JP2005101787A - Radio communication system and receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To rapidly detect a circumferential radio network when a radio communication terminal detects the circumferential radio network. <P>SOLUTION: A radio communication system includes a channel signal receiving unit 13 which receives a channel signal. A subcarrier extracting unit 22 extracts a subcarrier included in the channel signal. A receiving level detector 26 detets each receiving level of the subcarrier. An error detector 31 detects an error from the subcarrier. A channel specifying unit 41 specifies the corresponding channel from the receiving level of each subcarrier. A channel estimating unit 42 estimates during using of the specified channel. A channel deciding unit 43 decides an unuse of the channel estimated during using when the error is detected, and decides during using of the channel when the error is not detected. A channel list 610 holds states of the respective channels. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wireless communication system and a receiving apparatus, and more particularly to a wireless communication system and a receiving apparatus for wirelessly connecting to a network in a limited space, a processing method therefor, and a program for causing a computer to execute the method.

  In recent years, wireless communication systems that provide connection to wireless networks in public places other than home have been developed. For example, an environment for providing connection to the Internet or the like at a station, an airport, a hotel, a coffee shop, or a street corner is being prepared.

  In such a system, when a user connects a wireless communication terminal to a wireless network, it is necessary to know which wireless channel is available. When connecting to a wireless network in a familiar environment such as an office or home as before, where is the access point or terminal of the wireless connection destination by inquiring to the administrator who manages the wireless network? Then, it is possible to easily know which wireless communication channel the wireless connection destination access point or terminal operates. Therefore, it is possible to estimate the area where wireless communication is possible with the wireless connection destination access point or the terminal, determine the position of the wireless communication terminal, and determine the wireless communication channel to be connected.

  However, in a wireless communication system in a public place, the user cannot easily know where the access point or terminal connected to the wireless connection is, and what wireless channel is being operated. In many cases, it takes time and effort to search for an area where the destination access point or terminal can perform wireless transmission and reception, and to set up for wireless connection.

Therefore, in order to simplify a series of operations in which a user using a wireless communication terminal searches for a wireless network that can be connected at the current location and performs connection setting work with the wireless network, A method for automatically detecting a surrounding wireless network and providing a user with a user interface for setting up a wireless connection has been proposed. In this method, a wireless communication terminal periodically scans all channels of the wireless network to detect surrounding wireless networks (see, for example, Patent Document 1).
JP 2002-344458 A (FIG. 6)

  In the above-described conventional technology, a wireless communication terminal periodically scans all channels of the wireless network to detect surrounding wireless networks. For example, in the IEEE802.11g standard by the working group of the IEEE (American Institute of Electrical and Electronics Engineers) 802 standardization committee, a total of 13 wireless channels can be used. Will scan.

  However, in the method in which the wireless communication terminal scans the surrounding wireless network in this way, the period for detecting the surrounding wireless network becomes very long, and the original wireless communication is performed between the wireless communication terminal and the access point. There was a problem that the period to be performed was under pressure.

  Therefore, an object of the present invention is to quickly detect when a wireless communication terminal detects a surrounding wireless network.

  In order to solve the above-described problem, a receiving apparatus according to claim 1 of the present invention is an orthogonal frequency division multiplexing receiving apparatus arranged such that a part of a frequency band of a channel overlaps a part of a frequency band of another channel. A channel signal receiving means for receiving a signal of a certain channel; a subcarrier extracting means for extracting a subcarrier included in the channel signal from the received channel signal; and a reception level of each of the extracted subcarriers. The reception level detection means for detecting the channel, the channel specification means for specifying the corresponding channel from the reception level, the presumed that the specified channel is in use, and the adjacent channel whose frequency band overlaps with the received channel. Channel estimation means for determining that a channel not specified therein is unused. Thereby, when detecting the surrounding wireless network, the channel which may be used is identified, without scanning all the channels.

  The receiving apparatus according to claim 2 of the present invention is the receiving apparatus according to claim 1, further comprising error detection means for detecting an error from the extracted subcarrier, wherein the channel estimation means includes the channel signal. When the receiving means receives a channel signal and the error detecting means does not detect an error, it is determined that the receiving channel is in use. As a result, the channel that is normally received is determined to be in use.

  The receiving apparatus according to claim 3 of the present invention is the receiving apparatus according to claim 2, wherein the error detecting means detects an error for the channel estimated by the channel estimating means. The apparatus further includes channel determining means for determining that the channel is unused and determining that the channel is in use when the error detecting means does not detect an error. As a result, the channel that is estimated to be in use is determined to be unused or in use.

  The receiving device according to claim 4 of the present invention is the receiving device according to claim 1, wherein the channel estimation means, when the channel signal receiving means does not receive a channel signal, the channel and the channel and frequency. It is determined that neighboring channels with overlapping bands are unused. As a result, the channel in which the received signal is not detected and the neighboring channels are determined to be unused.

