JP2008042383A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make power consumption and a communication area compatible by being adapted to an installation environment and setting a carrier sense threshold. <P>SOLUTION: In the receiver 11, in a carrier sense operation performed by shifting from a suspension mode to a reception mode intermittently, when a reception electric field level detected in a reception electric field level detection means 6 is lower than a preset threshold level, a judgement means 8 judges carrier absence, interrupts a reception mode and shifts to the suspension mode. When it is the threshold level or higher, carrier presence is judged, and reception signals are demodulated by a demodulation means 10. A history means 9 obtains the ratio that the judgement means 8 judges the carrier presence in the carrier sense operation of a prescribed period or the prescribed number of times, and a threshold setting means 7 changes the threshold level set to the judgement means 8 so as to be low when the ratio is smaller than a prescribed value and changes the threshold level so as to be high when the ratio is larger than the prescribed value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a receiver constituting a wireless communication system. In particular, it takes the form of battery drive, etc., and the power is normally turned off as a sleep mode, and periodically shifts to the reception mode, activates the reception circuit to perform carrier sense, and transitions to the sleep mode again when there is no carrier. The present invention relates to a receiver that performs a standby reception operation to reduce power consumption.

  In recent years, there are an increasing number of wireless communication devices that are on standby for reception by battery driving in a specific low power wireless, Bluetooth (registered trademark), wireless LAN, or mobile phone. When wireless communication is performed by battery drive, if standby reception of a transmission signal from a partner communication device is performed by continuous reception, battery consumption increases and this becomes a practical problem. There are adverse effects such as the need to enlarge the battery, or the battery life is shortened and the battery needs to be replaced frequently. Since the standby reception power consumption is dominant in the power consumption of all communication operations, a method for reducing the power consumption has been proposed.

  In general, continuous reception is not performed, but normally, a sleep mode, that is, a power supply of a reception circuit is turned off so that a current does not flow or is small, and the reception mode is periodically changed to perform reception.

  At this time, in order to confirm whether transmission is performed from the partner communication device, a circuit for detecting the received electric field level is provided, and the received electric field level is confirmed in a short time (this operation is called carrier sense) and set in advance. If it is below the threshold level, the power is turned off immediately and a transition is made to the sleep mode. This reduces the time during which the circuit is operating and suppresses power consumption.

  If the threshold level of the carrier sense is set low, it can be determined that there is a carrier even when a weak reception signal is received, and the operation can be shifted to the reception demodulation operation. That is, the communication area can be enlarged.

  However, if the threshold level is lowered in this way, environmental noise and other unnecessary signals (such as communications from other distant systems) are erroneously determined as having a carrier, and the operation shifts to a reception demodulation operation. Since it takes a long time to determine (for example, noise), power consumption increases.

  As the environmental noise in the place where the receiver is installed, in addition to thermal noise, radiation from a device using a high clock signal such as a personal computer or a device using a large amplitude signal such as an inverter power supply tends to be large.

  In order to avoid erroneous detection of carriers due to unnecessary signals, there is a method of setting the threshold value high, but this is not desirable because it increases the possibility of determining that there is no carrier when a desired signal is incident.

  Patent Document 1 describes a method for avoiding the above. In other words, a method is used in which the received electric field level at the time of communication with the counterpart communication device is recorded, and when the received electric field level is high, the threshold value is set high. As a result, the threshold value is not lowered more than necessary, and sensing due to unnecessary signals such as noise can be avoided.

  Further, Patent Document 2 describes a method of reducing the time of unnecessary reception operation by determining in a short time that noise is detected instead of a desired signal when sensing with noise.

Patent Document 3 describes a method for preventing detection by noise by providing a circuit for detecting a received electric field level and a circuit for detecting a noise level in carrier sense.
JP 2004-186865 A Japanese Patent Laid-Open No. 10-32504 JP-A-11-103481

  However, it has been difficult to prevent unnecessary senses such as noise depending on the installation environment while securing a sufficient communication area with the above-described conventional method.

  That is, the method of the above-mentioned document 1 is effective only when there is one partner communication device and a sufficient received electric field level is obtained. When the partner communication device is far away, there is no effect because the threshold level is low. Further, since the communication area is reduced when the threshold value is increased, it is difficult to adapt to a system that communicates with a plurality of (especially different distances) or unspecified communication devices.

