JP5594074B2 - Receiver - Google Patents

Description

  The present invention relates to a receiving apparatus having a diversity function.

  The receiving apparatus has a diversity function for combining received signals obtained from a plurality of branch units in order to improve the quality of received signals. As a communication method between a transmission device and a reception device, for example, there are an Orthogonal Frequency Division Multiplexing (OFDM) method and an Orthogonal Frequency Division Multiple Access (OFDMA) method. These communication methods are collectively referred to as the OFDM communication method. The receiving apparatus described below is assumed to be an OFDM communication system compatible receiving apparatus.

  The receiving apparatus calculates a combined ratio of each received signal according to a carrier-to-noise ratio (CN ratio) calculated for each of the plurality of branch units. The CN ratio noise is mainly thermal noise generated in an RF processing unit (receiving unit) that performs down-converting a signal received via an antenna and performing orthogonal demodulation or the like. The receiving device combines the received signals based on the calculated combining ratio, and decodes the combined signal to obtain decoded data.

  The CN ratio calculation process includes, for example, a process of calculating a CN ratio using a guard interval (GI), a process of calculating a CN ratio using a guard band (GB), and a modulation error ratio (MER). There is a process of calculating the CN ratio by (Ratio).

JP 2005-260331 A

  In order to obtain high-quality decoded data, the CN ratio must be calculated with high accuracy and the composition ratio must be calculated with high accuracy. However, the calculation accuracy of the CN ratio may deteriorate depending on the propagation path state and the modulation method.

  When calculating the CN ratio using the guard interval GI, if there is a preceding / delayed wave due to multipath, the calculation accuracy of the CN ratio is improved due to intersymbol interference (ISI) from the previous symbol or the next symbol. May deteriorate. When calculating the CN ratio using the guard band GB, the calculation accuracy of the CN ratio may deteriorate due to intercarrier interference (ICI) caused by fading. When calculating the CN ratio using the modulation error ratio MER, if a signal modulated by a multi-level modulation method such as 16QAM (Quadrature Amplitude Modulation) or 64QAM is received, the CN ratio is calculated due to the short interval between the ideal reception signal points. Accuracy may be degraded.

  As described above, when the CN ratio calculation accuracy deteriorates due to the propagation path state or the modulation method, the combined ratio of the received signals obtained from the plurality of branch units cannot be calculated with high accuracy, and high-quality decoded data can be obtained. I can't.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a receiving apparatus that calculates a composite ratio of received signals obtained from a plurality of branch units with high accuracy.

A first aspect of the receiving device includes a plurality of branch units each including a receiving unit that receives a transmission signal and outputs the received signal, and a CN ratio calculation unit that calculates a plurality of types of CN ratios by different types of CN ratio calculation processing. When,
A branch CN ratio calculation unit that executes, for each of the plurality of branch units, a process of calculating a branch CN ratio indicating a CN ratio in the branch unit based on the plurality of types of CN ratios;
And a synthesizer that synthesizes the plurality of received signals according to the branch CN ratio.

  According to the first aspect, the composite ratio of received signals obtained from a plurality of branch units can be calculated with high accuracy. As a result, high-quality decoded data can be obtained.

It is a functional block diagram of the receiver which has the diversity reception function for demonstrating this Embodiment. It is the figure which showed the relationship between the electric power of a received signal, and the electric power of a thermal noise. It is a functional block diagram of a 1st CN ratio calculation part. It is a figure explaining CN ratio calculation processing by guard interval GI which a GI_CN ratio calculation part performs. It is a figure explaining intersymbol interference. It is a figure explaining the calculation process of CN ratio by the guard band GB which the GB_CN ratio calculation part performs. It is a figure explaining leakage power. It is a figure explaining the calculation process of CN ratio by the modulation error ratio MER which a MER_CN ratio calculation part performs. It is a 1st figure explaining the reason for which the calculation accuracy of CN ratio by modulation error ratio MER deteriorates. It is a 2nd figure explaining the reason why the calculation accuracy of CN ratio by modulation error ratio MER deteriorates. It is a functional block diagram explaining the receiving apparatus of 1st Embodiment. It is a figure explaining the calculation method of a dispersion value. It is a functional block diagram explaining the receiver of 2nd Embodiment.

  FIG. 1 is a functional block diagram of a receiving apparatus having a diversity receiving function for explaining the present embodiment.

  The receiving apparatus 1 includes a first branch unit 100 that receives a transmission signal and outputs a first reception signal R1, and a second branch unit 200 that outputs the second reception signal R2.

