JP2015012471A - Transmission control method and radio communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress performance deterioration due to interference even in a state of mixed radio waves from another communication device and a microwave oven using the same frequency band.SOLUTION: A transmission control method includes: determining defective packet transmission during communication by the number of reception errors; determining whether or not the electric field intensity of a reception signal exceeds a frequency exceeding a predetermined threshold; and switching a transmission rate in the transmission to a low rate by a predetermined width if the packet transmission is determined to be defective and the electric field intensity of the reception signal exceeds the predetermined threshold, to retransmit the packet while maintaining the state, and switching the transmission rate in the transmission to a lower rate than the low rate if the electric field intensity of the reception signal does not exceed the predetermined threshold, and if the defect is not yet improved, decreasing the transmission rate to a minimum rate.

Description

  The present invention relates to a transmission control method and a wireless communication apparatus that can suppress performance degradation due to interference caused by communication by other communication apparatuses using the same frequency band.

  In recent years, wireless LAN devices using the IEEE 802.11 standard have been widely used as wireless network devices. In addition to the use in conventional personal computers, the range of applications has expanded to use in mobile devices such as mobile phones. In these mobile devices, there is a demand for particularly energy-saving and highly efficient communication. strong. In this specification, the IEEE 802.11 standard is referred to as the 802.11 standard.

  The 2.4 GHz band in the frequency band used by the 802.11 standard wireless LAN apparatus can be operated without a license in Japan, for example, and many wireless network apparatuses are standardized. As a wireless device using the 2.4 GHz band, for example, Bluetooth using a frequency hopping method (FHSS: Frequency Hopping Spread Spectrum) is widely used (Bluetooth is a registered trademark). In general homes, the microwave oven radiates electromagnetic noise in the 2.4 GHz band, and other frequency hopping cordless telephones also use the 2.4 GHz band.

  FIG. 15A shows the 2.4 GHz band used in the 802.11 standard. The 802.11 standard wireless LAN (wireless device) selects a channel to be used from among 13 channels set every 5 MHz, and performs carrier sense multiple access (CSMA) in the physical layer. This is because the wireless device performs carrier sense on the band before transmission, transmits if a signal from another device is not detected, and refrains from transmission if a signal higher than a certain threshold level is detected. In particular, in the 802.11 standard, it is necessary to observe a rule called Clear Channel Assessment (CCA) with preamble detection. This is CCA busy when a carrier sense is detected in a certain channel, and detection of preamble detection of a signal emitted by another 802.11 standard device is detected in the received signal regardless of the received electric field strength. , You must refrain from transmitting on that channel. That is, when another nearby 802.11 device is transmitting, the wireless device cannot transmit even if the reception field strength is small.

  Further, in the 802.11 standard, it is determined that two or more channel intervals are used apart from each other in order to prevent the occurrence of inter-channel interference with other 802.11 standard devices. For example, when a signal that seems to be from another 802.11 standard device is detected in [Ch1], adjacent [Ch2] and [Ch3] cannot be used. When a signal that seems to be from another 802.11 standard device is detected in [Ch5], adjacent [Ch3], [Ch4], [Ch6], and [Ch7] cannot be used.

  FIG. 15B shows a state in which the Bluetooth (BT) signal causes interference in the 802.11 channel. Bluetooth also performs carrier sense before determining the channel to be used, and determines the channel to be used in FHSS. However, it is inevitable that the 802.11 standard overlaps with the frequency in use and causes interference with a certain probability. The carrier sense threshold of Bluetooth is not as strict as the 802.11 standard, and even when another signal of a level higher than the level when the 802.11 standard refrains from transmission is detected, it is below the threshold determined by Bluetooth. If so, transmission may occur. Thus, the 2.4 GHz band can be operated without a license, but if other wireless devices such as Bluetooth devices or microwave ovens are nearby, communication speed performance may be degraded due to radio wave interference, When Bluetooth starts to transmit nearby or the microwave oven starts to operate, a situation may occur in which transmission cannot be performed indefinitely until there is no interference source.

  In addition, when a microwave oven is used nearby, a strong disturbance wave in the 2.4 GHz band is radiated intermittently. During the period in which the interference wave is radiated, the 802.11 standard device cannot start wireless communication under the influence of the interference wave. Therefore, in order to realize power-saving and high-efficiency wireless communication using the 2.4 GHz band, the interference level radiated by the microwave oven is detected in the wireless communication device, and the degree of influence it has on its own communication is determined. It is important to select the channel to be used while evaluating.

  2. Description of the Related Art Conventionally, there are the following wireless communication apparatuses that predict this type of microwave interference wave (for example, Patent Document 1). The interference wave radiated by a general microwave oven is synchronized with the frequency of the commercial AC power supply or an integral multiple of the frequency when the microwave oven is used. Periods are repeated periodically. In the wireless communication device disclosed in Patent Document 1, an RSSI signal indicating the intensity of a received radio wave received by an antenna radiates a disturbance wave with a period of high frequency emission when the received radio wave is from a microwave oven. The periodicity comprised with the period which is not carried out is shown. In Patent Document 1, the wireless communication device predicts the time zone in which the microwave oven radiates the jamming wave by detecting the timing at which the jamming wave is generated and the timing at which the jamming wave stops by detecting the periodicity of the RSSI signal. I can do it.

  In addition, in Patent Document 2, when a communication channel used by a base station device (base station) is selected from a plurality of channels, first, a channel being used by another base station device is detected, and then, A channel that is used when the received signal strength of a radio wave transmitted by another base station device in the detected busy channel is detected and there is no communication channel whose received signal strength is less than or equal to a predetermined value over a predetermined bandwidth. The communication channel used by the base station apparatus according to the received signal strength is selected.

