JP2008113265A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver capable of reducing influence due to a fluctuation in a frequency offset after antenna switching in switching of directional antennas. <P>SOLUTION: The receiver receives a broadcast signal through one antenna selected among a plurality of antennas provided with different directivity and is provided with: a broadcast signal receiving part; a tuner part for acquiring a baseband signal from the broadcast signal received by the broadcast signal receiving part; a frequency offset detecting part for detecting a frequency offset of the baseband signal obtained by the tuner part; an antenna switching control part for determining to switch an antenna for receiving the broadcast signal among the plurality of antennas in accordance with a receiving state based on the baseband signal and outputting information showing the directivity of the antenna of a switching destination; a frequency control part for synthesizing the baseband signal with a transmission frequency of a transmitting side on the basis of the frequency offset and the information showing the direction of the antenna; and a demodulation part for demodulating the baseband signal subjected to frequency synchronization by the frequency control part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that receives, for example, an orthogonal frequency division multiplexing (OFDM) signal used in terrestrial digital broadcasting with a plurality of antennas.

  In recent years, with the development of communication technology, digitization in various broadcasts has progressed, and terrestrial television broadcasts are also shifting from analog broadcasts to digital broadcasts. In this terrestrial digital television broadcast, the OFDM system, which is a multi-carrier transmission system using a plurality of carriers simultaneously, is employed. In order to receive a broadcast signal of a desired channel in a digital broadcast receiver using this OFDM system, it is important to reproduce the synchronization frequency control value (carrier frequency) for the desired channel, and among these, it is reproduced. The accuracy of the control of the carrier frequency is required, and for this reason, a pull-in process (carrier synchronization) for frequency synchronization is performed.

  Here, the difference between the transmission frequency on the transmission side and the reception frequency on the reception side is referred to as a frequency offset, and the quality of the reception signal will be significantly degraded unless this frequency deviation is corrected accurately.

  When the above pull-in process is performed, a control loop for converging to a synchronization frequency control value (carrier frequency) for a desired channel is realized. In addition, in order to shorten the convergence time to the synchronization frequency control value (carrier frequency) by the pull-in process, the correction control step width of the frequency offset that is a change width for changing the synchronization frequency control value (carrier frequency) is set large. . This frequency offset correction control step width is a value set by a frequency offset (frequency error) within a subcarrier interval, and corresponds to a loop gain for a control loop for obtaining a synchronous frequency control value (carrier frequency).

The following Patent Document 1 discloses a technique for starting a pull-in process in order to reset a receiver and obtain a new synchronization when a loss of synchronization is detected. This technology increases the frequency offset correction control step width (loop gain) at the time of performing the pull-in processing to increase the synchronization speed. On the other hand, when the pull-in period ends, the frequency offset correction control step width The value of (loop gain) is decreased, the calculation accuracy of the frequency offset correction value is increased, and the synchronization accuracy is increased.
WO 2003/032543 Publication

  In general, in diversity receivers using ESPAR antennas (directivity switching antennas) that estimate the direction of arrival of desired radio waves and autonomously direct the antenna pattern, when receiving while switching the directivity, In the case of the case and the case of the directional pattern, there is a difference in variation (magnitude) of the received frequency offset due to the influence of the Doppler shift based on the directivity.

  For this reason, in such a switching diversity receiver having a plurality of antennas, when synchronization is lost, usually the receiver synchronization processing is reset, and the frequency offset correction control step width (loop gain) is set small. Then, a new synchronization process is performed by adjusting the frequency offset fluctuation to converge.

  However, if the synchronization is not lost in the antenna switching of the receiver having a plurality of directional antennas, the synchronization processing is not reset, and an arbitrary period after the antenna switching (the period until the synchronization frequency control value converges). ), Which affects the accuracy of the synchronous frequency control value.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a receiving device that reduces the influence of fluctuations in frequency offset after antenna switching when switching directional antennas.

  In view of the above problems, the present invention has the following features.

  The invention of claim 1 is a receiving device, which receives a broadcast signal via one antenna selected from a plurality of antennas having different directivities, and receives the broadcast signal reception unit and the broadcast signal reception unit. A tuner unit that acquires a baseband signal from a received broadcast signal, a frequency offset detection unit that detects a frequency offset of the baseband signal obtained by the tuner unit, and a reception status based on the baseband signal, An antenna switching control unit that determines switching of the antenna that receives the broadcast signal between the plurality of antennas, and that outputs information indicating the directivity of the antenna to be switched to, and the baseband signal, the frequency A frequency control unit that synchronizes with the transmission frequency on the transmission side based on information indicating the offset and the directivity of the antenna; Characterized in that it comprises a demodulator for demodulating the base band signal frequency synchronization has been performed by the frequency control unit.

  With this feature, it is possible to realize more accurate frequency correction synchronization processing corresponding to the selected antenna, and in particular, it is possible to prevent performance deterioration of the received signal after switching.

