JP3732766B2 - Multi-channel digital broadcast pseudo signal generator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a multi-channel digital broadcast pseudo signal generator for generating a digital broadcast pseudo signal in order to confirm the transmission performance of terrestrial digital broadcast waves.
[0002]
[Prior art]
Terrestrial Integrated Services Digital Broadcasting (ISDB-T) is scheduled to start in 2003 in Kanto, Kinki and Chukyo, and in other regions by 2006. .
[0003]
For this reason, studies and development of devices that support transmission of terrestrial digital broadcast waves are already underway for devices for hearing aids, CATV transmission devices, TV receivers, and the like. For example, the transmission path must transmit a plurality of terrestrial digital broadcast signals, and the receiver must receive a plurality of terrestrial digital broadcast signals and normally receive a target wave. For this reason, finally, it is necessary to confirm the performance of terrestrial digital broadcast wave transmission performance by actually receiving and transmitting a plurality of terrestrial digital broadcast waves, and a signal simulating the radio wave emission situation after the start of terrestrial digital broadcast is required.
[0004]
The following three methods are currently conceivable for generating a plurality of terrestrial digital broadcast waves that simulate the radio wave emission situation after the start of terrestrial digital broadcast.
(1) Prepare multiple digital terrestrial broadcast modulators.
[0005]
(2) As shown in FIG. 7, the output of one terrestrial digital broadcast modulator (OFDM (Orthogonal Frequency Division Multiplex) modulator) 31 is set by a plurality of RF converters (frequency converters) 32, respectively. Convert to channel frequency and output.
[0006]
(3) Receive the digital terrestrial test broadcast from the Tokyo Pilot Experiment Council, convert it to multiple frequencies with multiple frequency converters, and output it.
[0007]
[Problems to be solved by the invention]
Although the confirmation test of the terrestrial digital broadcast wave transmission performance can be performed by the above three methods, there are the following problems.
The method (1) is most ideal, but it is very expensive because a plurality of actual broadcast modulators are used.
In the method (2), the output of one terrestrial digital broadcast modulator 31 is frequency-converted by a plurality of RF converters 32, so that the output signal is a plurality of synchronized signals of the same spectrum, that is, symbol timing and modulation. It becomes exactly the same signal until the terrestrial digital broadcasting starts, and it differs from the actual radio wave emission situation, and the test according to the actual situation cannot be performed.
Since the method (3) receives radio waves emitted in the air, there are problems such as different stability and C / N ratio (Carrier to Noise ratio) depending on the location.
[0008]
The present invention has been made to solve the above-described problems, and is a multi-channel digital broadcast pseudo signal generator that can be configured at low cost and can generate a multi-channel digital broadcast pseudo signal in accordance with an actual situation. The purpose is to provide.
[0009]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a multi-channel digital broadcast pseudo signal generation device that generates an OFDM signal and an IF frequency signal that conforms to the specifications of digital terrestrial broadcasting in accordance with a synchronization clock generated based on an externally synchronized external reference signal. A plurality of OFDM signal generators that convert, process and output the signals, and IF frequency signals output from the plurality of OFDM signal generators by a synchronization clock generated based on the external synchronization reference signal a plurality of RF converters for converting and outputting the, characterized in that comprising a plurality of RF mixers for outputting from one output terminal by mixing OFDM signal of multi-channel output from the RF converter.
[0010]
As described above, an OFDM signal conforming to the terrestrial digital broadcasting specification is generated by a plurality of OFDM signal generators and converted to an IF frequency signal, and each IF frequency signal is set to a frequency of a set channel by an RF converter. After being converted to, a digital broadcast pseudo signal with a different waveform can be generated for each channel by mixing with an RF mixer and outputting from one output terminal, and a multi-channel digital broadcast pseudo signal that matches the actual situation can be generated. Can be generated. Moreover, the structure is simple and can be manufactured at low cost.