  In Patent Document 3, when the combination of channels used by the base station is appropriately selected, the received signal strength of the radio wave detected in the used frequency band is measured, and other data is measured from the measured data of the received signal strength. Extracting measurement data related to the base station of the wireless communication system, calculating an index value indicating the received signal strength of the interference signal of each channel based on the received signal strength included in the extracted measurement data, The index value of each channel is weighted and added based on the interference table. Based on the interference level of each frequency channel, the influence of interference is minimized among the predetermined channel combinations composed of frequency channels with no frequency overlap. A selection of a certain channel combination is disclosed.

JP 2002-111603 A JP 2012-175545 A Japanese Patent No. 4886647

  However, in the conventional wireless communication apparatus, the microwave oven emits radiation under the situation where a radio wave mixed with various radio waves including a wireless communication is recognized as a received radio wave as shown in FIG. It is difficult to detect the periodicity of the disturbing wave, and if other signals are mixed, the channel overlapping the microwave oven may be selected without detecting the operation of the microwave oven.

  In order to solve the above-described problems with the conventional wireless communication apparatus, the present invention avoids errors and achieves high efficiency even in a situation where a radio wave including a variety of radio waves including a microwave oven is recognized as a received radio wave. An object of the present invention is to provide a transmission control method and a wireless communication apparatus that realizes reliable wireless communication.

  The transmission control method according to one aspect of the present invention transmits a packet on a channel permitted to be used by a carrier sense operation, determines whether the packet is transmitted or not based on the presence or absence of an error, and determines that the packet transmission is defective. When the field strength of the received signal exceeds a predetermined threshold in the channel, the transmission rate for transmitting the packet is switched to a low rate that is reduced by a predetermined width, and the low rate state is maintained to maintain the packet rate. If retransmission is performed and packet transmission is determined to be bad and the electric field strength of the received signal does not exceed a predetermined threshold in the channel, the transmission rate for transmitting packets is lowered to a rate lower than the low rate. Retransmit the packet.

  The transmission control method according to one aspect of the present invention determines whether or not the electric field strength of a signal exceeds a predetermined threshold, and further detects a predetermined preamble in received data during a carrier sense operation. Use / prohibition, and in a channel permitted to be used by the carrier sense operation, if the number of reception errors exceeds a predetermined threshold and the electric field strength of the signal exceeds a predetermined first threshold, transmission due to interference The transmission rate is lowered to a minimum value that is lower by a predetermined width, and thereafter the packet is retransmitted while maintaining the state reduced to the minimum value, the number of reception errors exceeds a predetermined threshold, If the electric field strength of the signal does not exceed the second threshold value smaller than the first threshold value, it is determined that the transmission is poor due to multipath, and the transmission rate is lowered to a rate lower than the low rate. And re-transmission of the packet, a time when the after the transmission rate was conducted retransmission of packets is lowered to a lower rate than the lower rate even failure does not improve further reduce the transmission rate.

  A radio communication apparatus according to an aspect of the present invention includes a transmission unit that transmits a signal, a reception unit that receives a signal, and a carrier sense operation that performs a signal reception operation while switching a reception frequency of the reception unit. A received wave strength determination unit that determines whether the electric field strength of the received signal exceeds a predetermined threshold, a CCA detection unit that detects a predetermined preamble in received data during the carrier sense operation, and the CCA A determination unit that determines a communication failure according to a detection result by the detection unit and the reception wave intensity determination unit, and a determination that the determination unit determines that the communication is defective, and the reception wave intensity determination unit determines the electric field strength of the reception signal in the channel. When the predetermined threshold is exceeded, the transmission rate for transmitting the packet is switched to a low rate that is lowered by a predetermined width, and the low rate state is maintained to maintain the packet rate. The transmission rate is determined to be lower than the low rate when transmission is performed and the determination unit determines that the reception signal strength is not good and the reception wave strength determination unit does not exceed the predetermined threshold value in the channel. And a communication control unit that retransmits packets at a low rate.

  According to the present invention, it is possible to avoid errors and realize highly efficient wireless communication even in a situation where a wide variety of radio waves including a wireless communication device or microwave oven of another standard are mixed. be able to.

System configuration diagram when implemented in a base unit of a cordless telephone as an embodiment of a wireless communication apparatus of the present invention The block diagram which shows the structure which performs communication of the 802.11 standard of the radio | wireless communication apparatus in embodiment of this invention Explanatory drawing which shows recording information for every channel in the communication control part of the radio | wireless communication apparatus in embodiment of this invention Flowchart for controlling carrier sense operation of radio communication apparatus in an embodiment of the present invention Explanatory drawing which shows an example of the result of the carrier sense operation | movement of a wireless LAN band in the radio | wireless communication apparatus in embodiment of this invention Explanatory drawing which shows the example of the interference electric wave of the microwave oven detected by one channel by the carrier sense operation | movement of the radio | wireless communication apparatus in embodiment of this invention, and the cumulative count value of a counter Explanatory drawing which shows the example of the cumulative count value of a counter when the interference electromagnetic wave of the microwave oven detected by one channel by the carrier sense operation | movement of the radio | wireless communication apparatus in embodiment of this invention is comparatively weak Explanatory drawing which shows the weighting table used for carrier sense operation | movement in the radio | wireless communication apparatus in embodiment of this invention Flowchart for accurately determining a used channel of a wireless communication device in an embodiment of the present invention Flowchart for more accurately determining a channel used by a wireless communication device in an embodiment of the present invention Explanatory drawing which shows the effect of the interference detection mode of the radio | wireless communication apparatus in embodiment of this invention Explanatory drawing which shows the weak electric field detection mode of the radio | wireless communication apparatus in embodiment of this invention Flowchart for performing transmission rate change control of wireless communication apparatus in an embodiment of the present invention Explanatory drawing which shows the effect of the weak electric field detection mode of the radio | wireless communication apparatus in embodiment of this invention Explanatory drawing showing the 2.4 GHz band used in the 802.11 standard

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a system configuration when implemented in a base unit of a cordless telephone as an embodiment of a wireless communication apparatus of the present invention. Reference numeral 20 denotes a base unit of the cordless telephone according to the present embodiment, and reference numeral 21 denotes a cordless telephone set that can communicate with the base unit 20 by DECT standard communication. Base unit 20 is wired to PSTN line 22. The base unit 20 also has a function as a repeater of the 802.11 standard wireless LAN.

