JP5118918B2 - Method and apparatus for selecting an access point in a wireless local network - Google Patents

Description

  The present invention relates to a method and apparatus for selecting an access point (AP, Access Point) in a wireless local network, and in particular, an access to the AP by detecting the degree of busyness of each channel that can be used by a wireless terminal. Access in the association and reassociation process in the wireless local network, which can estimate the influence of hidden terminals when reducing the collision between the rising packets and improve the performance of the entire wireless local network The present invention relates to a method and an apparatus for selecting points.

  In accordance with the promotion of standardization, wireless local networks (WLANs) are designed to provide high-speed wireless access services to the Internet due to their low cost and high transmission rate. It is being widely applied to. In particular, in a large-scale application for WLAN, a basic service set (BSS) defined in the IEEE 802.11 standard, which is a basic unit (cell) of a plurality of wireless local networks, overlaps. Seamless cover can be realized. In this way, the problem of selecting BSS, so-called AP, comes out.

  The IEEE 802.11 series is the most widely applied standard for wireless local networks. The IEEE 802.11 series usually exists as two different network structure types. One is a self-organizing WLAN without a wireless access point, and here, all wireless terminals communicate directly with each other. The other is a frame-type WLAN, and its basic unit is a basic service set including one wireless access point and a plurality of wireless terminals. In the frame-structured WLAN, all wireless terminals can realize inter-terminal communication in the network via the AP, and a plurality of BBSs can configure an extended service set (ESS) to realize an extended coverage.

  In a conventional wireless local network, there are a plurality of cover overlap areas, so that each wireless terminal makes a selection for an access point when entering the WLAN service area to determine which cell to access. There is a need. For this reason, when a wireless terminal enters the WLAN service area, it sequentially scans the wireless channel to detect whether there is an access point available in its neighborhood, and usually the strongest received signal energy indication (RSSI) Is selected and associated with it, it joins the BSS where the AP is located.

  FIG. 1 shows a schematic diagram in which a wireless terminal selects an access point in a wireless local network. As shown in FIG. 1, access points AP1 and AP2 operate in two non-overlapping channels, respectively. The wireless terminal MT1 is a wireless terminal associated with AP1, and the wireless terminal MT2 is a wireless terminal associated with AP2. The user MT3 individually scans for available radio channels when entering the WLAN, and determines and selects a BSS to join according to the strongest received signal energy indication from the AP1 and AP2. The IEEE 802.11 standard defines two channel scan methods, passive scan and main scan (as shown in FIG. 2). Passive scanning refers to a wireless terminal sensing each wireless channel sequentially and selecting an access point by detecting beacon packet energy periodically transmitted from the AP (see FIG. 2A). As shown). A beacon packet contains some specific information in the current cell. The user can extract correlated information from the received beacon packet. For example, the rate set and channel utilization rate supported by the cell. The main scan refers to sequentially transmitting a probe request packet (Probe Request) on each wireless channel after the wireless terminal enters the WLAN. Upon receiving the packet, the access point AP returns a probe response packet (Probe Response). The probe response packet includes correlated information in the corresponding cell. The wireless terminal selects an access point by detecting energy from the probe response packet (as illustrated in FIG. 2B).

  If the communication status in the BBS already associated with the wireless terminal changes according to the dynamic change of the network and the service quality for the wireless terminal cannot be guaranteed, it is necessary to re-associate with the AP. Similarly, there is a selection problem for the access point.

  The process of selecting the access point can be easily realized, but this method only considers the situation of the new access node itself. If the service loads of the two BBSs are not evenly distributed, selecting the AP with the strongest signal energy weights the load of the BBS having a high service density, which causes a decrease in the performance of the entire system. For this reason, a more effective AP selection method has already been submitted.

  In the most commonly used 802.11 products, the access point is usually selected by adopting a determination method for the strongest received signal energy indication (RSSI). That is, when one mobile node can detect two or more access points, the access point having the maximum RSSI is selected according to the received signal energy indication. In this method, when the load of both cells is different, one cell may be very congested while the other cell may have a margin, and each BBS may become unequal. It becomes a problem.

Thus, several conventional techniques for selecting an AP using a load have appeared. S. Misra and A. The paper published by Banerjee presents an AP selection method that considers the load. Here, each wireless terminal selects an access point that has the smallest current load and is located in the moving direction of the wireless terminal ( For example, refer nonpatent literature 1).

  A paper published by Hyun-wo Lee et al. Also considers the elements of loading (see Non-Patent Document 2, for example). This paper proposes that an optimal access point is selected by inserting the number of wireless terminals and the amount of service (bits / second) in the current BSS into beacons and probe response packets.

  In addition, S.M. Vasudevan, K.M. Papageianaki, C.I. Diot, J.A. Kurose, and D.W. A paper published by Towsley presents a method for estimating an acquirable bandwidth using a difference between a time stamp in a beacon packet and a target beacon transmission time (TBTT) (for example, see Non-Patent Document 3). ). However, the premise of such estimation is that beacon packets and data packets are transmitted with the same priority. However, in practice, beacon packets are transmitted with priority over data, which leads to inaccurate estimation.

  T.A. A paper published by Korakis et al. Also suggests estimating the usable bandwidth in consideration of the bidirectional link rate (see, for example, Non-Patent Document 4). However, such a method is applied only to the medium access control (MAC) of the point coordination function (PCF, Point Coordination Function), and the distributed cooperation function (DCF) widely applied to wireless local network products. , Distributed Coordination Function).

