FM broadcasting systems, FM transmitters, and FM repeaters

Abstract

The FM transmitting device generates a monaural composite signal by mixing a transmission signal modulated by a monaural audio signal with a broadcast signal obtained by delaying the monaural audio signal by an adjustment delay time. The FM repeater generates a monaural composite signal by mixing a transmission signal extracted from a received higher-level station wave with a broadcast signal obtained by delaying the monaural audio signal demodulated from the transmission signal by a relay delay time. The adjustment delay time is set to a time longer than the transmission delay time from the higher-level station to the relay station. The relay delay time is set to a length obtained by subtracting the transmission delay time from the adjustment delay time.

Description

[Technical field]

[0001] The present disclosure relates to a technique for relaying broadcast waves of an FM broadcast system. [Background technology]

[0002] FM synchronized broadcasting is known, in which frequency-modulated audio broadcast waves of the same frequency and program are transmitted from multiple transmitting stations (hereafter referred to as "host stations"). FM stands for Frequency Modulation. In FM synchronized broadcasting, in areas where broadcast waves from multiple host stations are received overlapping with approximately the same strength, the host station must adjust the delay time so that the broadcast waves are received simultaneously. In addition, in general broadcasting systems, relay transmitting stations (hereafter referred to as "relay stations") are installed to expand the receiving area.

[0003] A relay station receives a higher-level station wave, which is a broadcast wave from a higher-level station, and retransmits the relayed wave. If a relay station receives a relayed wave that is stronger than the higher-level station wave at the same frequency, a loop oscillation occurs and the relay becomes impossible. In response to this, the following Patent Document 1 describes a technology for canceling unnecessary waves such as loop oscillations contained in the received wave at the relay station. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-157756 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the relayed wave is delayed with respect to the higher-level station wave, in areas where the higher-level station wave and the relayed wave are received at the same time, there is a problem in that the delay times cannot be adjusted.

[0006] One aspect of the present disclosure is to provide a technology that enables adjustment of the delay time between a higher-level station wave transmitted from a higher-level station and a relayed wave transmitted from a relay station in an area where the higher-level station wave and the relayed wave are received overlapping in an FM broadcasting system. [Means for solving the problem]

[0007] One embodiment of the present disclosure is an FM broadcasting system. The FM broadcasting system includes an FM transmitting device and an FM relay device. The FM transmitting device is configured to transmit a higher station wave FM-modulated by a monaural composite signal. The FM relay device is configured to receive a higher station wave transmitted from the FM transmitting device, and transmit a relay wave FM-modulated by a monaural composite signal reproduced from the higher station wave. The monaural composite signal has a structure in which a broadcasting signal, which is a monaural audio signal, is superimposed on the band of the L+R signal in the stereo composite signal, and a transmission signal modulated by the broadcasting signal is superimposed on the band of the LR signal in the stereo composite signal. The monaural composite signal also has a structure in which the pilot signal in the stereo composite signal is omitted. The FM transmitting device is configured to generate a monaural composite signal by mixing the transmission signal modulated by the monaural audio signal and the broadcasting signal obtained by delaying the monaural audio signal by an adjustment delay time. The FM repeater is configured to generate a monaural composite signal by mixing a transmission signal extracted from a received higher-level station wave with a broadcast signal obtained by delaying a monaural audio signal demodulated from the transmission signal by a relay delay time. The adjustment delay time is set to a time longer than the transmission delay time from the FM transmitter to the FM repeater. The relay delay time is set to a length obtained by subtracting the transmission delay time from the adjustment delay time.

[0008] With this configuration, the delay time of the broadcast signal contained in the relay wave can be adjusted so that the broadcast signal contained in the relay wave and the broadcast signal contained in the higher station wave are received at the same time near the FM relay device.

[0009] Another aspect of the present disclosure is an FM transmission device. The FM transmission device includes a modulation unit, a delay unit, a mixing unit, an FM modulation unit, and a higher-level station transmission unit. The modulation unit is configured to generate a transmission signal modulated by an input monaural audio signal. The delay unit is configured to generate a broadcast signal by delaying the monaural audio signal by an adjustment delay time. The mixing unit is configured to generate a monaural composite signal by mixing the transmission signal generated by the modulation unit and the broadcast signal generated by the delay unit. The FM modulation unit is configured to generate a transmission signal that is FM modulated by the monaural composite signal generated by the mixing unit. The higher-level station transmission unit is configured to transmit a higher-level station wave based on the transmission signal generated by the FM modulation unit. The monaural composite signal has a structure in which a broadcast signal is superimposed on a band of the L+R signal in the stereo composite signal, and a transmission signal is superimposed on a band of the LR signal in the stereo composite signal. In addition, the monaural composite signal has a structure in which a pilot signal in the stereo composite signal is omitted. The adjustment delay time is set to a time longer than the transmission delay time from the transmission of the higher-level station wave to the FM repeater that repeats the higher-level station wave.

[0010] Such a configuration can be used as an FM transmitting device that constitutes the above-mentioned FM broadcasting system.

