JP2007158423A - Diversity reception method and receiver utilizing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the possibility of deterioration in the characteristics of a synthesized multicarrier signal while reducing an increase in the amount of processing. <P>SOLUTION: A selector 12 selects two multicarrier signals identified by an identification section 22 from a plurality of multicarrier signals. A synthesizer 20 executes the composition of a carrier unit to the two multicarrier signals selected by the selector 12. An intensity ratio deriver 24 derives the difference of signal intensity in carrier units between the two multicarrier signals. A calculator 26 calculates the number of carriers where the derived difference in the signal intensity becomes larger than a first threshold. A determination section 28 decides switching to an unselected multicarrier signal in the plurality of multicarrier signals to one of the two multicarrier signals to be selected, when the number of carriers calculated by the calculator 26 becomes larger than a second threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reception technique, and more particularly to a diversity reception method for receiving a signal by a plurality of antennas and a reception apparatus using the same.

An OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, which is one of the multicarrier schemes, is a communication scheme that enables high-speed data transmission and is strong in a multipath environment. On the other hand, in mobile communication, due to the influence of multipath fading, the received power changes greatly as the mobile station moves. For this reason, when the OFDM modulation method is used for mobile communication, a combined diversity reception technique is used as a countermeasure against multipath fading (see, for example, Patent Document 1).
JP 2004-112155 A

  In general, when combining a plurality of received signals to which the OFDM modulation scheme is applied, combining diversity is performed in units of subcarriers. When combining two received signals corresponding to one subcarrier, if the intensity of one received signal is large and the intensity of the other received signal is small, the influence of the noise contained in the received signal with low intensity is In some cases, it may cover the synthesized signal. As a result, the influence of noise included in the synthesized signal is increased. In addition, if there are a large number of such subcarriers, the reception characteristics may deteriorate due to the combined diversity. In order to reduce the appearance of such a state, increasing the number of reception signals to be combined by increasing the number of antennas is one of the candidates. However, in such a case, the circuit scale and processing amount become large.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a reception technique that reduces the possibility of deterioration of the characteristics of a combined multicarrier signal while reducing an increase in processing amount. .

  In order to solve the above problems, a receiving device according to an aspect of the present invention includes a specifying unit that specifies at least two multicarrier signals to be selected from among a plurality of multicarrier signals sequentially received by a plurality of antennas, A selecting unit that selects at least two multicarrier signals specified by the specifying unit, and a combining unit that performs combining in units of carriers with respect to at least two multicarrier signals selected by the selecting unit. The identifying unit has a first threshold between a deriving unit for deriving a difference in signal strength and a difference in signal strength derived in the deriving unit for each carrier between at least two multicarrier signals selected by the selecting unit. A calculation unit for calculating the number of carriers larger than the value, and when the number of carriers calculated in the calculation unit is larger than the second threshold, of at least two multicarrier signals to be selected And a determining unit that determines switching to an unselected multicarrier signal among a plurality of multicarrier signals.

  The “difference in signal strength” may be derived from a ratio or may be derived from a difference, and it is only necessary to know at least two difference values. When the difference in signal intensity is derived by the ratio, the ratio value is smaller from “1” such as “0.1”, or “1” such as “10”. It is equivalent to becoming larger apart from. Further, when the difference is derived by the difference, it can be said that the difference in signal strength is large when the absolute value of the difference is large.

  The “first threshold value” is a predetermined value, and the value is defined by simulation or experiment. In addition, when the above-described difference in signal strength is derived by the ratio, there may be two first threshold values. For example, “0.5” and “2.0” are defined as threshold values. “The difference in signal intensity is larger than the first threshold value” corresponds to the case where the ratio is smaller than 0.5 and the ratio is larger than 2.0. The “second threshold value” is a predetermined value, and is defined by simulation, experiment, or the like.

  According to this aspect, if the difference in strength between at least two multicarrier signals to be combined is large, one of the multicarrier signals to be combined is changed to another multicarrier signal. The increase in noise included in the signal can be suppressed.

