JP2006128791A - Handover control device in radio terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a handover control device in a radio terminal which enables radio LAN equipment to correctly predict area limitation and to activate handover. <P>SOLUTION: The device has a configuration provided with a beacon signal measurement device for receiving each beacon signal of a used channel of each of previously determined access points, taking out beacon information such as the reception level or reception ratio of the beacon signal, and judging the propriety of handover of a radio terminal on the basis of the beacon information; a retry measurement device for measuring retry information such as a retry rate or the number of times of retries during communication on a transmitter side of the radio terminal; and a handover controller for referring to the beacon information from the beacon signal measurement device and the retry information from the retry measurement device, and activating the handover if at least any one of a first condition not more than a first limit value previously determined in the beacon information and a second condition not more than a second limit value previously determined in the retry information is satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a handover control apparatus in which a wireless terminal changes an access point for a network.

As a technology for constructing a wireless LAN, IEEE (Institute of Electrical and Electronics Engineers) 802.11 is known. IEEE 802.11 defines an infrastructure mode in which a wireless LAN terminal can establish a link only with a specific wireless LAN terminal called an AP (Access Point), and an ad hoc mode in which wireless LAN terminals can directly communicate with each other. The operation in which the wireless LAN terminal switches the link destination AP in the infrastructure mode is called handover. The handover activation condition is not defined in IEEE 802.11. In general, a method of determining from the reception rate of beacon signals periodically transmitted by the AP and the reception level of beacon signals is used (see Patent Document 1).
JP 2003-153327 A

  A conventional handover processing procedure using the reception level of the beacon signal will be described with reference to FIG. The receiver 12 receives a packet transmitted from the AP via the antenna 1, and sends a control packet to the handover controller 15 and a data packet to the packet processor 16. The receiver 12 sends the reception level of the beacon signal received from the AP to the beacon signal measuring device 14. Further, the transmitter 13 transmits the data packet from the packet processor 16 and the control system packet from the handover controller 15 to the AP via the antenna 1. The beacon signal measuring device 14 determines whether or not a handover is necessary from the reception level of the beacon signal transmitted from the receiver 12. When the beacon signal measuring device 14 determines that the handover is necessary, the beacon signal measuring device 14 sends a handover request notification to the handover controller 15. Upon receiving the handover request notification, the handover controller 15 gives an AP search request for searching for a handover candidate AP to the transmitter 13. The receiver 12 sends an AP search response from the handover candidate AP to the handover controller 15. When there is a handover candidate AP better than the current AP in the AP search response, the handover controller 15 gives a control system packet including a link establishment request to the transmitter. When the handover candidate AP accepts the link establishment of the wireless LAN terminal, it returns a link establishment response, and the wireless LAN terminal receives the link establishment response, thereby completing the handover.

In IEEE802.11, the transmitting wireless LAN terminal must expect a response (ACK: Acknowledge) from the receiving wireless LAN terminal after transmitting the packet. If no ACK is returned, the wireless LAN terminal on the transmission side determines that the packet has not reached the wireless LAN terminal on the reception side, and tries retransmission (retry) within the range of the maximum number of retries set in advance. If an ACK is not returned even if the maximum number of retries is performed, the wireless LAN terminal on the transmission side discards the packet and tries to transmit the next packet. Since the retry of the maximum number of retries is performed when the packet loss occurs, the increase of the packet loss, that is, the increase of retries. In addition, since one-to-N communication such as multicast or broadcast does not require ACK, no retry occurs.
Technologies for performing voice calls over IP (Internet Protocol) are collectively referred to as VoIP (Voice over IP). Instantaneous packet loss of VoIP packets does not affect call quality. However, continuous packet loss causes degradation of call quality.

  As described above, as a general handover activation condition, a method of determining from the reception rate of the beacon signal periodically transmitted by the AP and the reception level of the beacon signal is used. However, this method has a problem as an activation condition during a call in VoIP. Call quality deteriorates, that is, retry increases before continuous packet loss occurs, but the beacon signal is broadcast and no retry occurs, so the call quality cannot be determined from the beacon signal, It can be said that the area limit cannot be accurately known from the beacon signal. Therefore, AP search must be started at an early stage so as not to go out of the area before handover under any circumstances. However, if the AP search is too early, another AP cannot be searched and the handover fails, and the AP search is repeated again. FIG. 6 shows a system in which AP search is started when the reception level of the beacon signal is less than or equal to the required value D, and handover is successful when the difference between the reception levels of AP1 and AP2 is greater than or equal to the threshold value h. When the wireless LAN terminal moves toward AP2 after establishing a link with AP1, the wireless LAN terminal starts to repeat the AP search from the B1 point and succeeds in the handover at the A point, but the reception level is D or less until the B2 point is exceeded. Therefore, the AP search is repeated. Such repeated AP search operations cause degradation of call quality depending on the AP search time, and become a factor of consuming power and radio bandwidth. There is no guarantee that point A is within the area.