  Further, a receiving device according to claim 5 of the present invention is an orthogonal frequency division multiplexing receiving device arranged so that a part of a frequency band of a channel overlaps a part of a frequency band of another channel, A channel signal receiving means for receiving a channel signal, a subcarrier extracting means for extracting a subcarrier included in the channel signal from the received channel signal, an error detecting means for detecting an error from the extracted subcarrier, A reception level detection means for detecting the reception level of each of the extracted subcarriers, a channel specification means for specifying a corresponding channel from the reception level, and when the channel signal reception means does not receive a channel signal, Confirm that the channel and the neighboring channel whose frequency band overlaps with the channel are unused, and When the signal receiving means receives a channel signal and the error detecting means does not detect an error, it is determined that the receiving channel is in use, and the channel signal receiving means receives the channel signal. If the error detection means detects an error, it is assumed that the specified channel is being used, and the channel that has not been specified among the neighboring channels that overlap the frequency band with the received channel. Channel estimation means that determines that the channel estimation means is unused, and the channel detection means determines that the channel is unused when the error detection means detects an error. Channel determining means for determining that the channel is in use when the error detecting means does not detect an error; ; And a channel list which holds the state of each channel inferred or determined to be unused or in use in the serial channel estimation unit or the channel defining means. As a result, when detecting the surrounding wireless network, the channel that may be used is first identified without scanning all the channels, and the state is determined by narrowing down to the identified channel. This brings about the effect.

  A receiving apparatus according to claim 6 of the present invention is the receiving apparatus according to claim 5, which conforms to the IEEE802.11g standard. In the orthogonal frequency division multiplexing system according to the IEEE802.11g standard, a part of the frequency band of the channel is arranged so as to overlap a part of the frequency band of the other channel, which is particularly useful when the present invention is applied.

  According to a seventh aspect of the present invention, there is provided a wireless communication system comprising an access point connected to a network and a signal transmitted from the access point, wherein a part of the frequency band of the channel is equal to that of another channel. A radio communication system comprising: a terminal that scans an orthogonal frequency division multiplexing signal arranged so as to overlap a channel, wherein the terminal includes channel signal receiving means for receiving a signal of a channel; and the received channel signal Subcarrier extraction means for extracting subcarriers included in the channel signal from the above, error detection means for detecting errors from the extracted subcarriers, and reception levels for detecting the reception levels of each of the extracted subcarriers Detecting means, channel specifying means for specifying the corresponding channel from the reception level, and If the channel signal receiving means does not receive the channel signal, it is determined that the channel and the neighboring channel whose frequency band overlaps with the channel are unused, and the channel signal receiving means receives the channel signal, and When the error detection means does not detect an error, it is determined that the reception channel is in use, and the channel signal reception means receives a channel signal and the error detection means detects an error. Channel estimation means for estimating that the specified channel is in use and determining that a channel that has not been specified among neighboring channels whose frequency band overlaps with the received channel is unused, and the channel The error detection means detected an error for the channel that the guessing means assumed to be in use. In this case, it is determined that the channel is unused, and if the error detection unit does not detect an error, the channel determination unit determines that the channel is in use, and the channel estimation unit or the channel. And a channel list that holds the state of each channel that is estimated or determined to be unused or in use by the determination means. Thus, when a terminal in a wireless communication system detects a surrounding wireless network, it first identifies a channel that may be used without scanning all the channels, The effect is that the state is determined by squeezing.

  Also, the scan method according to claim 8 of the present invention includes a channel list that holds a state of each channel arranged so that a part of the frequency band of the channel overlaps a part of the frequency band of the other channel. First scanning procedure for receiving a signal set to a predetermined channel, holding the state of the channel in the channel list and identifying a channel that is assumed to be in use among the neighboring channels of the channel When the signal is received by setting to the specified channel and an error has occurred, the unused state is held in the channel list, and when no error has occurred, And a second scan procedure for holding the state in use in the channel list. As a result, when detecting surrounding wireless networks, channels that may be used in the first scanning procedure are first identified and narrowed down to the identified channels without scanning all channels. In this way, the state is determined in the second scanning procedure.

  The scan method according to claim 9 of the present invention is the scan method according to claim 8, wherein the first scan procedure is performed when the channel and the frequency band of the channel overlap each other when the channel signal is not received. If it is determined that the channel is unused and a channel signal is received and no error is detected, it is determined that the receiving channel is in use and a channel signal is received and an error occurs. When a channel is detected, the channel being used is estimated from the reception level of the subcarrier, and the channel that was not estimated to be used is unused among the reception channel and the neighboring channel in which the frequency band overlaps with the reception channel. It is determined. As a result, the channel and its neighboring channels are determined to be unused for a channel in which no received signal is detected, and the channel that is normally received is determined to be in use.

  According to a tenth aspect of the present invention, there is provided a program comprising: a channel list that holds a state of each channel arranged so that a part of a frequency band of a channel overlaps a part of a frequency band of another channel; A first scan procedure for receiving a signal set to a predetermined channel, holding a state of the channel in the channel list, and identifying a channel that is assumed to be in use among neighboring channels of the channel; When the signal is received by setting to the specified channel and an error has occurred, the state that it is not used is held in the channel list and is used when no error has occurred. And causing the computer to execute a second scan procedure for maintaining the channel list in the channel list. As a result, when detecting surrounding wireless networks, channels that may be used in the first scanning procedure are first identified and narrowed down to the identified channels without scanning all channels. In this way, the state is determined in the second scanning procedure.