  Here, the reception status is determined based on the reception power level of the antenna used at that time as a parameter. That is, when the reception power is high, it is determined that the reception situation is good, or when the reception power is low, the reception situation is bad.

  The reception status is judged from the value of this parameter, and the antenna is switched. This is an idea based on the diversity reception method, and it is possible to obtain a high-quality reception signal by selecting an antenna with high reception power.

  The frequency offset is a difference between the transmission frequency and the reception frequency. The receiver corrects this shift and performs FFT (Fast Fourier Transform) and demodulation.

The invention of claim 2
The receiving apparatus according to claim 1, wherein the frequency control unit includes a correction signal generation unit that generates a correction signal for synchronizing a loop filter and a transmission frequency on a transmission side, and the frequency control unit includes the frequency control unit, Based on information indicating the directivity of the antenna, a filter coefficient to be set in the loop filter is set, and the loop filter uses the filter coefficient and the frequency offset to provide a frequency offset correction value to the correction signal generation unit. Is output to the correction signal generation unit, and the correction signal generation unit generates the correction signal using the frequency offset correction value.

  This feature enables appropriate frequency synchronization tracking for any directional antenna, and can improve the accuracy of frequency synchronization.

  The invention of claim 3 is a receiving apparatus, which receives a broadcast signal via one antenna selected from a plurality of antennas having different directivities, and receives the broadcast signal reception unit and the broadcast signal reception unit. A tuner unit that acquires a baseband signal from a received broadcast signal, a frequency offset detection unit that detects a frequency offset of the baseband signal obtained by the tuner unit, and a maximum value and a minimum value of the frequency offset in a predetermined period A frequency offset holding unit that obtains a difference between the values and a reception state based on the baseband signal are determined to switch the antenna that receives the broadcast signal among the plurality of antennas, and the switching is performed. An antenna switching control unit that outputs information indicating the directivity of the antenna, and the frequency for the baseband signal. A frequency control unit that synchronizes with a transmission frequency on a transmission side based on a difference between an offset and a maximum value and a minimum value of the frequency offset; and a demodulation that demodulates the baseband signal that is frequency-synchronized by the frequency control unit A part.

  With this feature, it is possible to determine the frequency offset variation from the maximum and minimum frequency offset values in a given period, and to implement more accurate frequency correction synchronization processing corresponding to this variation, and to prevent performance degradation of the received signal be able to.

  According to a fourth aspect of the present invention, in the receiving device according to the third aspect, the frequency control unit includes a correction signal generation unit that generates a correction signal for synchronizing the loop filter and the transmission frequency on the transmission side, The frequency control unit sets a filter coefficient to be set in the loop filter based on a difference between the frequency offset and a maximum value and a minimum value of the frequency offset, and the loop filter sets the filter coefficient and the frequency offset. A frequency offset correction value to be provided to the correction signal generation unit is obtained and output to the correction signal generation unit, and the correction signal generation unit generates the correction signal using the frequency offset correction value. It is characterized by.

  With this feature, appropriate frequency synchronization tracking corresponding to the variation determined from the maximum value and the minimum value of the frequency offset in a predetermined period can be performed, and the accuracy of frequency synchronization can be improved.

  According to a fifth aspect of the present invention, in the receiving device according to the fourth aspect, when the frequency offset holding unit determines that the polarities of the maximum value and the minimum value of the frequency offset in a predetermined period are different, the frequency control unit Is characterized in that a filter coefficient is set in the loop filter in order to converge the frequency offset in a short period of time.

  This feature makes it possible to appropriately follow frequency synchronization in response to a change in directivity polarity determined from the maximum value and minimum value of the frequency offset in a predetermined period, thereby improving the accuracy of frequency synchronization. In particular, since the polarity can be determined even if the predetermined period is a short period, the frequency correction synchronization process can be speeded up, and the frequency synchronization tracking can be realized at high speed.

  A sixth aspect of the present invention is the receiving apparatus according to any one of the third to fifth aspects, wherein the filter coefficient is determined based on a type of antenna directivity.

  With this feature, filter coefficients are set for various antennas, so that it is possible to improve the frequency offset correction accuracy in the synchronization processing, and to improve the reception characteristics.

  Note that the broadcast signal receiving unit in the claims corresponds to the input unit 12 of the diversity receivers 10, 20, 30, 40 according to the embodiment. The tuner unit in the claims corresponds to the tuner 24 of the diversity receiver 10 according to the embodiment. The frequency control unit in the claims corresponds to the AFC control unit 17, the loop filter 18, the correction signal generation unit 19, and the multiplier 20 of the diversity receivers 10, 20, 30, and 40 according to the embodiments.

  The features of the present invention and the technical significance thereof will become more apparent from the following description of embodiments. However, the following embodiment is only one embodiment of the present invention, and the meaning of the present invention or the terms of each constituent element is limited to those described in the following embodiment. is not.

