JP2005130010A - Radio lan system and communication control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio LAN system capable of suppressing an influence of an interference wave due to a reflection wave to be low. <P>SOLUTION: An access point 1 performs radio communication with a radio terminal 2 by OFDM, and performs a return test of test pattern data for measuring an error rate for a guard interval time of the OFDM by providing a plurality of candidate values in the guard interval time. The access point 1 transmits a control signal for setting a guard interval time at the time of acquiring the best error rate in a radio terminal 2, and the radio terminal 2 can demodulate the data from the access point 1 while suppressing the influence of the interference wave due to the unwanted reflection wave to be low by setting the guard interval time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wireless LAN system that performs communication by OFDM and a communication control method thereof.

  As the use of the Internet progresses, a wireless LAN is adopted as a high-speed access line that takes advantage of no need to install a cable as a means for providing a high-speed access line to users. However, since the frequency band that can be used by the wireless LAN is limited, as a method of accessing the wireless LAN by efficiently sharing the same frequency with many wireless LAN terminals, high multiplicity and multipath reflection can be taken. An OFDM (Orthogonal Frequency Multiplexing Modulation) system (hereinafter referred to as OFDM) that has an effect of avoiding interference due to the above is employed (see Non-Patent Document 1, for example).

  In this wireless LAN using OFDM, an access point which is a wireless station of the wireless LAN and a wireless terminal receive and detect signal data in order to avoid the influence of interference waves due to multiple reflections from surroundings such as buildings and structures ( A time window for demodulation is provided, and a guard interval time during which no signal is extracted is set in the time window. However, since the guard interval time is a fixed value (“0.8 microseconds”), the distance range in which the effect of reducing the influence of the interference wave is obtained is limited in the guard interval time.

  In addition to the guard interval time, there is a method of incorporating a diversity method using a plurality of antennas as a method for improving the influence of interference waves (see, for example, Patent Document 1).

However, this method has a problem that a radio terminal requires a plurality of antennas and the terminal device becomes large.
JP 2001-148647 A (page 19, FIG. 5) IEEE 802.11a (The Institute of Electrical and Electronics Engineers Wireless LAN Standard 802.11a)

  In an OFDM wireless LAN used to improve frequency utilization efficiency, a time window for detecting a received signal is provided in order to prevent the wireless terminal from being affected by multiple reflections from surrounding structures. Guard interval time is set before and after the window. However, since this guard interval time is a fixed value, there is a problem that a sufficient effect of reducing the influence of interference waves cannot be obtained in a distance range that does not cover the guard interval time.

  Moreover, as a method for reducing the influence of interference waves exceeding the set guard interval time, there is a method using antenna diversity, but there is a problem that the size of the wireless LAN terminal is increased.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a wireless LAN system capable of suppressing the influence of interference waves caused by reflected waves.

  In order to achieve the above object, a wireless LAN system of the present invention is a wireless LAN system including a plurality of wireless stations that communicate with each other by an OFDM method, and the first wireless station has a guard interval time set in advance. Test pattern data is transmitted / received between the second radio station and first guard interval setting means for transmitting control information for changing the setting of the guard interval time to the second radio station receiving it. Loop test means for measuring the error rate of the test pattern data, and the second radio station receives the test pattern data transmitted from the first radio station and sends it back. Second guard interval setting means for receiving the control information transmitted from the radio station and setting a guard interval time for the device to demodulate the received signal; Characterized by comprising.

  The wireless LAN system communication control method of the present invention is a wireless LAN system communication control method comprising a plurality of wireless stations communicating by OFDM, wherein the first wireless station and each of the second wireless stations Each includes the same table to which a list number corresponding to each of a plurality of guard interval times is assigned, and the first wireless station refers to the table with respect to the second wireless station. A packet including a number and first test pattern data is generated and transmitted, and the list number read from the packet received by the second wireless station from the first wireless station is referred to the table. Receiving the second test pattern data obtained by sending the first test pattern data demodulated at the set guard interval time back to the first radio station; And the second test pattern data are compared and collated, and a loopback test for measuring the error rate is repeatedly performed by changing the list number, and the guard interval in which the best error rate is obtained among the measured error rates is obtained. A time is selected, a list number corresponding to the selected guard interval time is transmitted to the second radio station, a guard interval time to be demodulated by the second radio station is set, and the second radio station is set. Is characterized by demodulating a packet of message data transmitted from the first radio station at the set guard interval time.

