores, while updating, information on the Euclidean distances (r1 to r16) of received symbols used in calculating the log-likelihood ratios (LLRs) for UL decoding for a predetermined number of received symbols (received LDM symbols) (step S12). Fig. 10(b) shows an example of storage of information on the Euclidean distances (r1 to r16 corresponding to symbol numbers #1 to #3 indicated by subscripts) of received symbols (for example, symbol numbers #1 to #3) used in calculating the log-likelihood ratios (LLRs) in the UL LLR calculation unit 23 in the Euclidean distance storage unit 25E. Although Figure 10(b) only shows three received symbols with symbol numbers #1 to #3, the Euclidean distance storage unit 25E is configured to temporarily store information on the Euclidean distances (r1 to r16) of received symbols corresponding to the code length of the error correction code, based on its operating principle.

[0102] Then, in the receiving device 20 according to the second embodiment, as in the first embodiment, the error correction decoding unit 24 performs a decoding process corresponding to an error correction coding process (LDPC code or the like) predetermined for UL on the transmitting side on the UL signal indicated by the log-likelihood ratio (LLR) obtained from the LLR calculation unit 23, and generates decoded bits of the UL signal as a decoding result and outputs the decoded bits to the outside.

[0103] Here, in the receiving device 20 according to the second embodiment, the reference point decision unit 25R narrows down the reference points used for calculating the log-likelihood ratio (LLR) for LL decoding for each received symbol based on the decoded bits of the UL, as in the first embodiment. However, unlike the first embodiment, a Euclidean distance selection unit 26E is provided as a function of the reference point decision unit 25R. With respect to the received symbols (received LDM symbols) decoded for the UL signal by the error correction decoding unit 24, the Euclidean distance selection unit 26E selects and reads out the Euclidean distance of the reference point used for LL decoding from the Euclidean distances of the reference points stored in the Euclidean distance storage unit 25E based on the decoded bits of the UL for each received symbol, and outputs the selected Euclidean distance to the LLR calculation unit for LL 27E (step S13).

[0104] Next, unlike in the first embodiment, the receiving device 20 of the second embodiment calculates, as a series of operations from the decoding of the UL signal in the error correction decoding unit 24, a log-likelihood ratio (LLR) for each received symbol (received LDM symbol) using only the Euclidean distance selected for LL decoding by the Euclidean distance selection unit 26E by the LLR calculation unit 27E (step S14).

[0105] That is, the UL LLR calculation unit 23 calculates the log likelihood ratio (LLR) by replacing the Euclidean distances (r1 to r16) with probabilities. For example, the probability P 10 and the probability that the first bit a1 is 1, P 11 can be expressed as equations (1) and (2), and the LLR (likelihood) of the first bit a1 of the received symbol #1 shown in FIG. 10(a) is expressed as LLR 1_♯1 Then, it can be expressed as in equation (3). The LLR (likelihood) of the second bit a2 of received symbol #1 can also be obtained in the same way as equations (1) to (3). In equations (1) and (2), σ represents the variance of white noise added to the received symbol calculated from the received C / N, and σ2 represents the noise power.

[0106]

number

[0107]

number

[0108]

number

[0109] Next, in the receiving device 20 according to the second embodiment, as in the first embodiment, the error correction decoding unit 28 performs a decoding process corresponding to an error correction coding process (such as an LDPC code) predetermined for LL on the transmitting side on the UL signal obtained from the LLR calculation unit 27R, and generates decoded bits of the LL signal as the decoding result and outputs the decoded bits to the outside.

[0110] In this way, in the UL decoding process in the second embodiment, similarly to the first embodiment, for example, all possible symbol positions of the LDM symbol are used as reference points, and the Euclidean distances (r1 to r16) between the received symbol and each reference point are calculated (see FIG. 10(a)), and then converted into probabilities, and the LLR calculation unit 23 calculates the log-likelihood ratio (LLR) for UL, and the error correction decoding unit 24 generates decoded bits for UL.

[0111] However, in the second embodiment, the Euclidean distances (r1 to r16) calculated for all reference points corresponding to all possible symbol positions of the LDM symbol are stored in the Euclidean distance storage unit 25E. Then, as shown in Fig. 10(b), the Euclidean distance selection unit 26E selects, from the Euclidean distance storage unit 25E, a Euclidean distance required to calculate an LL log-likelihood ratio (LLR) indicating the likelihood of a bit as an LL signal, based on the UL decoding result. The LL LLR calculation unit 27E calculates the LL log-likelihood ratio (LLR) using only this selected Euclidean distance, and the error correction decoding unit 28 generates decoded bits for LL.