  Compared to the maximum RSSI method, the above method considers more factors such as load, direction of travel, bi-directional transmission, etc., and can provide superior system performance under certain scenarios. However, none of the above prior art considers the influence of node distribution. In one cell, in the downlink direction, the access point can sense all wireless terminals within the coverage area, whereas in the uplink direction, the wireless terminal cannot sense the presence of hidden terminals and is hidden from each other. When the node becomes a data packet at the same time, a collision occurs in the receiving node, so that the performance of the hidden terminal is severer than that of the non-hidden terminal.

  FIG. 3 shows how the system throughput changes with an increase in the number of wireless terminals in one BSS environment. As can be seen from FIG. 3, when there is a hidden terminal, the number of nodes increases, leading to a significant decrease in throughput. Therefore, it is necessary to estimate the influence of the hidden terminal using the downlink information sent by the AP in consideration of the node distribution state so that the access point with the smallest influence of the hidden terminal is selected and associated / re-associated. is there.

Considering the wide range of applicability and expandability of the frame-type WLAN, it is necessary to study the selection problem when a wireless terminal detects a plurality of APs in a large-scale application environment toward the frame-type WLAN. The IEEE 802.11 standard (see “ANSI / IEEE Std 802.11-1999 Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications”, 1999). A non-overlapping channel is adopted to avoid interference between adjacent BBSs. Here, it is assumed that the plurality of BBSs detected by the wireless terminal work in different non-overlapping channels, that is, there is no interference between adjacent cells.
S. Misra and A.M. Banerjee “A Novel Load Sensitive Algorithm for AP selection in 4G Networks” (see CODEC 2003, Calcutta, INDIA, 2003) Hyun-wo Lee et al. “Performance of an effective method for association admission control in public wireless LAN systems” (see VTC2004-Fall) S. Vasudevan, K.M. Papageianaki, C.I. Diot, J.A. Kurose, and D.W. Towsley “Facitating Access Point Selection in IEEE 802.11 Wireless Networks” (see ACM Internet Measurement Conference, New Orleans, LA, October, 2005). T.A. Korakis et al., “Link Quality based Association Mechanism in IEEE 802.11h compliant. Wireless LANs” (in Worksshop on Resource Allocation in Wis. Et.

  In view of the above problems, the present invention reduces the collision of rising packets by estimating the influence of hidden terminals when accessing the AP by detecting the busyness of the channels in the channels that can be used by the wireless terminal. An object of the present invention is to provide a method and apparatus for selecting an access point in a wireless local network, which can improve the performance of the entire wireless local network.

According to one aspect of the present invention, a method for selecting an access point in a wireless network comprising: a. A step of the wireless terminal performs a channel scan for the channel in the network, receives the channel information transmitted from the access point, extracts a channel utilization factor u _k from the information, b. Determining a maximum supportable data transmission rate v _k for the currently scanned channel based on the received channel information; c. The channel occupation probability r _k within the scan time interval is statistically processed, and the hidden terminal influence factor f _k is calculated based on the channel utilization rate u _k , the highest data transmission rate v _k , and the channel occupation probability r _k. Calculating, d. The basic service set in which the above steps a to c are performed on all channels accessible to the wireless terminal, an AP is selected based on the calculated hidden terminal influence factor f _k , and the selected access point is located Subscribing to the method.

According to another aspect of the invention, a method for selecting an access point in a wireless network comprising: a. Wireless terminal, the steps of: transmitting a probe request packet to the access point in the network, and receives a probe response packet returned from the access point, extracts a channel utilization factor u _k from the information, b. Determining a maximum supportable data transmission rate v _k for the currently scanned channel based on the received channel information; c. The channel occupation probability r _k within the scan time interval is statistically processed, and the hidden terminal influence factor f _k is calculated based on the channel utilization rate u _k , the highest data transmission rate v _k , and the channel occupation probability r _k. D. Steps a to c described above are performed on all channels accessible to the wireless terminal, an access point AP is selected based on the calculated hidden terminal influence factor f _k, and the base where the selected access point is located Subscribing to a service set.

According to still another aspect of the present invention, an apparatus for selecting an access point in a wireless network, channel scan means for performing channel scan on a channel in the network and receiving channel information returned from the access point; extracting channel utilization u _k from the information received by the channel scan means, determination means for determining the maximum data transmission rate v _k supportable channel currently scanned based on the channel information received, determined means storing a channel utilization u _k, maximum data transmission rate v _k obtained, statistically processes the probability r _k channel occupied in the time interval of the scan, the channel utilization u _k, the maximum data transmission rate v _k , based on the probability for the channel occupied _{r k,} Re and calculating storing means for calculating a terminal influencing factors f _k, calculating the storage means on the basis of the f _k calculated for each channel, the access point selection unit which selects an access point, based on the result of the access point selection unit selects And a transmission / reception means for transmitting / receiving information via a wireless interface.

Acquisition According to still yet another aspect of the present invention, a method for selecting an access point in a wireless network, receiving the instruction information of the channel usage in a wireless network, the channel utilization u _k from the received information and a step of determining the supportable maximum data transmission rate v _k, when the scan time is less than the minimum scan hours, the steps of the wireless terminal is statistically processes the probability r _k channel occupied that sensing, the channel utilization The hidden terminal influence factor f _k is calculated based on u _k , the highest data transmission rate v _k , and the channel occupation probability r _k , and the access point AP is selected based on the calculated hidden terminal influence factor f _k To the basic service set where the designated access point is located And providing a method.