  According to the present invention, a test pattern data loopback test is performed between two wireless stations performing OFDM communication, for example, between a wireless LAN access point using OFDM communication and a wireless terminal, to check the optimum value of the guard interval time. By setting the guard interval time with the best error rate from the access point to the wireless terminal, it is possible to communicate between the two wireless stations while suppressing the influence of the interference wave caused by the reflected wave.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of an embodiment of a wireless LAN system according to the present invention.

  In FIG. 1, the wireless LAN system includes an access point 1 and a plurality of wireless terminals 2 (# 1 to #n). Each wireless terminal 2 (# 1 to #n) communicates with the access point 1 using OFDM. To communicate. Each wireless terminal 2 (# 1 to #n) communicates with the access point 1 by a random access method conforming to the IEEE802.11a specification, and performs the same access and communication control. Now, only the wireless terminal 2 is described.

  The wireless terminal 2 receives the radio wave transmitted from the access point 1, but simultaneously receives the reflected waves #a to #c from the buildings 3a, 3b, and 3c in addition to the direct wave from the access point 1. .

  FIG. 2 is a diagram showing the relationship between these direct waves #s and the reflected waves #a to #c in the wireless terminal 2.

  In FIG. 2, in the OFDM modulation, modulation / demodulation is performed in units of one symbol including a guard interval time G and a net symbol time B. For example, if the reflection delay time is within the set time of the guard interval time G set on the receiving side like the reception delay time Ab of the reflected wave #b from the building 3b, the influence of the reflected wave is removed. The received data corresponding to the net symbol (time) B can be correctly reproduced.

  However, for example, when the distance between the building 3c and the wireless terminal 2 is large and the reception intensity of the reflected wave #c is large, the reflected wave #c having a large delay time Ac is directly applied to the wave #s. Since the signal B is received as interference noise in the symbol B of the received signal, the signal cannot be detected correctly.

  Therefore, in such a case, if the guard interval time G is set as large as Gx, the interference component can be removed. However, if the guard interval time is set too large, the effective power decreases and becomes weak against noise. The guard interval time has an optimum time because the error rate is deteriorated and the transmission efficiency is lowered.

  The wireless LAN system according to the embodiment of the present invention greatly affects devices and circuits by adding a negotiation for setting a guard interval time after a communication speed setting negotiation performed when the wireless terminal 2 and the access point 1 start communication. Instead, the guard interval time is set in a compensatory manner to reduce and eliminate the influence of the interference wave.

  With respect to setting of the guard interval time, negotiation is performed between two facing radio stations, with one serving as a master and the other serving as a slave. In the following description, the operation is described with the wireless LAN access point 1 as the master and the wireless terminal 2 as the slave. When two-way communication is performed between these wireless stations, negotiation is performed in which the relationship between the master and the slave is reversed, but the operation may be performed by reversing the relationship between the access point 1 and the wireless terminal 2. Therefore, the operation of setting the guard interval time will be described below using the former combination.

  3 and 4 are functional block diagrams of the access point 1 and the wireless terminal 2 of the wireless LAN system according to the embodiment of the present invention.

  In FIG. 3, the access point 1 includes a network interface IF1, a MAC unit MC1, a communication control unit CC1, an antenna AT1, and a radio unit RF1 including a transmission unit TX1 and a reception unit RX1.

