JP2006303590A - Communication devices, access point and wireless lan system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sustain a primary transmission rate by avoiding collision of packets. <P>SOLUTION: The transmission device applicable to a second wireless communication system using a frequency band, including a plurality of frequency bands for use in a first wireless communications system entirely comprises sections (50, 51), having compatibility with the first wireless communications system and generating an occupancy signal for informing the first wireless communications system such that the second wireless communications system occupies the wireless medium, a section (51) for detecting a free frequency band among the plurality of frequency bands for use in a first wireless communications system, and a section (500) for transmitting an occupancy signal in a detected frequency band, each time a free frequency band is detected at the detecting section (51). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a communication device, an access point, and a wireless LAN system that transmit a signal that occupies a wireless medium.

  Conventionally, in addition to a wireless LAN system compliant with the IEEE 802.11b standard (hereinafter abbreviated as “11b”) having a transmission rate of 11 Mbit / s, IEEE 802.11a having a maximum transmission rate of 54 Mbit / s ( Hereinafter, abbreviated as “11a”.) A wireless LAN system compliant with the standard has been proposed. Further, IEEE802.11g (hereinafter abbreviated as “11g”) having a feature obtained by adding IEEE802.11b and IEEE802.11a has been proposed. Hereinafter, in the wireless LAN system based on these standards, both the access point and the station are referred to as “legacy terminal”, the legacy access point is referred to as “legacy AP”, and the legacy station is referred to as “legacy STA”.

  In recent years, a high speed of 100 Mbit / s class is required in a wireless LAN. As one of the achievement techniques, as shown in FIG. 24, a technique for improving the transmission rate by using a frequency band n times (n is a natural number) that of a legacy terminal has been proposed. Hereinafter, both an access point and a station in a wireless LAN system that performs such high-speed transmission are referred to as “HT (High Throughput) terminal”, an HT access point as “HTAP”, and an HT station as “HTSTA”. In FIG. 24, the HT terminal includes a frequency band used by the legacy terminal, and uses, for example, a frequency band having a bandwidth three times that of the legacy terminal. Currently, the HT terminal and the legacy terminal communicate with each other using the same frequency band, that is, coexistence of different wireless LAN systems is being studied.

  Conventionally, as an example in which different wireless LAN systems coexist using the same frequency band, there is coexistence of the 11b system and the 11g system. This wireless LAN system adopts a configuration as shown in FIG. That is, the 11g access point 100 controls both the 11g station 101 and the 11b station 102.

  In the case of such a configuration, as illustrated in FIG. 26, the 11g station 101 can perform high-speed transmission by transmitting a data frame using a modulation method based on OFDM (Orthogonal Frequency Division Multiplexing). However, the station 102 of 11b recognizes it as an interference signal from another system because the OFDM signal is not the signal of 11b. Depending on the signal level, the station 102 of 11b may transmit the data frame by a modulation method based on CCK (Complementary Code Keying). In such a case, packet collision occurs and throughput is reduced.

  Therefore, as shown in FIG. 27, the 11g station 101 can demodulate at the station 102 of 11b and the IEEE802.11 (hereinafter abbreviated as “11”) not shown before transmitting the OFDM signal. A CTS (Clear To Send: signal notifying completion of reception) is transmitted by a modulation method based on DSSS (Direct Sequence Spread Spectrum). Accordingly, NAV (Network Allocation Vector: transmission suppression by virtual carrier sense) is set for the station 102 of 11b and the 11 station (not shown) to avoid collision.

  Here, the CTS frame format adopts the configuration shown in FIG. That is, the frame control unit 103 as a MAC (Media Access Control) header, a duration unit 104, a receiver address 105, and an FCS (Frame Check Sequence) unit 106 are configured. Other terminals that have received such a CTS set NAV in the section described in the duration unit 104 to suppress transmission. Thereby, a collision is avoided.

Also, even when the 11b station 102 is transmitting first, the 11g station 101 can demodulate or recognize the transmission signal of the 11b station 102, and thus collision can be avoided. That is, as shown in FIG. 29, the 11g station 101 demodulates (or recognizes) the data frame (CCK) transmitted from the 11b station 102, sets a back-off so that no collision occurs, and then An OFDM signal is transmitted.
Satoshi Hori and four others, “Examination of high-speed wireless LAN based on system capacity”, 2002 IEICE General Conference B-5-250 Hideaki Matsue and 1 other, "802.11 High-Speed Wireless LAN Textbook", IDG Japan, 2003 IEEE Std 802.11g-2003

  Here, when HTAP communicates with HTSTA, as shown in FIG. 2, it is conceivable to perform all of beacons, control frames, and data frames as notification signals transmitted at regular intervals by HT transmission. Thereby, high-speed transmission is realized. Hereinafter, a series of procedures shown in FIG. 2 is referred to as an “HT sequence”.