  The first branch unit 100 includes a first RF processing unit (reception unit) 101, an A / D unit 102, and an A / D unit that down-convert a signal received via the antenna 10 and execute orthogonal demodulation and the like. And a GI removal unit 103 that removes the guard interval GI from the output signal 102. Furthermore, the first branch unit 100 includes an FFT unit 104 that performs FFT processing on the effective symbol from which the guard interval GI has been removed, and a propagation path estimation / compensation unit 105. The propagation path estimation / compensation unit 105 estimates propagation path characteristics based on the phase and amplitude of pilot symbols (pilot signals), and estimates propagation path characteristics of data symbols that are not pilot symbols based on the estimated propagation path characteristics. Then, compensation processing for removing the propagation path characteristic from the data symbol is executed based on the estimated propagation path characteristic. Hereinafter, the output signal of the propagation path estimation / compensation unit 105 is referred to as a first received signal R1.

  The second branch unit 200 has elements having the same functions as the first branch unit 100, and receives a transmission signal via the antenna 20, a second RF processing unit 201, an A / D unit 202, and a GI removal unit. 203, FFT section 204, and propagation path estimation / compensation section 205 have the same functions as RF processing section 101, A / D section 102, GI removal section 103, FFT section 104, and propagation path estimation / compensation section 105. Hereinafter, the output signal of the propagation path estimation / compensation unit 205 is referred to as a second received signal R2.

  Furthermore, the receiving device 1 calculates the first branch CN ratio (CN1) calculated by the CN ratio calculation unit (shown in FIG. 3) in the first branch unit 100 and the CN ratio in the second branch unit 200. A first combination which is a combination ratio (W1: W2) of the first reception signal R1 and the second reception signal R2 based on the second branch CN ratio (CN2) calculated by the unit (illustrated in FIG. 3) A synthesis ratio calculation unit 300 that calculates the ratio W1 and the second synthesis ratio W2 is provided. This combination ratio (W1: W2) is a so-called weighting coefficient for combining the reception signals R1 and R2. As will be described later, this weighting coefficient increases the combined ratio of the received signals of the branch units with a good CN ratio and decreases the combined ratio of the received signals of the branch units with a poor CN ratio.

  The composite ratio calculation unit 300 calculates the CN ratio composite ratio Wi by, for example, (Equation 1), where N branch units and the CN ratio of each branch unit is CNi. i indicates a branch unit number. In the case of FIG. 1, i is 1,2.

  In this way, the reception signal combination ratio of the branch unit with a good CN ratio (high CN ratio) is increased, and the reception signal combination ratio of the branch unit with a low CN ratio (low CN ratio) is reduced.

  The composition ratio calculation unit 300 outputs the first composition ratio W1 and the second composition ratio W2 calculated based on (Equation 1) to the multipliers 311 and 312 respectively.

  The multiplier 311 multiplies the first reception signal R1 by the first synthesis ratio W1 and outputs the output signal to the adder 320. The multiplier 312 multiplies the second reception signal R2 by the second synthesis ratio W2, and outputs the output signal to the adder 320. The adder 320 adds the output signal of the multiplier 311 and the output signal of the multiplier 312 and outputs the result to the decoding unit 330. The decoding unit 330 decodes the output signal of the adder 320 and outputs it to a subsequent application (not shown).

  Next, CN ratio noise will be described. Thermal noise occurs when the RF processing unit (reception unit) 101 down-converts a signal received via the antenna 10 and performs orthogonal demodulation. The RF processing unit 101 amplifies the received signal with a predetermined gain when the received signal power is weak, and adjusts the received signal power to a desired power. Will occur. For the same reason, thermal noise is also generated in the RF processing unit 201.

  FIG. 2 is a diagram showing the relationship between the power of the received signal and the power of thermal noise, where the vertical axis indicates power and the horizontal axis indicates frequency. 2A shows the power of the received signal R21 and noise N21 in the first RF processing unit 101, and FIG. 2B shows the power and noise of the received signal R22 in the second RF processing unit 201. The power of N22 is shown. It is assumed that the received power of the first RF processing unit 101 is less than the desired power, and the received power of the second RF processing unit 201 is the desired power. The reason why the received power is reduced in this way is because, for example, there are obstacles around the antenna 10.

  As shown in the left graph of FIG. 2A, when the power of the reception signal R21 is low, the RF processing unit 101 amplifies the reception signal R21 and adjusts the power. Here, the power is increased to, for example, 4/3 times (gain 4/3) to obtain a desired power. At this time, the power of the received signal R21 is increased and adjusted to the received signal R21 ', and the power of the noise N21 is also increased to become the noise N21'. On the other hand, as shown in FIG. 2B, since the received signal R22 has a desired power, the power of the received signal R22 is not amplified (gain 1). In this case, the power of the noise N22 is not amplified. In FIG. 2, the power of the noise N21 and the noise N22 is substantially the same level, but the noise power may differ depending on the magnitude of the gain value.

  As is apparent from the above description, the CN ratio (first branch CN ratio) of the first branch unit is worse than the CN ratio (second branch CN ratio) of the second branch unit.

  Therefore, based on the calculated branch CN ratio, the received signals R1 and R2 of each branch unit are weighted, and the weighted received signals are added to obtain a decoding signal.

(CN ratio calculation)
Next, the CN ratio calculation process will be described.

