JP2011166227A - Communication system and synchronization establishing method of communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system for communicating a packet in a comparatively small data amount with high efficiency to a monitoring and control system where a punctuality of a data transmission and reception is required. <P>SOLUTION: A transmitter transmits preamble data in synchronization with a period prior to a transmission of a data frame transmitted per predetermined period. A receiver matches a reception timing and the transmission period of the transmitter by receiving the preamble data, and receives the data frame transmitted in synchronization with the period. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a communication system for communicating data, and a synchronization establishment method for the communication system.

In general, a wireless LAN standardized by IEEE 802.11, a wireless PAN standardized by IEEE 802.15, and the like are known as networks for transmitting and receiving data.
As shown in FIG. 5, a transmitter that performs wireless communication based on the specifications of such a wireless network includes a reference oscillator that oscillates a predetermined frequency, a carrier oscillator that inputs the output of the reference oscillator and generates a wireless carrier wave, and this carrier wave. It comprises a modulator that modulates a radio carrier wave generated by an oscillator with transmission data and outputs modulation data, and an amplifier that amplifies the modulation data output from the modulator and transmits it via an antenna. That is, the radio carrier wave generated by the carrier wave oscillator is modulated by the modulator using the transmission data, and the modulated modulation data is amplified by the amplifier, fed to the antenna, and radiated as a radio wave to the radio line.
In addition, a signal transmitted from the transmitter is input to the receiver via an antenna. The receiver amplifies the input signal (reception signal) with an amplifier, and the mixer frequency-converts the amplified reception signal using a radio carrier wave output from a carrier wave oscillator. The gain control unit that inputs the output of the mixer controls the gain of the amplifier so that the signal amplitude to the demodulator (that is, the mixer output) reaches a predetermined level. Similarly, a timing detector that inputs the output of the mixer detects the demodulation timing of the received signal and activates the demodulator. Based on this activation, the demodulator demodulates the received signal and outputs received data.

A data communication method between a transmitter and a receiver configured in this way is generally transmitted by adding a code string (bit synchronization signal) called a preamble to the beginning of transmission data when the transmitting station transmits data, The receiver is configured to detect reception of the preamble to match reception timing (bit sampling timing) and receive data following the preamble (see, for example, Patent Document 1).
The invention described in Patent Document 1 is configured to receive an input signal including a preamble and data, and to detect the preamble in two stages. In this way, the detection of the preamble is accelerated, and as a result, the preamble can be detected even if the preamble length is short. This is intended to shorten the preamble by devising the receiving circuit.
As described above, the structure of the frame transmitted and received with the preamble added at the beginning of the data is composed of the header part for storing the address and communication speed and the payload part for storing the information (data body) to be transmitted and received. Has been. In general, this frame is transmitted with a preamble added (FIG. 6).

JP 2007-124618 A

By the way, in recent years, studies are being made to apply wireless communication to industrial uses for monitoring and control of plants and factories. Most of the data handled in such industrial applications is control data for controlling input / output devices and state data input via sensors. For this reason, the amount of data transmitted and received between stations, not limited to radio, can be relatively small. For example, the amount of data transmitted / received between stations is often only a few tens of bytes including information such as addresses.
Further, an industrial system that handles data as described above is required to have a fixed data refresh cycle (control cycle) (refresh data within a predetermined time), that is, real-time performance and high reliability. For example, assuming a system in which data is updated by sequentially transmitting / receiving data from one terminal to several terminals, when transmission / reception of all the terminals is completed in 1 ms, the data transmission / reception time allocated to one terminal is less than 100 μs. It is desirable to be.
However, although the wireless communication speed in the above-mentioned IEEE 802.11 is 54 Mbps at the maximum, the minimum 10 μs is spent for transmitting the preamble. Therefore, when the IEEE802.11 communication specification is applied to a system with a relatively small amount of data as described above, the problem is that the length of the frame (effective data) is relatively small with respect to the length of the preamble. There was a problem of poor communication efficiency.

In the IEEE802.11 communication specification, the maximum preamble transmission time is 192 μs. In such a case, since it exceeds 100 μs only by transmitting the preamble, it is difficult to apply the IEEE802.11 communication specification to a system that requires real-time performance as described above.
The present invention has been made in view of the above-described problems, and its object is to provide a highly efficient packet with a relatively small amount of data for a monitoring / control system that requires punctuality of data transmission / reception. It is an object of the present invention to provide a wireless communication system that communicates with each other and a synchronization establishment method for the communication system.