  However, as shown in FIG. 30, when the HT terminals 110 to 112 and the legacy terminals 113 and 114 perform communication in the same frequency band, they may recognize transmission signals from other terminals. Can not. For this reason, the HT terminals 110 to 112 and the legacy terminals 113 and 114 recognize transmission signals from other terminals as interference signals from other systems, and packet collisions frequently occur. As a result, the throughput decreases. That is, there is a problem that the communication speed between the legacy terminals and between the HT terminals is significantly reduced.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a high-speed wireless LAN system capable of avoiding packet collision and maintaining an original transmission rate.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the communication device according to the present invention is a communication device applied to a second wireless communication system that uses a frequency band including all of a plurality of frequency bands used in the first wireless communication system, An occupancy signal generator that is compatible with the first radio communication system and generates an occupancy signal that notifies the first radio communication system that the second radio communication system occupies a radio medium; A detection unit that detects a vacant frequency band among a plurality of frequency bands used in the first wireless communication system, and is detected each time a vacant frequency band is detected by the detection unit. And a transmitter that transmits the occupied signal in a frequency band.

  Thus, every time a vacant frequency band is detected, an occupancy signal is transmitted in the detected frequency band. Therefore, the first radio communication system and the first band including the use band of the first radio communication system are transmitted. When the two wireless communication systems coexist, the second wireless communication system can control the transmission of the first wireless communication system for each band used, and the number of terminals and communication in the first wireless communication system can be controlled. The influence of the state is minimized, and each wireless communication system can perform highly efficient communication without causing packet collision.

  (2) Further, in the communication device according to the present invention, the occupying signal generation unit generates an occupying signal that allows the second wireless communication system to occupy a wireless medium for a maximum period.

  As described above, when the second wireless communication system transmits the occupied signal from the vacant channel band and occupies the band, the occupied signal that can occupy the wireless medium for the maximum period is generated. It becomes possible to occupy all bands. Then, by transmitting a signal that occupies the entire band after completion of the initially set occupation period, the data of the terminal of the first wireless communication system is not collided with the data of the terminal of the first wireless communication system. The number and the influence of the communication status are minimized, and the transmission can be performed efficiently.

  (3) Further, in the communication device according to the present invention, the occupancy signal generator first generates an occupancy signal that allows the second radio communication system to occupy the radio medium for a maximum period, and the second and subsequent times. At the end of the maximum period, the second radio communication system generates an occupancy signal that ends the period of occupying the radio medium.

  As described above, when the second wireless communication system occupies the band by transmitting the occupancy signal from the vacant channel band, the entire occupancy period is maximized by maximizing the occupancy period set first. Can be occupied. Further, since the second radio communication system generates an occupancy signal for ending the period in which the second wireless communication system occupies the radio medium at the end of the maximum period after the second time, all the occupancy periods are ended simultaneously after the end of the first occupancy period. After that, by transmitting a signal that occupies the entire band, it is possible to transmit data efficiently without minimizing the influence of the number of other terminals and the communication status without colliding with the data of other terminals. .

  (4) Further, in the communication device according to the present invention, the detection unit detects a communication end time of a frequency band in which transmission is finally ended based on a communication state in the first wireless communication system, and the occupation The signal generator generates an occupancy signal that ends a period during which the second wireless communication system occupies a wireless medium at the detected communication end time.

  In this way, since the second wireless communication system generates an occupancy signal for ending the period during which the second wireless communication system occupies the wireless medium at the communication end time of the frequency band where transmission ends lastly, This eliminates the need to transmit an occupancy signal. After the first occupation period ends, by transmitting a signal that occupies the entire band, the data is not collided with the data of other terminals, minimizing the influence of the number of other terminals and communication status, and efficiently It becomes possible to transmit.

  (5) Further, in the communication device according to the present invention, the transmission unit is set at a frame interval and at random in the first wireless communication system with reference to a time at which transmission in the first wireless communication system ends. The backoff period in the second radio communication system is shorter than the total period of backoff periods in which the frame interval in the second radio communication system and the total period of randomly set backoff periods are shorter. A period is set and the occupation signal is transmitted.

  Thus, since the backoff period in the second wireless communication system is set and the occupation signal is transmitted, the second wireless communication system occupies before the backoff period of the first wireless communication system ends. A signal can be transmitted. As a result, it is possible to further suppress the influence of the number of terminals and the communication state in the first wireless communication system.

  (6) Moreover, in the communication apparatus according to the present invention, after the longest occupation period ends, the transmission unit occupies again all of a plurality of frequency bands used in the first wireless communication system. It is characterized by transmitting a signal.