  FIG. 3 is a functional block diagram of the first CN ratio calculation unit 110 included in the first branch unit 100. The second branch unit 200 also has the same CN ratio calculation unit as the first CN ratio calculation unit 110. The GI_CN ratio calculation unit 111 executes a guard interval CN ratio calculation process for calculating a CN ratio based on a guard interval GI of a transmission signal modulated by adding a guard interval GI to an effective symbol. The GB_CN ratio calculation unit 112 executes a guard band CN ratio calculation process that calculates a CN ratio based on power in a guard band region that is provided at both ends of a frequency region where data is transmitted and data is not transmitted. The MER_CN ratio calculation unit 113 executes a modulation error ratio CN ratio calculation process for calculating a CN ratio based on the modulation error ratio MER. Details of each of the calculation units 111 to 113 will be described later. In the following description, the CN ratio calculated by any one of the GI_CN ratio calculation unit 111, the GB_CN ratio calculation unit 112, and the MER_CN ratio calculation unit 113 is set as the first branch CN ratio.

  FIG. 4 is a diagram for explaining the CN ratio calculation process by the guard interval GI executed by the GI_CN ratio calculation unit 111. An OFDM symbol 41 included in a signal transmitted from the OFDM transmitter is composed of a GI 41a and an effective symbol 41b. The guard interval GI41a is obtained by adding (copying) the same data as the rear end portion 41b 'of the effective symbol 41b to the head portion of the effective symbol 41b. The guard interval GI41a is provided in order to reduce the influence of the preceding wave / delayed wave due to multipath. As an example, the symbol 41 has a digital signal of N sample points from 0 to N−1, the guard interval GI 41a has a digital signal of Ng sample points from 0 to Ng−1, and an effective symbol 41b. Has a digital signal of (N-1-Ng) sample points.

  The guard interval GI41a and the copy source 41b 'of the GI41a are the same data, but there is no correlation between the noise added thereto. Accordingly, if the sampling point of the symbol included in the received signal is t (sample time) and the power of the symbol corresponding to this t is R (t), the GI 41a of the symbol point t = 0 to Ng−1 and t = Nu. In the difference of GI41b ′ of ˜N−1, the received signal is canceled and only noise is obtained, so that noise power can be generally calculated by (Equation 2).

  Further, since the noise component is removed from the average value of the GI 41a and the copy source 41b ', the signal power is generally approximate but can be calculated by (Equation 3).

  Therefore, the CN ratio becomes (Expression 4) from (Expression 2) and (Expression 3).

  The GI_CN ratio calculation unit 111 calculates the CN ratio based on the guard interval GI from the output signal of the A / D unit 102 using (Equation 4). At this time, the CN ratio can be calculated with higher accuracy as the part of the guard interval GI to be calculated is longer, that is, as the integration period is longer.

  However, if there is a preceding / delayed wave due to multipath, intersymbol interference from the preceding wave symbol and the delayed wave symbol occurs in the guard interval GI 41a and the copy source 41b 'included in the main wave symbol. As a result, the number of GI samples that can be used for the above calculation decreases, and the CN ratio calculation accuracy decreases.

  FIG. 5 is a diagram for explaining the intersymbol interference, and shows a preceding wave symbol 61 and a delayed wave symbol 71 with respect to the main wave symbol 51. The main wave symbol 51 is the same as the symbol 41 in FIG. The leading portion 51 a (vertical stripe portion) of the main wave symbol 51 is a portion that receives intersymbol interference of a symbol (not shown) before the delayed wave symbol 71. The rear end portion 51 b (horizontal stripe portion) of the main wave symbol 51 is a portion that receives intersymbol interference of a symbol (not shown) after the preceding wave symbol 61.

  As a result of receiving the intersymbol interference in this way, the guard interval GI portion 51c that is the target of effective calculation of the CN ratio is different from the guard interval GI head portion 51a that receives the intersymbol interference from the entire guard interval GI portion. This is a portion excluding the rear end portion 51d of the same guard interval GI as the portion 51b receiving the same. Therefore, the CN ratio must be calculated with the portion 51c that is not subject to intersymbol interference as the effective calculation target of the CN ratio. Since the sample points of the portion 51c are Nd to Ng-Na-1, the calculation formula of the CN ratio in this case is as (Equation 5).

  As described above, when there is a preceding wave / delayed wave due to multipath, the portion of the guard interval GI that is a CN ratio calculation target is shortened. As a result, the number of samples for which the CN ratio is calculated decreases, and the CN ratio calculation accuracy decreases.

  Next, a CN ratio calculation process using the guard band GB will be described.

