JPH098725A - Preamble synchronizing communication system effectively utilizing preamble for additional information transmission - Google Patents

Abstract

PURPOSE: To maintain satisfactory communication quality by dealing with the reduction of received electric field intensity or the generation of interference wave. CONSTITUTION: Transmissive data containing preamble data are transmitted by a first communication station, the transmitted data are received by a second communication station and a preamble for synchronizing is effectively utilized for additional information transmission while using the preamble data. Two communication states are detected at least and when one communication state is detected, the preamble data are formed by a first pattern (step S12) but when the other communication state is detected, the preamble data are formed by a second pattern different from the front pattern (step S14). When the preamble data have the first pattern, the second communication station is operated corresponding to one communication state and when the preamble data have the second pattern, the communication station is operated corresponding to the other communication state.

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, reception at both stations may occur because the distance between the base station and the mobile station changes momentarily as the mobile station moves, or due to various fading including Rayleigh fading. The electric field strength decreases.
Alternatively, even in a general communication system, it is often the case that sufficient communication quality cannot be secured due to interference due to transmission waves from other stations. Today, effective countermeasures against such defects are required.

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 these and the information is discarded. . In this way, under a low received electric field strength or an interference wave of a strong strength, the control signal cannot sufficiently play its role, and as a result, control for re-establishing a communication link is required for communication of information data such as voice. It had to be done before and the call was interrupted.

[0004]

In view of the above points, 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 generation of an interference wave. With the goal.

[0005]

In a communication system according to the present invention, a first communication station transmits transmission data including preamble data, a second communication station receives the transmission data, and synchronization is performed using the preamble data. In the communication system, the first communication station detects at least two communication states, and when one of the communication states is detected, forms the preamble data in a first pattern, When the other is detected, the preamble data is formed with a second pattern different from the first pattern, and the second communication station is in the communication state when the preamble data has the first pattern. When the preamble data has the second pattern, the operation corresponding to one is performed, and the operation corresponding to the other of the communication states is performed. It is characterized in that to perform.

[0006]

According to the preamble synchronous communication system using the preamble having the information adding function of the present invention, at least two communication states are detected in the first communication station,
When one communication state is detected, the preamble data is formed by the first pattern, and when the other communication state is detected, the preamble data is formed by the second pattern different from the first pattern. In the second communication station, when the transmission data from the first communication station is received and the preamble data in the transmission data has the first pattern, the operation corresponding to one communication state is performed, and the preamble data Has a second pattern, the operation corresponding to the other communication state is performed.

[0007]

The present invention will be described in detail below with reference to the drawings. First, the present invention is applied to a communication system that uses a preamble for synchronization, and FIG. 1 shows a practical example of time-series transmission data generated in such a system and a preamble arranged in the transmission data. Shows.

In FIG. 1, for example, in a period called a frame, a transmission time zone assigned to a transmission system (or a reception time zone assigned to a reception system) is a pilot signal, a preamble and data (voice, etc.). (Main information data) is stored in a predetermined number of time slots. 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 continuously stored in seven time slots between the first pilot signal and the next pilot signal.

The pilot signal, preamble and data are modulated as shown in FIG. 2, for example. FIG.
Is 16QAM (Quadrature Amplitude Modulation)
4 shows the signal point arrangement when transmission data is generated, and 16 values (“0” to “1” that can be taken by one sample of transmission data with the in-phase component I and the quadrature component Q as orthogonal axes
5 ") on the Cartesian coordinates.

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

(I) “0” → “0” → “2” → “10”
The data is stored in the time slot assigned to the preamble in FIG. 1 in the order of “→ 10” → “8” → “0”. This pattern is the result obtained by calculation, and each specific value is selected so that the maximum detection gain can be obtained when the preamble is detected in the receiving system (so that the autocorrelation coefficient becomes maximum). It is formed by combining or arranging.

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

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

Focusing on such characteristics, in the present invention, (i)
The pattern (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. Based on this point, if the preamble patterns are switched for each communication state and transmitted, the receiving system only performs the process of identifying both patterns, without sacrificing the detection gain (that is, the characteristics of the amplitude and the phase). However, there is a possibility that the detection gain may be lowered because of the disadvantage of "0", "2", "8", "1".
It is possible to know where the communication state is, without using a value other than 0 ".