  With this configuration, it is possible to perform communication of the second wireless communication system after suppressing transmission to the first wireless communication system and occupying the wireless medium. Thereby, collision of packets can be avoided and a reduction in throughput can be prevented. As a result, communication can be performed at the original transmission rate in the second wireless communication system.

  (7) Moreover, the access point which concerns on this invention is provided with the communication apparatus in any one of Claims 1-6.

  According to this access point, every time a vacant frequency band is detected, the occupied signal is transmitted in the detected frequency band. Therefore, the first wireless communication system and the band used for the first wireless communication system are transmitted. The second wireless communication system can control the transmission of the first wireless communication system for each band used, and the terminal of the first wireless communication system The influence of the number and communication state is minimized, and each wireless communication system can perform highly efficient communication without causing packet collision.

  (8) Further, a wireless LAN system according to the present invention is characterized by comprising an access point according to claim 7 and a station.

  According to this wireless LAN system, every time a vacant frequency band is detected, an occupied signal is transmitted in the detected frequency band. Therefore, the first wireless communication system and use of the first wireless communication system are used. When the second wireless communication system including the band coexists, the second wireless communication system can control the transmission of the first wireless communication system for each band used, and the terminal in the first wireless communication system Thus, the wireless communication system can perform highly efficient communication without causing packet collision.

  According to the present invention, every time a vacant frequency band is detected, an occupied signal is transmitted in the detected frequency band. Therefore, the first radio communication system and the use band of the first radio communication system are reduced. When the second wireless communication system includes the second wireless communication system, the second wireless communication system can control the transmission of the first wireless communication system for each band used, and the number of terminals in the first wireless communication system Thus, the wireless communication system can perform highly efficient communication without causing packet collision.

  Next, embodiments of the present invention will be described with reference to the drawings. As an example to which the wireless communication system according to the present invention is applied, there is a case where there is a wireless LAN system using different wireless bandwidths in the same frequency band.

  In this wireless LAN system, a wireless LAN system that uses a narrow band is referred to as a legacy terminal, and a wireless LAN system that uses a wide band is referred to as an HT (High Throughput) terminal. In this wireless LAN system, the HT terminal uses a frequency band n times (n is a natural number) that of the legacy terminal. In the example shown in FIG. 24, the HT terminal uses a frequency band whose bandwidth is three times that of the legacy terminal. Thereby, high-speed transmission is realized between HT terminals.

  Further, the HT terminal is compatible with the legacy terminal in all frequencies (all bands) for communication with the HT terminal, and occupies the radio medium in a format that can be demodulated by the legacy terminal (for example, CTS). An occupancy signal that notifies that is transmitted. Thereby, the HT terminal logically occupies time for performing the HT sequence with respect to the legacy terminal. In the present embodiment, the occupation signal is CTS. It is also possible to use CF-poll or MACframe as an occupied signal instead of CTS.

  FIG. 1 shows a state in which an HT terminal transmits to all frequency bands using an occupancy signal for notifying a legacy terminal that it occupies a wireless medium, and performs communication in the HT terminal after occupying the band. FIG. As shown in FIG. 1, when an HT terminal has a free transmission band, it notifies that the legacy terminal occupies the wireless medium in a format (eg, CTS) that can be demodulated and recognized by the legacy terminal. An occupancy signal is transmitted. Thereby, NAV (Network Allocation Vector: transmission suppression by virtual carrier sense) can be set with respect to a legacy terminal, and an HT sequence can be transmitted without collision of packets.

  Here, when HT terminals (HT access point HTAP and HT station HTSTA) communicate with each other, as shown in FIG. 2, beacons, control frames, and data frames are transmitted as notification signals transmitted at regular intervals. It is conceivable to perform everything by HT transmission, thereby realizing high-speed transmission. Hereinafter, a series of procedures shown in FIG. 2 is referred to as an “HT sequence”.

  Here, as shown in FIG. 3, the HT terminal and a plurality of legacy terminals exist in the same frequency band and packet collision occurs. For example, as shown in FIG. 4, each legacy terminal uses a channel. In the case where communication is performed, the HT terminal has no transmission bandwidth in the transmission band at the same time and cannot transmit the occupied signal. Therefore, all legacy terminals using the band can communicate. Until it is finished, the HT terminal cannot transmit data. That is, the HT terminal greatly affects the transmission timing and the number of legacy terminals and the communication state, cannot transmit HT terminal data within a desired period, and may not be able to perform highly efficient communication. Therefore, in the wireless LAN system according to the present embodiment, this is solved using the following method.

(First embodiment)
FIG. 5 is a block diagram showing a configuration of a transmitter of an HT terminal applied to the wireless LAN system according to the first embodiment. In the transmitter 500 of the HT terminal, the MAC circuit 50 controls the transmission / reception method, the frame format, and the like of transmission data under the control of the control circuit. The band information to be transmitted and the period of NAV (Network Allocation Vector: transmission suppression by virtual carrier sense) are also defined. The error correction encoder 52 performs error correction encoding on the signal input from the MAC circuit 50. The modulator 53 performs modulation such as BPSK, QPSK, and 16QAM on the signal input from the error correction encoder 52.

