Radio station and carrier sense method

Abstract

To provide a radio station and a carrier sense method capable of increasing the accuracy of carrier sense.SOLUTION: A detection unit 16 included in a radio station 1 detects a signal level at a specified transmission frequency by applying a time window determined according to the time length of a beacon used in radio communication to an actual signal obtained from a result of digitally converting an electric signal based on a radio wave captured by an antenna 10. A discrimination unit 17 discriminates whether or not a transmission band including the transmission frequency is being used for radio communication from the detected signal level.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wireless station and a carrier sense method. [Background technology]

[0002] A wireless communication device connected to a WLAN (Wireless Local Area Network) performs wireless communication in the 2.4 GHz or 5 GHz band allocated for WLAN communication. The wireless communication device detects an available channel to prevent interference with wireless communication performed by other wireless communication devices. An example of this type of wireless communication device is disclosed in Patent Document 1.

[0003] The receiving device disclosed in Patent Document 1 estimates whether or not a channel is in use from the reception level of a received channel signal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-101787 A Summary of the Invention [Problem to be solved by the invention]

[0005] Radio stations with secondary services are required not to cause harmful interference to radio stations with primary services. Therefore, when radio stations with secondary services communicate in the 2.4 GHz or 5 GHz band, they must perform carrier sense to determine whether other radio communication devices are performing wireless communication in the transmission band including the transmission frequency in order to prevent interference with wireless communication performed by other wireless communication devices with primary services. For example, the output of WLAN devices, which are radio stations with primary services, is a maximum of 10 milliwatts, while the output of amateur radio stations, which are radio stations with secondary services, can be several watts or more. Therefore, radio waves output by amateur radio stations can affect WLAN devices located at a distance. Therefore, in order to prevent interference with wireless communication performed by other wireless communication devices, it is necessary to improve the accuracy of carrier sense in amateur radio stations.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a wireless station and a carrier sensing method that can improve the accuracy of carrier sensing. [Means for solving the problem]

[0007] In order to achieve the above object, a radio station according to a first aspect of the present invention comprises: a detection unit that detects a signal level at a specified transmission frequency by applying a time window determined according to a time length of a beacon used in wireless communication to an actual signal obtained as a result of digitally converting an electric signal based on a radio wave captured by an antenna; a determination unit that determines whether or not a transmission band including the transmission frequency is being used for the wireless communication based on the signal level detected by the detection unit; Equipped with.

[0008] Preferably, the detection unit detects the signal level by applying the time window having a length that matches the minimum time length of the beacon output by the wireless communication device performing the wireless communication to the actual signal.

[0009] Preferably, the detection unit detects the signal level by applying the time window determined according to the time length of the beacon used in WLAN (Wireless Local Area Network) communication based on an orthogonal frequency division multiplexing system to the actual signal.

[0010] Preferably, a reception processing circuit that digitally converts an electric signal based on the radio wave captured by the antenna and down-converts it to generate an IF signal in an intermediate frequency band; a first oscillator having a variable frequency that outputs a first reference signal; an extraction unit that performs complex frequency conversion on the IF signal based on the first reference signal and generates a first complex signal by limiting the frequency band to a predetermined band centered on the frequency of the first reference signal; a frequency control unit that adjusts a frequency of the first reference signal in response to a specified transmission frequency, The detection unit detects the signal level by applying the time window to the real signal obtained from the first complex signal.

[0011] Preferably, the device further includes a plurality of variable frequency second oscillators that output second reference signals having different frequencies from each other, a plurality of the detection units that acquire the second reference signal from different second oscillators; the frequency control unit adjusts a frequency of the second reference signal output by each of the second oscillators in accordance with the transmission frequency and a bandwidth of a transmission band including the transmission frequency; each of the detection units detects the signal level by applying the time window to the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal; The determination unit determines whether or not the transmission band is being used for the wireless communication based on the signal levels detected by each of the detection units.

[0012] Preferably, the frequency control unit adjusts a frequency of the second reference signal for any of the second oscillators so that a complex signal obtained by complex frequency converting the first complex signal based on the second reference signal output by the second oscillator exhibits a spectrum centered on a component of the transmission frequency.

[0013] Preferably, the wireless communication device further includes an operation unit that accepts a designation of the transmission frequency and an instruction to transmit in either a narrowband mode or a wideband mode in which the transmission band is wider than that of the narrowband mode, When transmission in the wideband mode is specified by the operation unit, the discrimination unit discriminates whether or not the transmission band is being used for the wireless communication from the signal level detected by each of the detection units, and when transmission in the narrowband mode is specified by the operation unit, the discrimination unit discriminates whether or not the transmission band is being used for the wireless communication from the signal level detected by the detection unit by applying the time window to the real signal obtained from a complex signal indicating a spectrum centered on the transmission frequency component.