  According to the present invention, when the wireless communication terminal detects a surrounding wireless network, an excellent effect of realizing quick detection can be achieved.

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

  FIG. 1 is a diagram showing an overall configuration of a radio communication system according to an embodiment of the present invention. In this wireless communication system, the communication device 3 connected to the network 4 functions as an access point. The communication device 3 that functions as an access point is installed in a public place such as a station, an airport, a hotel, a coffee shop, or a street corner. In addition, this access point normally provides connection through one channel per unit. However, in a situation where the access points of the other party cannot be seen from each other, a plurality of access points may use the same channel.

  The user tries to connect to the network 4 using the communication device 1 functioning as a terminal. An information processing apparatus 2 such as a personal computer can be connected to the communication apparatus 1. The user gives an instruction from an instruction device such as a keyboard of the information processing apparatus 2 and confirms the display content using a display device such as a liquid crystal display.

  As a usage form in a public place, it is possible to temporarily operate at a fixed position as in a coffee shop, but more generally, it is necessary to assume a situation in which it can always move. Therefore, it should be assumed that even when communication is being performed using a certain channel, a use mode in which an available channel is scanned is assumed.

  FIG. 2 is a diagram illustrating a configuration example of the communication device 1 according to the embodiment of the present invention. The communication device 1 includes a wireless communication unit 100, a baseband processing unit 200, a communication control unit 300, and a system control unit 400, which are connected by a system bus 490. The wireless communication unit 100 and the baseband processing unit 200 mainly perform physical layer processing, and the communication control unit 300 mainly performs logical layer MAC (Media Access Control) sublayer processing. Further, the system control unit 400 controls the entire communication device 1.

  The wireless communication unit 100 is for performing wireless communication with the outside of the communication device 1, and includes a transmission unit 110 that transmits a wireless signal, a reception unit 130 that receives a wireless signal, a transmission unit 110, and reception. And an antenna switch 120 that switches the antenna between the units 130. The antenna 101 is connected to the antenna switch 120. The transmission unit 110 performs orthogonal modulation on the baseband signal from the baseband processing unit 200 to generate an intermediate signal in a predetermined intermediate frequency band, and further converts it into a high-frequency signal and transmits it. The receiving unit 130 converts the received high-frequency signal into an intermediate signal, and generates a baseband signal by performing orthogonal demodulation.

  The baseband processing unit 200 is for performing modulation / demodulation of a baseband signal. The modulation unit 210 supplies the baseband signal to the transmission unit 110 and the demodulation unit demodulates the baseband signal supplied from the reception unit 130. 230. The modulation unit 210 modulates the transmission packet into a baseband signal. In the OFDM (Orthogonal Frequency Division Multiplexing) scheme in the IEEE802.11g standard, after performing convolutional coding, the bits of the transmission packet are interleaved. After rearranging, dividing and modulating the subcarriers, inverse Fourier transform is performed to generate a signal in which all subcarriers are synthesized in the time domain. A guard interval is inserted to avoid multipath interference. On the other hand, the demodulator 230 demodulates the received baseband signal into a received packet. In OFDM modulation according to the IEEE802.11g standard, the guard interval is removed and then demultiplexed into subcarriers by Fourier transform. Demodulated for each carrier. Then, after the bit arrangement is returned by the deinterleaving process, the convolutional code for error correction is decoded.

  The communication control unit 300 performs processing in the MAC sublayer, and performs predetermined processing by interpreting a MAC header in a MAC frame described later. In addition, the communication control unit 300 has a function of checking the FCS (frame check sequence) added for each MAC frame and detecting the occurrence of an error.

  The system control unit 400 controls the entire communication apparatus 1 and includes a processor 410 that performs processing, a memory 420 that stores a work area and the like, and an interface 430. For example, the information processing apparatus 2 such as a personal computer is connected to the interface 430. The information processing apparatus 2 may be physically connected to the outside of the communication apparatus 1 or may be connected so that the communication apparatus 1 is built in the information processing apparatus 2.

  FIG. 3 is a diagram showing a configuration example of the demodulator 230 in the embodiment of the present invention. The demodulator 230 includes a guard interval removal circuit 231, a discrete Fourier transformer 232, a subcarrier demodulator 233, a deinterleave circuit 234, an error correction circuit 235, a subcarrier power level calculator 236, network power Level calculator 237.

  The guard interval removal circuit 231 is a circuit for removing the guard interval from the baseband signal. In OFDM, redundant signals called guard intervals are inserted on the transmission side in order to avoid interference of multipath delayed waves. It is the role of the guard interval removal circuit 231 to remove this guard interval. The OFDM multicarrier signal from which the guard interval is removed is supplied to the discrete Fourier transformer 232.

  The discrete Fourier transformer 232 is a circuit that extracts the frequency component of the signal expressed on the time axis, and has a function of demultiplexing each subcarrier signal from the multicarrier signal from which the guard interval is removed. These demultiplexed subcarrier signals are supplied to a subcarrier demodulator 233 and a subcarrier power level calculator 236.