  The deriving unit derives the signal strength in units of carriers for each of at least two multicarrier signals selected by the selecting unit, and the calculating unit outputs one of the at least two multicarrier signals. When the corresponding signal strengths are both smaller than the third threshold value, the number of carriers may be added even if the difference in signal strength corresponding to the carrier is equal to or less than the first threshold value. In this case, since the switching is determined in consideration of not only the relative strength between the multicarrier signals but also the absolute strength, the accuracy in determining the switching can be improved.

  When the plurality of received multicarrier signals are all subjected to inverse Fourier transform, the selector performs Fourier transform on at least two selected multicarrier signals, and then combines the results with the combiner. And the derivation unit performs processing on the multicarrier signal Fourier-transformed by the selection unit, and the determination unit is an unselected multicarrier signal among a plurality of multicarrier signals and vice versa. The multicarrier signal to be switched to may be determined based on the intensity of the Fourier-transformed multicarrier signal. In this case, in order to determine the multicarrier signal to be switched to, the intensity of the unselected multicarrier signal is measured before the Fourier transform, so that it is possible to improve the characteristics while reducing the processing delay. Switching to the carrier signal can be executed.

  Another aspect of the present invention is a diversity reception method. The method includes: identifying at least two multicarrier signals to be selected among a plurality of multicarrier signals sequentially received by a plurality of antennas; selecting at least two identified multicarrier signals; and selecting Performing a carrier unit synthesis on the at least two multicarrier signals. The identifying step includes a step of deriving a difference in signal strength for each carrier between at least two selected multi-carrier signals, and a difference in the derived signal strength is greater than a first threshold value. Calculating a number of carriers and, if the calculated number of carriers is greater than a second threshold, a plurality of multicarrier signals for one of at least two multicarrier signals to be selected. A step of determining switching to an unselected multicarrier signal.

  The deriving step derives the signal strength for each carrier for each of at least two multicarrier signals selected in the selecting step, and the calculating step includes one of at least two multicarrier signals. If the signal strength corresponding to the carrier is smaller than the third threshold value, even if the difference in signal strength corresponding to the carrier is equal to or less than the first threshold value, the number of carriers may be added. Good.

  In the selecting step, when a plurality of received multi-carrier signals are all subjected to inverse Fourier transform, Fourier transform is performed on at least two selected multi-carrier signals, and then the results are combined. The step of outputting and deriving performs processing on the multicarrier signal Fourier-transformed by the selecting step, and the step of determining comprises selecting an unselected multicarrier among a plurality of multicarrier signals The multicarrier signal to be switched to may be determined based on the strength of the multicarrier signal that is a signal and subjected to inverse Fourier transform.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a recording medium, a computer program, etc. are also effective as an aspect of the present invention.

  According to the present invention, it is possible to reduce the possibility that the characteristics of the synthesized multicarrier signal will deteriorate while reducing the increase in the processing amount.

  Before describing the present invention in detail, an outline will be described. An embodiment of the present invention relates to a receiving apparatus compatible with the ISDB-T system which is one of terrestrial digital television standards. The ISDB-T method uses an OFDM modulation method which is one of multicarrier modulations. Here, “5617” subcarriers are used. The receiving apparatus selects two of multicarrier signals received by a plurality of antennas, for example, four antennas. In addition, the receiving apparatus performs combining diversity in units of subcarriers on the two selected multicarrier signals. At that time, even if the strength of one multicarrier signal is large for one subcarrier, if the strength of the other multicarrier signal is small, the influence of noise contained in the other multicarrier signal is synthesized. Affects the signal. Furthermore, when the number of such subcarriers increases, the quality of the combined multicarrier signal deteriorates. In order to cope with this, the receiving apparatus according to the present embodiment operates as follows.

  The receiving apparatus compares the strengths of the two selected multicarrier signals in units of subcarriers. That is, the ratio of signal strength is calculated for each subcarrier. Here, if the signal strength ratio is close to “1”, it can be said that both signal strengths are close. If the signal intensity ratio is far from “1”, that is, if the signal intensity is a small value or a large value, it can be said that one signal intensity is small. The receiving apparatus calculates the number of subcarriers whose signal strength ratio is away from “1”. Furthermore, if the calculated number of subcarriers among the subcarriers “5617” is greater than the threshold value, the receiving apparatus determines that the difference in strength between the two selected multicarrier signals is large. To do. As a result, the receiving apparatus switches one of the two multicarrier signals to be selected to another multicarrier signal.