  Reference numeral 23 denotes an 802.11 standard wireless LAN access point (AP), and reference numeral 24 denotes a smart phone capable of communication using the 802.11 standard wireless LAN. The base unit 20 of the cordless telephone according to the present embodiment can communicate with the smart phone 24 by an 802.11 standard wireless LAN. The base unit 20 of the cordless telephone registers a slave unit 21 that can communicate with the DECT standard and a smart phone 24 that can communicate with the 802.11 standard as a slave unit, and the smart phone 24 is also used as one of the slave units. it can. For example, the smartphone 24 can be used to make a voice call via the PSTN line, and the smartphone 24 can be used for registering or editing a telephone directory.

  In FIG. 1, the base unit 20 is a place where a communication signal (Bluetooth is a registered trademark) from another communication device that overlaps the wireless LAN band, for example, a Bluetooth device (BT device) 25, or a radio wave from the microwave oven 26 interferes. Is located.

  FIG. 2 is a block diagram showing a configuration for performing communication according to the 802.11 standard of base unit 20 in the embodiment of the present invention. In FIG. 2, 1 is a transmission / reception antenna, 2 is a transmission / reception switching circuit, 3 is a reception circuit in a wireless reception unit, and 4 is a transmission circuit in a wireless transmission unit.

  In the wireless reception unit, 5 is a reception frequency conversion unit, 6 is a bandpass filter that passes a signal with a bandwidth of one channel of the 802.11 standard, 7 is a radio demodulation unit, and 8 is a reception baseband signal processing unit.

  In the wireless transmission unit, 9 is a transmission baseband signal processing unit, 10 is a modulation unit, 11 is a bandpass filter that limits the signal bandwidth to the width of one channel, and 12 is a transmission frequency conversion unit.

  The receiving circuit 3 receives and amplifies the received radio wave from the transmission / reception switching circuit 2. The reception frequency conversion unit 5 performs frequency conversion. The frequency-converted signal is limited to the bandwidth for one channel by the band pass filter 6. The radio demodulation unit 7 performs high frequency demodulation processing on the reception signal that has passed through the bandpass filter 6, generates a reception baseband signal S 1, and outputs the reception baseband signal S 1 to the reception baseband signal processing unit 8.

  The reception baseband signal processing unit 8 receives the reception baseband signal S1, performs baseband signal processing and media access control, and generates reception data S2. The reception baseband signal processing unit 8 outputs information on the reception error to the communication control unit 13 when a reception error occurs.

  The transmission baseband signal processing unit 9 receives the transmission data S3, performs baseband signal processing, and outputs a transmission baseband signal S4. The transmission baseband signal S4 is modulated by CDMA by the modulation unit 10 and up-converted to a transmission frequency band by the transmission frequency conversion unit 12. The transmission circuit 4 performs predetermined amplification on the up-converted signal to generate a transmission radio wave. The transmission radio wave is radiated to the outside from the transmission side output of the transmission / reception switching circuit 2 via the transmission / reception antenna 1.

  The communication control unit 13 controls communication according to the 802.11 standard, and controls operations for carrier sense and clear channel assessment (CCA) before starting communication.

  The CCA detection unit 14 receives the reception baseband signal S 1 from the radio demodulation unit 7, performs 802.11 standard preamble detection, and passes the result to the communication control unit 13. When the communication control unit 13 receives information indicating that the preamble has been detected from the CCA detection unit 14 in the carrier sense before the start of communication, the communication channel of that time is used by other 802.11 standard communication devices. Judge that you are doing.

  The counter 15 counts the number of times that the received signal strength exceeds a predetermined threshold for each channel during the carrier sense operation. That is, the counter 15 counts up when the received signal strength exceeds a predetermined threshold, and counts down when the received signal strength falls below the predetermined threshold, based on information from the received wave strength determination unit 17 described later. Information from the CCA detection unit 14 and the counter 15 is passed to the communication control unit 13.

  The reception level detector 16 measures the signal strength of the reception signal band-limited by the bandpass filter 6 and outputs an RSSI value P1 indicating the signal strength. The received wave intensity determination unit 17 determines whether or not the RSSI value P1 indicating the signal intensity exceeds a threshold value, and passes the determination result to the communication control unit 13 and the counter 15.

  The threshold storage unit 18 stores various thresholds for determination by the received wave intensity determination unit 17. The threshold storage unit 18 stores a predetermined threshold value for the received signal strength during the carrier sense operation and a threshold value used in the control of an interference detection mode and a weak electric field detection mode, which will be described later.

  The received radio wave is received by the transmission / reception antenna 1 and then input to the bandpass filter 6 through the reception circuit 3 to be band-limited. The received signal that has passed through the bandpass filter 6 is demodulated by the radio demodulator 7.

  The reception level detection unit 16 outputs an RSSI value P1 indicating the received signal strength, and the received wave strength determination unit 17 determines whether or not the RSSI value P1 indicating the signal strength exceeds a threshold value. The determination result is passed to the counter 15 according to the request. A threshold for determining the signal strength by the received wave intensity determination unit 17 is stored in the threshold storage unit 18.

  When the CCA detection unit 14 fails to detect the preamble of the IEEE802.11 standard packet (no preamble is detected), the communication control unit 13 determines the received wave strength determination result for the received wave strength determination unit 17 at that time. Request. Accordingly, the received wave intensity determination unit 17 determines whether or not the received wave intensity at that time exceeds a threshold value, and passes the determination result to the counter 15.

  The counter 15 counts up when it is determined that the received wave intensity exceeds the threshold value, and counts down when the received wave intensity falls below the threshold value. For example, when receiving on channel 8, when the received radio wave including the interference wave from the microwave oven is strong on the channel 8, and the RSSI value P1 exceeds the threshold value, the counter 15 counts up and If the disturbance wave continues, the count-up is repeated. However, when the received wave intensity determination is made at the timing when the interference wave from the microwave oven is interrupted, the counter 15 counts down because the RSSI value P1 does not exceed the threshold value.