  FIG. 6 is a diagram for explaining the CN ratio calculation processing by the guard band GB executed by the GB_CN ratio calculation unit 112, where the horizontal axis represents the frequency, the vertical axis represents the power of the received signal Fr, and the noise N described in FIG. Indicates power. The reception signal Fr is composed of a plurality of subcarriers Sb. In wireless communication, a frequency band (also referred to as a guard band GB) in which data (symbol) is not transmitted is set in order to eliminate the influence on the adjacent wireless system and the adjacent channel and the influence from the adjacent wireless system and the adjacent channel. Data is not transmitted in this guard band region. In FIG. 6, guard band regions GB1 and GB2 are provided at both ends of the frequency region W1 where data is transmitted. Theoretically, the power of the guard band regions GB1 and GB2 does not include the power of the reception signal Fr but is only the power of noise N. Therefore, only the power of noise N can be calculated by measuring the power of noise N in guard band regions GB1 and GB2. Therefore, the CN ratio can be calculated by comparing the power of the noise N in the guard band regions GB1 and GB2 and the power of the subcarrier Sb (received signal Fr) other than the guard band regions GB1 and GB2.

  The number of sample points (number of subcarriers) in the frequency region W1 where data is transmitted is Nd, the number of sample points in the guard band region GB1 is Ngl (sample points 0 to Ngl-1), and the sample points in the guard band region GB2 Where Ngr (sample points Ngl + Nd to Ngl + Nd + Ngr-1), k is the number of the sample point corresponding to a certain frequency, and r (k) is the power of the frequency of the sample point specified by number k, the CN ratio is It can be calculated by (Equation 6).

  The GS_CN ratio calculation unit 112 calculates the CN ratio based on the guard band GB from the output signal of the FFT unit 104 using (Equation 6).

  However, the power of subcarriers transmitting symbols may leak into the guard band region, and the CN ratio calculation accuracy may deteriorate. This leakage will be described.

  FIG. 7 is a diagram for explaining this leakage, and corresponds to FIG. For example, when the receiving apparatus is moving, a fading phenomenon occurs in which the received signal intensity changes due to the Doppler effect and the phase of the received signal is shifted. As a result, the subcarrier frequency shifts and inter-carrier interference occurs. Due to the frequency shift of the subcarrier, the power component of a certain subcarrier affects the power component of an adjacent subcarrier. For this reason, the power of the received signal Fr may leak into the guard band regions GB1 and GB2. Symbol L in FIG. 7 indicates this leakage power.

  As a result of the generation of the leakage power L as described above, even if the power of the guard band regions GB1 and GB2 is measured, the measurement power includes not only the power of the noise N but also the leakage power L. N power cannot be measured. As a result, the calculation accuracy of the CN ratio decreases.

  Next, a CN ratio calculation process using the modulation error ratio MER will be described.

  FIG. 8 is a diagram for explaining a CN ratio calculation process using the modulation error ratio MER executed by the MER_CN ratio calculation unit 113, and shows a constellation of the first received signal R1 output by the propagation path estimation / compensation unit 105. Here, the vector of the ideal reception signal point of the symbol is T8, and the vector of the actual reception signal point of the symbol is R8. The ideal reception signal point indicates a signal point when a signal is received in an ideal environment free from propagation path distortion and noise, that is, a transmission signal on the constellation assigned by the transmission apparatus. A difference vector between the vector T8 and the vector R8, that is, an error vector is set to E8. In this constellation, since the channel estimation / compensation processing has already been completed, the channel distortion in the channel is removed, and only the influence of noise appears. Therefore, for example, if the error vector E is time-averaged, the noise described in FIG. 2 can be calculated. Also, the sum of error vectors E of a plurality of symbols transmitted by a plurality of subcarriers in the frequency domain W1 shown in FIGS. 6 and 7 is calculated, and this sum is calculated as the number of subcarriers described above. Noise power can be obtained by averaging. Note that the symbol for which the error vector E is calculated is not a pilot symbol but a data symbol.

  Further, since the magnitude of the vector T8 is signal power, the CN ratio can be calculated by dividing this signal power by the noise power. The MER_CN ratio calculation unit 113 calculates the CN ratio based on the modulation error ratio MER from the output signal R1 of the propagation path estimation / compensation unit 105 using the calculated signal power and noise power.

  However, the calculation accuracy of the CN ratio by the modulation error ratio MER may deteriorate due to the difference in the modulation method.

  FIGS. 9 and 10 are diagrams for explaining the reason. FIG. 9 shows a constellation in which the modulation method is QPSK (Quadrature Phase Shift Keying), and FIG. 10 shows that the modulation method is 16 QAM (16 Quadrature Amplitude Modulation). A constellation is shown, and in the figure, black dots indicate ideal reception signal points and white dots indicate actual reception signal points.

  When the modulation method shown in FIG. 9 is QPSK, it is assumed that the ideal reception signal point T9 on the constellation becomes the actual reception signal point R9 due to the influence of noise. At this time, the error vector E9 is calculated by calculating the distance between the actual reception signal point R9 and the reception signal point R9 and the shortest ideal reception signal point T9.

