1. Field of the Invention
The present invention relates to a terminal station having a handover function and a base station, configuring a mobile communication system.
2. Description of the Related Art
Researchers have actively studied a high-speed mobile station using wireless local area network (wireless LAN) technologies. They have particularly focused on a technology to implement high-speed, accurate, and seamless handover in a situation that the mobile station is moving.
Japanese Patent Application Laid-open No. 2003-318804, for example, discloses a radio-communication control method of preventing occurrence of call breaks in a situation a mobile station and a base station are connected to each other via radio. In the radio-communication control method, the mobile station re-transmits control data to the base station depending on quality of downlink communications in a direction from the base station to the mobile station. More particularly, when the mobile station detects deterioration of the downlink communications, the mobile station adjusts parameters concerning re-transmission of the control data, and re-transmits the control data based on the adjusted parameters. The parameters includes number of re-transmissions, interval between the re-transmissions, and electric-power level at which the control data is re-transmitted.
Japanese Patent Application Laid-open No. 2005-323034 discloses a handover method of implementing effective radio communications. More particularly, the terminal station (mobile station) transmits a disconnect-request signal to the current base station, to which the terminal station is currently being connected, to perform handover. The number of re-transmissions of the disconnect-request signal is set to a level lower than usual. Thereby, it takes shorter time from detection of a next base station to which the terminal station is to be connected to start of connecting process, which shortens data break time due to handover.
In the conventional technologies disclosed in Japanese Patent Application Laid-open No. 2003-318804 and Japanese Patent Application Laid-open No. 2005-323034, however, the terminal station determines whether the re-connecting process or the handover process is to be performed based on an electric-power level of signals that is received from the base station solely. If the electric-power level decreases accidentally due to fluctuation of the electric power of signals received from the base station when the terminal station is inside a coverage area of the base station, there is possibility that the terminal station misunderstands that the communication quality deteriorates and determines that handover is to be performed in an unnecessary situation.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to an aspect of the present invention, there is provided a terminal station that makes up a radio communication system with a base station. The terminal station includes an uplink quality information collecting unit that transmits, when there is no uplink data transmission from the terminal station for a predetermined time, dummy data to a base station that is currently connected to the terminal station, and collects uplink-quality information that is generated by transmitting the dummy data to the base station and a handover determining unit that determines whether to perform a handover based on the uplink-quality information collected by the uplink quality information collecting unit.
Furthermore, according to another aspect of the present invention, there is provided a terminal station that makes up a radio communication system with a plurality of base stations. The terminal station includes an uplink quality information collecting unit that periodically transmits dummy data to a base station that a base station currently connected to the terminal station, and collects uplink-quality information that is generated by transmitting the dummy data to the base station and a handover determining unit that determines whether to perform a handover based on the uplink-quality information collected by the uplink quality information collecting unit.
Moreover, according to still another aspect of the present invention, there is provided a base station that makes up a radio communication system with a terminal station. The base station includes a downlink quality information collecting unit that transmits, when there is no downlink data transmission for a predetermined time, dummy data to a terminal station that is currently connected to the base station, and collects downlink-quality information that is generated by transmitting the dummy data to the terminal station and an information transmitting unit that transmits the downlink-quality information collected by the downlink quality information collecting unit to the terminal station, based on which the terminal station determines whether to perform a handover.
Furthermore, according to still another aspect of the present invention, there is provided a base station that makes up a radio communication system with a terminal station. The base station includes a downlink quality information collecting unit that periodically transmits dummy data to a terminal station that is currently connected to the base station, and collects downlink-quality information that is generated by transmitting the dummy data to the terminal station and an information transmitting unit that transmits the downlink-quality information collected by the downlink quality information collecting unit to the terminal station, based on which the terminal station determines whether to perform a handover.
