Radio station and carrier sense method

Abstract

To provide a radio station and a carrier sense method capable of increasing the sensitivity of carrier sense.SOLUTION: A frequency determination unit 20 included in a radio station 1 determines a target frequency for carrier sense from the band of a subcarrier at least part of which is included in a transmission band among a plurality of subcarriers of a channel determined for radio communication based on an orthogonal frequency division multiplexing system. A detection unit 16 detects a signal level at the target frequency for an actual signal obtained as 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 the transmission band is being used for radio communication from the signal level.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] A wireless communication device connected to a WLAN (Wireless Local Area Network) performs wireless communication based on the OFDM (Orthogonal Frequency Division Multiplex) method in the 2.4 GHz or 5 GHz band allocated to 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 subcarrier contained in 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] A radio station for a secondary service is required not to cause harmful interference to a radio station for a primary service. Therefore, when a radio station for a secondary service communicates in the 2.4 GHz or 5 GHz band, the radio station for a secondary service needs to perform carrier sense to determine whether or not other radio communication devices are performing radio communication in a transmission band including the transmission frequency in order to prevent interference with the radio communication of the primary service performed by other radio communication devices. Since the transmission frequency of a radio station for a secondary service is set according to a user's operation, the transmission frequency may be a frequency that is out of the peak of the subcarrier of a radio signal based on the OFDM system transmitted from a radio station for a primary service. In this case, if the radio station for a secondary service performs carrier sense based on the signal level of a signal included in the transmission band centered on the transmission frequency, the radio station may erroneously determine that the transmission band is not in use.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a wireless station and a carrier sense method that are capable of improving the sensitivity of carrier sense. [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 frequency determination unit that, when at least a portion of a transmission band including a designated transmission frequency overlaps with at least a portion of a band of at least one of a plurality of channels defined for wireless communication based on an orthogonal frequency division multiplexing system, determines a target frequency of carrier sense from a band of a subcarrier of a plurality of subcarriers of the channel, at least a portion of which is included in the transmission band; a detection unit that detects a signal level at the target frequency of an actual signal obtained by digitally converting an electric signal based on a radio wave captured by an antenna; a determination unit that determines whether or not the transmission band is being used for the wireless communication based on the signal level detected by the detection unit; Equipped with.

[0008] Preferably, when a centre frequency of the subcarrier, at least a part of which is included in the transmission band, is included in the transmission band, the frequency determination unit determines the target frequency from the centre frequency.

[0009] Preferably, when center frequencies of a plurality of the subcarriers are included in the transmission band, the frequency determination unit determines the center frequency closest to the transmission frequency as the target frequency.

[0010] Preferably, when the central frequencies of a plurality of the subcarriers are included in the transmission band, the frequency determination unit determines the central frequency that is closest to the center of the band of the channel having those subcarriers as the target frequency.

[0011] Preferably, when a center frequency of each of the subcarriers, at least a portion of which is included in the transmission band, is outside the transmission band, the frequency determination unit determines the target frequency to be the upper limit or lower limit of the transmission band that overlaps with the subcarrier.

[0012] Preferably, when at least a portion of the transmission band overlaps with at least a portion of the bands of a plurality of the channels, the frequency determination unit determines the target frequency from the band of a subcarrier of a plurality of subcarriers of the channel, at least a portion of which is included in the transmission band, for each of the channels, at least a portion of which is included in the transmission band.

[0013] Preferably, the frequency determination unit determines, as the target frequencies, a frequency based on a band of a subcarrier at least a part of which is included in the transmission band among the plurality of subcarriers of the channel, and the transmission frequency.

[0014] 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, and at least a portion of the transmission band including the transmission frequency specified by the operation unit overlaps with at least a portion of the band of at least one of the multiple channels, the frequency determination unit determines the target frequency from the band of a subcarrier of a channel, at least a portion of which is included in the transmission band, and when transmission in the narrowband mode is specified by the operation unit, the frequency determination unit sets the transmission frequency specified by the operation unit as the target frequency.

[0015] Preferably, when at least a portion of the transmission band overlaps with at least a portion of the band of at least one of a plurality of channels defined for WLAN (Wireless Local Area Network) communication based on an orthogonal frequency division multiplexing system, the frequency determination unit determines a target frequency for carrier sensing from a subcarrier band of a plurality of subcarriers of the channel, at least a portion of which is included in the transmission band.