  When the modulation method shown in FIG. 10 is 16QAM, it is assumed that the ideal reception signal point T10a on the constellation becomes the actual reception signal point R10 due to the influence of noise. At this time, the calculation of the error vector is not performed by calculating the distance (error vector E10) between the actual reception signal point R10 and the ideal reception signal point T10a, but this actual reception signal point R10 and this This is performed by calculating the distance (error vector E10 ′) between the reception signal point R10 and the shortest ideal reception signal point T10b. In this case, since it becomes impossible to calculate an accurate error vector, the CN ratio calculation accuracy deteriorates.

  As described above, the calculation accuracy of the CN ratio by the guard interval GI is deteriorated due to intersymbol interference due to multipath, and the calculation accuracy of the CN ratio by the guard band GB is deteriorated by interference between carriers due to the fading phenomenon. In addition, the calculation accuracy of the CN ratio by the modulation error ratio MER deteriorates by receiving a signal modulated by the multi-level modulation method. As a result, it is not possible to calculate the synthesis ratio of received signals obtained from a plurality of branch units with high accuracy, and it is impossible to obtain high quality received data.

  Therefore, in this embodiment, the branch CN ratio is calculated with high accuracy in accordance with the degradation state of the CN ratio calculation accuracy according to the propagation path state and the modulation method.

<First Embodiment>
FIG. 11 is a functional block diagram illustrating the receiving device according to the first embodiment. The second CN ratio calculation unit 210 has the same functions as the GI_CN ratio calculation unit 111, the GB_CN ratio calculation unit 112, and the MER_CN ratio calculation unit 113 of the first CN ratio calculation unit 110, and calculates the GI_CN ratio calculation unit 211 and the GB_CN ratio calculation. Unit 212 and MER_CN ratio calculation unit 213. Note that the same functional blocks as those described in FIGS. 1 and 2 are denoted by the same reference numerals and description thereof is omitted. The first CN ratio calculation unit 110 may include any two or three of the GI_CN ratio calculation unit 111, the GB_CN ratio calculation unit 112, and the MER_CN ratio calculation unit 113. In the following description, 3 Will be described as having one. The same applies to the second CN ratio calculation unit 210. In the following description, the case where the receiving apparatus has two branch units 100 and 200 will be described as an example. However, as will be described later, the receiving apparatus may have three or more branch units.

  The branch CN ratio calculation unit 301 calculates a branch CN ratio indicating a CN ratio in each branch unit based on a plurality of types of CN ratios (hereinafter abbreviated as a branch CN ratio calculation process). , Executed for each second branch unit 200. The branch CN ratio of the first branch unit 100 is defined as a first branch CN ratio, and the branch CN ratio of the second branch unit 200 is defined as a second branch CN ratio.

  The branch CN ratio calculation process will be specifically described. The GI_CN ratio calculation unit 111, the GB_CN ratio calculation unit 112, and the MER_CN ratio calculation unit 113 of the first CN ratio calculation unit 110 each calculate a CN ratio for each symbol. Note that the CN ratio may be calculated for each of a plurality of symbols. Next, the branch CN ratio calculation unit 301 calculates, for each of a plurality of types of CN ratios calculated by the first CN ratio calculation unit 110, a dispersion value indicating the amount of dispersion of these CN ratios in the time direction.

  FIG. 12 is a diagram illustrating a method for calculating the variance value. 12A shows CN ratios (CNa (1) to CNa (n)) by the guard interval GI calculated by the GI_CN ratio calculation unit 111 in the time direction, and FIG. 12B shows the GB_CN ratio calculation unit 112. FIG. 12C shows the CN ratio (CNb (1) to CNb (n)) by the guard band GB calculated by FIG. 12 in the time direction. FIG. 12C shows the CN ratio (CNc) by the modulation error ratio MER calculated by the MER_CN ratio calculation unit 113. (1) to CNc (n)) are shown in the time direction. These CN ratios are calculated for each symbol, for example.

  There are various methods for calculating the CN ratio dispersion value. For example, the average value of CN ratios of CNa (1) to CNa (k-1) is calculated. Then, the difference between the average value CNa (avg) and CNa (k) is defined as a variance value Va (k) of CNa (k). Hereinafter, similarly, a difference between the average value CNa (avg) and CNa (k + 1) is defined as a variance value Va (k + 1) of CNa (k + 1). This dispersion value calculation processing is also executed for the CN ratio (CNb (k) to CNb (n)) based on the guard band GB and the CN ratio (CNc (k) to CNc (n)) based on the modulation error ratio MER.

  As another method for calculating the variance value of the CN ratio, for example, the difference between CNa (k−1) and CNa (k) may be calculated, and this difference may be used as the variance value of CNa (k). Here, it is assumed that the CN ratio having a large variance value has low reliability (accuracy).