  An object of the present invention is to provide a handover control apparatus in a wireless terminal in which a wireless LAN device can accurately predict an area limit and start a handover.

  In order to solve this problem, the handover control apparatus in the wireless terminal according to the present invention uses a retry in addition to the beacon signal as a handover activation condition.

That is, a handover control apparatus in a wireless terminal according to the present invention is a wireless terminal connected to a network via a wireless line,
Receiving each beacon signal from a predetermined use channel of each access point, extracting beacon information such as the reception level or reception rate of the beacon signal, and determining whether the wireless terminal needs to be handed over from the beacon information A beacon signal measuring instrument;
A retry measuring device for measuring retry information such as a retry rate and the number of retries during communication on the transmitting side of the wireless terminal;
With reference to the beacon information from the beacon signal measuring device and the retry information from the retry measuring device, the first condition that the beacon information is equal to or less than a predetermined first limit value, and the retry A handover controller that activates a handover when at least one of a second condition whose information is equal to or less than a predetermined second limit value is satisfied.

The retry measuring device can be configured to measure retry information such as a retry rate and the number of retries during communication on the transmitting side and the receiving side of the wireless terminal.
The wireless terminal includes a diversity controller connected to a plurality of antennas, and the beacon signal measuring device and the retry measuring device measure the beacon information and the retry information for each antenna of the plurality of antennas. The handover controller further includes a first condition in which all the beacon information for each antenna is equal to or less than the first limit value, and all the retry information for each antenna is the second condition. When at least one of the second conditions equal to or less than the limit value is satisfied, the handover can be activated.
The wireless terminal further includes a call state monitor,
When the call state monitor detects that the wireless terminal is in a call, the handover controller refers to the retry information from the retry measuring device and starts handover.
The handover controller is configured to start handover by referring to the beacon information from the beacon signal measuring device when the call state monitor detects that the wireless terminal is not in a call. can do.

As an example, a method for determining the area limit from the retry rate of a VoIP packet during a call will be described. When the retry rate is p and the maximum number of retries is n, the packet loss rate is obtained by the following equation.
Packet loss rate = 1 − {(1−p) + p · (1−p) + p · p · (1−p) +... + ^Pn · (1−p)}
= P ^{n + 1} (1)
FIG. 7 shows the correlation between the retry rate and the packet loss rate obtained from the above equation (1) when the maximum number of retries n is 3. Assuming that the area limit is a packet loss rate of 5%, the retry rate of the area limit is about 47.3% from the above equation (1).

FIG. 8 shows a wireless LAN composed of two APs (AP1, AP2). When the wireless LAN terminal moves while making a call toward AP2 after establishing a link with AP1, it knows that the retry rate exceeds 47.3% at point A ′ and is an area limit, and starts AP search.
As is clear from the above description, the area limit can be determined from the retry by using the retry as a handover activation condition during a call. As a result, the AP search can be started at the area limit regardless of the environment, and if the areas overlap appropriately, the operation of repeating the AP search does not occur. Consumption and bandwidth consumption can be suppressed. However, since no retry occurs during non-calling, it must be determined from the reception level of the beacon signal during non-calling.

  As apparent from the above description, according to the present invention, it is possible to generate a handover control device that starts a handover by accurately predicting an area limit.

  Examples of the present invention will be described below.

FIG. 1 is a configuration diagram showing an example of a handover control apparatus according to the present invention. FIG. 2 shows an operation flowchart of the handover controller 6. The handover controller 6 determines the handover activation from the beacon information and the retry information. Here, the beacon information includes, for example, a beacon reception level, a beacon reception rate, the number of beacons received, and the retry information includes, for example, a retry rate and the number of retries.
The handover controller 6 sets the beacon signal measuring device 4 and the retry measuring device 5 (S1), and waits for notifications from the measuring devices 4 and 5 (S2). Information necessary for measurement by each measuring instrument 4, 5, for example, a threshold value, a measurement cycle, etc., is given to each measuring instrument 4, 5 by the handover controller 6, or is preset in each measuring instrument 4, 5. There must be. The beacon signal measuring device 4 measures the beacon information obtained from the receiver 2, and the retry measuring device 5 measures the retry information of the transmitter 3. Each of the measuring devices 4 and 5 individually counts the beacon information and the retry information measured for each given period and tests “whether it is a handover request notification” (S3), and at least one of the counting results has a threshold value. When it exceeds (S3 test is YES), the handover controller 6 is notified. Upon receiving this notification, the handover controller 6 sends an AP search request to the transmitter 3 (S4), performs a test of “candidate AP?” (S5), and the test becomes YES and a candidate AP is found. If so, a link establishment operation is attempted (S6).
With this device, for example, the retry measuring device 5 can refer to the retry rate, and the beacon signal measuring device 4 can refer to the beacon signal reception rate, so that the area limit can be predicted from the retry rate of the VoIP packet during a call. When the user goes out of the area during a call, it can be determined from the reception rate of the beacon signal.