Moreover, according to still another aspect of the present invention, there is provided a radio communication system comprising a terminal station and a base station. The terminal station includes an uplink quality information collecting unit that transmits, when there is no uplink data transmission from the terminal station for a predetermined time, dummy data to a base station that is currently connected to the terminal station, and collects uplink-quality information that is generated by transmitting the dummy data to the base station and a handover determining unit that determines whether to perform a handover based on the uplink-quality information collected by the uplink quality information collecting unit. The base station includes a downlink quality information collecting unit that transmits, when there is no downlink data transmission for a predetermined time, dummy data to a terminal station that is currently connected to the base station, and collects downlink-quality information that is generated by transmitting the dummy data to the terminal station and an information transmitting unit that transmits the downlink-quality information collected by the downlink quality information collecting unit to the terminal station, based on which the terminal station determines whether to perform a handover.
Furthermore, according to still another aspect of the present invention, there is provided a radio communication system comprising a terminal station and a base station. The terminal station includes an uplink quality information collecting unit that periodically transmits dummy data to a base station that a base station currently connected to the terminal station, and collects uplink-quality information that is generated by transmitting the dummy data to the base station and a handover determining unit that determines whether to perform a handover based on the uplink-quality information collected by the uplink quality information collecting unit. The base station includes a downlink quality information collecting unit that periodically transmits dummy data to a terminal station that is currently connected to the base station, and collects downlink-quality information that is generated by transmitting the dummy data to the terminal station and an information transmitting unit that transmits the downlink-quality information collected by the downlink quality information collecting unit to the terminal station, based on which the terminal station determines whether to perform a handover.
Moreover, according to still another aspect of the present invention, there is provided a radio communication system comprising a terminal station and a base station. The terminal station includes an uplink quality information collecting unit that transmits, when there is no uplink data transmission from the terminal station for a predetermined time, dummy data to a base station that is currently connected to the terminal station, and collects uplink-quality information that is generated by transmitting the dummy data to the base station and a handover determining unit that determines whether to perform a handover based on the uplink-quality information collected by the uplink quality information collecting unit. The base station includes a downlink quality information collecting unit that transmits, when there is no downlink data transmission for a predetermined time, dummy data to a terminal station that is currently connected to the base station, and collects downlink-quality information that is generated by transmitting the dummy data to the terminal station and an information transmitting unit that transmits the downlink-quality information collected by the downlink quality information collecting unit to the terminal station, based on which the terminal station determines whether to perform a handover.
Furthermore, according to still another aspect of the present invention, there is provided a radio communication system comprising a terminal station and a base station. The terminal station includes an uplink quality information collecting unit that periodically transmits dummy data to a base station that a base station currently connected to the terminal station, and collects uplink-quality information that is generated by transmitting the dummy data to the base station and a handover determining unit that determines whether to perform a handover based on the uplink-quality information collected by the uplink quality information collecting unit. The base station includes a downlink quality information collecting unit that periodically transmits dummy data to a terminal station that is currently connected to the base station, and collects downlink-quality information that is generated by transmitting the dummy data to the terminal station and an information transmitting unit that transmits the downlink-quality information collected by the downlink quality information collecting unit to the terminal station, based on which the terminal station determines whether to perform a handover.
Moreover, according to still another aspect of the present invention, there is provided a method of determining whether to perform a handover in a terminal station that makes up a radio communication system with a base station. The method includes monitoring an uplink data transmission from the terminal station to a base station that is currently connected to the terminal station; transmitting, when a result of monitoring at the monitoring indicates that there is no uplink data transmission for a predetermined time, dummy data to the base station; collecting uplink-quality information that is generated by transmitting the dummy data to the base station; and determining whether to perform the handover based on the uplink-quality information collected at the collecting.
Furthermore, according to still another aspect of the present invention, there is provided a method of determining whether to perform a handover in a terminal station that makes up a radio communication system with a base station. The method includes transmitting periodically dummy data to a base station that is currently connected to the terminal station; collecting uplink-quality information that is generated by transmitting the dummy data to the base station; and determining whether to perform the handover based on the downlink-quality information collected at the collecting.