  In view of the fact that the CN ratio having a large variance value has low reliability, the branch CN ratio is calculated. An example of a method for calculating the branch CN ratio will be described. First, a method of setting the CN ratio corresponding to the minimum variance value as the branch CN ratio will be described. The branch CN ratio calculation unit 301 performs a variance value Va (k) of CNa (k) by the guard interval GI, a variance value Vb (k) of CNb (k) by the guard band GB, and a modulation error in a symbol Sk at a certain time Tk. The minimum variance value is obtained from the variance value Vc (k) of CNc (k) based on the ratio MER. For example, it is assumed that this minimum variance value is the variance value Va (k) in the guard interval GI. In this case, CNa (k), which is the CN ratio by the guard interval GI corresponding to the minimum variance value Va (k), is adopted as the first branch CN ratio in the symbol Sk at a certain time Tk.

  Similarly, the branch CN ratio calculation unit 301 calculates, for each of a plurality of types of CN ratios calculated by the second CN ratio calculation unit 210, a dispersion value indicating the amount of dispersion of these CN ratios in the time direction. Then, the CN ratio corresponding to the minimum variance value in the symbol Sk at a certain time Tk is adopted as the second branch CN ratio.

  Then, the synthesis ratio calculation unit 300 uses (Equation 1) to calculate a synthesis ratio according to the first branch CN ratio and the second branch CN ratio. Next, the synthesizer including the multipliers 311 and 312 and the adder 320 in FIG. 11 is based on the synthesis ratio calculated by the synthesis ratio calculation unit 300, and the first received signal R1 and the second received signal R2 Received signal).

  Here, the composition ratio of the first branch unit 100 calculated by the composition ratio calculation unit 300 is defined as a first composition ratio W1, and the composition ratio of the second branch unit 200 is defined as a second composition ratio W2. The composition ratio calculation unit 300 outputs the first composition ratio W1 to the multiplier 311 and outputs the second composition ratio W2 to the multiplier 312.

  Multiplier 311 multiplies the received signal (symbol Sk), which is the CN ratio calculation target, by first synthesis ratio W 1, and outputs the output signal to adder 320. Similarly, the multiplier 312 multiplies the reception signal that is the calculation target of the CN ratio by the second synthesis ratio W2, and outputs the output signal to the adder 320.

  The adder 320 adds the output signal of the multiplier 311 and the output signal of the multiplier 312 and outputs the result to the decoding unit 330. Thereafter, the branch CN ratio is similarly calculated for the symbol Sk + 1 at time Tk + 1, and the synthesis ratio is calculated.

  As another example of the calculation method of the branch CN ratio, there is a method of calculating the branch CN ratio by reducing the ratio of the CN ratio having a large variance value. This calculation method will be described below.

  First, as described above, the branch CN ratio calculation unit 301 calculates a variance value of the CN ratio with respect to the time direction for each of a plurality of types of CN ratios. Then, each weighting coefficient to be multiplied for each CN ratio is calculated according to the variance value, and the branch CN ratio is calculated based on each weighting coefficient. Specifically, each weighting coefficient is multiplied for each CN ratio, and the multiplication results are added.

  (Expression 7) is an example of an expression applied when calculating the branch CN ratio.

  The weighting coefficient to be multiplied to the CN ratio CNa by the guard interval GI is the denominator of (Expression 7) and the reciprocal of the variance value Va of the CN ratio CNa. The weighting coefficient by which the CN ratio CNb by the guard band GB is multiplied is the reciprocal of the denominator of (Expression 7) and the variance value Vb of the CN ratio CNb. The weighting coefficient by which the CN ratio CNc based on the modulation error ratio MER is multiplied is the reciprocal of the denominator of (Expression 7) and the variance value Vc of the CN ratio CNc.

  By calculating the branch CN ratio in this way, the optimum branch CN ratio in each branch unit can be calculated according to the degradation state of the CN ratio calculation accuracy depending on the propagation path state and the modulation method. As a result, the composite ratio of the received signal can be calculated with high accuracy, and high-quality decoded data can be obtained.

<Second Embodiment>
By the way, the accuracy of the CN ratio calculated by a certain process may be extremely low and may not be used for calculating the branch CN ratio. For example, it is assumed that the influence of multipath is large and the delay profile of the received signal of the first branch unit 100 is longer than the time corresponding to the guard interval length. This delay profile shows the arrival delay time characteristics of multipath generated on the propagation path. In such a case, the portion 51c of the guard interval GI that is the target of effective calculation of the CN ratio described in FIG. 5 becomes 0, and the CN ratio calculated by the guard interval GI cannot be used in the calculation of the branch CN ratio. .

  Further, for example, when the receiving apparatus 2 moves at a high speed, if the fading frequency increases, the amount of leakage power to the guard subcarrier described with reference to FIG. 7 may increase. As a result, the CN ratio calculation accuracy by the guard band GB decreases. In such a case, if the fading frequency exceeds a predetermined threshold, the CN ratio calculation accuracy by the guard band GB is extremely low in the calculation of the branch CN ratio, and the CN ratio by the guard band GB cannot be used.

  Furthermore, when a signal modulated using a multi-level modulation method such as 64QAM is received, the CN ratio calculation accuracy by the modulation error ratio MER becomes extremely low, and the CN ratio by the modulation error ratio MER cannot be used. Sometimes.