[0011]
The multi-channel digital broadcast pseudo signal generator according to the second invention generates an OFDM signal conforming to the specifications of terrestrial digital broadcast, converts the OFDM signal into an IF frequency signal according to a synchronization clock, and outputs the signals. An OFDM signal generator, an IF distributor that distributes signals of IF frequency output from the plurality of OFDM signal generators, and a plurality of OFDM signal generators are provided corresponding to the OFDM signal generators and distributed by the IF distributor A plurality of RF converters that convert a signal of IF frequency converted to a frequency of a set channel by a synchronous clock and output the mixed signal and a multi-channel OFDM signal output from the RF converter and output from one output terminal comprising a vessel, a plurality of OFDM signal generation unit, as a synchronization clock, external synchronization reference And to that generated by arbitrarily switching the synchronous clock that is generated by the oscillator of the clock generation unit provided for each channel by items, the IF distributor, IF inputted from the respective OFDM signal generating unit A first mode in which a signal of a frequency is output to a corresponding RF converter as it is, and a second mode in which an output signal of any one OFDM signal generator connected to the input terminal is selected and distributed to all RF converters Mode, wherein the first mode and the second mode are switched by mode switching means.
[0012]
As described above, the IF distributor has the first and second operation modes, and the operation mode can be switched to the mode switching means, so that the output mode of the digital broadcast pseudo signal can be set to plural, CATV transmission paths and receiver tests can be performed with high accuracy and efficiency by simulating radio wave emission conditions after the start of digital broadcasting.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the overall configuration of a multi-channel digital broadcast pseudo signal generator according to an embodiment of the present invention. FIG. 1 shows an example in which a 10-channel digital broadcast pseudo signal is generated.
[0014]
In FIG. 1, reference numerals 1-1 to 1-10 denote OFDM signal generators, to which a 10 MHz clock is input as an external synchronization reference signal. The OFDM signal generators 1-1 to 1-10 generate a predetermined operation clock based on an external synchronization reference signal or a 10 MHz clock oscillated by an internal oscillation element, and synchronize with this operation clock to generate an OFDM (Orthogonal Frequency). Division Multiplex (orthogonal frequency division multiplexing) signal is generated, converted to an IF frequency centered at 37.15 MHz, for example, and output. An OFDM signal is a signal in which symbols modulated with random data are repeatedly output in conformity with ISDB-T (Terrestrial Integrated Services Digital Broadcasting) specifications for mode, guard interval, and modulation method. . Details of the OFDM signal generators 1-1 to 1-10 will be described later.
[0015]
The OFDM signal output from the OFDM signal generators 1-1 to 1-10 after being converted to the IF frequency is sent to the RF converters 4-1 to 4-10 via the IF distributor 2. The IF distributor 2 includes a first mode in which each IF signal input from the OFDM signal generators 1-1 to 1-10 is directly output to the corresponding RF converters 4-1 to 4-10, and one input signal. For example, it includes a second mode in which an IF signal input from the OFDM signal generator 1-1 is selected and distributed to all the RF converters 4-1 to 4-10. The mode and the second mode can be arbitrarily switched.
[0016]
Further, the 10 MHz external synchronization reference signal and the channel setting signal are input to the RF converters 4-1 to 4-10. Although not shown, the RF converters 4-1 to 4-10 include a clock generation unit and an oscillation element that generates a 10 MHz clock such as a crystal resonator. The clock generator generates a necessary synchronization clock by arbitrarily switching between a 10 MHz clock by the internal oscillation element and a 10 MHz external synchronization reference signal inputted from the outside.
[0017]
The RF converters 4-1 to 4-10 operate in synchronization with the synchronous clock generated by the internal clock generation unit, and the IF signal output from the IF distributor 2 is set to the frequency of the designated channel based on the channel setting signal. And input to the RF mixer 5. The RF mixer 5 mixes the OFDM signals of the respective channels output from the RF converters 4-1 to 4-10, and outputs the mixed signals from one output terminal via one cable 6.
[0018]
Channel setting in the RF converters 4-1 to 4-10, that is, the frequency of a carrier wave of cable television broadcasting using a frequency from 90 MHz to 770 MHz is from 93 MHz to 767 MHz, for example, 93 MHz, 99 MHz, 105 MHz,. ..., 767 MHz, and a frequency set at an interval of 6 MHz are selected and shifted to a frequency higher by 1/7 MHz (= 142.857... KHz) than that frequency. The frequency band used by the standard system for digital broadcasting is 5.6 MHz. Note that the RF converters 4-1 to 4-10 can switch between a frequency defined by the enforcement regulations of the Cable Television Broadcasting Law and a frequency not adding 1/7 MHz.
