Symbol decision device and repeater

Abstract

To provide a symbol determination instrument and a relay device that can maintain the quality of retransmission symbols even in an area where constellations overlap and prevent deterioration in reception characteristics in a receiver when reproduction relay is performed for a layered division multiplex (LDM) signal.SOLUTION: A symbol determination instrument for generating a retransmission symbol by symbol determination processing for a reception symbol of a signal to which layered division multiplexing (LDM) is applied as a layered transmission method, generates a soft determination replica of a lower layer (LL) for each prescribed signal point of an upper layer (UL) for the reception symbol, combines by multiplying the soft determination replica by a symbol probability of the upper layer, and thereby generates the retransmission symbol. A relay device includes a transmission path equalization unit and the symbol determination instrument.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a symbol determiner and a repeater device, and more particularly to a symbol determiner and a repeater device that determine the symbol of a received signal and generate a retransmission symbol in digital signal transmission. [Background technology]

[0002] In recent years, research into advanced terrestrial television broadcasting (hereinafter referred to as the "advanced method") has been progressing in order to realize new terrestrial broadcasting services. The advanced method improves transmission efficiency compared to the current terrestrial broadcasting transmission method (ISDB-T: Integrated Services Digital Broadcasting-Terrestrial) by, for example, adopting LDPC (Low Density Parity Check) code as an error correcting code, increasing the number of carrier modulation multi-values, and introducing NUC (Non Uniform Constellation) which makes the signal point arrangement non-uniform. In order to realize broadcasting using the advanced method, it is necessary to study the construction of a broadcasting network using the advanced method.

[0003] In the current terrestrial broadcasting transmission system in Japan, the effectiveness of regenerative relay, which improves the degradation of signal quality due to fading and frequency characteristic distortion by combining channel equalization in the frequency domain and symbol judgment in MFN (Multi-Frequency Network) broadcast wave relay, has been confirmed and is widely used (Non-Patent Document 1).

[0004] Figure 7 shows a model of MFN broadcast wave relay. The broadcast network is made up of a master station (upper station) 1, a relay station (relay device) 2, and a receiver 3. Master station 1 generates a modulated wave signal and outputs broadcast waves at a predetermined frequency. Relay station 2 receives the broadcast waves from master station 1, compensates for the signal quality using equalization determiner 200, and retransmits the signals at a frequency different from that of the received signal. Receiver 3 is a receiving device installed, for example, in each home, and receives and demodulates the relayed and retransmitted broadcast waves.

[0005] The equalization determiner 200 of the relay station (relay device) 2 will be described. The equalization determiner 200 compensates for frequency characteristic distortion of the received signal by channel equalization, and outputs a retransmission signal from which noise components have been removed by symbol decision. The equalization determiner 200 includes an FFT unit 210, a transmission path estimation unit 220, a transmission path equalization unit 230, a symbol decision unit 240, and an IFFT unit 250.

[0006] An FFT (Fast Fourier Transform) unit 210 performs a fast Fourier transform on a received signal transmitted, for example, by an OFDM (Orthogonal Frequency Division Multiplexing) method, and detects a signal (symbol) of each carrier wave (subcarrier).

[0007] The transmission channel estimation unit 220 estimates the transmission channel characteristics of the communication line. For example, by using a scattered pilot (SP) signal or the like arranged in each carrier wave, the transmission channel characteristics of the communication line are estimated and interpolated, and the like, to estimate the transmission channel characteristics of the communication line collectively.

[0008] The transmission channel equalization unit 230 performs equalization processing on each symbol based on the transmission channel characteristics estimated by the transmission channel estimation unit 220. In this way, each symbol obtained from the received signal is corrected, and a received symbol from which distortion due to the transmission channel has been removed is generated. When the equalization determiner 200 performs symbol determination, the transmission channel equalization unit 230 outputs the received symbol to the symbol determination unit 240, and when the equalization determiner 200 does not perform symbol determination, the transmission channel equalization unit 230 outputs the received symbol from which distortion has been removed to the IFFT unit 250.

[0009] The symbol decision unit 240 converts the received symbol after transmission path equalization (channel equalization) into an optimal symbol based on a specified signal point constellation, and outputs it as a retransmission symbol. In conventional terrestrial digital broadcasting, symbol decision is a hard decision that rematches the received symbol after channel equalization to the nearest point of the specified signal point constellation.

[0010] An IFFT (Inverse Fast Fourier Transform) unit 250 performs an inverse fast Fourier transform on the received symbols output from the transmission path equalization unit 230 or the retransmission symbols generated by the symbol decision unit 240 to generate a retransmission signal.

[0011] Fig. 8 is a diagram for explaining each symbol in the equalization determiner 200. Fig. 8(a) is a constellation showing the transmission symbols output from the master station 1. Here, a case is shown in which the transmission signal is transmitted by unevenly allocated carrier modulation in 256QAM (Quadrature Amplitude Modulation) that is being considered for adoption in advanced systems. The vertical axis is the I (In-Phase) axis, and the horizontal axis is the Q (Quadrature) axis.

[0012] Fig. 8(b) shows the result of performing transmission path equalization processing on the received symbols received by relay station 2. Since the received symbols are subject to noise during transmission, they form a constellation with a distribution around the specified signal point arrangement.

[0013] 8(c) shows a retransmission symbol (hard decision symbol) generated by the symbol decider 240 in conventional terrestrial digital broadcasting. Since hard decision processing is performed to rematch the received symbol to the nearest point of the specified signal point constellation, the retransmitted hard decision symbol has noise removed and has the same constellation as the transmission symbol (a) from the parent station.