[0014] A carrier sense method according to a second aspect of the present invention includes: A carrier sense method performed by a wireless station, comprising: A time window determined according to the time length of a beacon used in wireless communication is applied to the actual signal obtained as a result of digitally converting an electrical signal based on radio waves captured by an antenna, thereby detecting the signal level at a specified transmission frequency. From the signal level, it is determined whether or not a transmission band including the transmission frequency is being used for the wireless communication. Effect of the Invention

[0015] The wireless station according to the present invention can improve the accuracy of carrier sense by detecting the signal level of an actual signal using a time window determined according to the time length of a beacon used in wireless communication. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram showing a configuration of a radio station according to a first embodiment of the present invention; [Diagram 2] FIG. 1 is a block diagram showing a configuration of a carrier sense unit according to a first embodiment; [Diagram 3] A flowchart showing an example of an operation of a carrier sense process performed by a wireless station according to the first embodiment. [Figure 4] FIG. 13 is a diagram showing an example of a relationship between a transmission band of a radio station according to a second embodiment and a spectrum of subcarriers in WLAN communication; [Diagram 5] FIG. 11 is a block diagram showing a part of a configuration of a radio station according to a second embodiment. [Figure 6] A block diagram showing a configuration of a band adjusting unit according to a second embodiment. [Figure 7] FIG. 11 is a block diagram showing a configuration of a carrier sense unit according to a second embodiment. [Figure 8] FIG. 11 is a block diagram showing a modified example of the configuration of a radio station according to the second embodiment. [Figure 9] FIG. 2 is a diagram showing a hardware configuration of a wireless station according to an embodiment of the present invention. [Figure 10] FIG. 13 is a diagram showing a modification of the hardware configuration of a wireless station according to an embodiment. [Figure 11] FIG. 1 is a diagram showing an example of implementation of a wireless station according to an embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a wireless station and a carrier sensing method according to an embodiment of the present invention will be described in detail with reference to the drawings, in which the same or equivalent parts are denoted by the same reference numerals.

[0018] (Embodiment 1) The wireless station 1 shown in FIG. 1 is capable of communicating in the 2.4 GHz or 5 GHz band allocated for WLAN (Wireless Local Area Network) communication. In the 2.4 GHz or 5 GHz band, WLAN communication based on the Orthogonal Frequency Division Multiplex (OFDM) method is performed. When the wireless station 1 is instructed to transmit in the 2.4 GHz or 5 GHz band, the wireless station 1 performs carrier sense to determine whether or not other wireless communication, specifically WLAN communication, is being performed in the transmission band including the designated transmission frequency in order to prevent interference with WLAN communication performed by wireless communication devices in the 2.4 GHz or 5 GHz band. The wireless station 1 detects the signal level in the transmission frequency using a time window determined according to the time length of a beacon used in wireless communication, and determines whether or not the transmission band is being used for wireless communication from the signal level.

[0019] The wireless station 1 includes an antenna 10, a reception processing circuit 11, an extraction unit 12, a demodulation unit 13, a DAC (Digital-to-Analog Converter) 14, an output unit 15, a detection unit 16, a discrimination unit 17, a mode control unit 18, an operation unit 19, a frequency control unit 20, a first oscillator 31, and an RF (Radio Frequency) oscillator 32.

[0020] The antenna 10 captures radio waves from wireless communication devices, such as radio stations and relay devices, and outputs an electrical signal based on the captured radio waves to a reception processing circuit 11.

[0021] The reception processing circuit 11 digitally converts the electrical signal acquired from the antenna 10 and down-converts it to generate an IF (Intermediate Frequency) signal in an intermediate frequency band. In detail, the reception processing circuit 11 has a receiving unit 41 and an ADC (Analog-to-Digital Converter) 42.

[0022] The receiving unit 41 performs signal processing such as filtering, attenuation, amplification, and frequency conversion on the electrical signal acquired from the antenna 10. For example, the receiving unit 41 has a filter, specifically, a BPF (Band Pass Filter), an attenuator, an LNA (Low Noise Amplifier), a mixer, and the like.

[0023] The receiver 41 multiplies the electrical signal that has been filtered by the BPF and passed through the attenuator and LNA by the RF reference signal output by the RF oscillator 32 in a mixer, thereby adjusting the frequency of the electrical signal to a frequency band that can be processed by the ADC 42. For example, the receiver 41 performs the above-mentioned signal processing on the 5.6 GHz electrical signal to convert the 5.6 GHz electrical signal into an electrical signal of several hundred MHz, for example, an electrical signal of 300 MHz, and outputs the converted electrical signal to the ADC 42.

[0024] The ADC 42 digitally converts the electrical signal that has been signal-processed by the receiving unit 41, and down-converts the data obtained by the digital conversion to generate an IF signal. For example, the IF signal is a real signal having a frequency of less than 100 MHz. The ADC 42 outputs the IF signal to the extraction unit 12.

[0025] The extraction unit 12 performs complex frequency conversion on the IF signal based on a first reference signal LOS1 output from a frequency-variable first oscillator 31, and generates a first complex signal CS1 that is an I / Q (In-Phase / Quadrature-Phase) signal by limiting the IF signal to a predetermined band centered on the frequency of the first reference signal LOS1. The extraction unit 12 outputs the first complex signal CS1 to the demodulation unit 13 and the detection unit 16.