[0019]
FIG. 2 shows the allowable range of the modulated wave spectrum of the carrier wave. With respect to the carrier frequency, the relative attenuation at ± 2.79 MHz is 0 dB, the relative attenuation at ± 2.86 MHz is −20 dB, the relative attenuation at ± 3.00 MHz is −27 dB, and the relative attenuation at ± 4.36 MHz is It is −50 dB.
[0020]
Next, the detailed configuration of the OFDM signal generators 1-1 to 1-10 will be described with reference to FIG. FIG. 3 shows the configuration of the OFDM signal generator 1-1, but the other OFDM signal generators 1-2 to 1-10 have the same configuration.
[0021]
In FIG. 3, reference numeral 11 denotes an arbitrary waveform generator, which receives a 4 × 512/63 MHz (32.507936... MHz) clock from the clock generator 12. The arbitrary waveform generation unit 11 generates an address for the waveform bank unit 13 in synchronization with the clock, reads out waveform data from the waveform bank unit 13 based on the address, stores the waveform data in the high-speed internal memory, and stores the data in the internal memory. The read waveform data is repeatedly read and output to the IF converter 14 at the next stage.
[0022]
The clock generation unit 12 includes an oscillation element 17 that generates a 10 MHz clock, such as a crystal resonator, and arbitrarily switches between the clock of the oscillation element 17 and an external synchronization reference signal of 10 MHz input from the outside. Can be used.
[0023]
Based on the 10 MHz external synchronization reference signal or the output signal of the oscillation element 17, the clock generation unit 12 has a clock of 4 × 512/63 MHz (32.507936... MHz) and 512/63 + 37.15 MHz (45.276984... MHz). Generates a clock, inputs a 4 × 512/63 MHz (32.507936... MHz) clock to the arbitrary waveform generation unit 11, and locally oscillates a 512/63 + 37.15 MHz (45.276984... MHz) clock to the IF converter 14. Input as a signal.
[0024]
The waveform bank unit 13 includes a plurality of memories, for example, 16 EPROMs, and digital broadcast pseudo signal waveform data, that is, OFDM (Orthogonal Frequency Division Multiplex) signals are registered in advance in each EPROM. The OFDM signal registered in each EPROM is composed of a plurality of symbols modulated with random data in conformity with ISDB-T (Terrestrial Integrated Services Digital Broadcasting) specifications for the mode, guard interval, and modulation method. ing. Details of the method of generating the OFDM signal registered in each EPROM will be described later. Further, different waveform data are registered in the 16 EPROMs in the waveform bank section 13 and can be selected by 16 waveform selection buttons provided on the front panel section 15.
When the waveform selection button on the front panel unit 15 is operated, the corresponding EPROM is selected, and the waveform data registered in advance is read by addressing the EPROM by the arbitrary waveform generation unit 11.
[0025]
The arbitrary waveform generation unit 11 stores the waveform data read from the waveform bank unit 13 in a high-speed internal memory, and then repeatedly reads out the waveform data from the internal memory, sequentially performs D / A conversion, and performs a center frequency of 512/63 MHz (8.1269985). ... (MHz) signal is generated and input to the IF converter 14. The IF converter 14 receives a signal having a center frequency of 512/63 MHz (8.1269985... MHz) input from the arbitrary waveform generator 11 and a local oscillation frequency 512/63 + 37.15 MHz (45.276984... MHz) from the clock generator 12. Is converted to an IF frequency (intermediate frequency) centered on 37.15 MHz and output to the IF distributor 2.
[0026]
FIG. 4 shows a method for generating an OFDM signal to be registered in each EPROM of the waveform bank unit 13. In FIG. 4, reference numeral 21 denotes a random data generation / mapping means for generating random data using a random function of numerical calculation software, for example. Further, the random data generating / mapping means 21 performs, for example, QPSK modulation or QAM modulation with the random data and outputs it as a carrier of a digital broadcast pseudo signal. This carrier is output as complex data (Re: real number, Im: imaginary number).