  According to the present invention, according to the conventional wireless local network standard IEEE802.11 protocol, there is no need to change the existing frame format of IEEE802.11e, which is easy to implement and has backward interchangeability. As a result, it is possible to obtain a method and apparatus for selecting an access point in a wireless local network that can reduce collisions between rising packets and improve the performance of the entire wireless local network.

  The above and other objects and novel features of the present invention will become more fully apparent when the following description of the embodiments is read in conjunction with the accompanying drawings.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, details and functions that are not necessary for the present invention are omitted in the description so as not to obscure an understanding of the present invention.

  According to the present invention, it is necessary to allow a wireless terminal to access a cell that is least affected by a hidden terminal. The method of the present invention includes two parts, initial association and reassociation. The initial association means that when the wireless terminal accesses the WLAN for the first time, one access point is selected by adopting the passive or main scanning mode. As time goes on, the node distribution in the network changes constantly. Therefore, the wireless terminal needs to update its access point to complete further optimization. If the access point conforms to the IEEE 802.11 protocol, it is necessary to subscribe an information field indicating the channel utilization rate to the downlink beacon and the probe response packet. If the access point conforms to the IEEE 802.11e protocol, it is not necessary to change the beacon and the probe response packet.

FIG. 4 is a schematic diagram showing a quality of service basic service set load element (QBSS load element) in a frame format of a beacon and a probe response packet defined in accordance with the 802.11e standard. What is shown in FIG. 4 is the contents included in the capability information therein. The current format includes an element ID field, a length field, a station count field, a channel utilization rate, and an available access capacity field. Here, the channel utilization is that the channel utilization u _k to be obtained from the channel information of the access point of the present invention. Therefore, in the method of the present invention, it is not necessary to add a new domain or change the frame format in the IEEE802.11e system. On the other hand, if the access point is a traditional IEEE 802.11 access point, it is necessary to subscribe to channel reservation information in the beacon and probe response packet for channel utilization information indicating the channel utilization rate. . It should be noted that the present invention is not limited to this, and channel utilization may be indicated in a similar manner.

  The wireless terminal can extract information indicating the channel utilization rate in the beacon and the probe response packet by a passive scanning method or a main scanning method.

Hereinafter, the process of selecting an access point by the wireless terminal will be described in detail with reference to FIG. FIG. 5 is a flowchart illustrating a process for selecting a wireless access point in a wireless local network according to an embodiment of the present invention. First, in step S501, when a wireless terminal enters the WLAN service area, the wireless terminal initializes parameters and sequentially scans channels. Here, k denotes the number of channels that are trying The current scan, u _k is the channel utilization of the channel, N is the is available total number of channels to which the wireless terminal supports. Upon initialization, it sets the number k of the channel currently scanned 1 sets u _k to minus one. This indicates that the wireless terminal has not yet received information on the channel usage rate. In step S502, it is determined whether the number of already scanned channels exceeds the total number of available channels supported by the wireless terminal. If the number of already scanned channels has not yet exceeded the total number of available channels (“NO” in step S502), the flow moves to step S503 to perform channel scanning. This step includes two methods, passive scan and main scan (see FIG. 2). In the case of passive scanning, the wireless terminal senses the channel and detects reception of a beacon packet. On the other hand, if it is a main scan, the wireless terminal senses channel idle, then transmits a probe request packet (Probe Request) and waits for a response to the probe response packet. Next, in step S504, it is determined whether the reception of the beacon packet or the probe response packet from the AP is successful. If the received beacon packet or the probe response packet from the AP is successful, in step S505, it extracts the information of a channel utilization field from the capability information elements of these packets, and records or updates as u _k. Subsequently, in step S506, the maximum data transmission rate v _k that can be supported by the wireless terminal is estimated. As an example, based on the received beacon or probe response packet energy or the received carrier signal interference noise ratio (SINR), the maximum data transmission rate v _k that can be supported by the wireless terminal is estimated. It is determined whether the scan time has reached the minimum scan time _Tmin . If "YES", the flow proceeds to step S508, the recorded as r _k by statistically processing the channel private use ratios sensed in time to scan the channel, in step S509, the according to the following formula (1) Estimate accessible measurements, ie hidden terminal influence factor f _k .

f _k = max (0, L _data / v _k * (u _k −r _k )) (1)
Here, L _data is an average length of a data packet to be transmitted by the wireless terminal. In step S510, the value of k is incremented, and the process returns to step S502 to prepare for scanning for the next channel.

In equation in step S509 (1), u _k can reflect the proportion fullness in The current cell, i.e. the channel is occupied, r _k is a sensing possible around the nodes of the wireless terminal, Represents the time that a non-hidden node occupies a channel. Therefore, the (u _k −r _k ) term is actually produced by the hidden terminal, and becomes a channel occupation situation in which the wireless terminal cannot sense immediately. In the transmission process, the transmission time of the data packet waiting to be transmitted also affects the transmission. The longer the transmission time, the greater the probability that a packet from the hidden terminal will produce a collision, and the greater the possibility of being affected by the hidden terminal. Therefore, the ratio “L _data / v _k ” between the length of the data waiting to be transmitted and the maximum data transmission rate v _k (determined by the received energy or SINR) that can be supported, that is, using the transmission time of the data packet, the hidden terminal Evaluate the impact of. The closer the wireless terminal is to the AP, the greater the signal level or carrier interference to noise ratio (SINR) received by the wireless terminal, and the higher the data transmission rate v _k supported by the wireless terminal, the “L _data / v _k ” term Becomes smaller. Similarly, the shorter the length of the data packet waiting for transmission, the smaller the “L _data / v _k ” term, and the greater the possibility that the wireless terminal will access the access point.

