JP2009290299A - Carrier sense circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier sense circuit capable of operating, without reduction in the communication efficiency, even if the circuit operates under an environment where communication-enabled noise exists. <P>SOLUTION: At the carrier sense circuit 30, a second FFT (fast-fourie Transform) portion 31 performs FFT on a received digital signal outputted from ADC (analog to digital converter) 21 to compute frequency spectrum, and a noise-extracting portion 32 performs noise extracting processing to determine whether noise is received or not, using the frequency spectrum computed at the second FFT portion 31. If it is determined that noise is received, a carrier determination portion 35 determines carrier sensing, based on a signal where noise component is removed by a noise cancellation portion 33. In addition, the carrier determination portion 35 compares an RSSI (receiving signal strength Indicator) of the signal with a first reference value to determine whether carrier waves of a communication channel exist or not, based on a time wave signal acquired by inverse Fourier transform at a second IFFT portion 34. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a carrier sense circuit built in a communication device for digital wireless communication.

  Conventionally, under a circumstance where there are a plurality of communication apparatuses that perform communication using a plurality of carriers (carriers) as represented by wireless LAN such as IEEE802.11a adopting an OFDM (Orthogonal Frequency Division Multiplex) transmission method. A digital wireless communication system that transmits and receives packet data between communication devices by wireless communication is known.

Also, a CSMA (Carrier Sense Multiple Access) system is known as one of access controls used in such a digital wireless communication system.
In this CSMA system, when a communication device that intends to transmit data detects a carrier wave (carrier) of a communication channel used for communication with a communication device of a reception destination by a carrier sense circuit built in the own device, Control is performed so as not to cause interference with signals from other communication devices by transmitting data while waiting until a communication channel becomes available.

In the carrier sense circuit, the RSSI (Received Signal Strength Indicator) of the received signal in standby is compared with a reference value based on the carrier sense level defined for each digital wireless communication system, and the RSSI determines the reference value. When exceeding, it determines with the carrier (communication carrier) of a communication channel existing, and when RSSI is below a reference value, it determines with there being no communication carrier (for example, refer patent document 1).
JP 2003-110527 A

  By the way, in the digital wireless communication system as described above, the transmission side transmits packet data that has been subjected to encoding processing that encodes an error correction code and interleave processing that distributes a code string, and the reception side transmits received packet data. Configured so that communication is possible even if there is some noise in the communication channel by performing de-interleaving processing that rearranges in the order of the original code sequence and decoding processing by Viterbi decoding of the rearranged code sequence Has been.

  For example, as shown in FIG. 9, among noises leaking into the frequency band of the communication channel (own communication system band), RSSI slightly exceeds the reference value (for example, incoming radio waves from other communication systems) When only the RSSI corresponding to a specific frequency exceeds the second reference value (for example, an incoming radio wave from another communication system / device), it can be regarded as noise that can be communicated in the digital wireless communication system.

  However, in a communication device having a conventional carrier sense circuit, even in an environment where there is noise that can be communicated (hereinafter referred to as a noise environment), if the RSSI exceeds a reference value, it is uniform. In other words, it is determined that the communication channel is not available, so that there is a case where the standby state is unnecessarily transmitted and the transmission opportunity is missed, and the communication efficiency is lowered.

  In order to solve the above-described problems, an object of the present invention is to provide a carrier sense circuit that can avoid reducing communication efficiency even in a noise environment.

  The carrier sense circuit according to claim 1, which is made to achieve the above object, is a circuit that is built in a communication device that performs communication using a communication channel including a plurality of carrier waves and performs carrier sense of the communication channel. The FFT processing means calculates the frequency spectrum of the digital reception signal by performing fast Fourier transform on the digital reception signal obtained by digital conversion of the signal received via the communication channel.

  When the noise extraction unit extracts the noise component of the digital reception signal when the frequency spectrum calculated by the FFT processing unit satisfies a preset noise condition, the carrier determination unit extracts the noise component by the noise extraction unit. If so, carrier sense is performed based on the noise removal spectrum obtained by removing the noise component from the frequency spectrum.