[0016] Preferably, a reception processing circuit that digitally converts the electrical signal 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; a variable frequency second oscillator that outputs a second 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 the transmission frequency and adjusts a frequency of the second reference signal in response to a difference between the transmission frequency and the target frequency, The detection unit detects a signal level of the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal.

[0017] Preferably, a reception processing circuit that digitally converts the electrical signal 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; a plurality of variable frequency second oscillators that output second reference signals having different frequencies from each other; 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 the transmission frequency and adjusts a frequency of the second reference signal in response to a difference between the transmission frequency and the target frequency, a plurality of the detection units each corresponding to a different second oscillator; the detection unit detects a signal level of the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal output from the associated second oscillator, the frequency control unit adjusts a frequency of the second reference signal output by each of the second oscillators in accordance with a difference between the transmission frequency and the target frequency determined for each of the channels by the frequency determination unit; 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.

[0018] A carrier sense method according to a second aspect of the present invention includes: A carrier sense method performed by a wireless station, comprising: When at least a part of a transmission band including a specified transmission frequency overlaps with at least a part of a band of at least one of a plurality of channels defined for wireless communication based on an orthogonal frequency division multiplexing system, a target frequency of carrier sense is determined from a band of a subcarrier of a plurality of subcarriers of the channel, at least a part of which is included in the transmission band; Detecting a signal level at the target frequency for an actual signal obtained as a result of digitally converting an electric signal based on the radio wave captured by an antenna; From the signal level, it is determined whether or not the transmission band is being used for the wireless communication. Effect of the Invention

[0019] A wireless station according to the present invention determines a target frequency for carrier sense from a band of a subcarrier at least a part of which is included in a transmission band among a plurality of subcarriers of a channel. The wireless station can improve the sensitivity of carrier sense by detecting a signal level at the target frequency determined from the band of the subcarrier. [Brief description of the drawings]

[0020] [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] A flowchart showing an example of an operation of a carrier sense process performed by a wireless station according to the first embodiment. [Diagram 3] FIG. 1 is a diagram showing an example of a relationship between a transmission band of a radio station according to a first embodiment and a spectrum of a subcarrier in WLAN communication; [Figure 4] FIG. 13 is a diagram showing another example of the relationship between the transmission band of the radio station according to the first embodiment and the spectrum of the subcarriers in WLAN communication; [Diagram 5] FIG. 13 is a diagram showing another example of the relationship between the transmission band of the radio station according to the first embodiment and the spectrum of the subcarriers in WLAN communication; [Figure 6] FIG. 11 is a block diagram showing a part of a configuration of a radio station according to a second embodiment. [Figure 7] 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; [Figure 8] FIG. 11 is a block diagram showing a modification of a part of the configuration of a radio station according to a 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

[0021] 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.

[0022] (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 a transmission band including a specified transmission frequency in order to prevent interference with WLAN communication in the 2.4 GHz or 5 GHz band. The wireless station 1 determines a target frequency for carrier sense from the band of OFDM subcarriers included in the transmission band of the wireless station 1, and determines whether or not the transmission band is being used for wireless communication from the signal level at the target frequency.

[0023] 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 determination unit 20, a frequency control unit 21, a first oscillator 31, a second oscillator 32, and an RF (Radio Frequency) oscillator 33.

[0024] 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.

[0025] 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.

[0026] 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 includes a filter, specifically, a BPF (Band Pass Filter), an attenuator, an LNA (Low Noise Amplifier), a mixer, and the like.

[0027] The receiver 41 multiplies, in a mixer, the electrical signal that has been filtered by the BPF and passed through the attenuator and LNA with the RF reference signal output by the RF oscillator 33, 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.

[0028] The ADC 42 digitally converts the electrical signal that has been subjected to the signal processing in the receiving unit 41 to generate an IF signal, which is a real signal. The ADC 42 outputs the IF signal to the extraction unit 12.

[0029] 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.

[0030] 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.

[0031] 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 .

[0032] 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 .

[0033] The output unit 15 is, for example, a speaker, and outputs the analog signal acquired from the DAC 14 .

[0034] The detection unit 16 detects the signal level of a real signal obtained as a result of complex frequency conversion of the first complex signal CS1 based on the second reference signal LOS2 output by the frequency-variable second oscillator 32. The detection unit 16 outputs the detected signal level to the discrimination unit 17.