[0026] The extraction unit 12 includes, for example, a phase shifter, a complex mixer, a filter, and the like. In detail, the extraction unit 12 performs complex frequency conversion on the IF signal based on the first reference signal LOS1 to obtain a complex signal showing a spectrum centered on the frequency component of the first reference signal LOS1. For example, a complex signal showing a spectrum with the frequency of the first reference signal LOS1 as a reference of 0 Hz is obtained. The first complex signal CS1 is obtained by limiting the band of the complex signal to a predetermined band centered on 0 Hz. Note that a filter that limits to a predetermined band centered on 0 Hz can be obtained by combining an LPF (Low Pass Filter) for positive frequencies and an LPF for negative frequencies.

[0027] The demodulation unit 13 performs band limiting, downsampling, and the like on the first complex signal CS1, demodulates it using a predetermined demodulation method to generate a demodulated signal that is a real signal, and sends the demodulated signal to the DAC .

[0028] The DAC 14 converts the demodulated signal obtained from the demodulation unit 13 into an analog signal, and sends the analog signal to the output unit 15 .

[0029] The output unit 15 is, for example, a speaker, and outputs the analog signal acquired from the DAC 14 .

[0030] The detector 16 detects the signal level of a real signal obtained from the first complex signal CS1. The detector 16 outputs the detected signal level to the discriminator 17.

[0031] In detail, the detection unit 16 has a band adjustment unit 51 and a carrier sense unit 52. The band adjustment unit 51 limits the first complex signal CS1 to a determined band, thereby obtaining a second complex signal CS2 which is a complex signal to be subjected to carrier sensing by the carrier sense unit 52. The band adjustment unit 51 downsamples the first complex signal CS1 to, for example, 48 kSPS (Kilo Samples Per Second), limits the band to a band centered on 0 Hz, and generates the second complex signal CS2. The band adjustment unit 51 outputs the second complex signal CS2 to the carrier sense unit 52.

[0032] The carrier sense unit 52 converts the second complex signal CS2 acquired from the band adjusting unit 51 into a real signal, and detects the signal level of the real signal. The carrier sense unit 52 sends the detected signal level to the discrimination unit 17.

[0033] As shown in FIG. 2, the carrier sense unit 52 includes an LPF 61, a converter 62, a BPF 63, an RMS (Root Mean Square) detector 64, a logarithmic amplifier 65, a gain compensator 66, a peak hold circuit 67, and a signal voltage detector 68.

[0034] The LPF 61 is applied to each of the positive and negative frequencies of the second complex signal CS2. For example, when the cutoff frequency of the LPF 61 is set to 10 kHz, the second complex signal CS2 that has passed through the LPF 61 is limited to a band having a width of 20 kHz centered at 0 Hz.

[0035] The converter 62 converts the second complex signal CS2 that has passed through the LPF 61 into a real signal. In detail, the converter 62 has a local oscillator 71 that outputs a conversion reference signal having a constant frequency, mixers 72 and 74, a phase shifter 73, and an adder 75.

[0036] The local oscillator 71 outputs a conversion reference signal of, for example, 12 kHz to the mixer 72 and the phase shifter 73 .

[0037] The mixer 72 multiplies the conversion reference signal output from the local oscillator 71 by the I signal of the second complex signal CS2 that has passed through the LPF 61, and outputs the result to the adder 75.

[0038] The phase shifter 73 shifts the phase of the conversion reference signal output from the local oscillator 71 by 90 degrees and outputs the result to the mixer 74 .

[0039] The mixer 74 multiplies the conversion reference signal, the phase of which has been shifted by 90 degrees by the phase shifter 73, by the Q signal of the second complex signal CS2 that has passed through the LPF 61, and outputs the result to the adder 75.

[0040] The adder 75 generates a real signal by adding the outputs of the mixers 72 and 74, and outputs the real signal to the BPF 63. The real signal shows a spectrum centered on the frequency of the conversion reference signal output by the local oscillator 71. For example, the real signal shows a spectrum centered on 12 kHz.

[0041] By converting a complex signal into a real signal by the converter 62, it is possible to reduce the amount of calculation during carrier sensing.

[0042] The BPF 63 limits the band of the real signal in accordance with the width of the transmission band of the wireless station 1, and outputs the band-limited real signal to the RMS detector 64. When the wireless station 1 communicates in a narrowband mode with a bandwidth of 10 kHz or less, the BPF 63 limits the band of the real signal to a bandwidth of 5 KHz or 10 kHz.

[0043] The RMS detector 64 detects the effective value of the real signal by applying a time window to the acquired real signal. The RMS detector 64 outputs the detected effective value to the logarithmic amplifier 65. The length of the time window is determined according to the time length of a beacon used in WLAN communication, which is wireless communication. In detail, the length of the time window corresponds to the minimum value of the time length of a beacon output by a wireless communication device, specifically, a WLAN device. The RMS detector 64 uses a time window with a length equivalent to 20 points at 48 kSPS, that is, a length of about 400 μsec.

[0044] The length of the time window is preferably determined by the minimum value of the time length of the beacon actually transmitted by the WLAN device. In other words, when the minimum value of the time length of the beacon actually transmitted by the WLAN device is greater than the minimum value of the time length of the beacon defined by the WLAN standard, the length of the time window may be longer than the minimum value of the time length of the beacon defined by the WLAN standard. By matching the length of the time window to the minimum value of the time length of the beacon, it is possible to suppress the generation of noise caused by the time window being longer than the signal length. As a result, the accuracy of the carrier sense is improved.