[0014] In this way, the relay station 2 can improve the quality of the relay signal by the equalization determiner 200.

[0015] In the advanced system, operation with more multi-value carrier modulation is expected, but it is difficult to directly apply the regenerative relay technology used in terrestrial digital broadcasting to the advanced system. In other words, in the advanced system, when hard symbol decisions are used in the relay station 2, the symbol error rate tends to increase more than in the case of terrestrial digital broadcasting, and erroneous information is retransmitted. This causes a problem that error correction may not function effectively in the receiver 3. To address this problem, a method has been reported that improves signal quality degradation in broadcast wave relay even in the advanced system by applying regenerative relay using soft decision replicas (symbols replicated by soft decision processing) (Non-Patent Document 2).

[0016] When the symbol decision unit 240 performs soft symbol decision on the received symbol in Fig. 8(b) and outputs a soft decision replica as a retransmitted symbol, the constellation of the retransmitted soft decision symbol becomes as shown in Fig. 8(d). The retransmitted symbol that has been soft decision processed becomes a signal containing noise, but when the receiver 3 performs LDPC decoding, the receiving characteristics are improved compared to the case of hard decision processing.

[0017] Meanwhile, in terrestrial broadcasting transmission systems, Layered Division Multiplexing (LDM) is being considered as a method for multiplexing services (hereinafter referred to as layers) with different transmission tolerances in the physical layer (Non-Patent Document 3). Unlike other layered transmission systems, LDM is a method for combining multiple layers by assigning a power ratio to each layer. Below, we will explain Layered Division Multiplexing (LDM), which is the premise of the present invention.

[0018] 9 is an example of a block diagram of a transmission device (modulation processing) of a hierarchical division multiplexing (LDM) system. The transmission device 300 includes error correction coding units 310 and 320, carrier modulation units 311 and 321, interleaving units 312 and 322, power adjustment units 313 and 323, a synthesis unit 330, an OFDM framing unit 340, a reference signal generation unit 341, a TMCC signal generation unit 342, an additional information signal generation unit 343, an IFFT unit 350, an orthogonal modulation unit 360, and a GI addition unit 370. The error correction coding units 310 to power adjustment units 313 process mobile reception hierarchical data, and the error correction coding units 320 to power adjustment units 323 process fixed reception hierarchical data.

[0019] The error correction coding unit 310 divides the input mobile reception hierarchical data into blocks of a predetermined block length and performs error correction coding for each block. For example, an LDPC code is used as the error correction code.

[0020] The carrier modulation unit 311 maps the error correction encoded data onto the IQ plane using a predetermined modulation method (e.g., QPSK: Quadrature Phase-Shift Keying) for each carrier, generates a carrier modulation signal (data carrier symbol), and outputs it to the interleaving unit 312.

[0021] The interleaving unit 312 rearranges the symbols. It performs at least one of frequency interleaving, which rearranges the carrier numbers of symbols that are originally adjacent to each other to distribute the data in frequency, and time interleaving, which rearranges the symbols of each carrier in the time direction to distribute the data in time. The interleaved data is output to the power adjustment unit 313.

[0022] The power adjustment unit 313 adjusts the symbols of the mobile reception layer data to a predetermined power and outputs the symbol data after the power adjustment to the combining unit 330.

[0023] Similarly, the fixed reception hierarchical data undergoes error correction coding in an error correction coding unit 320, mapping to an IQ plane in a carrier modulation unit 321, symbol rearrangement in an interleave unit 322, and power adjustment in a power adjustment unit 323. Note that the modulation method for the fixed reception hierarchical data can be a modulation method with a large modulation multi-level number (for example, 64QAM: Quadrature Amplitude Modulation).

[0024] The combiner 330 combines (by vector addition) the power-adjusted modulated signal of the mobile reception layer and the modulated signal of the fixed reception layer to generate a combined symbol.

[0025] The OFDM framing unit 340 arranges the combined symbols (data symbols) to generate an OFDM segment frame, and outputs it to the IFFT unit 350. The reference signal generating unit 341 generates a pilot signal (e.g., an SP signal), the TMCC signal generating unit 342 generates a TMCC (Transmission and Multiplexing Configuration and Control) signal, and the additional information signal generating unit 343 generates information to be added to a specific signal (corresponding to additional information of an Auxiliary Channel in terrestrial digital broadcasting). The OFDM framing unit 340 inserts these control information symbols in addition to the data symbols to generate an OFDM segment frame.

[0026] The IFFT unit 350 performs IFFT (Inverse Fast Fourier Transform) processing on the input OFDM segment frame to generate I and Q signals converted into a time axis.

[0027] The quadrature modulation section 360 performs quadrature modulation on the I signal and Q signal to generate an effective symbol signal.

[0028] The GI (Guard Interval) adding unit 370 inserts a guard interval, which is a copy of the latter half of the effective symbol signal, at the beginning of the effective symbol signal input from the orthogonal modulation unit 360. The guard interval is inserted to reduce inter-symbol interference when receiving an OFDM signal, and is set so that the delay time of a multipath delayed wave does not exceed the guard interval length. The output of the GI adding unit 370 becomes the OFDM transmission signal.

[0029] FIG. 10 is a diagram for explaining a process of combining layers in layer division multiplexing (LDM).

[0030] In FIG. 10, A denotes symbols (constellation) of the mobile reception hierarchical layer generated by the error correction coding unit 310 to the interleaving unit 312 in FIG. 9, and here, the QPSK modulation scheme is shown as an example.

[0031] Moreover, B is the symbol (constellation) of the fixed reception layer generated by the error correction coding unit 320 to the interleaving unit 322 in FIG. 9, and here, a modulation scheme of a non-uniform constellation in 64QAM is shown as an example.