  In the methods of References 2 and 3, since it is determined that the carrier is present once in the carrier sense operation, and a procedure for determining whether the signal is an unnecessary signal by extending the time of the reception operation is taken, a certain time is required until the determination. Therefore, there is a problem in that the power-on time of the receiving circuit is extended and power consumption increases.

  In order to solve the above-described conventional problems, the receiver of the present invention includes a reception electric field level detection means, a determination means, a history means, a threshold setting means, and a demodulation means, and transits from the sleep mode to the reception mode intermittently. A carrier sense operation is performed, and in the carrier sense operation, the determination unit determines that there is no carrier when the reception electric field level detected by the reception electric field level detection unit is less than a preset threshold level, and interrupts the reception mode. The receiver transits to the sleep mode and determines that there is a carrier when the threshold level is equal to or higher than the threshold level and demodulates the received signal by the demodulating means, and the history means has a predetermined period or a predetermined number of times. In the carrier sense operation, the ratio determined by the determination means that there is a carrier is obtained, and the threshold value setting means determines that the ratio is smaller than a predetermined value. The threshold value set in the determination means is changed to be lower, and the threshold level set in the determination means is changed to be higher when the ratio is larger than a predetermined value. It is.

  Since the carrier sense threshold value is varied according to the state of unnecessary signals to be installed, unnecessary sensing can be suppressed to reduce power consumption, and the communication area can be maximized.

  Since the receiver of the present invention varies the carrier sense threshold according to the state of an unnecessary signal to be installed, it is possible to suppress unnecessary sensing to reduce power consumption and to obtain a maximum communication area.

The receiver of the first invention comprises a received electric field level detecting means, a determining means, a history means, a threshold value setting means, and a demodulating means, and intermittently transits from the sleep mode to the receiving mode to perform a carrier sense operation. In the carrier sense operation, the determination means determines that there is no carrier when the reception electric field level detected by the reception electric field level detection means is less than a preset threshold level, interrupts the reception mode, and transitions to the sleep mode. And a receiver that demodulates a received signal by the demodulating means by determining that there is a carrier when the threshold level is equal to or higher than the threshold level,
The history means obtains a ratio that the determination means determines that there is a carrier in the carrier sense operation for a predetermined period or a predetermined number of times, and the threshold setting means determines the determination means when the ratio is smaller than a predetermined value. The threshold level set to be set to be lower, and when the ratio is larger than a predetermined value, the threshold level set to the determination means is changed to be higher.

  Since the carrier sense threshold value is varied according to the state of the unnecessary signal in the installed environment, unnecessary sensing can be suppressed to reduce power consumption, and the communication area can be maximized.

  A receiver according to a second aspect of the invention comprises a reception electric field level detection means, a determination means, a first counter means, a second counter means, a threshold value setting means, and a demodulation means, and intermittently switches from a pause mode to a reception mode. The carrier sense operation is performed by transition, and in the carrier sense operation, the determination unit determines that there is no carrier when the reception electric field level detected by the reception electric field level detection unit is less than a preset threshold level, and the reception mode Is interrupted, transitions to the sleep mode, determines that there is a carrier when the threshold level is equal to or higher than the threshold level, and demodulates the received signal by the demodulating means, and the count completion number of the first counter means is M, the number of completions of counting by the second counter means is N (where M> N), and the first counter means performs the carrier sense operation. The second counter means counts the number of times the determination means determines that there is a carrier in the carrier sense operation, and the threshold value setting means indicates that the count number of the first counter means is When the count number of the second counter means reaches N before M, the threshold value set in the determination means is changed to be higher and the first and second counter means are changed. When the count number of the first counter means becomes M, and the count number of the second counter means is N or less, the threshold level set in the determination means is low. And the first and second counter means are reset.

  In addition, a simple counter is used to obtain the rate at which it is determined that there is a carrier due to an unnecessary signal input, and the threshold level is immediately changed when the second counter reaches the completion number N. When the level of an unnecessary signal increases, it can react immediately and suppress power consumption.

