JP2008005373A - Communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication apparatus capable of surely restoring asynchronous data by using an extracted data clock. <P>SOLUTION: A data clock directly extracted from a terminal of a central processing unit is entered into a data clock amplifier 100 to amplify a signal. A frequency lock type transmitter 120 obtains a frequency of a subcarrier. A modulator 130 mixes a data signal amplified by a data signal amplifier 110 with the subcarrier. A modulation signal is inputted to a modulation signal amplifier 140 and then applied to a DBM 160. The DBM 160 modulates a carrier and the signal-amplified subcarrier modulation signal. The modulated signal is power-amplifier by a power amplifier 190 and sent from an antenna. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the technical field to which the present invention belongs, when a digital signal is modulated at a high frequency, the digital signal is transmitted as a radio wave, the digital signal is demodulated by receiving the radio wave, the demodulated digital signal is the same as the digital signal before the high frequency modulation. It belongs to the technical field of a signal correction method for enhancing the performance. In particular, in a radio wave transmitted from a moving wireless facility, it is intended to supplement the change in the carrier frequency due to the Doppler effect and the change in the length of the signal wave, thereby improving the signal reproducibility.

  As a method of performing data communication by modulating a digital signal at high frequency, a synchronous method and an asynchronous method are general methods. The synchronous type uses a high frequency of GHz (gigahertz) band or higher, and is used to send data to a large capacity at a relatively high speed at a line-of-sight distance. On the other hand, the asynchronous type is mainly used in an application field in which small data is simply transmitted, and the carrier frequency is generally 1 GHz or less. Asynchronous mode is characterized by low network characteristics compared to synchronous mode, so the range of application fields is wide. A typical example of the asynchronous mode is the RS232C start-stop mode. The feature of the start mode is that it recognizes the start bit and captures the data between the start bit and the stop bit. However, since the data clock is not sent in the start mode, there is spike noise in the signal wave. When mixed, it was difficult to determine whether the waveform was noise or signal.

For this reason, a method of transmitting the same signal a plurality of times, a method of transmitting a code for determining whether data is correct or not, and the like are generally performed (see Patent Document 1). In any case, the number of transmissions and the transmission time are increased, and when this wireless device is driven by a battery, the battery life is shortened. Similarly, there is a method to determine the data clock period of the data transmitted from the preamble and use this value as the data clock value, but it was not possible when the wavelength of the radio wave changed due to the Doppler effect or fading. .
JP 2004-72288 A

  The purpose of the present invention is to modulate a data clock with data at high frequency and send it as a radio wave to the receiving side. The receiving side takes out the data clock from the radio wave and reliably restores it using the data clock from which asynchronous data is taken out. Make things a challenge. A specific problem is the method.

  When two different signals are subjected to high frequency modulation, generally used binary FSK or OOK high frequency modulation methods cannot be used. That is, a modulation method that emits a plurality of radio waves at the same time, for example, a telephone-type modulation method is required. However, when two different digital signals are modulated by the telephone-type modulation method, it is necessary to modulate each digital signal into an audio signal having a different wavelength and then input it to the telephone-type modulator. In addition, when two different audio signals are modulated simultaneously, there is a problem that the signal is predicted to be distorted by intermodulation, and the structure of the radio apparatus itself becomes complicated in order to suppress the intermodulation distortion. Accordingly, there is a problem of efficiently transmitting two signals while suppressing the complexity of the wireless device.

  Further, when there is a legal restriction on output by sending two signals, the high-frequency output of each signal is halved compared to the case of sending one signal. When the output is halved, a problem arises that the communication distance is shortened as compared with the case of sending one signal. Therefore, sending two signals without reducing the communication distance becomes a problem.

  The communication device of the present invention converts the data clock of the central processing circuit into a sine wave, and multiplies the sine wave to use it as a subcarrier. Then, a modulated wave obtained by modulating the baseband data converted into the serial format with the subcarrier is used as data. The modulated wave may be modulated by a single side band modulation by modulating the modulated wave to a frequency used for transmission, performing wireless communication at the modulated high frequency.

  The communication device of the present invention includes a detection circuit that detects the high frequency and extracts the subcarrier and data. The communication device of the present invention divides the subcarrier extracted by detection and converts it to a square wave and uses it as a data clock.

  The communication device of the present invention demodulates the baseband data using the data clock.

  The communication device of the present invention is capable of transmitting a data clock and data in the same frequency band while using a modulation circuit having a general modulation system. A wireless device with a structure that sends data and data clock at different frequencies is found, but it is affected by fading due to different frequencies, and in the room the signal is physically amplified and attenuated due to the difference in frequency due to wall reflection. In order to improve the situation, it is necessary to use a large-scale device such as a diversity antenna. However, by performing modulation and detection using the method of the present invention, a wireless device can be made smaller and cheaper.