  In the following description, the received signal is a signal sequence using multicarriers. In this specification, a signal sequence may be referred to as a multicarrier signal, and a signal of an arbitrary symbol may be referred to as a multicarrier signal. Both shall be used without specific indication.

  FIG. 1 shows a configuration of a receiving apparatus 100 according to an embodiment of the present invention. The receiving apparatus 100 includes a first antenna 10a, a second antenna 10b, a fourth antenna 10d, which are collectively referred to as an antenna 10, a selection unit 12, and a tuner 14, a first tuner 14a, a second tuner 14b, and an AGC control unit 16. The first FFT unit 18a, the second FFT unit 18b, the synthesis unit 20, the specifying unit 22, and the control unit 30, which are collectively referred to as the FFT unit 18, are included. The specifying unit 22 includes an intensity ratio deriving unit 24, a calculating unit 26, and a determining unit 28.

  The antenna 10 receives a radio frequency signal via a transmission path. Here, the radio frequency signal is a multicarrier signal. As described above, since the ISDB-T system is an object of description, the number of subcarriers included in the multicarrier signal is “5617”, and a pilot signal is arranged in a scattered format in the multicarrier signal. . Since the number of antennas 10 is “4”, four multicarrier signals are received. Since the four multicarrier signals are transmitted from a single transmission device (not shown), they include the same signal component, but are received through different transmission paths, and therefore have different values.

  The selection unit 12 receives a plurality of multicarrier signals respectively received by the plurality of antennas 10 and selects two multicarrier signals from the plurality of multicarrier signals. Here, at least two multicarrier signals specified by the specifying unit 22 described later are selected. Further, the selection unit 12 outputs at least two selected multicarrier signals.

  The tuner 14 converts the frequency of the received multicarrier signal from a radio frequency to a baseband. At this time, the tuner 14 selects a program of a channel corresponding to the broadcast station to be viewed from the received multicarrier signal by fixing the reception frequency to a predetermined value. Note that “program” refers to a program that is being broadcast, but here the contents thereof are also included. That is, the program may indicate broadcast audio, broadcast video, and combinations thereof. The first tuner 14a and the second tuner 14b execute similar processing in parallel.

  The AGC control unit 16 determines a gain value for the two multicarrier signals input from the tuner 14 and adjusts the gain of the amplifier included in the tuner 14 according to the determined value. Since the AGC control unit 16 may be realized by a known technique, a description thereof is omitted here. The AGC control unit 16 determines a common gain value for the amplifiers included in each of the first tuner 14a and the second tuner 14b. Therefore, the intensity ratio between the two multicarrier signals selected by the selection unit 12 and the ratio between the two multicarrier signals output from the tuner 14 have the same value.

  The FFT unit 18 performs FFT on the multicarrier signal from the tuner 14. As a result, the signal frequency-converted to baseband in the tuner 14 is converted into a frequency domain signal. As described above, the frequency domain signal has “5617” subcarriers.

  The synthesizer 20 performs carrier unit synthesis on the two multicarrier signals from the FFT unit 18. Here, it is assumed that the maximum ratio synthesis is executed as the synthesis. In addition, in order to execute the maximum ratio combining diversity, the combining unit 20 performs an operation as follows. Combining section 20 estimates each channel coefficient for the subcarriers including the pilot signal from the pilot signals included in each of the plurality of multicarrier signals. For this purpose, the combining unit 20 extracts subcarriers in which pilot signals are arranged from the multicarrier signal. Here, since the subcarrier in which the pilot signal is arranged is defined in advance, the combining unit 20 performs extraction while using the definition. Further, the channel coefficient estimation is performed using the extracted signal value and the pilot signal value in the subcarrier. Transmission path estimation may be performed by a known technique, for example, by complex multiplication of the inverse value of the pilot signal and the value of the signal at the extracted subcarrier.

