JP2007143090A - Radio communication terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication terminal capable of accurately selecting an antenna or a directional pattern of which the reception characteristics are is high, even during packet reception in an infrastructure mode, and performing reception by switching to the selected antenna or the directional pattern. <P>SOLUTION: The wireless LAN device 10 communicates with an access point, while selecting and switching a plurality of antennas 11, comprising a MAC header analysis section 15 for analyzing the transmission source address and destination address of a packet, while receiving the packet demodulated from a signal received by an antenna 11, and a receiving status measuring section 16 for selecting an antenna during the reception of a packet, based on a result measuring the receiving status of the antenna, when the MAC header analysis section 15 has determined that the transmission source address is an address that is the access point under connection as well as that the destination address is not own station. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wireless communication terminal that communicates with an access point via an antenna.

  In recent years, wireless LANs are rapidly spreading not only to corporations but also to general households because of the convenience of moving terminals freely. IEEE 802.11b (hereinafter referred to as 11b), IEEE 802.11a (hereinafter referred to as 11a), IEEE 802.11g (hereinafter referred to as 11g) and the like have already been defined as wireless LAN communication standards.

  11b defines the DSSS (Direct Sequence Spread Spectrum) system, 11a defines the OFDM (Orthogonal Frequency Division Multiplexing) system, and 11g supports both of these DSSS and OFDM systems. It is prescribed. At present, products compliant with the 11a and 11g standards, which have high communication speeds, are attracting attention, and products combining 11a / 11b / 11g are becoming widespread.

  In addition, in order to connect a terminal such as a personal computer to a wireless LAN compliant with the above-mentioned standard, generally, a PC card compliant with a standard such as PCMCIA (Personal Computer Memory Card International Association) is used. Many of the wireless LAN products including PC cards employ a so-called selective diversity system in which two or more antennas are built in and communication is performed by switching to an antenna having a high signal strength by a switch. This selection diversity system is widely used in the field of mobile radio communications such as mobile phone devices as well as wireless LANs.

  The conventional diversity selection method in the field of mobile radio communication selects and receives the antenna that received the strongest reception power from among the multiple antennas provided, and the reception power received by the antenna falls below a certain threshold. This is a method of switching and receiving with an antenna having a reception power equal to or higher than a threshold value.

  However, with this method, there is a problem that when the switching occurs only at a specific reception power, or when the reception power of both antennas falls below the threshold, the antennas are continuously switched and reception becomes impossible. It was.

  In the technique disclosed in Patent Document 1, in order to solve the above problem, the threshold value is changed according to the transition of received power, or the threshold value is compared with a fixed value. The switching operation is stopped.

  However, in the case of the antenna switching method using the threshold value as described above, since the selected antenna does not switch during reception, the receiving state cannot be observed for antennas other than the selected antenna. It cannot be said that the reception state of the antenna after the switching is necessarily better than that of the antenna before the switching. Therefore, there is a problem that a sufficient diversity effect cannot be obtained.

Furthermore, even if the reception power of the antenna is strong, it is affected by the effects of multipath fading and interference waves of adjacent channels. That is, even if the reception power is strong, the frequency characteristics in the band are not uniform due to multipath fading, which is one of the main factors that change the transmission characteristics, and a bit error occurs, causing a reception error. Further, when the transmitting station of the adjacent channel is installed nearby, the signal strength in the band increases due to the leakage power of the transmitting station.
Therefore, even when the reception power is strong, it is not always a good reception state, and it can be understood that the reception power alone is not enough to grasp the reception state more accurately.

  In order to solve the problem that a bit error due to multipath signal distortion occurs regardless of the received signal strength, the technique disclosed in Patent Document 2 uses a bit error such as a CRC (Cyclic Redundancy Check) code or a parity code. A detector is used to switch antennas based on information about whether or not bit errors are included.

  The 2.4 GHz band, which is a frequency band used for wireless LANs, is called an ISM band, and is used for microwave ovens and medical devices in addition to wireless communication devices. In addition to the problem that the throughput decreases due to the wireless LAN in recent years, there is a problem of radio wave interference between adjacent groups using the same channel with the spread of wireless LAN. Furthermore, in the 2.4 GHz band, the channels are arranged at intervals of 5 MHz, and the spectrum with the adjacent channel overlaps, so that radio wave interference with the wireless LAN device arranged in the adjacent channel becomes a problem.

  In a wireless LAN, since it is difficult to specify the directivity of an antenna because a terminal moves freely, omnidirectional antennas are often used in the wireless LAN.