[0011] Another aspect of the present disclosure is an FM relay device. The FM relay device includes a relay receiving unit, a signal extracting unit, a relay demodulating unit, a relay delay unit, a relay mixing unit, a relay FM modulating unit, and a relay transmitting unit. The relay receiving unit is configured to receive a higher-level station wave FM modulated by a monaural composite signal. The signal extracting unit is configured to extract a transmission signal from a reception signal received by the relay receiving unit. The relay demodulating unit is configured to demodulate the transmission signal to generate a monaural audio signal. The relay delay unit is configured to generate a broadcast signal by delaying the monaural audio signal generated by the relay demodulating unit by a relay delay time. The relay mixing unit is configured to generate a monaural composite signal by mixing the transmission signal extracted by the signal extracting unit and the broadcast signal generated by the relay delay unit. The relay FM modulating unit is configured to generate a relay signal FM modulated by the monaural composite signal generated by the relay mixing unit. The relay transmitting unit is configured to transmit a relay wave based on the relay signal generated by the relay FM modulating unit. The mono composite signal has a structure in which a broadcast signal is superimposed on the band of the L+R signal in the stereo composite signal, and a transmission signal modulated by the broadcast signal is superimposed on the band of the LR signal in the stereo composite signal. The mono composite signal also has a structure in which the pilot signal in the stereo composite signal is omitted. The mono composite signal included in the higher station wave is set so that the broadcast signal is delayed by the adjustment delay time from the transmission signal. The adjustment delay time is set to a time longer than the transmission delay time from the FM transmitting device that transmits the higher station wave to the FM repeater. The relay delay time is set to a length obtained by subtracting the transmission delay time from the adjustment delay time.

[0012] Such a configuration can be used as an FM relay device that constitutes the above-mentioned FM broadcasting system. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram showing an overview of an FM broadcasting system. [Diagram 2]FIG. 2 is an explanatory diagram showing the spectrum of a monaural composite signal used in the first embodiment in comparison with the spectrum of a stereo composite signal. [Diagram 3] 1 is a block diagram of an FM transmitting device constituting a higher-level station of an FM broadcasting system in a first embodiment. [Figure 4] 1 is a block diagram of an FM relay device constituting a relay station of an FM broadcasting system in a first embodiment. [Diagram 5] FIG. 1 is an explanatory diagram showing the relationship between higher-level station waves, relay waves, and loopback waves in an FM broadcasting system. [Figure 6] 1 is an explanatory diagram showing the waveforms of a broadcast signal and a relay signal and a delay adjustment method. [Figure 7] FIG. 11 is an explanatory diagram showing another format of the spectrum of the broadcast signal and the relay signal. [Figure 8] FIG. 11 is an explanatory diagram illustrating the spectrum of a monaural composite signal used in the second embodiment. [Figure 9] FIG. 11 is a block diagram of a signal processing unit of an FM transmitting device in a second embodiment. [Figure 10] FIG. 11 is a block diagram of a relay processing unit of an FM relay device in a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0015] [1. First embodiment] [1-1. System configuration] The FM broadcasting system 100 of the first embodiment includes a host station 101 and one or more relay stations 102, as shown in FIG.

[0016] The upper station 101 converts audio signals distributed via a specified transmission network into signals of a specified format and transmits them to the broadcast area A1. The upper station 101 and other upper stations (not shown) form an SFN that transmits broadcast waves obtained by frequency modulating (hereinafter, FM modulating) carrier waves of the same frequency using the same distributed audio signals, thereby achieving FM synchronous broadcasting (hereinafter, simply synchronous broadcasting). SFN is an abbreviation for Single Frequency Network.

[0017] The FM broadcasting system 100 uses a monaural composite signal, which is a new composite signal created by utilizing the mechanism of a stereo composite signal used in FM stereo broadcasting. As shown in Fig. 2, a mono composite signal for one channel includes frequency components in the frequency band 50Hz to 53kHz used in the stereo composite signal. Specifically, the mono composite signal includes a broadcast signal superimposed on the band 50Hz to 15kHz of the L+R signal in the stereo composite signal, and a transmission signal superimposed on the band 23kHz to 53kHz of the LR signal in the stereo composite signal. Also, unlike the stereo composite signal, the mono composite signal omits the 19kHz pilot signal.

[0018] The broadcast signal is a mono audio signal used for playback on FM radio receivers.

[0019] The transmission signal is a signal with a lower sideband of 23k to 38kHz and an upper sideband of 38k to 53kHz with a suppressed carrier of 38kHz, obtained by carrier suppression amplitude modulation of a 38KHz carrier by a broadcasting signal.

[0020] An FM radio receiver that receives a mono composite signal reproduces the 50Hz to 15kHz broadcast signal as a mono audio signal because the mono composite signal does not contain a pilot signal. In other words, the mono composite signal can be received by existing FM radio receivers.

[0021] Furthermore, the host stations 101 use a clock synchronized with a one-second pulse signal (hereinafter, 1 pps) acquired using GPS or QZSS to control the FM modulation characteristics, including the timing of FM modulation, so that they are uniform among the multiple host stations 101. GPS is an abbreviation for Global Positioning System. QZSS is an abbreviation for Quasi-Zenith Satellite System, a Japanese quasi-zenith satellite system.

[0022] The relay station 102 is provided to enable listening to programs in areas (hereinafter, hard-of-hearing areas) that cannot be covered by the upper station 101 due to geographical influences, etc. The relay station 102 is placed within the broadcast area A1 of the upper station 101, receives a broadcast signal from the upper station 101, and realizes relay broadcasting by retransmitting it at the same frequency to the broadcast area A2, which includes the hard-of-hearing areas.

[0023] In the following, an area where the broadcast area A1 of the upper station 101 and the broadcast area A2 of the relay station 102 overlap each other is referred to as an overlapping area Ad.

[0024] [1-2. Configuration of the transmitting device] An FM transmitting device 1 constituting the upper station 101 will be described.