  Subsequently, the combining unit 20 interpolates transmission path coefficients that should appear periodically, with one subcarrier as a unit. That is, the synthesis unit 20 interpolates the transmission path coefficient in the time direction. For example, when transmission path coefficients are derived for every four symbols, the synthesis unit 20 derives transmission path coefficients for symbols between these by interpolation. Here, linear interpolation is used for interpolation, but is not limited thereto, and a predetermined approximate expression may be used. Further, extrapolation may be performed while using channel coefficients at other symbol numbers.

  Through the above processing, continuous channel coefficients are derived in the subcarriers in which pilot signals are arranged. Furthermore, the synthesis unit 20 interpolates the transmission path coefficient in the frequency direction. More specifically, the combining unit 20 derives the transmission path coefficient for each subcarrier included in the multicarrier signal by interpolating the transmission path coefficient for the subcarrier including the pilot signal. This corresponds to calculating the transmission path coefficient for each of a plurality of multicarrier signals in units of subcarriers.

  The synthesizer 20 weights each of the two multicarrier signals from the FFT unit 18 using a transmission path coefficient. At this time, weighting in units of subcarriers is executed. Note that the complex conjugate value of the transmission path coefficient is used for weighting. Finally, the synthesis unit 20 adds the two weighted multicarrier signals in units of subcarriers.

  Here, problems that may occur in the multicarrier signal synthesized as described above will be described. 2A to 2B show multicarrier signals selected by the selection unit 12. Here, for ease of explanation, a multicarrier signal before being synthesized by the synthesis unit 20 is shown. FIG. 2 (a) shows one of two multicarrier signals. The horizontal axis in the figure corresponds to the frequency, the “subcarrier number” is shown, and the vertical axis in the figure shows the signal strength. The “subcarrier number” is a number assigned to identify a subcarrier. For example, a subcarrier number having a small value is assigned to a subcarrier having a low frequency. Here, subcarrier numbers from “1” to “5617” are shown. In FIG. 2A, the signal strength is particularly small at subcarrier numbers “2” and “5616”.

  FIG. 2B shows the remaining of the two multicarrier signals. The signal intensity shown in FIG. 2 (b) has a larger value than the signal intensity shown in FIG. 2 (a). Therefore, the difference in signal strength between the two in one subcarrier is large. In particular, the difference in signal strength between the subcarriers “2” and “5616” is large. Since the signal strength of the multicarrier signal shown in FIG. 2 (a) is smaller than the signal strength of the multicarrier signal shown in FIG. 2 (b), the influence of noise in the former is more than the influence of noise in the latter. Is also big. As a result, the influence of noise on the multicarrier signal obtained by combining the two may be larger than the influence of noise on the multicarrier signal shown in FIG. At that time, the quality of the synthesized multicarrier signal is worse than the quality of the multicarrier signal shown in FIG.

  Returning to FIG. The identifying unit 22 selects at least two multicarriers to be selected from among a plurality of multicarrier signals respectively received by the plurality of antennas 10 so as to reduce the possibility that the quality deteriorates at the time of combining as described above. Identify the signal. The specifying unit 22 is configured as follows.

  The intensity ratio deriving unit 24 receives the two multicarrier signals converted into the frequency domain by the FFT unit 18. The intensity ratio deriving unit 24 measures the signal intensity for each subcarrier for each of the two multicarrier signals. The intensity ratio deriving unit 24 derives a difference in signal intensity between the two multicarrier signals in units of subcarriers. Here, the ratio of the two signal strengths is derived as the difference in signal strength. Specifically, the ratio of signal strengths is calculated using one of the two multicarrier signals as the denominator and the other as the numerator. For example, the signal strength of the multicarrier signal from the first FFT unit 18a is defined to be a denominator.

  FIG. 3 shows processing in the specifying unit 22. In FIG. 3, the subcarrier numbers are shown on the horizontal axis, as in FIGS. 2 (a) to 2 (b). On the vertical axis, the signal intensity ratio is shown. Here, “1” on the vertical axis indicates that the signal intensity ratio is “1”. This corresponds to the two signal strengths having the same value. In the subcarrier numbers “2” and “5616” in FIG. 3, the signal strengths of the two are greatly different. The other description regarding FIG. 3 is mentioned later.