  The access point 1 transmits / receives a message signal from / to a connection destination LAN or server via the network interface IF1, and transmits / receives a message to / from the wireless terminal 2 logged in to the own device. The MAC unit MC1 relays a message between the network interface IF1 and the radio unit RF1 by performing a MAC (Media Access Control) process according to the control of the communication control unit CC1. The radio unit RF1 transmits and receives a data packet that has been subjected to packet formatting and header information processing by the MAC unit MC1 to and from the radio terminal 2 via the antenna AT1. OFDM modulation / demodulation processing is executed by the radio unit RF1.

  The communication control unit CC1 monitors and controls the packets transmitted and received by the MAC unit MC1 to and from the radio unit RF1, performs a loopback test for measuring the error rate, sets a transmission rate with the radio terminal 1, and sets a guard interval. Control time setting.

  In FIG. 4, the wireless terminal 2 includes a terminal interface IF2, a MAC unit MC2, a communication control unit CC2, an antenna AT2, and a wireless unit RF2 including a transmission unit TX2 and a reception unit RX2. The operation is the same as the operation of the access point 1 except that the guard interval time described later is set and the communication partner is the access point 1.

  5 and 6 are functional block diagrams showing functional elements for setting the guard interval time of the access point 1 and the wireless terminal 2 of the wireless LAN system of the present invention.

  In FIG. 5, the receiving unit RX1 of the access point 1 amplifies and frequency-converts the received signal from the antenna AT1, and further performs AD conversion. The digitally converted received signal is subjected to FFT conversion and a baseband signal. And a guard interval setting unit (hereinafter referred to as a GI setting unit) GI1 for setting a guard interval time applied in a period for executing the FFT.

  In FIG. 5, the error rate measurement function is indicated by a block. However, the error rate measurement may be performed by the MAC unit MC1 or the communication control unit CC1. Further, the communication control unit CC1 is attached with a table T that lists candidates for setting the guard interval time.

  In FIG. 6, the reception unit RX2 of the wireless terminal 2 includes a conversion processor PR2, a demodulation FFT unit FT2, and a GI setting unit GI2 having functions similar to those of the reception unit RX1 of the access point 1. Further, the communication control unit CC2 is attached with the same table T that lists candidates for setting the same guard interval time as the communication control unit CC1.

  The GI setting unit GI1 of the access point 1 and the GI setting unit GI2 of the wireless terminal 2 set the guard interval time according to the control of the communication control unit CC1 and the communication control unit CC2, respectively. The guard interval time setting candidate values are listed in the table T in advance.

  Hereinafter, the operation in which the communication control unit CC1 monitors the packet received from the radio unit RF1 to the MAC unit MC1 and measures the error rate during the loopback test in which the access point 1 sets the guard interval time with the radio terminal 2 will be described. do.

  FIG. 7 is a diagram of a table T that lists examples of guard interval time set values.

  In FIG. 7, the guard interval time is a default to which the list number 3 is assigned “0.8 microseconds” which is the specification value of the wireless LAN of the IEEE802.11a specification. Each guard interval time of “0.2”, “0.4”, “0.8”, “1.0”, “1.2”, “1.6”, “2.0” microseconds (G in FIG. 2) is set corresponding to each of the list numbers 1-7. Here, the default time per symbol is “4 microseconds” in the IEEE802.11a specification, and the effective symbol time (B in FIG. 2) is “3.2 microseconds”.

  The stored contents of the table T are the same in the internal memories of the communication control unit CC1 of the access point 1 and the communication control unit CC2 of the wireless terminal 2.

  The setting of the guard interval time is written in the header information of the packet transmitted from the access point 1 to the wireless terminal 2, and the wireless terminal 2 reads the information and sets a predetermined value.

  FIG. 8 is a diagram illustrating a configuration of packets transmitted and received between the access point 1 and the wireless terminal 2 in the wireless LAN system according to the embodiment of this invention.

  Between the access point 1 and the wireless terminal 2, the test signal (test pattern data) or message data is transmitted / received with the packet data shown in FIG. 8.