Moreover, according to still another aspect of the present invention, there is provided a method of transmitting downlink-quality information to a terminal station from a base station in a radio communication system. The method includes monitoring a downlink data transmission to a terminal station that is currently connected to the base station; transmitting, when a result of monitoring at the monitoring indicates that there is no downlink data transmission for a predetermined time, dummy data to the terminal station; collecting downlink-quality information that is generated by transmitting the dummy data to the terminal station; and transmitting the downlink-quality information collected at the collecting to the terminal station, based on which the terminal station determines whether to perform a handover.
Furthermore, according to still another aspect of the present invention, there is provided a method of transmitting downlink-quality information to a terminal station from a base station in a radio communication system. The method includes transmitting periodically dummy data to a terminal station that is currently connected to the base station; collecting downlink-quality information that is generated by transmitting the dummy data to the terminal station; and transmitting the downlink-quality information collected at the collecting to the terminal station, based on which the terminal station determines whether to perform a handover.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings.
The RF unit 12 converts a frequency of a received signal that is received from an external device via the antenna 11 or an input signal that is received from the baseband unit 13. The baseband unit 13 baseband-processes the received signal that is received from the RF unit 12 and a signal to be transmitted that is received from the MAC unit 14. The MAC unit 14 processes a MAC layer. The dummy-packet transmitting/receiving unit 15 transmits/receives a dummy packet. The handover determining unit 16 determines based on information acquired from the MAC unit 14 or the dummy-packet transmitting/receiving unit 15 whether handover is to be performed. The wired I/F unit 17 is used to connect an external device such as a laptop personal computer to the terminal station 1 so that the external device can transmit/receive data via the terminal station 1. Data received from the base station is called “uplink data”, while data to be transmitted to the base station is called “downlink data”.
Given below is an explanation about operations in which the terminal station 1 performs handover and switches the current base station to another with reference to
As shown in
The terminal station 1 monitors whether uplink data that is received from the external device via the wired I/F unit 17 is transmitted to the current base station, in addition to processing of the received beacon signal. When a predetermined period has passed since the last transmission of the uplink data, the terminal station 1 transmits dummy data (i.e., uplink dummy packet shown in
Given below are explanations about unit-based operations of the terminal station 1. Upon receiving the uplink data from the wired I/F unit 17, the MAC unit 14 performs required processing to transmit the received uplink data to the base station, and sends to the dummy-packet transmitting/receiving unit 15 a notice that the uplink data has been transmitted (hereinafter, “notice of uplink-data transmission”, see <11> shown in
Upon transmitting the uplink data, the terminal station 1 collects the uplink radio-quality information using the transmitted uplink data in the same manner as collecting the uplink radio-quality information using the transmitted dummy packet. More particularly, the MAC unit 14 collects the uplink radio-quality information, and sends the collected uplink radio-quality information to the handover determining unit 16.
The handover determining unit 16 determines from both the downlink radio-quality information and the uplink radio-quality information whether handover is to be performed (see, a latter half described in <13> shown in
Alternatively, the handover determining unit 16 determines whether handover is to be performed not periodically but inconstantly in response to occurrence of an event, for example, deterioration of the uplink communication. For example, when it is determined that the transmission rate of the uplink data is lower than a threshold or that the number of re-transmissions of the uplink data is larger than a threshold, the handover determining unit 16 checks the downlink radio-quality information and determines whether handover is to be performed. Still alternatively, the handover determining unit 16 determines whether handover is to be performed in response to occurrence of re-transmission.
Upon determining that handover is to be performed, the handover determining unit 16 sends a command to the RF unit 12 and the baseband unit 13 via the MAC unit 14 to start handover. Upon receiving the command, the RF unit 12, the baseband unit 13, and the MAC unit 14 performs handover, and thus the current base station is switched to the next base station.
The terminal station 1 sets, for example, a predetermined address as the destination address of the dummy packet. If receiving a packet with the predetermined address as the destination address, the base station discards the received packet (i.e., dummy packet) without transmitting the received packet to the destination address.