  Returning to FIG. The calculation unit 26 calculates the number of subcarriers in which the difference in signal strength derived by the intensity ratio deriving unit 24 is greater than a predetermined threshold value. As described above, since the signal strength ratio is derived as a difference, the case where the signal strength is larger than the predetermined threshold is larger than the case where the signal strength is smaller than “1”. It corresponds to the case. In FIG. 3, two threshold values “A” and “B” are provided for the intensity ratio, and the calculation unit 26 sub-corresponds to a signal intensity having a value smaller than the threshold value “A”. The number of subcarriers corresponding to the carrier or the signal intensity having a value larger than the threshold “B” is calculated. In FIG. 3, subcarriers with subcarrier numbers “2” and “5616” are to be calculated.

  Returning to FIG. The above calculation is performed in units of “5617” subcarriers included in one symbol. That is, the calculation unit 26 executes the calculation in the subcarrier “5617”, and when the calculation for the subcarrier “5617” is completed, outputs the calculation result and the subcarrier “5617”. The calculation starts from “0”. When the signal strength corresponding to one subcarrier is smaller than another threshold value in each of at least two multicarrier signals, the strength ratio corresponding to the subcarrier may be close to “1”. Add the number of subcarriers. That is, when the two signals to be added have low intensities, it is considered that the influence of noise is increased by the synthesis.

  The determination unit 28 compares the number of subcarriers calculated by the calculation unit 26 with a threshold value. Here, the threshold value is “C”. Furthermore, when the number of subcarriers is greater than the threshold value “C”, the determination unit 28 selects one of the two multicarrier signals to be selected from among the plurality of multicarrier signals. Determine switching to the selected multi-carrier signal. For example, the threshold “C” is set to “2000” for the subcarrier “5617” that is the unit of calculation. In addition, as the multicarrier signal to be switched, the one having a larger number of subcarriers having a small signal strength is selected in the calculation result.

  For example, a multicarrier signal from the first antenna 10a (hereinafter referred to as “first multicarrier signal”) and a multicarrier signal from the second antenna 10b (hereinafter referred to as “second multicarrier signal”) are selected. As the intensity ratio, (the intensity of the first multicarrier signal) / (the intensity of the second multicarrier signal) is calculated in units of subcarriers. Among the intensity ratios included in the calculation by the calculation unit 26, the number of subcarriers corresponding to the intensity ratio that is smaller than the threshold value “A” in FIG. 3 is greater than the threshold value “B” in FIG. If there are more subcarriers corresponding to the ratio, the strength of the first multicarrier signal is to be switched. Further, the determination unit 28 may compare the strength of the entire first multicarrier signal with the strength of the entire second multicarrier signal, and determine the smaller one as a switching target.

  In the case of the above example, as an unselected multicarrier signal, a multicarrier signal from the third antenna 10c (hereinafter referred to as “third multicarrier signal”) and a multicarrier signal from the fourth antenna 10d (hereinafter, “ A fourth multi-carrier signal). The determination unit 28 selects a multicarrier signal having a longer unselected period as a switching destination candidate from among the third multicarrier signal and the fourth multicarrier signal. FIG. 4 shows an example of an antenna selected by the determination unit 28. Times “t1”, “t2”, “t3”, and the like correspond to arbitrary timings at which switching is performed. The multicarrier signal “# 1” corresponds to the first multicarrier signal, and the multicarrier signal “# 2” corresponds to the second multicarrier signal. Others are the same. Also, in FIG. 4, a plurality of “# 1” corresponds to the first multicarrier signal, but since the times are different, the values of these multicarrier signals are different from each other.

