JP3073666B2 - Preamble synchronous communication system using preamble for transmitting additional information - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system for synchronizing using preamble data (hereinafter, simply referred to as preamble).

[0002]

2. Description of the Related Art In mobile communication, for example, the distance between a base station and a mobile station changes every moment as the mobile station moves, or various fadings including Rayleigh fading cause reception at both stations. The electric field strength decreases.
Alternatively, in general communication systems, it often happens that sufficient communication quality cannot be ensured due to interference caused by transmission waves from other stations. Today, effective countermeasures against such defects are required.

[0003] However, once the received electric field strength becomes low or a strong interference wave is generated, an error is detected in the control signal itself for avoiding the error by error detection or the like, and the information is discarded. . As described above, under the low reception electric field strength or the interference wave of the strong reception, the control signal cannot sufficiently play its role, and as a result, control for re-establishing the communication link is performed for communication of information data such as voice. Call had to be made beforehand and the call was interrupted.

[0004]

SUMMARY OF THE INVENTION In view of the above, the present invention provides a communication system capable of maintaining a good communication quality by coping with a decrease in received electric field strength and occurrence of an interference wave. With the goal.

[0005]

A communication system according to the present invention transmits transmission data including preamble data in a first communication station, receives the transmission data in a second communication station, and synchronizes using the preamble data. Communication system, wherein the first communication station communicates during a call.
And detecting at least two communication states, forming the preamble data in the first pattern when detecting one of the communication states, and different from the first pattern when detecting the other of the communication states. The preamble data is formed in a second pattern, and the second communication station performs an operation corresponding to one of the communication states when the preamble data has the first pattern, and the preamble data is transmitted in the second pattern. When the pattern has the pattern No. 2, the operation corresponding to the other of the communication states is performed so that
The operation for maintaining good communication quality at the second communication station side.
It is characterized by performing a work .

[0006]

According to the preamble synchronous communication system using the preamble having the information adding function of the present invention, during a call
In the first communication station, at least two communication states are detected. When one communication state is detected, preamble data is formed in a first pattern, and when the other communication state is detected, the first pattern is formed. Preamble data is formed by a second pattern different from the pattern. In the second communication station, the transmission data from the first communication station is received, and when the preamble data in the transmission data has the first pattern, an operation corresponding to one communication state is performed, and the preamble data is transmitted. Has the second pattern, the operation corresponding to the other communication state is performed. You
That is, to maintain good communication quality on the second communication station side
Operation, for example, channel shift, increase of transmission power, etc.
Is performed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. First, the present invention is applied to a communication system that synchronizes using a preamble, and FIG. 1 shows a practical example of transmission data in a time series generated in such a system and a preamble arranged in the transmission data. Is shown.

In FIG. 1, for example, in a period called a frame, a transmission time zone allocated to a transmission system (or a reception time zone allocated to a reception system) includes a pilot signal, a preamble, and data (speech or the like). ) Is divided into a predetermined number of time slots for storing main information data). In the one time zone, the pilot signal, the preamble, and the data are stored in the time slots at the specified positions. The preamble is stored near the beginning of one transmission / reception time zone, and is stored continuously in seven time slots from the first pilot signal to the next pilot signal.

The pilot signal, preamble and data are subjected to modulation as shown in FIG. 2, for example. FIG.
Is 16QAM (Quadrature Amplitude Modulation)
Shows the signal point constellation when transmission data is generated, and 16 values (“0” to “1”) that one sample of transmission data can take with the in-phase component I and the quadrature component Q as orthogonal axes.
5 ") on the rectangular coordinates.

According to this, the 16 signal points are arranged in a grid, and the transmission data of each value is subjected to modulation processing so that the distance between the signal points is relatively long. Also, specific values advantageous for use in the preamble include “0”,
“2”, “8”, and “10” are given. These values are characterized in that the amplitude of the modulated signal is large and the phase difference between them is large. As the pattern actually used for the preamble, as shown by the inward arrow in FIG.