The subcarrier power level calculator 236 is a circuit that calculates the reception level for each subcarrier demultiplexed by the discrete Fourier transformer 232. The output of the discrete Fourier transformer 232 is complex data for each subcarrier, and indicates the respective voltage levels of the I axis and the Q axis. Therefore, when this complex data is expressed as V _I and V _Q , the power levels P _I and P _Q of each axis are obtained from Ohm's law.
P _I = V _I ² / R
P _Q = V _Q ² / R
It becomes. Where R is an impedance of 50 ohms.

Therefore, the power level P as a subcarrier, that is, the reception level is
P = SQRT (P _I ² + P _Q ² )
Represented as: However, SQRT means a square root.

  The network power level calculator 237 is a circuit that calculates a reception level as a network. Specifically, the sum of the reception levels for each subcarrier calculated by the subcarrier power level calculator 236 is the reception level as the network. Calculation results by the subcarrier power level calculator 236 and the network power level calculator 237 are supplied to the system control unit 400.

  The subcarrier demodulator 233 is a circuit that demodulates the digital signal for each demultiplexed subcarrier. The deinterleave circuit 234 is a circuit that restores the order of bits rearranged by the interleaving process at the time of transmission. The error correction circuit 235 is a circuit that decodes a convolutional code for error correction. For example, the Viterbi decoding method is employed. This Viterbi decoding is an error correction method for estimating the most suitable data sequence as a convolutionally encoded data sequence. The received signal that has been completed up to this error correction is supplied to the communication control unit 300 and is subjected to processing in the MAC sublayer.

  FIG. 4 is a diagram showing a frame configuration of a MAC frame in the IEEE 802.11 standard. This MAC frame includes a frame control 701, a duration / ID 702, addresses 1 to 4 (703 to 705 and 707), a sequence control 706, a frame body 708, and an FCS (frame check sequence) 709. . An area from frame control 701 to address 4 (707) is called a MAC header.

  The frame control 701 is an area for holding various control information, and includes, for example, a frame type and a type of transmitting / receiving station. The duration / ID 702 is an area for holding a scheduled period of using the wireless line.

  Addresses 1 to 4 (703 to 705 and 707) are areas indicating a destination address, a transmission source address, and the like. Which address is held in each area depends on the type of the transmission / reception station in the frame control 701 described above. Different. The sequence control 706 is an area indicating the sequence number of the MAC frame and the fragment number for the fragment.

  The frame body 708 is a data body transferred by the MAC frame. In some control frames, the frame body 708 may not exist. FCS 709 is a cyclic redundancy check code (CRC) that combines a MAC header and a frame body 708, and is used to detect an error for each frame.

  FIG. 5 is a diagram illustrating a functional configuration of the communication device 1 according to the embodiment of the present invention. This functional configuration includes a channel signal reception unit 13, a subcarrier extraction unit 22, a reception level detection unit 26, an error detection unit 31, a channel identification unit 41, a channel estimation unit 42, a channel determination unit 43, A channel list 610.

  The channel signal receiving unit 13 receives a signal of a certain channel, and corresponds to the receiving unit 130 in the wireless communication unit 100 in FIG. The subcarrier extraction unit 22 extracts subcarriers included in the channel signal from the channel signal received by the channel signal reception unit 13, and corresponds to the discrete Fourier transformer 232 in the demodulation unit 230 of FIG.

  The reception level detection unit 26 detects the reception level of each subcarrier extracted by the subcarrier extraction unit 22, and corresponds to the subcarrier power level calculator 236 in the demodulation unit 230 of FIG.

  The error detection unit 31 detects an error from the subcarrier extracted by the subcarrier extraction unit 22, and corresponds to a function in the communication control unit 300 of FIG. The error detection unit 31 detects an error in units of frames using the FCS 709 in the MAC frame of FIG.

  The channel identification unit 41 identifies a corresponding channel from the reception level of each subcarrier detected by the reception level detection unit 26, and is a function realized by the processor 410 in the system control unit 400 of FIG.

  The channel estimation unit 42 estimates that the channel specified by the channel specification unit 41 is in use. Further, the channel estimation unit 42 determines that a channel received by the channel signal reception unit 13 and a channel that has not been specified among the neighboring channels whose frequency bands overlap with the reception channel are unused. However, when a received signal is not detected by the channel signal receiving unit 13, it is determined that the channel and a neighboring channel whose frequency band overlaps with the channel are unused. Even when the channel signal receiver 13 detects a received signal, if no error is detected by the error detector 31, it is determined that the channel is in use. The channel estimation unit 42 is a function realized by the processor 410 in the system control unit 400 of FIG. Further, the channel state determined or estimated by the channel estimation unit 42 is held in the channel list 610.

  When the error detection unit 31 detects an error for the channel estimated to be in use by the channel estimation unit 42, the channel determination unit 43 determines that the channel is unused, and the error detection unit 31 If no error is detected, it is determined that the channel is in use. The channel determination unit 43 is a function realized by the processor 410 in the system control unit 400 of FIG. The channel state determined by the channel determination unit 43 is held in the channel list 610.