In order to achieve the above-described problem, a communication system according to claim 1 of the present invention is a communication system having a transmitter for transmitting data at predetermined intervals and a receiver for receiving data transmitted from the transmitter. The transmitter transmits the preamble data according to the cycle prior to transmitting the data every cycle, and the receiver adjusts the reception timing by receiving the preamble data and then transmitted by the transmitter every cycle. It is characterized by receiving data.
The communication system according to claim 2 is the communication system according to claim 1, wherein the transmitter generates a transmission timing for each predetermined period, and a storage means for outputting data according to the transmission timing. And a preamble storage means for storing the preamble data in the storage means, and a transmission means for transmitting the preamble data stored in the storage means by the preamble storage means and outputted from the storage means in accordance with the transmission timing. .
The communication system according to claim 3 is the communication system according to claim 1, wherein the receiver generates reception timing having a period equal to the period, and when the preamble data is received, according to the reception. It is characterized by comprising reception timing correction means for matching reception timing and reception means for receiving data according to the reception timing corrected by the reception timing correction means.

The communication system according to claim 4 includes a master station and a slave station, and transmits and receives data at a predetermined cycle. The master station generates a transmission timing at a predetermined cycle. First storage means for outputting data in accordance with the transmission timing, preamble storage means for storing preamble data in the storage means prior to data exchange, and stored in the first storage means by the preamble storage means And a preamble transmission means for transmitting the preamble data output from the first storage means according to the transmission timing, and the slave station sends response data for responding to the preamble data transmitted from the master station to the second storage means. Response data storage means for storing, and second storage means by this response data storage means Characterized in that it comprises a response data transmission means for transmitting upon receipt of the preamble data transmitted the stored response data from the master station.
A synchronization establishment method according to claim 5 is a method for establishing synchronization between a master station and a slave station of a communication system having a master station and a slave station, and transmitting and receiving data at a predetermined cycle. Prior to transmission / reception, preamble data is transmitted to the slave station according to the cycle. When the slave station receives the preamble data, the slave station transmits a response frame in response to the preamble data to the master station, and the master station receives the response frame. Thus, synchronization with the slave station is established.

  The synchronization establishment method according to claim 6 is a synchronization establishment method between the master station and the slave station of the communication system according to claim 5, wherein synchronization completion information is added to the response frame, and the master station completes synchronization. The transmission of preamble data toward the slave station is repeated every period until a response frame to which information is added is received.

According to the present invention, the transmitter is configured to transmit the preamble data in synchronization with the predetermined period prior to transmitting the data every predetermined period. On the other hand, the receiver adjusts the reception timing to the transmission cycle of the transmitter by receiving the preamble data, and the receiver is configured to receive data frames transmitted at predetermined intervals by the transmitter.
Therefore, according to the present invention, since the reception timing of the receiver is matched with the transmission timing of the transmitter in advance prior to the transmission of the data frame by the transmitter, the preamble attached to the head of the data frame becomes unnecessary. Therefore, since the present invention does not need to add a preamble when transmitting a data frame, high-efficiency wireless communication is possible, especially while maintaining a highly efficient and punctuality of a packet with a relatively small amount of data. Can communicate.

1 is a block diagram of a wireless transmitter and a wireless receiver according to Embodiment 1 of the present invention. 3 is a transmission timing chart of the wireless transmitter according to the first embodiment of the present invention. It is a block diagram of the radio | wireless transmitter / receiver which concerns on Example 2 of this invention. It is a transmission / reception timing chart of a radio | wireless transmitter / receiver according to Example 2 of this invention. It is a block diagram of the conventional radio transmitter and radio receiver. It is a figure which shows the structure of the conventional preamble.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings of FIGS. These drawings are for explaining an embodiment of the present invention, and the present invention is not limited by these drawings. Further, the same components are denoted by the same reference numerals.