(I) "0" → "0" → "2" → "10"
It is stored in the time slot allocated to the preamble in FIG. 1 in the order of “10” → “8” → “0”. This pattern is a result obtained by calculation, and each specific value is selected so that the maximum detection gain is obtained when the preamble is detected in the receiving system (so that the autocorrelation coefficient becomes the maximum). , Combined or arranged.

Here, since the practical modulation and demodulation constellation is two-dimensional, the preamble pattern obtained as a result of the calculation as shown in (i) above always has the same self-phase relation as the pattern formed in the reverse order. Will have a number. That is, the pattern formed by being arranged in the direction opposite to the arrangement direction of the above (i) is, as shown by the outward arrow in FIG.

(Ii) “0” → “0” → “8” → “1”
0 ”→“ 10 ”→“ 2 ”→“ 0 ”, and in the part“ “8” → “10” → “10” → “2” ”, each specific value in the arrangement direction opposite to (i) Are lined up. Since (ii) also has the largest autocorrelation coefficient, it is possible to carry a preamble as in the case of the pattern (i).

Focusing on such characteristics, in the present invention, (i)
(Forward pattern) is treated as a preamble pattern in the first communication state, and the pattern (ii) (reverse pattern) is treated as a preamble pattern in the second communication state. If the preamble pattern is switched for each communication state and transmitted based on such a purpose, the receiving system only needs to perform the discrimination processing of both patterns without sacrificing the detection gain at all (that is, the characteristics of the amplitude and the phase). , "0", "2", "8", "1"
Without using a value other than "0"), it is possible to know which state the communication state is in.

In the following, a TDMA (Time Division Multiple Access) communication apparatus according to an embodiment of the present invention will be described in more detail. FIG.
Shows the configuration of such a communication device. In FIG. 3, antenna 1 is an antenna for both transmission and reception, and has a TD
The D (Time Division Duplex) method is adopted. The terminal of the antenna 1 is connected to one of the receiving unit 3 and the transmitting unit 4 via the antenna switch 2. In this example, the antenna switch 2 sets the connection with the receiving unit 3 to a steady state.

In the receiving section 3, a high-frequency signal, which is a signal received by the antenna 1 and received through the antenna switch 2, is band-limited by a band-limiting filter (BPF) 5 and supplied to a high-frequency amplifier 6. The signal amplified by the high frequency amplifier 6 is supplied to the down converter 8 via the band limiting filter 7. The down converter 8 performs frequency conversion for mixing the supplied high frequency signal with the local oscillation signal from the VCO 9 to generate an intermediate frequency signal. This intermediate frequency signal is digitized by an A / D converter 10 and then supplied to a DSP (digital signal processor) 11.

The DSP 11 detects the supplied digitized intermediate frequency signal. That is, in order to detect a baseband signal such as a voice signal and a control signal included in the received signal, the digitized intermediate frequency signal is subjected to, for example, the above-described 16QAM demodulation processing to obtain demodulated data. Supply. The DSP 11 also tests, on a bit-by-bit (or sample-by-bit) basis, whether or not a preamble pattern has arrived in the received signal together with the demodulation process. This verification processing is achieved by comparing the patterns (i) and (ii) previously stored in the DSP 11 with the demodulated data obtained by sequentially performing the demodulation processing. Then, whether the demodulated data matches one of the two patterns, or (i), (i)
When the autocorrelation coefficient of the pattern i) substantially coincides with the autocorrelation coefficient of demodulated data obtained by sequentially demodulating, the arrival of the preamble is detected, and frame synchronization is established. Channel coding logic circuit 12
Indicates that the demodulated data from the DSP 11 is transmitted to the CPU for each frame.
19, the communication data in the demodulated data is transmitted to the voice CODEC (codec) 21 or the data input / output interface 22.
The control data in the demodulated data is transferred to the CPU 19. This time slot decomposition in the channel coding logic circuit 12 involves an operation as a decoder for decoding demodulated data. The data transferred to the voice CODEC 21 is converted into an analog signal there, and is output as sound from a speaker 26 through a speaker amplifier 24. If the communication data is voice data, the data is supplied to the voice CODEC 21. If the communication data is not voice data, the data is supplied to the data input / output interface 22.