  If a directional antenna is used in a wireless LAN, emission of radio waves in unnecessary directions is reduced during transmission, and radio wave interference with other terminals can be mitigated. Furthermore, since radio wave energy can be concentrated and radiated in the direction of the transmitting terminal, the transmission power efficiency can be improved compared to the omnidirectional antenna. Conversely, at the time of reception, reception sensitivity is improved and radio wave interference with other terminals is mitigated. That is, if a directional antenna is used, radio wave interference with other devices or terminals, which has been a problem in the past, can be mitigated.

  By the way, in recent years, variable directivity antennas such as ESPAR antennas that can electronically change directivity have been developed. This variable directivity antenna is attracting attention because it can be reduced in size, power consumption and cost as compared with a conventional phased array antenna, and the directivity can be easily controlled. However, the directivity control method is still in the investigation stage, and there are few examples where the variable directivity antenna is actually used in the wireless LAN.

  In Patent Document 3, as a directivity control method for a variable directivity antenna, a directivity pattern having directivity in one direction out of directivities that the variable directivity antenna can take during reception during a period in which packets are not transmitted and received. Select and direct the directivity pattern to the control circuit to perform directivity scan, measure the quality of the received signal in each directivity pattern with the transceiver circuit, and determine the directivity pattern Yes.

Further, in Patent Document 4, a beacon signal is transmitted using an omni pattern, a beacon signal is received using a rotating sector pattern, and a packet signal is detected by detecting the azimuth angle, reception power, and wireless station ID of the beacon signal. The directivity pattern at the time of transmitting is determined. Further, in the reception flow, the received signal is detected when the variable beam antenna is rotationally scanned and a received signal having a received power equal to or higher than a predetermined threshold is received.
JP-A-8-84104 JP-A-6-303218 JP 2002-353867 A JP 2003-332971 A

  As described above, the conventional technique has been described. However, in the technique disclosed in Patent Document 2, since the antenna is not switched during reception, the reception state cannot be observed with an antenna other than the selected antenna. There is a problem that cannot be obtained.

  Conventionally, a wireless LAN device does not perform an antenna selection operation during packet reception, but performs an antenna selection operation by determining the reception power of two antennas for each packet using a packet preamble signal. The reception period of the short preamble signal in the OFDM system used in / 11g is as short as 8 μsec, and within this period, AGC processing, correlation detection processing, synchronization processing, and rough adjustment of frequency offset must be performed. Therefore, if the antenna selection operation is performed for each packet as in the conventional case, these processes must be performed in a short period of time, and the accuracy of these processes deteriorates, resulting in a packet detection error and throughput. There was a problem of causing a decrease. Thus, since switching processing must be performed in a short time even with two antennas, it is difficult to cope with an increase in the number of two or more antennas.

  By the way, in the wireless LAN infrastructure mode, a basic access point and a plurality of terminals constitute a network. Since each terminal communicates only with the access point of the connected own station, the terminal should perform the antenna selection operation only for the transmission packet from the connected access point of the own station. In addition, even if each terminal receives a signal from another station even if it is a signal from an access point, it is not always necessary to process the signal from the other station.

  Moreover, in the technique disclosed in Patent Document 3, it is usually unpredictable when data is transmitted from another terminal, and thus there is a problem that performing a directional scan operation leads to a decrease in throughput. Arise. Furthermore, there is a problem that transmission / reception of packets that are not directly related to communication for transferring directional data when performing directional scanning causes an increase in power consumption.

  In the technique disclosed in Patent Document 4, the short preamble signal in the OFDM scheme used in 11a and 11g is as short as 8 μsec, and automatic gain control, correlation detection, synchronization processing, and frequency offset are within this period. Coarse adjustments must be made. Furthermore, when performing rotational scanning while waiting for reception signal detection, it takes time until detection of the reception signal, but since it is necessary to perform these processes in a short period of time, the accuracy of these processes deteriorates, As a result, there has been a problem that a packet detection error is caused and throughput is lowered.

  Therefore, in order to fully demonstrate the effects of the variable directivity antenna, it is possible to switch to all directivity patterns in a state where processing for detecting a packet is ensured without reducing the throughput, and the reception state is It is desirable to switch to the best antenna directivity.

  In view of such a problem, the present invention is a wireless communication terminal capable of accurately selecting an antenna or directivity pattern having good reception characteristics even during packet reception and switching to the selected antenna or directivity pattern in the infrastructure mode. The purpose is to provide.