In step S507, if the current scan time is smaller than the minimum scan _Tmin time, the process returns to step S503 to continue scanning the channel. It should be noted that the setting of the minimum scan time is determined by the beacon cycle length, the data packet length, the data packet transmission rate, the number of wireless terminals in the current BBS, the service distribution, and the like. Should satisfy that a gentle transmission situation can be obtained within the scanning time. The larger the T _min , the more accurate the channel occupancy rate statistical processing, but the access delay increases. On the other hand, although the error of the statistical processing as T _min is less increases, the access delay is reduced. In application, an appropriate value may be set according to simulation, environment, or specific requirements.

Return to step 504 once again. Here, if the wireless terminal has not successfully received a beacon or a probe response packet in the channel scan process, this means that it has received data but has not received it successfully and after sending a probe request packet. That no data has been received within the threshold time. Then, the flow moves to step S511, where it is detected whether _uk is 0 or more. If “YES”, the terminal has received a beacon packet or a probe response packet within the channel scan period. It is expressed that there is. At this time, the flow proceeds to step S507, and the channel occupation ratio is calculated when the scan time reaches the minimum scan time _Tmin . If “NO” is determined in step S511, that is, if _uk is smaller than 0, it is expressed that the terminal has not received a beacon packet or a probe response packet within the current channel scan period. Yes. At this time, the flow moves to step S512 to determine whether or not the maximum scan time _Tmax has been reached. If the maximum scan time has not yet been reached, the flow returns to step S503 to continue scanning the kth channel. Here, in the passive scanning method, sensing is continued, whereas in the main scanning method, the probe request packet is retransmitted according to the basic MAC access process, and the above process is repeated. If it is determined in step S512 that the scan time has already reached the maximum scan time _Tmax , _fk is set to infinity in step S513. This indicates that the channel cannot be used. The flow then moves to step S510, increments the value of k, and returns to step S502 to prepare for the scan for the next channel.

When the wireless terminal finishes scanning for all wireless channels (YES in step S502), the flow proceeds to step S514, and the above steps are performed for all channels accessible to the wireless terminal, and the calculation is performed. The access point AP is selected based on the hidden terminal influencing factor f _k and joins the basic service set in which the selected access point is located. Preferably, an access point having a value of f _k that is minimum and not infinite is selected, associated with it, and subscribed to the basic service set.

  FIG. 6 shows an arrangement block diagram of an apparatus for selecting a wireless access point in a wireless local network according to an embodiment of the present invention. Hereinafter, an arrangement example of a device for selecting a wireless access point according to the present invention will be described in detail.

  In order to avoid confusion between the present invention and the prior art, in the description, details and functions that are not necessary for the present invention are omitted, and only portions related to the present invention will be described. This point can be understood by those skilled in the art.

A device for selecting the access point is included in a wireless terminal. The device for selecting an access point according to the present invention includes a transmission / reception device 61, a channel scanning device 62, an access point selection device 63, a determination device 64, and a calculation storage device 65. The transmission / reception device 61 changes the channel according to the results output by the channel scanning device 62 and the access point selection device 63, and transmits / receives information through the wireless interface. The channel scanning device 62 scans the channel state and transmits the scan result to the determination device 64. When the channel scanning device 62 instructs the start of scanning for a new channel, it initializes parameters to the calculation storage device 65 and changes the channel operated by the transmission / reception device 61. The determination device 64 receives the result from the channel scanning device 62 and makes a determination. If the channel scanning device 62 receives non-noise information in the scanning process or does not receive any data within a threshold time after the transmission of the probe request packet, the determining device 64 determines that the channel scanning device 62 is a beacon packet or probe. It is determined whether or not the response packet is correctly received. If it is a beacon packet or a probe response packet, the packet is put in the calculation storage device 65 and processed. If not, decision unit 64, u _k in the channel to detect whether a 0 in the calculation memory 65 at hand yet. If YES, the determination device 64 instructs the channel scan device 62 to continue scanning the channel until it is determined that the scan time has reached or exceeded the minimum scan time. At this time, the determination device 64 notifies the calculation storage device 65 that the correlation information is calculated. If u _k is not zero, continue to perform the scan time is whether or not the decision has been reached on the maximum scan time. Under the condition that the maximum scan time has already been reached, the calculation storage device 65 is notified that the channel occupation ratio f _k is set to infinity. If not, it instructs the scanning device 62 to continue scanning the channel. Here, in the passive scan method, sensing is continued, whereas in the main scan method, the probe request packet is retransmitted according to the basic MAC access process, and the process is repeated. Further, the determination device 64 further receives the information calculated by the calculation storage device 65 and determines whether or not all the channels have been scanned. If YES, the channel scan device 62 is instructed to scan the next channel. Otherwise, the access point selection device 63 is instructed to select an access point based on f _k calculated by the calculation storage device 65.