  A packet signal (test pattern data or message data) transmitted / received in a wireless LAN is a PLCP header (about 100 bytes) for synchronization on the receiving side, and a PLCP header (24 bytes) describing parameters defining the operation of the physical layer. ), MAC (media access control) MAC header mh (24 to 30 bytes) describing media layer control parameters, data frame df (0 to 231.0 bytes) carrying message data itself, FCS for error control (Frame Check Sequence) Frame (4 bytes) or the like.

  The PLCP header further includes fields of SYNC (16 bytes), SFD (2 bytes), signal (1 byte), service (1 byte), frame length (2 bytes), and CRC (2 bytes).

  The PLCP preamble and the PLCP header are transmitted at the lowest transmission speed (for example, 6 Mbps in IEEE802.11a) of the wireless LAN specification, and the transmission speed of the MAC header mh and the data frame df is described in the signal field of the PLCP header. ing.

  Accordingly, the access point 1 or the wireless terminal 2 that has received the test pattern data or the message signal can demodulate the MAC header mh and the data frame df at the transmission rate specified in the signal field.

  FIG. 9 is a table showing transmission rates of wireless LANs set in accordance with IEEE 802.11a. In FIG. 9, IEEE802.11a shows a transmission rate set stepwise between 6 Mbps and 54 Mbps by OFDM modulation.

  In a wireless LAN operating in accordance with the IEEE802.11a specification, the wireless terminal 2 transmits and receives test signals to and from the access point 1 according to the procedure defined in the specification when the power is turned on, and sequentially starts from the fastest transmission speed of 54 Mbps. A transmission rate at which a predetermined error rate is obtained between the access point 1 and the wireless terminal 2 is set by falling back to a slow transmission rate.

  In the wireless LAN system according to the embodiment of the present invention, after the transmission rate is set, an operation for further setting a guard interval time is performed. In the following description, the access point 1 and the wireless terminal 2 are connected in order to avoid congestion. A detailed description of the transmission speed setting operation procedure is omitted.

  FIG. 10 is a flowchart showing operations of the access point 1 and the wireless terminal 2 in the wireless LAN system according to the embodiment of the present invention.

  In FIG. 10, the flow on the left side of the drawing shows the operation procedure of the access point 1, and the flow on the right side shows the operation procedure of the wireless terminal 2.

  Here, the access point 1 and the wireless terminal 2 perform login access control to the access point 1 by a procedure according to IEEE 802.11a in order to start communication after the wireless terminal 2 is turned on. At this time, the speed setting is negotiated with the default guard interval time of “0.8 microseconds”. As a result, for example, a bit error rate of 0.5 × 10 (minus the fourth power) and a transmission speed of 36 Mbps are obtained. It is assumed that it has been set (steps s1, s1-1 in FIG. 10).

  Subsequently, the access point 1 checks whether or not the error rate of the data received by the wireless terminal 2 is improved by adjusting the guard interval time, so that an error occurs when there is an influence of a reflected wave having a longer delay time. Communication is performed with test pattern data in which the guard interval time is set to “1.0 microseconds” longer than the default that can be expected to improve the rate.

  In the following description, the access point 1 initially receives the guard interval time fixed to the default “0.8 microseconds”, and performs the setting operation of the guard interval time in the wireless terminal 2. After that, the setting of the guard interval time at the access point 1 is carried out with the wireless terminal 2, but the procedure is the same as that of the wireless terminal 2 and can be easily guessed. Description is omitted.

  The communication control unit CC1 of the access point 1 refers to the table T and transmits a command for setting the guard interval time to “1.0 microseconds” to the MAC processing unit MC1. The MAC processing unit MC1 writes the guard interval time list number “4” and the mark “S” indicating the test pattern data packet in the MAC header mh of FIG. A packet in which a command set to “second” and test pattern data for error rate measurement are written in the data frame df is generated and transmitted to the transmitter TX1.

  When receiving the packet from the MAC unit MC1, the transmission unit TX1 transmits a packet including a guard interval setting command and test pattern data to the wireless terminal 2 via the antenna AT1 (step s2 in FIG. 10).

  When receiving the packet from the access point 1 via the antenna AT2, the wireless terminal 2 outputs the packet to the demodulation FFT unit FT2 via the conversion processor PR2.