  Therefore, in the second embodiment, the calculation of the branch CN ratio is executed without using such a CN ratio under a situation where the accuracy of the CN ratio calculated by a certain process can be assumed to be extremely low.

  FIG. 13 is a functional block diagram of the receiving device 3 according to the second embodiment. In addition, about the same functional block as the functional block demonstrated in FIG. 11, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The delay profile measurement unit 341 measures the delay profile of the received signal for each of the first branch unit 100 and the second branch unit 200. There are various methods for measuring the delay profile. For example, the delay profile measuring unit 341 performs a process of calculating a correlation value by shifting a replica of this symbol for each sampling point with respect to the symbol of the received signal, that is, a so-called sliding correlation process. Then, the delay profile is measured by the difference between the sampling point (time) corresponding to the maximum peak of the correlation value and the sampling point corresponding to the peak of the correlation value in the vicinity of the maximum peak. This correlation value is calculated when the GI removal unit (103, 203) removes the guard interval GI, and is input from the GI removal unit (103, 203).

  When a delay profile longer than the time corresponding to the symbol guard interval GI length is measured, the branch CN ratio calculation unit 301 uses the guard interval GI calculated by the CN ratio calculation unit of the branch unit from which the delay profile is measured. Without calculating the CN ratio variance value, calculate the CN ratio variance value by the guard band GB and the CN ratio variance value by the modulation error ratio MER, and calculate the branch CN ratio corresponding to this symbol from these variance values. To do.

  The fading frequency measurement unit 342 measures the fading frequency of the received signal for each of the first branch unit 100 and the second branch unit 200. There are various methods for measuring the fading frequency. For example, the fading frequency measurement unit 342 measures, with respect to a plurality of pilot symbols, a deviation (error vector) between an ideal reception signal point of the pilot symbol and an actual reception signal point of the pilot symbol in the time direction. Then, the fading frequency is measured based on this deviation with respect to the time direction. This error vector has already been calculated by the propagation path estimation / compensation section (105, 205) and is input from the propagation path estimation / compensation section (105, 205).

  When a fading frequency equal to or higher than a predetermined threshold is measured, the branch CN ratio calculation unit 301 calculates a variance value of the CN ratio by the guard band GB calculated by the CN ratio calculation unit of the branch unit in which the fading frequency is measured. First, the CN ratio variance value based on the guard interval GI and the CN ratio variance value based on the modulation error ratio MER are calculated, and the branch CN ratio corresponding to this symbol is calculated based on these variance values.

  Further, when the reception device 3 receives a transmission signal modulated by a predetermined modulation method such as 64QAM, in which the CN ratio calculation accuracy by the modulation error ratio MER is greatly reduced, the branch CN ratio calculation unit 301 In this calculation process, the variance value of the CN ratio based on the modulation error ratio MER is not calculated, but the variance value of the CN ratio based on the guard interval GI and the variance value of the CN ratio based on the guard band GB are calculated. A branch CN ratio corresponding to the symbol is calculated. Note that the modulation scheme information of the transmission signal can be obtained by receiving a control signal including the modulation scheme transmitted by the transmission apparatus. In the case of terrestrial digital broadcasting, this control signal is a TMCC (Transmission and Multiplexing Configuration Control) signal.

  By doing so, the branch CN ratio can be calculated without using a CN ratio with extremely low accuracy, so that the calculation accuracy of the branch CN ratio does not decrease. Also, in calculating the branch CN ratio, since the variance value of the CN ratio with extremely low accuracy is not calculated, the processing load is reduced and the calculation speed of the branch CN ratio is improved.

  In the above embodiment, two branch units have been described, but three or more branch units may be used. In this case, the branch CN ratio calculation unit executes a process of calculating the branch CN ratio for each of a plurality of branch units based on a plurality of types of CN ratios. Then, the synthesis ratio calculation unit 300 calculates the synthesis ratio by (Equation 1) according to the plurality of branch CN ratios.

  The above embodiment is summarized as follows.

(Appendix 1)
A plurality of branch units each having a reception unit that receives a transmission signal and outputs a reception signal; and a CN ratio calculation unit that calculates a plurality of types of CN ratios by different types of CN ratio calculation processing;
A branch CN ratio calculation unit that executes, for each of the plurality of branch units, a process of calculating a branch CN ratio indicating a CN ratio in the branch unit based on the plurality of types of CN ratios;
And a synthesizer that synthesizes the plurality of received signals according to the branch CN ratio.

(Appendix 2)
In Appendix 1,
The branch CN ratio calculation unit calculates a dispersion value indicating a dispersion amount of the CN ratio in the time direction for each of the plurality of types of CN ratios in the branch CN ratio calculation process, and calculates a CN ratio corresponding to the minimum dispersion value. A receiving apparatus having a branch CN ratio.