[0035] In detail, the detection unit 16 has a frequency conversion unit 51 and a carrier sense unit 52. The frequency conversion unit 51 performs complex frequency conversion on the first complex signal CS1 based on the second reference signal LOS2 output from the second oscillator 32, and generates a second complex signal CS2 by limiting the first complex signal CS1 to a predetermined band centered on the frequency of the second reference signal LOS2. The frequency conversion unit 51 outputs the second complex signal CS2 to the carrier sense unit 52. In detail, by performing complex frequency conversion on the first complex signal CS1 based on the second reference signal LOS2, a complex signal showing a spectrum centered on the frequency component of the second reference signal LOS2 is obtained. For example, a complex signal showing a spectrum with the frequency of the second reference signal LOS2 as a reference of 0 Hz is obtained. By limiting the band of the complex signal to a predetermined band centered on 0 Hz, a second complex signal CS2, which is a complex signal to be carrier sensed by the carrier sense unit 52, is obtained.

[0036] The carrier sense unit 52 converts the second complex signal CS2 acquired from the frequency conversion unit 51 into a real signal and detects the signal level of the real signal. In detail, the carrier sense unit 52 converts the second complex signal CS2 into a real signal based on a reference signal supplied from an oscillator with a fixed frequency (not shown). The carrier sense unit 52 determines the effective value of the real signal using an RMS (Root Mean Square) detector and converts the effective value into a dB value using a logarithmic amplifier. The carrier sense unit 52 outputs the dB value to the discrimination unit 17 as the detected signal level.

[0037] The discrimination unit 17 discriminates whether or not the transmission band is being used for wireless communication, specifically, for WLAN communication based on the OFDM system, 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 considered 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 considered that the transmission band of the wireless station 1 is not being used for wireless communication.

[0038] 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).

[0039] The operation unit 19 accepts operation instructions, specifically, instructions 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, which has a wider transmission band than the narrowband. 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.

[0040] The wideband mode is, for example, an ATV (Amateur Television) mode that requires a transmission band of 17 MHz. When an operation in the transmission mode is instructed and an instruction to transmit in either the narrowband mode or the wideband mode is received as well as a specification of the transmission frequency, the operation unit 19 sends an instruction to operate in the transmission mode to the mode control unit 18, and outputs to the frequency determination unit 20 an instruction to operate in the transmission mode based on the transmission frequency and the specified narrowband mode or wideband mode.

[0041] When the frequency determination unit 20 acquires the transmission frequency from the operation unit 19, the frequency determination unit 20 determines a target frequency for carrier sense from the transmission frequency. The frequency determination unit 20 outputs the target frequency determined as the transmission frequency to the frequency control unit 21.

[0042] The frequency control unit 21 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. The frequency control unit 21 controls the second oscillator 32 in accordance with the difference between the transmission frequency and the target frequency and adjusts the frequency of the second reference signal LOS2 output by the second oscillator 32. The frequency control unit 21 controls the RF oscillator 33 in accordance with the transmission frequency and adjusts the frequency of the RF reference signal output by the RF oscillator 33.

[0043] The first oscillator 31, the second oscillator 32, and the RF oscillator 33 are local oscillators whose frequencies are variable under the control of the frequency control section 21.

[0044] 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. 2, 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 a transmission frequency to the frequency determination unit 20, and the frequency determination unit 20 determines a target frequency for carrier sense from the transmission frequency (step S12). The frequency determination unit 20 sends the transmission frequency and the determined target frequency to the frequency control unit 21.

[0045] In WLAN communication, multiple channels with a fixed bandwidth are defined by the standard. Each channel contains multiple subcarriers. For example, in the IEEE802.11a / g / n / ac standard, one channel with a bandwidth of 20 MHz contains 63 subcarriers with a bandwidth of 312.5 KHz.

[0046] An example of the spectrum of multiple subcarriers included in one channel is shown in Figure 3. In Figure 3, the area surrounded by the dotted line indicates the transmission band including the transmission frequency Ft. In the example of Figure 3, a subcarrier whose center frequency is the center frequency F1c of the channel is not set.

[0047] When at least a portion of the transmission band including the specified transmission frequency, i.e., the transmission frequency acquired from the operation unit 19, overlaps with at least a portion of the band of at least one of the multiple channels defined for WLAN communication, the frequency determination unit 20 determines the target frequency for carrier sensing from the band of a subcarrier of which at least a portion is included in the transmission band among multiple subcarriers of the channel.