  The channel list 610 indicates the state of each channel and is held in the memory 420 in the system control unit 400, for example.

  FIG. 6 is a diagram showing a configuration example of the channel list 610 in the embodiment of the present invention. This channel list 610 holds a basic service set identifier (BSSID) 612, a reception level 613, and a status 614 for each channel number 611.

  The basic service set identifier 612 is an identifier assigned to each basic service set, and is used to identify a network. Here, the basic service set refers to a network composed of one access point and at least one terminal. As the basic service set identifier 612, the MAC address of the access point is actually used.

  The reception level 613 represents the reception level of the corresponding channel in terms of dBm. The unit of dBm is a decibel expression by a power ratio based on 1 mW of power. The reception level 613 is preferably 70 dBm or more for practical use. This reception level 613 holds a value supplied from the network power level calculator 237.

  The status 614 represents the usage status of the corresponding channel. There are three types of usage states, for example, “in use (confirmed)”, “in use (estimation)”, and “unused (confirmed)”. That is, whether the channel is in use or unused is indicated, and if it is unknown, it is indicated that the channel is estimated to be in use. The status 614 is initially set to a provisional value by the channel estimation unit 42, and the channel determination unit 43 finally determines the channel estimated to be in use. A specific procedure for setting the status 614 will be described later.

  FIG. 7 is a diagram showing a channel arrangement of the OFDM scheme in the IEEE 802.11g standard. The 2.4 GHz band used by the IEEE 802.11g standard is called an ISM (industrial scientific medical) band. In the IEEE802.11g standard, the bandwidth of 100 MHz in the 2.4 GHz band is divided into 13 channels of 5 MHz each.

  Each channel is defined such that a part of the frequency band overlaps with other channels. In this case, when interference is received from another system, the center frequency can be shifted in order to avoid the interference. When the 2.4 GHz band is used in the same place, three channels can be secured so that the frequency bands do not overlap each other.

  Each channel is composed of a total of 53 channels from −26 to +26, with the subcarrier number of the center frequency being 0. The center subcarrier number 0 is not used for actual communication because the deterioration due to imperfection of the analog circuit is large. Also, the four subcarriers with subcarrier numbers -21, -7, +7, and +21 are used for transmission of pilot signals necessary for reception phase rotation correction. Therefore, the remaining 48 subcarriers are used for substantial data communication.

  FIG. 8 is a diagram showing an arrangement of subcarriers in a channel according to the IEEE 802.11g standard. In FIG. 8, as an example, the correspondence relationship with subcarriers in the preceding and following channels # 3, # 4, # 5, # 7, # 8, and # 9 is shown with the channel # 6 as the center.

  That is, subcarrier numbers −26 to −22 of channel # 6 overlap in frequency with subcarrier numbers +22 to +26 of channel # 3. Further, subcarrier numbers −26 to −6 of channel # 6 overlap in frequency with subcarrier numbers +6 to +26 of channel # 4. Further, the frequency of subcarrier numbers −26 to +10 of channel # 6 overlaps with the subcarrier numbers −10 to +26 of channel # 5. Further, subcarrier numbers −10 to +26 of channel # 6 overlap in frequency with subcarrier numbers −26 to +10 of channel # 7. Further, subcarrier numbers +6 to +26 of channel # 6 overlap in frequency with subcarrier numbers -26 to -6 of channel # 8. Further, subcarrier numbers +22 to +26 of channel # 6 overlap in frequency with subcarrier numbers −26 to −22 of channel # 9. Note that a channel whose frequency overlaps with some subcarriers of a certain channel is referred to as a neighboring channel.

  Therefore, for example, by detecting the reception level of each subcarrier when channel # 6 is received, it is possible to estimate which channel in the vicinity of channel # 6 is in use by the distribution of the subcarrier. it can.

  For example, when a predetermined reception level is detected in subcarrier numbers −26 to −22 when channel # 6 is received, it can be estimated that channel # 3 is in use. Similarly, the use state can be estimated for other neighboring channels. However, if a predetermined reception level cannot be detected in any subcarrier even if channel # 6 is set and received, channel # 6 and its neighboring channels, channels # 3, # 4, # 5, It is determined that # 7, # 8, and # 9 are unused. Also, when channel # 6 is set and a received signal is detected, if error is not detected by error detector 31 and reception is successful, it is determined that channel # 6 is in use. . Conversely, if an error is detected by the error detection unit 31 when channel # 6 is set and a received signal is detected, it is determined that channel # 6 is unused and, among its neighboring channels, The channels that are not estimated to be in use by the reception level detection for each subcarrier described above (in the above example, channels # 4, # 5, # 7, # 8, and # 9) are determined to be unused. .

  As a predetermined reception level for detecting subcarriers, for example, about 30 dBm to 70 dBm can be assumed.

  Next, the channel scan operation of the communication apparatus 1 according to the embodiment of the present invention will be described with reference to the drawings.

  FIG. 9 is a diagram illustrating a channel scan operation procedure of the communication device 1 according to the embodiment of the present invention. First, when receiving a detection request for a surrounding wireless network, the communication device 1 sets the reception mode in the physical layer to the OFDM mode (step S910). Then, the communication device 1 lowers the synchronization detection threshold so that synchronization can be pulled in even when the reception level is low (step S920). Further, the communication device 1 clears the contents of the status 614 in the channel list 610 (step S930).