  Under the control of the control circuit 51, the switch 54 switches the signal input from the modulator 53 to the symbol repetition circuit 55 or the IFFT circuit 56 and outputs it. The symbol repetition circuit 55 generates a signal of a desired transmission band for the signal input from the switch 54 by control according to the transmission band information from the control circuit 51. The symbol repetition circuit 55 can take a plurality of types of configurations as follows.

  FIG. 6 is a diagram showing a schematic configuration of the first symbol repetition circuit 55a. The input signal is repeatedly assigned in OFDM symbol units only to the band channel to be transmitted according to the transmission band information from the control circuit 51, and a null signal is assigned to the others. Here, it is an example when it is desired to transmit signals of the lower two channel bands. FIG. 7 is a diagram showing a schematic configuration of the second symbol repetition circuit 55b. A circuit that repeats an input signal n times in OFDM symbol units and a filter 55x that filters a band other than a band in which the signal that has been repeated n times is desired to be transmitted are included. The filter 55x can be varied according to the transmission band information from the control circuit 51 so as to pass only the band to be transmitted. FIG. 7 shows an example where it is desired to transmit a signal only to the lowest channel band. Further, in this example, the position of the filter 55x is on the output side in the symbol repetition circuit 55. However, as in the third symbol repetition circuit 55c shown in FIG. Alternatively, the filters 55y-1 to 55y-3 may be provided.

  The above filter may be located outside the symbol repetition circuit 55, or may be located anywhere as long as it has the same function. Alternatively, the filter circuit 57 in the preceding stage of the antenna 58 in FIG. 5 can be varied according to the band to be transmitted.

  In FIG. 5, the IFFT circuit 56 converts the signal input from the switch 54 or the symbol repetition circuit 55 from a frequency signal to a time signal. The filter circuit 57 passes and outputs only a signal in a desired band among the output signals of the IFFT circuit 56, and the output signal is transmitted by the antenna 58.

  In the transmitter of this HT terminal, when the output from the modulator 53 is directly output to the IFFT circuit 56 by the switch 54, the transmission of the HT signal using the bandwidth n times that of the legacy terminal as shown in FIG. Can be performed. Further, when the output from the modulator 53 is output to the IFFT circuit 56 via the symbol repetition circuit 55 by the switch 54, as shown in FIG. 10, the legacy signal is stacked in the frequency axis. Transmission is possible. FIG. 10 shows an example in which a signal is transmitted over the entire band.

  Further, in the following description, a portion including the transmission circuit 500a, the MAC circuit 50, and the control circuit 51 excluding the symbol repetition circuit 55 in FIG. Further, a portion including the transmission circuit 500 a including the symbol repetition circuit 55, the MAC circuit 21, and the control circuit 21 a is defined as an occupied signal generation unit 502. That is, the control circuit 51 included in the occupancy signal generation unit 502 instructs transmission of the legacy signal, and outputs transmission signal data from the MAC circuit 50 to the transmission circuit 500a, thereby transmitting a signal compatible with the legacy terminal. Then, the control circuit 51 included in the transmission unit 501 instructs transmission of the HT signal, and the transmission signal data is output from the MAC circuit 50 to the transmission circuit 500a, thereby transmitting a signal compatible with the HT terminal. And

  In the above description, the symbol repetition circuit 55 is arranged between the modulator 53 and the IFFT circuit 56. However, the present invention is not limited to this. Other configurations may be adopted as long as the same function as this configuration is achieved.

  FIG. 11 is a block diagram showing a configuration of a receiver of the HT terminal applied to the wireless LAN system according to the first embodiment. In the receiver 1100 of the HT terminal, a process of passing only a signal in a desired band is performed on the radio signal received by the antenna 210 by the filter circuit 211. The output signal of the filter circuit 211 is converted from a time signal to a frequency signal by the FFT circuit 212. The demodulator 213 converts the signal input from the FFT circuit 212 into a bit string based on the signal point. The error correction decoder 214 performs error correction decoding on the signal input from the demodulator 213.

  The MAC circuit 215 reads out a frame transmission / reception method, a frame format, and the like based on a signal input from the error correction decoder 214 and outputs received data. Further, it is possible to recognize the occupied period of the band received from the received data from the MAC circuit 215 and other timing information. In addition, the signal of the legacy terminal can be recognized.