On the other hand, the analog audio signal from the microphone 25 is transmitted through the microphone amplifier 23 to the voice CO.
It is supplied to the DEC 21. The voice CODEC 21 digitizes the supplied audio signal in a predetermined format to generate a digital audio signal, and supplies the digital audio signal to the channel coding logic circuit 12 as communication data. The channel coding logic circuit 12 is further supplied with a digital signal of a predetermined format from the data input / output interface 22 as communication data. The channel coding logic circuit 12 transmits communication data from the voice CODEC 21 or the data input / output interface 22 to the CP.
It is inserted into the time slot specified by U19. The insertion into the time slot involves an operation as a coder that performs a predetermined code conversion. The output data of the channel coding logic circuit 12 thus obtained is the DSP1
Transferred to 1. The DSP 11 inserts one of the patterns shown in (i) and (ii) into a predetermined time slot in the frame as a preamble pattern according to the designation from the CPU 19, and transmits a series of data together with the transfer data from the channel coding logic circuit 12. While forming transmission data, for example, the above-described 1
A modulation process based on 6QAM is performed. The data obtained by the modulation processing is supplied to the transmission unit 4.

The transmitting section 4 converts the data received from the DSP 11 into an analog signal at the D / A converter 13 and supplies the analog signal to the up-converter 14. The up-converter 14 mixes the supplied signal with an oscillation signal from the VCO 15 and frequency-converts the mixed signal to a frequency to be transmitted. The frequency-converted signal is amplified by the pre-amplifier 16, further power-amplified by the power amplifier 17, supplied to the antenna 1 via the antenna switch 2, and radiated.

The modulation and demodulation processing of the DSP 11 is performed by a CPU.
(Central processing unit) 19. The switching operation of the antenna switch 2, the oscillation frequencies of the VCOs 9 and 15, and the amplification operation of the power amplifier 17 are controlled by the operation state of the DSP 11. The CPU 19 controls the DSP 11 in response to an operation from the keyboard 20, and controls the channel coding logic circuit 12 and the voice CODEC 21.
Each operation mode is controlled.

Such a configuration is based on a base station (or a master station).
And the mobile station (slave station), the communication form between the two stations is as follows. 4, 3
Fig. 3 shows a communication mode of the multiplex TDMA system. In FIG. 4, (a) shows a transmission / reception mode of one mobile station (first communication station), and includes an uplink period, which is a transmission period from the mobile station to the base station (second communication station), and a transmission period from the base station. A downlink period, which is a transmission period to the mobile station, is time-divisionally and alternately repeated. Then, the mobile station performs a transmission operation in a predetermined time zone (also referred to as a time slot) allocated to, for example, the head of an uplink period, and performs a reception operation in a predetermined time zone similarly allocated to the head of a downlink period. On the other hand, the base station performs reception in the up period and transmission in the down period almost in synchronization with the transmission / reception operation of the mobile station.

An example of a format of transmission data corresponding to a transmission operation period of the mobile station, that is, one frame is shown in FIGS. 4B and 4C. In the control channel, the transmission data includes, in order from the beginning, a ramp time (R) for transient response, a preamble (PR), a synchronization word (unique word: UW), a channel type (CI), and a call code of a partner station. An identification code (DA), an originating identification code (OA), which is a calling code of the own station, control data for link channel allocation, etc., and additional information for error detection (CRC:
Cyclic Redundancy Check). The transmission data on the communication channel includes, in order from the beginning, a ramp time (R) for transient response, a preamble (PR), a synchronization word (unique word: UW), a channel type (CI), communication data, and additional information for error detection ( CRC). Note that a guard time of a predetermined number of bits is usually provided between adjacent transmission / reception communication time zones, and a pilot signal is appropriately inserted into transmission data, but is omitted here.