  The communication control unit 13 is a count value recording unit that records the count value for each channel obtained from the counter 15, and a cumulative CCA value recording that counts the result of the CCA detection unit and the reception wave intensity determination result of the reception wave intensity determination unit. And a weighting parameter recording unit. FIG. 3 is an explanatory diagram showing recording of a cumulative count value, a cumulative CCA value, a weighting parameter, and usable / prohibited information for each channel in the storage unit of the communication control unit 13. In addition, the communication control unit 13 includes a weighting table, which will be described later, and a use channel recording unit that records use / prohibition of each channel.

  The counter 15 passes the information of the accumulated count value for each channel to the communication control unit 13, and the communication control unit 13 records the accumulated count value for each channel as shown in FIG. As described above, when the accumulated count value of a certain channel exceeds a predetermined level by the carrier sense operation, the communication control unit 13 prohibits the use of the channel.

  In addition, the communication control unit 13 receives information indicating that the preamble has been detected from the CCA detection unit 14 in the carrier sense before the start of communication, and the reception channel is used by other 802.11 standard communication devices. Judge that you are doing. At this time, the communication control unit 13 obtains the signal strength information of the received signal band-limited by the bandpass filter 6 from the received wave strength determination unit 17 and communicates the CCA value calculated based on the signal strength information. Record in the cumulative CCA value recording unit of the control unit 13. In the cumulative CCA value recording unit, the CCA value is accumulated and recorded, and the channel that exceeds the predetermined threshold value for the cumulative CCA value is determined to be prohibited.

  When the CCA detection unit 14 succeeds in detecting the preamble of the IEEE 802.11 standard packet (preamble is detected), the communication control unit 13 determines that the channel is prohibited from use as described above. In this case, the communication control unit 13 does not need to obtain the accumulated count value from the counter 15. If the preamble detection is successful, the accumulated count value of the counter 15 may be forcibly reset.

  FIG. 4 is a flowchart for the communication control unit 13 to control each unit for the carrier sense operation.

  In FIG. 4, n is a variable corresponding to the number of the reception channel, and in order to start from reception of channel 1 first, n = 1 is set in Step 1. In Step 2, the communication control unit 13 instructs the receiving circuit 3 to receive on channel n. If n = 1 here, the receiving circuit 3 adjusts the receiving frequency to the channel 1 and starts the receiving operation.

  In Step 3, the communication control unit 13 checks whether or not there is an IEEE 802.11 standard packet preamble in the received signal. If it is determined that there is a preamble based on the result of the CCA detection unit 14 (Step 3: YES), in Step 4, the communication control unit 13 checks whether the received signal is a Beacon of the IEEE 802.11 standard.

  When the signal received at Step 4 is a Beacon of the IEEE 802.11 standard (Step 4: YES), at Step 5, the communication control unit 13 determines that the channel is prohibited, and the used channel recording unit in the communication control unit 13 To record. In Step 6, the communication control unit 13 also determines that the adjacent channel adjacent to the channel in which the preamble is detected is prohibited from being used by the number of channels corresponding to the signal level of the signal in which the Beacon is detected. 13 to the used channel recording unit. For example, in the example of FIG. 5 to be described later, when Beacon is detected in channel 5, in addition to channel 5, channels 3, 4 and channels 6, 7 are determined to be prohibited.

  In Step 7, the communication control unit 13 checks whether or not the variable n corresponding to the number of the reception channel has reached 13 which is the last number. If n has not reached 13 (Step 7: NO), the variable n is incremented in Step 8, and the communication control unit 13 returns to Step 2 and instructs the reception circuit 3 to receive in the next channel. When n has reached 13 (Step 7: YES), the process returns to Step 1 to set n = 1, and the communication control unit 13 instructs the reception circuit 3 to receive on the first channel (channel 1).

  When the preamble of the IEEE802.11 standard packet is not detected in the received signal in Step 3 described above (Step 3: NO), the process proceeds to Step 9, and the communication control unit 13 sends the received wave intensity at that time to the received wave intensity determining unit 17 Request the judgment result. Accordingly, the received wave intensity determination unit 17 determines whether or not the received wave intensity exceeds the threshold value as described above, passes the determination result to the counter 15, and the counter 15 counts up or down.

  The communication control unit 13 obtains the accumulated count value from the counter 15 at Step 10, and determines whether the channel is usable or prohibited based on the accumulated count value at Step 11. If the communication control unit 13 can use the information in Step 11, the communication control unit 13 records the information of “usable” for the channel (Step 12), and proceeds to Step 7. If it is prohibited in Step 11, the communication control unit 13 records information of “use prohibited” for the channel (Step 13), and proceeds to Step 7.

  If the IEEE 802.11 standard Beacon is not detected in the received signal in Step 4 (Step 4: NO), the communication control unit 13 obtains the accumulated CCA value in Step 14, and based on the accumulated CCA value in Step 15. To determine whether the channel can be used.

  If it is usable in Step 15, the communication control unit 13 records “usable” information for the channel (Step 16), and proceeds to Step 7. If it is prohibited in Step 15, the communication control unit 13 records the information “prohibited use” for the channel (Step 17), and proceeds to Step 7.

  FIG. 5 shows a state of the wireless LAN band in the present embodiment. In this embodiment, it is assumed that an 802.11 standard wireless LAN base station and a slave unit affect the band of about 20 MHz for communication.

  In the example of FIG. 5, another 802.11 standard access point (AP) 23 in the vicinity uses the channel 5. The base unit (wireless communication apparatus) 20 of the present embodiment performs a carrier sense operation, detects a preamble in channel 5, and further detects a Beacon of the 802.11 standard, so that the channel according to the clear channel assessment (CCA) 5 (5Ch) is prohibited.