  The demodulating FFT unit FT2 is still performing a process of demodulating the guard interval time into a baseband packet with the default “0.8 microseconds”, and the MAC processing unit MC2 receives the packet containing the test pattern data and the like. Send. Then, the MAC processing unit MC2 reads the test mark “S” and the list number “4” from the MAC header mh of the received packet.

  The communication control unit CC2 monitors the packet received by the MAC unit MC2, and if it reads the test mark “S”, it determines that it has received test pattern data for the loopback test. Similarly, when the list number “4” is read, the table T is referred to and the guard interval time is set to “1.0 microsecond” in the GI setting unit GI2. The GI setting unit GI2 sets the demodulating FFT unit FT2 to demodulate with the guard interval time of “1.0 microseconds” until the guard interval time is set to “1.0 microseconds” and is changed and set later. Control.

  Further, the communication control unit CC2 performs setting change control of the guard interval time, sets the test pattern data received by the MAC unit MC2 as it is in the data frame df, and sets the mark “S” in the MAC header mh. Control is performed to generate a packet of return test pattern data and transmit it via the transmitter TX2 and the antenna AT2 (step s3 in FIG. 10).

  In the access point 1, the demodulated FFT unit FT1 demodulates the packet received via the antenna 1 and the processor unit PR1, and the return test pattern data is extracted from the demodulated signal and transmitted to the MAC unit MC1. The communication control unit CC2 measures the error rate by comparing the returned test pattern data with the previously transmitted test pattern data (here, “0.8 microseconds” of the default list number “3”). The error rate (# 3) is assumed to be 0.6 × 10 (minus the fourth power).) The error rate is stored in the internal memory (step s4 in FIG. 10).

  Next, the access point 1 retransmits the packet set with the test pattern data and the mark “S” to the wireless terminal 2 (step s5 in FIG. 10).

  The wireless terminal 2 receives the packet signal of the test pattern data in the same manner as when the previous test pattern data was received, but this time, the demodulation FFT unit FT2 sets the guard interval time to “1.0 microsecond”. The received packet signal is demodulated by changing (step s6 in FIG. 10).

  The test pattern data demodulated at the guard interval time of “1.0 microsecond” is transmitted to the MAC unit MC2. Then, according to the control of the communication control unit CC2, the MAC unit MC2 newly generates a packet loaded with the test pattern data as return test pattern data, and transmits the packet to the access point 1 via the transmission unit TX2 and the antenna AT2 (FIG. 10 steps s7).

  The access point 1 measures the error rate (# 4) of the return test pattern data when the received packet has a guard interval time of “1.0 microsecond” as in the previous time (step s8 in FIG. 10).

  Here, the measured error rate (# 4) is improved from the error rate (# 3) 0.6 × 10 (minus the fourth power) in the case of the guard interval time of the previous “0.8 microseconds”, for example, It is assumed that it is 1.0 × 10 (minus the fifth power) (step s9 in FIG. 10 is Yes).

  Therefore, the communication control unit CC2 determines that the communication quality is improved if the guard interval time is increased.

  Then, the communication control unit CC1 refers to the table T and sends a command for setting the number “5” for setting the guard interval time to “1.2 microseconds” longer and the mark “S” in the MAC unit MC1. Send to MC1. As a result, a packet in which the number “5” for resetting the guard interval time to “1.2 microseconds” and the mark “S” indicating the test pattern data is set from the access point 1 is generated, and the wireless terminal 2 (step s10 in FIG. 10).

  When the wireless terminal 2 receives this packet, the communication control unit CC2 monitors the signal of the MAC unit MC2, reads the guard interval time setting number “5” and the mark “S”, and uses the guard interval time setting signal. I interpret it as being. (When step s11 of FIG. 10 is Yes).

  Then, the communication control unit CC2 sets the guard interval time to “1.2 microseconds” of the number “5” in the GI setting unit GI2. Further, the communication control unit CC2 transmits a command for mounting “ACK” as a reception response to the data frame df to the MAC unit MC2, and receives the setting change of the guard interval time from the wireless terminal 2 to the access point 1. An “ACK” response notifying that it has waited is transmitted (step s12 in FIG. 10).