(Appendix 3)
In Appendix 1,
The branch CN ratio calculation unit calculates a dispersion value indicating a dispersion amount of the CN ratio with respect to the time direction for each of the plurality of types of CN ratios in the branch CN ratio calculation process, and the CN ratio according to the dispersion value A receiving device that calculates each weighting coefficient to be multiplied every time and calculates a branch CN ratio based on each weighting coefficient.

(Appendix 4)
In any one of supplementary notes 1 to 3,
The CN ratio calculation unit is provided at both ends of a frequency interval where data is transmitted, guard interval CN ratio calculation processing for calculating a CN ratio based on the guard interval of a transmission signal modulated by adding a guard interval to an effective symbol. Two types of guard band CN ratio calculation processing for calculating a CN ratio based on power in a guard band region where the data is not transmitted and modulation error ratio CN ratio calculation processing for calculating a CN ratio based on a modulation error ratio, or A receiving apparatus that executes three types of CN ratio calculation processes.

(Appendix 5)
In Appendix 4,
And a delay profile measuring unit for measuring a delay profile of the received signal for each branch unit by the guard interval,
The branch CN ratio calculation unit calculates the guard interval CN ratio calculated by the CN ratio calculation unit of the branch unit in which a delay profile longer than the time corresponding to the guard interval length is measured in the branch CN ratio calculation process. A receiving device that does not calculate the variance value of the CN ratio of processing.

(Appendix 6)
In Appendix 4,
And a fading frequency measuring unit for measuring a fading frequency of the received signal for each of the plurality of branch units by using a pilot symbol,
The branch CN ratio calculation unit calculates a CN ratio of the guard band CN ratio calculation process calculated by the CN ratio calculation unit of the branch unit in which the fading frequency equal to or higher than a predetermined threshold is measured in the branch CN ratio calculation process. A receiving device that does not calculate a variance value.

(Appendix 7)
In Appendix 4,
When a transmission signal modulated by a predetermined modulation method is received, the branch CN ratio calculation unit does not calculate a variance value of the CN ratio of the modulation error ratio CN ratio calculation process in the branch CN ratio calculation process. apparatus.

DESCRIPTION OF SYMBOLS 1, 2, 3 ... Receiver, 100 ... 1st branch unit, 200 ... 2nd branch unit, 10, 20 ... Antenna, 101 ... 1st RF processing part, 201 ... 2nd RF processing part, 102 , 202 ... A / D section, 103, 203 ... GI removal section, 104, 204 ... FFT section, 105, 205 ... propagation path estimation / compensation section, 110 ... first CN ratio calculation section, 210 ... second CN Ratio calculation unit, 111, 211... GI_CN ratio calculation unit, 112, 212... GB_CN ratio calculation unit, 113, 213... MER_CN ratio calculation unit, 300. Multiplier 320... Adder 330 330 Decoding unit 341 Delay profile measuring unit 342 Fading frequency measuring unit

Claims (5)

A plurality of branch units each having a reception unit that receives a transmission signal and outputs a reception signal; and a CN ratio calculation unit that calculates a plurality of types of CN ratios by a plurality of types of CN ratio calculation processing different from each other ;
A branch CN ratio calculation unit that executes, for each of the plurality of branch units, a process of calculating a branch CN ratio indicating a CN ratio in the branch unit based on the plurality of types of CN ratios;
And a synthesizer that synthesizes the plurality of received signals according to the branch CN ratio. In claim 1,
The branch CN ratio calculation unit calculates a dispersion value indicating a dispersion amount of the CN ratio in the time direction for each of the plurality of types of CN ratios in the branch CN ratio calculation process, and calculates a CN ratio corresponding to the minimum dispersion value. A receiving apparatus having a branch CN ratio. In claim 1,
The branch CN ratio calculation unit calculates a dispersion value indicating a dispersion amount of the CN ratio with respect to the time direction for each of the plurality of types of CN ratios in the branch CN ratio calculation process, and the CN ratio according to the dispersion value A receiving device that calculates each weighting coefficient to be multiplied every time and calculates a branch CN ratio based on each weighting coefficient. In any of claims 1 to 3,
The CN ratio calculation unit is provided at both ends of a frequency interval where data is transmitted, guard interval CN ratio calculation processing for calculating a CN ratio based on the guard interval of a transmission signal modulated by adding a guard interval to an effective symbol. Two types of guard band CN ratio calculation processing for calculating a CN ratio based on power in a guard band region where the data is not transmitted and modulation error ratio CN ratio calculation processing for calculating a CN ratio based on a modulation error ratio, or A receiving apparatus that executes three types of CN ratio calculation processes. In claim 4,
And a delay profile measuring unit for measuring a delay profile of the received signal for each branch unit by the guard interval,
The branch CN ratio calculation unit calculates the guard interval CN ratio calculated by the CN ratio calculation unit of the branch unit in which a delay profile longer than the time corresponding to the guard interval length is measured in the branch CN ratio calculation process. A receiving device that does not calculate the variance value of the CN ratio of processing.

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