[0032] Power adjustment units 313 and 323 adjust the power of the mobile reception hierarchical signal and the fixed reception hierarchical signal, and assign a power ratio (ratio of average power of transmission signals) to the two. Here, the power ratio is the ratio of the power of the mobile reception hierarchical signal to the power of the fixed reception hierarchical signal (mobile reception hierarchical power / fixed reception hierarchical power), and in the range of power ratio ≧0 dB, the power of the fixed reception hierarchical signal is smaller than the power of the mobile reception hierarchical signal.

[0033] 10C shows the constellation of the transmission signal (transmission symbol) resulting from combining (vector addition) the signal of the mobile reception layer and the signal of the fixed reception layer in combiner 330. The constellation of the transmission signal is a constellation in which four 64QAMs are arranged with four QPSK signal points at the center, and the number of signal points is 256 (=4×64).

[0034] Figure 11 shows the relationship between the power ratio and the constellation of the LDM signal. Here, the modulation method for the mobile reception layer is QPSK, and the modulation method for the fixed reception layer is 64QAM-NUC. Figure 11 shows the constellations of the LDM signal (combined signal) at each power ratio when the power ratio between the two (mobile reception layer power / fixed reception layer power) is changed to (a) 2 dB, (b) 4 dB, (c) 6 dB, and (d) 8 dB.

[0035] Hereinafter, the mobile reception layer is referred to as the upper layer (UL) and the fixed reception layer is referred to as the lower layer (LL) (the upper layer may be abbreviated to "UL" and the lower layer to "LL"). A smaller power ratio increases the power of the fixed reception layer (LL), improving the reception characteristics of the fixed reception layer. However, as shown in Figures 11(a) and (b), when observing the constellation of an LDM signal with a small power ratio, there are areas where the constellations of fixed reception layers with different UL symbols overlap. In these areas, the relationship between the signal points and the transmission bit strings does not follow the Gray code arrangement.

[0036] FIG. 12 is a diagram showing an example of the relationship between signal points and bit strings of LDM.

[0037] In Figure 12, the modulation method for the mobile reception layer (2 bits) is QPSK, the modulation method for the fixed reception layer (6 bits) is 64QAM-NUC, and the power ratio is 2 dB. Signal points are distinguished by the difference in the number of bits between adjacent signal points. Each signal point has a bit string of 8 bits (= 2 bits + 6 bits). In areas where the constellations overlap, there is a difference of 2 bits or more between adjacent signal points. [Prior art documents] [Non-patent literature]

[0038] [Non-Patent Document 1] Kazuhiko Shibuya, "Relay Station Technology", Journal of the Institute of Image Information and Television Engineers, vol.64, no.5, 2010, pp.666-671 [Non-Patent Document 2] Shogo Kawashima et al., "MFN Broadcast Wave Relay Using Soft-Decision Replicas in Advanced Terrestrial Broadcasting," ITE Technical Report, vol. 44, no. 19, BCT2020-64, 2020, pp. 13-16 [Non-Patent Document 3] Liang Zhang, et al., “Layered-Division-Multiplexing: Theory and Practice”, IEEE Trans. Broadcast, vol.62, no.1, (2016), pp.216-232 Summary of the Invention [Problem to be solved by the invention]

[0039] Equalization decision filters using symbol soft decision have been evaluated to a certain extent for their application to broadcast wave relay, but no study has been conducted on the application of previously proposed symbol soft decision to LDM signals.

[0040] 13 is an example of a block diagram of a conventional symbol soft decision device. The symbol soft decision device 50 includes an LLR calculation unit 51, a symbol probability calculation unit 52, a soft decision replica generation unit 53, and an output unit of a specified signal point arrangement (UL+LL) 54. In the conventional method, the mobile reception layer is not separated for the received symbols of LDM, and a soft decision replica is generated from all the specified signal points collectively.

[0041] The number of multi-value bits in the upper layer (UL) is VUL [bit], and the number of modulation multi-values ​​is M (= 2 VUL ), the number of multi-value bits in the lower layer (LL) is VLL [bit], and the number of modulation multi-values ​​is N (=2 VLL ), an LLR (Log Likelihood Ratio) calculation unit 51 calculates the log likelihood ratio (LLR) of each bit of the received symbol for M·N signal point candidates (all specified signal points) obtained by combining UL and LL, based on the distance from the received symbol.

[0042] The symbol probability calculation unit 52 calculates the probability (symbol probability) of transmission at each signal point candidate based on the calculated log-likelihood ratio (LLR).

[0043] The soft decision replica generation unit 53 weights (multiplies) all the specified signal points supplied from the output unit of the specified signal point constellation (UL+LL) 54 by the symbol probability and takes the sum of the weighted values ​​to generate a soft decision replica.

[0044] The symbol soft decision device 50 can be used as the symbol decision section 240 of the equalization decision device 200 in FIG. 7, and the output soft decision replica becomes a retransmission symbol.

[0045] Fig. 14 shows the relationship between the power ratio and reception characteristics of the LDM based on the above-mentioned conventional technology. In broadcast wave relay using LDM signals, the required C / N (here, the bit error rate (BER) after LDPC decoding is 1.0×10 -7 The results of evaluating the above with computer simulations are compared for different equalization decision processes. The horizontal axis is the power ratio, and the vertical axis is the required C / N [dB] at the receiver.

[0046] In Figure 14, "equalization only" indicates the required C / N at the receiver when only processing (channel equalization) by the transmission path equalization unit 230 of the equalization determiner 200 in Figure 7 is performed, and a retransmission signal is sent without processing by the symbol determination unit 240 (as "no determination").