  Then, the wireless terminal 2 sets the newly set guard interval time “1.2 microseconds” and waits for the test pattern data to be transmitted from the access point 1.

  When the access point 1 receives the “ACK” response from the wireless terminal 2, the access point 1 transmits a packet loaded with the test pattern data, the command number “5”, and the mark “S” to the wireless terminal 2 (step s13 in FIG. 10). ).

  Then, the wireless terminal 2 transmits data obtained by demodulating the received packet with a guard interval time of “1.2 microseconds” to the access point 1 as return test pattern data (step s14 in FIG. 10).

  Similarly, the access point 1 performs a loopback test with the guard interval time changed, and measures the error rate (# 5) for the return test pattern data (step s8 in FIG. 10).

  For example, when the guard interval time is received at “1.2 microseconds” of “5”, the error rate (# 5) is set to 1.0 × 10 (minus the fifth power) this time. The loopback test is repeated until the error rate (#n) with respect to the latest guard interval time can be regarded as equivalent to the error rate (# n-1) of the previous measurement (when step s9 in FIG. 10 is No and step s15 is Yes).

  In the above description, only the signal of the number “5” and the mark “S” for setting the guard interval time are set from the access point 1, and the test pattern data including the bit pattern is not transmitted. The reason is that the test pattern data used for comparison and verification is a new long bit that requires a transmission time each time the guard interval time is changed if the same data that was sent when the guard interval time was first set is used repeatedly. This is because pattern test pattern data need not be used, and communication time can be shortened.

  That is, the guard interval time setting operation is terminated when the error rate (#n) with respect to the most recently set guard interval time can be regarded as equivalent to the previous error rate (n-1). Then, the access point 1 sets the latest set list number, for example, “5” in the MAC header mh, generates a packet in which message data is mounted in the data frame df, and transmits the packet to the wireless terminal 2.

  Also, if the error rate (# 7) is still improving when the guard interval time is set to “2.0 microseconds” of the longest number “7”, “2.0 microseconds”. The setting operation of the guard interval time is terminated. Then, the access point 1 sets “7” in the MAC header mh, generates a packet in which message data is mounted in the data frame df, and transmits the packet to the wireless terminal 2.

  When the wireless terminal 2 after the end of setting receives message data, the communication control unit CC2 determines that the message data is addressed to the wireless terminal 2 because the mark “S” is not set in the MAC header mh. Then, in the wireless terminal 2, the data demodulated at the guard interval time (“2.0 microseconds if it is the longest”) set when the message data is received is transmitted from the MAC unit MC2 via the terminal interface IF2. , Perform communication to be output to an external personal computer or the like.

  Further, when the wireless terminal 2 returns test pattern data demodulated with a guard interval time of “1.0 microseconds” to the access point 1 and the access point 1 measures the error rate (# 4), When it deteriorates to 1 × 10 (minus the fourth power) (when step s9 in FIG. 10 is No and step s15 is No), the guard interval time is set to be shortened (step in FIG. 10). s16).

  Then, the loopback test is performed in the same manner as when the guard interval time is increased, the guard interval time is set to “0.7 microseconds” of the number “2”, the similar loopback test is performed, and the minimum “0.6 Set the value that gives the best error rate up to "microseconds".

  When the error rate is degraded, the message data is set by setting only the number “3” in the MAC header mh for returning the guard interval time to the default “0.8 microseconds” as a method different from the above method. A data frame df is mounted and a packet of message data is transmitted. The shortest guard interval time may be communicated as a default “0.8 microseconds” (not described in the flowchart of FIG. 10).

  Note that the allowable range for determining whether or not the difference in error rate is equal (for example, (0.4 ± 0.1) × 10 (minus the fourth power)) of the wireless LAN operating environment, device, or system. The error range is appropriately set according to the operation parameter.