FIG. 1 is a configuration diagram according to the first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a transmitter that transmits data to a wireless line. Reference numeral 15 denotes a reference oscillator that oscillates at a predetermined frequency. Reference numeral 14 denotes a carrier oscillator that receives the output of the reference oscillator 15 and generates a radio carrier wave. Reference numeral 13 denotes a modulator that modulates a radio carrier wave with transmission data obtained through the buffer 11 and outputs modulated data. Reference numeral 16 denotes an amplifier that amplifies the modulation data output from the modulator 13 and transmits the modulation data to the radio line via the antenna 10.
Reference numeral 12 denotes a transmission timing generation unit that inputs the output of the reference oscillator and outputs the transmission timing every predetermined period, and can be easily realized by a counter or the like. This transmission timing is given to the buffer 11.
Transmission data is sequentially stored in the buffer 11 so as not to cause an underrun. The buffer 11 sequentially outputs the transmission data stored in the buffer 11 to the modulator 13 in accordance with the transmission timing. That is, the buffer 11 is a FIFO buffer, and the transmission data stored in the buffer is sequentially output to the modulator in synchronization with the transmission timing.
As described above, the transmitter 1 wirelessly transmits the transmission data stored in the buffer 11 at each transmission timing. The transmission data handled in this embodiment is preamble data or a data frame described later.

The transmission data is sequentially stored in the buffer 11 by a control processor (not shown) or the like. For example, when transmitting the preamble data, the preamble data having a predetermined bit pattern is set in the buffer 11 by the preamble storage means executed by the control processor. The preamble data set in this way is transmitted in synchronization with the transmission timing.
In FIG. 1, reference numeral 2 denotes a receiver that receives data from a wireless line. A reference oscillator 24 oscillates at a predetermined frequency. The oscillation frequency of the reference oscillator 24 is equal to the oscillation frequency of the reference oscillator 15 provided in the transmitter 1. Reference numeral 23 denotes a carrier wave oscillator that receives the output of the reference oscillator 24 and generates a radio carrier wave. The frequency of this radio carrier wave is equal to the frequency generated by the carrier wave oscillator 14 provided in the transmitter 1.
Subsequently, 21 is an amplifier that amplifies and outputs a received signal input via the antenna 20 under the control of a gain control unit 25 described later. A mixer 22 converts the frequency of the received signal obtained via the amplifier 21 using a radio carrier wave. A gain control unit 25 receives the output of the mixer 22 and controls the gain of the amplifier 21 so that the amplitude of the signal to the demodulator 27 becomes appropriate. A timing detection unit 26 receives the output signal of the mixer 22, detects the demodulation timing of the received signal, and activates the demodulator 27. Reference numeral 27 denotes a demodulator that demodulates a received signal and outputs received data based on activation from the timing detection unit 26.

In this way, the receiver 2 frequency-converts the received signal received via the antenna 20 by the mixer 22, and the reception timing detector 26 detects the demodulation timing of the received signal based on the frequency-converted signal. Then, the demodulator 27 is activated, and the demodulator 27 demodulates the received signal according to the demodulation timing.
Based on such a configuration, data output from the transmitter 1 is transmitted in a frame as shown in FIG. In FIG. 2, the time axis flows from left to right, and P1, P2,... Pn are preamble data. D1, D2 and D3 are data frames in which a header such as address information and a data body (payload) to be originally transmitted / received are stored. T is a transmission interval time of a frame transmitted at each transmission timing generated by the transmission timing generation unit 12, and a constant period of 1 ms is maintained. In this example, the frame transmission interval is made to coincide with the control cycle (data update cycle between terminals). The preamble data and the data frame have the same length.
In this example, each data length is 50 bytes. For example, if the modulation rate is 10 Mbps, the time for transmitting each frame is 40 μs.
Similarly, the movement of the transmitter 1 and the receiver 2 will be described with reference to FIG. In FIG. 2, the transmitter 1 transmits preamble data a plurality of times every period T prior to the transmission of the data frame. For this number of times, a number for completing the reception timing detection of the timing detection unit 26 of the receiver 2 and the gain control of the gain control unit 25 may be transmitted. Subsequently, the transmitter 1 transmits a data frame in synchronization with the period T.