[0027]
The carrier output from the random data generation / mapping means 21 is output as complex time waveform data by an inverse Fourier transform (IFFT) means 22.
[0028]
After the time waveform is generated by the inverse Fourier transform means 22, the rear end portion of the OFDM symbol is added as a card interval to the front end of the OFDM symbol by the guard interval adding means 23. By adding this guard interval, the spectrum of the OFDM signal is widened, so the spectrum limiting means 24 removes the out-of-band spectrum by the digital LPF.
[0029]
The signal from which the out-of-band spectrum has been removed by the spectrum limiting means 24 is upsampled to a quadruple frequency by the quadruple upsampling means 25 and taken out through the quadruple upsampling filter 26. This is a process for finally obtaining a signal having a center frequency of 512/63 MHz (8.126985... MHz).
[0030]
The quadrature upsampling filter 26 output signal is orthogonally modulated by the orthogonal modulation means 27 to obtain an OFDM signal (time waveform) having a center frequency of 512/63 MHz (8.126985... MHz). The quadrature modulation means 27 uses the sin and cos signals as local oscillation frequency signals and performs quadrature modulation. With respect to the signal after the quadrature modulation, the spectrum limiting means 28 removes the out-of-band spectrum, takes it out as a final OFDM time waveform signal, and stores it in the waveform bank unit 13.
[0031]
In the generation of the OFDM signal, the random data generation / mapping means 21 or the like sets OFDM parameters in accordance with ISDB-T, generates a plurality of types of waveform signals, and a plurality of EPROMs provided in the waveform bank unit 13. Register with. Therefore, an arbitrary waveform can be selected by selecting EPROM.
[0032]
The OFDM parameter based on ISDB-T is
Carrier modulation method: DPQSK, QPSK, 16QAM, 64QAM,
Number of carriers: Mode 1: 1405, Mode 2: 2809, Mode3: 5617,
Guard interval: 1/32, 1/16, 1/8, 1/4,
It has become. The number of symbols is “31 symbols” when the guard interval is 1/32 in Mode 1 and “6 symbols” when the guard interval is 1/4 in Mode 3.
[0033]
The OFDM signal to be registered in the waveform bank unit 13 does not have to be completely compliant with ISDB-T. For example, the characteristics of the amplitude characteristics can be obtained by conforming to ISDB-T with respect to Mode, FFT period, modulation method, and guard interval length. Is made the same as the OFDM signal of ISDB-T.
[0034]
FIG. 5 shows an example of parameter setting when 12 types of patterns are generated as OFDM signals to be registered in the EPROM of the waveform bank unit 13. That is, 12 types of signal patterns are set by combining 3 types of modes (Mode 1 to Mode 3), 2 types of carrier modulation schemes (QPSK, 64QAM), and 2 types of guard intervals (1/32, 1/4). .
[0035]
If a 4 Mbit memory is used as the EPROM in the waveform bank section 13, an OFDM signal (Mode 1, guard interval 1/32) can be output in 31 symbols.
[0036]
Next, the overall operation of the above embodiment will be described with reference to FIG.
In the multi-channel digital broadcast pseudo signal generator shown in FIG. 1, when the operation mode of the IF distributor 2 is switched to the first mode by the mode selector switch 3, as shown in FIG. The OFDM signals (IF frequency signals) output from the generators 1-1 to 1-10 pass through the IF distributor 2 and are sent to the corresponding RF converters 4-1 to 4-10 as they are. At this time, when the operation of each clock generator 12 (see FIG. 3) of the OFDM signal generators 1-1 to 1-10 is switched to the operation based on the 10 MHz clock output from the oscillation element 17, each OFDM signal generator 1 -1 to 1-10 output an OFDM signal having an independent spectrum and timing that are not related to each other in an asynchronous state.
[0037]
The OFDM signals output from the OFDM signal generators 1-1 to 1-10 are sent to the corresponding RF converters 4-1 to 4-10 via the IF distributor 2 and converted to the frequency of the set channel. The Then, the signals of the channels output from the RF converters 4-1 to 4-10 are mixed by the RF mixer 5 and sent to the circuit under test or the device under test via the single cable 6. .