  For this reason, according to the carrier sense circuit of the present invention, it is erroneously determined that the communication channel is not free due to noise transmitted from another communication system or electronic device (hereinafter referred to as erroneous determination of carrier sense). As a result, it is possible to prevent the transmission opportunity from being missed after the standby state is unnecessarily.

Therefore, according to the carrier sense circuit of the present invention, it is possible to prevent the communication efficiency from being lowered even in an environment where noise that can be communicated exists.
Further, in the carrier sense circuit of the present invention, the carrier determination means, for example, as claimed in claim 2, the signal of the noise removal signal based on the noise removal signal obtained by performing inverse Fourier transform on the noise removal spectrum. When the strength exceeds the first reference value defined in advance, it is determined that the carrier of the communication channel exists, and when the signal level of the noise removal signal is equal to or lower than the first reference value, it is determined that the carrier of the communication channel does not exist. May be.

  According to the carrier sense circuit configured as described above, carrier sense can be performed by a simple process by comparing the RSSI of the noise removal signal and the first reference value. The carrier determination means may perform carrier sense by performing threshold determination using an integral value of amplitude on the noise removal spectrum without performing inverse Fourier transform on the noise removal signal.

  By the way, as described in claim 3, the noise condition is that all frequencies are selected with an average amplitude value of a selected point that is a frequency point having a frequency exceeding a second reference value defined in advance in the frequency spectrum as a selected amplitude value. It suffices if the ratio of the selected amplitude value to the average amplitude value of the points (hereinafter referred to as the first amplitude ratio) exceeds a preset first threshold value.

  In this case, when only a specific frequency point receives noise (hereinafter referred to as frequency selective noise) that greatly exceeds the second reference value, the first amplitude ratio exceeds the first threshold value, and as a result, the frequency selective noise. It is possible to prevent erroneous determination of carrier sense due to.

  Alternatively, as described in claim 4, the noise condition is that, in the frequency spectrum, an average amplitude value of a GB point that is a frequency point corresponding to a guard band band of a communication channel is a GB amplitude value, and a GB point is selected from a selection point. The ratio of the signal amplitude value to the GB amplitude value (hereinafter referred to as the second amplitude ratio) is less than a preset second threshold value, using the average amplitude value of the signal point that is the removed frequency point as the signal amplitude value. That's fine. The second threshold value may be set to a value that satisfies the SN ratio necessary for the demodulation processing of the digital reception signal, regarding the signal amplitude value as the signal level and the GB amplitude value as the noise level.

  In this case, when noise that uniformly exceeds the second reference value (hereinafter referred to as frequency non-selective noise) is received in the frequency band of the communication channel, the second amplitude ratio falls below the second threshold value, and as a result, frequency non-selectivity. An erroneous determination of carrier sense due to noise can be prevented.

Embodiments of the present invention will be described below with reference to the drawings.
<Overall configuration of communication device>
FIG. 1 is a block diagram illustrating a schematic configuration of a communication device 1 according to the present embodiment.

  As shown in FIG. 1, a communication device 1 is a device used in a digital wireless communication system S that performs OFDM communication, and transmits and receives an RF signal that is a signal in a frequency band assigned in advance for each communication system. 2, an PHY unit 4 that performs physical layer control (digital signal processing) in data communication, and a MAC unit 5 that performs access control defined by a communication standard.

  Among these, when the signal is input from the PHY unit 4, the RF unit 3 performs RF transmission processing for transmitting the RF signal generated by up-converting the input signal via the antenna 2, and via the antenna 2. When the RF signal is received, RF reception processing is performed to down-convert the received signal into a signal in a frequency band suitable for digital signal processing performed by the PHY unit 4.

  When a transmission request is made from the upper layer 6 that exchanges data with a personal computer (PC) or the like, the MAC unit 5 adds a header information to the data string to generate a MAC frame, and the generated MAC When the MAC transmission process for transferring the frame to the PHY unit 4 is executed and the MAC frame is received from the PHY unit 4, the header information of the MAC frame is analyzed and restored to the original data string, and the MAC is transferred to the upper layer 6 Perform receive processing.