The preambles in the transmission data on the control channel and the communication channel are shown in (d) and (e) of FIG.
Is shown in While the mobile station recognizes that the first communication state is, for example, a normal state, the preamble takes the value of (i) as shown in (d), and the preamble is, for example, an abnormal state as the second communication state. While (1) is recognized, the value of (ii) is taken.

Although FIG. 4 mainly shows the transmission mode of the mobile station, the same transmission data as (b) to (e) can be obtained in the transmission mode of the base station (ie, the reception mode of the mobile station). Sent to mobile station. FIG. 5 shows an operation until communication is performed. In FIG. 5, first, in response to an incoming call or an outgoing call, the mobile station radiates a transmission wave including control data of a link establishment request based on operation of the keyboard 20 from the antenna 1. When the base station receives a request for establishing a link channel from the mobile station to the base station on the control channel, the base station radiates a transmission wave including control data of a link establishment response from antenna 1 so as to perform link channel allocation to the mobile station. .

After shifting to the communication channel in response to the link establishment response, the mobile station supplies a synchronization burst to the base station, the base station supplies a synchronization burst, and sets the communication mode from the mobile station to the base station. Supply of request, response to communication mode setting from base station, supply of call setting request from mobile station to base station, response to call setting from base station, supply of function / authentication request from base station to mobile station, A call is made after a response to a function / authentication request from the mobile station, a call from the base station to the mobile station, and a response. These are performed based on communication data.

Next, preamble switching and response control performed by the mobile station and the base station during a call will be described in more detail. FIG.
9 shows a procedure of a preamble selection process executed by SP11. In FIG. 6, the DSP 11 performs demodulation processing on the data received from the A / D converter 10 during a call, that is, during the reception period R of the mobile station assigned to the downlink period under the establishment of the frame synchronization as described above. Error detection processing by CRC is performed on the demodulated data obtained for each frame. In this error detection process, it is determined whether or not an error, that is, a missing or erroneous demodulated data, has been detected continuously over M frames (M is a natural number and a predetermined appropriate number) (step S11). ). If it is determined in step S11 that the occurrence of the CRC error has not been repeated M times, the DSP 11 selects the preamble of FIG. 4D (step S12), and ends the processing of this flowchart. Thereafter, when the transmission operation period T of the mobile station allocated to the downlink period as shown in FIG. 4A arrives, the selected normal preamble, the communication data from the channel coding logic circuit 12, and other data are transmitted. To form transmission data as shown in FIG. 4C, modulate this, and transfer it to the transmission unit 4 (D / A converter 13). At this time, an oscillation frequency for converting to a transmission frequency by the DSP 11 is set in the VCO 15, and the up-converter 14 mixes the output analog signal of the D / A converter 13 with a signal of the oscillation frequency set in the VCO 15, The power is supplied to the power amplifier 17 via the pre-amplifier 16. At this time, the power amplifier 17 receives an operation command from the DSP 11, and the antenna switch 2 receives a switching command from the DSP 11 to supply a signal from the transmitting unit 4 to the antenna 1. The transmission signal including the preamble is radiated by the antenna 1.

On the other hand, if it is determined in step S11 that the occurrence of the CRC error has continued M times, the DSP 1
1 further determines the level of the received electric field strength (step S13). In this level determination, the DSP 11 has a function of detecting the received electric field strength based on the value of the digital signal received from the A / D converter 10, and determines whether or not the detected received electric field strength is larger than a specified value. Determine. If it is determined in step S13 that the received electric field strength is larger than the specified value, the DSP 11 selects the preamble of FIG. 4E (step S12), and ends the processing of this flowchart. Thereafter, similarly in the transmission operation period T, the selected abnormal preamble, the communication data from the channel coding logic circuit 12 and other data form transmission data as shown in FIG. 4C, modulate the transmission data, and After the frequency is up-converted and the power is amplified, a transmission signal including an abnormal preamble is radiated from the antenna 1.

