JP4492244B2 - Receiving machine - Google Patents

Description

  The present invention relates to a receiver of a communication system that performs data communication using radio waves. In particular, the present invention relates to a receiver that waits for a plurality of channels and mainly performs data communication of short packets.

  In recent years, a system for remotely controlling devices using wireless has attracted attention. The wireless system is advantageous in that the degree of freedom of installation of the device and the controller is higher than that in the wired system, and construction for connecting the devices is unnecessary. As the radio band, a low-power radio of 400 MHz band or 2.4 GHz band is used. In particular, a telemeter / telecontrol channel is prepared as a specific low-power radio band in the 400 MHz band (see Non-Patent Document 1).

  In the device control, it is required that the device on the receiver side sequentially reacts with the control data from the transmitter side. Therefore, communication using a short packet having a relatively short data length for wireless transmission is used.

  FIG. 8 shows a configuration of a communication packet in a wireless section used in the packet communication as described above. FIG. 9 shows the carrier sense operation of the conventional receiver.

  FIG. 9 shows the passage of time from left to right. This example is a system in which three channels are used as standby channels, and a transmitter transmits a signal through an empty channel (other devices are not communicating). In FIG. 9, (1), (2), and (3) represent carrier sense timings of the first channel, the second channel, and the third channel, respectively. As shown in FIG. 9, the radio circuit is continuously receiving operation, and the carrier sensing operation of each channel is continuously performed.

  As shown in FIG. 8, the communication packet sent from the transmitter is composed of a plurality of header slots and subsequent data slots. As the number of used channels N = 3, the number of header slots M = 2N, that is, six header slots are provided. Multiple header slots are provided because the receiver side scans the three channels in order and performs carrier sense operation. At this time, noise and other device signals are used in a channel different from the channel used by the transmitter. When a carrier sense is detected, it takes a certain time (usually about 1.5 header slots) to identify the signal by the demodulation operation, that is, to determine that the signal is not intended for the own device. This is to prevent the reception of the signal of the other channel from being missed. That is, the six header slots are provided to keep the header information flowing for a time necessary for the carrier sensing to be reliably performed for three channels, and can be called dummy slots.

  When carrier sense is performed, it is necessary to repeat headers of at least 1.5 header slots × 3 channels = 4.5 header slots for signal identification. In this case, the number of repetitions can be five, but the channel of the receiver Considering the time required for switching, it is desirable to repeat 6 headers.

  The reason why the above 1.5 header is necessary is that the timing at which the carrier sense is performed is not necessarily the position at which the bit synchronization signal starts, and the sensing is performed at an arbitrary position. This is because it takes time for one header. Further, it is necessary to add a time until the bit synchronization is completed. It should be noted that the transmitter transmits a signal using any channel that is free (the carrier was sensed in advance and the signal was not sensed) among the N channels.

  Now, if the number of repetitions M of the header slot is large, the time length of the communication packet increases and the communication time becomes long. This is because, for example, when the receiver is connected to a device to control the device, the response time (immediate response) of the control is impaired. Therefore, the receiver is set to a continuous operation state, and the three channels are sequentially and continuously. By performing carrier sense, the number of header slot repetitions M is designed to be as small as possible.

  When the receiver determines that there is a carrier in the carrier sense operation, the receiver performs a bit synchronization operation. The bit synchronization operation is continued substantially over the time length of one header slot. When bit synchronization cannot be established here, continuous carrier sensing for three channels is performed again. When bit synchronization is established, the next frame synchronization signal is received.

Further, when the frame synchronization is established, the next subsequent identification signal is received. The identification signal includes information of system and device identification IDs or header slot numbers (1 to 6 in this example). If it is determined from the identification signal that the signal is a communication signal to the own device, the next data slot is received. The data slot stores the contents of data to be transmitted from the transmitter to the receiver.
"ARIB STD-T67 Specified Low Power Radio Station Standard for Radio Equipment for Telemeters, Telecontrol and Data Transmission" (Radio Industry, July 2000)

  However, since the conventional receiver performs carrier sensing by continuous reception operation, there is a problem that power consumption is relatively large and it is not suitable for battery driving. Or when controlling a battery drive apparatus, there existed a problem that the quick response property of control was impaired.