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

In the receiver 3, a high frequency signal which is a signal received by the antenna 1 and passed through the antenna switch 2 is band-limited by a band limiting filter (BPF) 5 and then 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 to mix the supplied high frequency signal with the local oscillation signal from the VCO 9 to generate an intermediate frequency signal. The intermediate frequency signal is digitized by the 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 demodulated by, for example, the above 16QAM to obtain demodulated data, and the channel coding logic circuit 12 is provided. Supply. The DSP 11 also tests, for each bit (or each sample), whether or not a preamble pattern has arrived in the received signal along with the demodulation process. This verification process is achieved by comparing the patterns (i) and (ii) previously stored in the DSP 11 with the demodulated data obtained by the sequential demodulation process. The demodulated data matches either one of the two patterns, or (i), (i
When the autocorrelation coefficient of the pattern i) and the autocorrelation coefficient of the demodulated data obtained by the sequential demodulation process substantially match, the arrival of the preamble is detected and the frame synchronization is established. Channel coding logic circuit 12
Is the CPU for each frame of the demodulated data from the DSP 11.
The time slot corresponding to the designation of 19 is decomposed, and the communication data in the demodulated data is transferred 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 operation as a decoder for decoding the demodulated data. The data transferred to the voice CODEC 21 is converted into an analog signal there, and is acoustically output from the speaker 26 through the speaker amplifier 24. If the communication data is voice data, it is supplied to the voice CODEC 21, and if it is not voice data, it is supplied to the data input / output interface 22.

On the other hand, the analog voice signal from the microphone 25 is transmitted to the voice CO through the microphone amplifier 23.
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 it as communication data to the channel coding logic circuit 12. The channel coding logic circuit 12 is further supplied from the data input / output interface 22 with a digital signal of a predetermined format as communication data. The channel coding logic circuit 12 sends the communication data from the voice CODEC 21 or the data input / output interface 22 to the CP.
It is inserted in the time slot designated by U19. The insertion into this time slot is accompanied by 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 DSP 1
Forwarded to 1. The DSP 11 inserts one of the patterns shown in (i) and (ii) above into a predetermined time slot in the frame as a preamble pattern according to a 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 the transmission data, for example, the above-mentioned 1 is added to the transmission data.
Modulation processing 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 in the D / A converter 13 and supplies it to the up converter 14 as an analog signal. The up-converter 14 mixes the supplied signal with the oscillation signal from the VCO 15 to perform frequency conversion into a frequency to be transmitted. The frequency-converted signal is amplified by the pre-stage amplifier 16, further power-amplified by the power amplifier 17, and supplied to the antenna 1 through the antenna switch 2 to be radiated.

The modulation and demodulation processing of the DSP 11 is performed by the CPU
It is also controlled by the (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 operating state of the DSP 11. The CPU 19 controls the DSP 11 according to the operation from the keyboard 20, and also controls the channel coding logic circuit 12 and the voice CODEC 21.
Control each operation mode of.

[0021] Such a configuration has a base station (or master station).
And the mobile station (slave station), the communication mode between the two stations is as follows. Figure 3
The communication form of a multiplex TDMA system is shown. In FIG. 4, (a) shows a transmission / reception mode of one mobile station (first communication station), and an up 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. The downlink period, which is the 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) assigned to the beginning of the uplink period, and performs a reception operation in the same predetermined time zone assigned to the beginning of the 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 the transmission operation period of the mobile station, that is, an example of the format of the transmission data corresponding to one frame is shown in (b) and (c) of FIG. In the control channel, this transmission data is a transient response ramp time (R), a preamplifier (PR), a synchronization word (unique word: UW), a channel type (CI), and a call code of the partner station in order from the beginning. Identification code (DA), calling identification code (OA) which is the calling code of the local station, control data for link channel allocation, and additional information for error detection (CRC:
Cyclic Redundancy Check). The transmission data in the communication channel includes a transient response ramp time (R), a preamble (PR), a synchronization word (unique word: UW), a channel type (CI), communication data, and additional information for error detection (from the beginning). CRC). Note that a guard time of a predetermined number of bits is usually placed between adjacent transmission / reception communication time zones, and a pilot signal is appropriately inserted in the transmission data, but this is omitted here.

The preambles in the transmission data on the control channel and the communication channel are (d) and (e) in FIG.
Is shown in While the mobile station recognizes that it is in the normal state as the first communication state, the preamble takes the value of (i) above such as (d), and is in the abnormal state as the second communication state. While recognizing, takes the value of (ii) above.

Although FIG. 4 mainly shows the transmission mode of the mobile station, even in the transmission mode of the base station (that is, the reception mode of the mobile station), the transmission data equivalent to (b) to (e) are transmitted. 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 the operation of the keyboard 20 from the antenna 1. When the base station receives a link channel establishment request 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 the antenna 1 to perform link channel allocation to the mobile station. .

After shifting to the communication channel by the link establishment response, the synchronization burst is supplied from the mobile station to the base station, the synchronization burst is supplied from the base station to the mobile station, and the communication mode is set 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.