  In carrying out the present invention, the data transfer rate was set to 500 bps (bits per second). This value is 250 Hz when converted to frequency. However, when data is wirelessly installed, the reception efficiency can be increased by reducing the sideband width of the data as much as possible. In the present invention, Manchester code conversion is performed, and the converted data is modulated into subcarriers. A frequency lock type transmission circuit was used as a circuit for transmitting a subcarrier synchronized with the period of the data clock from the data clock, and the frequency was 500 times the data transfer frequency. That is, the frequency of the subcarrier is 250 kHz. Further, the desired carrier frequency for modulating the signal modulated by the subcarrier is 315 MHz.

  A transmission circuit for transmitting data and a data clock in this embodiment will be described. FIG. 1 is a schematic diagram for explaining a transmission circuit. FIG. 1 shows a signal shape that changes when the circuit block passes through the circuit block. Input from a central processing unit (not shown) that controls data is the data itself and the data clock. Data is converted from parallel format to serial format using UART (Universal Asynchronous Receiver Transmitter). In recent years, since the UART is mounted in the central processing unit, the internally mounted UART is used in this embodiment. The data clock taken directly from the terminal of the central processing unit is put into the data clock amplifier 100 to amplify the signal. The frequency lock type oscillator 120 measures the interval between the change point from 1 to 0 of the input digital signal and the next change point from 1 to 0, and generates a sine wave with the measured interval as a half cycle. This is a transmission circuit that multiplies a sine wave by 500 times to obtain a subcarrier frequency (see FIG. 2). Next, the data signal amplified by the data signal amplifier 110 and the subcarrier are put into the modulator 130 and mixed. The modulation here is simple amplitude modulation. Here, since the frequency of the subcarrier is 250 KHz and the data speed is 500 bps, that is, 250 Hz, when the data is simply amplitude-modulated, the frequency band occupied by the primary sideband of the modulated wave is 250 KHz. ± 250 Hz. In the Manchester method, since data 1 is converted into 10 and data 0 is converted to 01, there are two possibilities of 1 and 1 or 0 and 0 continuing. However, the number of data in Manchester conversion for 1 bit of basic data is 2 bits. Therefore, it means twice the basic data, that is, 500 Hz. Since 500 Hz is a frequency when data of 1 and 0 come alternately, when the data arrangement becomes 00 or 11, it becomes a frequency of 250 Hz, which is half of 500 Hz. This means that the width of the first sideband of the Manchester conversion data modulated by the subcarrier is 250 Hz from 250 Hz to 500 Hz up and down from the center of the subcarrier. When this condition is applied to the bandpass filter 150 of FIG. 1, referring to FIG. 3, the lower limit of the cut frequency of the bandpass filter 150 is the subcarrier frequency 250 KHz-250 Hz, and the upper limit is the subcarrier frequency. 250 KHz + 500 Hz. In this example, an RC type high-pass filter was used in combination with an RC type passive blow pass filter. Here, since the frequency filter has a skirt characteristic, the actual cut frequency was increased by 50 Hz on the low-pass filter side to 250.55 KHz and increased by 50 KHz on the high-pass filter side to 249.80 KHz.

  Next, since the signal passed through the passive filter was attenuated, it was applied to the DBM 160 after entering the modulation signal amplifier 140.

  In this example, since the DBM 160 with an amplifier circuit was commercially available, an integrated type (TA7320P manufactured by Toshiba Corporation) was used. The carrier wave 315 MHz is transmitted in one stage using a PLL (phase lock loop) type transmitter 170. This carrier wave and the sub-carrier modulated signal that has been amplified are input to the DBM 160 for modulation. The output of the DBM 160 has a waveform in which the carrier wave 315 MHz is suppressed from the normal amplitude modulator output of 315 MHz. The circuit of FIG. 1 after the signal amplification circuit is similar to a telephone-type single sideband transmitter. The telephone-type single sideband transmitter handles voice, so when modulating using the DBM160, the modulation frequency is once modulated at a frequency around 9 MHz with good modulation efficiency and stability, and then the desired frequency while multiplying. In general, the signal handled in the present invention is a digital signal, that is, it is only necessary to be able to determine 1 or 0, and a carrier wave having a desired frequency for the purpose of downsizing the apparatus. Direct modulation at 315 MHz.

  Here, a method of suppressing unnecessary portions of the signal modulated by the DBM 160 by the crystal filter 180 will be described with reference to FIG. The modulation output of the DBM 160 has a target sideband waveform with respect to the frequency at which the carrier wave exists. Although the output of the DBM 160 can be directly amplified and emitted from the antenna, it is disadvantageous to noise because the frequency occupancy is wide and a wide frequency band must be received during reception. Therefore, a method was adopted in which one unnecessary one was suppressed and the remaining one was amplified twice.

  As the crystal filter 180, a 7-element ladder type was used. Since it is a very common crystal filter 180, it was used for the purpose of reducing availability and price. Finally, the modulated wave that has passed through the crystal filter 180 is amplified by the power amplifier 190 and transmitted from the antenna. When the signal waveform sent out from the antenna is expressed by taking the frequency on the horizontal axis, it appears to be a 3AH waveform in the form of a carrier wave and a sideband on one side, or a radio wave form, but the signal wave corresponding to the subcarrier is data As the clock fluctuates, its width changes in the frequency direction.