[0112] That is, the LL LLR calculation unit 27E can calculate the LL log-likelihood ratio (LLR) based on the Euclidean distance used to calculate the LLR in the UL LLR calculation unit 23 and information on the UL decoded bits indicating the UL decoding result. In particular, based on the UL decoding result, it is possible to select the Euclidean distance required to calculate the LL log-likelihood ratio (LLR) from the Euclidean distances (r1 to r16) used to calculate the UL log-likelihood ratio (LLR), thereby avoiding the use of Euclidean distances unnecessary for LL in probability calculation. That is, in the Euclidean distance accumulation unit 25E, it is possible to narrow down the LL reference points from the UL decoding result among the Euclidean distances for all reference points accumulated for the received symbol, so it is not necessary to calculate the Euclidean distance again.

[0113] More specifically, to explain the reduction in the calculation load, in the conventional "batch demodulation" process, the probability P' that the third bit a3 is 0 is 30 and the probability that the third bit a3 is 1, P' 31 is expressed as in equations (4) and (5). In equations (4) and (5), σ represents the variance of the white noise added to the received symbol, which is calculated from the received C / N ratio, and σ 2 represents the noise power.

[0114]

number

[0115]

number

[0116] On the other hand, in this embodiment, the Euclidean distance required to calculate the log-likelihood ratio (LLR) for LL is selected based on the UL decoding result. For example, when UL=00 (a1=0, a2=0) of received symbol #1, the probability that the third bit a3 is 0 is P 30 and the probability that the third bit a3 is 1, P 31 can be expressed as in equations (6) and (7), and the LLR (likelihood) of the third bit a3 of the received symbol #1 is expressed as LLR 3_♯1 Then, it can be expressed as in equation (8). The LLR (likelihood) of the fourth bit a4 of received symbol #1 can also be obtained in the same way as equations (6) to (8). In equations (6) and (7), σ represents the variance of white noise added to the received symbol calculated from the received C / N, and σ 2 represents the noise power.

[0117]

number

[0118]

number

[0119]

number

[0120] As described above, in the second embodiment, compared to the first embodiment, the information on the Euclidean distance for each reference point used in the calculation of the log-likelihood ratio (LLR) for UL by the LLR calculation unit 23 is stored in the Euclidean distance storage unit 25E for the received symbol, so that it is possible to omit the Euclidean distance calculation related to the calculation of the log-likelihood ratio (LLR) for LL, thereby reducing the processing cost.

[0121] The receiving performance of the second embodiment is equivalent to that of the first embodiment (see FIGS. 6 and 7), and is advantageous in that at least the amount of calculation related to the Euclidean distance calculation can be reduced compared to the first embodiment.

[0122] Therefore, according to the receiving device 20 of the second embodiment of the present invention, as a receiving process of the layer division multiplexing (LDM) method, the reference point for decoding LL is narrowed down from the UL decoding result, and further, the recalculation of the Euclidean distance required for decoding LL is omitted, thereby realizing good receiving performance with high noise resistance equivalent to or greater than that of SIC, and furthermore, the cost for receiving process can be significantly reduced compared to SIC.

[0123] Although the above-described embodiments have been described as representative examples, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. For example, in the above-described embodiments, only the LDM symbols shown in Figures 2 and 10(a) are described in which the UL and LL modulation schemes are QPSK, and only examples in which an LDPC code is used as the error correction code are described. However, the UL and LL modulation schemes may be different, such as π / 2-shift BPSK, 8PSK, 16APSK, etc., in addition to QPSK. Furthermore, various error correction codes, not limited to LDPC codes, may be used. Therefore, the present invention is not limited to the above-described embodiments, but is limited only by the claims. [Industrial Applicability]

[0124] According to the present invention, it is possible to realize good reception performance with high noise resistance equivalent to or greater than that of SIC as reception processing for a hierarchical division multiplexing (LDM) system, and furthermore, it is possible to significantly reduce the cost of reception processing compared to SIC, and therefore it is useful for use in LDM system transmission systems. [Explanation of symbols]

[0125] 10 LDM transmitter 11 Error correction coding section for UL 12 UL mapping section 13 Error correction coding section for LL 14 Mapping section for LL 15 Power adjustment section 16 Synthesis section 17 Quadrature modulation section 18 transmitting antennas 20 LDM receiving device according to the present invention 20S SIC type receiving device according to the prior art 20B Prior art collective demodulation type receiving device 21 Receiving antenna 22 Quadrature demodulation section 23 LLR calculation unit for UL 24 Error correction decoder for UL 25 Replica signal generator 25R Reference point determination unit according to the first and second embodiments of the present invention 25E Euclidean distance storage unit according to the second embodiment of the present invention 26 Subtraction section 26E Euclidean distance selection unit according to the second embodiment of the present invention LLR calculation unit for 27,27B LL 27R LLR calculation unit for LL according to the first embodiment of the present invention 27E LLR calculation unit for LL according to the second embodiment of the present invention 28 Error correction decoding unit for LL