  In the MAC transmission process, when it is determined that the communication channel used for communication with the communication device of the reception destination is free based on the carrier sense determination result described later from the PHY unit 4, the data is transmitted, When it is determined that the communication channel is not available, data is transmitted while waiting until the communication channel is available, so that control is performed so as not to interfere with signals from other communication devices.

<Configuration of PHY unit>
As shown in FIG. 2, the PHY unit 4 receives a PHY transmission unit 7 that executes a PHY transmission process for generating a transmission signal when receiving a MAC frame from the MAC unit 5, and a reception signal that is down-converted from the RF unit 3. Then, it comprises a PHY receiver 8 that executes a PHY reception process for extracting a MAC frame.

Among these, the PHY transmitting unit 7 encodes a bit string representing a MAC frame output from the MAC unit 5 into an error correction code (here, a convolutional code), and an encoded bit string output from the encoder 11. The interleaver 12 that performs order rearrangement (interleave processing) and the encoded bit sequence that has been subjected to the interleave processing by the interleaver 12 are mapped to 2 ^N QAM symbol points every N bits (that is, primary modulation is performed). ) Modulation unit 13.

  The PHY transmitter 7 uses M (M is an integer of 2 or more) subcarriers to use the output of the modulator 13 (hereinafter referred to as primary modulation symbol) for orthogonal frequency division multiplexing (OFDM). Corresponding to the first IFFT unit 14 for generating a data sequence representing an OFDM symbol (that is, a secondary modulation symbol) by performing inverse FFT conversion, and a data sequence output from the first IFFT unit 14 at the beginning of the data sequence described later A preamble unit 15 that adds a preamble to be output, and a DAC 16 that outputs a signal obtained by digital-analog conversion of a data string output from the preamble unit 15 to the RF unit 3.

  On the other hand, the PHY receiving unit 8 generates a data string by performing analog-digital conversion on an input signal from the RF unit 3, and data and a frame for performing FFT conversion from the data string generated by the ADC 21. A synchronization detection unit 22 that detects a preamble representing a break (that is, detects the timing at which the FFT conversion operation starts), and FFT conversion of the data sequence generated by the ADC 21 at the timing detected by the synchronization detection unit 22 And a first FFT unit 23 that demodulates the primary modulation symbols corresponding to the subcarriers.

  The PHY receiver 8 also includes a demodulator 24 that generates an n-bit soft decision value based on the primary modulation symbol demodulated by the first FFT unit 23, and an evaluation value for evaluating the reception level of the received signal. The level detector 25 to be generated and a weighting coefficient are set based on the evaluation value generated by the level detector 25, and the weighted coefficient is multiplied by each of the soft decision values generated by the demodulator 24, thereby correcting the corrected softness. Based on the output of the weight control unit 26 that generates a code string composed of determination values, the deinterleaver 27 that rearranges the order of the code strings generated by the weight control unit 26 to the original order, and the output of the deinterleaver 27 And a Viterbi decoder 28 that performs decoding to generate a received bit string.

  Furthermore, the PHY receiver 8 includes a carrier sense circuit 30 that performs carrier sense of a communication channel used by the communication apparatus 1 based on a reception signal (hereinafter referred to as a digital reception signal) that has been analog-digital converted by the ADC 21. ing.

  In the present embodiment, the encoder 11, the interleaver 12, the modulation unit 13, the first IFFT unit 14, the preamble unit 15 of the PHY transmission unit 7, the synchronization detection unit 22, the first FFT unit 23 of the PHY reception unit 8, and the demodulation. The unit 24, the level detector 25, the weight control unit 26, the deinterleaver 27, and the Viterbi decoder 28 are realized as processing executed according to a logic circuit.