On the other hand, the receiver 2 receives the frame (FIG. 2) transmitted by the transmitter 1. The reception timing detection unit 26 provided in the receiver 2 receives the output of the reference oscillator 24 and generates a reception timing signal having a period T. This is achieved by a counter or the like, and this counter is configured to output a reception timing signal in a preset state. The reception timing detection unit 26 configured as described above constantly monitors whether the received data is preamble data.
When detecting the preamble data, the reception timing detection unit 26 presets a counter in accordance with this detection. A reception timing signal is output simultaneously with the presetting of the counter. In this way, the reception timing signal is corrected in synchronization with the detection of the preamble data, and the period T is maintained until new preamble data is detected. That is, the reception timing detection unit 26 adjusts the reception timing to the transmission timing of the transmitter 1 by detecting the preamble data and correcting the reception timing signal. Thereafter, the reception timing is kept synchronized with the transmission timing of the transmitter 1. Therefore, if the receiver captures the data frame according to the corrected reception timing, the data frame can be normally received.

Further, the gain control unit 25 controls the gain of the amplifier 21 so that the signal amplitude to the demodulator 27 is appropriate for each reception timing output by the reception timing detection unit 26. Since this control is gradually executed every time the preamble data is received, the control is continued until a predetermined number of preamble data is received and an appropriate gain is obtained. When an appropriate gain is obtained and the gain control is completed, the gain control unit 25 outputs an enable signal for enabling the demodulation function to the demodulator 27. Thereafter, the demodulator 27 can appropriately demodulate the data frame.
Since the synchronization between the transmitter and the receiver is thus established, the synchronization is maintained, so that the data frame transmitted every period T is sent to the receiver 2 without adding a preamble to the head of the data frame. Received. Therefore, a preamble is not required when data frames are transmitted and received, and highly efficient wireless communication is possible.
Since the carrier wave and transmission data of the transmitter 1 are generated using a common clock source (reference oscillation 15), synchronization between the carrier wave and the transmission data is always ensured.
At this time, the coherence time obtained from the Doppler shift, which is the speed of fluctuation of the characteristics of the wireless channel, is sufficiently long with respect to the data transmission / reception cycle. When the radio is fixed, the fading speed (Doppler shift) generated by the movement of the radio is defined by the moving speed of the reflecting object of the radio wave existing around. Also, the coherence time is calculated by the reciprocal of the Doppler shift.

For this reason, for example, when the radio carrier frequency is 2.4 GHz and the moving speed of the reflector is 4 km / h (about the moving speed of a person), the Doppler shift is about 200 Hz and the coherence time is 5 ms. If the coherence time is 5 ms with respect to the frame transmission interval time of 1 ms, it is an allowable time in which the characteristics of the wireless line do not vary greatly, and therefore communication can be performed while maintaining synchronization between the transceivers.
When considering the relationship between the coherence time and the radio communication cycle (frame transmission interval time), the radio channel characteristics at time t can be represented by the frequency response h (f, t). In general, if the interval between any two times t1 and t2 is within the coherence time, it can be considered that h (f, t1) = h (f, t2). For this reason, if the frame transmission interval is shorter than the coherence time, the radio channel characteristics do not change. That is, if a frame shorter than the frame transmission interval time is transmitted, the wireless channel characteristics do not change.

FIG. 3 is a configuration diagram according to the second embodiment of the present invention. 3 and 1 denoted by the same reference numerals have the same functions. In FIG. 3, reference numeral 3 denotes a transceiver that communicates data bidirectionally via a wireless line. The output of the reference oscillator 15 is input to each of the carrier wave oscillator 14, the transmission timing generation unit 32, and the reception timing detection unit 26. SW31 is switching means such as a selector. The transmitter / receiver 3 communicates with other transmitters / receivers by switching the transmission band and the reception band when the SW 31 is switched by the transmission / reception switching signal. Reference numeral 30 denotes an antenna.
The transmission timing generation unit 32 divides the clock of the reference oscillator 15 by a counter and outputs the transmission timing every period T, so that the transmission timing is output based on the signal from the reception timing detection unit 26. It has become. That is, the transmission timing output from the transmission timing generation unit 32 is a signal obtained by ORing the counter output and the signal from the reception timing detection unit 26.
The transceiver 3 transmits the transmission data stored in the buffer 11 through the modulator 13 and the amplifier 16 according to the transmission timing generated by the transmission timing generation unit 12. At this time, the data path is selected so that the SW 31 supplies the transmission data to the antenna 30. Further, at the time of reception, the data path is selected so that the SW 31 outputs a signal received from the antenna to the amplifier 21. In this way, the transceiver 3 performs wireless communication by selecting either the transmission or reception data path by the SW 31.