The wireless communication terminal of the present invention is a wireless communication terminal that communicates with an access point while selecting and switching a plurality of antennas, and the source address of the packet during reception of a packet demodulated from a signal received by the antenna And the analysis unit that analyzes the destination address, and the analysis unit determines that the transmission source address is the address of the access point that is connected and the destination address is not the local station, And a reception state measurement unit that selects the antenna during reception of the packet based on the measurement result.
With this configuration, if it is determined that the source address is the address of the connected access point and the destination address is not the local station, antenna selection is performed during packet reception based on the result of measuring the antenna reception state. Therefore, unnecessary antenna switching can be prevented, and an antenna having good reception characteristics can be accurately selected even during packet reception, and switching to the selected antenna can be performed.

In addition, the wireless communication terminal of the present invention includes a reception time calculation unit that calculates the reception time of one of the packets, and the reception state measurement unit selects the antenna when the reception time is a predetermined threshold value or more. It has the structure to do.
With this configuration, if the threshold value is set large, it is possible to take time to measure the reception state, so that an antenna with good reception characteristics can be selected with higher accuracy.

In addition, the reception state measurement unit of the wireless communication terminal of the present invention has a configuration in which the antenna is selected at a timing just before the end of reception in the reception time.
With this configuration, it is possible to more accurately select an antenna with good reception characteristics by delaying the timing of the antenna selection operation and measuring the reception state of each antenna immediately before receiving the next packet of the next station as much as possible.

In addition, the reception state measurement unit of the wireless communication terminal of the present invention calculates a frequency flat characteristic corresponding to each antenna when selecting the antenna, and among the calculated discreteness of each frequency flat characteristic , An antenna having a frequency flatness characteristic having the smallest discreteness is selected.
With this configuration, the discreteness of each frequency flat characteristic can be measured, and an antenna having good reception characteristics that is less affected by multipath fading and adjacent channel interference waves can be selected and switched.

In addition, the reception state measurement unit of the wireless communication terminal of the present invention calculates a frequency flat characteristic corresponding to each antenna when selecting the antenna, and all the discrete degrees of the calculated frequency flat characteristics are all When the frequency is equal to or smaller than the predetermined threshold, the antenna having the largest reception power is selected.
With this configuration, when the frequency flatness characteristics are all below a predetermined threshold, the antenna with the highest received power is selected. Since it is considered that the influence of the interference wave of the adjacent channel is small, an antenna having good reception characteristics can be selected with high accuracy.

The wireless communication terminal of the present invention is a wireless communication terminal that communicates with an access point while selecting and switching the directivity of a variable directivity antenna, and is receiving a packet demodulated from a signal received by the variable directivity antenna The analysis unit that analyzes the source address and the destination address of the packet, and the analysis unit determines that the source address is the address of the connected access point and the destination address is not the local station A reception state measuring unit that selects directivity of the variable directional antenna during reception of the packet based on a result of measuring the reception state of the variable directional antenna.
With this configuration, in the infrastructure mode, it is possible to accurately select a directivity pattern with good reception characteristics even during packet reception, and switch to the selected directivity pattern for reception.

In addition, the wireless communication terminal of the present invention includes a reception time calculation unit that calculates the reception time of one of the packets, and the reception state measurement unit has the variable directional antenna when the reception time is equal to or greater than a predetermined threshold. The directivity is selected.
With this configuration, if the threshold value is set large, it is possible to take time to measure the reception state, so that an antenna with good reception characteristics can be selected with higher accuracy.

In addition, the reception state measurement unit of the wireless communication terminal of the present invention has a configuration in which the directivity of the variable directivity antenna is selected at a timing just before the end of reception in the reception time.
With this configuration, a directivity pattern with good reception characteristics can be selected with higher accuracy by measuring the reception state of each directivity pattern immediately before receiving the next packet of the next station as much as possible.

In addition, the wireless communication terminal according to the present invention selects a directivity of the variable directivity antenna and switches the packet, and when a response packet to the transmitted packet is not returned even if the packet is transmitted, the packet for retransmission is predetermined. It has a configuration in which the directivity of the variable directivity antenna is switched to omnidirectional when transmitted a number of times.
With this configuration, for example, when the location of the wireless communication terminal is suddenly moved and radio waves cannot be received, the antenna directivity is switched to non-directional so that packets can be received from all directions. By doing so, the antenna directivity selection operation can be performed again.

In addition, the radio communication terminal of the present invention, after selecting and switching the directivity of the variable directivity antenna, when the beacon packet is not received at an allowable time that determines an allowable beacon packet reception interval, It has a configuration for switching the directivity of the variable directivity antenna to non-directional.
With this configuration, for example, when the location of the wireless communication terminal is suddenly moved and radio waves cannot be received, the antenna directivity is switched to non-directional so that packets can be received from all directions. By doing so, the antenna directivity selection operation can be performed again.