[0025] As shown in FIG. 3, the FM transmitting device 1 includes a signal processing unit 2, a transmitting unit 3, a power amplifier 4, and a transmitting antenna 5.

[0026] The signal processing unit 2 may be realized entirely by hardware, or at least a part of it may be realized by processing executed by a microcomputer having a processor 201 and a memory 202 which is a non-transient tangible recording medium. In this case, various functions realized by the microcomputer are realized by the processor 201 executing a program stored in the memory 202 which is a non-transient tangible recording medium.

[0027] The signal processing unit 2 includes an audio signal input unit 21, a pre-emphasis unit 22, a delay adjustment unit 23, a transmission signal generation unit 24, a signal addition unit 26, and an FM modulation unit 27.

[0028] The audio signal input unit 21 inputs, via the connector 20, an audio signal for FM broadcasting that is distributed to each upper station 101 via a predetermined transmission network. The audio signal input unit 21 adjusts the timing of the audio signal based on a clock synchronized to 1 pps so that the synchronization points added to the audio signal are synchronized among the multiple upper stations 101. The timing adjusted here is called inter-station synchronization timing.

[0029] The pre-emphasis 22 amplifies high frequency components of the audio signal in order to correct noise that increases as the frequency increases during FM reception.

[0030] The delay adjustment unit 23 adjusts the delay amount so that the synchronization point added to the audio signal is delayed from the inter-station synchronization timing by a preset adjustment delay time, and outputs the signal. This adjustment delay time is set to be sufficiently longer (for example, 10 ms) than the worst-case transmission delay from the upper station 101 to the relay station 102. The audio signal whose delay has been adjusted by the delay adjustment unit 23 becomes a broadcast signal.

[0031] The transmission signal generating unit 24 amplitude-modulates a 38 kHz carrier wave with the audio signal output from the pre-emphasis 22, and removes the carrier wave component from the modulated signal with a filter, thereby generating a transmission signal.

[0032] The signal adding unit 26 mixes the broadcast signal output from the delay adjustment unit 23 and the transmission signal output from the transmission signal generating unit 24 to generate a monaural composite signal having a spectrum as shown in FIG.

[0033] Also, as shown in Fig. 6, the broadcast signal and the transmission signal included in the higher station wave, which is the broadcast wave transmitted by the FM transmitter 1, are mixed at a timing where the broadcast signal is delayed from the transmission signal by an adjustment delay time. Note that in Fig. 6, the transmission signal is shown not with the waveform of the transmission signal itself, but with the waveform of the audio signal demodulated from the transmission signal, that is, with the same waveform as the audio signal used as the broadcast signal.

[0034] 3, the FM modulation unit 27 calculates an FM modulation degree Δf for each unit period Δt for the transmission signal output from the signal adding unit 26, and calculates an instantaneous phase change Δθ from the FM modulation degree Δf. The FM modulation unit 27 generates an I signal representing the in-phase component of the transmission signal and a Q signal representing the quadrature component, i.e., a transmission IQ signal, from the instantaneous phase change Δθ.

[0035] The transmitter 3 includes a quadrature converter (hereinafter, QMOD) 31, a digital-to-analog converter (hereinafter, D / A converter) 32, a local signal generator 33, a mixer 34, and an amplifier 35.

[0036] The QMOD 31 multiplies the transmission IQ signal generated by the signal processing unit 2 by two carrier signals that are orthogonal to each other, and adds the results to generate an FM modulated transmission signal.

[0037] The D / A converter 32 converts the transmit signal, represented as a sequence of digital values, into an analog signal. In the description of the processing downstream of the D / A converter 32, "signal" means an analog signal.

[0038] The local signal generator 33 generates a local signal LO for up-converting the frequency of the transmission signal.

[0039] Mixer 34 generates a broadcast signal RF by mixing the transmission signal generated by D / A converter 32 and the local signal LO generated by local signal generator 33 and up-converting the frequency of the transmission signal. The broadcast signal RF is a signal in the frequency band (for example, 76 MHz to 108 MHz) used in FM radio broadcasting.

[0040] The amplifier 35 amplifies the broadcast signal RF generated by the mixer 34 and supplies the amplified signal to the power amplifier 4 .

[0041] The power amplifier 4 further amplifies the broadcast signal generated by the transmitter 3 and supplies it to the transmitting antenna 5. The power amplifier 4 is an amplifier that is set according to the size of the broadcast area A1 covered by the upper station 101, and may be connected in multiple stages or may be omitted.

[0042] The transmitting antenna 5 transmits a broadcast wave corresponding to the broadcast signal RF toward the broadcast area A1.

[0043] [1-3. Configuration of FM repeater] The FM repeater device 10 constituting the repeater station 102 will now be described.

[0044] As shown in FIG. 4, the FM repeater 10 includes a receiving antenna 11, a receiving section 12, a relay processing section 13, a transmitting section 14, a power amplifier 15, and a transmitting antenna 16.

[0045] In the following, as shown in FIG. 5, a broadcast wave that arrives directly from the transmission antenna 5 of the FM transmission device 1 (i.e., the upper station 101) to the receiving antenna 11 of the FM repeater 10 (i.e., the relay station 102) is referred to as an upper station wave D. A reproduced broadcast wave transmitted from the transmission antenna 16 of the FM repeater 10 is referred to as a relay wave Dr. Also, the relay wave Dr that goes around from the transmission antenna 16 to the receiving antenna 11 is referred to as a return wave U0 to Un. The return waves U0 to Un are numbered in order of the strength of reception at the receiving antenna 11. Usually, the return wave U0 with the highest reception strength is a direct wave that reaches the receiving antenna 11 directly from the transmission antenna 16. The other return waves U1 to Un are reflected waves that are reflected by some object and reach indirectly. All of the return waves U0 to Un have a waveform that is attenuated and delayed from the relay wave Dr.