  The carrier sense circuit 30 of this embodiment is connected to the synchronization detection unit 22 and the Viterbi decoder 28, and a signal indicating the start of the PHY reception process (hereinafter referred to as a demodulation start signal) is received from the synchronization detection unit 22. When input, the carrier sense is stopped, and when a signal indicating the end of the PHY reception process (hereinafter referred to as a demodulation end signal) is input from the Viterbi decoder 28, the carrier sense is started.

<Carrier sense circuit>
FIG. 3 is a block diagram showing a configuration of the carrier sense circuit 30 to which the present invention is applied.
As shown in FIG. 3, the carrier sense circuit 30 includes a second FFT unit 31 that calculates a frequency spectrum of the digital received signal by performing a fast Fourier transform (FFT) on the digital received signal output from the ADC 21, and a second FFT unit 31. The noise extraction unit 32 that performs noise extraction processing for determining whether noise is received from the frequency spectrum calculated by the above and extracting a noise component according to the determination result, and removing the noise component extracted by the noise extraction unit 32 And a noise canceling unit 33. The second FFT unit 31 is configured to perform the FFT process at intervals of a time T2 (for example, T2 = T1 / N; N is a natural number) smaller than the OFDM symbol time T1.

  The carrier sense circuit 30 also includes a second IFFT unit 34 that restores a waveform (time waveform) on the time axis by performing inverse Fourier transform on the frequency spectrum input via the noise canceling unit 33, and a second IFFT unit 34. By comparing the signal level based on the restored time waveform with the first reference value defined in advance, whether or not the carrier of the communication channel exists (that is, other communication devices in the digital wireless communication system S transmit A carrier determination unit 35 that performs determination (hereinafter referred to as carrier sense determination).

  Note that the first reference value of this embodiment is defined as a value based on the carrier sense level determined by the standard of the digital wireless communication system S. Further, the carrier determination unit 35 determines that the carrier of the communication channel (hereinafter referred to as communication carrier) exists when the signal strength (RSSI) of the input signal from the second IFFT unit 34 exceeds the first reference value, When the RSSI is equal to or less than the first reference value, it is determined that there is no communication carrier, and these carrier sense determination results are output to the MAC unit 5.

<Noise extraction processing>
Here, FIG. 4 is a flowchart showing details of the noise extraction processing executed by the noise extraction unit 32. The noise extraction process is repeatedly executed at the processing interval of the second FFT unit 31.

  As shown in FIG. 4, in the noise extraction process, first, of the frequency spectrum calculated by the second FFT unit 31, there is a frequency point (hereinafter referred to as a selection point) whose amplitude exceeds a preset second reference value. It is determined whether or not to perform (S110). As shown in FIG. 5A, the second reference value of the present embodiment is a state in which a received signal does not enter (for example, a state in which the antenna terminal is terminated, or external noise enters the antenna 2 in an anechoic chamber). In other words, it is defined as the value obtained by adding a margin to the signal level of the internal noise measured in the non-existing state.

If it is determined that the selected point exists (S110; YES), the average amplitude value obtained by averaging the amplitude values of all the selected points is set as the selected amplitude value A _{ave select} , and the average amplitude obtained by averaging the amplitude values of all the frequency points. A first amplitude ratio R ₁ (= A _{ave select} / A _{ave all} ) represented by a ratio of a selected amplitude value A _{ave select to} a value (hereinafter referred to as an average amplitude value of all frequency points) A _{ave all} is calculated (S120 ).

Next, it is determined whether or not the first amplitude ratio R ₁ calculated in S120 exceeds a preset first threshold value α (S130). If it exceeds the first threshold value α (S130; YES), the selection point A noise-on signal indicating the frequency and amplitude value (hereinafter referred to as noise information) is output to the noise canceling unit 33 (S160), and S110 is re-executed.

As shown in FIG. 5B, the first threshold value α in the present embodiment is all except for a frequency point (hereinafter referred to as a GB point) corresponding to the guard band of the communication channel used by the communication device 1. A frequency spectrum of a signal for the digital wireless communication system S (hereinafter referred to as the own system signal) whose amplitude value at the frequency point slightly exceeds the second reference value is calculated, and the first amplitude ratio R ₁ obtained from the calculation result is calculated. Set based on.