[0047] In FIG. 14, "soft decision" indicates the required C / N in the receiver when the conventional soft decision processing described in FIG. 13 is performed in the symbol decision section 240 of the equalization decision unit 200 in FIG.

[0048] Moreover, "without relay" refers to a case where no signal relay processing is performed, and indicates the required C / N at the receiver when it is assumed that a transmission signal from the master station is transmitted at the position of the relay station.

[0049] As shown in Figure 14, when regenerative relay is performed using the conventional soft decision method, the required C / N ratio deteriorates in the range where the power ratio is small, and the required C / N ratio increases compared to "equalization only", which performs channel equalization alone.

[0050] The reason for this is believed to be that in the conventional symbol soft decision method, in areas where LL constellations overlap, the received symbol is remapped in a direction different from the specified signal point by the symbol soft decision, resulting in degradation of reception characteristics when the power ratio is small.

[0051] Therefore, in consideration of the above problems, an object of the present invention is to provide a symbol determiner and a relay device that can maintain the quality of retransmitted symbols even in areas where constellations overlap, and suppress deterioration of the receiving characteristics at the receiver, when performing regenerative relay on a signal to which hierarchical division multiplexing (LDM) is applied as a hierarchical transmission method. [Means for solving the problem]

[0052] In order to solve the above problems, the symbol decider of the present invention is a symbol decider that generates a retransmission symbol by symbol decision for a received symbol of a signal to which hierarchical division multiplexing (LDM) is applied as a hierarchical transmission method, and is characterized in that the symbol decider generates a soft decision replica of a lower layer (LL) for each specified signal point of an upper layer (UL) for the received symbol, and generates the retransmission symbol by multiplying the soft decision replica by a symbol probability of the upper layer and combining them.

[0053] It is also desirable for the symbol decider to include a soft decision replica generation unit which generates a soft decision replica of a lower hierarchy for the received symbol, assuming each case of specified signal points of a higher hierarchy, a symbol probability calculation unit which calculates a symbol probability for each specified signal point of the higher hierarchy, a multiplication unit which multiplies the soft decision replica generated by the soft decision replica generation unit by the symbol probability calculated by the symbol probability calculation unit, and a combination unit which combines multiplication results of the multiplication unit for all specified signal points of the higher hierarchy.

[0054] Furthermore, it is desirable that the symbol decider generates the soft decision replica by having the soft decision replica generation unit remove a specified signal point of an assumed higher layer from the received symbol, calculate a log-likelihood ratio (LLR) of each bit of the lower layer from the remaining component, calculate a symbol probability of each specified signal point of the lower layer from the log-likelihood ratio (LLR), weight each specified signal point of the lower layer by the calculated symbol probability of each specified signal point, take a sum, and add the specified signal point of the assumed higher layer.

[0055] Furthermore, it is desirable that the symbol decision unit calculates a logarithmic likelihood ratio (LLR) of each bit of the received symbol based on all specified signal points obtained by combining the upper layer and the lower layer, calculates symbol probabilities of all specified signal points from the logarithmic likelihood ratio (LLR), and calculates the symbol probability for each specified signal point of the upper layer by taking the sum of the symbol probabilities corresponding to each specified signal point of the upper layer from among the calculated symbol probabilities of all specified signal points.

[0056] In order to solve the above problems, the symbol decider of the present invention is a symbol decider that generates a retransmission symbol by symbol decision for a received symbol of a signal to which hierarchical division multiplexing (LDM) is applied as a hierarchical transmission method, and is characterized in that it generates a soft decision replica based on all specified signal points obtained by combining an upper layer (UL) and a lower layer (LL) for the received symbol, and selects either the soft decision replica or the received symbol as the retransmission symbol depending on a bit likelihood.

[0057] It is also desirable that the symbol decider comprises an LLR calculation unit that calculates a log-likelihood ratio (LLR) of each bit of the received symbol, an LLR decision unit that decides an absolute value of the log-likelihood ratio (LLR) of a bit of a higher layer, a soft-decision replica generation unit that generates, for the received symbol, a soft-decision replica based on all specified signal points that combine the higher layer and the lower layer, and a symbol switching unit that switches the retransmission symbol to the soft-decision replica or the received symbol based on a decision result of the LLR decision unit.

[0058] In addition, if the absolute value of the log-likelihood ratio (LLR) of a bit in a higher layer falls below a predetermined threshold even for one bit, it is desirable for the symbol determiner to determine that the received symbol is in an area where constellations of a lower layer with different bits in a higher layer overlap, and to treat the received symbol as a retransmission symbol.

[0059] In order to solve the above problems, the relay device of the present invention is a relay device for signal transmission that applies hierarchical division multiplexing (LDM) as a hierarchical transmission method, and is characterized in that it comprises a transmission path equalization unit that performs equalization processing on each symbol of a received signal based on transmission path characteristics, and a symbol determiner that generates a retransmission symbol for the equalized received symbol. Effect of the Invention

[0060] According to the symbol determiner and relay device of the present invention, when performing regenerative relay on a signal to which hierarchical division multiplexing (LDM) is applied as a hierarchical transmission method, it is possible to maintain the quality of the retransmitted symbols even in areas where constellations overlap, and suppress deterioration of the receiving characteristics at the receiver. [Brief description of the drawings]