[0046] In addition, the FM repeater 10 transmits the broadcast signal reproduced from the transmission signal included in the higher station wave D at the same timing as the timing at which the broadcast signal included in the higher station wave D is received.

[0047] Returning to Fig. 4, the receiving antenna 11 is disposed so as to receive the higher-level station wave D. The receiving antenna 11 may be an omnidirectional antenna or a directional antenna. The higher-level station wave D is an FM-modulated wave that has been FM-modulated by a monaural composite signal.

[0048] The receiving unit 12 includes an amplifier 41, a local signal generator 42, a mixer 43, an A / D converter 44, and a quadrature demodulator (hereinafter, QDEM) 45.

[0049] The amplifier 41 amplifies the signal received from the receiving antenna 11 .

[0050] The local signal generator 42 generates a local signal LO for down-converting the frequency of the received signal supplied from the receiving antenna 11 .

[0051] The mixer 43 mixes the received signal amplified by the amplifier 41 with a local signal LO supplied from a local signal generator 42, thereby down-converting the frequency of the received signal.

[0052] The A / D converter 44 samples the received signal down-converted by the mixer 43 at a preset sampling frequency. In the description of the processing upstream of the A / D converter 44 in the FM repeater 10, the "signal" means an analog signal, and in the description of the processing downstream of the A / D converter 44, the "signal" means a series of digital values. The sampling frequency of the A / D converter 44 is set to about several tens of MHz in order to remove wideband noise components (or broadcast waves of other channels) other than the desired channel (i.e., the band assigned to the broadcast wave D). Specifically, it is set to an integer multiple of the sampling frequency for signal processing, for example, 49.152 MHz. Also, by setting the sampling frequency to an integer multiple of the sampling frequency for signal processing, downsampling, which will be described later, can be performed simply.

[0053] The QDEM 45 performs a Hilbert transform on the received signal to obtain an in-phase component and a quadrature component for each sample value of the received signal, thereby complexifying the received signal. Specifically, the received signal is multiplied by two carrier signals that are orthogonal to each other (i.e., have a phase difference of 90°) to generate an I signal representing the in-phase component and a Q signal representing the quadrature component. The I signal and the Q signal are baseband signals. The I signal and the Q signal may be downsampled to a frequency that covers a band twice or more the FM modulated signal, for example, to 768 kHz, to reduce the number of data, thereby reducing the computation load in the subsequent relay processing unit 13. The sampling frequency for this signal processing may be set to a frequency other than 768 kHz as long as it can sufficiently cover the band of the FM modulated signal.

[0054] Hereinafter, the I signal and the Q signal generated by the receiving unit 12 are collectively referred to as a received IQ signal.

[0055] The relay processing unit 13 extracts a transmission signal from the reception IQ signal generated by the reception unit 12, and demodulates an audio signal from the extracted transmission signal. Furthermore, the relay processing unit 13 generates a broadcast signal by adding a predetermined delay to the demodulated audio signal, and generates an FM modulated I signal and Q signal from a monaural composite signal generated by combining the transmission signal, the broadcast signal, and the transmission wave identification signal. Details of the relay processing unit 13 will be described later. Hereinafter, the I signal and Q signal generated by the relay processing unit 13 are collectively referred to as a transmission IQ signal.

[0056] The transmitting unit 14 includes a QMOD 71, a D / A converter 72, a mixer 73, and an amplifier 74. The QMOD 71, the D / A converter 72, the mixer 73, and the amplifier 74 are similar to the QMOD 31, the D / A converter 32, the mixer 34, and the amplifier 35 in the FM transmitting device 1, and therefore a description thereof will be omitted. However, the mixer 73 up-converts the relay signal using a local signal LO generated by the local signal generator 42 in the receiving unit 12. The local signal LO may be generated by a local signal generator provided separately from the local signal generator 42.

[0057] The power amplifier 15 further amplifies the relay signal generated by the transmitter 14 and supplies it to the transmitting antenna 16. The power amplifier 15 is an amplifier that is set according to the size of the broadcast area A2 covered by the relay station 102, and may be connected in multiple stages or may be omitted.

[0058] The transmitting antenna 16 transmits a relay wave Dr in response to the relay signal toward the broadcast area A2.

[0059] [1-3-1. Relay processing unit] The relay processing unit 13 includes a signal regenerating unit 50 and a loop interference removing unit 60 .

[0060] The functions of relay processing unit 13 may be realized entirely by hardware, or at least a part of them may be realized by processing executed by a microcomputer having processor 131 and memory 132 which is a non-transient physical recording medium. In this case, the various functions realized by the microcomputer are realized by processor 131 executing a program stored in memory 132.

[0061] [1-3-2. Signal playback section] The signal reproducing unit 50 includes a channel filter (hereinafter, CH filter) 51, an FM linear detection unit 52, a filter 53, an audio signal demodulation unit 55, a delay adjustment unit 56, a signal addition unit 57, and an FM modulation unit 58.

[0062] The CH filter 51 extracts, from the received IQ signal supplied from the receiver 12 via the interference remover 60, a signal within a possible frequency range of an FM modulated carrier wave.