On the other hand, when the first amplitude ratio R ₁ is equal to or less than the first threshold value α (S130; NO), the average amplitude value obtained by averaging the amplitude values of all GB points is set as the GB amplitude value A _{ave guard} , and the GB point is selected from the selected point. The average amplitude value obtained by averaging all amplitude values at the removed frequency points (hereinafter referred to as signal points) is expressed as a ratio of the signal amplitude value A _{ave signal} to the GB amplitude value A _{ave guard as} the signal amplitude value A _{ave signal.} A second amplitude ratio R ₂ (= A _{ave signal} / A _{ave guard} ) is calculated (S140).

Then, it is determined whether or not the second amplitude ratio R ₂ calculated in S140 is lower than a preset second threshold value β (S150). If the second amplitude ratio R2 is lower than the second threshold value β (S150; YES), noise information (ie, , A noise-on signal indicating the frequency and amplitude value of the selected point) is output to the noise canceling unit 33 (S160), and S110 is re-executed. Incidentally, the second threshold value β of the present embodiment, as shown in FIG. 5 (c), the signal level of the signal amplitude value A _{ave Signal,} the GB amplitude value A _{ave guard} regarded as noise level, PHY receiving process (i.e. The second amplitude ratio R ₂ that is equal to or less than a value satisfying the SN ratio required for the demodulation process).

On the other hand, if it is determined that there is no selection point of the frequency spectrum (S110; NO), or when the second amplitude ratio R ₂ is a second threshold value β or more (S150; NO), it does not receive the noise A noise off signal indicating this is output to the noise canceling unit 33 (S170), and S110 is executed again.

<Processing example>
In the noise extraction processing executed in this way, as shown in FIG. 6A, the received signal is noise (hereinafter referred to as frequency selective noise) in which only a specific frequency point significantly exceeds the second reference value. If there is, the first amplitude ratio R ₁ exceeds the first threshold value α, and a data string representing the frequency (f ₁₁ ) and amplitude value (A ₁₁ ) of the selected point is output to the noise cancellation unit 33 as noise information. Examples of the frequency selective noise include electromagnetic waves (harmonics) flowing out from a microwave oven, a mobile phone, or a PC.

Also, as shown in FIG. 6B, if the received signal is noise that uniformly exceeds the second reference value in the frequency band of the communication channel used by the communication device 1 (hereinafter referred to as frequency non-selective noise), The second amplitude ratio R ₂ falls below the second threshold value β, and the frequency (f _{1 to} f ₃ , f _{6 to} f ₁₂ , f ₁₅ , f ₁₆ ) and the amplitude value (A _{1 to} A ₃ , a ₆ ~A _12, a _15, a data string representing the a ₁₆₎ is output to the noise cancellation unit 33. In addition, as frequency non-selective noise, the interference wave etc. which are transmitted from another radio | wireless communications system are mentioned, for example.

On the other hand, as shown in FIGS. 7A and 7B, the received signal is a combination of the own system signal and frequency selective noise or frequency non-selective noise (hereinafter simply referred to as “noise”). If so, the first amplitude ratio R ₁ is equal to or less than the first threshold value α and the second amplitude ratio R ₂ is equal to or greater than the second threshold value β, and a noise off signal indicating that no noise is received is sent to the noise canceling unit 33. Is output.

<Operation example>
In the carrier sense circuit 30 configured as described above, if the noise extraction unit 32 determines that the noise is received, the carrier determination unit 35 removes the noise component by the noise cancellation unit 33 (hereinafter referred to as noise). Carrier sense determination is performed by comparing the RSSI of the removal signal) and the first reference value.

  In the carrier sense circuit 30, if the noise extraction unit 32 determines that at least the own system signal (specifically, the signal of the communication channel used in the own system) is received, the carrier determination unit 35 causes the noise cancellation unit 33. The carrier sense determination is performed by comparing the RSSI of the digital reception signal input without removing the noise component and the first reference value.