  In general, carrier sensing by intermittent reception is used to extend the battery life with battery driving, but in this case, carrier sensing during the reception suspension period cannot be performed, and thus transmission is performed from the transmitter side. It is necessary to extend the transmission packet time.

  That is, it is necessary to increase the number of repetitions M of the header slot and to make the repetition time of the header slot longer than the total time required for the carrier sense for the rest time and the subsequent three channels.

  For the above reasons, in battery-powered equipment, it is impossible to achieve both quick response of control and battery life.

  Further, as a method of operating with reduced power consumption as an intermittent operation, carrier sensing of all channels is continuously performed after the reception operation is paused, and then enters a pause state again (that is, “pause (1) ( (2) (3) Pause (1) (2) (3) Pause, etc.) In order to reduce the number of header slots, it is necessary to set the pause time considerably short.

  This means that it is necessary to receive bit synchronization, frame synchronization, and identification signals when carrier sensing is performed on noise and communication signals from other devices, but this increases the time required for carrier sensing of the target channel. (That is, “pause (1) reception (2) reception (3) reception, pause (1) reception (2) reception (3) desired wave reception”). That is, in an operation in which carrier sense for three channels is continuously performed after a pause, it is almost impossible to secure a pause time or it is necessary to increase the number of header slots.

In order to solve the above-described conventional problems, the receiver of the present invention is used in a communication mode in which communication is performed using any of predetermined N channels, and a bit synchronization signal and a frame transmitted from the transmitter are used. A receiver that receives a transmission packet including a plurality of header slots each including a synchronization signal and an identification signal and a data slot following the plurality of header slots, and sets the N channels to 1 at a _first predetermined time interval T 1. The intermittent carrier sense is performed by sequentially switching channels.

Then, by performing carrier sense by one channel at a certain time T ₁ interval, out to obtain downtime significantly very comparable to the continuous carrier sense function, be thereby reducing the power consumption of the receiver it can.

  The receiver of the present invention can obtain a reception function equivalent to continuous carrier sense even in intermittent carrier sense operation, and can reduce power consumption without impairing quick response.

The first invention includes carrier sense means and demodulation means, and is used in a communication mode in which communication is performed using any one of N predetermined channels. The bit synchronization signal and frame synchronization transmitted from the transmitter are used. signal and is an identification signal receiver for receiving a transmission packet including a plurality of header slots and the plurality of header slots subsequent data slots each containing one channel the N channels at a first predetermined time T ₁ interval By performing the intermittent carrier sense by switching sequentially one by one, even with intermittent carrier sense, communication can be performed with a transmission packet length equivalent to that of continuous carrier sense, and the power consumption of the receiver can be greatly reduced.

In the second invention, the first predetermined time T ₁ is set to a range represented by T ₂ <T ₁ <(2N−1) / N × T ₂ with respect to the time length T ₂ of one header slot. As a result, the pause time of the intermittent carrier sense operation can be extended, and the power consumption can be reduced.

A third invention is the first predetermined time T ₁ is time length of one header time length of a bit synchronous signal time included in the length T ₂ and the header slots slot T ₃ and the frame sync signal T ₄ Is set in the range indicated by T ₂ <T ₁ <T ₂ + T ₃ + T ₄ , so that even when the channel sense and the bit synchronization and the frame synchronization are achieved, the header slot of the necessary channel signal is always obtained. Can be received.

According to a fourth aspect of the present invention, the first predetermined time T ₁ is T ₂ <T ₁ <T ₂ + T _{3 with} respect to the time length T ₂ of the header slot and the time length T ₃ of the bit synchronization signal included in the header slot. By setting to the range indicated by (2), it becomes possible to always receive the header slot of the signal of the necessary channel even when carrier sense is performed in each channel and bit synchronization is achieved.

The fifth invention is provided with a demodulating means and is used in a communication mode in which communication is performed using any one of N predetermined channels, and a bit synchronization signal, a frame synchronization signal, and an identification signal transmitted from a transmitter. the a receiver for receiving a transmission packet including a plurality of header slots and the plurality of header slots subsequent data slots each containing the N channels by sequentially switching one channel at a first predetermined time T ₁ interval By performing the bit synchronization operation of the received signal, communication can be performed at a low reception level up to the reception sensitivity point of the receiver, so that the communication distance can be increased.

According to a sixth aspect of the present invention, the first fixed time T ₁ is set to a range represented by T ₂ <T ₁ <2 × T ₂ with respect to the time length T ₂ of one header slot, It is possible to receive signals from a plurality of channels while performing communication at the sensitivity point.