[0063] The FM linear detection unit 52 uses the received IQ signal from which unnecessary components have been removed by the CH filter 51 to calculate the phase of the received signal for each preset unit period Δt, and calculates an instantaneous phase change Δθ, which is the difference from the phase calculated in the immediately preceding unit period Δt. The unit period Δt is set to a sampling period Ts, which is the reciprocal of the sampling frequency for signal processing, or an integer multiple thereof. Then, a monaural composite signal including the broadcast signal, the transmission signal, and the transmission wave identification signal is extracted by performing Δf detection, which replaces the calculated instantaneous phase change Δθ with an FM modulation index using a conversion table or conversion formula prepared in advance.

[0064] The filter 53 is configured by, for example, a band-pass filter, and removes the broadcast signal from the monaural composite signal supplied from the FM linear detection unit 52 to extract the transmission signal.

[0065] The audio signal demodulation unit 55 generates a monaural audio signal by demodulating the amplitude-modulated transmission signal. Specifically, the transmission signal is mixed with a signal of 38 kHz (i.e., the frequency of the carrier wave used for the amplitude modulation), and the difference signal between the two signals is extracted as an audio signal by a filter.

[0066] The delay adjustment unit 56 adjusts the delay of the audio signal so that the audio signal demodulated by the audio signal demodulation unit 55 is delayed by the relay delay time from the reception timing of the transmission signal. The relay delay time is a time obtained by subtracting the transmission delay time from the upper station 101 to the relay station 102 from the adjustment delay time, as shown in Fig. 6. In other words, the relay delay time is set so that the broadcast signal included in the upper station wave D and the broadcast signal included in the relay wave Dr are received at the same timing near the relay station 102, which is the overlap area Ad.

[0067] The signal adder 57 mixes the transmission signal extracted by the filter 53 with the broadcast signal, which is a delay-adjusted audio signal, to generate a monaural composite signal.

[0068] The FM modulation unit 58 generates a transmission IQ signal that is FM modulated by the monaural composite signal generated by the signal addition unit 57. The specific operation is similar to that of the FM modulation unit 27 in the FM transmission device 1, and therefore a description thereof will be omitted here.

[0069] [1-3-3. Loopback removal section] The loop interference elimination unit 60 includes a CH filter 61 , a correlation analysis unit 62 , a profile storage unit 63 , an adaptive filter 64 , and a subtractor 65 .

[0070] The CH filter 61 extracts a signal in a frequency range that an FM modulated carrier wave can take, from the transmission IQ signal generated by the signal regenerator 50. The CH filter 61 is a filter similar to the CH filter 51 described above.

[0071] The correlation analysis unit 62 calculates the time axis correlation between the received IQ signal output from the interference removal unit 60 during the interference detection period and the transmitted IQ signal supplied from the CH filter 61. The interference detection period is a period during which the delay time for the transmission signal included in the transmitted IQ signal is 0 to ΔTr. ΔTr is an interference setting time that is set to a value greater than the maximum time required for the relay wave Dr transmitted from the transmitting antenna 16 to be received by the receiving antenna 11 as the interference wave U. The interference setting time ΔTr is set by adjusting the number of taps of the adaptive filter 64, and is set to, for example, about 100 μs.

[0072] The correlation analysis unit 62 cuts out the received IQ signal and the transmitted IQ signal for every preset convolution calculation time To (<ΔTr). Then, during the interference wave detection period 0 to ΔTr, the transmission IQ signal is sequentially delayed by the time of the sampling period Ts, and the received IQ signal for the convolution calculation time To is multiplied by the complex conjugate signal of the transmitted IQ signal to perform convolution calculation. The convolution calculation time To is set to a time in which the signal waveform can be sufficiently identified, for example, about 10 ms to identify an audio signal mainly having a frequency of 100 Hz to several kHz.

[0073] Based on the time axis correlation that is the result of the convolution operation, the correlation analysis unit 62 extracts a maximum correlation value that is the maximum value of the correlation coefficient and a delay time DL (where DL ≠ 0) at which the maximum correlation value is obtained. Then, the correlation analysis unit 62 stores the signal strength A, phase θ, and delay time DL of the delayed wave estimated from the extraction result as a delay profile. The delay profile is stored in the profile storage unit 63, which is a memory whose contents can be rewritten. Hereinafter, the delay profile generated by the correlation analysis unit 62 and stored in the profile storage unit 63 is referred to as the delay profile.

[0074] Moreover, a delay profile generated for each convolution calculation time To is referred to as a generated profile, and a delay profile already stored in the profile storage unit 63 is referred to as an existing profile.

[0075] If there is no existing profile whose delay time DL matches the generated profile, the correlation analysis unit 62 additionally stores the generated profile in the profile storage unit 63. If there is an existing profile whose delay time DL matches the generated profile, the correlation analysis unit 62 updates the content of the existing profile by adding the signal strength A and phase θ of the generated profile to the signal strength A and phase θ of the existing profile.

[0076] As a result of the processing in the correlation analysis unit 62, a plurality of delay profiles with different delay times DL are stored in the profile storage unit 63. The delay profile is information that represents the state of the feedback waves U0 to Un received by the receiving antenna 11.

[0077] The adaptive filter 64 generates a replica IQ signal based on each of the delay profiles stored in the profile storage unit 63. The replica IQ signal is a signal obtained by delaying a transmission IQ signal by a delay time DL based on the delay time DL, signal strength A, and phase θ indicated in the delay profile, adjusting the amplitude based on the signal strength A, and adjusting the phase based on the phase θ. The replica IQ signal is a general term for a replica I signal and a replica Q signal whose phase is different by 90° from that of the replica I signal. Hereinafter, the replica IQ signal generated by the adaptive filter 64 is referred to as a replica IQ signal. The adaptive filter 64 generates replica IQ signals in the same number as the number of delay profiles.