The processing in step S14 is as follows.
Even if the received electric field strength is not so low, since there is a continuous error in the received data on the time axis, it is determined that an interference wave that hinders good reception and demodulation has started to occur, and the present mobile station and the base station have This is performed in order to inform the base station that it is necessary to switch from the link channel No. to another link channel obtained by the link channel establishment operation on the control channel as shown in FIG.

On the other hand, if it is determined in step S13 that the received electric field strength is equal to or less than the specified value, the DSP 11
Shifts to a routine for generating control data for a link channel establishment request (step S15), and ends the processing of this flowchart. Thereafter, in the transmission operation period T, transmission data as shown in FIG. 4B including the generated control data is formed, modulated, and subjected to frequency up-conversion and power amplification, and the link from the antenna 1 is transmitted. A transmission signal including the channel establishment request will be radiated. The transmission of the control data is performed on a control channel. In step S15, the DSP 11 performs the link channel establishment operation on the control channel as shown in FIG. 5 earlier because the reception data has a continuous error on the time axis and the reception field strength is considerably low. All of the obtained link channel candidates including the current link channel between the mobile station and the base station are determined to be inappropriate due to a change in the communication environment or state, and the link channel establishing operation is performed again. Has been made.

For the processing in FIG. 6, the base station is required to perform an operation according to the received preamble as shown in FIG. FIG. 7 shows a procedure of a preamble receiving process executed by the DSP 11 in the base station. In FIG. 7, the DSP 11 is a reception period of the base station assigned to the uplink period (that is, corresponds to T in FIG. 4A).
In, it is determined whether or not a normal preamble has been detected from the demodulated data obtained by performing demodulation processing on the received data from the A / D converter 10 (step S21). When the detection of the normal preamble is determined in step S21, the DSP 11 recognizes that the reception state of the mobile station is good, and continues the communication with the mobile station on the current channel (step S22). The process ends.

When it is determined in step S21 that a normal preamble has not been detected, the DSP 11 determines whether an abnormal preamble has been detected from the demodulated data (step S23). When the detection of the abnormal preamble is determined in step S23, the DSP 11 recognizes that the reception state of the mobile station is poor, shifts to another channel, and starts communication with the mobile station on the other channel ( Step S24), the processing of this flowchart ends. By detecting the abnormal preamble in step S23, the base station DSP11 can immediately recognize that the influence of the interference wave has begun on the mobile station side. It is possible to quickly switch to another link channel. The link channel to be switched to is selected from link channel candidates other than the current channel obtained by the link channel establishment operation on the control channel as shown in FIG. Therefore, there is no need to perform a link channel establishment operation on the control channel, so that communication on the communication channel is not interrupted.

If it is determined in step S23 that the abnormal preamble has not been detected, the process proceeds to step S22.
This flow occurs when neither the normal nor abnormal preamble is detected, but it is considered that a sudden preamble transmission or reception error occurs.In this case, the communication on the current channel is continued and the normal or abnormal preamble is restarted. Waiting for the arrival of.

In the above, it has been described that the mobile station detects the occurrence of an interference wave, sends an abnormal preamble to the base station, and the base station detects the abnormal preamble and changes the channel, but the reverse function is also possible. However, it is also possible to have both functions together. That is, the function of the base station detecting the occurrence of the interference wave and transmitting the abnormal preamble to the mobile station, and the function of the mobile station detecting the abnormal preamble and changing the channel can be simultaneously achieved by the configuration of FIG. With the configuration of FIG. 3, there is no need to change the hardware to implement the present invention. For example, normal and preamble patterns can be stored in a ROM in the DSP 11 and the processing executed by the DSP 11 and the processing shown in FIGS.