[0045] The logarithmic amplifier 65 converts the effective value obtained from the RMS detector 64 into a dB value, and outputs the dB value to the gain compensator 66 .

[0046] The gain compensator 66 compensates for the gain of the frequency component that is attenuated during down-conversion in the reception processing circuit 11. The gain compensator 66 outputs the gain-compensated dB value to the peak hold circuit 67.

[0047] The peak hold circuit 67 holds the peak of the input dB value for a certain period of time, for example, 3 msec, and outputs it to the signal voltage detector 68.

[0048] The signal voltage detector 68 detects the signal level, specifically, the amplitude value of the output of the peak hold circuit 67 from the output of the peak hold circuit 67 , and outputs the detected signal level to the discriminator 17 .

[0049] The discrimination unit 17 discriminates whether or not the transmission band is being used for wireless communication from the signal level acquired from the detection unit 16. In detail, the discrimination unit 17 discriminates whether or not the signal level acquired from the detection unit 16 is equal to or higher than a threshold. If the signal level is equal to or higher than the threshold, it can be determined that the transmission band of the wireless station 1 is being used for wireless communication. The discrimination unit 17 sends the discrimination result to the mode control unit 18. If the signal level is lower than the threshold, it can be determined that the transmission band of the wireless station 1 is not being used for wireless communication.

[0050] Because the carrier sense section 52 provided in the detection section 16 has a peak hold circuit 67, the discrimination section 17 can accurately acquire the peak value even if the detection timing in the detection section 16 differs from the timing at which the discrimination section 17 acquires the signal level from the detection section 16.

[0051] The mode control unit 18 switches between the transmission mode and the reception mode based on the discrimination result obtained from the discrimination unit 17 and the operation instruction obtained from the operation unit 19. When the mode control unit 18 switches to the transmission mode, the wireless station 1 becomes able to transmit radio waves from the antenna 10 to other communication devices by a transmission circuit (not shown).

[0052] The operation unit 19 accepts an operation instruction, specifically, an instruction to operate in either the transmission mode or the reception mode. When the operation unit 19 is instructed to operate in the transmission mode, the operation unit 19 accepts a designation of a transmission frequency. Similarly, when the operation unit 19 is instructed to operate in the reception mode, the operation unit 19 accepts a designation of a reception frequency.

[0053] When an instruction to operate in the transmission mode is received and a transmission frequency designation is received, the operation unit 19 outputs an instruction to operate in the transmission mode to the mode control unit 18 and the frequency control unit 20 .

[0054] The frequency control unit 20 controls the first oscillator 31 in accordance with the transmission frequency, and adjusts the frequency of the first reference signal LOS1 output by the first oscillator 31. Specifically, the frequency control unit 20 matches the frequency of the first reference signal LOS1 to the frequency of the IF signal when an electrical signal whose frequency matches the transmission frequency is input to the reception processing circuit 11. The frequency control unit 20 controls the RF oscillator 32 in accordance with the transmission frequency, and adjusts the frequency of the RF reference signal output by the RF oscillator 32.

[0055] The first oscillator 31 and the RF oscillator 32 are local oscillators whose frequencies can be varied under the control of the frequency control section 20 .

[0056] In order to prevent interference with WLAN communication, the wireless station 1 having the above configuration starts carrier sense processing when the operation unit 19 receives an instruction for transmission in a transmission mode. As shown in Fig. 3, the operation unit 19 repeats the processing of step S11 while PTT (Push To Talk) is not pressed (step S11; No). When the PTT of the operation unit 19 is pressed (step S11; Yes), the operation unit 19 sends the transmission frequency to the frequency control unit 20, and the frequency control unit 20 adjusts the frequencies of the first reference signal LOS1 and the RF reference signal based on the transmission frequency (step S12).

[0057] The frequency control unit 20 adjusts the frequency of the first reference signal LOS1 by controlling the first oscillator 31 according to the transmission frequency. Specifically, the frequency control unit 20 adjusts the frequency of the first reference signal LOS1 to the frequency of the IF signal when an electrical signal whose frequency coincides with the transmission frequency is input to the reception processing circuit 11.

[0058] The frequency control unit 20 adjusts the frequency of the RF reference signal by controlling the RF oscillator 32 according to the transmission frequency. Specifically, the frequency control unit 20 adjusts the frequency of the RF reference signal so that the frequency of the electrical signal output by the receiving unit 41 is included in a frequency range that can be processed by the ADC 42.

[0059] The reception processing circuit 11 digitally converts the electrical signal acquired from the antenna 10, and down-converts it to generate an IF signal (step S13). The reception processing circuit 11 outputs the IF signal to the extraction unit 12.

[0060] The extraction unit 12 performs complex frequency conversion on the IF signal based on the first reference signal LOS1 output from the first oscillator 31, and generates a first complex signal CS1 by band-limiting (step S14). In step S12, the frequency of the first reference signal LOS1 is adjusted according to the transmission frequency, so that the first complex signal CS1 generated in step S14 exhibits a spectrum centered on the component of the transmission frequency.

[0061] The detector 16 generates a real signal from the first complex signal CS1 and detects the signal level of the real signal (step S15). The detector 16 detects the signal level of the real signal obtained from the first complex signal CS1, which indicates a spectrum centered on the component of the transmission frequency.