  ADVANTAGE OF THE INVENTION According to this invention, when switching a directional antenna, the influence of the frequency offset fluctuation | variation after switching can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
(Example 1)
FIG. 1 is a block diagram showing a configuration of a diversity receiver 10 according to the first embodiment.

  The diversity receiver 10 includes a directivity switching antenna 11, an input unit 12, a tuner 13, a high frequency circuit 14, an A / D converter 15, a frequency offset detection unit 16, an AFC control unit 17, a loop filter 18, and a correction signal generation unit 19. , A multiplier 20, an FFT (Fast Fourier Transform) unit 21, a demodulation unit 22, an antenna switching control unit 23, an AFC circuit 24, and a main control unit (not shown).

  A signal received by a directivity switching antenna 11 having a plurality of directivities and input from an input unit 12 is selected by a tuner 13 and a signal of a desired channel is extracted. Subsequently, the frequency of the received signal is lowered to the baseband by the high frequency circuit 14, and then converted into a digital signal by the A / D converter 15. This converted digital signal includes a frequency offset (frequency error) from the transmission frequency on the transmission side. This is because the reference source for generating the local frequency of each transceiver (frequency generated in each transceiver) is different between the transceivers.

  The frequency offset detector 16 detects a frequency offset (frequency error) from the carrier frequency on the transmission side and the carrier frequency on the reception side. Information detected by the frequency offset detector 16 is output to the loop filter 18.

  The antenna switching control unit 23 measures the received power based on the received signal converted into a digital signal by the A / D converter 15, detects the reception status based on the received power, and determines whether the antenna needs to be switched. decide. More specifically, the antenna switching control unit 23 includes an electric field strength measuring unit therein and measures the electric field strength (received power). At this time, if the value of the electric field intensity is smaller than, for example, −60 dBm (dBm: unit indicating absolute power), it is determined that the reception status is bad and the antenna is switched. Here, when the transmission power of the transmitting station is the reference power (0 dBm), the received power is the power that has received the free space basic propagation loss (60 dBm), that is, the transmission power (0 dBm) −the living space basic propagation loss (60 dBm). ) = Received power (−60 dBm). A value of “−60 dBm” is considered as a value indicating weak to medium electrolysis as a reception level, and a switching effect is easily obtained.

For example, when a mobile unit moves toward a base station such as a broadcasting station, select a suitable directional antenna according to the reception status at that time so that an antenna having directivity in the traveling direction of the mobile unit is selected. Switch to this.
For this antenna switching, an antenna selection method adopted by a diversity receiver or the like having a plurality of antennas can be used. For example, spatial diversity is used, and among the plurality of antennas, the received signal level is Always select the highest antenna.

  When the antenna switching control unit 23 determines that the antenna needs to be switched, the antenna switching control unit 23 selects the antenna to be switched to, specifically, the forward directivity antenna and the backward directivity of the directivity switching antenna 11. Information indicating either an antenna or an omnidirectional antenna is transmitted to the input unit 12 and the AFC control unit 17. On the other hand, when it is determined that antenna switching is not required, information indicating that antenna switching is not required is transmitted to the AFC control unit 17.

  Information regarding the antenna switching output from the antenna switching control unit 23 is transmitted to the input unit 12 and the AFC control unit 17. When the information indicating the antenna switching is transmitted from the antenna switching control unit 23, the input unit 12 is instructed to switch among the front directional antenna, the rear directional antenna, and the omnidirectional antenna of the directional switching antenna 11. Switch to another antenna to receive the signal.

  The AFC control unit 17 is information indicating the antenna switching transmitted from the antenna switching control unit 23, that is, information indicating which antenna to switch to among the forward directional antenna, the backward directional antenna, and the omnidirectional antenna. And a filter coefficient (loop gain) to be set for the loop filter 18 in the AFC circuit 24 is determined based on this. In the present embodiment, the AFC control unit 17 includes a table (for example, FIG. 2 shown below) that defines a filter coefficient (loop gain), and a filter coefficient (loop gain) corresponding to information indicating antenna directivity. Is obtained with reference to a table defining filter coefficients (loop gain).

  FIG. 2 shows an example of filter coefficients (loop gain) set for each of the forward directional antenna, the backward directional antenna, and the omnidirectional antenna. In this example, when switching to the front or rear directional antenna, the filter coefficient (loop gain) “0.1” is set for the loop filter 18 and the loop gain is set high. Thus, by increasing the loop gain, the synchronization pull-in time can be shortened and the convergence of the filter can be accelerated.

  When switching to a right or left directional antenna or an omnidirectional antenna, the filter coefficient (loop gain) “0.01” is set for the loop filter 18 and the loop gain is set low. Thus, by reducing the loop gain, it is possible to lengthen the synchronization pull-in time and improve the accuracy of filter convergence.

  The loop filter 18 integrates the frequency offset (frequency error) value obtained from the input signal for an arbitrary period (for example, 10 symbols) using the filter coefficient (loop gain) set by the AFC control unit 17, It is a filter that configures a feedback loop for calculating an average value of frequency offset values and determines the response of the feedback loop. The greater the filter coefficient (loop gain) set for this filter, the faster the response.