Claims

1. A receiving device of a hierarchical division multiplexing (LDM) system, an orthogonal demodulation unit that receives an LDM signal in which two modulated signals, a high layer (UL) and a low layer (LL), are multiplexed with different power levels and orthogonally modulated in the same frequency band and transmitted, and performs orthogonal demodulation processing to extract an LDM symbol; an LLR calculation unit for UL that regards the LDM symbol as a symbol for UL, calculates a log-likelihood ratio using all symbol positions that the LDM symbol can take or a reference point that indicates a symbol position according to a modulation method predetermined for UL, and generates a UL signal that indicates the log-likelihood ratio; an error correction decoding unit for UL that performs a predetermined error correction decoding process for UL on the UL signal and generates decoded bits of the UL signal; a reference point determination unit that determines a reference point to be used in calculating a log-likelihood ratio for LL decoding according to the decoded bits of the UL signal by narrowing down reference points that indicate symbol positions that LL symbols in the received LDM symbols can take from among reference points that indicate all symbol positions that LDM symbols can take, based on the decoded bits of the UL signal; an LLR calculation unit for LL that calculates a log-likelihood ratio for a received LDM symbol corresponding to the UL signal based only on the reference point determined by the reference point determination unit and generates an LL signal indicating the log-likelihood ratio; an error correction decoding unit for LL that performs a predetermined error correction decoding process for LL on the LL signal to generate decoded bits of the LL signal; A receiving device comprising:

2. 2. The receiving device according to claim 1, wherein the UL error correction decoding unit adds identification information that enables the reference point determination unit to identify the LDM symbol corresponding to the UL signal, and feeds back a decoding result indicating the decoded bits of the UL signal to the reference point determination unit.

3. 3. The receiving device according to claim 2, wherein the LLR calculation unit for LL performs delay adjustment on the received LDM symbol variably based on the identification information in order to generate an LL signal corresponding to the UL signal, and then calculates a log-likelihood ratio for the received LDM symbol corresponding to the UL signal using only the reference point determined by the reference point determination unit, and generates an LL signal indicating the log-likelihood ratio.

4. 2. The receiving device according to claim 1, wherein the LLR calculation unit for LL performs delay adjustment on the received LDM symbol for a fixed time period for generating the LL signal corresponding to the UL signal, and then calculates a log-likelihood ratio for the received LDM symbol corresponding to the UL signal using only the reference point determined by the reference point determination unit, and generates an LL signal indicating the log-likelihood ratio.

5. the LLR calculation unit for UL calculates a log-likelihood ratio using reference points indicating all possible symbol positions of the LDM symbol; a Euclidean distance storage unit that temporarily stores, while updating, information on the Euclidean distance to each reference point for each received LDM symbol used in calculating the log-likelihood ratio indicated as the UL signal, for a predetermined number of symbols; the reference point determination unit includes a Euclidean distance selection unit that selects, for each LDM symbol decoded for the UL signal by the UL error correction decoding unit, a Euclidean distance of a reference point to be used for decoding the LL signal from among the Euclidean distances of the reference points stored in the Euclidean distance storage unit, based on the decoded bits of the UL signal; 2. The receiving device according to claim 1, wherein the LLR calculation unit for LL calculates a log-likelihood ratio for the received LDM symbol corresponding to the UL signal using only the Euclidean distance selected by the Euclidean distance selection unit for decoding the LL signal, and generates an LL signal indicating the log-likelihood ratio.

6. A receiving method for a layer division multiplexing (LDM) system, comprising: receiving an LDM signal in which two modulated signals, a high layer (UL) and a low layer (LL), are multiplexed with different power levels and orthogonally modulated in the same frequency band and transmitted; and performing orthogonal demodulation processing to extract an LDM symbol; a step of regarding the LDM symbol as a UL symbol, calculating a log-likelihood ratio using all possible symbol positions of the LDM symbol or a reference point indicating a symbol position according to a predetermined modulation method for UL, and generating a UL signal indicating the log-likelihood ratio; performing a predetermined error correction decoding process for UL on the UL signal to generate decoded bits of the UL signal; determining a reference point used for calculating a log-likelihood ratio for LL decoding according to the decoded bits of the UL signal by narrowing down reference points indicating symbol positions that can be taken by LL symbols in the received LDM symbols from among reference points indicating all symbol positions that can be taken by LDM symbols; calculating a log-likelihood ratio for a received LDM symbol corresponding to the UL signal based solely on the reference point determined by the step, and generating an LL signal indicative of the log-likelihood ratio; a step of performing an error correction decoding process predetermined for LL on the LL signal to generate decoded bits of the LL signal; A receiving method comprising:

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