[0038]
Therefore, in the case of FIG. 6A, 10 digital independent digital broadcast pseudo signals are output in an asynchronous state. In this case, the RF converters 4-1 to 4-10 generate the synchronization clock using the external synchronization reference signal of 10 MHz in the internal clock generation unit, or the 10 MHz output from the internal oscillation element. A synchronous clock may be created using a clock.
[0039]
Next, when the operation mode of the IF distributor 2 is switched to the second mode by the mode changeover switch 3, the IF distributor 2 has one input signal, for example, an OFDM signal generator 1 as shown in FIG. -1 is selected and distributed to all RF converters 4-1 to 4-10. The RF converters 4-1 to 4-10 each convert the same OFDM signal distributed by the IF distributor 2 into the frequency of the setting channel. Then, the signals of the channels output from the RF converters 4-1 to 4-10 are mixed by the RF mixer 5 and sent to the circuit under test or the device under test via the single cable 6. .
[0040]
As described above, in the case of FIG. 6B, the OFDM signal output from one OFDM signal generator 1-1 is selected by the IF distributor 2 and distributed to the RF converters 4-1 to 4-10. Therefore, digital broadcast pseudo signals having the same spectrum and timing are output from the RF converters 4-1 to 4-10. In this case, the RF converters 4-1 to 4-10 generate the synchronization clock using the external synchronization reference signal of 10 MHz in the internal clock generation unit, or the 10 MHz output from the internal oscillation element. A synchronous clock may be created using a clock.
[0041]
Next, the operation mode of the IF distributor 2 is switched to the first mode by the mode selector switch 3, and the OFDM signal generators 1-1 to 1-10 and the RF converters 4-1 to 4-10 are externally connected to 10 MHz. When the circuit is switched to operate in synchronization with the synchronization reference signal, the circuit is in the connection state shown in FIG.
[0042]
In FIG. 6 (c), OFDM signal generators 1-1 to 1-10 generate OFDM signals having independent spectra and timings, and having synchronized frequencies, that is, frequencies having an orthogonal relationship. The OFDM signals output from the OFDM signal generators 1-1 to 1-10 are distributed by the IF distributor 2 to the corresponding RF converters 4-1 to 4-10. The RF converters 4-1 to 4-10 operate in synchronization with the external synchronization reference signal of 10 MHz, and receive the OFDM signals transmitted from the OFDM signal generators 1-1 to 1-10 via the IF distributor 2. Convert to the frequency of each setting channel.
[0043]
As a result, the RF converters 4-1 to 4-10 output digital broadcast pseudo signals having independent spectrums and timings and synchronized in frequency (in an orthogonal relationship). Then, the signals of the channels output from the RF converters 4-1 to 4-10 are mixed by the RF mixer 5 and sent to the circuit under test or the device under test via the single cable 6. .
As described above, in the case of FIG. 6C, 10 independent digital broadcast pseudo signals can be output in a synchronized state.
[0044]
As shown in the above embodiment, the operation mode of the IF distributor 2 is switched by the mode selector switch 3, and the external synchronization in the OFDM pseudo signal generators 1-1 to 1-10 and the RF converters 4-1 to 4-10 is performed. By switching between the reference signal and the output signal of the internal oscillation element, basically three types of signal output modes can be selected, and the radio wave emission situation after the start of terrestrial digital broadcasting can be simulated. As a result, the CATV transmission line and receiver can be tested with high accuracy and efficiency.
[0045]
In the above embodiment, the case of generating a digital broadcast pseudo signal of 10 channels has been described as an example, but any other number of channels can be set.
[0046]
【The invention's effect】
As described above in detail, according to the present invention, an OFDM signal conforming to the specifications of digital terrestrial broadcasting is generated and converted into an IF frequency signal by a plurality of OFDM signal generation units, and each IF frequency signal is further converted into an IF frequency signal. After converting to the frequency of the setting channel with the RF converter, mixing with the RF mixer and outputting from one output terminal, the structure is simple and can be manufactured at low cost, and digital broadcast pseudo signals with different waveforms for each channel can be produced. It is possible to generate a multi-channel digital broadcast pseudo signal that matches the actual situation. In addition, by configuring the IF distributor so that the operation mode can be switched, the digital broadcast pseudo signal output mode can be set to a plurality, and the radio wave emission situation after the start of terrestrial digital broadcasting can be simulated to The receiver can be tested with high accuracy and efficiency.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of a multi-channel digital broadcast pseudo signal generator according to an embodiment of the present invention.