  As described above, in the wireless LAN system according to the embodiment of the present invention, the influence of the interference wave due to multipath reflection is prevented by performing the negotiation for setting the guard interval time between the access point and the wireless terminal, and the throughput is further increased. Communication that improves communication quality, such as improving.

  Such a setting of the guard interval time is particularly effective when applied in combination with adjustment of the beam pattern of the antenna. For example, in an inter-LAN bridge that connects two LANs, unnecessary reflection is achieved by using a directional antenna for communication between the access point 1 and the wireless terminal 2 that are connected between the two LANs. Remove waves.

  For example, if you adjust the tilt angle of the directional antenna of the access point to extend the transmission cover area range far, but set the antenna beam so that it does not cover a short distance, generation of unwanted reflected waves, wireless terminals other than desired etc. The received radio waves from other radio stations can be suppressed. Therefore, the combination of the present invention and the antenna beam setting has a great effect of removing undesirable reflected waves and received radio waves, and between the LANs further expanding the wireless communication area between the remote access point and the wireless terminal. A bridge can be realized.

  In the above description, communication between the access point 1 and the wireless terminal 2 has been described as an example. However, wireless communication between two wireless terminals 2 (for example, (# 1) and (# 2)) is performed. The present invention may be applied to an ad hoc mode to be performed.

  In this case, for example, the wireless station that becomes the master may perform the operation of setting the guard interval time by the wireless terminal 2 that transmits the transmission request first becoming the master.

  Further, the guard interval time setting method in the present embodiment may set the guard interval time only for one-way communication between the access point 1 and the wireless terminal 2.

1 is a configuration diagram of a wireless LAN system according to an embodiment of the present invention. The figure which shows the guard interval time of OFDM modulation. The block diagram which shows the functional element of the access point of the wireless LAN system concerning the Example of this invention. The block diagram which shows the functional element of the radio | wireless terminal of the wireless LAN system concerning the Example of this invention. The block diagram which shows the functional element which performs the guard interval time setting of the access point of the wireless LAN system concerning the Example of this invention. The block diagram which shows the functional element which performs the guard interval time setting of the radio | wireless terminal of the wireless LAN system concerning the Example of this invention. The figure of the table which shows one example of the guard interval time in the wireless LAN system concerning the Example of this invention. The figure which shows the packet structure transmitted by wireless LAN. A transmission rate table of packets transmitted by a wireless LAN. 5 is a flowchart showing the operation of the wireless LAN system according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Access point 2 Radio | wireless terminal 3a-3c Building house Ab, Ac The reception delay time G of the reflected wave from a building house, Gx Guard interval time B Symbol time RF1, RF2 Radio | wireless part TX1, TX2 Transmitter part RX1, RX2 Receiver part CC1, CC2 communication control unit MC1, MC2 MAC unit IF1 network interface IF2 terminal interface PR1, PR2 conversion processor FT1, FT2 demodulation FFT unit GI1, GI2 guard interval setting unit T table

Claims (10)