  A receiver according to a third aspect of the invention demodulates the received signal by the demodulating means when the judging means judges that there is a carrier, and when the demodulated signal is a desired signal, the second counter means It does not count. When communication is performed by receiving a desired signal, the threshold value is not included in the number of counts for determining the threshold value. Therefore, even if the desired signal is frequently communicated, the threshold value is not changed high. Stable communication can be performed.

  The receiver according to the fourth aspect of the present invention further includes noise squelch means, and only when the determination means determines that there is a carrier in the carrier sense operation and the noise squelch means determines that the received signal is a noise component. The second counter means counts. Since the threshold value is included in the count number that is determined only when it is received in noise, the threshold value can be changed to a high value even if communication with other systems other than the desired signal is frequently performed. And stable communication.

According to a fifth aspect of the present invention, in the carrier sense operation, the determination means compares the average value or representative value of the detection values obtained by the reception electric field level detection means with a threshold level to determine the presence or absence of a carrier. Judgment. Since the threshold value is determined using a plurality of reception level detection values, the carrier presence / absence determination accuracy is improved, the threshold value is not changed sensitively, and communication is not unstable.

  A receiver according to a sixth aspect of the invention varies the predetermined value according to a threshold level set in the determination means. Then, the threshold level does not change more than necessary, and the communication area does not become too small or the signal of a distant communication device is not received too much.

  A receiver according to a seventh aspect of the present invention varies the value of M or N according to a threshold level set in the determination means. Then, the threshold level does not change more than necessary, and the communication area does not become too small or the signal of a distant communication device is not received too much.

  Hereinafter, the present embodiment 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 block diagram showing a configuration of a receiver according to the first embodiment. In FIG. 1, 1 is an antenna, 2 is a reception means, 3 is a transmission means, 4 is a local signal source, 5 is a demodulation means, 6 is a reception electric field level detection means, 7 is a threshold setting means, 8 is a determination means, 9 is a history means, 10 is a control means, and 11 is a receiver. Moreover, the component enclosed with the broken line represents that the control means 10 is controlling these components.

  The present embodiment is a receiver that is driven by a battery and waits for and receives a transmission signal from a counterpart communication device. In order to reduce power consumption during standby reception, the sleep mode is intermittently changed to the reception mode, and the circuit is powered on. In addition, after the reception operation is performed, the sleep mode is set and the power of most circuits is turned off.

  Now, in the reception mode, a reception signal incident from the antenna 1 is input to the reception means 2. The receiving means 2 is composed of an LNA, a mixer, a filter and the like, and is constituted by a general superheterodyne receiving circuit.

  The signal from the local signal source 4 is input as a local signal to the mixer of the receiving means 2 and the received signal is converted to an intermediate frequency. The intermediate frequency signal that is the output of the receiving means 2 is input to the demodulating means 5 and the received electric field level detecting means 6.

  The received electric field level detecting means 6 detects the received electric field level at an early stage after the transition from the sleep mode to the received mode. Here, the received electric field level detecting means 6 is constituted by an RSSI circuit (Received Signal Strength Indicator).

  The threshold setting setting means 7 sets a threshold level when the determination means 8 determines the presence or absence of a carrier. Then, as will be described later, the threshold level set in the determination means 8 is updated when determination of threshold level change occurs. Here, the threshold level is stored in the determination unit. However, the threshold level may be stored in the control unit 10 that controls the entire receiver 11 or may be configured to include a separate threshold level storage unit.

  Transition from the sleep mode to the reception mode is performed, and the determination unit 8 compares the detection value of the reception electric field level detection unit 6 with the threshold level set by the threshold setting unit 7 to determine the presence or absence of the carrier. This operation is called a carrier sense operation.

  When the determination unit 8 determines that the received electric field level is lower than the threshold level in the carrier sense operation, the reception is interrupted and the mode is changed to the sleep mode. If the received electric field level is equal to or higher than the threshold level, the demodulating means 5 is used to demodulate data.

  When the predetermined data reception is completed, the mode is changed to the sleep mode, or the continuous reception operation is continued for a certain time to wait for a signal from the partner communication device, or the data is transmitted to the partner communication device. After doing so, transition to sleep mode. And it is operated by the operation of repeating the pause mode and the reception mode intermittently.