  At time “t1”, “# 1” and “# 2” are selected, and the determination unit 28 sets “# 2” as a switching target. Here, it is assumed that the period in which “# 3” is not selected is longer than the period in which “# 4” is not selected. Therefore, the determination unit 28 selects “# 3” as the switching destination. At time “t2”, “# 1” and “# 3” are selected, and the determination unit 28 sets “# 1” as a switching target. The determination unit 28 selects “# 4” as the switching destination. At time “t3”, “# 3” and “# 4” are selected, and the determination unit 28 sets “# 4” as a switching target.

  The determination unit 28 selects “# 2” having a longer period than “# 1” as the switching destination. At time “t4”, “# 2” and “# 3” are selected, and the determination unit 28 sets “# 2” as a switching target. The determination unit 28 selects “# 1” as the switching destination. At time “t5”, “# 1” and “# 3” are selected, and the determination unit 28 sets “# 1” as a switching target. The determination unit 28 selects “# 4” as the switching destination. At time “t6”, “# 3” and “# 4” are selected. Returning to FIG. The determination unit 28 outputs information on the selected multicarrier signal to the selection unit 12.

  This configuration can be realized in terms of hardware by a CPU, memory, or other LSI of any computer, and in terms of software, it is realized by a program having a reception function loaded in the memory. The functional block realized by those cooperation is drawn. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  The operation of the receiving apparatus 100 having the above configuration will be described. FIG. 5 is a flowchart showing a procedure of diversity processing by the receiving apparatus 100. The antenna 10 receives a plurality of multicarrier signals, respectively (S10). The selection unit 12 selects two multicarrier signals from the received multicarrier signals (S12). The FFT unit 18 performs FFT processing on the two selected multicarrier signals (S14). The synthesizer 20 derives a transmission path characteristic for each of the two multicarrier signals subjected to the FFT processing (S16). In addition, the combining unit 20 performs equalization processing on each of the two multicarrier signals while using the derived transmission path characteristics (S18). The synthesizer 20 synthesizes the two equalized multicarrier signals (S20).

  FIG. 6 is a flowchart illustrating a procedure of antenna switching processing by the specifying unit 22. The intensity ratio deriving unit 24 derives the intensity ratio of a plurality of multicarrier signals in units of subcarriers (S50). The calculator 26 calculates the number of subcarriers whose intensity ratio is not between the thresholds “A” and “B” in FIG. 3 (S52). If the number of subcarriers calculated by calculation unit 26 is larger than threshold “C” (Y in S54), determination unit 28 determines switching of the multicarrier signal and outputs switching information (S56). . Furthermore, the determination unit 28 causes the selection unit 12 to perform switching (S58). On the other hand, if the number of subcarriers calculated by the calculation unit 26 is not greater than the threshold “C” (N in S54), the determination unit 28 ends the process.

  Hereinafter, modifications of the receiving apparatus 100 described so far will be described. In the embodiment, the identification unit 22 selects a multicarrier signal having a long period that is not selected as a switching destination when determining switching of the multicarrier signal. In the modification, the criteria for selecting the switching destination are different from those in the embodiment. In the modification, a multicarrier signal having a large signal strength is selected as a switching destination. The number of tuners 14 is smaller than the number of antennas 10. In general, the signal strength is measured by the strength of the signal converted to the intermediate frequency or baseband frequency by the tuner 14. Therefore, in order to measure the strength of the multicarrier signal that is a candidate for the switching destination, another tuner 14 needs to be provided. However, the provision of another tuner 14 increases the circuit scale.

  On the other hand, when the switching destination is selected after the switching is determined, the strength ratio deriving unit 24 can measure the signal strength of the switching destination candidate multicarrier signal. However, the intensity ratio deriving unit 24 measures the intensity of the signal converted into the frequency domain by the FFT unit 18. As a result, the processing delay required for measuring the signal intensity increases, and the selection of the switching destination is delayed. In the modification, the signal strength of the multicarrier signal converted into the frequency domain by the tuner 14 already provided is measured before being converted into the frequency domain by the FFT unit 18. As a result, the processing delay can be reduced while suppressing an increase in circuit scale.