[0061] [Figure 1] FIG. 2 is an example of a block diagram of a symbol determiner according to the first exemplary embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of a soft decision replica generating unit (LL). [Diagram 3] FIG. 2 is a diagram illustrating an example of the configuration of a symbol probability calculation unit (UL). [Figure 4] FIG. 11 is an example of a block diagram of a symbol determiner according to a second exemplary embodiment of the present invention. [Diagram 5] FIG. 11 is a diagram illustrating the relationship between the LLR threshold and reception characteristics. [Figure 6] FIG. 11 is a diagram showing the relationship between the power ratio and the reception characteristics of the LDM according to the present invention. [Figure 7] FIG. 1 is a diagram showing a model of MFN broadcast wave relay. [Figure 8] FIG. 11 is a diagram illustrating each symbol in an equality determiner. [Figure 9] FIG. 1 is an example of a block diagram of a transmission device using a hierarchical division multiplexing (LDM) system. [Figure 10] FIG. 1 is a diagram for explaining a process of combining layers in layer division multiplexing (LDM). [Figure 11] FIG. 13 is a diagram showing the relationship between the power ratio and the constellation of an LDM signal. [Figure 12] FIG. 1 is a diagram illustrating an example of the relationship between signal points and bit strings of an LDM. [Figure 13] FIG. 1 is an example of a block diagram of a conventional symbol soft decision device. [Figure 14] FIG. 1 is a diagram showing the relationship between the power ratio and the reception characteristics of LDM according to the conventional technology. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] Hereinafter, an embodiment of the present invention will be described. In the embodiment, the upper layer (UL) is a mobile reception layer and the lower layer (LL) is a fixed reception layer, but the settings of the upper layer and lower layer of layer division multiplexing (LDM) are not limited to this. How to use the upper layer and lower layer can be set arbitrarily depending on the purpose, the transmission method to be applied, etc.

[0063] (First embodiment) FIG. 1 is an example of a block diagram of a symbol decider according to a first embodiment of the present invention. In the first embodiment, a soft decision replica is generated in consideration of a signal point in a mobile reception layer (upper layer). A symbol decider 100 according to this embodiment includes a soft decision replica generator (LL) 10, a symbol probability calculator (UL) 20, a multiplier 30, and a combiner 40. A received symbol that has been subjected to channel equalization processing based on the transmission path characteristics is input to the symbol decider 100. In this embodiment, the number of multi-level bits in the upper layer (UL) is VUL [bit], the number of modulation multi-levels is M (=2 VUL ), the number of multi-value bits in the lower layer (LL) is VLL [bit], and the number of modulation multi-values ​​is N (=2VLL ) shall be used.

[0064] The soft decision replica generation unit (LL) 10 assumes each case of the M specified signal points in the upper layer (UL) for the received symbol (for example, when it is the m-th specified signal point (0 ≤ m < M)), and generates a soft decision replica only for the lower layer (LL).

[0065] The symbol probability calculation unit (UL) 20 calculates the symbol probability that is the m-th specified signal point in the upper layer (UL).

[0066] The multiplication unit 30 multiplies the soft decision replica generated by the soft decision replica generation unit (LL) 10 and the symbol probability calculated by the symbol probability calculation unit (UL) 20.

[0067] The combining unit 40 accumulates and combines the values of the M multiplication results output from each multiplication unit 30. The replica of the received symbol thus generated is used as the retransmission symbol.

[0068] In FIG. 1, M processing blocks having the soft decision replica generation unit 10, the symbol probability calculation unit 20, and the multiplication unit 30 are described in parallel. However, one processing block may be used M times to perform the calculation process for each of the M specified signal points in the UL.

[0069] FIG. 2 shows an example of the configuration of the soft decision replica generation unit (LL) 10. In the soft decision replica generation unit (LL) 10, assuming the m-th specified signal point in the UL, soft decision processing is performed on the component (LL component) remaining after removing the UL specified signal point from the received symbol, and a soft decision replica for the LL is generated.

[0070] The soft decision replica generation unit (LL) 10 includes an addition unit (subtraction unit) 11, an output unit of the specified signal point arrangement (UL) 12, an LLR calculation unit (LL) 13, a bit probability calculation unit (LL) 14, a symbol probability calculation unit (LL) 15, a soft decision replica generation unit (LL) 16, an output unit of the specified signal point arrangement (LL) 17, and an addition unit 18.

[0071] The addition unit (subtraction unit) 11 subtracts the m-th specified signal point of the UL from the received symbol. By this process, an LL component based on the m-th specified signal point arrangement 12 of the UL is output.

[0072] The LLR calculation unit (LL) 13 calculates the log-likelihood ratio LLR for each bit of the LL. Let the modulation order of the UL be M (= 2 VUL ), the modulation order of the LL be N (= 2 VLL ), the specified signal point arrangement of the UL be s UL m (0 ≤ m < M), the specified signal point arrangement of the LL be s LL n (0 ≤ n < N), and their IQ values be s UL m,I , s UL m,Q , s LL n,I , s LL n,Q . Also, let the real part of the received symbol be x I , the imaginary part be x Q , and the noise variance be σ 2 . Then, the LLR of the k-th bit of the LL when the specified signal point of the UL is s UL m is given by the following equation (1). LL m,k

[0073]

Equation

[0074] Here, s LL k.0 , s LL k,1 are the sets of signal points representing 0 and 1 for the k-th bit respectively, G is the power of the LL, and taking IL as the power ratio, it is 10 -IL / 10 / (1 + 10 -IL / 10 ).

[0075] The bit probability calculation unit (LL) 14 calculates the bit probability of each bit of the LL from the calculated LLR. λ LL kis the bit probability P LL k.0 and the bit probability P LL k.1 Since this is the logarithmic ratio of

[0076]

number

[0077] Therefore, the probability P LL k.0、 P LL k.1 is λ LL k It is expressed by the following equation (3).