  The receiver of the HT terminal measures the electric field strength of the signal by the electric field strength measuring unit 216 after passing only the signal of the desired band through the signal received from the antenna 210 by the filter circuit 211. The output of the electric field strength measuring unit 216 is input to the control circuit 51 shown in FIG. Here, the electric field intensity measurement unit 216 in the reception circuit 1100a constitutes a detection unit 217a. That is, the electric field intensity in each frequency band is measured, and when the electric field intensity is a predetermined value or less, it is determined that the frequency band is free. The transmitter 500 and the receiver 1100 constitute a communication device.

  In the above description, the electric field strength measuring unit 216 is branched from the latter stage of the filter circuit 211. However, the present invention is not limited to this, and any other configuration may be adopted as long as the same function as this configuration is achieved. good.

  Next, the operation of the wireless LAN system according to the first embodiment configured as described above will be described.

  FIG. 12 is a flowchart illustrating the operation of the wireless LAN system according to the first embodiment, and FIG. 13 is a diagram illustrating a state in which the HT terminal according to the first embodiment performs transmission control on the legacy terminal. It is.

  First, the number of bands m occupied by the HT terminal starts from 0, and the electric field strength is measured (step S1). Next, a vacant band is searched for in a transmittable band (CH1 to CH3 in FIG. 13). In FIG. 13, first, the HT terminal recognizes that CH3 is free (step S2), and creates an occupancy signal CTS for occupying CH3 (step S3). This CTS includes NAV period information for CH3. Included and the maximum duration is set. The NAV set for this maximum period is NAVmax. Then, the created occupancy signal is transmitted (step S4), and the HT terminal occupies CH3.

  Next, the number of occupied bands is added to m (step S5), and it is determined whether m = 3 (step S6). If not m = 3, the process proceeds to step S1 and the above steps are repeated. That is, the HT terminal searches for an empty channel from CH1 and CH2. In FIG. 13, it is determined that CH2 is free, and the HT terminal transmits CTS to CH2 when it can be determined that it is free, and NAVmax is assigned to CH2 to occupy the band. Next, the HT terminal determines whether CH1 is available. When it is determined that CH1 is free, the HT terminal transmits a CTS to CH1, allocates NAVmax in CH1, and occupies the band.

  In step S6, if m = 3, it is determined whether or not the end point (t = t1) of the first NAVmax period has been reached (step S7). If not t = t1, the determination in step S7 is performed. repeat. When t = t1, NAV is assigned again to CH1 to CH3 and the band is occupied (step S8). Thus, after occupying the bandwidth of CH1 to CH3, the HT sequence is transmitted (step S9). The setting period of the NAV to be retransmitted depends on the HT sequence length.

  As described above, when the HT terminal transmits the CTS from the vacant channel band and occupies the band, by setting the NAV to the maximum, it is possible to occupy all the bands in this NAVmax section. . Then, after the period of the first NAV (in the case of FIG. 13, NAVmax of CH3) is transmitted, a signal occupying the entire band is transmitted, so that the number of other terminals and the communication status can be reduced without colliding the data with the data of other terminals. Thus, it is possible to transmit efficiently.

  In the above, when the CTS to be initially set does not set the NAV of the maximum period (cannot be set), the entire bandwidth transmitted by the HT terminal may not be occupied during the NAV period. When it is determined that the entire bandwidth transmitted by the HT terminal is not occupied at the end of the NAV period, the occupation signal CTS is transmitted again only to the occupied band, and is occupied by other terminals during the occupation period. Wait for the available channel to be free. This operation continues until all the transmission bandwidth is occupied.

(Second Embodiment)
The configurations of the transmitter and receiver of the HT terminal of the wireless LAN system according to the second embodiment are the same as those of the first embodiment.

  Next, the operation of the wireless LAN system according to the second embodiment will be described. FIG. 14 is a flowchart showing the operation of the wireless LAN system according to the second embodiment, and FIG. 15 is a diagram showing how the HT terminal according to the second embodiment performs transmission control on the legacy terminal. is there.

  First, the number of bands m occupied by the HT terminal starts from 0, and the electric field strength is measured (step T1). Next, an available band is searched for in a transmittable band (CH1 to CH3 in FIG. 15). In FIG. 15, first, the HT terminal recognizes that CH3 is free (step T2), and determines whether or not the number of occupied bands m is 0 (step T3). If m = 0, an occupancy signal CTS for occupying CH3 is created (step T4). This CTS includes NAV period information for CH3, and a maximum period is set. The NAV set for this maximum period is NAVmax.

  On the other hand, if m = 0 is not satisfied in step T3, an occupancy signal CTS for setting the NAV that ends at the same time as the end time t1 of the NAVmax is created (step T5).