  As described above, the present invention provides a wireless communication terminal capable of accurately selecting an antenna or directivity pattern having good reception characteristics even during packet reception and switching to the selected antenna or directivity pattern for reception.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  1 and 3 are diagrams showing a configuration example of a wireless LAN device according to an embodiment of a wireless communication terminal of the present invention. Only functional units related to antenna switching are shown, and functional units related to reception and transmission are omitted. The wireless LAN device according to the embodiment of the wireless communication terminal of the present invention communicates with one basic access point in the wireless LAN infrastructure mode.

  Example 1 according to the embodiment of the present invention will be described below.

  1 includes a plurality of antennas 11, an antenna switching unit 12 that switches antennas 11, an RF unit 13 that receives an RF signal from the antenna 11, a demodulation unit 14 that demodulates the RF signal, and a demodulator of the RF signal. The MAC header analysis unit 15 that analyzes a MAC (Media Access Control) header included in the obtained packet and the reception state measurement unit 16 that measures the reception state of the antenna 11 are configured.

  The wireless LAN device 10 has two antennas 11, but may have three or more. The reception state measurement unit 16 may be provided in the demodulation unit 14. The packet obtained by demodulating the RF signal is, for example, compliant with IEEE 802.11.

  Here, FIG. 2 shows a basic format of a MAC frame in IEEE 802.11. Regarding the MAC header of the data frame transmitted from the access point, normally, Address 1 is the destination MAC address, Address 2 is the BSSID, and Address 3 is the source MAC address, that is, the MAC address of the access point.

  Hereinafter, the operation of the wireless LAN device 10 will be described with reference to FIGS. 1 and 2.

  First, the MAC header analysis unit 15 analyzes the MAC header during reception of a packet obtained by demodulating the RF signal.

  Here, the MAC header analysis unit 15 determines whether or not the destination MAC address is addressed to another terminal that is not its own station, and the transmission source MAC address is the MAC address of the connected access point.

  Note that when the destination MAC address is the MAC address of the local station, that is, the wireless LAN device 10, the wireless LAN device 10 does not perform the antenna selection operation in order to process the body part information other than the MAC header in the received packet. If the source MAC address is an access point of another station, communication with the access point of the other station is not necessary in the embodiment of the present invention, and therefore the antenna selection operation is not performed.

  Next, when the MAC header analysis unit 15 determines that the destination MAC address is addressed to another terminal and the transmission source MAC address is the MAC address of the connected access point, the reception state measurement unit 16 An antenna selection operation is performed, the reception state of the antenna 11 is measured to determine the antenna with the best reception state, and the antenna switching unit 12 switches to the best antenna when the reception state measurement unit 16 determines.

  Since the wireless LAN device 10 performs an antenna selection operation during packet reception, if the best antenna is determined based on the received power, it is considered that there is some variation depending on the determined symbol. The measurement unit 16 may measure the reception state of the antenna 11 by averaging the reception power of the reception signal at each antenna, or may measure the reception state of the antenna 11 by calculating a frequency flat characteristic. .

  Example 2 according to the embodiment of the present invention will be described below.

  The wireless LAN device 20 illustrated in FIG. 3 includes a plurality of antennas 11, an antenna switching unit 12 that switches the antennas 11, an RF unit 13 that receives an RF signal from the antennas 11, a demodulation unit 14 that demodulates the RF signal, and a demodulator of the RF signal. A MAC header analysis unit 15 that analyzes a MAC (Media Access Control) header included in the obtained packet, a reception state measurement unit 26 that measures the reception state of the antenna 11, and reception that calculates the reception time of one packet It is comprised by the time calculation part 27.

  Of the components constituting the wireless LAN device 20, the same components as those constituting the wireless LAN device 10 described in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  Hereinafter, the operation of the wireless LAN device 20 will be described with reference to the drawings.

  First, the MAC header analysis unit 15 analyzes the MAC header during reception of a packet obtained by demodulating the RF signal.

  Here, the MAC header analysis unit 15 determines whether the destination MAC address is addressed to another terminal and the transmission source MAC address is the MAC address of the connected access point.

  Next, when the MAC header analysis unit 15 determines that the destination MAC address is addressed to another terminal and the transmission source MAC address is the MAC address of the connected access point, the reception time calculation unit 27 The reception time per packet is calculated from the data size information of the received packet and the transmission rate. The reception state measurement unit 26 performs an antenna selection operation when the reception time calculated by the reception time calculation unit 27 is equal to or greater than a predetermined threshold.

  Here, a diagram for explaining the reception time of the received packet is shown in FIG. FIG. 4 illustrates an AP that is an access point, a wireless LAN device 20, and a STA that is a wireless terminal that communicate in compliance with 11a in a wireless LAN infrastructure mode.