  Next, a method of receiving the radio wave emitted from the antenna in FIG. 1, detecting the received radio wave to extract the data clock component and data, and comparing the data clock component and the extracted data to extract accurate data will be described. To do.

  FIG. 5 is a schematic diagram showing a receiving circuit. The radio wave input from the antenna is first suppressed by the band pass filter 500. In this embodiment, the band pass filter 500 using SAW (surface acoustic wave element) is used, and the pass band is ± 1 MHz with respect to 315 MHz. Next, the radio wave that has passed through the band pass filter 500 is amplified by a high frequency amplifier circuit 510 and applied to a DSM (double balance modulator) 520. In this case, since the DBM 520 functions as a demodulator, it is demodulated as a single sideband signal. In this case, the PLL oscillator 530 generates the same frequency as that of the carrier wave, that is, a high frequency of 315 MHz. This is so-called zero carrier wave detection. On the output side of the DBM 520, the 1 kHz signal wave modulated by the 250 kHz subcarrier and the subcarrier appears on the higher frequency side than the subcarrier. Further, the output signal of DBM 520 is detected by envelope detection 540. The envelope detection 540 is a circuit composed of a diode, a resistor, and a capacitor. First, a circuit that rectifies an input wave with a diode and separates a carrier wave and a modulated signal wave with the time constant of a resistor and a capacitor. Therefore, the signal wave and the subcarrier can be separated by passing the output signal of the DBM 520 through the envelope detection 540.

  Next, the subcarrier is shaped into a square wave for use as a slicer signal. Since the subcarrier is rectified by the envelope detection 540, the subcarrier is a simple circuit that becomes 1 when the threshold set by the subcarrier shaper 550 is exceeded and becomes 0 below the threshold. Since the subcarrier has a frequency 500 times that of the data clock, the subcarrier is frequency-divided by using the frequency divider 570 in order to obtain an appropriate signal as a slicer. In this embodiment, 10 slices are appropriate values for each data bit, and the output of the subcarrier shaper 550 is divided by 50. During this time, the data signal wave demodulated by the envelope detection 540 is applied to the signal slice circuit via the delay circuit and the amplifier circuit 560 in order to synchronize with the slicer. Next, the divided slicer signal is applied to the signal slicing circuit 580 to slice the demodulated data signal. The sliced result is applied to the signal comparison circuit 590, and the signal wave is extracted as a square wave. The extracted signal is amplified by a signal amplifier 600.

  FIG. 6 shows the relationship between the three signals, the slice signal, the demodulated data signal, and the output signal of the signal comparator. The waveform of the data signal extracted by the envelope detection 540 suppresses all sidebands except for the first sideband on the USB (upper sideband) side when the data signal is modulated on the subcarrier on the transmission side. Therefore, the data waveform after the envelope detection 540 has a sine wave shape. In the signal comparison circuit 590, whether the value of the sliced data signal exceeds the threshold value is compared, and thereafter, a logical OR is performed between the slicer signals to determine 1 or 0. FIG. 6 shows an ideal case. Since the actual waveform is disordered, the results of performing 10 slices are rarely the same. In this case, 1 or 0 of the data signal bit is determined based on an empirical rule. In the case of this example, when 60% or more had the same value, that value was taken as the result for the 10 slices.

  The present invention is effective as a method for discriminating noise from a signal in a noisy environment or when a signal is attenuated and approaches a noise level. As a place with a high noise level, a place with a lot of machinery such as a factory, a vicinity of a power line, etc. can be raised. Examples of cases where the signal is attenuated include cases where the communication distance is long and transmission power is low.

Schematic diagram of transmitter circuit Frequency lock transmitter Characteristics of bandpass filter Characteristics of crystal filter Schematic diagram of receiver circuit Slicer signal, data signal wave and signal comparison output

Explanation of symbols

100 Data clock amplifier 110 Data signal amplifier 120 Frequency lock type oscillator 130 Modulator 140 Modulation signal amplifier 150, 500 Band pass filter 160, 520 DBM
170, 530 PLL transmitter 180 Crystal filter 190 Power amplifier 510 High-frequency amplifier 540 Envelope detection 550 Subcarrier shaper 560 Delay circuit and amplification circuit 570 Frequency division 580 Signal slice circuit 590 Signal comparison circuit 600 Signal amplification

Claims (7)

A communication device that converts a data clock of a central processing circuit into a sine wave and multiplies the sine wave to use it as a subcarrier. The communication device according to claim 1, wherein a modulation wave obtained by modulating baseband data converted into a serial format with the subcarrier is used as data. The communication apparatus according to claim 2, wherein the modulated wave modulates the modulated wave to a frequency used for transmission and performs wireless communication at the modulated high frequency. The communication apparatus according to claim 3, wherein the modulated wave is performed by single-sideband modulation. 5. The communication device according to claim 3, further comprising a detection circuit that detects the high frequency and extracts the subcarrier and data. 5. The communication device according to claim 4, wherein the subcarrier extracted by detection is frequency-divided and then converted into a square wave and used as a data clock. The communication device according to claim 6, wherein baseband data is demodulated by the data clock.

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