  Next, the generated occupied signal is transmitted (step T6), the number of occupied bands is added to m (step T7), and it is determined whether m = 3 (step T8). If not m = 3, the process proceeds to step T1, and the above steps are repeated. That is, the HT terminal searches for an empty channel from CH1 and CH2. In FIG. 15, it is determined that CH2 is free, and the HT terminal transmits CTS to CH2 when it can be determined that it is free, and assigns a NAV in CH2 in a period in which the end time is the same as NAVmax of CH3. Occupy the band. Next, the HT terminal determines whether CH1 is available. When it is determined that CH1 is free, the HT terminal transmits a CTS to CH1, assigns a NAV in CH1 in a period in which the end time is the same as the NAVmax of CH3, and occupies the bandwidth.

  In step T8, if m = 3, it is determined whether or not the end point (t = t1) of the first NAVmax period has been reached (step T9). If not t = t1, the determination in step T9 is performed. repeat. When t = t1, NAV is again assigned to CH1 to CH3 to occupy the band (step T10). Thus, after occupying the bandwidth of CH1 to CH3, the HT sequence is transmitted (step T11). The setting period of the NAV to be retransmitted depends on the HT sequence length.

  As described above, when the HT terminal transmits the CTS from the vacant channel band and occupies the band, it is possible to occupy all the bands within this NAVmax section by maximizing the NAV that is initially set. It becomes possible. Then, after the period of the first NAV (in the case of FIG. 15, NAVmax of CH3) is transmitted, a signal that occupies the entire band is transmitted, so that the number of other terminals and the communication status can be reduced without colliding data with the data of other terminals. Thus, it is possible to transmit efficiently.

  Further, in the subsequent occupation (occupation of CH1, CH2), by assigning a NAV in a period in which the end time is the same as the initially set NAVmax (CH3 NAVmax), and by occupying the bandwidth, It is possible to accurately transmit the transmission information of the terminal itself.

(Third embodiment)
The configurations of the transmitter and the receiver of the HT terminal of the wireless LAN system according to the third embodiment are the same as those in the first embodiment. Here, in FIG. 11, the filter circuit 211, the FFT circuit 212, the demodulator 213, the error correction decoder 214, and the MAC circuit constitute a detection unit 217b. That is, the detection unit 217b configured by each of these blocks recognizes the communication status of the legacy terminal and detects a free band by the HT terminal demodulating the CTS and data of the legacy terminal.

  Next, the operation of the wireless LAN system according to the third embodiment will be described. FIG. 16 is a flowchart illustrating the operation of the wireless LAN system according to the third embodiment, and FIG. 17 is a diagram illustrating a state in which the HT terminal according to the third embodiment performs transmission control on the legacy terminal. is there. First, the number of bands m occupied by the HT terminal starts from 0, and a signal is received from the legacy terminal (step R1). Since the HT terminal can demodulate the CTS and data transmitted by the legacy terminal, the communication status can be grasped in the band to be transmitted by the HT terminal. When the HT terminal tries to transmit, it recognizes the communication state of the bandwidth to be transmitted (CH1 to CH3 in FIG. 17) (step R2). In FIG. 17, it is recognized that other terminals transmit in the order of CH3 → CH2 → CH1.

  Next, the occupied signal timing tn (n is a band, n = 1, 2, 3) of the HT terminal is set (step R3). Then, an occupancy signal of the HT terminal is created in each band (step R4). In step R4, the length of the NAV of each band is determined. Next, it is determined whether or not t = tn (step R5). If t = tn is not satisfied, the determination in step R5 is repeated. On the other hand, if t = tn in step R5, the number of occupied bands is added to m (step R6), and it is determined whether m = 3 (step R7). If m = 3 is not satisfied, an occupied signal of band n is transmitted (step R8), the process proceeds to step R5, and the above steps are repeated.

  In this case, the occupancy signal CTS is allocated and transmitted to CH3 by recognizing that CH3 is free first, and the HT terminal occupies CH3. This CTS includes NAV period information for CH3, and assigns a NAV for the period until the data end time of CH1 that is finally recognized as vacant to occupy the bandwidth. Next, when CH2 becomes available, an occupancy signal CTS is allocated and transmitted, and the HT terminal occupies CH2. This CTS includes NAV period information for CH2, and assigns a NAV for the period until the data end time of CH1, which is finally recognized as vacant, to occupy the bandwidth.

  On the other hand, if m = 3 in step R7, the NAV is assigned again to CH1 to CH3 to occupy the band (step R9). That is, the HT terminal occupies the band by allocating NAV to CH1 to CH3 again at the time when CH1 becomes empty (that is, when the CH3 and CH2 NAV ends). Thus, after occupying the bandwidth of CH1 to CH3, the HT sequence is transmitted (step R10). The setting period of the NAV to be retransmitted depends on the HT sequence length.