  If it is determined in the carrier sense operation that the carrier is present, the receiving and demodulating operation is performed using the demodulating unit 5 under the control of the control unit 10, but the received signal is not a desired signal as a result of analyzing the received data by the demodulating operation, that is, there is a carrier. It takes a long time to determine that the determined signal is an unnecessary signal such as noise or communication of another system. Specifically, the time required for detection of the received electric field level by the carrier sense operation is about 1 to 10 bits, but in order to determine whether the signal is a desired signal by the demodulation operation, several tens to several hundred bits are used. Cost. Since the carrier sense operation measures the envelope amplitude of the intermediate frequency signal of the received signal using the RSSI circuit, the measurement is completed in a short time. However, since the demodulation operation is performed by analyzing the received data, the carrier sense operation is 10 times or more. It takes time.

  Therefore, in order to reduce power consumption, it is necessary to avoid erroneously determining that there is a carrier due to noise or the like in the carrier sense operation as much as possible.

  In the receiver of this embodiment, carrier sense operation is performed intermittently. The history unit 9 records the number of times the determination unit 8 determines that there is a carrier (for example, 3 times) at the time when the carrier sense operation is performed a plurality of times (for example, 20 times) as a history, Obtained (in the above example, the ratio is 3/20 = 0.15). Then, the threshold level set in the determination means from the next time is changed depending on whether the ratio is larger or smaller than a predetermined value (for example, 0.1). When the ratio is smaller than a predetermined value, the threshold level is changed to be low. When it is larger, the threshold value is changed to be higher (in the above example, the ratio obtained by the history means is 0.15 and is larger than the predetermined value 0.1, so the threshold level is set higher by 1 dB).

  Specifically, the threshold is set to the received electric field level of −110 dBm, the carrier sense operation is performed at intervals of 3 seconds, and when the carrier sense operation is performed 20 times (required time 60 seconds at this time), the carrier sense operation is performed. The number of times determined to be present is checked, and if the number is 3 or more, the threshold is changed to −109 dBm from the next carrier sense operation. If the number of times of determination that the carrier is present is 1 or less, the threshold value is changed to -111 dBm from the next time.

  By continuously performing the above operation, the threshold level can be set so that the ratio of erroneously determining that there is a carrier due to noise or the like is about 2/20. When the receiver is installed in an environment where the noise level is low, the threshold level is changed to be lower than -110 dBm so that a weak received signal can be sensed by carrier, so that power consumption does not increase. The communication area can be maximized. Here, the reception demodulation operation is shifted to a frequency of about 2/20 and the reception time is extended. This frequency is 10% of the total carrier sense operation, and the effect on the power consumption increase due to this reception time extension is compared. It can be said that it is small.

  The predetermined value (2/20 in the above) can be set arbitrarily. In particular, when the increase in power consumption is desired to be suppressed, the predetermined value is set to a small value (for example, 1/100), and particularly when priority is given to the communication area, the predetermined value is set to a large value (for example, 1/5).

  In general, in order to perform stable communication by wireless communication, it is better to set the carrier sense level lower. The radio wave propagation environment changes from moment to moment, and the reception level fluctuates. This is because if there is transmission when the level drops, there is a possibility that reception will fail without sensing because the level is lower than the carrier sense level.

  However, depending on the installation environment, the noise level emitted from the peripheral device may be high, and it may be frequently sensed, and the battery may be exhausted by repeating the reception and demodulation operation each time. In this case, if the carrier sense threshold is not set a little higher, battery consumption will be accelerated.

  In other words, the carrier sense threshold level is set as low as possible, but when the environment is bad, the threshold level is changed to a higher value in order to ensure both battery life. However, at this time, there is a demand for setting as low as possible within a range that does not greatly affect battery consumption. In the configuration of the present embodiment, the threshold level can be varied up and down so that the optimum threshold level as described above is automatically obtained even when the environment changes.

  Factors that determine that there is a carrier other than the desired signal can be broadly classified into noise and signals from communication devices of other systems.