  In addition, the influence range extends to a band of 20 MHz centering on channel 5, and the received electric field strength of signals of other base station apparatuses in channel 5 is very strong. Therefore, base unit 20 has a plurality of channels on both sides. Increase weight to limit usage. Accordingly, in the example of FIG. 5, the use of two channels on the low frequency side and two channels on the high frequency side (5 channels in total of 3 Ch to 7 Ch) centering on the master device 20 channel 5 is prohibited.

  Also in channel 3, a signal output by another 802.11 standard device is received and a preamble is detected. However, since the electric field strength of the signal in channel 3 is relatively weak, base unit 20 uses a relatively light weight that restricts the use of the channels on both sides, so that one channel on the low frequency side centering on channel 3 Only one channel on the high frequency side is prohibited. Accordingly, the base unit 20 searches for a channel to be used from the remaining channels 1 and 8-13.

  In FIG. 5, a signal output from another 802.11 standard device is also received in channel 1 and a preamble is detected. Base unit 20 prohibits use of channel 1 in accordance with CCA with preamble detection even if the signal source is far away and the electric field strength is very weak. Accordingly, the base unit 20 searches for a use channel from the remaining 8 to 13 channels. As for channel 11, signals from other base station apparatuses are received, and base unit 20 prohibits use of channel 11 in accordance with clear channel assessment (CCA) with preamble detection.

  The CCA detection operation is performed every time an individual channel is searched in the carrier sense, and the counter 15 counts up when there is CCA detection as described above. The counter 15 counts up every time the channel 5, channel 3, and channel 1 are searched. In the example of FIG. 5, interference radio waves are generated by the microwave oven in the frequency range of channel 5 to channel 8.

  FIG. 6 shows an example of the interference wave of the microwave oven detected by the channel 8 and the accumulated count value of the counter 15, for example. Microwave ovens do not always emit jamming waves. For example, in channel 8, when the received wave intensity determination unit 17 determines that the signal intensity exceeds a threshold value (stored in the threshold storage unit 18) (×), a count-up instruction is sent to the counter 15. Counts up at that time. When it is determined that the signal intensity is below the threshold (O), a countdown instruction is sent to the counter 15, and the counter 15 is down at that time.

  The accumulated count value of the counter 15 is passed to the communication control unit 13. As shown in FIG. 6, the communication control unit 13 determines that the channel is prohibited when the accumulated count value of the counter 15 exceeds a predetermined level. When calculated from the conventional Dirtyness algorithm, the channel 8 shown in FIG. 5 may be enabled, but the channel 8 is determined to be prohibited from use according to the accumulated count value of the counter 15 of the present embodiment. The counter 15 is reset to “0” when it receives information indicating the presence of preamble detection from the CCA detector 14.

  FIG. 7 shows an example when the interference wave of the microwave oven detected in a certain channel (for example, channel 9) is relatively weak. The counter 15 counts up when the received signal strength determination unit 17 determines that the signal strength exceeds the threshold value (x), and counts down when the signal strength falls below the threshold value (◯). In the example of FIG. 7, since the cumulative count value of the counter 15 does not exceed a predetermined level, the communication control unit 13 determines that the channel can be used. In the above example, base unit 20 according to the present embodiment performs transmission using channel 9.

  As described above, in the present embodiment, in parallel with the detection operation of the CCA detection unit 14, the threshold value determination of the signal strength in the reception wave strength determination unit 17 is performed, and the accumulated count value of the counter 15 is updated. As a result, in the base unit (wireless communication apparatus) 20, even if the CCA detection unit 14 does not detect the preamble of the 802.11 standard packet, the channel can be used / not used based on the accumulated count value of the counter 15. Since prohibition can be determined and there is little possibility of selecting a channel with heavy interference, highly efficient operation can be performed.

  FIG. 8 schematically shows a weighting table prepared in the communication control unit 13. In FIG. 8, for example, if the signal strength of a channel (for example, 5Ch) in which a preamble of another apparatus is detected is less than −80 dBm, the weighting parameter of the channel in which the preamble is detected is “60”, For example, the weighting parameter of 4Ch, 6Ch, is “8”, the weighting parameter of two adjacent channels (eg, 3Ch, 7Ch,) is “7”, and the weighting parameter of three adjacent channels (eg, 2Ch, 8Ch,) is “6”.

  If the signal strength of the channel in which the preamble is detected is not less than −80 dBm and less than −65 dBm, the weighting parameter of the channel in which the preamble is detected is “70”, and the weighting parameter of the adjacent channel is “16”. The weighting parameter for the two adjacent channels is “14”, and the weighting parameter for the three adjacent channels is “12”.

  Also, if the signal strength of the channel in which the preamble is detected is −50 dBm or more, the weighting parameter of the channel in which the preamble is detected is “90”, the weighting parameter of the next adjacent channel is “32”, and two adjacent The weighting parameter for the next channel is “28”, and the weighting parameter for the three adjacent channels is “24”.

  Thus, as the signal strength of the channel in which the preamble is detected increases, the weighting parameter values of the channels on both sides increase.

  The weighting parameter of the channel in which the preamble is detected and the weighting parameter of the adjacent channel selected from the weighting table are integrated for each channel and recorded in the above-described weighting parameter recording unit. Then, the communication control unit 13 prohibits the use of the channel when the integrated value of the weighting parameter exceeds a predetermined threshold. As the signal strength of the channel in which the preamble is detected becomes stronger, the weighting parameter values of the channels on both sides are larger, so that the channels on both sides are more likely to be prohibited. On the other hand, when the signal strength of the channel in which the preamble is detected is very weak, the value of the weighting parameter of the channels on both sides is small, so that the channels on both sides can be prohibited from being prohibited in some cases.

  FIG. 9 is a flowchart for the communication control unit 13 to control each unit when the defective channel is determined not only by the above-described cumulative count value but also by the integrated value of the weighting parameter for each channel during the carrier sense operation. Show. In FIG. 9, n is a variable corresponding to the number of the receiving channel. Step 1 to Step 4, and Step 7 and Step 8 are controlled in the same manner as in FIG.

