Method for determining link quality in wireless network system

Provided is a method for determining network link quality between a master station and slave stations in a wireless network system having a synchronous superframe structure. The method for determining link quality in a wireless network system includes determining whether the current station is a master or a slave, when the current station is a master, comparing a time value during which the latest packets were received from slaves and a maximum time value during which the slaves are not obliged to exchange packets with the master after accessing a network, and determining link quality between the slaves and the master according to the comparison result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2015-0017337, filed on Feb. 4, 2015, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a method for determining link quality in a wireless network system and, more particularly, to a method for determining network link quality between a master station and slave stations in a wireless network system in which communication is performed using a synchronous superframe structure.

BACKGROUND

Some elements constituting a personal wireless network as illustrated inFIG. 1may be considered. The most basic element is a station. Here,FIG. 1is a view illustrating connection relationships between stations in a general personal wireless network system.

In general, a piconet is established when two or more stations operating in the same radio frequency channel exist within a personal activity area.

Stations are classified as a master M and slaves S1, S2, S3, and S4depending on roles thereof.

The master M manages the entirety of the piconet and only one master may exist in the piconet. The master M controls the slaves S1, S2, S3, and S4by broadcasting beacons to the plurality of slaves S1, S2, S3, and S4.

The slaves S1, S2, S3, and S4may transmit and receive data under the management of the master M. In general, the master M internally has information of the slaves S1, S2, S3, and S4, and thus, when the slaves S1, S2, S3, and S4are connected to the master M, the master M performs communication using the information of the slaves S1, S2, S3, and S4. Here, a structure of a superframe transmitted and received between the master M and the slaves S1, S2, S3, and S4is as illustrated inFIG. 2.

As illustrated inFIG. 2, the structure of a superframe includes a beacon period, a contention period, and a data allocation period, and length so the periods are variable.

During the beacon period, the master transmits a beacon packet including network reference information to the slaves.

During the contention period, the slaves and the master transmit and receive a command packet such as a network join request/separation request/permission, a resource allocation request/permission, a connection request/permission, and the like, in a random access manner. Here, during the contention period, exclusive access to a medium through an exclusive allocation by the master is not guaranteed, and thus, each station (the master and the slaves) access a medium by using a carrier sense multiple access/collision avoidance (CSMA/CA).

During the data allocation period, each station exclusively accesses a medium during a time slot distributed to each station. The master distributes a time slot of the data allocation period to each station by using a time division multiple access (TDMA) scheme. Here, each station may exclusively access the medium during the distributed time slot, and each station may transmit and receive data to and from other station in a one-to-one correspondence manner, without intervention of the master, during the allocated time slot.

FIG. 2illustrates a structure of a superframe of data allocation periods with respect to slaves S1to S4when a data allocation period of the master is M and the overall number of the slaves is 4 (S1to S4).

In the wireless network system, when the master M and the slaves S1to S4perform communication, communication may be interrupted for a long period of time for various reasons such as radio interference between the master M and the slaves S1to S4, propagation cutoff due to an obstacle, defective hardware, and the like, in many cases.

FIG. 3is a view illustrating an example in which a radio link between the master station M and the slave stations S1, S2, S3, and S4is disconnected in a personal wireless network system.

In a case in which the wireless network is disconnected as illustrated inFIG. 3, the master M may consider that there is no data for the slaves S1, S2, S3, and S4to transmit to the master M so slave data is not received, and thus, the master M may not discriminate whether there is a problem with a link physically or whether the slaves S1, S2, S3, and S4have no data to be transmitted for a long period of time.

Similarly, the slaves S1, S2, S3, and S4receive beacons from the master M so the slaves S1, S2, S3, and S4are synchronized with the master M, but, here, beacons are received even when data is not properly transmitted and received, and thus, the slaves S1, S2, S3, and S4continue to request transmission from the master M.

Thus, even though there is a problem with a link physically between the master M and the slaves S1, S2, S3, and S4, the master M continues to wait to receive beacon signals from the slaves S1, S2, S3, and S4, and in addition, when the number of slaves increases in a state in which the master M stores information of the slaves S1, S2, S3, and S4which have already been interrupted in communication, other slaves may lose an opportunity for accessing a network, increasing a waste of memory resource.