In the above description, the preamble is switched when an interference wave is generated. However, the preamble may be switched when the received electric field strength decreases. The method of detecting the decrease in the received electric field strength is not limited to the method of detecting by the processing of the DSP 11 based on the value of the data received from the A / D converter 10 as described above, and there are various methods. The configuration shown may be used to detect a decrease in the received electric field strength. FIG.
Shows a part of the structure of the receiving system, other parts are omitted, and the same parts as those in FIG. 3 are denoted by the same reference numerals. In FIG. 8, the down converter 8 is B
A sensitivity signal corresponding to the received electric field strength is generated based on the received signal from the PF 7, and this sensitivity signal is used as one input of the comparator 30. The sensitivity signal is, for example, an RSSI (Received Signal Strength) of an input received signal detected in an internal circuit of a so-called active down converter.
th Indicator) value. A reference voltage from a constant voltage source 31 is applied to the other input of the comparator 30.
The comparator 30 compares the sensitivity signal with the reference voltage,
When it is determined that the sensitivity signal is smaller than the reference voltage, for example, a high-level determination signal is generated and supplied to the CPU 19.
The CPU 19 switches the preamble as described above when detecting that the discrimination signal has become high while monitoring the level change of the discrimination signal.

In short, the present invention is characterized in that the transmission information per frame is increased by one bit by switching the preamble, in other words, the preamble is used not only for synchronization but also for transmission of additional information. The switching of the preamble according to the present invention can also be used for frame identification in multi-frame configuration and transmission of alarm information. Further, when there is a margin in the detection gain of the preamble in the receiving system, by slightly sacrificing the autocorrelation coefficient, not only completely inverted patterns such as (i) and (ii) but also other patterns can be used. If used for the preamble, it is possible to transmit more information, that is, one or more bits of information.

In the above description, the channel is switched when an abnormal preamble is received and detected. However, the present invention is not limited to this. The transmission power may be increased, and the mobile station may receive and detect the abnormal preamble. If detected, the mobile station may perform handover / roaming. Various processes can be considered when the preamble is switched as described above. In addition, a process such as display corresponding to the content of the preamble or notification by voice or the like can be considered.

In the above description, the modulation method is 1
Although 6QAM is adopted and TDMA is adopted as a communication system, it is a matter of course that the present invention is not particularly limited to these. The present invention is applicable to general communication systems that synchronize using preamble data, and it is needless to say that each component can be designed and modified.

[0038]

As described above in detail, according to the preamble synchronous communication system of the present invention, at the first communication station, at least two communication states are detected, and when one of the communication states is detected, the first communication station detects the first communication state. The preamble data is formed in a pattern, and when the other communication state is detected, the preamble data is formed in a second pattern different from the first pattern. In the second communication station, the transmission data from the first communication station is received, and when the preamble data in the transmission data has the first pattern, an operation corresponding to one communication state is performed, and the preamble data is transmitted. Has the second pattern, the operation corresponding to the other communication state is performed. As a result, it is possible to maintain a good communication quality by coping with a decrease in the received electric field strength and occurrence of an interference wave.

[Brief description of the drawings]

FIG. 1 is a diagram showing an arrangement of transmission data in a time series in a conventional preamble synchronous communication system.

FIG. 2 is a signal point arrangement diagram when transmission data is generated by 16QAM.

FIG. 3 is a block diagram illustrating a configuration of a TDMA communication apparatus according to an embodiment of the present invention.

4 shows a triple TDMA as an operation example of the communication apparatus of FIG. 3;
The figure which shows the communication form of a system.

FIG. 5 is a diagram showing a mode until the base station and the mobile station start a call as an operation example of the communication apparatus in FIG. 3;

FIG. 6 is an exemplary flowchart showing the procedure of a preamble selection process executed by a DSP in the communication apparatus of FIG. 3;

FIG. 7 is an exemplary flowchart showing the procedure of a preamble reception process executed by the DSP in the communication apparatus of FIG. 3;

FIG. 8 is a block diagram of a partial configuration of a receiving system for explaining another example of a method of detecting a decrease in the received electric field strength.