FIG. 2 is a view showing an allowable range of a modulated wave spectrum of a carrier wave in the same embodiment.
FIG. 3 is an exemplary block diagram showing a detailed configuration of an OFDM signal generator in the embodiment;
FIG. 4 is a view showing a method for generating an OFDM signal to be registered in a waveform bank unit in the same embodiment.
FIG. 5 is a diagram showing a parameter setting example of an OFDM signal registered in a waveform bank unit in the same embodiment.
FIG. 6 is an operation explanatory diagram when the operation mode of the IF distributor is switched in the embodiment;
FIG. 7 is a diagram showing an example of creating a conventional terrestrial digital broadcast signal.
[Explanation of symbols]
1-1 to 1-10 ... OFDM pseudo signal generator 2 ... IF distributor 3 ... mode selector switches 4-1 to 4-10 ... RF converter 5 ... RF mixer 6 ... cable 11 ... arbitrary waveform generator 12 ... clock Generating unit 13 ... Waveform bank unit 14 ... IF converter 15 ... Front panel unit 17 ... Oscillating element 21 ... Random data generating / mapping unit 22 ... Inverse Fourier transform unit 23 ... Guard interval adding unit 24 ... Spectrum limiting unit 25 ... 4 Double upsampling means 26... 4 times upsampling filter 27... Quadrature modulation means 28.

Claims (4)

A plurality of OFDM signal generators for generating an OFDM signal conforming to the specifications of terrestrial digital broadcasting in accordance with a synchronization clock generated based on an external synchronization reference signal inputted externally , converting the signal into an IF frequency signal, and processing and outputting the signal; A plurality of RF converters for converting the signals of the IF frequency output from the plurality of OFDM signal generators into a frequency of a setting channel by a synchronization clock generated based on the external synchronization reference signal, and the plurality of RFs A multi-channel digital broadcast pseudo signal generator comprising an RF mixer that mixes multi-channel OFDM signals output from a converter and outputs the mixed signals from one output terminal. The plurality of OFDM signal generation units and the plurality of RF converters are provided for each channel of the plurality of OFDM signal generation units and the plurality of RF converters as synchronization clocks generated by the external synchronization reference signal. The multi-channel digital broadcast pseudo signal generator according to claim 1, wherein a clock generated by an oscillation element of the generated clock generator is arbitrarily switched to be a synchronous clock . A plurality of OFDM signal generators that generate OFDM signals conforming to the specifications of digital terrestrial broadcasting, convert the OFDM signals to IF frequency signals according to the respective synchronization clocks, and output the signals, and output from the plurality of OFDM signal generators An IF distributor for distributing a signal of IF frequency and a plurality of OFDM signal generators are provided, and the IF frequency signal distributed by the IF distributor is converted to a frequency of a set channel by a synchronization clock. A plurality of RF converters that output and an RF mixer that mixes multi-channel OFDM signals output from the RF converter and outputs the mixed signals from one output terminal;
The plurality of OFDM signal generation units, as the synchronization clock, the one generated by the external synchronization reference signal and the one generated by the oscillation element of the clock generation unit provided for each channel is arbitrarily switched to a synchronization clock,
The IF distributor includes a first mode in which a signal having an IF frequency input from each of the OFDM signal generators is directly output to a corresponding RF converter, and any one OFDM signal generator connected to an input terminal. And a second mode in which the output signal is selected and distributed to all RF converters, and the first mode and the second mode are switched by mode switching means. Generator. The plurality of RF converters can be arbitrarily switched between a clock generated by an external synchronization reference signal and a clock generated by an oscillation element of a clock generation unit provided for each channel as the synchronization clock. 4. The multi-channel digital broadcast pseudo signal generator according to 3.

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