  After the preparation up to this point is completed, the communication device 1 performs a first-stage scan called a speculative scan (step S940). As a result of this guess scan, the status 614 of each channel in the channel list 610 is set to, for example, “in use (confirmed)”, “in use (estimate)”, or “unused (confirmed)”.

  Then, the communication device 1 performs a second-stage scan called a definite scan (step S950). In this definite scan, reception is performed for the channel estimated to be in use in the deterministic scan, and it is determined that the channel is in use or not used, and the status is set in the status 614 in the channel list 610.

  Thereafter, the communication device 1 restores the synchronization detection threshold lowered in step S920 (step S960).

  FIG. 10 is a diagram showing an operation procedure of the speculative scan (step S940) in the embodiment of the present invention. In this guess scan, first, a predetermined channel is set (step S941), and a signal is received (step S942). Here, the channels to be set can be scanned more efficiently if they are spaced apart from each other, for example, channels # 1, # 6, and # 11.

  As a result, when a received signal is not detected in the channel set in step S941 (hereinafter referred to as current channel) (step S943), the current channel and a channel in which a part of the frequency band overlaps (hereinafter referred to as a neighboring channel). The status 614 of “.” Is determined to be unused (step S945).

  When a received signal is detected in the current channel (step S943), if no error is detected by the error detection unit 31 (step S944), it is determined that the current channel status 614 is in use (step S946). ). On the other hand, when a received signal is detected in the current channel (step S943), but an error is detected by the error detecting unit 31 (step S944), the channel specifying unit 41 specifies a channel from the neighboring channels (step S944). S947), it is estimated that the status 614 of the specified channel (hereinafter referred to as a specific channel) is in use (step S948). Further, the status 614 of the neighboring channel other than the specific channel and the current channel is determined to be unused (step S948).

  If these procedures are completed for the above-mentioned predetermined channels (for example, channels # 1, # 6, and # 11) (step S948), the speculative scan is completed, and the process proceeds to the next definite scan (step S950). .

  FIG. 11 and FIG. 12 are diagrams showing a procedure for channel identification (step S947) in the embodiment of the present invention. Here, channel #i (i is an integer from 1 to 13) having subcarriers as shown in FIG. 8 is assumed. Further, when a value exceeding the range of 1 to 13 is designated as the channel number, the processing is ignored.

  First, when channel #i is set as the current channel and a signal is received when subcarrier numbers -26 to -22 are detected (step S971), channel # [i-3] is used. The possibility is identified (step S972). On the other hand, when subcarrier numbers -26 to -22 are not detected (step S971), channel # [i-3] is not specified and is handled as a neighboring channel of the current channel as usual (step S973).

  If subcarrier numbers -21 to -6 are further detected (step S974), it is specified that channel # [i-2] may be used (step S975). On the other hand, if subcarrier numbers -21 to -6 are not detected (step S974), channel # [i-2] is not specified and is treated as a neighboring channel of the current channel as usual (step S976).

  If subcarrier numbers -5 to +10 are further detected (step S977), it is specified that channel # [i-1] may be used (step S978). On the other hand, if subcarrier numbers -5 to +10 are not detected (step S977), channel # [i-1] is not specified and is treated as a neighboring channel of the current channel as usual (step S979).

  When subcarrier numbers +22 to +26 are detected (step S981), it is specified that channel # [i + 3] may be used (step S982). On the other hand, when sub-carrier numbers +22 to +26 are not detected (step S981), channel # [i + 3] is not specified and is treated as a neighboring channel of the current channel as usual (step S983).

  If subcarrier numbers +6 to +21 are further detected (step S984), it is specified that channel # [i + 2] may be used (step S985). On the other hand, if subcarrier numbers +6 to +21 are not detected (step S984), channel # [i + 2] is not specified and is treated as a neighboring channel of the current channel as usual (step S986).

  If subcarrier numbers −10 to +5 are further detected (step S987), it is specified that channel # [i + 1] may be used (step S988). On the other hand, if subcarrier numbers −10 to +5 are not detected (step S987), channel # [i + 1] is not specified and is treated as a neighboring channel of the current channel as usual (step S989).

  FIG. 13 is a diagram showing an operation procedure of the definite scan (step S950) in the embodiment of the present invention. This definite scan has a role of determining whether a channel presumed to be used in the deductive scan is in use or not used. First, it is checked whether or not there is a channel estimated to be in use as the status 614 of the channel list 610 (step S951). If there is a channel that is estimated to be in use, the channel is set as the current channel (step S952), and a signal is received (step S953).

  As a result, if no error is detected by the error detection unit 31 (step S954), it is determined that the current channel status 614 is in use (step S955). On the other hand, if an error is detected by the error detection unit 31 (step S954), the status 614 of the current channel is determined to be unused (step S956).

  The above processing is performed for the channels estimated to be used in the speculative scan, and when the status 614 is determined for all channels (step S951), the final scan is finished.