The base station to which the terminal station can be connected as the next base station (hereinafter, “potential next-base station”) is only one in the above example. If the terminal station receives the beacon signal from a plurality of potential next-base stations, the terminal station collects the downlink radio-quality information separated based on each base station. The terminal station selects, before handover, the next base station from among the potential next-base stations using a plurality of pieces of the downlink radio-quality information. The terminal station selects the next base station in a manner, for example, described in Japanese Patent Application Laid-open No. 2005-323034.
The terminal station of the first embodiment collects the uplink radio-quality information using the transmitted uplink data. Moreover, the terminal station collects the uplink radio-quality information by transmitting the dummy packet if there is no uplink data to be transmitted for a predetermined period. The conventional terminal station determines whether handover is to be performed based on only the downlink radio-quality information that is obtained from the beacon signal. The terminal station of the first embodiment, in contrast, determines whether handover is to be performed based on both the downlink radio-quality information and the uplink radio-quality information. As a result, possibility of wrong handover determination decreases, which implements the effective radio communications.
Given below is an explanation about handover-control operations performed by a terminal station 1a according to a second embodiment of the present invention. As described above, the uplink-data monitoring cycle is independent of the handover monitoring cycle in the first embodiment. In contrast, the uplink-data monitoring cycle is equivalent to the handover monitoring cycle in the second embodiment. The structure of the terminal station 1a is similar to the structure of the terminal station 1 (see,
When the terminal station 1a receives the beacon signal, a MAC unit 14a collects the downlink radio-quality information and a handover determining unit 16a stores therein the collected downlink radio-quality information in the same manner as the terminal station 1 does.
In the terminal station 1a, in contrast to the terminal station 1, the handover determining unit 16a monitors transmission of the uplink data. More particularly, the MAC unit 14a sends the notice of uplink-data transmission to the handover determining unit 16a (see, <21> shown in
The handover determining unit 16a determines whether handover is to be performed by checking the uplink radio-quality information and the downlink radio-quality information stored therein periodically with the handover monitoring cycle shown in
If conditions to perform handover and conditions to transmit the dummy packet are satisfied at the same time, the terminal station 1a performs handover without transmitting the dummy packet. More particularly, the handover determining unit 16a first determines whether handover is to be performed. When handover is not to be performed, the handover determining unit 16a then determines whether the uplink data has been transmitted in the last interval. With this configuration, the dummy packet is not transmitted in an unnecessary situation, which makes it possible to perform the various determination processes in an efficient manner.
The terminal station of the second embodiment sets the handover monitoring cycle synchronized with the uplink-data monitoring cycle, and determines whether handover is to be performed before determining whether the dummy packet is to be transmitted. The terminal station determines whether handover is to be performed based on the uplink radio-quality information that is obtained using the transmitted dummy packet or the like and the downlink radio-quality information that is obtained using the received beacon signal. In this manner, it is possible to obtain, while obtaining the same effects as in the first embodiment, the simpler management of the monitoring cycles and the efficient dummy-packet transmission in which no dummy packet is transmitted in the unnecessary situation.
Given below is an explanation about handover-control operations performed by a terminal station 1b according to a third embodiment of the present invention. As described above, the terminal station 1 or 1a monitors transmission of the uplink data, and determines whether the dummy packet is to be transmitted based on the result of monitoring. In contrast, the terminal station 1b periodically transmits the dummy packet with regardless of the result of monitoring. The structure of the terminal station 1b is similar to the structure of the terminal station 1 (see,
When the terminal station 1b receives the beacon signal, a MAC unit 14b collects the downlink radio-quality information and a handover determining unit 16b stores therein the collected downlink radio-quality information in the same manner as the terminal station 1 does.
The terminal station 1b, in contrast to the terminal station 1 or 1a, does not monitor transmission of the uplink data. A dummy-packet transmitting/receiving unit 15b acquires the uplink radio-quality information by periodically transmitting the dummy packet with regardless of presence of the uplink data to be transmitted (see, <31> shown in
When transmitting the uplink data, the terminal station 1b collects the uplink radio-quality information using the transmitted uplink data in the same manner when transmitting the dummy packet. More particularly, the MAC unit 14b collects the uplink radio-quality information and sends the collected uplink radio-quality information to the handover determining unit 16b.