  In addition to thermal noise, noise is greatly affected by noise and spurious components radiated from devices using high-frequency clock signals such as personal computers and devices equipped with inverter power supplies. Therefore, the noise level tends to be low outdoors (especially other than urban areas), and the noise level tends to be high indoors (especially in the vicinity of the device). Therefore, it is desirable to reduce the threshold value outdoors to secure a communication area, and to increase the threshold value indoors to avoid unnecessary signals causing carriers and increasing power consumption.

  The present embodiment is characterized in that the movement of the threshold level as described above can be automatically varied according to the environment.

  In addition, as signals of other systems, there are signals of other systems that use the same channel (transmission signals from communication devices that are not communication partners). If signals from other systems are frequently received, the threshold value is changed to a higher side, and the communication area may be reduced. As to the avoidance of this, as will be described later, it is only necessary to identify that the signal of the other system is not a noise component so as not to be included in the number of false senses. As a method for determining that it is not a noise component, there are a method for confirming whether a demodulated data includes a bit synchronization signal or a frame synchronization signal, and a method for determining whether it is a noise component by a noise squelch means.

  By the way, if the control method of the present embodiment is changed so as to increase the threshold value, the communication area is reduced, but the effect of this is substantially small. The reason will be described below.

In an environment where the noise level is high, the S / N ratio of the received signal is lowered, so that the reception sensitivity at the time of data demodulation by the demodulating means is deteriorated and the area becomes narrow. For example, in the case of an FSK modulated signal, the S / N ratio required for demodulation (BER (Bit error rate) = 10 ⁻² ) is about 6 dB. The required S / N ratio varies depending on the modulation method.

That is, in an environment where the noise level is high, even if carrier sensing is performed, the BER necessary for the subsequent reception demodulation operation cannot be secured. Therefore, when the threshold is increased to determine that there is no carrier and reception is interrupted, the threshold is decreased to determine that there is a carrier and the reception time is extended to shift to demodulation operation. There is not much difference in various communication areas. Rather, since the adverse effect of increasing the power consumption due to the extension of the reception time is great, it is more advantageous to reduce the power consumption if the reception operation is interrupted by raising the threshold value of carrier sense.

(Embodiment 2)
FIG. 2 is a block diagram showing a configuration of a receiver according to the second embodiment. In FIG. 2, 12 is a first counter means, and 13 is a second counter means. The same components as those in the first embodiment are denoted by the same reference numerals.

  The feature of this embodiment is that the first and second counters are used.

  Using this, the ratio of carrier presence in the carrier sense operation is obtained. The control when using the first and second counter means will be described below.

  The first counter means 12 represents the number of times that the carrier sense operation has been performed, and the second counter means 13 represents the number of times that it has been determined that there is a carrier.

  The control means 10 counts up the first counter means 8 every time the carrier sense operation is performed after the transition from the sleep mode to the reception mode. When the determination means 8 determines that there is a carrier in the carrier sense operation, the second counter means 9 is incremented.

  Here, the count completion numbers of the first and second counting means are M and N, respectively. Specifically, M = 20 and N = 2 are set.

  A carrier sense operation is performed every 3 seconds, and the first counter means 12 is counted up. When the second counter means 13 reaches N, the first and second counter means are reset, and the threshold value setting means 7 sets the threshold value one step higher (for example, 1 dB).

  However, if the first counter means 8 reaches M before the second counter means 13 reaches N, the first and second counter means are reset, and the threshold setting means 7 Lower the threshold by one step (eg 1 dB).

  By repeating the above, the ratio of having a carrier can be reduced to about 1/20. The lowest threshold value can be automatically set under the condition that the increase in power consumption due to reception of unnecessary signals is relatively small.

  Then, by selecting the completion numbers M and N of the first and second counter means to arbitrary values, it is possible to change the target (priority) for suppressing the increase in power consumption and securing the communication area. For example, if the number of completions N is increased, the threshold value is changed to a lower side, and the frequency of sensing with noise is allowed to be increased, giving priority to expansion of the communication area.

  In this embodiment, the environment of the place where the receiver is installed changes. For example, when the noise level suddenly increases at a certain timing, the carrier sense threshold level is immediately increased, and the reception demodulation operation is frequently performed. It is possible to prevent an increase in power consumption due to the occurrence of the problem.