[0048] When the center frequency of a subcarrier, at least a part of which is included in the transmission band, is included in the transmission band, the frequency determination unit 20 determines the target frequency from the center frequency. In the example of Fig. 3, the center frequencies of multiple subcarriers are included in the transmission band, which is the area surrounded by the dotted line. It is preferable that the frequency determination unit 20 determines the target frequency from the center frequency of the subcarrier closest to the transmission frequency Ft.

[0049] In the example of Fig. 3, the transmission frequency Ft is located between adjacent subcarriers. Among the subcarriers adjacent to each other across the transmission frequency Ft, the center frequency of one subcarrier is F1s(k-1), and the center frequency of the other subcarrier is F1s(k). In the example of Fig. 3, the center frequency F1s(k) is closer to the transmission frequency Ft than the center frequency F1s(k-1). Therefore, the frequency determination unit 20 sets the center frequency F1s(k) as the target frequency for carrier sense.

[0050] As shown in FIG. 2, the frequency control unit 21 adjusts the frequencies of the first reference signal LOS1, the second reference signal LOS2, and the RF reference signal based on the transmission frequency and the target frequency obtained in step S12 (step S13).

[0051] The frequency control unit 21 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 21 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.

[0052] The frequency control unit 21 adjusts the frequency of the second reference signal LOS2 by controlling the second oscillator 32 according to the difference between the transmission frequency and the target frequency. Specifically, the frequency control unit 21 adjusts the frequency of the second reference signal LOS2 to the difference between the transmission frequency and the target frequency.

[0053] The frequency control unit 21 adjusts the frequency of the RF reference signal by controlling the RF oscillator 33 according to the transmission frequency. Specifically, the frequency control unit 21 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.

[0054] 2, 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 S14). The reception processing circuit 11 outputs the IF signal to the extraction unit 12.

[0055] 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 S15). In step S13, 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 S15 exhibits a spectrum centered on the component of the transmission frequency.

[0056] The detection unit 16 generates a real signal from the first complex signal CS1 and detects the signal level (step S16). In detail, the detection unit 16 performs complex frequency conversion on the first complex signal CS1 based on the second reference signal LOS2 output by the second oscillator 32, and generates a second complex signal CS2 by band limiting. The detection unit 16 generates a real signal from the second complex signal CS2 and detects the signal level of the real signal. In step S13, the frequency of the second reference signal LOS2 is adjusted according to the difference between the transmission frequency and the target frequency, so that the second complex signal CS2 generated in step S16 shows a spectrum centered on the component of the target frequency. The detection unit 16 generates a real signal from the second complex signal CS2 showing a spectrum centered on the component of the target frequency, and detects the signal level of the real signal.

[0057] The discrimination unit 17 determines whether the signal level is equal to or higher than the threshold (step S17). If the signal level is less than the threshold (step S17; 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 S18). As a result, the wireless station 1 can transmit in the transmission band that includes the transmission frequency specified by the operation unit 19.

[0058] If the signal level is equal to or higher than the threshold (step S17; 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 S19). As a result, the wireless station 1 is restricted from transmitting in the transmission band that includes the transmission frequency specified by the operation unit 19.

[0059] As described above, the wireless station according to the first embodiment performs carrier sensing at a target frequency determined from the subcarrier band, and therefore, it is possible to improve the sensitivity of the carrier sensing. Specifically, it is possible to improve the sensitivity of the carrier sensing by performing carrier sensing at the center frequency of the subcarrier.

[0060] The wireless station 1 according to the first embodiment can be modified in various ways in addition to those described above. First, the method of determining the target frequency is not limited to the above example. As an example, as shown in Figures 4 and 5, when the center frequency of each subcarrier is outside the transmission band, the frequency determination unit 20 may set the upper limit or lower limit of the transmission band that overlaps with the subcarrier as the target frequency.

[0061] 4, the subcarrier to which the highest frequency is assigned in the channel overlaps with the lower limit of the transmission band. In this case, the frequency determination unit 20 sets the lower limit of the transmission band as the target frequency.

[0062] 5, the subcarrier to which the smallest frequency is assigned in the channel overlaps with the upper limit of the transmission band. In this case, the frequency determination unit 20 sets the upper limit of the transmission band as the target frequency.