[Description of Signs of Main Parts]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Antenna switch 3 Receiver 4 Transmitter 5, 7 BPF 6 High frequency amplifier 8 Down converter 9, 15 VCO 10 A / D converter 11 DSP 12 Channel coding logic circuit 13 D / A converter 14 Up converter 16 Preamble Amplifier 17 Power amplifier 19 CPU 20 Keyboard 21 Voice CODEC 22 Data input / output interface 23 Microphone amplifier 24 Speaker amplifier 25 Microphone 26 Speaker 30 Comparator 31 Constant voltage source

Claims (9)

(57) [Claims] 1. A communication system in which a first communication station transmits transmission data including preamble data, and a second communication station receives the transmission data and synchronizes using the preamble data. The communication station detects at least two communication states during a call , forms the preamble data with the first pattern when detecting one of the communication states, and forms the preamble data when detecting the other of the communication states. Forming the preamble data in a second pattern different from the first pattern, the second communication station performs an operation corresponding to one of the communication states when the preamble data has the first pattern; It said second copies by performing an operation corresponding to the other of the communication state when the preamble data has the second pattern Good at the station side
A preamble synchronous communication system characterized by performing an operation for maintaining excellent communication quality . 2. One of the communication states is a low interference state in which an electric field intensity of an interference wave generated in a communication channel between the first communication station and the second communication station is equal to or less than a predetermined value. 2. The preamble synchronous communication system according to claim 1, wherein the other of the communication states is a high interference state in which the electric field strength of the interference wave is higher than a predetermined value. 3. The transmission data includes error detection additional information, and the first communication station performs the reception data obtained by receiving the transmission data transmitted from the second communication station. As a result of the error detection processing by the error detection additional information, the error of the transmission data is detected a predetermined number of times continuously and the high interference state is detected only when the received electric field strength is larger than a predetermined value. 3. The preamble synchronous communication system according to claim 2, wherein: 4. One of the communication states is a high-sensitivity state in which a reception electric field strength of the first communication station with respect to a transmission wave from the second communication station is equal to or more than a predetermined value, and the other of the communication states is 2. The preamble synchronous communication system according to claim 1, wherein said reception electric field strength is in a low sensitivity state lower than a predetermined value. 5. The second communication station maintains a communication operation with the first communication station on the communication channel when the preamble data has the first pattern, and the second communication station transmits the preamble data to the second communication station. Has the pattern of the first communication channel in a communication channel different from the communication channel.
5. The preamble synchronous communication system according to claim 2, wherein the operation shifts to a communication operation to a communication station. 6. The second communication station maintains transmission power of a transmission signal to the first communication station when the preamble data has the first pattern, and the preamble data matches the second pattern. 5. The preamble synchronous communication system according to claim 2, wherein the transmission power is increased when the communication device has the preamble. 7. The first pattern includes a plurality of specific values having a maximum autocorrelation coefficient among possible values of the transmission data in a predetermined modulation scheme, and an array of the specific values. 8. The pattern according to claim 1, wherein the second pattern has a portion formed by the specific values and formed by arranging the specific values in a direction opposite to an arrangement direction of the specific values. 9. A preamble synchronous communication system according to any one of the preceding claims. 8. The preamble synchronous communication system according to claim 7, wherein said predetermined modulation scheme is a QAM scheme. 9. The predetermined modulation method is a 16QAM method, and the first pattern is “0”,
“0”, “2”, “10”, “10”, “8”, “0”
The second pattern includes "0", "0", "8", "10", and "1" in order from the top.
9. The preamble synchronous communication system according to claim 8, wherein the preamble synchronous communication system comprises a specific value of an array of "0", "2", and "0".