  Thus, according to the embodiment of the present invention, a predetermined channel is received by receiving a predetermined channel in the speculative scan, and a channel that may be used is identified, and the in-use or not-used channel is confirmed by a subsequent definite scan. Determine to use one. As a result, the state of each channel can be grasped more quickly than when all the channels are scanned one by one.

  The embodiment of the present invention is an example for embodying the present invention and has a corresponding relationship with the invention-specific matters in the claims as shown below, but is not limited thereto. However, various modifications can be made without departing from the scope of the present invention.

  That is, in claim 1, the channel signal receiving means corresponds to the channel signal receiving unit 13, for example. The subcarrier extracting means corresponds to the subcarrier extracting unit 22, for example. The reception level detection unit corresponds to the reception level detection unit 26, for example. Channel specifying means corresponds to the channel specifying unit 41, for example. The channel estimation means corresponds to the channel estimation unit 42, for example.

  Further, in claim 2, the error detection means corresponds to, for example, the error detection unit 31.

  Further, in claim 3, the channel determination means corresponds to the channel determination unit 43, for example.

  Further, in claim 5, channel signal receiving means corresponds to the channel signal receiving unit 13, for example. The subcarrier extracting means corresponds to the subcarrier extracting unit 22, for example. An error detection unit corresponds to the error detection unit 31, for example. The reception level detection unit corresponds to the reception level detection unit 26, for example. Channel specifying means corresponds to the channel specifying unit 41, for example. The channel estimation means corresponds to the channel estimation unit 42, for example. The channel determination unit corresponds to the channel determination unit 43, for example. The channel list corresponds to the channel list 610, for example.

  In claim 7, the network corresponds to the network 4, for example. An access point corresponds to the communication device 3, for example. A terminal corresponds to the communication device 1, for example. The channel signal receiving means corresponds to the channel signal receiving unit 13, for example. The subcarrier extracting means corresponds to the subcarrier extracting unit 22, for example. An error detection unit corresponds to the error detection unit 31, for example. The reception level detection unit corresponds to the reception level detection unit 26, for example. Channel specifying means corresponds to the channel specifying unit 41, for example. The channel estimation means corresponds to the channel estimation unit 42, for example. The channel determination unit corresponds to the channel determination unit 43, for example. The channel list corresponds to the channel list 610, for example.

  In claims 8 and 10, the first scan procedure corresponds to, for example, a speculative scan (step S940). The second scan procedure corresponds to, for example, a definite scan (step S950).

  The processing procedure described in the embodiment of the present invention may be regarded as a method having a series of these procedures, and a program for causing a computer to execute these series of procedures or a recording medium storing the program May be taken as

  As an application example of the present invention, for example, when a mobile terminal is to be connected to an access point installed in a public place, the present invention can be applied when scanning the channel.

It is a figure which shows the whole structure of the radio | wireless communications system in embodiment of this invention. It is a figure which shows one structural example of the communication apparatus 1 in embodiment of this invention. It is a figure which shows the example of 1 structure of the demodulation part 230 in embodiment of this invention. It is a figure which shows the frame structure of the MAC frame in IEEE802.11 specification. It is a figure which shows the function structure of the communication apparatus 1 in embodiment of this invention. It is a figure which shows the example of 1 structure of the channel list 610 in embodiment of this invention. It is a figure which shows the channel arrangement | positioning of the OFDM system in the IEEE802.11g standard. It is a figure which shows the arrangement | positioning of the subcarrier in the channel in IEEE802.11g specification. It is a figure which shows the operation | movement procedure of the channel scan of the communication apparatus 1 in embodiment of this invention. It is a figure which shows the operation | movement procedure of speculative scanning (step S940) in embodiment of this invention. It is a figure which shows the procedure of the first half of the channel specification (step S947) in embodiment of this invention. It is a figure which shows the procedure of the latter half of the channel specification (step S947) in embodiment of this invention. It is a figure which shows the operation | movement procedure of the definite scan (step S950) in embodiment of this invention.

Explanation of symbols

1 Communication device (terminal)
2 Information processing device 3 Communication device (access point)
4 Network 13 Channel Signal Receiving Unit 22 Subcarrier Extraction Unit 26 Reception Level Detection Unit 31 Error Detection Unit 41 Channel Identification Unit 42 Channel Estimation Unit 43 Channel Determination Unit 100 Wireless Communication Unit 101 Antenna 110 Transmission Unit 120 Antenna Switcher 130 Reception Unit 200 Baseband processor 210 Modulator 230 Demodulator 231 Guard interval removal circuit 232 Discrete Fourier transformer 233 Subcarrier demodulator 234 Deinterleave circuit 235 Error correction circuit 236 Subcarrier power level calculator 237 Network power level calculator 300 Communication controller 400 system control unit 410 processor 420 memory 430 interface 490 system bus 610 channel list

Claims (10)