  For this reason, for example, when only noise is received, the carrier sense circuit 30 outputs a carrier sense determination result indicating that another communication apparatus is not transmitting to the MAC unit 5 and receives noise. Even in this case, if the system signal is received, the carrier sense determination result indicating that another communication apparatus is transmitting can be output to the MAC unit 5.

In the above embodiment, the second FFT unit 31 corresponds to an FFT processing unit, the noise extraction unit 32 corresponds to a noise extraction unit, and the carrier determination unit 35 corresponds to a carrier determination unit.
<Effect of this embodiment>
As described above, the carrier sense circuit 30 according to the present embodiment performs carrier sense determination based on a signal (noise removal signal) obtained by removing a noise component from a digital reception signal, and therefore transmits from another communication system or electronic device. It is possible to prevent erroneous determination that the communication channel is not free due to the noise that is received, and as a result, it is possible to prevent the transmission state from being missed after the standby state is unnecessarily.

Therefore, according to the carrier sense circuit 30 of the present embodiment, it is possible to prevent the communication efficiency from being lowered even in an environment where noise that can be communicated exists.
The carrier sense circuit 30 is connected to the synchronization detector 22 and the Viterbi decoder 28. When a demodulation start signal is input from the synchronization detector 22, the carrier sense is stopped, and the demodulation is terminated from the Viterbi decoder 28. When a signal is inputted, carrier sense is started.

For this reason, it is not necessary to perform processing related to unnecessary carrier sense during reception of the own system signal addressed to the communication device 1, and it is possible to prevent processing from being complicated.
In the carrier sense circuit 30, the second FFT unit 31 performs FFT processing at an interval of time T2 that is smaller than the OFDM symbol time T1, and therefore performs carrier sense determination with quick response to noise and received signals. Can do.

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  For example, in the carrier sense circuit 30 of the above-described embodiment, the carrier determination unit 35 performs the carrier sense determination based on the RSSI of the signal that has been inverse Fourier transformed by the second IFFT unit 34, but is not limited thereto. Instead, as shown in FIG. 8, the second IFFT unit 34 is omitted, and carrier sense is performed by determining a threshold value using the integral value of the amplitude on the frequency spectrum calculated by the second FFT unit 31. Also good.

  In addition, the carrier sense circuit 30 of the above embodiment stops carrier sensing when a demodulation start signal is input from the synchronization detection unit 22, and starts carrier sense when a demodulation end signal is input from the Viterbi decoder 28. However, the present invention is not limited to this, and the carrier sense determination may be performed continuously. In this case, the noise extraction process may be stopped when a demodulation start signal is input, and the noise extraction process may be started when a demodulation end signal is input.

Furthermore, in the carrier sense circuit 30 of the above embodiment, when the first amplitude ratio R ₁ exceeds the first threshold value α or the second amplitude ratio R ₂ falls below the second threshold value β by the noise extraction process. In addition, the noise cancellation unit 33 is configured to remove the noise component of the frequency spectrum. However, the present invention is not limited to this, and for example, the noise component is removed even when the own system signal is included. It may be configured.

In the noise extraction process of the above embodiment, when it is determined that there is no selection point, or when the second amplitude ratio R ₂ is equal to or greater than the second threshold value β, noise off indicating that no noise is received. Although the signal is output to the noise canceling unit 33, the present invention is not limited to using the noise off signal, and may be configured not to output noise information. In this case, if noise information (noise-on signal) is not input from the noise extraction unit 32, the noise cancellation unit 33 may be defaulted so as to pass the frequency spectrum to the subsequent stage without performing noise cancellation.

  By the way, in the communication apparatus 1 of the said embodiment, although the MAC part 5 is comprised so that only the determination result of carrier sense may be received from the carrier sense circuit 30, it is not limited to this, For example, carrier sense A process for receiving noise information from the circuit 30 and performing transmission using a frequency band other than the frequency of the noise may be performed, or a process for changing the signal level of the transmission signal may be performed.