  When a preamble is detected in a channel at Step 3 and a Beacon of the 802.11 standard is detected at Step 4, signal strength measurement and weight determination are performed at Step 20. That is, as shown in FIG. 8, the weighting parameter of the channel where Beacon is detected and the weighting parameter of the adjacent channel are integrated for each channel and recorded in the weighting parameter recording unit in the communication control unit 13.

  In Step 21, it is determined whether or not the integrated value of the weighting parameter exceeds a predetermined threshold. If there is a channel whose integrated value of the weighting parameter exceeds the predetermined threshold, the communication control unit 13 uses the channel. Prohibit. As the signal strength of the channel in which the preamble is detected becomes stronger, the weighting parameter values of the channels on both sides are larger, so that the channels on both sides are more likely to be prohibited.

  When the preamble of the IEEE802.11 standard packet is not detected in the received signal in Step 3 described above (Step 3: NO), the process proceeds to Step 22, and the communication control unit 13 performs signal strength measurement and count determination. That is, in Step 22, as in Step 9 shown in FIG. 4, the communication control unit 13 requests the reception wave intensity determination unit 17 for the reception wave intensity determination result at that time. Accordingly, the received wave intensity determination unit 17 determines whether or not the received wave intensity exceeds the threshold value as described above, passes the determination result to the counter 15, and the counter 15 counts up or down. The communication control unit 13 obtains the accumulated count value from the counter 15 and determines whether the channel is usable or prohibited based on the accumulated count value. In Step 22, the communication control unit 13 records “usable” information for the channel if usable, records “use prohibited” information for the channel if prohibited, and proceeds to Step7.

  When the Beacon of the IEEE802.11 standard packet is not detected in the received signal in Step 4 described above (Step 4: NO), the process proceeds to Step 23, and the communication control unit 13 performs the process for the channel recorded in the cumulative CCA value recording unit. The cumulative CCA value is read out, and the use / prohibition of the channel is determined based on the cumulative CCA value. If the cumulative CCA value exceeds a predetermined value, the communication control unit 13 records “use prohibited” information for the channel, and if the cumulative CCA value does not exceed the predetermined value, the communication control unit 13 sets “available” for the channel. Is recorded, and the process proceeds to Step 7.

  As described above, in the control of FIG. 9, the communication control unit 13 determines whether or not the channel is usable based on not only the accumulated count value but also the accumulated value of the weighting parameter for each channel and the accumulated CCA value. By doing this, it is possible to select an appropriate channel while avoiding interference as much as possible.

  FIG. 10 shows the control performed by the communication control unit 13 in order to determine the priority order of the used channels more accurately based on the above-mentioned accumulated count value, accumulated cost value, and accumulated CCA value during the carrier sense operation. A flowchart is shown.

  In FIG. 10, in Step 31, the communication control unit 13 reads the accumulated cost value. In Step 32, the communication control unit 13 selects the cleanest channel with the lowest cost value (= n channel) based on the accumulated cost value. The communication control unit 13 obtains the cumulative count value of the channel from the counter 15 at Step 33, and determines whether the channel can be used / prohibited based on the cumulative count value at Step 34.

  If it is determined in step 34 that the channel (n channel) is “usable”, in step 35, the communication control unit 13 reads the accumulated CCA value of the channel. In Step 36, the communication control unit 13 finally determines whether the channel can be used / prohibited based on the accumulated CCA value for the channel. When it is determined in Step 36 that the channel is “usable”, in Step 37, the communication control unit 13 starts communication using the channel (n channel).

  If it is determined “prohibited” in Step 34 or “prohibited” in Step 36, the communication control unit 13 reads the accumulated cost value in Step 38, and then selects a channel having a clean cost value (m channel). Returning to Step 33, the communication control unit 13 obtains the accumulated count value of the next clean cost value channel (m channel) from the counter 15 in Step 33, and uses the channel based on the accumulated count value in Step 34. Judge whether it is possible or not.

  As described above, since the determination based on the cumulative count value and the determination based on the cumulative CCA value are preferentially performed on a channel with a cleaner cumulative cost value, the processing efficiency is high.

  Hereinafter, an embodiment in which the interference detection mode and the weak electric field mode are combined will be described. For example, a microwave oven does not always emit an interference wave as described above, and there is an OFF time zone even during operation as shown in FIG. Normally, in the 802.11 standard communication, when an error occurs as shown on the left side of FIG. 11, the transmission rate (transmission rate) is lowered next time and transmission is performed, so that the packet length becomes longer by the amount of the reduced speed. If the error is repeated, the transmission rate is further lowered, so that the packet length is gradually increased. Finally, the trial is continued with the longest length, and if the error is still not resolved, it is determined that the packet transmission has failed and the communication is disconnected. Therefore, conventionally, even if the interference partner is a microwave oven and there is an OFF time zone during operation, if the packet length is maximized, the probability that the packet will hit the interference is high, and the possibility of success is low.

  The base unit (wireless communication apparatus) 20 according to the present embodiment switches to the interference detection mode when an error is detected as shown on the right side of FIG. 11, and does not continue to gradually reduce the transmission rate over time. The transmission rate is reduced to a predetermined moderate rate (for example, 24 Mbps) at once, and the transmission rate dropped once is maintained, and retransmission is switched back. For example, in order to pass a packet in the time zone when the microwave oven is OFF, it is desirable to set the minimum transfer rate with the transmission rate as one paragraph to 5.5 Mbps. However, the transmission rate is adjusted so that it does not fall below a level that can be transferred during the Burst-OFF time of the interference source.

  On the other hand, in the 2.4 GHz band, a house surrounded by thick concrete is strong in multipath, and when carrying a mobile communication device, the electric field strength fluctuates drastically even if there is a slight change in position, and the call is easily disconnected. Occur. Normally, in the communication of the 802.11 standard, when an error occurs as shown on the left side of FIG. 12, the transmission rate is lowered to make it easier for the communication partner to receive.