[0078]

number

[0079] The symbol probability calculation unit (LL) 15 calculates the symbol probability of each specified signal point of the LL based on the bit sequence of the symbol and each bit probability. LL n is expressed as the following equation (4).

[0080]

number

[0081] Here b LL n,k s LL n indicates 0 / 1 for the kth bit of the bit string represented.

[0082] The soft decision replica generator (LL) 16 generates a symbol probability R LL n Multiply the two together.

[0083] The adder 18 multiplies the symbol probability by each specified signal point of LL and adds the result to the m-th specified signal point arrangement 12 of UL serving as a reference to generate a soft decision replica of LL for the m-th specified signal point of UL.

[0084] That is, for the UL specified signal point s UL m the soft decision replica y m of LL is obtained by weighting the LL specified signal point s LL n with the symbol probability R LL n and taking the sum.

[0085]

Equation

[0086] Fig. 3 shows an example of the configuration of the symbol probability calculation unit (UL) 20. In the symbol probability calculation unit (UL) 20, similar to the conventional method, the LLR and the symbol probability are calculated based on all the M·N specified signal points obtained by synthesizing UL and LL, and the symbol probability of the m-th specified signal point of UL is obtained.

[0087] The symbol probability calculation unit (UL) 20 includes an LLR calculation unit (UL+LL) 21, a bit probability calculation unit (UL+LL) 22, a symbol probability calculation unit (UL+LL) 23, and a symbol probability calculation unit (UL) 24.

[0088] The LLR calculation unit (UL+LL) 21 first calculates, from the received symbol and the specified signal point arrangement s j (0 ≦ j < M·N) of the modulation multilevel number M·N obtained by synthesizing UL and LL, the LLR of each bit, λ l (0 ≦ l < VUL+VLL) based on the following equation (6).

[0089]

Equation

[0090] Here, Sl,0 , S l,1 are sets of signal points where the l-th bit represents 0 or 1, with the UL bits being the upper bits and the LL bits being the lower bits.

[0091] Next, the bit probability calculation unit (UL+LL) 22 calculates the calculated LLR, λ l Based on this, the bit probability of each bit is calculated using the above equations (2) and (3).

[0092] Next, the symbol probability calculation unit (UL+LL) 23 calculates the symbol probability Rj for the combined UL and LL signal point constellation from the bit sequence of each symbol and the calculated bit probability based on equation (4).

[0093] The symbol probability calculation unit (UL) 24 calculates R j The mth prescribed signal point s UL m The sum of the symbol probabilities corresponding to the UL signal point s UL m The symbol probability R UL m can be calculated using the following equation (7).

[0094]

number

[0095] As described above, the symbol probability calculation unit (UL) 20 calculates the symbol probability R UL m and outputs it to the multiplication unit 30.

[0096] The multiplication unit 30 multiplies the soft-decision replica y m and the symbol probability R UL m Find the product of .

[0097] All UL specified signal points UL mThe soft-decision replica y m and the symbol probability R UL m The products are added in the combiner 40 to determine the final retransmission symbol y as shown in the following equation (8).

[0098]

number

[0099] The above is an overview of how to determine a retransmission symbol in the symbol determiner 100 of the first embodiment. According to this embodiment, it is possible to appropriately generate a retransmission symbol for a received symbol of an LDM signal.

[0100] The symbol decider 100 of the first embodiment can be used as the symbol decider 240 of the equalization decider 200 of Fig. 7. That is, a relay device can be configured that includes the transmission path equalization unit 230 that performs equalization processing on each symbol based on the transmission path characteristics, and the symbol decider 100 of the first embodiment that generates a retransmission symbol for the equalized received symbol.

[0101] In the first embodiment, as described later, since it is possible to generate a soft decision replica having better reception performance than a reception symbol obtained by only equalization processing at any power ratio, it is possible to use the output of the symbol decider 100 as a transmission symbol for all reception symbols without setting a "no decision" route in which the transmission path equalization unit 230 outputs directly to the IFFT unit 50. According to the relay device of this embodiment, it is possible to suppress deterioration of the reception characteristics in the receiver 3.

[0102] Second Embodiment 4 is an example of a block diagram of a symbol decision unit according to the second embodiment of the present invention. In the second embodiment, in an area where constellations in which errors are likely to occur in soft-decision replicas overlap (an area where LL constellations with different UL bits overlap), the channel equalization result is retransmitted without performing regeneration relay using the soft-decision replica.

[0103] To achieve this, it is necessary to determine whether the constellations are in an overlapping region based on the IQ value of the received symbol. As a means of determining this, attention is paid to the fact that the overlapping region of the constellations is a point where signal points with different bits for the mobile reception layer (for example, QPSK) are close to each other. That is, for all OFDM subcarriers, the LLR, which is the ratio of the probability (bit likelihood) that each bit is 0 or 1, is calculated based on the distance between the received symbol and the specified signal point arrangement (UL+LL). The closer this LLR value is to 0, the more difficult it is to determine whether a bit is 0 or 1. By utilizing this property, by observing the LLR of the bits for the mobile reception layer among the LLRs output from the log likelihood ratio (LLR) calculation unit, if this value is close to 0, it is possible to realize a process of retransmitting a received symbol that has been subjected to only propagation path equalization without generating a soft decision replica for that subcarrier. That is, in this embodiment, either the soft decision replica or the received symbol is set as the retransmission symbol according to the bit likelihood.

[0104] The symbol decision unit 110 of this embodiment shown in Fig. 4 includes an LLR calculation unit 51, an LLR decision unit 60, a soft decision replica generation unit 53, an output unit of a specified signal point arrangement (UL+LL) 54, and a symbol switching unit 70. A received symbol that has been subjected to channel equalization processing based on the transmission path characteristics is input to the symbol decision unit 110. Note that Fig. 4 shows an example in which QPSK (number of multi-level bits = 2) is used for UL and 64QAM (number of multi-level bits = 6) is used for LL.