Further, in the communication device 1 of the above embodiment, the carrier sense determination result is used for the MAC transmission process, but the present invention is not limited to this, and may be applied to the PHY reception process (that is, the demodulation process).
In the PHY unit 4 of the above embodiment, the units 11 to 15 of the PHY transmitting unit 7 and the units 22 to 28 of the PHY receiving unit 8 are realized as processes executed according to a logic circuit. However, it may be realized as processing executed by a microcomputer according to a program prepared in advance.

  In addition, the PHY unit 4 of the above embodiment is configured for transmission / reception of OFDM signals, but is not limited thereto, and may be configured for communication performed on a communication channel including a plurality of carriers (carriers). For example, you may be comprised so that it may be used for the communication which combined OFDM technique and CDMA technique.

The block diagram which shows schematic structure of the communication apparatus 1 of this embodiment. FIG. 3 is a block diagram showing a configuration of a PHY unit 4 in the communication device 1. The block diagram which shows the 1st structural example of the carrier sense circuit 30 of this invention. The flowchart which shows the detail of the noise extraction process which the noise extraction part 32 performs. Frequency spectrum diagram for explaining the second reference value, the first amplitude ratio R _1, and a second amplitude ratio R _2. The frequency spectrum figure for demonstrating the case where a noise component is extracted by noise extraction processing. The frequency spectrum figure for demonstrating the case where a noise component is not extracted by noise extraction processing. The block diagram which shows the 2nd structural example of the carrier sense circuit 30 of this invention. The frequency spectrum figure for demonstrating the conventional problem.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Communication apparatus, 2 ... Antenna, 3 ... RF part, 4 ... PHY part, 5 ... MAC part, 6 ... Upper layer, 7 ... PHY transmission part, 8 ... PHY reception part, 11 ... Encoder, 12 ... Interleaver, DESCRIPTION OF SYMBOLS 13 ... Modulation part, 14 ... 1st IFFT part, 15 ... Preamble part, 16 ... DAC, 21 ... ADC, 22 ... Synchronization detection part, 23 ... 1st FFT part, 24 ... Demodulation part, 25 ... Level detector, 26 ... Weight Control unit 27 ... deinterleaver 28 ... Viterbi decoder 30 ... carrier sense circuit 31 ... second FFT unit 32 ... noise extraction unit 33 ... noise cancel unit 34 ... second IFFT unit 35 ... carrier determination unit .

Claims (4)

A carrier sense circuit that is built in a communication device that performs communication using a communication channel composed of a plurality of carrier waves and performs carrier sense of the communication channel,
FFT processing means for calculating a frequency spectrum of the digital reception signal by performing a fast Fourier transform on the digital reception signal obtained by digital conversion of the signal received via the communication channel;
When the frequency spectrum calculated by the FFT processing unit satisfies a preset noise condition, a noise extraction unit that extracts a noise component of the digital reception signal;
When the noise extraction unit extracts the noise component, carrier determination unit that performs carrier sense based on a noise removal spectrum obtained by removing the noise component from the frequency spectrum;
A carrier sense circuit comprising:   When the signal strength of the noise removal signal exceeds a predetermined first reference value based on a noise removal signal obtained by performing an inverse Fourier transform on the noise removal spectrum, the carrier determination means The carrier sense circuit according to claim 1, wherein it is determined that a carrier wave exists.   In the noise condition, the selected amplitude with respect to the average amplitude value of all frequency points, with an average amplitude value of a selection point that is a frequency point whose amplitude exceeds a second reference value defined in advance in the frequency spectrum as a selection amplitude value. The carrier sense circuit according to claim 1, wherein the ratio of values exceeds a preset first threshold value.   The noise condition is a frequency point obtained by removing an average amplitude value of a GB point, which is a frequency point corresponding to a guard band band of the communication channel, in the frequency spectrum, and removing the GB point from the selected point. 4. The carrier sense according to claim 3, wherein a ratio of the signal amplitude value to the GB amplitude value is less than a preset second threshold value using an average amplitude value of the signal points as a signal amplitude value. 5. circuit.