  The seventh invention further comprises level detection means, and when carrier sense is detected in a certain channel, carrier sense is continuously performed for all other channels, and the level of the received signal of each channel is detected by the level detection means. By detecting and performing the demodulation operation of the channel that is the level of the largest received signal in the detection, it is possible to receive the signal addressed to itself more preferentially than the reception of the signal of the other system at a distant place. Reduction in power and improvement in communication reliability can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a timing chart showing the timing of the carrier sense operation of the receiver according to the first embodiment. FIG. 2 is a block diagram showing the overall configuration of the receiver.

  In FIG. 2, 1 is an antenna, 2 is a high-frequency filter, 3 is an LNA (Low Noise Amplifier), 4 is a mixer, 5 is a local oscillator, 6 is a channel selection filter, 7 is a demodulation means, 8 is a carrier sense means, Level detection means.

  The high frequency signal from the transmitter input to the antenna 1 is amplified by the LNA 3 via the high frequency filter 2. Then, the signal from the local oscillator 5 is mixed by the mixer 4 and converted to a low frequency (intermediate frequency) signal. Further, unnecessary channel components are removed by the channel selection filter 6. The output of the channel selection filter 6 is input to the demodulation means 7, carrier sense means 8 and level detection means 9.

  Here, the carrier sense means 8 outputs a signal with carrier sense when the power level of the received signal input to the antenna terminal is equal to or higher than a predetermined level (carrier sense level). The demodulating means has a function of demodulating the input modulation signal and outputs it as data. Further, it is considered as a demodulating means including a function for analyzing the contents of data.

  The level detection means is for measuring the power level of the received signal input to the antenna, and can be configured to be shared with a part of the level determination means of the carrier sense circuit. The carrier sense means determines the magnitude relationship with respect to the set threshold value, but the level detection means has a function of outputting the level magnitude as a numerical value.

FIG. 1 shows the passage of time from left to right. In FIG. 1, (1), (2), and (3) represent carrier sense timings of the first channel, the second channel, and the third channel, respectively. Then, the receiver is set to a dormant state during the time (T _{1 in the} figure) between the carrier sense of a certain channel (for example, the first channel) and the next channel (for example, the second channel), and the power consumption is reduced. .

Here, T ₁ is set such that T ₂ <T ₁ <(2N−1) / N × T ₂ with respect to the duration T ₂ of one header slot included in the transmission packet of FIG. (N: natural number).

  This will be described because it can be derived from the conditions for receiving the transmission signal in any of the three channels at the worst up to the final header slot.

FIG. 3 is an explanatory diagram showing the relationship between the carrier sense operation and the transmission packet. Every T ₁ , carrier sense is intermittently performed as the first channel, the second channel, the third channel, the first channel, and so on. Here, it is assumed that the transmitter starts transmission on the first channel immediately after performing the carrier sense operation on the first channel. The receiver senses the carrier of the second channel and the third channel, and performs the carrier sense of the first channel again. If the timing at this time is before the start timing of the last header slot, the receiver receives the last header slot. be able to.

When the number of header slots is 2 × N, the time until the last slot is given by (2 × N−1) × T ₂ , and it is necessary to perform carrier sense for N channels within this time The maximum value of the sense interval is obtained as (2N−1) / N × T ₂ .

In addition, since it takes a maximum of time T ₂ to receive bit synchronization in the header slot when there is carrier sense, the lower limit value of T ₁ is T ₂ . That T ₁ can be extended up to a length of at least T _2. Therefore, the range of T ₁ is
T ₂ <T ₁ <(2N−1) / N × T ₂
It can be specified in

Now, the power consumption when the above operation is used will be described. As a specific time, when T ₂ = 50 msec and N = 3, T ₁ = 83 msec using the relationship of T ₁ = (2N−1) / N × T ₂ . Here, assuming that the required carrier sense time is 4 milliseconds, the time during which the reception circuit is operating is reduced to 4/83 = about 1/20 compared to the continuous reception operation. Alternatively, if the relationship of T ₁ = T ₂ is used, T ₁ = 50 ms, so that 4/50 = about 1/12. Thus, according to the method of the present embodiment, the power consumption is reduced to 1/12 to 1/20 in the above example by taking the range of T ₂ <T ₁ <(2N−1) / N × T _2. It becomes possible to do.