  Here, a symbol indicates transmission information in an arbitrary period in a transmitted continuous signal, and a frequency offset (frequency error) is generated in units of symbols. According to the standard of terrestrial digital broadcasting (mode 3), one symbol is transmitted at 1008 μs.

  The frequency offset (frequency error) value obtained for each symbol may or may not be a value close to each symbol. In particular, when the frequency offset (frequency error) value varies as in the latter case, when the frequency offset (frequency error) value is calculated as a frequency offset correction value for each symbol, the convergence accuracy of the loop filter is degraded or converged. Prolongs time. Therefore, in order to prevent the influence due to the fluctuation of the frequency offset (frequency error) value and improve the convergence accuracy of the filter, the average value of the frequency offset (frequency error) of each symbol is used, and such an average value is obtained. Therefore, the average value of the frequency offset values is calculated by integrating the period in which the maximum value and the minimum value of the frequency offset (frequency error) can be detected.

  In this manner, the average value of the frequency offset values obtained by the loop filter 18 is input to the correction signal generation unit 19 as the frequency offset correction value F.

  The correction signal generator 19 includes an NCO (Numerical Controlled Oscillator) that is an oscillator that outputs a sine wave, and its oscillation frequency is controlled by an input value. The sine wave output from the correction signal generator 15 is supplied to the complex multiplier 20 and is multiplied by the received signal.

  In the multiplier 20, the received signal converted into the digital signal is multiplied by the frequency correction signal generated by the correction signal generation unit 19. Thereby, a signal from which a frequency offset (frequency error) has been removed from the digital signal can be obtained.

  The input signal corrected by the multiplier 20 is converted by the FFT unit 21 from time domain data to an OFDM signal for each subcarrier. The OFDM signal converted by the FFT unit 21 is demodulated into a TS (transport stream) signal by the demodulation unit 22 by a demodulation method corresponding to the modulation method of the received data.

  A main control unit (not shown) comprehensively controls each functional unit in the receiving apparatus.

  FIG. 3 is a flowchart schematically showing processing in synchronization control at the time of antenna switching in the present embodiment.

  First, it is assumed that a signal is stably received using a directional antenna having the highest received power among a plurality of directional antennas. At this time, the AFC control unit 17 sets the filter coefficient (loop gain) to be set in the loop filter 18 based on the directivity of the current antenna. The information indicating the antenna directivity holds information indicating the current antenna directivity.

  The signal received by the directivity switching antenna 11 and inputted from the input unit 12 is reduced in frequency to the baseband by the high frequency circuit 14, and then converted into a digital signal by the A / D converter 15. (Step S100).

  Next, the antenna switching control unit 23 determines whether or not to perform antenna switching based on the current reception status (step S101).

  When it is determined in step S101 that the antenna switching is not performed (No in step S101), the process proceeds to step S102, and the AFC control unit 17 determines that there is no change in the antenna directivity and the information indicating the antenna directivity is displayed. Information indicating the current antenna directivity is retained as it is without updating (step S102). Thereafter, the process proceeds to step S103.

  On the other hand, when it is determined in step S101 that antenna switching is to be performed (step S101 Yes), the process proceeds to step S107, and the AFC control unit 17 determines that there is a change in the antenna directivity, and indicates information indicating the antenna directivity. The information indicating the directivity of the switching destination antenna is held (step S106).

  Subsequently, the AFC control unit 17 determines a filter coefficient (loop gain) to be set in the loop filter 18 based on the information indicating the antenna directivity, and sets this in the loop filter 18 (step S103).

  The loop filter 18 integrates the frequency offset (frequency error) value obtained from the input signal for an arbitrary period using the set filter coefficient (loop gain), and calculates the average value of the frequency offset values. The average value of the obtained frequency offset values is input to the correction signal generation unit 19 as a frequency offset correction value F (step S104).

  The correction signal generation unit 19 generates a frequency correction signal (sine wave) based on the frequency offset correction value F input from the loop filter 18, and inputs this to the multiplier 20.

  The multiplier 20 multiplies the input signal converted into the digital signal in step S100 by the correction frequency signal generated by the correction signal generation unit 19, and removes a frequency offset (frequency error) included in the input signal ( Step S105).

  The input signal subjected to the correction process is subjected to FFT conversion by the FFT unit 21 and then demodulated by the demodulation unit 22 (step S106).

  In the diversity receiver 10 of the above embodiment, the directivity switching antenna 11 includes a forward directional antenna, a backward directional antenna, and an omnidirectional antenna, and has three types of directivities. However, the present invention is not limited to this, and a plurality of antennas may be used including directional antennas having other directivities such as rightward directivity and leftward directivity.

  In the diversity receiver 10 of the above embodiment, the antenna switching control unit 23 outputs information indicating that antenna switching is not required when it is determined that antenna switching is not required. It is also possible to detect whether the antenna is any one of the front directivity antenna, the rear directivity antenna, and the omnidirectional antenna of the directivity switching antenna 11 and output the detected antenna.