The handover determining unit 16b determines whether handover is to be performed based on the uplink radio-quality information and the downlink radio-quality information stored therein. The uplink radio-quality information includes information collected using the uplink data and information collected using the dummy packet. The handover determining unit 16 uses either latest information from among the uplink radio-quality information or all of the uplink radio-quality information.
The handover determining unit 16b can determine whether handover is to be performed at variable timing, i.e., periodically or in response to occurrence of the predetermined event in the same manner as the handover determining unit 16. The same procedure described in the first embodiment is also used in the third embodiment to determine whether handover is to be performed.
The terminal station 1b can stop transmission of the dummy packet when a high load is burdened on the uplink communication. For example, it is detected that the high load is burdened on the uplink communications, the MAC unit 14b stops transmission of the dummy packet.
The terminal station of the third embodiment collects the uplink radio-quality information by periodically transmitting the dummy packet with regardless of transmission of the uplink data. The terminal station determines whether handover is to be performed based on the uplink radio-quality information that is obtained using the dummy packet and the downlink radio-quality information that is obtained using the received beacon signal. In this manner, it is possible to obtain, while obtaining the same effects as in the first embodiment, the simpler control procedure excluding the uplink-data monitoring.
Given below is an explanation about handover-control operations performed by a terminal station 1c according to a fourth embodiment of the present invention. As described above, the terminal station 1, 1a, or 1b transmits the dummy packet to the current base station only. In contrast, the terminal station 1c transmits the dummy packet to both the current base station and the next base station. The structure of the terminal station 1c is similar to the structure of the terminal station 1 (see,
When the terminal station 1c receives the beacon signal, a MAC unit 14c collects the downlink radio-quality information and a handover determining unit 16c stores therein the collected downlink radio-quality information in the same manner as the terminal station 1 does.
The terminal station 1c monitors transmission of the uplink data. When a predetermined period has passed since the last transmission of the uplink data, the terminal station 1c transmits the dummy packet to both the current base station and the next base station, and collects uplink radio-quality information between the terminal station 1c and the current base station and uplink radio-quality information between the terminal station 1c and the next base station. The potential next-base station is only one in the example shown in
The terminal station 1c determines whether handover is to be performed based on the collected uplink radio-quality information and the collected downlink radio-quality information in the same manner as the terminal station 1 determines. If there is a plurality of potential next-base stations, the terminal station 1c selects the next base station from among the potential next-base stations using the uplink radio-quality information and the downlink radio-quality information about each of the potential next-base stations. The terminal station 1c selects the next base station, for example, in the manner described in Japanese Patent Application Laid-open No. 2005-323034 by comparing the potential next-base stations in the electric-power level of the received beacon signal, the uplink transmission rate at receiving the beacon signal, the electric-power level of the received ACK packet in response to the transmitted dummy packet, the number of re-transmissions of the dummy packet, and the transmission rate at transmitting the dummy packet.
The terminal station of the fourth embodiment collects the uplink radio-quality information by transmitting the dummy packet to the current base station and the next base stations when a predetermined period has passed since the last transmission of the uplink data. The terminal station determines whether handover is to be performed based on the uplink radio-quality information and the downlink radio-quality information. If there is a plurality of potential next-base stations, the terminal station selects the next base station from among the potential next-base stations based on the uplink radio-quality information and the downlink radio-quality information about each of the potential next-base stations. With this configuration, it is possible to decrease the possibility of wrong handover determination, and to select the best one as the next base station from among the potential next-base stations.
Moreover, the terminal station 1c having the same functions of the terminal station 1 collects the uplink radio-quality information about each of the potential next-base stations by transmitting the dummy packet to the potential next-base stations. In other words, the terminal station 1c is obtained by adding the featured function (i.e., function of acquiring the uplink radio-quality information by transmitting the dummy packet to the potential next-base stations) to the terminal station 1. Another terminal station can be obtained by adding the featured function to the terminal station 1a or 1b.