A wireless LAN system comprising a plurality of wireless stations communicating by OFDM,
The first radio station is
First guard interval setting means for transmitting control information for changing the setting of the guard interval time to a second radio station receiving at a preset guard interval time;
A loop test means for transmitting / receiving test pattern data to / from the second wireless station and measuring an error rate of the test pattern data;
The second radio station is
A guard interval time for receiving the control information transmitted from the first radio station and demodulating the received signal by receiving the test pattern data transmitted from the first radio station and sending it back. A wireless LAN system comprising: a second guard interval setting means for setting. The first radio station and the second radio station are:
A plurality of guard interval times, each having the same table with a list number;
The loopback test means of the first wireless station is:
In accordance with a predetermined list number order by collating the table, the first test pattern data is transmitted to the second radio station together with the list number,
The second radio station receives the first test pattern data according to a guard interval time set by checking the table with the list number received by the second guard interval setting means, demodulates the first test pattern data again, and The second test pattern data sent back to the first radio station is received, and the error rate is measured by comparing and comparing the transmitted first test pattern data with the received second test pattern data. Repeat the test by changing the list number,
The first guard interval setting means includes:
Select the guard interval time at which the best error rate was obtained in comparing each error rate measured by the loopback test,
A list number corresponding to the selected guard interval time is set in the control information and transmitted to the second radio station,
The second guard interval setting means of the second radio station is
When the control information is received from the first radio station, a message that sets the guard interval time corresponding to the list number set in the control information and is transmitted from the first radio station to the second radio station The wireless LAN system according to claim 1, wherein the packet is demodulated. The list number is
The corresponding guard interval time is given a list number in ascending order from short to long,
The loopback test means performs the loopback test by further raising the list number when the latest error rate has improved from the previously set default number according to the list number in ascending order from the previous error rate, and the latest error rate is When the error rate has deteriorated from the previous error rate, the list number is lowered and the loopback test is performed.
The first guard interval setting means selects the error rate as the best error rate when the latest error rate becomes the same as the previous error rate,
When the latest error rate is deteriorated from the previous error rate, the previous error rate is selected as the best error rate, and the previous list number is used as the control information for setting the guard interval time in the second radio station. The wireless LAN system according to claim 2, wherein transmission is performed. The first guard interval setting means includes:
Perform the loopback test according to the list number in the ascending order from a preset default list number,
When the latest error rate is worse than the error rate at the time of the default list number, it is determined that the best error rate can be obtained at the guard interval time corresponding to the default list number,
The wireless LAN system according to claim 3, wherein a default list number is transmitted to the second wireless station as the control information for setting a guard interval time. The first radio station is
It also has a directional antenna,
2. The radio according to claim 1, wherein communication is performed with the second radio station by setting a beam coverage area of the directional antenna to a distance in the vicinity of the specific second radio station. LAN system.   The wireless LAN system according to claim 1, wherein the first wireless station is a wireless LAN access point, and the second wireless station is a wireless terminal of the wireless LAN.   The wireless LAN system according to claim 1, wherein the second wireless station is a wireless LAN access point, and the first wireless station is a wireless terminal of the wireless LAN.   The wireless device according to claim 1, wherein the first wireless station is a first wireless terminal of a wireless LAN, and the second wireless station is a second wireless terminal of the wireless LAN. LAN system. A communication control method for a wireless LAN system composed of a plurality of wireless stations communicating by OFDM,
The first radio station and the second radio station are:
Each has the same table with a list number corresponding to each of a plurality of guard interval times,
The first radio station is
A packet composed of the list number and the first test pattern data is generated and transmitted to the second wireless station with reference to the table,
The first test pattern data obtained by demodulating the list number read from the packet received by the second radio station from the first radio station with a guard interval time set by referring to the table is again the first test pattern data. A loop test that receives second test pattern data sent back to one radio station, compares the transmitted first test pattern data with the received second test pattern data, and measures an error rate; Repeatedly changing the list number,
Selecting the guard interval time at which the best error rate was obtained from the measured error rates;
A control is performed to transmit a list number corresponding to the selected guard interval time to the second radio station and set a guard interval time to be demodulated by the second radio station,
The second radio station is
A communication control method for a wireless LAN system, wherein control is performed to demodulate a packet of message data transmitted from the first wireless station at the set guard interval time. The list number is
The corresponding guard interval time is numbered in ascending order from short to long,
The first radio station is
Perform the loop test according to the list number in the ascending order from a preset default number among the list numbers,
When the latest error rate is higher than the previous error rate, further increase the list number and perform the loopback test. When the latest error rate is the same as the previous error rate, the error rate is set to the best error rate. Select as a rate,
When the latest error rate has deteriorated from the previous error rate, the list number is lowered and the loopback test is performed. When the latest error rate is the same as the previous error rate, the error rate is best. And sending the latest list number as control information for setting the guard interval time to the second radio station,
Alternatively, when the latest error rate has deteriorated from the previous error rate, control is performed to set the default list number as a guard interval time in the second radio station. LAN system communication control method.

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