Also, the slaves S1, S2, S3, and S4are supposed to be synchronized with the master M through reception of beacons to transmit and receive data, and here, if data transmission is not properly performed, the slaves S1, S2, S3, and S4need to recognize the corresponding situation quickly and overcome the limitation or need to search for any other appropriate master nearby to access the network.

SUMMARY

Accordingly, the present invention provides a link quality determining method for effectively determining whether a physical link between a master station and slave stations has an error by monitoring network link quality between the master station and the slave stations in real time in a wireless network system in which communication is performed using a synchronous superframe structure

In one general aspect, a method for determining link quality in a wireless network system includes: determining whether the current station is a master or a slave; when the current station is a master, comparing a time value during which the latest packets were received from slaves and a maximum time value during which the slaves are not obliged to exchange packets with the master after accessing a network; and determining link quality between the slaves and the master according to the comparison result.

The determining of link quality may include: when the time value during which the latest packets were received from the slaves is greater than the maximum time value during which the slaves are not obliged to exchange packets with the master after accessing the network, determining that a link between a corresponding slave and the master has an error and disconnecting, by the master, a corresponding slave from the network; and deleting information regarding the corresponding disconnected slave.

The method may further include: when the current station is a slave, determining whether the number of times of failing to continually receive a beacon signal from the master is 0; when the number of times of failing to continually receive a beacon signal from the master is 0, determining whether the time value during which the latest packet was received from the master is greater than a threshold time with respect to the maximum time value during which the slave is not obliged to exchange packets with the master after accessing the network; when it is determined that the time value during which the latest packet was received from the master is greater than the threshold time with respect to the maximum time value during which the slave is not obliged to exchange packets with the master after accessing the network, transmitting, by the slave, a command indicating that the slave has been activated, to the master; determining whether the time value during which the latest packet was received from the master is greater than the maximum time value during which the slave is not obliged to exchange packets with the master after accessing the network, after the transmitting of a command; and when it is determined that the time value during which the latest packet was received from the master is greater than the maximum time value during which the slave is not obliged to exchange packets with the master after accessing the network, determining that there is an error with the link to the master and notifying about disconnection to the master.

When the number of times of failing to continually receive a beacon signal from the master is not 0 and the time value during which the latest packet was received from the master is smaller than the threshold time with respect to the maximum time value during which the slave is not obliged to exchange packets with the master after accessing the network, a link state with the master may be determined by determining whether the time value during which the latest packet was received from the master is greater than the maximum time value during which the slave is not obliged to exchange packets with the master after accessing the network.

The method may further include: when the time value during which the latest packet was received from the master is smaller than the maximum time value during which the slave is not obliged to exchange packets with the master after accessing the network, determining whether a beacon transmission time value of the master is greater than the maximum time value during which the slave is not obliged to exchange packets with the master; and when it is determined that the beacon transmission time value of the master is greater than the maximum time value during which the slave is not obliged to exchange packets with the master, determining that a beacon has not been received continually from the master for a long period of time so a link has been disconnected, and resetting an operation of the slave.

The method may further include: re-connecting to a previous master or requesting a connection to a new master of other channel, after the resetting of the slave.

DETAILED DESCRIPTION OF EMBODIMENTS

The advantages, features and aspects of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Throughout the specification, like numbers refer to like elements.

In describing embodiments of the present invention, a detailed description of known techniques associated with the present invention unnecessarily obscure the gist of the present invention, it is determined that the detailed description thereof will be omitted. Moreover, the terms used henceforth have been defined in consideration of the functions of the present invention, and may be altered according to the intent of a user or operator, or conventional practice. Therefore, the terms should be defined on the basis of the entire content of this specification.