When the decision unit 64 instructs the successful reception of the beacon packet or the probe response packet, the channel utilization u _k extracted from these packets, the maximum supportable data rate in accordance with the energy of these received packets v _k is determined and these results are placed in the calculation store 65. When the determination device 64 indicates that the scan time is equal to or longer than T _min , the calculation storage device 65 calculates the channel occupation ratio r _k and f _k = max (0 based on the existing u _k and v _k. , L _data / v _k * (u _k −r _k )). When the determination device 64 indicates that the scan time is _{equal to} or greater than _Tmax , the calculation storage device 65 sets f _k = inf (infinity). When the determination device 64 indicates that scanning for all channels has been completed, it instructs the access point selection device 63 to select an access point. The access point selection device 63 selects an access point AP based on the calculated hidden terminal influence factor f _k based on the information provided by the calculation storage device 65, and sets the basic service set in which the selected access point is located. join. Preferably, an access point with a minimum value of f _k and not infinite is selected to prepare for access, and the transmission / reception device 61 is notified that the access point operates on the channel on which the access point is operating.

  After accessing the network, the wireless terminal can change the operating channel according to the state in the network and reselect the access point using the above process, that is, reassociate.

According to the present invention, certain wireless terminal, when there is a request for association or re-association, and sequentially scans each channel, and acquires the channel utilization information u _k from the received beacon packet or the probe response packet, the received packet of based on the energy or SINR to determine a maximum data transmission rate v _k supportable, if the scan time is less than the minimum scan hours, the radio terminal by statistically processing the ratio r _k channel occupied that sensing of the Based on the value, f _k = max (0, L _data / v _k * (u _k −r _k )) is calculated, and the above steps are performed for all channels accessible to the wireless terminal. select an access point AP based on the hidden terminal influence factor f _k, to position the selected access point group To subscribe to the service set. Preferably, after all channels have been scanned, the channel having the smallest f _k and f _k is not infinite is selected and accessed.

  FIG. 7 is a timing chart when an access point is selected by a passive channel scan method based on an example of the present invention.

Here, two access points will be described as an example. It should be understood that the method of the present invention can be applied to any number of access points and is not particularly limited. The access point AP1 and AP2 operate on non-overlapping channels CH ₁ and each CH _2, but may transmit the beacon packet Beacon periodically at regular beacon intervals. According to the IEEE 802.11 protocol, when the access point detects channel busy at the target transmission time (TBTT, Target Beacon Transmission Time), it should transmit a beacon packet after waiting for channel idle. Therefore, the time interval at which the access points AP1 and AP2 transmit the beacon packet Beacon floats up and down at a constant beacon interval.

As shown in FIG. 7, at time T _1, the wireless terminal MT enters the WLAN network, or by causes such as quality of service is deteriorated, producing a request for access point selection or reselection. At this time, the radio terminal MT initializes parameters by the channel scanning device 62 and starts scanning for CH ₁ . At time T ₂ , the wireless terminal MT extracts the channel utilization rate u ₁ from the packet based on the determination by the determination device 64 that the channel scanning device 62 has successfully received the beacon packet from the AP ₁ , and calculates it. Provide to storage device 65 and store in it. At the same time, the determination device 64 further determines the maximum data transmission rate v ₁ that can be supported according to the energy of the received beacon packet, and stores it in the calculation storage device 65. After completing the extraction of the information and determining the maximum data transmission rate v ₁ that can be supported, the determination device 64 detects whether the scan time is _{equal to} or greater than the minimum scan time T _min . As shown in FIG. 7, since (T ₂ −T ₁ )> T _min is satisfied, the determination device 64 performs statistical processing on the channel occupation probability r ₁ within the time interval from T ₁ to T _2. 65, and f ₁ = max (0, L _data / v ₁ * (u ₁ −r ₁ )) is calculated based on the channel occupation probability r ₁ that can be statistically processed. Thereafter, when the determination device 64 detects that the scan for all channels has not yet been completed, the determination device 64 notifies the channel scan device 62 that the scan for the next channel CH ₂ is started.

At time T ₃ , based on the determination that the beacon packet from AP 2 has been successfully received by the determination device 64, the wireless terminal MT extracts the channel utilization rate u ₂ from the result and stores it in the calculation storage device. The maximum data transmission rate v ₂ that can be supported is determined based on the energy of the received beacon packet and stored in the calculation storage device 65. Thereafter, the determination device detects whether or not the scan time is _{equal to} or longer than the minimum scan time _Tmin . As shown in FIG. 7, since (T ₃ −T ₂ ) <T _min is satisfied, the determination device 64 continues scanning the channel until time T ₄ , and (T ₄ −T ₂ ) = T _min is satisfied. Satisfied.

At time T ₄ , the wireless terminal MT notifies the calculation storage device 65 that the channel occupation probability r ₂ during the time interval from T ₂ to T ₄ is statistically processed via the determination device 64, and f ₂ = max ( 0, L _data / v ₂ * (u ₂ −r ₂ )). Thereafter, when the determination device 64 detects that scanning for all channels has been completed, the determination device 64 selects the access point AP corresponding to the minimum value of f ₁ and f ₂ based on the calculation result of the calculation storage device 65. Is sent to the selection device 63. Here, if f ₁ and f ₂ are equal, one AP is selected randomly or according to another existing AP selection method such as maximum RSSI or minimum load.

After selection of the access point at time _{T 4} is completed, the wireless terminal MT emits an association or reassociation request to establish (Association Request / Reassociation Request). After successfully receiving the association or reassociation response packet (Association Response / Reassociation Response), the user joins the basic service set in which the selected access point is located.

  FIG. 8 is a timing chart of another example of selecting an access point using a passive channel scan method according to the present invention.