[0062] The discrimination unit 17 determines whether the signal level is equal to or higher than the threshold (step S16). If the signal level is less than the threshold (step S16; No), it is determined that wireless communication is not being performed in the transmission band, and the mode control unit 18 allows switching to the transmission mode (step S17). As a result, the wireless station 1 can transmit in the transmission band that includes the transmission frequency specified by the operation unit 19.

[0063] If the signal level is equal to or higher than the threshold (step S16; Yes), it is assumed that wireless communication is being performed in the transmission band, and the mode control unit 18 does not allow switching to the transmission mode (step S18). As a result, the wireless station 1 is restricted from transmitting when wireless communication is being performed in the transmission band that includes the transmission frequency specified by the operation unit 19.

[0064] As described above, the wireless station 1 according to the first embodiment can improve the accuracy of carrier sense by detecting the signal level of the actual signal using a time window determined according to the time length of the beacon used in wireless communication.

[0065] The wireless station 1 according to the first embodiment can be modified in various ways in addition to those described above. First, when the frequency of the electrical signal is included in a frequency band that can be processed by the ADC 42, the receiver 41 does not need to perform frequency conversion.

[0066] Secondly, the circuit between the antenna 10 and the detector 16 may be any circuit that enables the detector 16 to perform carrier sensing at the target frequency.

[0067] (Embodiment 2) The wireless station 1 according to the second embodiment operates in either a narrowband mode in which communication is performed in a narrowband, or a wideband mode in which communication is performed in a band wider than the narrowband. The wideband mode is, for example, an ATV (Amateur Television) mode that requires a transmission band of 17 MHz. When operating in the wideband mode, the wireless station 1 according to the second embodiment performs carrier sense at multiple frequencies included in the transmission band, as shown in FIG. 4. The wireless station 1 capable of performing carrier sense at multiple frequencies will be described in the second embodiment, focusing on the differences from the first embodiment.

[0068] In detail, the wireless station 1 performs carrier sensing at the transmission frequency Ft and frequencies F1, F2, F3, and F4 which are shifted from the transmission frequency Ft by ΔF1, ΔF2, ΔF3, and ΔF4, respectively.

[0069] 5, which shows a part of the configuration of the wireless station 1, in order to perform carrier sensing at the same timing in a plurality of frequencies, the wireless station 1 according to the second embodiment includes a plurality of detectors, specifically, detectors 16a, 16b, 16c, 16d, and 16e, and variable-frequency second oscillators 33a, 33b, 33c, 33d, and 33e that output second reference signals LOS2a, LOS2b, LOS2c, LOS2d, and LOS2e to the detectors 16a, 16b, 16c, 16d, and 16e, respectively. The detectors 16a, 16b, 16c, 16d, and 16e are associated with the second oscillators 33a, 33b, 33c, 33d, and 33e that are different from each other. Specifically, the detectors 16a, 16b, 16c, 16d, and 16e are associated with the second oscillators 33a, 33b, 33c, 33d, and 33e, respectively.

[0070] The operation unit 19 accepts an operation instruction, specifically, an instruction to operate in either the transmission mode or the reception mode. When the operation unit 19 is instructed to operate in the transmission mode, it accepts a designation of a transmission frequency and an instruction to transmit in either the narrowband mode or the wideband mode. Similarly, when the operation unit 19 is instructed to operate in the reception mode, it accepts a designation of a reception frequency and an instruction to receive in either the narrowband mode or the wideband mode.

[0071] The frequency control unit 20 controls the second oscillators 33a, 33b, 33c, 33d, and 33e in accordance with the difference between the transmission frequency and the frequency at which carrier sense is performed, and adjusts the frequencies of the second reference signals LOS2a, LOS2b, LOS2c, LOS2d, and LOS2e output by the second oscillators 33a, 33b, 33c, 33d, and 33e.

[0072] In detail, the frequency control unit 20 controls the second oscillator 33a to adjust the frequency of the second reference signal LOS2a to 0 Hz.

[0073] The frequency control unit 20 adjusts the frequency of the second reference signal LOS2b by controlling the second oscillator 33b according to the difference ΔF1 between the frequency F1 and the transmission frequency Ft. Specifically, the frequency control unit 20 adjusts the frequency of the second reference signal LOS2b to the difference ΔF1 between the frequency F1 and the transmission frequency Ft.

[0074] The frequency control unit 20 adjusts the frequency of the second reference signal LOS2c by controlling the second oscillator 33c according to the difference ΔF2 between the frequency F2 and the transmission frequency Ft. Specifically, the frequency control unit 20 adjusts the frequency of the second reference signal LOS2c to the difference ΔF2 between the frequency F2 and the transmission frequency Ft.

[0075] The frequency control unit 20 adjusts the frequency of the second reference signal LOS2d by controlling the second oscillator 33d in accordance with the difference ΔF3 between the frequency F3 and the transmission frequency Ft. Specifically, the frequency control unit 20 adjusts the frequency of the second reference signal LOS2d to the difference ΔF3 between the frequency F3 and the transmission frequency Ft.