The preamble switching and response control performed by the mobile station and the base station during a call will be described in more detail. FIG. 6 shows that in the mobile station D
The procedure of the preamble selection processing executed by SP11 is shown. In FIG. 6, the DSP 11 performs demodulation processing on the received data from the A / D converter 10 during the call, that is, in 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 for each frame on the demodulated data thus obtained. In this error detection process, it is judged whether or not an error, that is, a missing or error in the demodulated data is continuously detected over M frames (M is a natural number and a predetermined number) (step S11). ). If it is determined in step S11 that the CRC error has not occurred M times consecutively, the DSP 11 selects the preamble of FIG. 4D (step S12), and ends the processing of this flowchart. After that, 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 and communication data and other data from the channel coding logic circuit 12 are transmitted. Then, the transmission data as shown in FIG. 4C is formed, modulated and transferred to the transmission unit 4 (D / A converter 13). At this time, the oscillation frequency for converting into the transmission frequency is set in the VCO 15 by the DSP 11, and the up converter 14 mixes the output analog signal of the D / A converter 13 with the signal of the oscillation frequency set in the VCO 15. The power is supplied to the power amplifier 17 via the pre-stage 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 the signal from the transmitter 4 to the antenna 1. The transmission signal including the preamble will be radiated by the antenna 1.

On the other hand, if it is determined in step S11 that the CRC error has occurred M times consecutively, the DSP1
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 the detected received electric field strength is larger than a specified value. Determine. When it is determined in step S13 that the received electric field strength is larger than the specified value, the DSP 11 selects the preamble in FIG. 4E (step S12) and ends the process of this flowchart. Thereafter, similarly, in the transmission operation period T, the selected abnormal preamble and the communication data and other data from the channel coding logic circuit 12 form the transmission data as shown in FIG. 4C, modulate it, and The transmission signal including the abnormal preamble is radiated from the antenna 1 after the frequency is up-converted and the power is amplified.

In step S14, the DSP 11
Since the received data has continuous errors on the time axis even if the received electric field strength is not so low, it is determined that an interference wave that hinders good reception and demodulation is beginning to occur, and the current mobile station and base station This is done in order to inform the base station that it is necessary to switch from the above link channel to another link channel obtained by the link channel establishing 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 less than or equal to the specified value, then the DSP 11
Shifts to the routine for generating the control data of the link channel establishment request (step S15), and ends the processing of this flowchart. After that, in the transmission operation period T, transmission data as shown in FIG. 4B including the generated control data is formed, modulated, and then frequency up-converted and power amplified to perform linking from the antenna 1. A transmission signal including a channel establishment request will be radiated. The transmission of this control data is performed on the control channel. The process of step S15 is performed by the DSP 11 by the link channel establishing operation on the control channel as shown in FIG. 5, because the received data has continuous errors on the time axis and the received electric field strength is considerably low. To determine that all of the obtained link channel candidates including the current link channel between the mobile station and the base station are improper due to changes in the communication environment or state, and perform the link channel establishment operation again. Has been done.

In contrast to the processing of 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 preamble reception processing executed by the DSP 11 in the base station. In FIG. 7, the DSP 11 has a reception period of the base station assigned to the uplink period (that is, corresponds to T in FIG. 4A).
In step S21, it is determined whether a normal preamble is detected from the demodulated data obtained by demodulating the received data from the A / D converter 10. When it is determined in step S21 that the normal preamble is detected, the DSP 11 recognizes that the reception status of the mobile station is good, and continues communication with the mobile station on the current channel (step S22). The process ends.

When the normal preamble is not detected in step S21, the DSP 11 determines whether or not the abnormal preamble is detected from the demodulated data (step S23). When it is determined in step S23 that the abnormal preamble has been detected, 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 ( In step S24), the process of this flowchart ends. By detecting the abnormal preamble in step S23, the base station DSP11 can immediately recognize that the mobile station side is beginning to be affected by the interference wave, and in order to avoid the influence of this interference wave, the base station DSP11 can use the current link channel. You can quickly switch to another link channel. The link channel of the switching destination is selected from the link channel candidates excluding the current channel obtained by the link channel establishing operation on the control channel as shown in FIG. Therefore, since it is not necessary to perform the link channel establishing operation on the control channel, the communication on the communication channel is not interrupted.

When it is determined in step S23 that the abnormal preamble is not detected, the process proceeds to step S22.
This flow occurs when neither normal nor abnormal preamble is detected, but it is considered to be a sudden preamble transmission or reception error.In this case, communication on the current channel is continued and another normal or abnormal preamble is retransmitted. I am waiting for the arrival of.