[0078] The subtractor 65 subtracts the replica IQ signal generated by the adaptive filter 64 from the received IQ signal supplied from the receiving unit 12 , and supplies the result to the signal regeneration unit 50 .

[0079] [1-4. Operation] The operation of the system will now be described.

[0080] The FM transmitter 1 transmits a monaural composite signal including a broadcast signal and a transmission signal. The monaural composite signal uses the same band as the stereo composite signal, but since the pilot signal is not superimposed, existing FM radio receivers receive the broadcast wave as an FM monaural broadcast and reproduce the broadcast signal, which is a monaural audio signal. In other words, the transmission signal and the transmission wave identification signal are ignored in the FM radio receiver.

[0081] The signal reproducing unit 50 of the FM relay device 10 extracts a transmission signal from the received monaural composite signal and demodulates the extracted transmission signal to generate an audio signal. The signal reproducing unit 50 also delays the generated audio signal by the relay delay time to generate a broadcast signal, and generates a monaural composite signal by mixing this broadcast signal with the previously extracted transmission signal. The signal reproducing unit 50 then transmits the signal FM-modulated by the generated monaural composite signal as a relay wave Dr.

[0082] The transmission signal included in the relay wave Dr transmitted from the FM repeater 10 is delayed from the transmission signal included in the higher station wave D transmitted from the FM transmitter 1 by the transmission delay from the higher station 101 to the relay station 102. If the processing delay in the FM repeater 10 cannot be ignored, the transmission delay may include the processing delay in the FM repeater 10. Also, the broadcasting signal included in the relay wave Dr transmitted from the FM repeater 10 has the same timing as the broadcasting signal included in the higher station wave D received by the FM repeater 10.

[0083] In the loop interference removal unit 60 of the FM repeater 10, the correlation analysis unit 62 generates a delay profile (i.e., a delay profile) for the loop interference Ui (i=0, 1, ..., n) that is the strongest included in the received IQ signal. Therefore, first, a delay profile for the direct wave U0 is generated and stored in the profile storage unit 63. The adaptive filter 64 generates a replica IQ signal for the direct wave U0 according to the delay profile stored in the profile storage unit 63. The subtractor 65 subtracts the replica IQ signal from the received IQ signal, thereby removing the signal component based on the direct wave U0 from the received IQ signal.

[0084] Next, the loop wave elimination unit 60 performs the same processing on the received IQ signal from which the influence of the direct wave U0 has been eliminated, thereby generating a new delay profile for the reflected wave U1, which has the maximum intensity excluding the direct wave U0. The content of the delay profile stored in the profile storage unit 63 is updated by this newly generated delay profile. The adaptive filter 64 generates replica IQ signals for the direct wave U0 and the reflected wave U1 according to the delay profile stored in the memory. The subtractor 65 subtracts the replica IQ signal from the received IQ signal, thereby eliminating the signal components based on the direct wave U0 and the reflected wave U1 from the received IQ signal.

[0085] Thereafter, by repeating the same process, the signal components based on the interference waves U0 to Un are sequentially removed from the received IQ signal in descending order of reception strength.

[0086] [1-5. Correspondence of terms] In this embodiment, the delay adjustment unit 23 corresponds to an example of the delay unit of the present disclosure, and the delay adjustment unit 56 corresponds to an example of the relay delay unit of the present disclosure. In this embodiment, the signal addition unit 26 corresponds to an example of the mixer of the present disclosure, and the signal addition unit 57 corresponds to an example of the relay mixer of the present disclosure. In this embodiment, the transmission unit 3 corresponds to an example of the higher-level station transmission unit of the present disclosure, and the transmission unit 14 corresponds to an example of the relay transmission unit of the present disclosure. In this embodiment, the reception unit 12 corresponds to an example of the relay reception unit of the present disclosure. In this embodiment, the FM linear detection unit 52 corresponds to an example of the signal extraction unit of the present disclosure, and the audio signal demodulation unit 55 corresponds to an example of the relay demodulation unit of the present disclosure. In this embodiment, the correlation analysis unit 62 corresponds to an example of the profile generation unit of the present disclosure, and the adaptive filter 64 and the subtractor 65 correspond to an example of the suppression unit of the present disclosure. In this embodiment, the replica IQ signal corresponds to an example of the replica signal in the present disclosure.

[0087] [1-6. Effects] According to the embodiment described above in detail, the following effects are achieved.

[0088] (1a) In the FM broadcasting system 100, the FM transmitting device 1 constituting the higher station 101 transmits the higher station wave D that is FM-modulated by a monaural composite signal using the mechanism of FM stereo broadcasting. The monaural composite signal includes a broadcasting signal, which is a monaural audio signal, and a transmission signal, which is an amplitude-modulated signal of the broadcasting signal and is transmitted at an earlier timing than the broadcasting signal. Therefore, the FM repeater device 10 constituting the repeater station 102 can adjust the transmission timing of the broadcasting signal contained in the repeater wave Dr to coincide with the reception timing of the broadcasting signal contained in the higher station wave D by adjusting the delay time of the audio signal demodulated from the transmission signal contained in the higher station wave D. Moreover, such adjustment of the delay time of the broadcasting signal can be realized without making any changes to an existing FM radio receiver or causing a frequency deviation between the higher station wave D and the repeater wave Dr.