  That is, when the count value of the second counter means 13 reaches N, the threshold level is changed to a high level. At this time, the first counter 12 has not reached M times, but stops counting and immediately changes the threshold level.

As a result, it is possible to obtain the ratio of the carrier present after performing the carrier sense operation M times, and to complete the change of the threshold level in a short time compared to the case of changing the threshold level. And it is possible to prevent an increase in power consumption due to a sudden environmental change.

  In the receiver of the present embodiment, each means is controlled by the control means 10, that is, a microcomputer. Further, the threshold value detection means 7 and the first and second counter means 8 and 9 may be performed by a function in the microcomputer.

  FIG. 3 shows a flowchart of the operation.

  Starting from the start of reception, intermittent standby is repeated for repeating the operation of switching from the sleep mode to the reception mode every 3 seconds. First, when the mode is changed from the sleep mode to the reception mode (S1), the reception electric field level detection means 6 acquires the reception electric field level (S8) by the carrier sense operation. At this time, the first counter means 12 is counted up (S9). Then, the determination unit 8 compares the acquired received electric field level with a preset threshold level (S10), and if it is less than the threshold, transitions to the sleep mode and pauses for 3 seconds (S3).

  If the received electric field level is equal to or higher than the threshold (in S3), the second counter means 13 is counted up (S11). Then, the demodulating means 5 performs a demodulating operation (S12). Here, by confirming the contents of the demodulated data, it is discriminated whether the received signal is the desired signal (transmission signal of the partner communication device). If it is the desired signal, the received data is received, and the control means 10 receives the second counter. The means 13 is counted down.

  This countdown is for canceling the previous count-up, and is a measure for performing an operation of not counting up the second counter means 13 when the received signal is a desired signal. If it is not the desired signal, it transitions to the sleep mode and pauses for 3 seconds.

  The above operation is repeated every 3 seconds, and when the count number m of the first counter means 12 reaches the count completion number M, the threshold level is changed to a level one step lower (S15). Here, M is 20 as an example.

  If the count number n of the second counter means 13 reaches the count completion number N before m = M, the threshold level is changed to a level higher by one step (S16). Here, M is 2 as an example.

  In this manner, whether the threshold value is increased or decreased is determined depending on which of the first counter means 12 and the second counter means 13 reaches the count completion number first.

  By continuously performing the above operation, the threshold level at which a carrier is present is settled at a desired ratio. This threshold level is the most suitable level in the installation environment, and the balance between the increase in power consumption and the securing of the communication area has been achieved. The present embodiment is characterized in that the threshold level automatically changes to this optimum level.

  FIG. 4 shows an output waveform of the received electric field level detecting means. Plotting is performed for the case where the transmission signal (FSK modulated wave) of the partner communication device is received and the case where noise is received.

  When the transmission signal of the counterpart communication device is received, the detected amplitude fluctuation is small, but the noise greatly fluctuates. Since noise includes a wideband frequency component, the level detected by the RSSI circuit varies greatly with time.

  In the time range shown in FIG. 4 (60 seconds), there is only one carrier at a carrier sense timing every 3 seconds. Here, when the receiver is installed in an environment where the noise level is higher, the number of times the carrier is present increases. In this state, there is a problem that the rate of shifting to the reception demodulation operation increases and the battery consumption increases.

  Further, when the receiver is set in an environment where the noise level is lower, the ratio of determining that there is a carrier due to noise becomes small. In this state, the communication area can be expanded by setting the threshold level lower. In the present embodiment, the threshold level is raised or lowered according to the proportion of carriers, so that the optimum threshold value for the installed environment can be automatically set.

  In the above-described embodiment, the reception level is detected by the reception electric field level detecting means in the carrier sense operation, but the value measured once is used. However, during the carrier sense operation, the reception electric field level is measured a plurality of times and the plurality of times. It is also possible to perform a comparison with a threshold value after performing an arithmetic operation on the measured value. By using the measurement values a plurality of times, it is possible to reduce the ratio of determining that there is a carrier when receiving a noise component, and the threshold value does not rise or fall greatly, so that it is possible to stably wait for reception.

  If a method of obtaining an average value after removing a maximum value and a minimum value of a plurality of measured values is used, it is possible to remove a sudden reception level value and obtain a stable value.