  In the present embodiment, the number of used channels is three, but the present invention can be similarly applied when the number of channels is two or four or more.

(Embodiment 2)
FIG. 4 is a timing chart showing the timing of the carrier sense operation of the second embodiment. A receiver according to this embodiment will be described with reference to FIG. The feature of this embodiment is that the carrier sense time interval T ₁ is
T ₂ <T ₁ <T ₂ + T ₃ + T ₄
It is a point that is set in a range that satisfies. Here, T ₃ is the duration of the bit synchronization signal included in the header slot, and T ₄ is the duration of the frame synchronization signal included in the header slot. The fact that T ₁ can be extended to the maximum T ₂ + T ₃ + T ₄ is based on the idea described below.

  When there is carrier sense on a certain channel, the receiver performs bit synchronization operation. Here, consider a case where bit synchronization can be achieved but frame synchronization cannot be achieved. When frame synchronization cannot be established, the receiver stops the reception operation on the channel, and then proceeds to the carrier sense operation on the channel.

  Here, since frame synchronization can be obtained only in a system using the same frame synchronization signal as that of the own device, it is considered that frame synchronization is often not obtained with signals from other systems. Alternatively, by configuring the frame synchronization pattern of the own system to be a characteristic pattern different from that of the other system, it is possible to configure so that frame synchronization is hardly obtained except for signals from the own system.

Consider a case where a system is constructed on the assumption that frame synchronization cannot be achieved when a signal other than that addressed to itself is received. In this case, since the carrier sense timing of the receiver in each channel does not necessarily coincide with the start timing of the bit synchronization signal of the transmitter, in order to complete up to bit synchronization and frame synchronization, T ₂ + T ₃ + T at the maximum. _It is necessary to assume that it takes ₄ hours.

Even if a signal of noise or other device communication is received and a sense is detected, in order to be able to receive a signal of a channel addressed to the own device, a reception operation is performed on each channel for a time T ₂ + T ₃ + T _4. However, it is necessary to be able to receive the next channel signal addressed to the own device. Assuming a system that can ensure this, in other words, it is as follows. That is, even when there is no noise or signal destined for another device in each channel, it means that communication addressed to the own device can be received even if carrier sensing is intermittently performed at intervals of T ₁ = T ₂ + T ₃ + T _4. is doing.

From this, the range of T ₁ is
T ₂ <T ₁ <T ₂ + T ₃ + T ₄
Can be defined as a range of

  In this embodiment, the number M of header slot repetitions from the transmitter is M = 2 × N with respect to the number of channels N. However, the bit synchronization length and frame synchronization length with respect to the total header slot length are In a short system, the repetition number M may be smaller than the above. For example, there are cases where M = 2 × N−1, 2 × N−2, and the like can be selected.

(Embodiment 3)
FIG. 5 is a timing chart showing the timing of the carrier sense operation of the third embodiment. The receiver according to this embodiment will be described with reference to FIG. The feature of this embodiment is that the carrier sense time interval T ₁ is
T ₂ <T ₁ <T ₂ + T ₃
It is a point that is set in a range that satisfies. The fact that T ₁ can be extended to the maximum T ₂ + T ₃ is based on the idea described below.

  When there is carrier sense on a certain channel, the receiver performs bit synchronization operation. Here, when noise is received in each channel, bit synchronization cannot be obtained. That is, consider the case where a system is constructed on the condition that communication is established reliably even if there is interference due to noise.

In this case, a time of T ₂ + T _{3 at} the maximum is required to complete the bit synchronization based on the carrier sense timing of the receiver and the time relationship of the header slot from the transmitter. In order to be able to receive a signal addressed to the own device even when noise is received, even if a reception operation is performed on each channel for a time T ₂ + T ₃ , the channel addressed to the own device is next received. It must be able to be received when a signal is received. This means that even when there is no noise in each channel, communication addressed to itself can be received even if carrier sensing is performed at intervals of T ₁ = T ₂ + T ₃ .