[0089] (1b) In the FM repeater 10, a replica IQ signal used to remove signal components based on the interference waves U0 to Un from a received IQ signal is generated from a transmission IQ signal used to generate the repeater wave Dr, that is, a signal that is the source of the interference waves U0 to Un. Therefore, the FM repeater 10 can accurately suppress components based on the interference waves U0 to Un that cause oscillation.

[0090] [1-7. Modifications] In this embodiment, the monaural composite signal includes both a lower sideband signal and an upper sideband signal obtained by amplitude modulating a broadcasting signal. Since the monaural composite signal does not include a pilot signal, the signal in the L-R signal band is not demodulated by an FM radio receiver. Therefore, the broadcasting signal superimposed on this band does not need to be carrier suppression modulated, and for example, as shown in Modifications 1 and 2 of FIG. 7, an SSB (Single Side Band amplitude modulation) signal of only the upper sideband or only the lower sideband may be used. When an SSB modulated signal is used, it is sufficient that either the upper sideband or the lower sideband is included in the range of 23 kHz to 53 kHz, and as shown in Modification 3 of FIG. 7, the carrier frequency may be other than 38 kHz. In addition, the transmission signal is not limited to amplitude modulation, and other modulation methods, for example, digital modulation methods, may be used.

[0091] [2. Second embodiment] [2-1. Differences from the first embodiment] The second embodiment has a basic configuration similar to that of the first embodiment, and therefore differences will be described below. Note that the same reference numerals as those in the first embodiment indicate the same configuration, and the preceding description will be referred to.

[0092] In the first embodiment described above, the monaural composite signal is configured to include a broadcast signal and a transmission signal. In the second embodiment, a signal modulated by SSB as a broadcast signal is used as a transmission signal, and a signal for identifying a transmission wave is superimposed on an unused band among bands corresponding to the LR signals of the stereo composite signal, which is different from the first embodiment.

[0093] Also, a signal processing unit 2a belonging to the FM transmitting device 1 and a signal regenerating unit 50a belonging to the FM repeater 10 are partially configured differently from those in the first embodiment.

[0094] [2-2.Mono composite signal] In the monaural composite signal of this embodiment, a transmission signal and a transmission wave identification signal are superimposed on the band in which the LR signals are superimposed in the stereo composite signal, as shown in configuration example 1 of Fig. 8. For example, the lower sideband is used as the transmission signal, and the transmission wave identification signal is superimposed on 38 kHz to 53 kHz, which was assigned to the upper sideband.

[0095] The transmission wave identification signal is a signal for identifying which upper station 101 or which relay station 102 is the source of the generation of the monaural composite signal, and further the source of the broadcast wave FM-modulated by the monaural composite signal. The transmission wave identification signal is assigned a frequency belonging to an unused frequency band that is not used for broadcast signals and transmission signals, within the band of 0 to 53 kHz of the monaural composite signal. The transmission wave identification signal may be assigned different frequencies to each of the upper station 101 and the relay station 102. The transmission wave identification signal may also be a signal obtained by modulating a carrier wave of a frequency belonging to an unused frequency band by a unique identification number assigned to each of the upper station 101 and the relay station 102.

[0096] As shown in configuration example 2 of Figure 8, the mono composite signal may have the transmission signal centered at 38 kHz, and the transmission wave identification signal may be placed in a band between the broadcast signal and the transmission signal.

[0097] [2-3. Signal processing section of FM transmitter] As shown in FIG. 9, the signal processing unit 2a includes an identification signal adding unit 25 between a transmission signal generating unit 24 and a signal adding unit .

[0098] The identification signal assigning unit 25 assigns a transmission wave identification signal assigned to the FM transmitter 1 to the transmission signal generated by the transmission signal generating unit 24.

[0099] [2-4. Relay processing section of FM relay device] As shown in FIG. 10, the relay processing unit 13a includes a signal regenerating unit 50a and a loop interference removing unit 60. The loop interference removing unit 60 includes a signal regenerating unit 50a and a loop interference removing unit 60.

[0100] The signal regenerator 50 a includes an identification signal assigner 54 between a filter 53 and a signal adder 57 .

[0101] The identification signal assigning unit 54 is configured similarly to the identification signal assigning unit 25 , and assigns a transmission wave identification signal assigned to the FM repeater 10 to the transmission signal supplied from the filter 53 .

[0102] [2-5. Correspondence of terms] In this embodiment, the identification signal assigning unit 25 corresponds to an example of a higher-level station information assigning unit of the present disclosure, and the identification signal assigning unit 54 corresponds to an example of a relay station information assigning unit of the present disclosure.

[0103] [2-6. Effects] According to the second embodiment described above in detail, in addition to the effects (1a) to (1g) of the first embodiment described above, the following effect is also obtained.

[0104] (2a) The monochrome composite signal is superimposed with transmission wave identification information that distinguishes the higher-order station wave D from the relay wave Dr (and thus the return wave U). The transmission wave identification signal exists even during silence when the broadcast signal and transmission signal are at noise level, making it easier to analyze the return wave U and suppressing malfunctions during silence.

[0105] 3. Other embodiments Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments and can be implemented in various modified forms.

[0106] (3a) In the above embodiment, the technique of the present disclosure is applied to the FM broadcasting system 100 constituting an SFN, but may be applied to an FM broadcasting system constituting an MFN. MNF is an abbreviation for Multi-Frequency Network.