Similar to the example shown in FIG. 7, at time T ₁ , the wireless terminal MT performs parameter initialization via the channel scanning device 62 and starts scanning for CH ₁ . At time T _2, the wireless terminal MT has received the data over a channel scan device 62, judgment unit 64 determines that the data has not been received successfully. Then, although utilization u _k corresponding to the verge of the channels in the calculation memory 65 to detect whether or not it is greater than 0, since not received successfully the beacon packet in the channel scan period, u _k is still "-1" which is an initial value. Subsequently, the wireless terminal continues to scan the channel until the maximum scan time _Tmax is reached. At time T ₃ , when the determination device 64 of the wireless terminal MT indicates that the maximum scan time T _max has been reached, the determination device 64 notifies the calculation storage device 65 that f ₁ is set as infinity. Thereafter, when the determination device 64 detects that a channel that has not been scanned still remains, the determination device 64 notifies the channel scanning device 62 that scanning for the next channel CH ₂ is started. Operation from subsequent time T ₃ to time T ₅ is the same as the operation from time T _2, the examples shown in FIGS. 7 to time T _4, a description thereof will be omitted. Then, at time T ₅ , for the channel CH ₂ , the radio terminal MT calculates statistical processing of the channel occupation probability r ₂ within the time interval from time T ₃ to time T ₅ via the determination device 64. The storage device 65 is notified, and f ₂ = max (0, L _data / v ₂ * (u ₂ −r ₂ )) is calculated. Thereafter, the determination device 64 detects that scanning for all channels has been completed, and selects the access point AP corresponding to the minimum value of f ₁ and f ₂ based on the calculation result of the calculation storage device 65. Is sent to the selection device 63. f ₁ because becomes infinite, it can not be selected AP2 deer. At this time, the radio terminal MT issues an association / reassociation construction request (Association Request / Reassociation Request). After successfully receiving the association or reassociation response packet (Association Response / Reassociation Response), the user joins the basic service set in which the selected access point is located.

  FIG. 9 is a timing chart when an access point is selected by the main channel scan method according to another embodiment of the present invention.

At time T _1, the wireless terminal MT enters the WLAN network, or by causes such as quality of service is deteriorated, producing a request for access point selection or reselection. At this time, the wireless terminal MT performs parameter initialization through the channel scan device 62, transmission if it detects idle CH _1, probe request packet on the CH ₁ according medium access control protocol (P_Req, Probe Request) to To do. At time _{T 2,} the access point AP1 receives the probe request packet from the wireless terminal MT successfully, in response to the received packet and transmits the probe response packet (P_Res, Probe Response) a. The probe response packet includes usage information u ₁ at hand channel. At time T ₃ , the wireless terminal MT detects that the probe response packet has been successfully received from the MT via the determination device 64, and returns an acknowledgment packet (ACK). At the same time, the channel utilization rate u ₁ is extracted using the determination device 64 and stored in the calculation storage device 65. Further, the determination device 64 determines the maximum data transmission rate v ₁ that can be supported according to the energy of the received probe response packet, and stores it in the calculation storage device 65. At time T _4, the wireless terminal MT has finished the transmission of the ACK packet, scan time determines whether the minimum scan time T _min or more through the decision device 64. Since (T ₄ −T ₁ )> T _min , the determination device notifies the calculation storage device 65 that the channel occupation probability r ₁ within the time interval from T ₁ to T ₄ is statistically processed. Calculate f ₁ = max (0, L _data / v ₁ * (u ₁ −r ₁ )) value. Thereafter, when the determination device 64 detects that scanning for all channels has not been completed, the determination device 64 notifies the scanning device 62 that scanning for the next channel CH ₂ is started.

At time _{T 5,} the wireless terminal MT detects an idle CH _2, sends a probe request packet on the channel CH _2. The subsequent transmission of the probe response packet and the acknowledgment packet is the same as the above-described process within the time from T ₁ to T _4, and therefore the description thereof is omitted here. Thereafter, at time T ₆ , when the response of the acknowledgment ACK packet is completed, the wireless terminal MT determines that the scan time is shorter than the minimum scan time T _min via the determination device 64, that is, (T ₆ −T ₄ ) <T _min , and the determination device 64 notifies the scanning device 62 that the channel is continuously scanned by the time T ₇ , and (T ₇ −T ₄ ) = T _min is satisfied. Is done. At time T ₇ , the wireless terminal MT notifies the calculation storage device 65 that the channel occupation probability r ₂ within the time interval from time T ₄ to time T ₇ is statistically processed via the determination device 64, and f ₂ = Max (0, L _data / v ₂ * (u ₂ −r ₂ )) is calculated. Thereafter, when the determination device 64 detects that scanning for all channels has been completed, the determination device 64 selects the access point AP corresponding to the minimum value of f ₁ and f ₂ based on the calculation result of the calculation storage device 65. Is notified to the access point selection device 63. At this time, if f ₁ and f ₂ are equal, one AP is selected randomly or according to another existing AP selection method such as maximum RSSI or minimum load. After selection of the access point is completed at time _{T 7,} the wireless terminal MT emits an association or reassociation request to establish (Association Request / Reassociation Request), to subscribe to a selected basic service set by the access point AP is located was .