  First, the AP transmits a packet for 28 μsec to the STA, and then the STA transmits a packet for 28 μsec to the AP, and then the AP transmits a packet for 248 μsec to the STA, and then the STA A packet for 28 μsec is transmitted to the AP, and then the AP transmits a packet for 100 μsec to the wireless LAN device 20.

  By the way, the operation for determining whether or not to perform the antenna selection operation takes time including the preamble processing time, the signal field processing time, the MAC header analysis time, and the determination time of the antenna selection operation. Assuming that two symbols are used per antenna for the antenna selection operation, a threshold for determining whether or not to perform the antenna selection operation is set to 40 μsec in the wireless LAN device 20.

  That is, the reception state measurement unit 26 of the wireless LAN device 20 performs the antenna selection operation if the packet reception time is 40 μsec or more, and does not perform the antenna selection operation if it is less than 40 μsec. Although the threshold is set to 40 μsec, of course, the threshold can be set to an arbitrary time.

  The packet reception time may be the total packet reception time or the remaining time after the MAC header analysis. When the threshold is set to 40 μsec in the wireless LAN device 20, the packet for which the wireless LAN device 20 performs the antenna selection operation among the packets shown in FIG. 4 is the time when the packet for 248 μsec, which is filled with diagonal lines, is received.

  FIG. 5 is a diagram illustrating an example of the antenna selection operation based on the packet reception time in the wireless LAN device 20.

  FIG. 5A shows received packets in order of processing time when the wireless LAN device 20 performs an antenna selection operation. In FIG. 5B, the antenna selection operation is performed immediately after the wireless LAN device 20 determines that the packet is the target of the antenna selection operation. On the other hand, in FIG. 5C, the wireless LAN device 20 determines that the packet is the target of the antenna selection operation, and performs the antenna selection operation near the end of reception of the packet being received.

  Since the wireless LAN device 20 can be freely moved while communicating, the antenna having good reception characteristics changes every moment. Therefore, as shown in FIG. 5C, the timing of the antenna selection operation is delayed, and the reception state measurement unit 26 measures the reception state of each antenna immediately before receiving the next packet of the own station as much as possible. The LAN device 20 can select and switch an antenna having good reception characteristics with higher accuracy and can receive signals.

  In addition, since the wireless LAN device 20 performs an antenna selection operation during reception of a packet instead of a preamble, a slight variation occurs for each symbol when determining reception power. It is desirable to use each symbol on average. Therefore, when sufficient judgment time for the antenna selection operation can be obtained according to the reception time of the packet, the time required for the antenna selection operation can be increased by increasing the threshold value, or the judgment time for the antenna selection operation cannot be sufficiently obtained. In some cases, the threshold can be reduced so that the antenna selection operation is not performed.

  In addition, under the influence of multipath fading, the frequency characteristics in the reception band are not uniform. For example, in the case of a multicarrier modulation scheme such as OFDM, the reception intensity is not constant for each subcarrier.

  Therefore, the reception state measurement unit 26 calculates a frequency flat characteristic when performing an antenna selection operation. FIG. 6 shows an example of the calculation result of the frequency flatness characteristic represented by a 64 point FFT (Fast Fourier Transform) symbol for each antenna when the frequency flatness characteristic is used when determining the antenna selection operation in the wireless LAN device 20. FIG.

  From this result, it can be seen that the antenna B has a smaller spectral power discreteness (variation) for each subcarrier than the antenna A, and is less affected by multipath fading. Therefore, the reception state measurement unit 26 selects the antenna B having a small discrete degree.

  Here, as for the method of calculating the variation of the spectral power, the difference between the maximum power and the minimum power of the subcarriers may be set as a discrete degree as shown in FIG. 6, or the average power of all the subcarriers and the subcarriers may be calculated. A difference from the received power is obtained, and a value obtained by adding the obtained differences may be used as the discrete degree.

  Therefore, the wireless LAN device 20 uses the frequency flatness characteristic to measure the discreteness of the reception intensity for each subcarrier, and has a reception characteristic that is less affected by multipath fading and interference from adjacent channels. A good antenna can be selected and switched.

  Also, in each antenna, when the degree of spectral power discreteness for each subcarrier is less than or equal to a predetermined threshold, the antenna is switched to one having higher reception power.

  Accordingly, since the wireless LAN device 20 selects the antenna having the larger reception power when the frequency flatness characteristic is equal to or smaller than the predetermined threshold, when any antenna has a small degree of discreteness of the frequency flatness characteristic, multipath fading is performed. Since the influence and the influence of the interference wave of the adjacent channel are considered to be small, it is also useful to determine the antenna selection based on the reception power. Further, according to the present invention, by using the frequency flatness characteristic and the reception power in combination, it is possible to select an antenna having better reception characteristics and switch and receive signals.