FIG. 3 shows an example (second embodiment) of the configuration of the handover control apparatus according to the present invention. The difference from the first embodiment is in the operation of the retry measuring device 5a. The retry measuring device 5a determines not only the retry information of the transmitter 3 but also the retry information of the receiver 2 to activate the handover.
With this device, for example, when handover is performed during downlink communication such as reception of streaming video, if the transmission power of the AP is larger than the wireless LAN terminal, the packet from the AP can be received by the wireless LAN terminal. The ACK from the wireless LAN terminal may not reach the AP. In such a case, the area limit can be predicted from the retry rate of the packet received from the AP.

FIG. 4 shows another example (third embodiment) of the configuration of the handover control apparatus according to the present invention. The difference from the first embodiment is that the diversity technology of the wireless LAN device is taken into consideration. The receiver 2 has beacon information for each of the antennas 1a and 1b, and the transmitter 3 waits for retry information for each of the antennas 1a and 1b. Since each of the measuring devices 4 and 5 switches the antennas 1 a and 1 b by the diversity controller 8, the beacon information or the retry information is measured for each antenna and totaled for each period given to the handover controller 6. When the summation result of both antennas exceeds the threshold value, the handover controller 6 is notified.
With this device, the gain obtained by diversity can be applied to area limit prediction, and can be performed more accurately than area limit prediction.

FIG. 5 is a configuration diagram showing another example (Example 4) of the configuration of the handover control apparatus according to the present invention. . The difference from the first embodiment is that a call state monitor 9 for monitoring the call state is added in order to change the measuring device to be operated according to the call state. During a call, a handover activation is determined from retry information, and during a non-call, a handover activation is determined from beacon information.
With this device, the processing cost and power consumption can be reduced by stopping the operation of one of the measuring devices according to the call state.

  The present invention is used as a handover control apparatus for a wireless LAN (Local Area Network) terminal.

It is a block diagram of the hand-over control apparatus in Example 1 of this invention. It is an operation | movement flowchart of the handover controller used for this invention. It is a block diagram of the hand-over control apparatus in Example 2 of this invention. It is a block diagram of the hand-over control apparatus in Example 3 of this invention. It is a block diagram of the hand-over control apparatus in Example 4 of this invention. It is a figure for demonstrating the range which the repetition operation | movement of a handover starting generate | occur | produces. It is a characteristic view which shows the correlation (maximum retry number 3) of a retry rate and a packet loss rate. It is a figure for demonstrating the area limit prediction (maximum retry number 3) by a retry rate. It is a structural example figure of the conventional handover control apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Antenna 2 Receiver 3 Transmitter 4 Beacon signal measuring device 5, 5a Retry measuring device 6 Handover controller 7 Packet processor 8 Diversity controller 9 Call state monitor

Claims (4)

A wireless terminal connected to a network via a wireless line,
Receiving each beacon signal from a predetermined use channel of each access point, extracting beacon information such as the reception level or reception rate of the beacon signal, and determining whether the wireless terminal needs to be handed over from the beacon information A beacon signal measuring instrument;
A retry measuring device for measuring retry information such as a retry rate during communication on the transmitting side of the wireless terminal and the number of retries;
With reference to the beacon information from the beacon signal measuring device and the retry information from the retry measuring device, the first condition that the beacon information is equal to or less than a predetermined first limit value, and the retry A handover controller that activates a handover when at least one of a second condition in which the information is equal to or less than a predetermined second limit value is satisfied,
A handover control apparatus in a wireless terminal.   The wireless terminal according to claim 1, wherein the retry measuring device is configured to measure retry information such as a retry rate and the number of retries during communication on a transmitting side and a receiving side of the wireless terminal. The handover control apparatus in FIG. The wireless terminal includes a diversity controller connected to a plurality of antennas, and the beacon signal measuring device and the retry measuring device measure the beacon information and the retry information for each antenna of the plurality of antennas. The handover controller further includes a first condition in which all the beacon information for each antenna is equal to or less than the first limit value, and all the retry information for each antenna is the second condition. The handover control apparatus for a radio terminal according to claim 1, wherein the handover control apparatus is configured to activate handover when at least one of a second condition equal to or less than a limit value is satisfied. The wireless terminal further includes a call state monitor,
When the call state monitor detects that the wireless terminal is in a call, the handover controller refers to the retry information from the retry measuring device and starts handover.
The handover controller is configured to start handover by referring to the beacon information from the beacon signal measuring device when the call state monitor detects that the wireless terminal is not in a call. The handover control apparatus in a radio terminal according to claim 1, wherein

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