Given below is an explanation about handover-control operations according to a fifth embodiment of the present invention. As described above, the terminal station according to any one of the first embodiment to the fourth embodiments collects the uplink radio-quality information by transmitting the dummy packet to the base station. The terminal station determines whether handover is to be performed based on the collected uplink radio-quality information. In contrast, a base station of the fifth embodiment collects downlink transmission-quality information by transmitting a dummy packet to the terminal station. The base station transmits the collected downlink transmission-quality information to the terminal station. The terminal station determines whether handover is to be performed based on the received downlink transmission-quality information.
The RF unit 22 converts a frequency of a received signal that is received from an external device via the antenna 21 or an input signal that is received from the baseband unit 23. The baseband unit 23 baseband-processes the received signal that is received from the RF unit 22 and a signal to be transmitted that is received from the MAC unit 24. The MAC unit 24 processes a MAC layer. The dummy-packet transmitting/receiving unit 25 transmits/receives the dummy packet. The handover-information collecting unit 26 collects from the MAC unit 24 and the dummy-packet transmitting/receiving unit 25 the handover information that is used by the terminal station to determine whether handover is to be performed. The wired I/F unit 27 is used to connect the base station 2 with an external network such as a wireless LAN.
Given below is an explanation about handover-control operations performed by the base station 2 with reference to
The base station 2 is connected to a terminal station 1d that is obtained by adding a featured function of determining whether handover is to be performed using transmission-quality information received from the base station 2 to the terminal station 1, 1a, 1b, or 1c.
As shown in
Given below are explanations about unit-based operations of the base station 2. When the MAC unit 24 receives the downlink data from the wired I/F unit 27, the MAC unit 24 performs required processing to transmit the received downlink data to the terminal station 1d, and sends to the handover-information collecting unit 26 a notice that the downlink data has been transmitted (hereinafter, “notice of downlink-data transmission”, see <51> shown in
Upon transmitting the downlink data, the base station 2 collects the downlink transmission-quality information using the transmitted downlink data in the same manner as collecting the downlink transmission-quality information using the transmitted dummy packet. More particularly, the MAC unit 24 collects the downlink transmission-quality information, and sends the collected downlink transmission-quality information to the handover-information collecting unit 26.
As shown in
Upon receiving the downlink transmission-quality information from the base station 2, the terminal station 1d stores therein the received downlink transmission-quality information. The terminal station 1d collects the uplink radio-quality information and the downlink radio-quality information in the same manner as any one of the terminal stations 1, 1a, 1b, and 1c collects. The terminal station 1d determines whether handover is to be performed using the downlink transmission-quality information received from the base station 2, the uplink radio-quality information, and the downlink radio-quality information. The terminal station 1d determines whether handover is to be performed by using the same criteria that any one of the terminal stations 1, 1a, 1b, and 1c uses.
The base station 2 sets, for example, a predetermined address as the destination address of the dummy packet if receiving a packet with the predetermined address as the destination address, the terminal station 1d discards the received packet (i.e., dummy packet) without transmitting the received packet to the destination address.
The base station of the fifth embodiment collects the downlink transmission-quality information using the transmitted downlink data. Moreover, the base station collects the downlink transmission-quality information by transmitting the dummy packet if there is no downlink data to be transmitted for a predetermined period. The base station transmits the collected downlink transmission-quality information to the terminal station as information that is used to determine whether handover is to be performed. As a result, the possibility of wrong handover determination decreases.
The terminal station of the fifth embodiment determines whether handover is to be performed using the downlink transmission-quality information that is received from the base station, and the uplink radio-quality information and the downlink radio-quality information that the terminal station collects by itself using control described in any one of the first embodiment to the fourth embodiment. As a result, the terminal station obtains the possibility of wrong handover determination lower than the possibility that any one of the terminal stations of the first embodiment to the fourth embodiment obtains.