  As described above, when the HT terminal transmits the CTS from the vacant channel band and occupies the band, the HT terminal recognizes the communication state of the band to be transmitted, and finally, the channel vacated in each band by the information A period until the data end of the legacy terminal of the band is set. By setting the NAV in this way, when the data of the legacy terminal is completed, the occupation signal CTS is transmitted again to the entire band, and then the HT sequence is transmitted, so that the number of other terminals and the communication status can be determined without collision. The influence can be minimized, and the band can be occupied with the minimum CTS transmission.

(Fourth embodiment)
The configurations of the transmitter and the receiver of the HT terminal of the wireless LAN system according to the fourth embodiment are the same as those in the first embodiment.

  In the fourth embodiment, in the above first to third embodiments, after the HT terminal transmits the occupancy signal CTS from the vacant band and occupies the transmission bandwidth, after determining that it is vacant, The period (backoff) until CTS is transmitted is set to the minimum.

  FIG. 18 is a diagram illustrating a state in which the HT terminal according to the fourth embodiment performs transmission control on the legacy terminal. In FIG. 18, tb1 is a back-off time until the HT terminal transmits a CTS after it is determined that the band is free, and tb2 is a back-off time for the Legacy terminal to transmit the CTS. By setting tb1 <tb2, the HT terminal can preferentially occupy the band as shown in FIG. Then, by applying the fourth embodiment together with the NAV setting of the first to third embodiments, the influence of the number of other terminals and the communication status can be further minimized when the HT terminal performs communication. .

Here, an example of the definition of tb (tb1, tb2) will be described according to a wireless LAN system. tb corresponds to IFS + backoff shown in FIG. IFS (Inter Frame Space, frame interval) defines the minimum transmission signal interval before transmitting a signal. The state where transmission is possible from a busy state (a state where another terminal is using a desired transmission band) is defined. After recognizing, it waits for the time of IFS, and after confirming that transmission is possible at a random time called back-off, continues, it transmits its own terminal signal. (In FIG. 19, CTS is transmitted.)
This IFS has a fixed long time, and three types are defined depending on the type of data to be transmitted and the system control method, and a priority is assigned. FIG. 20 shows the priority of each IFS. As shown in FIG. 20, the time of each IFS is SIFS <PIFS <DIFS, SIFS (Short IFS) is assigned when transmitting ACK, and IFS and PIFS (PCF IFS) are centrally controlled. IFS and DIFS (DCF IFS) allocated to data transmission are IFS allocated to data transmission of the own terminal that is distributedly controlled.

  The back-off is a time that is randomly determined based on a random number value generated within a specified random number generation range CW.

  In the fourth embodiment, as shown in FIG. 21, when data of an HT terminal is transmitted, SIFS <HT terminal IFS <PIFS <DIFS is set. As a result, the HT terminal can preferentially occupy the band. Alternatively, when transmitting data of the HT terminal, the HT terminal back-off is set in a random number generation range that satisfies a random value satisfying (specified random number generation range of the HT terminal) <(CW). Thereby, it is possible to increase the probability that the HT terminal preferentially occupies the band. Further, as shown in FIG. 22, when transmitting data of the HT terminal, both the HT terminal IFS and the HT terminal back-off set as described above are set.

  FIG. 23 is a flowchart showing the operation of the wireless LAN system according to the fourth embodiment. First, a transmittable band is recognized (step P1), and it is determined whether or not it is an ACK (step P2). In the case of ACK, SIFS and backoff (tb0) are set (step P4) according to the generation of random numbers in the CW range (step P3). Next, it is determined whether or not t = tb0 (step P5). If t = tb0 is not satisfied, the determination in step P5 is repeated. In step P5, when t = tb0, ACK is transmitted (step P6), and the process ends.

  On the other hand, if it is not ACK at step P2, the IFS and backoff (tb1) of the HT terminal are set (step P8) in response to the generation of the specified random number of the HT terminal (step P7). Next, it is determined whether or not t = tb1 (step P9). If t = tb1 is not satisfied, the determination in step P9 is repeated. In step P9, if t = tb1, CTS or DATA is transmitted (step P10), and the process ends.

  As described above, according to the fourth embodiment, when the HT terminal performs communication, the influence of the number of other terminals and the communication status can be further minimized.

  In each of the embodiments described above, the case where wireless LAN systems using the same frequency band and different frequency bandwidths coexist has been described. However, the present invention is not limited to the wireless LAN system, and different frequency bands using the same frequency band. It can be applied to a wide range of wireless communication systems.