  7 and 8 are diagrams showing a configuration example of the wireless LAN apparatus according to the embodiment of the wireless communication terminal of the present invention. Only functional units related to antenna directivity switching are shown, and functional units related to reception and transmission are omitted. The wireless LAN device according to the embodiment of the wireless communication terminal of the present invention communicates with one basic access point in the wireless LAN infrastructure mode.

  Example 3 according to the embodiment of the present invention will be described below.

  The wireless LAN device 30 illustrated in FIG. 7 includes a variable directivity antenna 31, an antenna directivity control unit 32 that controls the directivity of the variable directivity antenna 31, an RF unit 33 that receives an RF signal from the variable directivity antenna 31, The demodulator 34 that demodulates the RF signal, the MAC header analyzer 35 that analyzes the MAC (Media Access Control) header included in the packet obtained by demodulating the RF signal, and the reception state of the variable directivity antenna 31 are measured. The reception state measuring unit 36 is configured.

  Although one variable directivity antenna 31 is shown in the figure, a plurality of variable directivity antennas 31 may be used and an antenna diversity system may be adopted. The reception state measurement unit 36 may be provided in the demodulation unit 34. The packet obtained by demodulating the RF signal is, for example, compliant with IEEE 802.11.

  Hereinafter, the operation of the wireless LAN device 30 will be described with reference to FIGS. 7 and 2.

  First, the MAC header analysis unit 35 analyzes the MAC header during reception of a packet obtained by demodulating the RF signal.

  Here, the MAC header analysis unit 35 determines whether the destination MAC address is addressed to another terminal that is not its own station, and the transmission source MAC address is the MAC address of the connected access point.

  In addition, when the destination MAC address is the MAC address of the local station, that is, the wireless LAN device 30, the wireless LAN device 30 does not perform the antenna selection operation in order to process the body part information other than the MAC header in the received packet. If the source MAC address is an access point of another station, communication with the access point of the other station is not necessary in the embodiment of the present invention, and therefore the antenna selection operation is not performed.

  Next, when the MAC header analysis unit 35 determines that the destination MAC address is addressed to another terminal and the transmission source MAC address is the MAC address of the connected access point, the reception state measurement unit 36 The antenna directivity selection operation is performed to measure the reception state of the variable directivity antenna 31, and the antenna directivity control unit 32 switches the directivity pattern based on the result measured by the reception state measurement unit 36, and receives Switch to the best directivity in the state.

  In general, the reception state measurement unit 36 averages the power of the reception signal in each directivity, but other physical layer parameters such as frequency flatness characteristics may be calculated. Of course, the directivity of the antenna is determined when it is determined that the frame does not need to be output to the upper layer by using a broadcast frame such as a beacon packet that does not necessarily need to be output to the upper layer every time. A selection operation may be performed.

  In addition, when the terminal is turned on or when the radio wave from the access point is lost, it is necessary to execute the antenna directivity selection operation or make the antenna directivity non-directional regardless of the frame determination operation.

  Example 4 according to the embodiment of the present invention will be described below.

  8 includes a variable directivity antenna 31, an antenna directivity control unit 32 that controls the directivity of the variable directivity antenna 31, an RF unit 33 that receives an RF signal from the variable directivity antenna 31, A demodulator 34 that demodulates the RF signal, a MAC header analyzer 35 that analyzes a MAC (Media Access Control) header included in the packet obtained by demodulating the RF signal, and a receiver that measures the reception state of the variable directivity antenna 31 The state measuring unit 46 and a reception time calculating unit 47 that calculates the reception time of one packet are configured.

  Of the components constituting the wireless LAN device 40, the same components as those constituting the wireless LAN device 30 described in the third embodiment are denoted by the same reference numerals, and description thereof is omitted.

  Hereinafter, the operation of the wireless LAN device 40 will be described with reference to the drawings.

  First, the MAC header analysis unit 15 analyzes the MAC header during reception of a packet obtained by demodulating the RF signal.

  Here, the MAC header analysis unit 15 determines whether the destination MAC address is addressed to another terminal and the transmission source MAC address is the MAC address of the connected access point.

  Next, when the MAC header analysis unit 15 determines that the destination MAC address is addressed to another terminal and the transmission source MAC address is the MAC address of the connected access point, the reception time calculation unit 47 The reception time per packet is calculated from the data size information of the received packet and the transmission rate.