  Further, the following values can be used as representative values.

  You may determine using the minimum value among several measured values. As a result, carrier sense due to noise can be reduced as much as possible. On the other hand, when the transmission signal is received instead of noise, the difference between the minimum value and the maximum value is small. Therefore, even if the minimum value is used as described above, there is little possibility of losing transmission from the other party. This has the effect of reducing only the frequency at which it occurs.

  Further, when the determination unit 8 determines that there is a carrier, the carrier sense operation may be extended and the determination may be made by detecting the received electric field level a plurality of times. When no carrier is found in a plurality of determination results, the carrier sense is interrupted and the mode is changed to the sleep mode. By controlling in this way, it is possible to prevent transition to reception demodulation due to noise.

  Further, an upper limit value and / or a lower limit value may be provided in the variable range of the threshold level. The upper limit is set in the variable range of the threshold level when the noise level is very large or the communication frequency by other communication devices is high and it is frequently determined that there is a carrier. It is for preventing that becoming too high.

  It can be used when performing an operation to secure a necessary communication area even at the expense of some increase in power consumption. Alternatively, it can be realized by setting a lower limit value of the variable range of the threshold value in order to prevent the carrier from being present in response to a signal from a remote communication device, that is, to limit the communication area to some extent.

  Further, when the threshold level reaches the upper limit value or when it reaches the lower limit value, it can be used for an operation such as sending an alarm message to the partner communication device as an abnormal state. This makes it possible for the other communication device to know that the environment where the receiver is located is in a bad environment where the noise level is high, and to obtain information for taking measures such as changing the installation location of the receiver. I can do it.

  In addition, a new effect can be obtained by making the reference (predetermined value) of the ratio of having a carrier, which is a material for determining whether to raise or lower the threshold level, being variable.

  That is, when the threshold level is low, the predetermined value is set smaller. For example, it is set to 1/20. Thereafter, as the environment deteriorates and the noise level increases, the threshold level increases. If the noise level is significantly increased here, the threshold level will be significantly increased, the communication area will be extremely small, and carrier sense will not be possible with the signal of the partner communication device, and communication will be unstable. It is thought that it will become.

  At this time, it is assumed that the current consumption is slightly increased and that the threshold level is prevented from rising excessively. In this case, when the threshold level rises above a certain value, the determination criterion (predetermined value) for the ratio of carrier presence is set to be larger. For example, it is set to 3/20. This can prevent the communication area from becoming extremely small.

  The change of the predetermined value may be changed linearly according to the threshold level, or may be changed by any method including stepwise change when it exceeds a certain value.

(Embodiment 3)
FIG. 5 is a block diagram showing a configuration of a receiver according to the second embodiment. In FIG. 5, 14 is a noise squelch means. In addition, the same code | symbol was attached | subjected about the component same as the said Embodiment 1 and 2.

  The feature of this embodiment is that a noise squelch means 14 is provided in addition to the reception electric field level detection means 6.

  The reception electric field level detection means 6 uses an RSSI circuit and detects the amplitude of the envelope of the intermediate frequency signal obtained by mixer conversion of the reception signal. Specifically, the current or voltage when the intermediate frequency signal is rectified What is necessary is just to obtain | require the amplitude of. The amplitude is output in response to both the signal from the counterpart communication device, which is a signal having a carrier characteristic (the signal component has a frequency peak), and the noise component (the signal component is spread over a wide band).

  On the other hand, the noise squelch means 14 has a property of reacting only when the received signal is a noise component. The specific operation of the noise squelch means measures the amplitude of the signal after passing through a band limiting filter that removes the signal component of the received signal (the signal including the modulation frequency component) from the signal obtained by detecting and demodulating the intermediate frequency signal. .

  If the noise squelch means 14 further detects noise when the received electric field level detection means 6 outputs an amplitude equal to or higher than the threshold level and the determination means 8 determines that there is a carrier, the second counter means 13 counts. Up. Thus, the second counter means counts up only when it is erroneously detected due to noise components.