[0107] (3b) Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Also, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Also, part of the configuration of the above embodiments may be omitted. Also, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

[0108] (3c) The present disclosure can be realized in various forms, including the FM transmitting device 1, FM repeater device 10, and FM broadcasting system 100 described above, as well as a program for causing a computer to function as the FM transmitting device 1 and the FM repeater device 10, a non-transient physical recording medium such as a semiconductor memory on which this program is recorded, and an FM wave relay method.

Claims

1. An FM transmitter configured to transmit a higher-level station wave FM-modulated by a monaural composite signal; an FM relay device configured to receive the higher-level station wave transmitted from the FM transmitter device and transmit a relay wave FM-modulated by the monaural composite signal reproduced from the higher-level station wave; Equipped with the mono composite signal has a structure in which a broadcast signal which is a mono audio signal is superimposed on the band of the L+R signal in the stereo composite signal, a transmission signal modulated by the broadcast signal is superimposed on the band of the L-R signal in the stereo composite signal, and a pilot signal in the stereo composite signal is omitted; the FM transmitter is configured to generate the mono composite signal by mixing the transmission signal modulated by the mono audio signal with the broadcast signal obtained by delaying the mono audio signal by an adjustment delay time; the FM repeater is configured to generate the monaural composite signal by mixing the transmission signal extracted from the received higher-level station wave and the monaural audio signal demodulated from the transmission signal with the broadcast signal delayed by a relay delay time; the adjustment delay time is set to a time longer than a transmission delay time from the FM transmitter to the FM relay device, The relay delay time is set to a length obtained by subtracting the transmission delay time from the adjustment delay time. FM broadcasting system.

2. 2. The FM broadcasting system according to claim 1, The mono composite signal has a structure in which a transmission wave identification signal indicating the source of the mono composite signal is further superimposed on the band of the L-R signal in the stereo composite signal. FM broadcasting system.

3. 1. An FM transmitting device, comprising: a modulation unit configured to generate a transmission signal modulated by an input monaural audio signal; a delay unit configured to generate a broadcast signal by delaying the monaural audio signal by an adjustment delay time; a mixer configured to mix the transmission signal generated by the modulating unit and the broadcast signal generated by the delay unit to generate a monaural composite signal; an FM modulation unit configured to generate a transmission signal that is FM modulated by the monaural composite signal generated by the mixer; a higher-level station transmitting unit configured to transmit a higher-level station wave based on the transmission signal generated by the FM modulation unit; Equipped with the mono composite signal has a structure in which the broadcast signal is superimposed on a band of an L+R signal in a stereo composite signal, the transmission signal is superimposed on a band of an L-R signal in the stereo composite signal, and a pilot signal in the stereo composite signal is omitted; The adjustment delay time is set to a time longer than a transmission delay time from the transmission of the higher-level station wave to an FM relay device that relays the higher-level station wave. FM transmitter.

4. 4. An FM transmitter according to claim 3, The apparatus further includes a higher-level station information adding unit that adds a transmission wave identification signal for identifying a transmission source of the higher-level station wave to the monaural composite signal. FM transmitter.

5. An FM repeater device, A relay receiving unit configured to receive a higher-level station wave FM-modulated by a monaural composite signal; a signal extraction unit configured to extract a transmission signal from the reception signal received by the relay reception unit; a relay demodulation unit configured to demodulate the transmission signal to generate a mono audio signal; a relay delay unit configured to generate a broadcast signal by delaying the monaural audio signal generated by the relay demodulation unit by a relay delay time; a relay mixer configured to generate the monaural composite signal by mixing the transmission signal extracted by the signal extractor and the broadcast signal generated by the relay delay unit; a relay FM modulation unit configured to generate a relay signal that is FM modulated by the monaural composite signal generated by the relay mixer; A relay transmitting unit configured to transmit a relay wave based on the relay signal generated by the relay FM modulation unit; Equipped with The mono composite signal is a structure in which the broadcast signal is superimposed on a band of an L+R signal in a stereo composite signal, the transmission signal modulated by the broadcast signal is superimposed on a band of an L-R signal in the stereo composite signal, and a pilot signal in the stereo composite signal is omitted; The monaural composite signal included in the higher-level station wave is set so that the broadcast signal is delayed by an adjustment delay time from the transmission signal, The adjustment delay time is set to a time longer than a transmission delay time from an FM transmitter transmitting the higher-level station wave to the FM relay device. The relay delay time is set to a length obtained by subtracting the transmission delay time from the adjustment delay time. FM repeater.

6. 6. An FM repeater according to claim 5, a relay station information adding unit that adds a transmission wave identification signal for identifying a transmission source of the relay wave to the monaural composite signal; FM repeater.

7. 7. An FM repeater according to claim 5 or 6, A profile generating unit configured to calculate a time axis correlation using the relay signal generated by the relay FM modulation unit and the received signal received during a circular wave detection period, and to generate a delay profile that is information including a maximum correlation value that is a maximum value of the time axis correlation, and a delay time of the relay signal with respect to the received signal when the maximum correlation value is obtained; a suppression unit configured to delay the relay signal generated by the relay FM modulation unit by the delay time according to the delay profile and adjust the strength and phase according to the maximum correlation value to generate a replica signal, and to subtract the replica signal from the received signal input to the signal extraction unit; The bypass wave detection period is set to a period from when the relay signal is generated by the relay FM modulation unit to when the bypass setting time has elapsed, using a bypass setting time that is set based on the time required for the relay wave transmitted by the relay transmission unit to be received by the relay reception unit as a bypass wave. FM repeater.