[0063] Secondly, the wireless station 1 may determine the target frequency from the band of subcarriers included in the transmission band as described above when transmitting in the wideband mode, and may set only the transmission frequency as the target frequency when transmitting in the narrowband mode. Specifically, when the frequency determination unit 20 receives an instruction to operate in the transmission mode based on the wideband mode from the operation unit 19, the frequency determination unit 20 determines the target frequency from the band of subcarriers included in the transmission band as described above. When the frequency determination unit 20 receives an instruction to operate in the transmission mode based on the narrowband mode from the operation unit 19, the frequency determination unit 20 sets the transmission frequency as the target frequency. By performing carrier sense only on the transmission frequency when transmitting in the narrowband mode in which the transmission band is narrow, the transmission operation of the wireless station 1 is prevented from being restricted by communication existing outside the transmission band.

[0064] Thirdly, 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.

[0065] Fourth, 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.

[0066] (Embodiment 2) The number of target frequencies for which the wireless station 1 performs carrier sensing is not limited to one. A wireless station 1 that performs carrier sensing for a plurality of target frequencies at the same timing will be described in the second embodiment, focusing on the differences from the first embodiment.

[0067] As shown in Fig. 6 showing a part of the configuration of the wireless station 1, the wireless station 1 according to the second embodiment includes a plurality of detectors and a plurality of second oscillators. In detail, the wireless station 1 includes detectors 16a, 16b, and 16c, and variable-frequency second oscillators 32a, 32b, and 32c that output second reference signals LOS2a, LOS2b, and LOS2c of different frequencies to the detectors 16a, 16b, and 16c, respectively. The detectors 16a, 16b, and 16c are associated with the second oscillators 32a, 32b, and 32c that are different from each other. Specifically, the detectors 16a, 16b, and 16c are associated with the second oscillators 32a, 32b, and 32c, respectively.

[0068] The configuration of the detectors 16a, 16b, and 16c 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 includes a frequency converter 51a and a carrier sense unit 52a. The detector 16b includes a frequency converter 51b and a carrier sense unit 52b. The detector 16c includes a frequency converter 51c and a carrier sense unit 52c.

[0069] The frequency converters 51a, 51b, and 51c have the same configuration as the frequency converter 51 included in the detector 16 included in the wireless station 1 according to the first embodiment. The frequency converters 51a, 51b, and 51c perform complex frequency conversion on the first complex signal CS1 based on the second reference signals LOS2a, LOS2b, and LOS2c output from the second oscillators 32a, 32b, and 32c, respectively, and perform band limitation to generate second complex signals CS2a, CS2b, and CS2c. The carrier sense units 52a, 52b, and 52c have the same configuration as the carrier sense unit 52 included in the detector 16 included in the wireless station 1 according to the first embodiment. The carrier sense units 52a, 52b, and 52c convert the second complex signals CS2a, CS2b, and CS2c into real signals, respectively, and detect the signal levels of the real signals.

[0070] The second oscillators 32a, 32b, and 32c have the same configuration as the second oscillator 32 included in the wireless station 1 according to embodiment 1. The second oscillators 32a, 32b, and 32c are controlled by the frequency control unit 21, so that the frequencies of the second reference signals LOS2a, LOS2b, and LOS2c are adjusted.

[0071] The wireless station 1 according to the second embodiment having the above configuration performs carrier sense for a plurality of target frequencies at the same timing. The operation unit 19 outputs to the frequency determination unit 20 an operation instruction for a transmission frequency and an operation in a transmission mode based on a specified narrowband mode or wideband mode.

[0072] As shown in FIG. 7, the transmission band may overlap with a plurality of channels. In the second embodiment, the transmission band overlaps with a portion of each of the channels CH1 and CH2. The frequency determination unit 20 determines the target frequency from the band of a subcarrier at least a portion of which is included in the transmission band among the plurality of subcarriers of the channels CH1 and CH2. For example, the frequency determination unit 20 determines the target frequency to be the center frequency F1s(63) of the subcarrier of the channel CH1 that is closest to the transmission frequency Ft among the center frequencies of the subcarriers included in the transmission band. The frequency determination unit 20 determines the target frequency to be the center frequency F2s(1) of the subcarrier of the channel CH2 that is closest to the transmission frequency Ft among the subcarriers included in the transmission band.

[0073] In the second embodiment, the frequency determining unit 20 sets the transmission frequency Ft as a target frequency in addition to the above-mentioned center frequencies F1s(63) and F2s(1).

[0074] 6 perform carrier sensing of the transmission frequency Ft and the center frequencies F1s(63) and F2s(1), respectively. The frequency control unit 21 controls the second oscillators 32a, 32b, and 32c in accordance with the differences between the transmission frequency Ft and the transmission frequency Ft and the center frequencies F1s(63) and F2s(1), respectively.