  As shown in FIG. 2, filter coefficients (loop gains) determined for each directional antenna such as a forward directional antenna, a backward directional antenna, and an omnidirectional antenna are set in advance and are appropriately set. You may comprise so that it may be referred.

  According to the above-described embodiment, since the synchronization processing is performed by applying the filter coefficient (loop gain) set for each antenna as the antenna is switched, the frequency offset (frequency error) after the pull-in for each antenna is generated. Corresponding to the situation, it is possible to perform appropriate synchronization processing such as synchronization processing that quickly converges and synchronization processing with high accuracy, and performance degradation can be prevented.

(Example 2)
FIG. 4 is a block diagram illustrating a configuration of the diversity receiver 20 according to the second embodiment.
In the diversity receiver 20 of FIG. 4, the same parts as those of the diversity receiver 10 of FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The diversity receiver 20 of FIG. 4 includes a frequency offset holding unit 25 in addition to the configuration of the diversity receiver 10 of FIG.

  Further, the main control unit (not shown) includes a timer therein, and realizes a timer function including counting processing. In the present embodiment, it is used for time measurement of a synchronization pull-in period that is performed for a predetermined period from the time of antenna switching. In the present embodiment, the synchronization pull-in period is a period of 10 symbols after antenna switching, and the result of this time measurement (whether or not it is in the synchronous pull-in period) is transmitted to the AFC control unit 17. The

  The frequency offset detection unit 16 detects a frequency offset (frequency error) from the carrier frequency on the transmission side and the carrier frequency on the reception side, and the detected information is output to the loop filter 18 and the frequency offset holding unit 25.

  The frequency offset holding unit 25 holds the frequency offset value in symbol units detected by the frequency offset detecting unit 16 for an arbitrary predetermined period, and calculates the difference α between the maximum value and the minimum value of the frequency offset value in the arbitrary predetermined period. Calculate and store, and output to the AFC control unit 17.

  Note that if this arbitrary predetermined period is too short, the accuracy of the fluctuation range of the received power is deteriorated. Therefore, in this embodiment, 10 symbols for which the fluctuation width of the received power is sufficiently measured as the arbitrary predetermined period. Period.

  Further, the frequency offset holding unit 25 receives the notification that the antenna is switched based on the information indicating the antenna switching output from the antenna switching control unit 23, and the maximum value and the minimum value of the held frequency offset value. And the difference α between the maximum value and the minimum value of the frequency offset value is newly calculated and stored, and is output to the AFC control unit 17.

Fig. 5 shows the distribution of antenna directivity and its frequency offset (frequency error). As shown in FIG. 5, when the variation in the frequency offset (frequency error) is small, or at the time of synchronization pulling, the value of the filter coefficient (loop gain) set in the loop filter 18 of the AFC circuit 24 is set to a small value, and the frequency offset (frequency Increase the accuracy of (error) convergence. Further, after the synchronization pull-in, the value of the filter coefficient (loop gain) set in the loop filter 18 of the AFC circuit 24 is set to be large so that the convergence of the frequency offset (frequency error) is accelerated.
On the other hand, when the dispersion of the frequency offset (frequency error) is large, or at the time of synchronization pull-in, the value of the filter coefficient (loop gain) set in the loop filter 18 of the AFC circuit 24 is set to be large so that the frequency offset (frequency error) converges Speed up. Further, after the synchronization pull-in, the value of the filter coefficient (loop gain) set in the loop filter 18 of the AFC circuit 24 is set to be small, and the accuracy of convergence of the frequency offset (frequency error) is increased.

The definition of large / small in the variation of frequency offset (frequency error) is determined experimentally based on the difference α between the maximum value and the minimum value of the frequency offset value calculated from the frequency offset holding unit 25.
In general, when a large value is set as the filter coefficient (loop gain) of the loop filter 18, the convergence time in the loop filter is shortened, but variation occurs, resulting in poor convergence accuracy. On the other hand, when a small value is set, the convergence time in the loop filter is delayed, but the variation is reduced and the convergence accuracy is improved.

  Using this feature, when synchronization is pulled in, the difference between the initial value and the value to be converged is large, so a large value is set as the filter coefficient (loop gain) to achieve early convergence.

  In addition, after the synchronization pull-in, since a certain degree of convergence has been achieved at the time of the above-mentioned synchronization pull-in, priority is given to the convergence accuracy over the convergence time, and a small value is set as the filter coefficient (loop gain) (of the frequency offset) Improve accuracy.

  In the embodiment in the first embodiment, the AFC control unit 17 sets the filter coefficient (loop gain) to be set in the loop filter 18 in the AFC circuit 24 based on the information indicating the antenna switching transmitted from the antenna switching control unit 23. In the present embodiment, the information indicating the antenna switching transmitted from the antenna switching control unit 23, whether or not the synchronization is being pulled in, and the maximum and minimum values of the frequency offset value are determined. Based on the value of the difference α, the filter coefficient (loop gain) to be set in the loop filter 18 of the AFC circuit 24 is determined.