An orthogonal frequency division multiplexing receiving apparatus arranged such that a part of a frequency band of a channel overlaps a part of a frequency band of another channel,
Channel signal receiving means for receiving a signal of a certain channel;
Subcarrier extraction means for extracting subcarriers included in the channel signal from the received channel signal;
Reception level detection means for detecting the reception level of each of the extracted subcarriers;
Channel specifying means for specifying a corresponding channel from the reception level;
Channel estimation means for estimating that the specified channel is in use and determining that a channel that has not been specified among neighboring channels whose frequency band overlaps with the received channel is unused. A receiving device. Error detection means for detecting an error from the extracted subcarriers;
The channel estimation means determines that the reception channel is in use when the channel signal reception means receives a channel signal and the error detection means does not detect an error. The receiving device according to claim 1. For the channel estimated by the channel estimation means, when the error detection means detects an error, it is determined that the channel is unused, and the error detection means does not detect an error. The receiving apparatus according to claim 2, further comprising channel determining means for determining that the channel is in use. 2. The channel estimation unit according to claim 1, wherein when the channel signal reception unit does not receive a channel signal, the channel estimation unit determines that the channel and a neighboring channel whose frequency band overlaps with the channel are unused. Receiver device. An orthogonal frequency division multiplexing receiving apparatus arranged such that a part of a frequency band of a channel overlaps a part of a frequency band of another channel,
Channel signal receiving means for receiving a signal of a certain channel;
Subcarrier extraction means for extracting subcarriers included in the channel signal from the received channel signal;
Error detection means for detecting an error from the extracted subcarriers;
Reception level detection means for detecting the reception level of each of the extracted subcarriers;
Channel specifying means for specifying a corresponding channel from the reception level;
If the channel signal receiving means does not receive a channel signal, it is determined that the channel and a neighboring channel whose frequency band overlaps with the channel are unused, and the channel signal receiving means receives the channel signal. If the error detection means does not detect an error, it is determined that the reception channel is in use, and the error detection means detects an error when the channel signal reception means receives a channel signal. Channel estimation means for estimating that the specified channel is in use and determining that a channel not specified among neighboring channels whose frequency band overlaps with the received channel is unused,
For the channel estimated by the channel estimation means, when the error detection means detects an error, it is determined that the channel is unused, and the error detection means does not detect an error. Includes a channel determination means for determining that the channel is in use,
A receiving apparatus comprising: a channel list that holds a state of each channel estimated or determined to be unused or in use by the channel estimation unit or the channel determination unit.   6. The receiving apparatus according to claim 5, wherein the receiving apparatus conforms to an IEEE802.11g standard. An access point connected to the network and an orthogonal frequency division multiplexing signal that is transmitted from this access point and is arranged so that part of the frequency band of the channel overlaps part of the frequency band of other channels. A wireless communication system comprising a terminal for scanning,
The terminal detects a signal from a channel signal receiving means for receiving a signal of a certain channel, subcarrier extracting means for extracting a subcarrier included in the channel signal from the received channel signal, and an error from the extracted subcarrier. Error detection means, reception level detection means for detecting the reception level of each of the extracted subcarriers, channel specification means for specifying the corresponding channel from the reception level, and the channel signal reception means receive the channel signal If not, it is determined that the channel and a neighboring channel whose frequency band overlaps with the channel are unused, and the channel signal receiving unit receives a channel signal, and the error detecting unit does not detect an error. If it is determined that the reception channel is in use, When the signal receiving means receives a channel signal and the error detecting means detects an error, it is assumed that the specified channel is in use, and the received channel and the frequency band overlap. A channel estimation means for determining that a channel not specified among the channels is unused, and a channel estimated by the channel estimation means when the error detection means detects an error, the channel detection means If the channel is determined to be unused and the error detection unit does not detect an error, the channel determination unit determines that the channel is in use, and the channel estimation unit or the channel determination unit A channel list that holds the state of each channel that is estimated to be in use or in use Wireless communication system, characterized in that. In a receiving apparatus including a channel list that holds a state of each channel arranged so that a part of a frequency band of a channel overlaps a part of a frequency band of another channel,
A first scan procedure for receiving a signal set to a predetermined channel, holding a state of the channel in the channel list, and identifying a channel that is assumed to be in use among neighboring channels of the channel;
When the signal is received by setting to the specified channel and an error has occurred, the state that it is not used is held in the channel list, and when no error has occurred, it is in use And a second scanning procedure for retaining the state of being in the channel list. In the first scanning procedure, when a channel signal is not received, the channel and a neighboring channel whose frequency band overlaps with the channel are determined to be unused, and an error is detected when the channel signal is received. If not, it is determined that the reception channel is in use, and if an error is detected when a channel signal is received, the channel being used is estimated from the reception level of the subcarrier, and the reception is performed. 9. The scanning method according to claim 8, wherein a channel that is not estimated to be in use among channels and neighboring channels whose frequency bands overlap with the channel is determined as unused. In a receiving apparatus including a channel list that holds a state of each channel arranged so that a part of a frequency band of a channel overlaps a part of a frequency band of another channel,
A first scan procedure for receiving a signal set to a predetermined channel, holding a state of the channel in the channel list, and identifying a channel that is assumed to be in use among neighboring channels of the channel;
When the signal is received by setting to the specified channel and an error has occurred, the state that it is not used is held in the channel list, and when no error has occurred, it is in use A program that causes a computer to execute a second scan procedure that holds the state of being in the channel list.

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