According to the present invention, the wireless terminal obtains the channel utilization degree r by the non-hidden terminal node within the sensing range by channel scanning, and based on the channel utilization rate information u mounted on the received beacon or probe response packet. Thus, the channel occupation ratio (ur) by the hidden terminal in the basic service set can be estimated. Furthermore, since the collision by the hidden terminal depends on the time of data packet transmission, the wireless terminal operates on the k-th channel according to f _k = max (0, L _data / v _k * (u _k −r _k )). Since the influence of the hidden terminal can be estimated, the access point with the smallest influence of the hidden terminal can be selected and accessed, and the total throughput of the system can be increased. The present invention adopts a frame format completely defined in a conventional communication protocol according to an existing protocol and can be easily realized, and thus has an excellent application value.

  Thus far, the present invention has been described in conjunction with the preferred embodiment. It should be understood by those skilled in the art that various modifications, replacements and additions can be made without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should not be understood as being limited to the specific embodiments described above, but is limited only by the scope of the appended claims.

FIG. 1 is a schematic diagram in which a wireless terminal selects an access point in a wireless local network. FIG. 2A and FIG. 2B are schematic diagrams illustrating a process in which a wireless terminal establishes an association with an access point in a wireless local network. FIG. 3 schematically illustrates a situation in which the system throughput changes as the number of wireless terminals increases in a BSS environment. FIG. 4 is a schematic diagram of fields correlating with channel utilization in the frame format of beacons and probe response packets used in accordance with an embodiment of the present invention. FIG. 5 shows a flowchart of a process for selecting a wireless access point in a wireless local network according to an embodiment of the present invention. FIG. 6 shows a block diagram of an apparatus for selecting a wireless access point in a wireless local network according to an embodiment of the present invention. FIG. 7 is an example of a timing chart illustrating a one-channel scan mode executed when an access point is selected according to the present invention. FIG. 8 is another example of a timing chart illustrating a one-channel scan mode executed when an access point is selected according to the present invention. FIG. 9 is an example of a timing chart illustrating another channel scan mode executed when an access point is selected according to the present invention.

Claims (37)