  The reception state measurement unit 46 performs an antenna selection operation when the reception time calculated by the reception time calculation unit 47 is equal to or greater than a predetermined threshold, measures the reception state, and the antenna directivity control unit 32 receives the reception state measurement unit 46. The directivity pattern is switched based on the result measured by the above, and the directivity is switched to the best directivity. In general, the reception state measurement unit 46 averages the power of the reception signal in each directivity, but other physical layer parameters such as frequency flatness characteristics may be calculated.

  Here, in order to explain the presence / absence of the antenna directivity selection operation according to the packet reception time in IEEE802.11a in the fourth embodiment, FIG. 4 is a diagram for explaining the reception time of the received packet. FIG. 4 illustrates an AP that is an access point, a wireless LAN device 20, and a STA that is a wireless terminal that communicate in compliance with 11a in a wireless LAN infrastructure mode.

  As an example, the variable directivity antenna 31 has four directivities, and when the reception time is short, the antenna directivity selection operation is not performed.

  First, the AP transmits a packet for 28 μsec to the STA, and then the STA transmits a packet for 28 μsec to the AP, and then the AP transmits a packet for 248 μsec to the STA, and then the STA A packet for 28 μsec is transmitted to the AP, and then the AP transmits a packet for 100 μsec to the wireless LAN device 40.

  By the way, the operation for determining whether or not to perform the antenna directivity selection operation requires time including the preamble processing time, the signal field processing time, the MAC header analysis time, and the antenna directivity determination time. It becomes. Assuming that two symbols are used per antenna for the antenna directivity selection operation, a threshold for determining whether or not to perform the antenna directivity selection operation is set to 56 μsec and to the wireless LAN device 40.

  That is, the reception state measurement unit 46 of the wireless LAN device 40 performs the antenna directivity selection operation if the packet reception time is 56 μsec or longer, and does not perform the antenna directivity selection operation if it is less than 56 μsec. Although the threshold value is set to 56 μsec, of course, the threshold value can be set to an arbitrary time.

  The packet reception time may be the total packet reception time or the remaining time after the MAC header analysis. When the threshold is set to 56 μsec and addressed to the wireless LAN device 40, the packet for which the wireless LAN device 40 performs the antenna directivity selection operation among the packets illustrated in FIG. 4 is filled in with diagonal lines illustrated in FIG. 4. Packet.

  FIG. 9 is a diagram illustrating an example of the antenna selection operation based on the packet reception time in the wireless LAN device 40, and is a diagram illustrating an example of the case where the variable directivity antenna 31 has four directivities.

  The packet shown in FIG. 9A is a received packet that is a target for performing antenna directivity selection operation. In FIG. 9B, the antenna directivity selection operation is performed immediately after the wireless LAN device 40 determines that the packet is a target packet for performing the antenna directivity selection operation based on the MAC header. On the other hand, in FIG. 9C, the wireless LAN device 40 performs the antenna directivity selection operation near the end of reception of the packet being received.

  In addition, since the wireless LAN device 40 can be freely moved while communicating, the antenna having good reception characteristics changes every moment. Therefore, as shown in FIG. 9C, the timing of the antenna directivity selection operation is delayed, and the reception state measurement unit 46 measures the state of each directivity pattern immediately before receiving the next packet of its own station as much as possible. Thus, the wireless LAN device 40 can select and switch the directivity pattern having good reception characteristics with higher accuracy and can receive the pattern.

  Further, since the wireless LAN device 40 performs an antenna directivity selection operation during reception of a packet instead of a preamble, a slight variation occurs for each symbol when determining reception power. Is preferably used by averaging each symbol of the received power. Therefore, if the determination time of antenna directivity selection operation is sufficient depending on the reception time of the packet, the time required for antenna directivity selection operation can be increased by increasing the threshold, or the antenna directivity selection operation can be performed. If this determination time is not sufficient, the threshold value can be reduced so that the antenna selection operation is not performed.

  If the packet reception time is short and the omnidirectional determination operation cannot be sufficiently performed, the wireless LAN device 40 stops performing the antenna directivity selection operation, shortens the time, or reduces the time to two or more packets. You may make it perform determination operation of each directivity across.

  Note that, after the antenna directivity selection operation is performed to determine the directivity, the wireless LAN device 40 repeatedly retransmits the transmission packet when the response packet from the transmission destination is not returned even if the packet is transmitted. If the threshold for the number of retransmissions is set to 3 in the wireless LAN device 40, the wireless LAN device 40 switches the antenna directivity to omnidirectional when the retransmission is performed 3 times. For example, when the location of the wireless LAN device 40 is suddenly moved and radio waves cannot be received, the antenna directivity is switched to non-directional so that packets can be received from all directions. The antenna directivity selection operation can be performed again.