FIG. 4 is a diagram showing transmission / reception between a master and a slave in a system configured such that one master and a plurality of (n) slaves communicate via a wireless line. A transmitter / receiver 3 is applied to each of the master and the slave.
As described above, the master transmits the preamble data P1 stored in the buffer 11 in synchronization with the transmission timing. The slave that has received the preamble data P1 outputs the reception timing by the reception timing detection unit 26, and the transmission timing generation unit 32 that has received the reception timing gives the transmission timing to the buffer 11. In synchronization with the transmission timing given to the buffer 11, the slave responds P1 ′ to the master. That is, P1 ′ is response data, and P1 ′ is stored in the buffer 11 by response data storage means executed by a control processor (not shown). The response data stored in this manner is transmitted when the preamble data is received from the master station.
At this time, the SW 31 switches the data path according to the reception timing so as to transmit the transmission data. At this time, the master is configured not to transmit data in response to the slave response by setting or the like. Thereafter, the master sequentially transmits preamble data to the slave every period T, and the slave responds to the preamble data. When the master transmits preamble data to all slaves and receives a response from the slave, it determines that synchronization has been established. Thereafter, the master transmits a data frame to the slave, and the slave transmits a response to the data frame.

The slave is configured to store and transmit synchronization completion information indicating completion of synchronization control and gain control in the response to the master for the preamble data, and the master receives a response including the synchronization completion information from the slave. If it is configured to continue transmitting preamble data to the slave, it is possible to establish more reliable wireless communication (wireless link).

1 Transmitter 2 Receiver 3 Transceiver 4 Transmitter (Conventional)
5 Receiver (conventional)
10, 20, 30, 40, 50 Antenna 11 Buffer 12 Transmission timing generator 13 Modulator 14 Carrier oscillator 15 Reference oscillator 16 Amplifier 21 Amplifier 22 Mixer 23 Carrier oscillator 24 Reference oscillator 25 Gain controller 26 Reception timing detector 27 Demodulator 31 selector 32 transmission timing generator

Claims (6)

In a communication system having a transmitter that transmits data at predetermined intervals and a receiver that receives data transmitted from the transmitter,
The transmitter is
Prior to sending data every cycle, sending preamble data according to the cycle,
The receiver
A communication system comprising: receiving the preamble data; and adjusting the reception timing to the period, and then receiving the data transmitted by the transmitter for each period. The communication system according to claim 1,
The transmitter is
Transmission timing generation means for generating transmission timing for each predetermined period;
Storage means for outputting data according to the transmission timing;
Preamble storage means for storing the preamble data in the storage means;
A communication system comprising: transmission means for transmitting the preamble data stored in the storage means by the preamble storage means and output from the storage means in accordance with the transmission timing. The communication system according to claim 1,
The receiver
Reception timing generating means for generating a reception timing having a period equal to the period;
Reception timing correction means for adjusting the reception timing according to the reception when the preamble data is received;
A communication system comprising receiving means for receiving the data in accordance with the reception timing corrected by the reception timing correcting means.


A communication system having a master station and a slave station and exchanging data every predetermined cycle,
The master station
Transmission timing generation means for generating transmission timing for each predetermined period;
First storage means for outputting data according to the transmission timing;
Preamble storage means for storing the preamble data in the storage means prior to sending and receiving the data;
Comprising preamble transmission means for transmitting the preamble data stored in the first storage means by the preamble storage means and output in accordance with the transmission timing from the first storage means;
The slave station
Response data storage means for storing response data for responding to preamble data transmitted from the master station in a second storage means;
A communication system comprising response data transmission means for transmitting the response data stored in the second storage means by the response data storage means when receiving the preamble data transmitted from the master station. . A method for establishing synchronization between a master station and a slave station in a communication system that has a master station and a slave station and exchanges data every predetermined cycle,
The master station
Prior to sending and receiving the data, the preamble data is transmitted to the slave station according to the cycle,
When the slave station receives the preamble data, it transmits a response frame responding to the preamble data to the master station,
The master station establishes synchronization with the slave station by receiving the response frame, and establishes synchronization between the master station and the slave station. A method for establishing synchronization between a master station and a slave station of the communication system according to claim 5,
Synchronization completion information is added to the response frame,
The master station and the slave station for establishing synchronization, wherein the master station repeats transmission of the preamble data to the slave station every cycle until receiving a response frame to which the synchronization completion information is added.

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