[0105] The LLR calculation unit 51 calculates the LLR for the received symbols of the LDM based on the lumped specified signal point arrangement (UL+LL) 54 without removing the UL. That is, λ l The calculated LLR is output to the soft decision replica generation unit 53, and the LLR of the UL bit is output to the LLR determination unit 60.

[0106] The LLR decision unit 60 decides the absolute value of the LLR of each bit of the UL, and outputs the decision result to the symbol switching unit 70. For example, when the absolute value of the LLR of all bits is equal to or greater than a predetermined threshold, the decision result is output to the symbol switching unit 70 indicating that the constellations are in a non-overlapping region (or an instruction to output a soft decision replica as a retransmission symbol). On the other hand, when even one bit falls below the predetermined threshold, the decision result is output indicating that the constellations are in an overlapping region (or an instruction to output a received symbol as a retransmission symbol).

[0107] The soft decision replica generation unit 53 calculates bit probabilities using equations (2) and (3) based on the LLR calculated by the LLR calculation unit 51, and calculates symbol probabilities for each signal point constellation in the same manner as equation (4). Then, the soft decision replica is generated by weighting the inputted specified signal point constellation (UL+LL) 54 by the symbol probabilities and taking the sum. The generated soft decision replica is output to the symbol switching unit 70.

[0108] The symbol switching unit 70 receives the received symbol and the soft decision replica output from the soft decision replica generation unit 53, and switches between outputting the received symbol or the soft decision replica based on the decision result from the LLR decision unit 60. Specifically, if all absolute values ​​of the UL LLRs are equal to or greater than a predetermined threshold, the soft decision replica is output as a retransmission symbol, and if the absolute value of the UL LLR falls below the predetermined threshold even by 1 bit, the symbol switching unit 70 performs processing to retransmit the received symbol as is.

[0109] The threshold value used for judgment by the LLR judgment unit 60 is set as follows. It is considered that the receiving characteristics in the receiver may change depending on the LLR threshold. Therefore, the results of evaluating the receiving characteristics in the receiver by changing the LLR threshold are shown in FIG. 5. It can be seen from FIG. 5 that the receiving characteristics (bit error rate) are optimal when the LLR is in the vicinity of 3.0. Therefore, it is desirable to set this value as the threshold.

[0110] The above is an overview of how to determine a retransmission symbol in the symbol determiner 110 of the second embodiment. According to the present embodiment, it is possible to prevent the signal quality from deteriorating in the area where the constellations overlap, as in the conventional method, and to maintain the quality of the retransmission symbol.

[0111] In the second embodiment, the amount of calculation is relatively small, so that a simple symbol decision device can be realized. In addition, when the LLR decision unit 60 determines that the bit likelihood of UL is ambiguous (0 / 1 decision is difficult) by the decision process, the calculation of the bit likelihood of the remaining LL and the generation of the soft decision replica can be stopped, so that a further reduction in the amount of calculation can be expected.

[0112] The symbol decider 110 of the second embodiment can be used as the symbol decider 240 of the equalization decider 200 of Fig. 7. That is, a relay device can be configured that includes the transmission path equalization unit 230 that performs equalization processing on each symbol based on the transmission path characteristics, and the symbol decider 110 of the second embodiment that generates a retransmission symbol for the equalized received symbol.

[0113] According to the relay device of this embodiment, the deterioration of the reception characteristics in the receiver 3 can be suppressed.

[0114] (Verification of effectiveness) 6 is a diagram showing the relationship between the power ratio and the reception characteristics of the LDM according to the present invention. The figure shows the results of evaluating the reception characteristics when receiving a retransmitted signal by applying the first and second embodiments, by computer simulation.

[0115] In FIG. 6, "equalization only" indicates the required C / N in the receiver when processing is performed only by the transmission path equalization unit 230 of the equalization determiner 200 in FIG. 7 and a retransmission signal is sent out.

[0116] "Conventional method" refers to the required C / N in the receiver when the conventional soft decision processing described with reference to FIG. 13 is performed.

[0117] The "first method" refers to the required C / N ratio in the receiver when the retransmission symbol is generated based on the first embodiment. The "second method" refers to the required C / N ratio in the receiver when the retransmission symbol is generated based on the second embodiment.

[0118] "No relay" refers to a case where no signal relay processing is performed, and indicates the required C / N at the receiver when it is assumed that a transmission signal from the master station is transmitted at the position of the relay station.

[0119] From the results in Fig. 6, it was confirmed that by using the present invention, the reception characteristics of the retransmitted LDM signal were improved even at a small power ratio. In addition, no significant difference was observed in the reception characteristics between the first and second embodiments.

[0120] As described above, by applying the present invention, it is possible to improve the signal quality degradation caused by broadcast wave relay even in the advanced method using LDM for hierarchical transmission, and it is possible to construct a broadcast network using broadcast wave relay.

[0121] Although the present invention has been described using an example of advanced broadcast wave relay, it goes without saying that the present invention can be applied to signal transmission of any digital signal using hierarchical division multiplexing.

[0122] In the above first and second embodiments, the configuration and operation of the symbol decision units 100 and 110 have been described, but the present invention is not limited to this, and may be configured as a method for generating retransmission symbols from received symbols. That is, for example, the present invention may be configured as a method for generating retransmission symbols including a step of generating soft decision replicas (LL) from received symbols, a step of calculating symbol probabilities (UL), a step of multiplying these, and a step of combining the multiplication results, according to the data flow in FIG. 1.