  FIG. 7 shows a configuration of a modified example of the receiving device 100. The receiving apparatus 100 is different from the receiving apparatus 100 in FIG. 1 and extracts portions necessary for the processing of the modified example. The receiving apparatus 100 includes an observation unit 40 as compared with the receiving apparatus 100 in FIG. ing. Here, the description will focus on the parts that are different from the receiving apparatus 100 of FIG. In order to simplify the description, the selection unit 12 selects a multicarrier signal received by the first antenna 10a and a multicarrier signal received by the second antenna 10b, and the determination unit 28 Assume that switching of a multicarrier signal received by the antenna 10b is determined.

  The selection unit 12 switches the input from the second antenna 10b to the input from the third antenna 10c based on an instruction from the determination unit 28 or the control unit 30. The selection unit 12 outputs the multicarrier signal input from the third antenna 10c to the second tuner 14b. As described above, the second tuner 14b frequency-converts the input multicarrier signal to baseband. The observation unit 40 measures the strength of the multicarrier signal from the second tuner 14b. Here, the multicarrier signal is a time-domain signal that has not been converted to the frequency domain, that is, a signal that has been subjected to IFFT.

  Subsequently, the selection unit 12 switches the input from the third antenna 10c to the input from the fourth antenna 10d based on an instruction from the determination unit 28 or the control unit 30. That is, the selection unit 12 operates so as to select an unselected multicarrier signal in the initial communication state. The second tuner 14b and the observation unit 40 operate as described above. As a result, the observation unit 40 acquires the strength of the multicarrier signal corresponding to the third antenna 10c and the strength of the multicarrier signal corresponding to the fourth antenna 10d.

  The determination unit 28 compares the strength of the multicarrier signal corresponding to the third antenna 10c measured by the observation unit 40 with the strength of the multicarrier signal corresponding to the fourth antenna 10d, and switches to the larger multicarrier signal. To decide. The determination unit 28 instructs the selection unit 12 to perform the determined switching.

  According to the embodiment of the present invention, if the strength between two multicarrier signals to be combined is greatly different, one of the multicarrier signals to be combined is changed to another multicarrier signal. It is possible to suppress an increase in noise included in the synthesized multicarrier signal. Moreover, since an increase in noise can be suppressed, reception characteristics can be improved. In addition, since switching between multicarrier signals is determined based on the ratio between the strengths of two multicarrier signals, it avoids the situation where the influence of noise contained in one multicarrier signal is large when combining. it can. In addition, since switching is determined in consideration of not only the relative strength between multicarrier signals but also the absolute strength, the accuracy in determining switching can be improved.

  In addition, since a multicarrier signal that has not been selected for a long period is selected as the multicarrier signal to be switched to, switching can be performed at high speed. In addition, since a multicarrier signal that has not been selected for a long period is selected as the multicarrier signal to be switched to, the processing can be simplified. In addition, since the strength of an unselected multicarrier signal is measured before Fourier transform in order to determine the switching destination multicarrier signal, the multicarrier is expected to improve characteristics while reducing the processing delay. Switching to a signal can be performed. In addition, since two selected multi-carrier signals are selected and then the selected two are combined, reception characteristics can be improved while suppressing an increase in circuit scale.

  In the above, this invention was demonstrated based on the Example. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and such modifications are also within the scope of the present invention. .

  In the embodiment of the present invention, the receiving apparatus 100 receives a digital television broadcast program. However, the present invention is not limited to this. For example, the receiving apparatus 100 may receive a radio broadcast program, and may further receive a signal in a wireless LAN using an OFDM modulation scheme. An example of the latter is a wireless LAN in the IEEE 802.11a standard. At this time, since the arrangement of pilot signals is different from that in the embodiment, the processing content may be changed according to the arrangement. According to this modification, the receiving device 100 can be applied to various communication systems and broadcast systems. In addition, the effect by this invention becomes large, so that there are many subcarriers. That is, it is sufficient that the OFDM modulation method is used.