It is a figure which shows a mode that it communicates in HT terminal, after transmitting to all the frequency bands which use the occupation signal which notifies that a HT terminal occupies a radio medium with respect to a legacy terminal, and occupying a band. It is a figure which shows the example of HT sequence. It is a figure which shows a mode that a packet collides when an HT terminal and several legacy terminals exist in the same band. It is a figure which shows an example in case an HT terminal cannot transmit CTS. It is a block diagram which shows the structure of the transmitter of the HT terminal applied to the wireless LAN system which concerns on 1st Embodiment. It is a figure which shows schematic structure of the 1st symbol repetition circuit 55a. It is a figure which shows schematic structure of the 2nd symbol repetition circuit 55b. It is a figure which shows schematic structure of the 3rd symbol repetition circuit 55c. It is a figure which shows a mode that an HT terminal transmits a signal using a specific zone | band. It is a figure which shows a mode that a legacy terminal transmits a signal using each zone | band. It is a block diagram which shows the structure of the receiver of the HT terminal applied to the wireless LAN system which concerns on 1st Embodiment. 3 is a flowchart showing an operation of the wireless LAN system according to the first embodiment. It is a figure which shows a mode that the HT terminal which concerns on 1st Embodiment performs transmission control with respect to a legacy terminal. 6 is a flowchart showing the operation of the wireless LAN system according to the second embodiment. It is a figure which shows a mode that the HT terminal which concerns on 2nd Embodiment performs transmission control with respect to a legacy terminal. 10 is a flowchart illustrating an operation of a wireless LAN system according to a third embodiment. It is a figure which shows a mode that the HT terminal which concerns on 3rd Embodiment performs transmission control with respect to a legacy terminal. It is a figure which shows a mode that the HT terminal which concerns on 4th Embodiment performs transmission control with respect to a legacy terminal. It is a figure explaining the definition of tb. It is a figure which shows the priority of IFS. It is a figure which shows the priority of IFS of an HT terminal. It is a figure which shows a mode that tb is set. It is a flowchart which shows operation | movement of the wireless LAN system which concerns on 4th Embodiment. It is a figure which shows the frequency band which an HT terminal and a legacy terminal use. It is a figure which shows schematic structure of the conventional wireless LAN system. It is a figure which shows the area of the data transmitted with the conventional wireless LAN system. It is a figure which shows the area of the data transmitted with the conventional wireless LAN system. It is a figure which shows a CTS frame format. It is a figure which shows the area of the data transmitted with the conventional wireless LAN system. It is a figure which shows a mode that a packet collides with the conventional wireless LAN system.

Explanation of symbols

50 MAC circuit 51 Control circuit 52 Error correction encoder 53 Modulator 54 Switch 55, 55a, 55b, 55c Symbol repetition circuit 55x Filter 55y-1 to 55y-3 Filter 56 IFFT circuit 57 Filter circuit 58 Antenna 103 Frame controller 104 Duration section 105 Receiver address 106 FCS section 210 Antenna 211 Filter circuit 212 FFT circuit 213 Demodulator 214 Error correction decoder 215 MAC circuit 216 Field strength measuring section 217a, 217b Detection section 500 Transmitter 500a Transmission circuit 501 Transmission section 502 Occupancy Signal generator 1100 Receiver 1100a Receiver circuit

Claims (8)

A communication device applied to a second wireless communication system that uses a frequency band including all of a plurality of frequency bands used in the first wireless communication system,
An occupancy signal generator that generates an occupancy signal that is compatible with the first radio communication system and notifies the first radio communication system that the second radio communication system occupies a radio medium. When,
A detecting unit for detecting a vacant frequency band among a plurality of frequency bands used in the first wireless communication system;
And a transmitter that transmits the occupancy signal in the detected frequency band each time a free frequency band is detected by the detector.   The communication apparatus according to claim 1, wherein the occupation signal generation unit generates an occupation signal that allows the second wireless communication system to occupy a wireless medium for a maximum period. The occupied signal generator is
Initially the second wireless communication system generates an occupancy signal that can occupy the wireless medium for a maximum period of time,
2. The communication device according to claim 1, wherein after the second time, at the end of the maximum period, an occupancy signal for ending a period in which the second wireless communication system occupies a wireless medium is generated. The detection unit detects a communication end time of a frequency band where transmission ends last based on a communication state in the first wireless communication system,
2. The communication device according to claim 1, wherein the occupying signal generation unit generates an occupying signal that ends a period during which the second wireless communication system occupies a wireless medium at the detected communication end time.   The transmission unit is configured so that the second interval is greater than a total period of frame intervals and a randomly set backoff period in the first wireless communication system with reference to a time at which transmission in the first wireless communication system ends. Setting the back-off period in the second radio communication system and transmitting the occupied signal so that a total period of frame intervals and a randomly set back-off period in the radio communication system of the second radio communication system is shortened. The communication device according to any one of claims 1 to 4, wherein:   The transmission unit transmits an occupation signal again to all of a plurality of frequency bands used in the first wireless communication system after the longest occupation period ends. The communication device according to claim 5.   An access point comprising the communication device according to any one of claims 1 to 6.   A wireless LAN system comprising the access point according to claim 7 and a station.

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