In the above description, 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 to change the channel, but the reverse function is also possible. It is also possible to have both functions. That is, the function of the base station detecting the occurrence of an interference wave and sending the abnormal preamble to the mobile station, and the mobile station detecting the abnormal preamble and changing the channel can also be achieved with the configuration of FIG. According to the configuration of FIG. 3, the hardware is not changed to implement the present invention. For example, the normal and preamble patterns are stored in the ROM of the DSP 11 and the processing of FIGS. 6 and 7 is added to the program executed by the DSP 11, which can be realized by a slight addition of software.

In the above description, the preamble is switched when the interference wave is generated, but the preamble may be switched when the received electric field strength is reduced. 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 received data from the A / D converter 10 as described above, but there are various methods. You may make it detect the fall of a received electric field strength by the structure as shown. FIG.
Shows a part of the configuration of the receiving system and omits the other parts, and the same parts as those in FIG. 3 are designated 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 detected by, for example, an internal built-in circuit of a so-called active down converter, which is an RSSI (Received Signal Strength) of an input received signal.
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 it detects that the discrimination signal has become high level 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. Therefore, the switching of the preamble according to the present invention can also be used for frame identification in the 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, the autocorrelation coefficient is sacrificed a little, so that not only the completely inverted pattern such as (i) and (ii) but also other patterns can be obtained. If it is used for the preamble, it is possible to transmit more information, that is, one bit or more.

Further, in the above description, when the abnormal preamble is received and detected, the channel is switched. 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 in this way. In addition, it is also possible to perform processing such as a display corresponding to the content of the preamble or a notification by voice or the like.

In the above, the modulation method is 1
Although 6QAM is adopted and TDMA is adopted as a communication system, it goes without saying that these are not particularly limited. The present invention is applicable to general communication systems that use preamble data for synchronization, and it goes without saying that design changes can be made to each component.

[0038]

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

[Brief description of drawings]

FIG. 1 is a diagram showing an array of time-series transmission data 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 showing the configuration of a TDMA communication device according to an embodiment of the present invention.

4 is a triple TDMA as an operation example of the communication device of FIG.
The figure which shows the communication form of a system.

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

6 is a flowchart showing a procedure of preamble selection processing executed by a DSP in the communication device of FIG.

7 is a flowchart showing a procedure of a preamble reception process executed by a DSP in the communication device of FIG.

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

[Explanation of symbols for main parts]

 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 Upconverter 16 Prefix 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)

[Claims] 1. A communication system in which transmission data including preamble data is transmitted in a first communication station, and the transmission data is received in a second communication station, and synchronization is performed using the preamble data. The communication station detects at least two communication states, forms the preamble data in a 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 above, and the second communication station performs an operation corresponding to one of the communication states when the preamble data has the first pattern, Has the second pattern, an operation corresponding to the other of the communication states is performed. System. 2. One of the communication states is a low interference state in which an electric field strength of an interference wave generated in a communication channel between the first communication station and the second communication station is a predetermined value or less, The preamble synchronous communication system according to claim 1, wherein the other communication state 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 additional information for error detection, 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 additional information for error detection, the high interference state is detected only when an error in the transmission data is detected a predetermined number of times in succession and the reception electric field strength is larger than a predetermined value. The preamble synchronous communication system according to claim 2. 4. One of the communication states is a high sensitivity state in which a received electric field strength of the first communication station with respect to a transmission wave from the second communication station is a predetermined value or more, and the other of the communication states is The preamble synchronous communication system according to claim 1, wherein the received 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 preamble data has the second pattern. Of the first channel on a communication channel different from the communication channel.
The preamble synchronous communication system according to claim 2, 3 or 4, wherein a communication operation to a communication station is performed. 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 has the second pattern. The preamble synchronous communication system according to claim 2, 3 or 4, wherein when it has, the transmission power is increased. 7. The first pattern has a plurality of specific values that maximizes an autocorrelation coefficient among values that can be taken by the transmission data in a predetermined modulation scheme, and an array of the specific values. 8. The pattern of 2 has a portion which is formed by arranging the specific values and is formed by arranging the specific values in a direction opposite to the arrangement direction of the specific values. The preamble synchronous communication system according to any one of the above. 8. The preamble synchronous communication system according to claim 7, wherein the predetermined modulation method is a QAM method. 9. The predetermined modulation method is a 16QAM method, and the first pattern is “0”, in order from the beginning.
"0", "2", "10", "10", "8", "0"
The second pattern consists of specific values of "0", "0", "8", "10", "1" in order from the beginning.
9. The preamble synchronous communication system according to claim 8, wherein the preamble synchronous communication system comprises specific values of an array of "0", "2", and "0".