From this, the range of T ₁ is
T ₂ <T ₁ <T ₂ + T ₃
Can be defined as a range of
In this embodiment, the number M of header slot repetitions from the transmitter is M = 2 × N with respect to the number of channels N, but in a system in which the bit synchronization length is short with respect to the total length of the header slot, In some cases, the number of repetitions M can be further reduced. For example, M = 2 × N−1, 2 × N−2, 2 × N−2, and so on. In this embodiment, it can be said that there is a high possibility that the number of repetitions M can be reduced as compared with the case of the second embodiment. Thereby, by reducing the number of header slots, the transmission packet length can be shortened and the communication time can be shortened. Further, it becomes possible to further improve the responsiveness such as device control.

(Embodiment 4)
FIG. 6 is a timing chart showing the timing of the bit synchronization operation according to the fourth embodiment of the present invention. A receiver according to this embodiment will be described with reference to FIG.

  The feature of this embodiment is that a bit synchronization operation is used instead of a carrier sense operation during reception standby. In the bit-synchronized operation, the receiver circuit is continuously operated, and thus the effect of reducing power consumption as in the above-described example cannot be obtained. However, the standby by the bit synchronization operation can communicate the input signal up to the sensitivity point of the receiver, so that the communication distance can be greatly extended.

  For example, in Japan's 400 MHz band specific low power radio, the carrier sense level is set to -107 dBm or the like at the antenna terminal, but in a general receiver, the sensitivity point is around -120 dBm. The difference 13 dB corresponds to a radio wave propagation distance in free space of 3 times or more, and a communication area area of 10 times or more. From this, it can be said that the merit of waiting by the bit synchronization operation is great.

In the present embodiment, it is assumed that the number of repetitions M of the header slot is reduced in order to shorten the transmission packet length from the transmitter. To reliably bit synchronization, it is necessary to continue the bit synchronization operation over time length T ₂ of the at least the header slots. Therefore, bit synchronization duration in each channel is required T ₂ or more.

  In addition, since the time required for the channel switching operation of the receiver and the time of the bit synchronization pattern necessary for bit synchronization (for example, the bit synchronization pattern for 8 bits) are required, 1.5 to 2 headers for each channel It takes time for slots.

However, considering the case where the number of repeated header slots is reduced to M = 2 × N = 6 (when N = 3), if the bit synchronization operation in each channel is performed over two header slots or more, all headers It is assumed that the bit synchronization operation for three channels cannot be completed within the slot time. Therefore, T ₁ needs to be set within 2 × T _{2 at the} maximum.

From the above, when T ₁ is set in a range defined by T ₂ <T ₁ <2 × T ₂ , communication can be performed without omission.

  As described above, in the receiver according to the present embodiment, the communication distance can be greatly increased.

(Embodiment 5)
FIG. 7 is a timing chart showing the timing of the bit synchronization operation according to the fifth embodiment of the present invention. A receiver according to this embodiment will be described with reference to FIG.

  The carrier sense timing of the present embodiment is the same as that of the first embodiment. The feature of this embodiment is that the carrier sense operation does not immediately shift to the bit synchronization operation when it is determined that the carrier sense is present, and after performing carrier sense and reception level detection of all channels, the channel with the highest reception level is detected. The bit synchronization operation is performed.

In Figure 7, it is without a carrier, first carrier sense timing (1) or carrier sense operation of the first channel, after a predetermined time T _1, the case where a presence carrier if noise such as in (2), that the second channel Represents. At this time, the carrier sense of (3) and (1), that is, the third channel and the first channel is performed without shifting to the reception operation of the second channel.

  The receiver according to the present embodiment performs a standby operation using three channels, but there is a possibility that carrier sense may occur in each channel due to noise or communication with other devices. Here, there is a high possibility that the reception level of the noise and the radio wave of other device communication is lower than the radio wave of communication addressed to the own device.

  Therefore, by detecting the reception level of all channels (3 channels) by the reception level detection means, receiving the channel with the highest level preferentially and taking bit synchronization, there is a possibility of failing to receive the communication addressed to itself. (In the case of FIG. 7, since the channel (1) has the highest reception level, (1) the channel synchronization after channel sense is performed after (2) and (3) carrier sense).

  In particular, when a receiver is installed near a noise source (for example, a personal computer, a television, an IH device, etc.), it is assumed that noise of a frequency of a specific channel is always received. In this case, there is a high possibility that carrier sense is erroneously caused by noise. Even in such a situation, if the method of the present embodiment is used, communication addressed to the own device can be received preferentially. Moreover, since the probability that the communication addressed to itself can be preferentially received is improved, useless reception time can be saved and power consumption can be reduced.