[0075] Since the target of the carrier sense of the detector 16a is the transmission frequency Ft, the difference between the transmission frequency and the target frequency can be considered to be 0. In other words, the frequency of the second reference signal LOS2a output by the second oscillator 32a can be considered to be 0 Hz. The frequency of the second reference signal LOS2b output by the second oscillator 32b is based on the difference between the transmission frequency Ft and the center frequency F1s (63). The frequency of the second reference signal LOS2c output by the second oscillator 32c is based on the difference between the transmission frequency Ft and the center frequency F2s (1).

[0076] In the detection unit 16a that performs carrier sensing at the transmission frequency Ft, it is preferable that the frequency conversion unit 51a generates the second complex signal CS2a by band-limiting the result of complex frequency conversion of the first complex signal CS1 based on the second reference signal LOS2a to match it to the transmission band in the narrowband mode.

[0077] The discrimination unit 17 discriminates 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, and 16c. In detail, the discrimination unit 17 discriminates whether or not the signal levels acquired from each of the detection units 16a, 16b, and 16c 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 discrimination unit 17 sends the discrimination result to the mode control unit 18.

[0078] As described above, when the transmission band overlaps with multiple channels, the radio station 1 according to embodiment 2 performs carrier sensing at the same timing for each channel, thereby making it possible to increase the sensitivity of the carrier sensing while preventing the carrier sensing processing time from becoming long.

[0079] In the wireless station 1 according to the second embodiment, the detectors 16a, 16b, and 16c have the same configuration, which prevents the configuration of the wireless station 1 and the manufacturing process from becoming complicated.

[0080] The wireless station 1 according to the second embodiment can be modified in various ways in addition to those described above. First, the method of determining the target frequency is not limited to the above example. As an example, in the example of Fig. 7, the frequency determination unit 20 may determine the center frequency F1s(61) of the subcarrier of the channel CH1 that is closest to the center of the band of the channel CH1 among the center frequencies of the subcarriers included in the transmission band as the target frequency. Also, the frequency determination unit 20 may determine the center frequency F2s(2) of the subcarrier of the channel CH2 that is closest to the center of the band of the channel CH2 among the subcarriers included in the transmission band as the target frequency.

[0081] As another example, the frequency determination unit 20 may not include the transmission frequency Ft in the target frequencies. In this case, the wireless station 1 may not include the detection unit 16a, but may include the detection units 16b and 16c.

[0082] As another example, the frequency determination unit 20 may set each of the upper limit and the lower limit of the transmission band as the target frequencies. In the example of Fig. 7, the lower limit of the transmission band is used for carrier sense to determine the presence or absence of WLAN communication in channel CH1, and the upper limit of the transmission band is used for carrier sense to determine the presence or absence of WLAN communication in channel CH2.

[0083] Secondly, the number of detectors is arbitrary and may be determined according to the channels of WLAN communication that need to be prevented from interference. For example, in the 2.4 GHz band of WLAN communication, there exists a frequency band in which three or more channels overlap. In this case, the wireless station 1 may be provided with four or more detectors.

[0084] Thirdly, the discrimination unit 17 may use a threshold value determined for each of the detection units 16a-16c to determine whether the signal level detected by each of the detection units 16a-16c is equal to or higher than the threshold value corresponding to each of the detection units 16a-16c. By using a threshold value corresponding to a frequency band, it is possible to improve the sensitivity of the carrier sense.

[0085] The modified example described in the embodiment 1 can also be applied to the embodiment 2. Specifically, the radio station 1 according to the embodiment 2 may determine the target frequency from the band of subcarriers included in the transmission band as described above when transmitting in the wideband mode, and may determine only the transmission frequency as the target frequency when transmitting in the narrowband mode.

[0086] 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 determination unit 20 and the carrier sense units 52b, 52c of the detection units 16b, 16c. When the carrier sense units 52b, 52c 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 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 at a frequency determined from the transmission frequency and the band of the subcarrier included in the transmission band as described above when transmitting in the wideband mode, and to perform carrier sense only for the transmission frequency when transmitting in the narrowband mode.

[0087] Furthermore, when the frequency of the electrical signal is included in a frequency band that can be processed by the ADC 42, the receiving unit 41 does not need to perform frequency conversion. In this case, the wireless station 1 according to the second embodiment does not need to include the RF oscillator 33.