A method for selecting an access point in a wireless network, comprising:
a. A step of the wireless terminal performs a channel scan for the channel in the network, receives the channel information transmitted from the access point, extracts a channel utilization factor u _k from the information,
b. Determining the maximum data transmission rate v _k that can be supported for the currently scanned channel based on the received channel information;
c. The channel occupation probability r _k within the scan time interval is statistically processed, and the hidden terminal influence factor f _k is calculated based on the channel utilization rate u _k , the highest data transmission rate v _k , and the channel occupation probability r _k. A calculating step;
d. Steps a to c described above are performed on all channels accessible to the wireless terminal, an access point AP is selected based on the calculated hidden terminal influence factor f _k, and the base where the selected access point is located Subscribing to a service set. Wireless terminal The method of claim 1, based on the energy information included in the received channel information, and determines a supportable maximum data transmission rate v _k. Step c, the scan time to detect whether the minimum scan time T _min above, if less than the scan time is a minimum scan time, receiving the channel information including the channel utilization u _k from the access point The method of claim 1, further comprising the step of continuing to scan the channel. The method according to claim 1, wherein the step of initializing a number of channels are channels utilization u _k and scan, and further comprising. The method of claim 1, further comprising: randomly selecting one of the access points having the same f _k when there are at least two access points having the same f _k in the wireless network. The method of claim 1, further comprising the step of calculating channel occupancy probabilities r _k and f _k under conditions where the minimum scan time has already been reached. The method further comprises selecting an access point AP corresponding to a minimum and not infinite value among the calculated hidden terminal influence factors f _k and joining a basic service set in which the selected access point is located. The method according to claim 1. The hidden terminal influence factor f _k is calculated based on the average length of data packets to be transmitted by the wireless terminal, the maximum data transmission rate v _k , the channel usage rate u _k , and the channel occupancy probability r _k. The method according to claim 1. Calculate f _k according to the following formula:
f _k = max (0, L _data / v _k * (u _k −r _k ))
_9. The method of claim 8, wherein L _data is an average length of a data packet to be transmitted by the wireless terminal, and k is a channel number currently being scanned. If the wireless terminal does not receive the channel information successfully, continue to scan for the channel to reach the maximum scan time T _max, when it reaches the maximum scan time T _max, the step of setting the f _k infinity The method of claim 1, further comprising: The method of claim 1, further comprising setting f _k as infinity when the maximum scan time is reached if the wireless terminal is not sensing any beacon packets. The method of claim 11, further comprising: if the wireless terminal has not sensed any beacon packets and continues to scan for the currently scanning channel when the maximum scan time has not yet been reached. . If the wireless terminal is not sensed any beacon packet, detects the channel utilization u _k is 0 or more, the step of calculating the probability r _k channel occupied when the scan time reaches the minimum scanning time T _min, The method of claim 1 further comprising: A method for selecting an access point in a wireless network, comprising:
a. Wireless terminal, the steps of: transmitting a probe request packet to the access point in the network, and receives a probe response packet returned from the access point, extracts a channel utilization factor u _k from the information,
b. Determining the maximum data transmission rate v _k that can be supported for the currently scanned channel based on the received channel information;
c. The channel occupation probability r _k within the scan time interval is statistically processed, and the hidden terminal influence factor f _k is calculated based on the channel utilization rate u _k , the highest data transmission rate v _k , and the channel occupation probability r _k. And steps to
d. Steps a to c described above are performed on all channels accessible to the wireless terminal, an access point AP is selected based on the calculated hidden terminal influence factor f _k, and the base where the selected access point is located Subscribing to a service set. Wireless terminal The method of claim 14, based on the energy information included in the received channel information, and determines a supportable maximum data transmission rate v _k. Step c, the scan time to detect whether the minimum scan time T _min above, if less than the scan time is a minimum scan time, receiving the channel information including the channel utilization u _k from the access point 15. The method of claim 14, further comprising the step of continuing to scan for the channel that is currently being scanned . The method of claim 14 the step of initializing the number of channels that are channel utilization rate u _k and scan, and further comprising. The method of claim 14, further comprising: randomly selecting one of the access points having the same f _k when there are at least two access points having the same f _k in the wireless network. The method of claim 14, further comprising the step of calculating channel occupancy probabilities r _k and f _k under conditions where the minimum scan time has already been reached. The method further comprises selecting an access point AP corresponding to a minimum and not infinite value among the calculated hidden terminal influence factors f _k and joining a basic service set in which the selected access point is located. The method according to claim 14. The hidden terminal influence factor f _k is calculated based on the average length of data packets to be transmitted by the wireless terminal, the maximum data transmission rate v _k , the channel usage rate u _k , and the channel occupancy probability r _k. 21. A method according to any of claims 14-20. Calculate f _k according to the following formula:
f _k = max (0, L _data / v _k * (u _k −r _k ))
The method according to claim 21, wherein L _data is an average length of a data packet to be transmitted by the wireless terminal, and k represents a channel number. If the wireless terminal does not receive the channel information successfully, continue to scan for the channel to reach the maximum scan time T _max, when it reaches the maximum scan time T _max, the step of setting the f _i as infinity 15. The method of claim 14, further comprising: 15. The method of claim 14, further comprising setting _fk as infinity when the maximum scan time is reached when the wireless terminal has not received a probe response packet after transmitting a probe request packet. the method of. If the wireless terminal does not receive the probe response packet after transmission of the probe request packet, it can not yet reached the maximum scan time, the step of retransmitting the probe request packet, to claim 24, further comprising The method described. If the wireless terminal does not receive the probe response packet after transmission of the probe request packet, when detecting a channel utilization u _k is 0 or more, the probability for channels occupied when the scan time reaches the minimum scanning time T _min r _k 15. The method of claim 14, further comprising the step of calculating An apparatus for selecting an access point in a wireless network, channel scan means for performing channel scan on a channel in the network and receiving channel information returned from the access point; and
A determining means for the channel utilization u _k extracted from the information received, to determine the maximum data transmission rate v _k supportable channel currently scanned based on the received channel information in the channel scan means,
Channel utilization u _k the determination unit has _acquired, and stores the highest data transmission rate v _k, by statistically processing the probability r _k channel occupied in the time interval of the scan, the channel utilization u _k, the maximum data transmission rate v _k , a calculation storage means for calculating the hidden terminal influence factor f _k based on the channel occupation probability r _k ;
An access point selection means for selecting an access point based on f _k calculated by the calculation storage means for each channel;
An apparatus comprising: a transmission / reception unit that changes a channel being accessed based on a result selected by the access point selection unit and transmits / receives information through a wireless interface. 28. The apparatus according to claim 27, wherein the channel scanning means initializes the parameters stored in the calculation storage means when instructed to start scanning for a new channel. The determination unit detects whether or not a scan time is equal to or longer than a minimum scan time T _min, and if the scan time is shorter than the minimum scan time, continues scanning for the currently scanned channel. Item 27. The apparatus according to Item 27. The hidden terminal influence factor f _k is calculated based on the average length of data packets to be transmitted by the wireless terminal, the maximum data transmission rate v _k , the channel usage rate u _k , and the channel occupancy probability r _k. 30. Apparatus according to any one of claims 27 to 29. The calculation storage means calculates f _k according to the following equation:
f _k = max (0, L _data / v _k * (u _k −r _k ))
The apparatus according to claim 30, wherein L _data is an average length of a data packet to be transmitted by the wireless terminal, and k represents a channel number. If the determination unit does not receive the channel information successfully, continue to scan for the channel to reach the maximum scan time T _max, when it reaches the maximum scan time T _max, the calculated storage means infinite is f _k 28. The apparatus of claim 27, wherein the apparatus is set as large. If the determination means has not sensed any beacon packet or has not received a probe response packet after transmitting a probe request packet, the calculation storage means sets f _k as infinity when the maximum scan time is reached. 28. The apparatus of claim 27. The access point selection means selects an access point AP corresponding to a minimum and not infinite value among the calculated hidden terminal influence factors f _k and joins a basic service set in which the selected access point is located. The apparatus of claim 27, further comprising a step. A method for selecting an access point in a wireless network, comprising:
Receiving channel usage indication information in a wireless network;
Obtaining a channel utilization rate u _k from the received information and determining a maximum data transmission rate v _k that can be supported;
When the scan time is less than the minimum scan hours, the steps the wireless terminal statistical probability r _k channel occupied that sensing, the channel utilization u _k, the maximum data transmission rate v _k, the probability for channels occupied r _k based on, the steps of: calculating a hidden terminal influence factor f _k, and select the access point AP based on the computed hidden terminal influence factor f _k, is selected access point subscribes to a basic service set is located, Including methods. 36. The method of claim 35, wherein if the maximum scan time has already been reached and channel information has not been successfully received, the calculation storage means sets _fk as infinity. The method further comprises selecting an access point AP corresponding to a minimum and not infinite value among the calculated hidden terminal influence factors f _k and joining a basic service set in which the selected access point is located. 36. The method of claim 35.

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