  In the embodiment of the present invention, the selection unit 12 selects two multicarrier signals. However, the present invention is not limited to this. For example, the selection unit 12 may select two or more multicarrier signals. In that case, the tuner 14 and the FFT unit 18 are provided according to the number of selected multicarrier signals, and the synthesis unit 20 synthesizes two or more multicarrier signals. The intensity ratio in the intensity ratio deriving unit 24 may be derived between each of two or more multicarrier signals, or may be derived between any two multicarrier signals. According to this modification, the reception characteristics can be improved by combining two or more multicarrier signals. That is, it is only necessary that the number of multicarriers received by the antenna 10 is larger than the number of multicarrier signals to be combined.

  In the embodiment of the present invention, the strength ratio deriving unit 24 calculates the ratio between the strengths of the two multicarrier signals. However, the present invention is not limited to this. For example, the strength ratio deriving unit 24 may calculate a difference between the strengths of the two multicarrier signals. Moreover, you may calculate the absolute value of a difference. In accordance with this, the calculation unit 26 may set a threshold value. According to this modification, the difference in intensity between the two multicarrier signals can be executed by the subtraction process, so that an increase in circuit scale can be suppressed. That is, the difference in intensity between the two multicarrier signals may be derived.

It is a figure which shows the structure of the receiver which concerns on the Example of this invention. FIGS. 2A to 2B are diagrams illustrating multicarrier signals selected by the selection unit of FIG. It is a figure which shows the process in the specific part of FIG. It is a figure which shows an example of the antenna selected in the determination part of FIG. It is a flowchart which shows the procedure of the diversity process by the receiver of FIG. It is a flowchart which shows the procedure of the switching process of the antenna by the specific | specification part of FIG. It is a figure which shows the structure of the modification of the receiver of FIG.

Explanation of symbols

  10 antennas, 12 selection units, 14 tuners, 16 AGC control units, 18 FFT units, 20 combining units, 22 specifying units, 24 intensity ratio deriving units, 26 calculating units, 28 determining units, 30 control units, 100 receiving devices.

Claims (4)

A specifying unit that specifies at least two multicarrier signals to be selected among a plurality of multicarrier signals sequentially received by a plurality of antennas;
A selection unit for selecting at least two multicarrier signals identified by the identification unit;
A combining unit that performs combining in units of carriers for at least two multi-carrier signals selected by the selecting unit;
The specific part is:
A derivation unit for deriving a difference in signal strength in units of carriers between at least two multicarrier signals selected by the selection unit;
A calculation unit that calculates the number of carriers in which the difference in signal strength derived in the deriving unit is greater than a first threshold;
When the number of carriers calculated in the calculation unit is larger than the second threshold, one of at least two multicarrier signals to be selected is not selected from the plurality of multicarrier signals. And a determining unit that determines switching to a multicarrier signal. The derivation unit derives a signal intensity for each of at least two multicarrier signals selected by the selection unit in units of carriers,
When the signal strength corresponding to one carrier of both of the at least two multi-carrier signals is smaller than the third threshold value, the calculation unit determines that the difference in signal strength corresponding to the carrier is the first The receiving apparatus according to claim 1, wherein the number of carriers is added even if the value is equal to or less than the threshold value. When the plurality of received multi-carrier signals are all subjected to inverse Fourier transform, the selection unit performs Fourier transform on at least two selected multi-carrier signals, and the result is Output to the synthesis unit,
The derivation unit performs processing on the multicarrier signal Fourier-transformed by the selection unit,
The determining unit determines a multicarrier signal to be switched to based on the strength of a multicarrier signal that is an unselected multicarrier signal among a plurality of multicarrier signals and that has been subjected to inverse Fourier transform. The receiving apparatus according to claim 1 or 2. Identifying at least two multicarrier signals to be selected from among a plurality of multicarrier signals sequentially received by a plurality of antennas;
Selecting at least two identified multi-carrier signals;
Performing carrier-by-carrier combining on the selected at least two multi-carrier signals,
The identifying step includes:
Deriving a difference in signal strength per carrier between at least two selected multi-carrier signals;
Calculating the number of carriers for which the derived signal strength difference is greater than a first threshold;
When the calculated number of carriers is larger than the second threshold value, an unselected multicarrier signal among a plurality of multicarrier signals is selected with respect to one of at least two multicarrier signals to be selected. A diversity receiving method comprising: determining to switch to.

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