WO2014178707A2

WO2014178707A2 - A system and method to reduce media access control (mac) layer handoff latency

Info

Publication number: WO2014178707A2
Application number: PCT/MY2014/000080
Authority: WO
Inventors: Mohammed Abobakr Ahmed BALFAQIH; Mohammad Hasbullah BIN MAZLAN; Siti Norhaizum Binti Mohamad HASNAN; Shariq Haseeb; Mohd Ariff BIN ABDULLAH
Original assignee: Mimos Berhad
Priority date: 2013-05-03
Filing date: 2014-04-28
Publication date: 2014-11-06
Also published as: MY181908A; WO2014178707A3

Abstract

The present invention relates to system and method for MAC layer handoff which comprises of multiple access points, a mobile device, and an access controller. It is used to minimize MAC layer handoff latency in centralized WLAN network and obviate scanning time during MAC layer handoff process. It is also used to reduce number of probed channels and waiting time for each channel response during probing phase. The system comprises at least one mobile device (110) connected to an access point (120), at least two access points (120), and an access controller connected to the at least two access point (120). The at least one mobile device (110) includes an AP Channel Receiver (111), the access controller (130) includes a Next AP Selector (140); and each access point (120) includes a Received Signal Strength Inspector (142).

Description

A SYSTEM AND METHOD TO REDUCE MEDIA ACCESS CONTROL (MAC)

LAYER HANDOFF LATENCY

FIELD OF INVENTION

The present invention relates to a system and method for media access control (MAC) layer handoff. More particularly, the present invention related to a system and method to reduce MAC layer handoff latency in centralized wireless local area network architecture. BACKGROUND OF THE INVENTION

Centralized wireless local area network (WLAN) is a system which enables the access controller to manage all the access point (AP) at the respective area. Public WLANs show a steady growth in the internet. However, as the user mobility increases, the small cell size of WLANs will induce frequent handoffs causing inevitable delays. When the notices that the current AP is no longer reachable, it performs a handoff. For handoff process, a mobile device actively broadcasts additional probe request and frames on each channel and expects to receive probe response from access points, apart from listening to beacon messages. The mobile device stays on each channel within min Channel Time to max Channel Time, depending on if the channel is active.

Min Channel Time is a minimum time that a mobile device spends on each channel when scanning. Max Channel Time is a maximum time that a mobile device spends on each channel when scanning. The min channel time and the max channel time is the duration to detect whether or not the channel is active. Some channels may have no active access point while others may have more than one active access point. After the scanning process, the mobile device may obtain several available access points on different active channels. It chooses the best one in terms of signal strength or signal-to-noise ratio and enters the authentication process. When the new access point successfully authenticates the mobile device association is performed. After the media access control (MAC) layer handoff procedures are completed, all the packets from or to the mobile device are relayed by the new access point.

In order to address the handoff latency, US patent publication no. 2009/0316658 A1 discloses methods and systems to monitor wireless signal strengths associated with wireless access points, and to initiate a handover procedure upon one or more thresholds. A handoff may be initiated prior to a loss of an existing network connection. But the handoff latency is not been reduced enormously as it is limited to the current access point only.

In European patent no 1653666 A1 , a method for fast radio link measurements of access point candidates for WLAN handover, a mobile device, an access point and program modules therefor is disclosed. The main idea of this method is that an access point that has received a probe request message from a mobile device does not send back probe message to the mobile device if the mobile device has indicated in the probe request message that it intends to perform radio link measurements. Instead of sending a probe response message, the access point only sends an acknowledgement message which will be used by the mobile device. However, the process of sending acknowledgment message also involves time delay during the transmission.

In US patent no. 7403506 B2, this prior art has disclosed seamless handoff method in wireless local area network. The method detects movement of a mobile node; prepares a handoff of the mobile node from a current fixed node to potential fixed nodes upon detecting movement of the mobile node; decides whether to handoff to one of the potential fixed nodes as a target fixed node; and performs the handoff from the current fixed node to the target fixed node. The handoff method enables the mobile station to quickly move its association from one access point to another by minimizing a probe delay which is a primary contributor to handoff delay. However, this method causes a scanning latency which is one of the main handoff latency components whereby the scanning process starts after suffering from loss of packets or poor performance for some time.

Therefore, there is a need to provide a system and method for handoff that addresses the above drawbacks.

SUMMARY OF INVENTION

The present invention provides a system (100) to reduce media access control (MAC) layer handoff latency. The system (100) comprises at least one mobile (110) connected to an access point (120), at least two access points (120), and an access controller connected to the at least two access point (120). Moreover, the system is characterized in that the at least one mobile device (110) includes an AP Channel Receiver (111) the access controller (130) includes a Next AP Selector (140) and each access point (120) includes a Received Signal Strength Inspector (142).

Preferably, the AP's Channel Receiver (111) includes a Next AP's Channel Receiver (112) for receiving the next AP's address and channel for the mobile device (110) to associate and authenticate; and a Neighbor AP Channels List Receiver (113) for receiving the list of all neighbor AP channel for the mobile device (110) to broadcast probe request message.