  FIG. 6 shows an example of a filter coefficient (loop gain) used for synchronization processing of each antenna with respect to the difference α between the maximum value and the minimum value of the frequency offset value.

  In the case where the synchronization processing is performed when the difference α between the maximum value and the minimum value of the frequency offset value is small, the filter coefficient (loop gain) is small with respect to the loop filter 18 (in FIG. 6, in the front-rear direction) For directional antennas: 0.01, for omnidirectional antennas: 0.001), set the convergence accuracy (of frequency offset). When α is large, a large filter coefficient (loop gain) is set for the loop filter 18 (in FIG. 6, for a directional antenna in the front-rear direction: 0.1, for an omnidirectional antenna: 0.1). Speed up convergence (of frequency offset). As a result, it is possible to increase the accuracy (frequency offset) at the time of pull-in or to speed up convergence, and to improve the processing efficiency at the time of pulling in various antennas.

  In addition, in the case where the synchronization processing is performed after the pull-in, when the difference α between the maximum value and the minimum value of the frequency offset value is small, the filter coefficient (loop gain) is large with respect to the loop filter 18 (in FIG. For directional antennas: 0.1, for omnidirectional antennas: 0.1), set (frequency offset) to speed up convergence. Also, when α is large, the filter coefficient (loop gain) is set to a small value for the loop filter 18 (in FIG. 6, 0.01 for a directional antenna in the front-rear direction and 0.001 for an omnidirectional antenna). To improve accuracy (of frequency offset). As a result, it is possible to increase the accuracy (frequency offset) after the pull-in or to speed up the convergence, and to improve the processing efficiency after the various antennas are pulled in.

  Further, when the difference α between the maximum value and the minimum value of the frequency offset value is intermediate between the above two cases, the filter coefficient (loop gain) is an intermediate value (in the front-rear direction in FIG. 6) with respect to the loop filter 18. For directional antennas: 0.05, for non-directional antennas: 0.01). As a result, the frequency offset can be converged with appropriate accuracy in an appropriate pull-in time.

  FIG. 7 is a flowchart schematically showing processing in synchronization control at the time of antenna switching in the present embodiment.

  First, it is assumed that a signal is stably received using a directional antenna having the highest received power among a plurality of directional antennas. At this time, the AFC control unit 17 sets the filter coefficient (loop gain) to be set in the loop filter 18 based on the directivity of the current antenna. The information indicating the antenna directivity holds information indicating the current antenna directivity.

  The signal received by the directivity switching antenna 11 and inputted from the input unit 12 is reduced in frequency to the baseband by the high frequency circuit 14, and then converted into a digital signal by the A / D converter 15. (Step S200).

  Next, the antenna switching control unit 23 determines whether or not to perform antenna switching based on the current reception status (step S201).

  If it is determined in step S201 that antenna switching is not performed (No in step S201), the process proceeds to step S202, and the frequency offset holding unit 25 does not calculate the difference α between the maximum value and the minimum value of the frequency offset value. Then, the difference α between the maximum value and the minimum value of the currently held frequency offset value is held as it is and is output to the AFC control unit 17 (step S202). The AFC control unit 17 retains the information indicating the current antenna directivity as it is without updating the information indicating the antenna directivity, assuming that there is no change in the antenna directivity. Thereafter, the process proceeds to step S203.

  On the other hand, when it is determined in step S201 that antenna switching is to be performed (step S201 Yes), the process proceeds to step S207, where the AFC control unit 17 uses the frequency offset value that has been held so far. The value of the difference α between the maximum value and the minimum value is cleared, a difference α between the maximum value and the minimum value of the frequency offset value is newly calculated, held, and output to the AFC control unit 17. The AFC control unit 17 retains information indicating the antenna directivity and information indicating the antenna directivity of the switching destination, assuming that there is a change in the antenna directivity (step S206).

  Subsequently, the AFC control unit 17 determines a filter coefficient (loop gain) to be set in the loop filter 18 based on the difference α between the maximum and minimum frequency offset values and information indicating the current antenna directivity. This is set in the loop filter 18. Here, based on the count from the antenna switching in the main control unit, the AFC control unit 17 is “during the pull-in period” if it is within a predetermined period (10 symbol periods in the present embodiment) from the antenna switching (FIG. 6). Filter coefficient (loop gain) corresponding to “during pulling in” is set, and “after pulling period” (in FIG. 6) if a predetermined period (10 symbol periods in the present embodiment) has elapsed since antenna switching. A filter coefficient (loop gain) corresponding to “after pull-in” is set (step S203).

  The loop filter 18 integrates the frequency offset (frequency error) value obtained from the input signal for an arbitrary period using the set filter coefficient (loop gain), and calculates the average value of the frequency offset values. The average value of the obtained frequency offset values is input to the correction signal generation unit 19 as the frequency offset correction value F (step S204).