[0088] 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 target frequency.

[0089] 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.

[0090] For example, each function of the wireless station 1 is realized by a processor 91 executing a program stored in a memory 92.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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 frequency conversion unit 51 may be realized by an FPGA (Field Programmable Gate Array) 61, another part of the demodulation unit 13 and the carrier sense unit 52 may be realized by a DSP (Digital Signal Processor) 62, and the discrimination unit 17, the mode control unit 18, the operation unit 19, the frequency determination unit 20, and the frequency control unit 21 may be realized by a CPU (Central Processing Unit) 63. The part of the demodulation unit 13 realized by the FPGA 61 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 62 may perform demodulation processing of the band-limited and downsampled first complex signal CS1.

[0096] Furthermore, the above-mentioned hardware configuration and flowchart are merely examples and can be changed or modified as desired. [Explanation of symbols]

[0097] 1 Radio station 10 Antennas 11 Reception processing circuit 12 Extraction part 13 Demodulation section 14 DAC 15 Output section 16, 16a, 16b, 16c Detector 17 Discrimination part 18 Mode control section 19 Control section 20 Frequency determination section 21 Frequency Control Section 31 First Oscillator 32, 32a, 32b, 32c Second oscillator 33 RF Oscillator 41 Receiving section 42 ADC 51, 51a, 51b, 51c Frequency conversion unit 52, 52a, 52b, 52c Carrier sense section 61 FPGA 62 DSP 63 CPU 90 Bus 91 Processor 92 Memory 93 Interface 94 Processing Circuit 95 Interface Circuit CS1 First complex signal CS2,CS2a,CS2b,CS2c Second complex signal LOS1 First reference signal LOS2, LOS2a, LOS2b, LOS2c Second reference signal

Claims

1. a frequency determination unit that, when at least a portion of a transmission band including a designated transmission frequency overlaps with at least a portion of a band of at least one of a plurality of channels defined for wireless communication based on an orthogonal frequency division multiplexing system, determines a target frequency of carrier sense from a band of a subcarrier of a plurality of subcarriers of the channel, at least a portion of which is included in the transmission band; a detection unit that detects a signal level at the target frequency of an actual signal obtained by digitally converting an electric signal based on a radio wave captured by an antenna; a determination unit that determines whether or not the transmission band is being used for the wireless communication based on the signal level detected by the detection unit; A radio station equipped with

2. the frequency determination unit determines the target frequency from a center frequency of the subcarrier, at least a portion of which is included in the transmission band, when the center frequency of the subcarrier is included in the transmission band; 2. The radio station according to claim 1.

3. when center frequencies of a plurality of the subcarriers are included in the transmission band, the frequency determination unit determines the center frequency that is closest to the transmission frequency as the target frequency. The radio station according to claim 2.

4. when center frequencies of a plurality of the subcarriers are included in the transmission band, the frequency determination unit determines the center frequency that is closest to the center of the band of the channel having the subcarriers as the target frequency. The radio station according to claim 2.

5. When a center frequency of each of the subcarriers, at least a portion of which is included in the transmission band, is outside the transmission band, the frequency determination unit determines an upper limit or a lower limit of the transmission band that overlaps with the subcarrier as the target frequency.

2. The radio station according to claim 1.

6. When at least a portion of the transmission band overlaps with at least a portion of the bands of the plurality of channels, the frequency determination unit determines the target frequency from a band of the subcarrier, at least a portion of which is included in the transmission band, among a plurality of subcarriers of the channel, for each of the channels, at least a portion of which is included in the transmission band. A radio station according to any one of claims 1 to 5.

7. the frequency determination unit determines, as the target frequency, a frequency based on a band of the subcarriers of the channel, at least a part of which is included in the transmission band, and the transmission frequency; A radio station according to any one of claims 1 to 5.

8. the frequency determination unit determines, as the target frequency, a frequency based on a band of the subcarriers of the channel, at least a part of which is included in the transmission band, and the transmission frequency; The radio station according to claim 6.

9. 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 the operation unit specifies transmission in the wideband mode, and when at least a portion of the transmission band including the transmission frequency specified by the operation unit overlaps with at least a portion of a band of at least one of the channels, the frequency determination unit determines the target frequency from a band of a subcarrier of a channel, at least a portion of which is included in the transmission band, and when the operation unit specifies transmission in the narrowband mode, the frequency determination unit determines the target frequency from a band of a subcarrier of the channel, at least a portion of which is included in the transmission band, and when the operation unit specifies transmission in the narrowband mode, the frequency determination unit determines the target frequency to be the transmission frequency specified by the operation unit. A radio station according to any one of claims 1 to 5.