  In this embodiment, the same carrier sense timing as in the first embodiment is used, but the present invention can be applied to the operation of the carrier sense timing as in the second to third embodiments.

  Further, in the case of waiting by continuous bit synchronization operation as in the fourth embodiment, the reception level of each channel is detected by the reception level detection means before performing the bit synchronization operation, and the reception level is the highest. By performing the bit synchronization operation preferentially for the channel, the communication addressed to the own device can be received more reliably.

  The demodulation operation refers to a process including a bit synchronization operation, a subsequent frame synchronization operation, and reception of an identification signal.

  As described above, the receiver according to the present invention can obtain a reception function equivalent to that of continuous carrier sense even in intermittent carrier sense operation, and can reduce power consumption without impairing quick response such as device control. Therefore, it can be applied as a receiver of a wireless communication system for performing device control and data transmission in a wide range of fields including home appliances and industrial devices.

Timing chart of carrier sense of receiver in Embodiment 1 of the present invention Configuration diagram of receiver in Embodiment 1 of the present invention Explanatory drawing which shows the relationship between the carrier sense operation | movement of the receiver in Embodiment 1 of this invention, and a transmission packet. Explanatory drawing which shows the relationship between the carrier sense operation | movement of the receiver in this Embodiment 2, and a transmission packet. Explanatory drawing which shows the relationship between the carrier sense operation | movement of the receiver in this Embodiment 3, and a transmission packet. Explanatory drawing showing the relationship between the bit synchronization operation of the receiver and the transmission packet in the fourth embodiment Explanatory drawing showing the relationship between the bit synchronization operation of the receiver and the transmission packet in the fifth embodiment Explanatory drawing showing the message structure of the transmitted packet Conventional receiver carrier sense timing diagram

Explanation of symbols

1 Antenna 2 High-frequency filter 3 LNA
4 mixer 5 local oscillator 6 channel selection filter 7 demodulation means 8 carrier sense means 9 reception level detection means

Claims (4)

A carrier sense means and a demodulator means are provided, which are used in a communication mode in which communication is performed using any one of N predetermined channels, and a bit synchronization signal, a frame synchronization signal, and an identification signal transmitted from a transmitter, respectively. A receiver for receiving a transmission packet comprising a plurality of header slots and a data slot following the plurality of header slots;
The N channels are sequentially switched one channel at a time during the first constant time T1 to perform intermittent carrier sensing , and during the first constant time T1, the sleep state is maintained.
The first fixed time T1 is a receiver set in a range represented by T2 <T1 <(2N−1) / N × T2 (N: natural number) with respect to a time length T2 of one header slot . A carrier sense means and a demodulator means are provided, which are used in a communication mode in which communication is performed using any one of N predetermined channels, and a bit synchronization signal, a frame synchronization signal, and an identification signal transmitted from a transmitter, respectively. A receiver for receiving a transmission packet comprising a plurality of header slots and a data slot following the plurality of header slots;
The N channels are sequentially switched one channel at a time during the first constant time T1 to perform intermittent carrier sensing, and during the first constant time T1, the sleep state is maintained.
The first predetermined time T1, the time length of one header slot T2, the duration T3 of the bit synchronization signal included in a header slot, the duration T4 of the frame synchronization signal included in a header slot, T2 <T1 < A receiver set in the range indicated by T2 + T3 + T4. A carrier sense means and a demodulator means are provided, which are used in a communication mode in which communication is performed using any one of N predetermined channels, and a bit synchronization signal, a frame synchronization signal, and an identification signal transmitted from a transmitter, respectively. A receiver for receiving a transmission packet comprising a plurality of header slots and a data slot following the plurality of header slots;
The N channels are sequentially switched one channel at a time during the first constant time T1 to perform intermittent carrier sensing, and during the first constant time T1, the sleep state is maintained.
The first fixed time T1 is a receiver set in a range represented by T2 <T1 <T2 + T3 with respect to a time length T2 of a header slot and a time length T3 of a bit synchronization signal included in the header slot . Furthermore, a level detection means is provided, and when carrier sense is detected in a certain channel, carrier sense is continuously performed for all other channels, and the level of the received signal of each channel is detected by the level detection means. The receiver according to any one of claims 1 to 3, which performs a demodulating operation of a channel having a maximum received signal level.

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