  The correction signal generation unit 19 generates a frequency correction signal (sine wave) based on the frequency offset correction value F input from the loop filter 18, and inputs this to the multiplier 20.

  The multiplier 20 multiplies the input signal converted into the digital signal in step S100 by the correction frequency signal generated by the correction signal generation unit 19, and removes a frequency offset (frequency error) included in the input signal ( Step S205).

  The input signal subjected to the correction process is subjected to FFT conversion by the FFT unit 21 and then demodulated by the demodulation unit 22 (step S206).

  In the diversity receiver 20 of the above-described embodiment, the frequency offset holding unit 25 calculates the difference α between the maximum value and the minimum value of the frequency offset value by using the maximum value of the frequency offset value and the minimum value of the frequency offset value. When the polarities are different, the difference α between the maximum value and the minimum value of the frequency offset value is regarded as large, and the frequency control unit sets a filter coefficient in the loop filter so as to converge the frequency offset in a short period of time. You can also.

  The above polarity is determined by the information of “moving direction of moving body” and “antenna directivity”. For example, the directionality of the moving direction may be positive, while the backward directivity may be negative. it can.

  As shown in FIG. 6, the filter coefficient (loop gain) determined for each directional antenna such as the forward directional antenna, the backward directional antenna, and the omnidirectional antenna is set in advance and is appropriately set. You may comprise so that it may be referred.

  According to the above-described embodiment, the synchronization processing is performed by applying the filter coefficient (loop gain) set corresponding to the magnitude of the variation in the frequency offset as the antenna is switched. Corresponding to the occurrence state of frequency offset (frequency error), it is possible to perform appropriate synchronization processing such as synchronization processing for rapid convergence and synchronization processing with high accuracy, and performance degradation can be prevented.

(Example 3)
FIG. 8 is a block diagram showing a configuration of diversity receiver 30 according to another embodiment.

  In the following description, the configuration from the directivity switching antenna 11 to the AFC circuit 24 in the embodiment in Example 2 is defined as a branch system, and the diversity receiver 30 of the present embodiment includes two branch systems (branch systems). 1 and a branch system 2) and a diversity combining unit 31. The operations in the two branch systems 1 and 2 are equivalent to the operations and functions described in the first embodiment.

  In addition, the main control unit (not shown) controls the switching of the directivity switching antenna 11 so as not to be performed simultaneously in the branch system 1 and the branch system 2. This is because when two antennas are switched simultaneously, discontinuity occurs in the received signal at the moment of antenna switching. That is, since there is a period during which a desired signal cannot be received, reception performance is degraded. For this reason, the antenna switching is controlled so that the two antennas are not switched simultaneously.

  In diversity combining section 30, the output signal after the FFT in each branch system is combined at the maximum ratio for each subcarrier. Here, the maximum ratio combining is a technique in which the received signals of all branches are made in phase and then combined with appropriate weights.

  Note that the diversity combining unit 30 outputs only a branch signal that does not perform antenna switching to the demodulating unit 31 without performing maximum ratio combining for symbols in which directivity antenna switching occurs.

  The reception signal output from the diversity combining unit 30 is demodulated in the demodulation unit 31 by a demodulation method corresponding to the modulation method.

  According to the embodiment, by combining the outputs from the two branch systems, it is possible to improve reception performance in a low C / N environment, and at the same time, antenna switching occurs in either branch system. Sometimes, the signal on the side where the antenna switching has occurred is not used, so that the reception performance can be prevented from deteriorating.

(Example 4)
FIG. 9 is a block diagram showing a configuration of diversity receiver 40 according to another embodiment.

  In the following description, the configuration from the directivity switching antenna 11 to the frequency offset holding unit 25 in the embodiment in Example 2 is defined as a branch system, and the diversity receiver 40 of this embodiment includes two branch systems ( The branch system 1 and the branch system 2) and a diversity combining unit 41 are provided, and the operations in the two branch systems 1 and 2 are equivalent to the operations and functions described in the first embodiment.

  In addition, the main control unit (not shown) controls the switching of the directivity switching antenna 11 so as not to be performed simultaneously in the branch system 1 and the branch system 2. This is because when two antennas are switched simultaneously, discontinuity occurs in the received signal at the moment of antenna switching. That is, since there is a period during which a desired signal cannot be received, reception performance is degraded. For this reason, the antenna switching is controlled so that the two antennas are not switched simultaneously.

  In diversity combining section 40, the output signal after FFT in each branch system is combined at the maximum ratio for each subcarrier. Here, the maximum ratio combining is a technique in which the received signals of all branches are made in phase and then combined with appropriate weights.

  Diversity combining section 40 outputs only a branch signal that does not perform antenna switching to demodulating section 41 without performing maximum ratio combining with respect to symbols for which directivity antenna switching occurs.