Hereinafter, a method for determining link quality in a wireless network system according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4is a view illustrating an example of a process of transmitting and receiving beacons and alive commands (AliveCmd) between the master station and the slave stations in the personal wireless network system,FIG. 5is a view illustrating a structure of a command frame transmitted from the slave stations to the master station in the personal wireless network system,FIG. 6is a view illustrating a process of transmitting an alive command (AliveCmd) from a slave station to the master station in the personal wireless network system, andFIG. 7is a view illustrating an example of a process in which acknowledgement (ACK) with respect to an alive command (AliveCmd) transmitted from a slave station to the master station fails to receive from the master station inFIG. 6.

First, as illustrated inFIG. 4, in order to determine whether a physical link between a master M and slaves S1, S2, S3, and S4, the slaves S1, S2, S3, and S4transmit AliveCmd to the master M periodically (Association TimeOut). Here, the AliveCmd is transmitted during a contention period (CSMA/CA), rather than during a data period (TDMA) in the superframe structure illustrated inFIG. 2. Here, the AliveCmd frame type transmitted during the contention period may be divided into a header hdr and a payload as illustrated inFIG. 5.

As illustrated inFIG. 5, the header hdr may include a transmission address (SRC) region and a reception DST region, and the payload may include a Cmd ID region and a Cmd payload region.

An AliveCmd command includes an address of a slave in the transmission address SRC region of the header and a master address in the reception address DTY region. Here, the master address is fixe to 0 all the time, the Cmd ID is a unique value not duplicated with other Cmd ID, and Cmd payload is not required.

A process of transmitting AliveCmd from a slave10to a master20will be described with reference toFIG. 6.

First, the slave10transmits a network access request (AssociationReqCmd) to the master20in step S601. Here, when transmitting the network access request (AssociationReqCmd) to the master20, the slave10provides Association TimeOut information. Here, AssociationTimeOut information refers to a maximum period of time during which the slave10are not obliged to exchange a packet with the master20after connected to the network.

Subsequently, the master20transmits an ACK message to the corresponding slave10according to the access request from the slave10, and selects a corresponding slave address SlaveID and transmits an access response command (AssociatoinRespCmd) for a data transmission request to the corresponding slave10in steps S602and S603.

Thereafter, the master20receives data from the slave10in step S604, and when the data is received, the master20transmits an ACK message with respect to the data transmission to the corresponding slave10in step S605.

After the data is transmitted from the slave10to the master20, if data transmitted from the slave10to the master20does not exist for a long period of time, the slave10transmits AliveCmd after a particular time (AssociationTimeOut-threshold) in order to inform the master20that the slave10is normally activated in steps S606and S607.

Subsequently, when a reception acknowledgement Ack message is received according to the transmission of AliveCmd, the slave10stops transmission of AliveCmd in step S608. Here, the threshold of a particular time at which the AliveCmd is transmitted is flexible depending on AssociationTimeOut and the number of maximum accesses of the maximum number of slaves.

InFIG. 6, when the slave10fails to receive the reception acknowledgement Ack message with respect to AliveCmd from the master20, the slave10continually transmits AliveCmd to the master20periodically as illustrated inFIG. 7in steps S708and S709. Here, operations in steps S701to S707are the same as those of steps S601to S607, and thus, detailed descriptions of the operations will be omitted

An operation for determining a state of a link when a data is transmitted and received between the slave and the master will be described by stages with reference toFIG. 8.

FIG. 8is a flow chart illustrating an operation of a method for determining link quality in a wireless network system according to an embodiment of the present invention. That is,FIG. 8shows an algorithm for determining whether network links between one master and several slaves are normal or defective, and such an algorithm determines quality of the network links periodically at every predetermined time CheckTimer.

As illustrated inFIG. 8, first, it is determined whether the current station is a master or a slave in step S801.

When the corresponding station is a master according to the determination, AliveTime and AssociationTimeOut of a first slave stored in the master are compared in steps S802, S803, and S804. Here, AliveTime is a time value at which the latest packets (data, command) were received from the slaves, and AssociationTimeOut is a maximum period of time during which the slaves are not obliged to exchange packets with the master after connected to the network. AssociationTimeOut is informed to the master when the slaves are connected to the network, and this value may be different between slaves.