  The response time of the noise squelch means 14 requires several times (ten bits length) about the response time of the received electric field level detection means 6, but the time (several times) required to determine erroneous detection from the demodulated data in the reception demodulation operation. It can be determined that the noise is a short time compared to 10 bits to several hundred bits. In the case of noise, power consumption can be suppressed by immediately transitioning to the sleep mode.

As described above, the receiver according to the present invention can set the threshold value low within a range in which the power consumption does not increase in accordance with the communication environment such as the noise environment and the communication frequency of the installation location. While suppressing, the maximum communication area can be obtained.

  This enables crime prevention and disaster prevention sensor terminals with built-in wireless devices in various sensors, wireless devices that are attached to gas meters, etc. to transmit and receive meter readings and device status via wireless communication, and in particular battery-powered due to low power consumption. It can be widely used as a receiver for wireless devices that require long-time operation.

1 is a block diagram showing the configuration of a receiver according to Embodiment 1 of the present invention. Block diagram showing a configuration of a receiver according to a second embodiment of the present invention. Communication flowchart showing the operation of the receiver according to the second embodiment of the present invention. The figure which shows the output waveform of the reception electric field level detection means of the receiver of Embodiment 2 of this invention Block diagram showing a configuration of a receiver according to a third embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Receiving means 3 Transmitting means 4 Local signal source 5 Demodulating means 6 Received electric field level detecting means 7 Threshold setting means 8 Judging means 9 History means 10 Control means 11 Receiver 12 First counter means 13 Second counter Means 14 Noise squelch means

Claims (7)

A reception field level detection unit, a determination unit, a history unit, a threshold value setting unit, and a demodulation unit, and intermittently transits from the sleep mode to the reception mode to perform a carrier sense operation. In the carrier sense operation, the determination unit Determines that there is no carrier when the received electric field level detected by the received electric field level detection means is less than a preset threshold level, interrupts the reception mode and transitions to the sleep mode, and exceeds the threshold level. A receiver that sometimes determines that there is a carrier and demodulates the received signal by the demodulation means,
The history means obtains a ratio that the determination means determines that there is a carrier in the carrier sense operation for a predetermined period or a predetermined number of times, and the threshold setting means determines the determination means when the ratio is smaller than a predetermined value. The receiver is changed so that the threshold level set to be lower, and when the ratio is larger than a predetermined value, the receiver is changed to increase the threshold level set in the determination means. A reception electric field level detection means, a determination means, a first counter means, a second counter means, a threshold value setting means, and a demodulation means;
The carrier sense operation is performed by intermittently transitioning from the sleep mode to the reception mode, and in the carrier sense operation, the determination means has a reception electric field level detected by the reception electric field level detection means less than a preset threshold level. Sometimes it is determined that there is no carrier, interrupts the reception mode and transitions to a dormant mode, and when it is equal to or higher than the threshold level, it is determined that there is a carrier and demodulates the received signal by the demodulation means,
The count completion number of the first counter means is M, the count completion number of the second counter means is N (where M> N), and the first counter means performs the carrier sense operation. The second counter means counts the number of times the determination means determines that there is a carrier in the carrier sense operation,
The threshold value setting means is set as the threshold value when the count number of the second counter means reaches the N before the count number of the first counter means reaches the M. The value level is changed to be higher, the first and second counter means are reset, and when the count number of the first counter means becomes the M, the count number of the second counter means is A receiver for changing the threshold level set in the determination means to be low and resetting the first and second counter means when N or less. The demodulating means demodulates the received signal when the determining means determines that there is a carrier, and the second counter means does not count when the demodulated signal is a desired signal. Receiving machine. In addition, noise squelch means is provided, and the second counter means counts only when the determination means determines that there is a carrier in the carrier sense operation and the noise squelch means determines that the received signal is a noise component. The receiver according to claim 2. 5. The carrier sensing operation according to claim 1, wherein in the carrier sense operation, the determination unit determines the presence or absence of a carrier by comparing an average value or a representative value of a plurality of detection values obtained by the reception electric field level detection unit with a threshold level. The receiver according to claim 1. The receiver according to claim 1, wherein the predetermined value is varied according to a threshold level set in the determination unit. The receiver according to any one of claims 2 to 5, wherein the value of N or M is varied according to a threshold level set in the determination means.

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