  The received signal output from the diversity combining unit 40 is demodulated in the demodulation unit 41 by a demodulation method corresponding to the modulation method.

  According to the embodiment, by combining the outputs from the two branch systems, it is possible to improve reception performance in a low C / N environment, and at the same time, antenna switching occurs in either branch system. Sometimes, the signal on the side where the antenna switching has occurred is not used, so that the reception performance can be prevented from deteriorating.

  As mentioned above, although embodiment which concerns on this invention was described, it cannot be overemphasized that this invention is not limited to this embodiment, and various changes are possible.

  The embodiment of the present invention can be appropriately modified in various ways within the scope of the technical puncture indicated in the claims.

3 is a block diagram showing a configuration of a diversity receiver according to Embodiment 1. FIG. It is a figure which shows an example of the filter coefficient (loop gain) corresponding to antenna directivity. 3 is a flowchart schematically showing processing in synchronous control according to the first embodiment. 6 is a block diagram illustrating a configuration of a diversity receiver according to Embodiment 2. FIG. It is a figure which shows distribution of antenna directivity and frequency offset (frequency error). It is a figure which shows an example of the filter coefficient (loop gain) corresponding to the difference of the maximum value of frequency offset (frequency error) and minimum value. 10 is a flowchart schematically showing processing in synchronous control according to the second embodiment. 10 is a block diagram showing a configuration of a diversity receiver according to Embodiment 3. FIG. FIG. 10 is a block diagram illustrating a configuration of a diversity receiver according to a fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diversity receiver 11 Directionality switching antenna 12 Input part 13 Tuner 14 High frequency circuit 15 A / D converter 16 Frequency offset detection part 17 AFC control part 18 Loop filter 19 Correction signal generation part 19 2nd synchronous correction control part 20 Multiplier 21 FFT (Fast Fourier Transform) part 22 Demodulation part 23 Antenna switching control part

Claims (6)

Receiving a broadcast signal via one antenna selected from a plurality of antennas having different directivities, and a broadcast signal receiving unit;
A tuner unit for obtaining a baseband signal from the broadcast signal received by the broadcast signal receiver;
A frequency offset detection unit for detecting a frequency offset of the baseband signal obtained by the tuner unit;
Antenna switching control for deciding to switch the antenna that receives the broadcast signal between the plurality of antennas according to the reception situation based on the baseband signal and outputting information indicating the directivity of the antenna to be switched to And
A frequency control unit that synchronizes with the transmission frequency on the transmission side based on the frequency offset and information indicating the directivity of the antenna with respect to the baseband signal;
And a demodulator that demodulates the baseband signal that has been frequency-synchronized by the frequency controller. The frequency control unit
Including a correction signal generation unit for generating a correction signal for synchronizing the loop filter and the transmission frequency on the transmission side;
The frequency control unit sets a filter coefficient to be set in the loop filter based on information indicating the directivity of the antenna,
The loop filter uses the filter coefficient and the frequency offset to obtain a frequency offset correction value to be given to the correction signal generation unit, and outputs this to the correction signal generation unit,
The receiving apparatus according to claim 1, wherein the correction signal generation unit generates the correction signal using the frequency offset correction value. Receiving a broadcast signal via one antenna selected from a plurality of antennas having different directivities, and a broadcast signal receiving unit;
A tuner unit for obtaining a baseband signal from the broadcast signal received by the broadcast signal receiver;
A frequency offset detection unit for detecting a frequency offset of the baseband signal obtained by the tuner unit;
Finding the difference between the maximum value and the minimum value of the frequency offset in a predetermined period, and holding the frequency offset holding unit,
Antenna switching control for deciding to switch the antenna that receives the broadcast signal between the plurality of antennas according to the reception situation based on the baseband signal and outputting information indicating the directivity of the antenna to be switched to And
For the baseband signal, based on the difference between the frequency offset and the maximum and minimum values of the frequency offset, a frequency control unit that synchronizes with the transmission frequency on the transmission side;
And a demodulator that demodulates the baseband signal that has been frequency-synchronized by the frequency controller. The frequency control unit
Including a correction signal generation unit for generating a correction signal for synchronizing the loop filter and the transmission frequency on the transmission side;
The frequency control unit sets a filter coefficient to be set in the loop filter based on a difference between the frequency offset and a maximum value and a minimum value of the frequency offset,
The loop filter uses the filter coefficient and the frequency offset to obtain a frequency offset correction value to be given to the correction signal generation unit, and outputs this to the correction signal generation unit,
The receiving apparatus according to claim 3, wherein the correction signal generation unit generates the correction signal using the frequency offset correction value. When the frequency offset holding unit determines that the polarities of the maximum value and the minimum value of the frequency offset in a predetermined period are different,
The receiving apparatus according to claim 4, wherein the frequency control unit sets a filter coefficient in the loop filter so as to converge the frequency offset in a short period. The receiving apparatus according to claim 3, wherein the filter coefficient is determined based on a type of directivity of an antenna.

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