[0123] Although the above-mentioned embodiment has been described as a representative example, it is clear to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the above-mentioned embodiment, and various modifications or changes can be made without departing from the scope of the claims. For example, the functions included in each block, each step, etc. described in the embodiment can be rearranged so as not to be logically inconsistent, and multiple configuration blocks, steps, etc. can be combined into one or divided. [Explanation of symbols]

[0124] 1 Master station 2. Relay station (relay device) 3 Receiver 10 Soft decision replica generator (LL) 11 Addition section (subtraction section) 12 Standard signal point arrangement (UL) 13 LLR calculation section (LL) 14-bit probability calculation unit (LL) 15 Symbol Probability Calculation Unit (LL) 16 Soft decision replica generator (LL) 17 Standard signal point arrangement (LL) 18 Addition section 20 Symbol Probability Calculation Unit (UL) 21 LLR calculation section (UL+LL) 22-bit probability calculation unit (UL+LL) 23 Symbol Probability Calculation Unit (UL+LL) 24 Symbol Probability Calculation Unit (UL) 30 Multiplication section 40 Synthesis section 50 symbol soft decision 51 LLR calculation unit 52 Symbol Probability Calculation Unit 53 Soft decision replica generator 54 Specified Signal Point Constellation 60 LLR judgment section 70 Symbol Switching Unit 100 Symbol Classifier 110 Symbol Classifier 200 Equalization judger 210 FFT section 220 Transmission path estimation unit 230 Transmission line equalization section 240 Symbol Judgment Unit 250 IFFT section 300 Transmitting device 310,320 Error correction coding section 311,321 Carrier Modulation Section 312,322 Interleave section 313,323 Power adjustment section 330 Synthesis Section 340 OFDM framing unit 341 Reference signal generator 342 TMCC signal generator 343 Additional Information Signal Generator 350 IFFT section 360 Quadrature Modulation Section 370 GI Addition Section

Claims

1. A symbol determiner that generates a retransmission symbol by symbol determination for a received symbol of a signal to which hierarchical division multiplexing (LDM) is applied as a hierarchical transmission method, a symbol decider for generating a soft decision replica of a lower layer (LL) for each specified signal point of an upper layer (UL) for the received symbol, and multiplying the soft decision replica by a symbol probability of the upper layer and combining the resulting replicas to generate the retransmission symbol,

2. 2. The symbol determiner according to claim 1, a soft decision replica generation unit that generates a soft decision replica of a lower layer for the received symbol assuming each case of a specified signal point of a higher layer; a symbol probability calculation unit that calculates a symbol probability for each specified signal point in a higher hierarchy; a multiplication unit that multiplies the soft decision replica generated by the soft decision replica generation unit by the symbol probability calculated by the symbol probability calculation unit; a synthesis unit that synthesizes the multiplication results of the multiplication unit for all specified signal points in the upper hierarchy; A symbol determiner comprising:

3. 3. The symbol determiner according to claim 2, the soft-decision replica generation unit calculates a log-likelihood ratio (LLR) of each bit of a lower layer from the remaining components after removing a specified signal point of an assumed higher layer from a received symbol, calculates a symbol probability of each specified signal point of the lower layer from the log-likelihood ratio (LLR), weights each specified signal point of the lower layer by the calculated symbol probability of each specified signal point, takes a sum, and adds the specified signal point of the assumed higher layer, thereby generating the soft-decision replica.

4. 3. The symbol determiner according to claim 2, the symbol probability calculation unit calculates a log-likelihood ratio (LLR) of each bit of a received symbol based on all specified signal points obtained by combining an upper layer and a lower layer, calculates symbol probabilities of all specified signal points from the log-likelihood ratios (LLR), and calculates a symbol probability for each specified signal point in the upper layer by taking the sum of the symbol probabilities corresponding to each specified signal point in the upper layer from among the calculated symbol probabilities of all specified signal points.

5. A symbol determiner that generates a retransmission symbol by symbol determination for a received symbol of a signal to which hierarchical division multiplexing (LDM) is applied as a hierarchical transmission method, A symbol decider characterized in that, for the received symbol, a soft decision replica is generated based on all specified signal points obtained by combining an upper layer (UL) and a lower layer (LL), and either the soft decision replica or the received symbol is set as a retransmission symbol according to a bit likelihood.

6. 6. The symbol determiner according to claim 5, a log-likelihood ratio (LLR) calculation unit that calculates a log-likelihood ratio (LLR) for each bit of the received symbol; an LLR determination unit that determines an absolute value of the log-likelihood ratio (LLR) of a bit of a higher layer; a soft decision replica generation unit that generates a soft decision replica based on all specified signal points obtained by combining the upper layer and the lower layer for the received symbol; a symbol switching unit that switches the retransmission symbol to the soft decision replica or the reception symbol based on a result of the determination by the LLR determination unit; A symbol determiner comprising:

7. 7. The symbol determiner according to claim 5, A symbol determiner characterized in that, when an absolute value of a log-likelihood ratio (LLR) of a bit in a higher layer falls below a predetermined threshold even for one bit, the symbol determiner determines that the received symbol is in an area where a constellation of a lower layer having a different bit in a higher layer overlaps, and sets the received symbol as a retransmission symbol.

8. A signal transmission relay device that applies hierarchical division multiplexing (LDM) as a hierarchical transmission method, a transmission path equalization unit that performs equalization processing on each symbol of a received signal based on a transmission path characteristic; A symbol determiner according to any one of claims 1 to 7, which generates retransmission symbols for equalized received symbols; A relay device comprising:

Images