10. 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 the operation unit specifies transmission in the wideband mode, and when at least a portion of the transmission band including the transmission frequency specified by the operation unit overlaps with at least a portion of a band of at least one of the channels, the frequency determination unit determines the target frequency from a band of a subcarrier of a channel, at least a portion of which is included in the transmission band, and when the operation unit specifies transmission in the narrowband mode, the frequency determination unit determines the target frequency from a band of a subcarrier of the channel, at least a portion of which is included in the transmission band, and when the operation unit specifies transmission in the narrowband mode, the frequency determination unit determines the target frequency to be the transmission frequency specified by the operation unit. The radio station according to claim 6.

11. 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 the operation unit specifies transmission in the wideband mode, and when at least a portion of the transmission band including the transmission frequency specified by the operation unit overlaps with at least a portion of a band of at least one of the channels, the frequency determination unit determines the target frequency from a band of a subcarrier of a channel, at least a portion of which is included in the transmission band, and when the operation unit specifies transmission in the narrowband mode, the frequency determination unit determines the target frequency from a band of a subcarrier of the channel, at least a portion of which is included in the transmission band, and when the operation unit specifies transmission in the narrowband mode, the frequency determination unit determines the target frequency to be the transmission frequency specified by the operation unit. The radio station according to claim 7.

12. When at least a part of the transmission band overlaps with at least a part of a band of at least one channel among a plurality of channels defined for WLAN (Wireless Local Area Network) communication based on an orthogonal frequency division multiplexing system, the frequency determination unit determines a target frequency for carrier sense from a band of a subcarrier of the channel, at least a part of which is included in the transmission band. A radio station according to any one of claims 1 to 5.

13. a reception processing circuit that digitally converts the electrical signal 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; a variable frequency second oscillator that outputs a second 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 the transmission frequency and adjusts a frequency of the second reference signal in response to a difference between the transmission frequency and the target frequency, the detection unit detects a signal level of the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal. A radio station according to any one of claims 1 to 5.

14. a reception processing circuit that digitally converts the electrical signal 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; a plurality of variable frequency second oscillators outputting second reference signals having different frequencies from each other; 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 the transmission frequency and adjusts a frequency of the second reference signal in response to a difference between the transmission frequency and the target frequency, a plurality of the detection units corresponding to the second oscillators different from each other, the detection unit detects a signal level of the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal output from the associated second oscillator, the frequency control unit adjusts a frequency of the second reference signal output by each of the second oscillators in accordance with a difference between the transmission frequency and the target frequency determined for each of the channels by the frequency determination unit; 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. The radio station according to claim 6.

15. a reception processing circuit that digitally converts the electrical signal 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; a variable frequency second oscillator that outputs a second 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 the transmission frequency and adjusts a frequency of the second reference signal in response to a difference between the transmission frequency and the target frequency, the detection unit detects a signal level of the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal. The radio station according to claim 7.

16. a reception processing circuit that digitally converts the electrical signal 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; a plurality of variable frequency second oscillators outputting second reference signals having different frequencies from each other; 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 the transmission frequency and adjusts a frequency of the second reference signal in response to a difference between the transmission frequency and the target frequency, a plurality of the detection units corresponding to the second oscillators different from each other, the detection unit detects a signal level of the real signal obtained as a result of complex frequency conversion of the first complex signal based on the second reference signal output from the associated second oscillator, the frequency control unit adjusts a frequency of the second reference signal output by each of the second oscillators in accordance with a difference between the transmission frequency and the target frequency determined for each of the channels by the frequency determination unit; 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. The radio station according to claim 8.

17. A carrier sense method performed by a wireless station, comprising: When at least a part of a transmission band including a specified transmission frequency overlaps with at least a part of a band of at least one of a plurality of channels defined for wireless communication based on an orthogonal frequency division multiplexing system, a target frequency of carrier sense is determined from a band of a subcarrier of a plurality of subcarriers of the channel, at least a part of which is included in the transmission band; Detecting a signal level at the target frequency for an actual signal obtained as a result of digitally converting an electric signal based on the radio wave captured by an antenna; determining whether or not the transmission band is being used for the wireless communication based on the signal level; Carrier sense method.

Images