[0076] The frequency control unit 20 adjusts the frequency of the second reference signal LOS2e by controlling the second oscillator 33e according to the difference ΔF4 between the frequency F4 and the transmission frequency Ft. Specifically, the frequency control unit 20 adjusts the frequency of the second reference signal LOS2e to the difference ΔF4 between the frequency F4 and the transmission frequency Ft.

[0077] The configuration of the detectors 16a, 16b, 16c, 16d, and 16e is the same as that of the detector 16 included in the wireless station 1 according to the first embodiment. In detail, the detector 16a has a band adjusting unit 51a and a carrier sense unit 52a. The detector 16b has a band adjusting unit 51b and a carrier sense unit 52b. The detector 16c has a band adjusting unit 51c and a carrier sense unit 52c. The detector 16d has a band adjusting unit 51d and a carrier sense unit 52d. The detector 16e has a band adjusting unit 51e and a carrier sense unit 52e.

[0078] Since the band adjustment units 51a-51e have the same configuration, the configuration of the band adjustment unit 51a is shown in Fig. 6. As shown in Fig. 6, the band adjustment unit 51a has a frequency conversion unit 81, a CIC (Cascaded Integrator-Comb) filter 82, and an FIR (Finite Impulse Response) filter 83. The frequency conversion unit 81 performs complex frequency conversion on the first complex signal CS1 based on a second reference signal LOS2a output from the second oscillator 33a. The first complex signal CS1 that has been complex frequency converted by the frequency conversion unit 81 is band-limited by the CIC filter 82 and the FIR filter 83, and is output to the carrier sense unit 52a as a second complex signal CS2a.

[0079] The second complex signal CS2a output by the band adjusting unit 51a is a complex signal showing a spectrum centered on the frequency component of the second reference signal LOS2a. Since the first complex signal CS1 input from the extracting unit 12 to the band adjusting unit 51a shows a spectrum centered on the component of the transmission frequency Ft, when the frequency of the second reference signal LOS2a is set to 0 Hz as described above, the second complex signal CS2a output by the band adjusting unit 51a shows a spectrum centered on the component of the transmission frequency Ft.

[0080] Similarly, the second complex signal CS2b output by the band adjusting unit 51b is a complex signal showing a spectrum centered on the frequency component of the second reference signal LOS2b. Since the first complex signal CS1 input from the extracting unit 12 to the band adjusting unit 51b shows a spectrum centered on the component of the transmission frequency Ft, when the frequency of the second reference signal LOS2b is adjusted according to the difference ΔF1 between the frequency F1 and the transmission frequency Ft as described above, the second complex signal CS2b output by the band adjusting unit 51b shows a spectrum centered on the component of the frequency F1.

[0081] Similarly, the second complex signal CS2c output by the band adjusting unit 51c is a complex signal showing a spectrum centered on the frequency component of the second reference signal LOS2c. Since the first complex signal CS1 input from the extracting unit 12 to the band adjusting unit 51c shows a spectrum centered on the component of the transmission frequency, when the frequency of the second reference signal LOS2c is adjusted according to the difference ΔF2 between the frequency F2 and the transmission frequency Ft as described above, the second complex signal CS2c output by the band adjusting unit 51c shows a spectrum centered on the component of the frequency F2.

[0082] Similarly, the second complex signal CS2d output by the band adjusting unit 51d is a complex signal showing a spectrum centered on the frequency component of the second reference signal LOS2d. Since the first complex signal CS1 input from the extracting unit 12 to the band adjusting unit 51d shows a spectrum centered on the component of the transmission frequency, when the frequency of the second reference signal LOS2d is adjusted according to the difference ΔF3 between the frequency F3 and the transmission frequency Ft as described above, the second complex signal CS2d output by the band adjusting unit 51d shows a spectrum centered on the component of the frequency F3.

[0083] Similarly, the complex signal output by the band adjusting unit 51e is the second complex signal CS2e that shows a spectrum centered on the frequency component of the second reference signal LOS2e. Since the first complex signal CS1 input from the extracting unit 12 to the band adjusting unit 51e shows a spectrum centered on the component of the transmission frequency, when the frequency of the second reference signal LOS2e is adjusted according to the difference ΔF4 between the frequency F4 and the transmission frequency Ft as described above, the second complex signal CS2e output by the band adjusting unit 51e shows a spectrum centered on the component of the frequency F4.

[0084] The configuration of the carrier sense unit 52a is similar to that of the carrier sense unit 52 included in the detection unit 16 included in the wireless station 1 according to the embodiment 1. The bandwidth of the BPF 63 included in the carrier sense unit 52a is set to, for example, 5 KHz or 10 kHz depending on the transmission bandwidth in the narrowband mode.

[0085] The carrier sense units 52b-52e have the same configuration, and as shown in FIG. 7, are configured similarly to the carrier sense unit 52 shown in FIG. 2 without the BPF 63.

[0086] The carrier sense units 52a-52e having the above configuration each perform carrier sense at the transmission frequency Ft and the frequencies F1, F2, F3, and F4. In other words, the carrier sense units 52a-52e each detect the signal level of an actual signal in a band including the transmission frequency Ft and the frequencies F1, F2, F3, and F4, and output the detected signal to the discrimination unit 17.