When AliveTime of a first slave is greater than AssociationTimeOut in step S804, the master determines that there is a problem with a link between the slave and the master, and releases the connection of the corresponding slave from the network in step S805. That is, when it is determined that there is a problem with a link with the slave, the master transmits DisconnectReq to the corresponding first slave to notify about the release connection thereof to the network.

After releasing the connection of the slave, the master deletes information of the corresponding slave such that other slaves may reuse the information in step S806.

After the step S806, the master performs the foregoing operation in the same manner on every other slaves connected to the network to determine a link state of each slave.

If, however, AliveTime of the first slave is equal to or smaller than AssociationTimeOut, the master determines that there is no problem with link quality of the first slave and performs an operation of determining a state of link quality with respect to a second slave, such as steps S804to S806.

In this manner, the same process is performed on every slave connected to the master to recognize network link quality of all of the master and the slaves.

When the corresponding station is a slave, rather than being a master in step S801, the slave determines whether BeaconFailCount is 0 in step S809. Here, BeaconFailCount indicates the number of times that the slave continually fails to receive a beacon from a master.

When BeaconFailCount is 0 according to the determination result in step S809, the slave determines whether AliveTime of the master is greater than AssociationTimeOut-threshold in step S810.

When BeaconFailCount is not 0, step S812is performed.

When AliveTime of the master is greater than AssociationTimeOut-threshold according to the determination result of step S810, the slave transmits AliveCmd to the master in order to inform the master that the slave (itself) has been activated in step S811.

If, however, AliveTime of the master is equal to or smaller than AssociationTimeOut-threshold, step S811is not performed and step S812is performed.

Subsequently, when BeaconFailCount is not 0 in step S809, if AliveTime of the master is equal to or smaller than AssociationTimeOut-threshold in step S810and step S811has been performed, it is determined whether AliveTime of the master is greater than AssociationTimeOut in step S812.

When AliveTime of the master is greater than AssociationTimeOut, the slave determines that a network link with the master is problematic, informs the master about network release (DisconnectReq(Master)) in step S813and performs resetting (Reset) in step S815.

However, when AliveTime of the master is equal to or smaller than AssociationTimeOut in step S812, the slave determines whether BeaconTime of the master is greater than AssociationTimeOut in step S814.

When BeaconTime of the master is greater than AssociationTimeOut according to the determination result, the slave is in a state of have not being received a beacon continually for a long period of time from the master, and thus, the slave determines that a link has been completely disconnected and performs resetting in step S815.

However, when BeaconTime of the master is equal to or smaller than AssociationTimeOut, the slave terminates the foregoing operation.

After being reset in step S815, the slave may be connected again according to the latest network situation, or may request connection to a completely new network in step S816. For example, when a bean is received but there is a problem with a data transmission, the slave lowers a transfer rate and accesses again to the previous master, or when a beacon is not received form a long period of time, the slave determines that a network link is severely poor and attempts to access a new master of other channel.

FIG. 9is a view illustrating TimeStamp timings stored in AliveTime of the Alive-related master AliveTime and slave AliveTime.

As illustrated inFIG. 9, as for master20AliveTime, TimeStamp is stored at a point in time at which a reception success acknowledgement ACK of Data, Command (AssociationReq, AliveTime, etc.) transmitted by the slave10is received.

As for slave10AliveTime, TimeStamp is stored at a point in time at which Data, Command (AssociationReq, AliveTime, etc.) received from slaves is received.

FIG. 10is a view illustrating a process of generating master BeaconTime and BeaconFailCount related to beacon reception.

As illustrated inFIG. 10, the master20BeaconTime in the slave10stores TimeStamp when a beacon is received from the master, and BeaconFailCount indicates the latest number when beacon reception has failed.

According to an embodiment of the present invention, since link quality between the master and several slaves is managed in real time, overall network performance may be enhanced.

Also, according to an embodiment of the present invention, a physical link disconnection and a logical link disconnection between a master and slaves may be discriminated, and a defective slave link may be quickly deleted, whereby resource of slaves within the master may be effectively managed.