  When beacon packets are transmitted from the access point at 100 msec intervals, it is assumed that the wireless LAN device 40 determines the directivity by performing an antenna directivity selection operation. When the allowable time for determining the allowable beacon packet reception interval is set to 150 msec in the wireless LAN device 40, the wireless LAN device 40 normally does not receive a beacon packet received at an interval of about 100 msec even if 150 msec or more elapses In some cases, the antenna directivity is switched to non-directional. For example, when the location of the wireless LAN device 40 is suddenly moved and radio waves cannot be received, the antenna directivity is switched to non-directional so that packets can be received from all directions. The antenna directivity selection operation can be performed again.

  As described above, the present invention has the effect of accurately selecting an antenna or directivity pattern with good reception characteristics even during packet reception, and switching to the selected antenna or directivity pattern for reception. This is useful as a wireless communication terminal having a conductive antenna.

1 is a diagram illustrating a configuration example of a wireless LAN device according to a first embodiment. The figure which shows the basic format of the MAC frame in IEEE802.11. FIG. 3 is a diagram illustrating a configuration example of a wireless LAN device according to a second embodiment. The figure for explaining the reception time of the received packet The figure which shows an example of the antenna selection operation | movement by the reception time of a packet The figure which shows an example of the calculation result of the frequency flat characteristic in each antenna FIG. 9 is a diagram illustrating a configuration example of a wireless LAN device according to a third embodiment. The figure which shows the structural example of the wireless LAN apparatus in Example 4. The figure which shows an example of the antenna selection operation | movement by the reception time of the packet in a wireless LAN apparatus

Explanation of symbols

10, 20, 30, 40 Wireless LAN device 11 Antenna 12 Antenna switching unit 13, 33 RF unit 14, 34 Demodulation unit 15, 35 MAC header analysis unit 16, 26, 36, 46 Reception state measurement unit 27, 47 Reception time calculation Unit 31 Variable directivity antenna 32 Antenna directivity control unit

Claims (10)

A wireless communication terminal that communicates with an access point while selecting and switching between a plurality of antennas,
An analysis unit that analyzes a source address and a destination address of the packet during reception of a packet demodulated from a signal received by the antenna;
When the analysis unit determines that the source address is the address of the connected access point and the destination address is not its own station, the analysis unit determines the packet based on the result of measuring the reception state of the antenna. A wireless communication terminal comprising: a reception state measurement unit that selects the antenna during reception. A reception time calculation unit for calculating the reception time of one of the packets;
The radio communication terminal according to claim 1, wherein the reception state measurement unit selects the antenna when the reception time is equal to or greater than a predetermined threshold.   The wireless communication terminal according to claim 2, wherein the reception state measurement unit selects the antenna at a timing just before the end of reception in the reception time.   The reception state measurement unit calculates a frequency flat characteristic corresponding to each antenna when selecting the antenna, and among the calculated discrete degrees of the frequency flat characteristic, the frequency flat characteristic having the smallest discrete degree The radio communication terminal according to any one of claims 1 to 3, wherein the antenna is selected.   The reception state measurement unit calculates a frequency flat characteristic corresponding to each antenna when selecting the antenna, and when the calculated discreteness of each frequency flat characteristic is less than or equal to a predetermined threshold, The radio communication terminal according to any one of claims 1 to 4, wherein the antenna having the largest is selected. A wireless communication terminal that communicates with an access point while selecting and switching the directivity of a variable directional antenna,
An analysis unit that analyzes a source address and a destination address of the packet during reception of a packet demodulated from a signal received by the variable directivity antenna;
When the analysis unit determines that the source address is the address of the connected access point and the destination address is not its own station, based on the result of measuring the reception state of the variable directivity antenna A wireless communication terminal comprising: a reception state measurement unit that selects directivity of the variable directivity antenna during reception of the packet. A reception time calculation unit for calculating the reception time of one of the packets;
The radio communication terminal according to claim 6, wherein the reception state measurement unit selects the directivity of the variable directivity antenna when the reception time is equal to or greater than a predetermined threshold.   The radio communication terminal according to claim 7, wherein the reception state measurement unit selects the directivity of the variable directivity antenna at a timing just before the end of reception in the reception time.   After selecting and switching the directivity of the variable directivity antenna, if a response packet to the transmitted packet is not returned even if the packet is transmitted, when the packet for retransmission is transmitted a predetermined number of times, the variable directivity antenna The radio communication terminal according to any one of claims 6 to 8, wherein directivity is switched to non-directivity.   After selecting and switching the directivity of the variable directional antenna, if the beacon packet is not received within the allowable time that determines the reception interval of the allowable beacon packet, the directivity of the variable directional antenna is omnidirectional The wireless communication terminal according to any one of claims 6 to 8, wherein the wireless communication terminal is switched to a wireless connection.

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