[0087] The determination unit 17 determines whether or not the transmission band is being used for wireless communication from the signal levels detected by each of the detection units 16a, 16b, 16c, 16d, and 16e. In detail, the determination unit 17 determines whether or not the signal levels obtained from each of the detection units 16a, 16b, 16c, 16d, and 16e are equal to or higher than a threshold. If at least any of the signal levels is equal to or higher than the threshold, it can be determined that the transmission band of the wireless station 1 is being used for wireless communication. The determination unit 17 sends the determination result to the mode control unit 18.

[0088] As described above, in the wideband mode, the wireless station 1 according to the second embodiment performs carrier sensing for multiple frequencies at the same timing, thereby making it possible to improve the accuracy of carrier sensing while preventing the carrier sensing processing time from becoming long.

[0089] In the wireless station 1 according to the second embodiment, the band adjusting units 51a, 51b, 51c, 51d, and 51e have the same configuration, and the carrier sense units 52b, 52c, 52d, and 52e have the same configuration. The only difference between the carrier sense unit 52a and the carrier sense units 52b-52e is the BPF 63. This prevents the configuration of the wireless station 1 from becoming complicated and the manufacturing process from becoming complicated.

[0090] The wireless station 1 according to the second embodiment can be modified in various ways in addition to those described above. First, the number of detectors is arbitrary and may be determined according to the transmission band of the wireless station 1, a bandwidth suitable for carrier sensing by the carrier sense unit 52, etc. For example, the wireless station 1 may include only the detectors 16a, 16b, and 16c among the detectors 16a-16e shown in FIG.

[0091] Secondly, when transmitting in the wideband mode, the wireless station 1 may determine whether or not wireless communication is taking place in the transmission band from the signal levels detected by each of the detectors 16a-16e as described above, and when transmitting in the narrowband mode, may determine whether or not wireless communication is taking place in the transmission band based only on the signal level detected by the detector 16a.

[0092] In detail, as shown in Fig. 8, the operation unit 19 outputs the transmission frequency and an operation instruction in the transmission mode based on the specified narrowband mode or wideband mode to the frequency control unit 20 and the carrier sense units 52b, 52c, 52d, and 52e of the detection units 16b, 16c, 16d, and 16e, respectively. When the carrier sense units 52b, 52c, 52d, and 52e receive an operation instruction in the transmission mode based on the wideband mode from the operation unit 19, they detect the signal level of the actual signal. When the carrier sense units 52b, 52c, 52d, and 52e receive an operation instruction in the transmission mode based on the narrowband mode from the operation unit 19, they do not detect the signal level of the actual signal. This allows the wireless station 1 to perform carrier sense over the wideband transmission band when transmitting in the wideband mode, and to perform carrier sense only on the transmission frequency when transmitting in the narrowband mode.

[0093] Thirdly, the discrimination unit 17 may use a threshold value determined for each of the detectors 16a-16e to determine whether the signal level detected by each of the detectors 16a-16e is equal to or higher than the threshold value corresponding to each of the detectors 16a-16e. By using a threshold value corresponding to a frequency band, it is possible to improve the accuracy of carrier sense.

[0094] The modifications described in the first embodiment can also be applied to the second embodiment. Specifically, in the wireless station 1 according to the second embodiment, when the frequency of the electrical signal is included in a frequency band that can be processed by the ADC 42, the receiver 41 does not need to perform frequency conversion. In this case, the wireless station 1 does not need to include the RF oscillator 32.

[0095] Furthermore, the circuit between the antenna 10 and the detector 16 may be any circuit that enables the detector 16 to perform carrier sensing at the transmission frequency.

[0096] 9, each of the above-described wireless stations 1 includes, as hardware components for controlling each unit, a processor 91, a memory 92, and an interface 93. The processor 91, the memory 92, and the interface 93 are connected to one another via a bus 90.

[0097] For example, each function of the wireless station 1 is realized by a processor 91 executing a program stored in a memory 92.

[0098] For example, the interface 93 is for connecting to other communication devices, external devices, etc. and establishing communication. The interface 93 has multiple types of interface modules as necessary.

[0099] 9, the wireless station 1 has one processor 91 and one memory 92, but the wireless station 1 may have multiple processors 91 and multiple memories 92. In this case, the multiple processors 91 and the multiple memories 92 may cooperate with each other to execute each function of the wireless station 1.

[0100] 10, the wireless station 1 may be realized by a processing circuit 94. The processing circuit 94 is connected to other communication devices, external devices, etc. via an interface circuit 95.

[0101] When the processing circuit 94 is a dedicated hardware, the processing circuit 94 has, for example, a single circuit, a composite circuit, a processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination of these, etc. Each unit of the wireless station 1 may be realized by an individual processing circuit 94, or each unit of the wireless station 1 may be realized by a common processing circuit 94.