  In the conventional 802.11 communication, if an error continues, the transmission rate is gradually lowered. However, it takes time until the transmission rate falls to the extent that the communication partner can actually receive, and the predetermined number of retransmissions is reached as it is. However, it often fails without success. In particular, when the above-mentioned multipath occurs, the electric field strength fluctuates greatly even if the position is finely changed, and the link may be disconnected without being able to cope with the multipath.

  Master unit (wireless communication apparatus) 20 according to the present embodiment switches to weak electric field detection mode when an error is detected during transmission, as shown on the right side of FIG. In this weak electric field detection mode, the transmission rate is reduced (increased packet length) with a relatively large width, not finely, and the packet is retransmitted. Further, if the error is still not improved even if the transmission rate is once reduced, the master unit 20 further reduces the transmission rate by a large width and retransmits, and even if the transmission rate becomes the lowest transmission rate (6 Mbps), it is still predetermined. Will be resent.

  FIG. 13 is a flowchart for the communication control unit 13 to control in combination with the interference detection mode and the weak electric field detection mode so that both interference waves such as a microwave oven and multipath can be flexibly handled during communication. . The communication control unit 13 receives information on the reception error from the reception baseband signal processing unit 8 and the electric field strength determination information from the reception wave strength determination unit 17, and maintains the transmission rate at a time as follows. Alternatively, the transmission rate is reduced with a large width and the packet length is increased for transmission, or the transmission rate is gradually reduced as usual.

  In FIG. 13, in Step 41, the communication control unit 13 determines whether or not the number of reception errors is greater than the Rate-Down threshold. When the number of reception errors becomes larger than the Rate-Down threshold (Step 41: YES), the communication control unit 13 determines whether or not the electric field strength is larger than the strong electric field threshold in Step 42. When the electric field strength becomes larger than the strong electric field threshold (Step 42: YES), the communication control unit 13 determines that there is a high possibility of receiving a strong electric field disturbance wave, and sets the transmission rate to the lowest rate in Step 43 ( For example, 24 Mbps).

  In Step 44, the communication control unit 13 sets a Timer until the next process in order to perform the rate change process at a predetermined cycle, and performs a waiting operation (for example, 0.5 seconds). When the predetermined waiting time elapses, the communication control unit 13 returns to Step 41 and determines the number of reception errors.

  As described above, when the number of reception errors is larger than the Rate-Down threshold value and the electric field strength is larger than the strong electric field threshold value, the interference detection mode is set, and thereafter, the transmission rate remains at the lowest rate (for example, 24 Mbps) and data is transmitted again. Sent.

  Even when the number of reception errors is larger than the Rate-Down threshold value in Step 41 (Step 41: YES), when the electric field strength is smaller than the strong electric field threshold value in Step 42 (Step 42: NO), the communication control unit 13 determines that the electric field strength is weak in Step 45. It is determined whether it is smaller than the threshold value.

  When the electric field strength is smaller than the weak electric field threshold value in Step 45 (Step 45: YES), the communication control unit 13 determines that there is a high possibility that multipath has occurred, and sets the transmission rate to half or less of the current state in Step 46. For example, when the current transmission rate is 54 Mbps, a setting of 24 Mbps or 12 Mbps, which is half or less, is set in Step 46. Then, the communication control unit 13 waits until the next process at Step 44 (for example, 0.5 seconds), and returns to Step 41 when a predetermined waiting time elapses.

  When the number of reception errors is relatively large (greater than the Rate-Down threshold) and the electric field strength is relatively small (smaller than the strong electric field threshold), the weak electric field detection mode is entered. The change of switching the transmission rate to half of the current level is repeated, and the transmission rate is reduced to 6 Mbps as shown in FIG. 12, for example.

  When the electric field strength is larger than the weak electric field threshold at Step 45 (Step 45: NO), the communication control unit 13 determines that there is a low possibility that multipath has occurred, and at Step 47, the transmission rate is only one level as in the conventional case. (For example, 54 Mbps → 48 Mbps, 48 Mbps → 36 Mbps).

  In Step 48, the communication control unit 13 determines whether the number of reception errors is smaller than the Rate-Up threshold. When the number of reception errors is smaller than the Rate-Up threshold (Step 48: YES), the communication control unit 13 determines that there is no strong electric field interference wave and multipath, and at Step 49, the transmission rate is one step as in the prior art. (For example, 6 Mbps → 9 Mbps, 36 Mbps → 48 Mbps). In Step 48, when it is determined that the number of reception errors is larger than the Rate-Up threshold (Step 48: NO), the communication control unit 13 does not change the transmission rate.

  As described above, when the number of reception errors is larger than the Rate-Down threshold value and the electric field strength exceeds the weak electric field threshold value, the transmission rate is dropped only once with a relatively high value as the lowest value (for example, 24 Mbps). (Wireless communication apparatus) 20 repeats transmission with the packet length fixed, so that the number of transmissions per unit time is kept relatively large. As a result, there is a high possibility that the packet transmission timing will match the valley where the electric field strength of the interference source is low (for example, when the microwave oven is OFF), and packet transmission is possible even when the microwave oven is operating nearby. There is a high possibility that a packet can be transmitted before it is determined as a failure.

  In addition, when a portable communication device is carried in a place where multipath is likely to be strong, the electric field strength often continues to fluctuate rapidly. However, in this embodiment, when the number of reception errors is larger than the Rate-Down threshold and the electric field strength does not exceed the weak electric field threshold, the transmission rate is greatly reduced as shown in FIG. The transmission rate is changed to a transmission rate that can be actually received over time, and the possibility of successful communication increases. As a result, it is possible to quickly cope with a sudden multipath.

  The present invention provides an access point that can select the best channel and reduce the influence of interference even under conditions in which radio waves including a variety of radio waves including a microwave oven are detected. It can be applied to repeaters, portable terminals and the like.