Given below is an explanation about handover-control operations performed by a base station 2a according to a sixth embodiment of the present invention. As described above, the base station 2 of the fifth embodiment monitors transmission of the downlink data, and transmits the dummy packet based on the result of monitoring. In contrast, the base station 2a transmits the dummy packet periodically with regardless of the result of monitoring. The structure of the base station 2a is similar to the structure of the base station 2 (see,
As shown in
As described in the explanation about the fifth embodiment, the terminal station 1d determines whether handover is to be performed based on the uplink radio-quality information, the downlink radio-quality information, and the downlink transmission-quality information.
In this manner, the base station according to the sixth embodiment collects the downlink transmission-quality information by periodically transmitting the dummy packet with regardless of transmission of the downlink data, and transmits the collected downlink transmission-quality information to the terminal station. With this configuration, it is possible to obtain, while obtaining the same effects as in the fifth embodiment, the simpler control procedure excluding the uplink-data monitoring.
Given below is an explanation about handover-control operations performed by a base station 2b according to a seventh embodiment of the present invention. The base station 2 or 2a transmits the dummy packet to the terminal station only when the base station 2 or 2a is currently being connected to the terminal station, i.e., the base station 2 or 2a is working as the current base station. In contrast, the base station 2b transmits the dummy packet to the terminal station even when the base station 2b is working as the next base station of the terminal station. The structure of the base station 2b is similar to the structure of the base station 2 (see,
As shown in
Another one of the base stations 2b working as the next base station (hereinafter, “base station 2b-2”) monitors data transactions between the base station 2b-1 and the terminal station 1d, i.e., monitors whether the base station 2b-1 transmits/receives data (including the dummy packet) to/from the terminal station 1d. Upon detecting a data transaction, i.e., when the base station 2b-1 collects the downlink transmission-quality information, the base station 2b-2 transmits the dummy packet to the terminal station 1d and collects using the transmitted dummy packet the downlink transmission-quality information between the terminal station 1d and itself.
Given below are explanations about unit-based operations of the base station 2b-2. A MAC unit 24b monitors data transactions between the base station 2b-1 and the terminal station 1d. Upon detecting the data transaction, the MAC unit 24b sends a notice of detection to a handover-information collecting unit 26b (see, <71> shown in
The terminal station 1d determines whether handover is to be performed using the uplink radio-quality information and the downlink radio-quality information that the terminal station 1d collects itself, the downlink transmission-quality information that is received from the base station 2b-1, and the downlink transmission-quality information that is received from the base station 2b-2. For example, the terminal station 1d extracts an electric-power level at which the base station receives the ACK packet from the terminal station id in response to the dummy packet that is transmitted from the base station to the terminal station 1d (hereinafter, “uplink packet electric-power level”) from each of the downlink transmission-quality information received from the base station 2b-1 and the downlink transmission-quality information received from the base station 2b-2. If the uplink packet electric-power level at the base station 2b-2 is higher than the uplink packet electric-power level at the base station 2b-1, the terminal station 1d determines that handover is to be performed. The terminal station 1d can set an offset. More particularly, assuming that the offset is α, the terminal station 1d determines that handover is to be performed when the uplink packet electric-power level at the base station 2b-2 is larger than a sum of the uplink packet electric-power level at the base station 2b-1 and α.
In this manner, if the terminal station is in a coverage area of the base station, the base station of the seventh embodiment collects the downlink transmission-quality information between the terminal station and itself with regardless of whether the terminal station is being connected to the base station currently. In other words, even if the base station is a possible next-base station, the base station collects the downlink transmission-quality information. The base station then transmits the collected downlink transmission-quality information to the terminal station. As a result, the terminal station obtains lower possibility of wrong handover determination.
As described above, according to an aspect of the present invention, it is possible to obtain lower possibility that handover is performed in an unnecessary situation, which implements the effective radio communications.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
Number | Date | Country | Kind |
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2008-106996 | Apr 2008 | JP | national |