[0102] A part of each function of the wireless station 1 may be realized by dedicated hardware, and the other part may be realized by software or firmware. For example, as shown in Fig. 11, in the wireless station 1, the extraction unit 12, a part of the demodulation unit 13, and the band adjustment unit 51 may be realized by an FPGA (Field Programmable Gate Array) 101, another part of the demodulation unit 13 and the carrier sense unit 52 may be realized by a DSP (Digital Signal Processor) 102, and the discrimination unit 17, the mode control unit 18, the operation unit 19, and the frequency control unit 20 may be realized by a CPU (Central Processing Unit) 103. The part of the demodulation unit 13 realized by the FPGA 101 may limit the band to a band to be subjected to demodulation processing by, for example, a CIC filter and an FIR filter, and downsample the band-limited first complex signal CS1. The other part of the demodulation unit 13 realized by the DSP 102 may perform demodulation processing of the band-limited and downsampled first complex signal CS1.

[0103] Furthermore, the above-mentioned hardware configuration and flowchart are merely examples and can be changed or modified as desired. [Explanation of symbols]

[0104] 1 Radio station 10 Antennas 11 Reception processing circuit 12 Extraction part 13 Demodulation section 14 DAC 15 Output section 16, 16a, 16b, 16c, 16d, 16e Detection unit 17 Discrimination part 18 Mode control section 19 Control section 20 Frequency control section 31 First Oscillator 32 RF Oscillator 33a, 33b, 33c, 33d, 33e Second oscillator 41 Receiving section 42 ADC 51, 51a, 51b, 51c, 51d, 51e Bandwidth adjustment unit 52, 52a, 52b, 52c, 52d, 52e Carrier sense section 61 LPF 62 Converter 63 BPF 64 RMS detector 65 Logarithmic Amplifier 66 Gain Compensator 67 Peak hold circuit 68 Signal Voltage Detector 71 Local Oscillator 72,74 Mixer 73 Phase shifter 75 Adder 81 Frequency conversion section 82 CIC Filter 83 FIR Filters 90 Bus 91 Processor 92 Memory 93 Interface 94 Processing Circuit 95 Interface Circuit 101 FPGA 102 DSP 103 CPU CS1 First complex signal CS2,CS2a,CS2b, CS2c, CS2d, CS2e Second complex signal LOS1 First reference signal LOS2a,LOS2b, LOS2c, LOS2d, LOS2e Second reference signal

Claims

1. a detection unit that detects a signal level at a specified transmission frequency by applying a time window determined according to a time length of a beacon used in wireless communication to an actual signal obtained as a result of digitally converting an electric signal based on a radio wave captured by an antenna; a determination unit that determines whether or not a transmission band including the transmission frequency is being used for the wireless communication based on the signal level detected by the detection unit; A radio station equipped with

2. the detection unit detects the signal level by applying the time window having a length that coincides with a minimum value of a time length of the beacon output by the wireless communication device that performs the wireless communication to the real signal.

2. The radio station according to claim 1.

3. The detection unit detects the signal level by applying the time window determined according to a time length of the beacon used in WLAN (Wireless Local Area Network) communication based on an orthogonal frequency division multiplexing system to the actual signal.

3. The radio station according to claim 1 or 2.

4. a reception processing circuit that digitally converts an electric signal based on the radio wave captured by the antenna and down-converts it to generate an IF signal in an intermediate frequency band; a first oscillator having a variable frequency that outputs a first reference signal; an extractor that performs complex frequency conversion on the IF signal based on the first reference signal and generates a first complex signal by limiting the frequency band to a predetermined band centered on the frequency of the first reference signal; a frequency control unit that adjusts a frequency of the first reference signal in response to a designated transmission frequency, the detection unit detects the signal level by applying the time window to the real signal obtained from the first complex signal.

3. The radio station according to claim 1 or 2.

5. The second oscillator further includes a plurality of variable frequency second oscillators that output second reference signals having different frequencies from each other, a plurality of the detection units that acquire the second reference signal from different second oscillators; the frequency control unit adjusts a frequency of the second reference signal output by each of the second oscillators in accordance with the transmission frequency and a bandwidth of a transmission band including the transmission frequency; each of the detection units detects the signal level by applying the time window to the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal; the determination unit determines whether or not the transmission band is being used for the wireless communication based on the signal levels detected by each of the detection units.

5. The radio station according to claim 4.

6. the frequency control unit adjusts a frequency of the second reference signal for any of the second oscillators so that a complex signal obtained by complex frequency converting the first complex signal based on the second reference signal output by the second oscillator exhibits a spectrum centered on a component of the transmission frequency. The radio station according to claim 5.

7. an operation unit that accepts a designation of the transmission frequency and an instruction to transmit in either a narrowband mode or a wideband mode in which the transmission band is wider than that of the narrowband mode; when transmission in the wideband mode is specified by the operation unit, the discrimination unit discriminates whether or not the transmission band is being used for the wireless communication from the signal levels detected by each of the detection units, and when transmission in the narrowband mode is specified by the operation unit, discriminates whether or not the transmission band is being used for the wireless communication from the signal levels detected by the detection units by applying the time window to the real signal obtained from a complex signal indicating a spectrum centered on a component of the transmission frequency. The radio station according to claim 5.

8. A carrier sense method performed by a wireless station, comprising: A time window determined according to the time length of a beacon used in wireless communication is applied to the actual signal obtained as a result of digitally converting an electrical signal based on radio waves captured by an antenna, thereby detecting the signal level at a specified transmission frequency. determining, from the signal level, whether or not a transmission band including the transmission frequency is being used for the wireless communication; Carrier sense method.

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