DESCRIPTION OF SYMBOLS 1 Transmission / reception antenna 2 Transmission / reception switching circuit 3 Reception circuit 4 Transmission circuit 5 Reception frequency conversion part 6,11 Band pass filter 7 Radio demodulation part 8 Reception baseband signal processing part 9 Transmission baseband signal processing part 10 Modulation part 12 Transmission frequency conversion part DESCRIPTION OF SYMBOLS 13 Communication control part 14 CCA detection part 15 Counter 16 Reception level detection part 17 Received wave strength determination part 18 Threshold value memory | storage part 20 Parent | base_unit 21 Slave | terminal 22 PSTN line 23 Access point (AP)
24 Smartphone 25 Bluetooth device 26 Microwave oven

Claims (13)

Send the packet on the channel that is allowed to use by carrier sense operation,
Judge whether the packet transmission is good or bad by the presence of an error,
When the packet transmission is determined to be bad and the electric field strength of the received signal in the channel exceeds a predetermined threshold, the transmission rate for transmitting the packet is switched to a low rate by a predetermined width, and the low rate Keep the state and retransmit the packet,
If it is determined that the packet transmission is bad and the electric field strength of the received signal does not exceed a predetermined threshold in the channel, the packet transmission rate is lowered to a rate lower than the low rate, and the packet is retransmitted. Do,
A transmission control method for a wireless communication apparatus. If it is determined that the packet transmission is bad and the electric field strength of the received signal exceeds the predetermined first threshold in the channel, the transmission rate for transmitting the packet is switched to a low rate by a predetermined width, and the low Keep the rate state and retransmit the packet,
If it is determined that the packet transmission is bad and the electric field strength of the received signal does not exceed the second threshold value smaller than the first threshold value in the channel, the transmission rate is lowered to a rate lower than the low rate to Resend,
The transmission control method according to claim 1. If it is determined that the packet transmission is bad and the electric field strength of the received signal exceeds the predetermined first threshold in the channel, the transmission rate for transmitting the packet is switched to a low rate by a predetermined width, and the low Keep the rate state and retransmit the packet,
If it is determined that the packet transmission is bad and the electric field strength of the received signal does not exceed the second threshold value smaller than the first threshold value in the channel, the transmission rate is lowered to a rate lower than the low rate and the packet is retransmitted. Do
Once the transmission rate is lowered to a rate lower than the low rate and the packet is retransmitted, if the defect does not improve, further reduce the transmission rate.
The transmission control method according to claim 1. When the packet transmission is determined to be defective and the electric field strength of the received signal does not exceed the first threshold value but exceeds the second threshold value, the transmission rate is gradually reduced by a width smaller than the predetermined width. ,
The transmission control method according to claim 3. When the number of reception errors exceeds a predetermined third threshold, it is determined that the packet transmission is bad.
The transmission control method according to claim 1. When the number of reception errors does not exceed the predetermined third threshold and does not exceed the fourth threshold smaller than the third threshold, the transmission rate is increased.
The transmission control method according to claim 1. Determine whether the signal field strength exceeds a predetermined threshold,
Furthermore, the use / prohibition of the channel is determined by detecting a predetermined preamble in the received data during the carrier sense operation,
In a channel permitted to be used by the carrier sense operation,
If the number of reception errors exceeds a predetermined threshold and the electric field strength of the signal exceeds a predetermined first threshold, it is determined that the transmission is defective due to interference, and the transmission rate is lowered to a minimum value lower by a predetermined width. Retransmit the packet while maintaining the state lowered to the minimum value,
If the number of reception errors exceeds a predetermined threshold and the electric field strength of the signal does not exceed a second threshold that is smaller than the first threshold, it is determined that transmission by multipath is defective, and the transmission rate is a rate lower than the low rate. And retransmit the packet to
Once the transmission rate is lowered to a rate lower than the low rate and the packet is retransmitted, if the defect is not improved, the transmission rate is further reduced.
A transmission control method for a wireless communication apparatus. A transmitter for transmitting a signal;
A receiver for receiving the signal;
A received wave strength determination unit that determines whether or not the electric field strength of the received signal exceeds a predetermined threshold for each channel during a carrier sense operation that performs a signal reception operation while switching the reception frequency of the reception unit;
A CCA detection unit for detecting a predetermined preamble in received data during the carrier sense operation;
A determination unit for determining a communication failure according to a detection result by the CCA detection unit and the received wave intensity determination unit;
A low rate in which the transmission rate for transmitting packets is reduced by a predetermined width when the determination unit determines that the signal is defective and the received wave intensity determination unit exceeds the predetermined threshold in the channel. To retransmit the packet while maintaining the low rate state,
When the determination unit determines that the reception signal strength is not good and the received wave strength determination unit does not exceed a predetermined threshold in the channel, the transmission rate for transmitting packets is reduced to a rate lower than the low rate. A communication control unit that lowers and retransmits the packet,
A wireless communication apparatus. The communication control unit
When the determination unit determines that the received signal is poor and the electric field strength of the received signal exceeds a predetermined first threshold value, the transmission rate for transmitting packets is switched to a low rate by a predetermined width, and the low Keep the rate state and retransmit the packet,
If the determination unit determines that the received signal does not exceed the second threshold value smaller than the first threshold value in the channel, the transmission rate is lowered to a rate lower than the low rate to reduce the packet Resend,
The wireless communication apparatus according to claim 8. The communication control unit lowers the transmission rate further if the defect does not improve even after retransmitting the packet once the transmission rate is lowered to a rate lower than the low rate,
The wireless communication apparatus according to claim 9. The communication control unit determines that the transmission of the packet is defective, and if the electric field strength of the received signal does not exceed the first threshold and exceeds the second threshold, the transmission rate is set to be greater than the predetermined width. Lower in steps with a fine width,
The wireless communication apparatus according to claim 9. The determination unit determines that the packet transmission is bad when the number of reception errors exceeds a predetermined third threshold;
The wireless communication apparatus according to claim 8. The communication control unit increases the transmission rate when the number of reception errors does not exceed the third threshold and does not exceed a fourth threshold smaller than the third threshold.
The wireless communication apparatus according to claim 12.