Preferably, the Next AP Selector (140) includes a Mobile Device Signal Strength Collector (137) for determining the signal strength of the mobile device (110) from all neighbour APs (120), a Next AP Manager (139) for checking the available capacity of neighbor APs (120) and detects candidate APs (120) and a Next AP decision Maker (138) for selecting the next access point's address and channel.

Preferably, the Received Signal Strength Inspector (142) includes a Signal Strength Capture (143) for checking mobile device's signal strength at neighbor APs (120) and a Signal Strength Transmitter (144) for sending the mobile device's signal strength to the Next AP Selector (140).

The present invention also provides a method to reduce media access control (MAC) layer handoff latency. The method is characterized by the steps of connecting a mobile device (110) to an access point (120); sending data to the access point (120) from the mobile device (110); if the RSSI of mobile device (110) is less than a first Threshold, collecting the received signal strength indication of the mobile device (110) for certain period by RSSI Collector (133) of an access controller (130); if RSSI pattern continuously decreasing until it becomes less than a second Threshold, informing the centralized neighbor graph (CNG) (136) on the status of the mobile device by the RSSI Change Checker (131); sending the neighbor AP channels to the mobile device (110) by the CNG (136); broadcasting a probe request message to neighbor AP channels by the mobile device (110); transmitting the mobile device's signal strength to the access controller ( 30) by the neighbors APs (120); checking whether all neighbor APs have sent mobile device's by the access controller (130); if all neighbor APs have sent mobile device's signal strength, checking the capacity and availability of the neighbor APs (120) by the access controller (130); calculating the average of collected RSSI of the mobile device (110) by the access controller (130); selecting the next access point (120) based on the highest average signal strength with available capacity; informing the mobile device (110) of the next access point (120) by the access controller (130); and if the RSSI is less than a handoff Threshold, roaming to the selected next access point (120) by the mobile device (110). Preferably, the step of sending data to the access point (120) from the mobile device (110) includes forwarding the Received Signal Strength Indication (RSSI) to the access controller (130) through IEEE 802.11 Frame Information by the access point (120). Preferably, if not all neighbor APs have sent mobile device's signal strength, re-transmitting mobile device's signal strength for certain times till the retransmissions reach the maximum capacity.

Preferably, the probe request message includes an Action No Acknowledgement message in its sub-type field of the message frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 shows a system (100) to reduce media access control (MAC) layer handoff latency according to an embodiment of the present invention. FIG. 2 shows a mobile device (110) of the system (100) of FIG. 1.

FIG. 3 shows an access controller (130) of the system (100) in FIG. 1. FIG. 4 shows an access point (120) of the system (100) of FIG. 1. FIG. 5(a-b) shows a flowchart of a method to reduce MAC layer handoff latency as performed by the system (100) according to an embodiment of the present invention.

DESCRIPTION OF THE PREFFERED EMBODIMENT

A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well known functions or constructions are not described in detail since they would obscure the description with unnecessary detail.

Referring to FIG. 1, there is shown a system (100) to reduce media access control (MAC) layer handoff latency in centralized wireless local area network architecture according to an embodiment of the present invention. The system (100) comprises of at least one mobile device (MD) (110), at least two access points (AP) (120) and an access controller (130).

Based on FIG. 2, the mobile device (110) comprises of an AP Channel Receiver (111) and a probe message transmitter (114). AP channel Receiver (111) comprises of a next AP Channel Receiver (112) and a Neighbour AP Channels List Receiver (113). Fundamentally, next AP channel Receiver (112) is a receiver which receives the next AP's address and channel for the mobile device (110) to associate and authenticate. Neighbor AP Channels List Receiver (113) is a receiver which receives the list of all neighbor AP channel for the mobile device (110) to broadcast probe request. For the access controller (130) as shown in FIG. 3, it includes a RSSI Change

Checker (131), a Centralized Neighbor Graph (CNG) (136) and a Next AP Selector (NAPS) (140). The RSSI Change checker (131) comprises of a first RSSI Change Checker (132), a RSSI Collector (133), a pattern decision (134) and a second RSSI Checker (135). The first RSSI Checker (131) and the second RSSI Change Checker (135) are used to detect the movement of the mobile device (110) whereas the RSSI Collector (133) is used to capture the RSSI during certain period of time. The pattern decision (134) is used for estimating the transition pattern of the RSSI of the mobile device (110) collected from IEEE 802.11 frame information. The transition pattern is used to determine the mobile device (110) movement direction. In other word, it is to determine whether the mobile device (110) leaves the coverage of the current AP or not.

The Centralized Neighbor Graph (CNG) (136) provides a mobility topology wireless network that shows the re-association relationship between a mobile device (110) and its neighbour AP (120). The access controller (130) constructs the CNG (136) during initial period of the network life based on the mobility of the mobile devices (110) between the APs (120). The CNG (136) is used to identify the candidate APs (120) that a mobile device could tolerably re-associate with.

The next AP selector (140) comprises a MD Signal Strength Collector (137), a Next AP decision Maker (138) and a NAP Manager (139). The MD Signal Strength Collector (137) is used to determine the signal strength of the mobile device (110) from all neighbour APs (120). The NAP Manager (139) is used to check the available capacity of neighbor APs (120) and detects candidate APs (120) while the Next AP decision Maker (138) selects the next access point's address and channel for the handoff of the mobile device (110).

In FIG. 4, there is shown an access point (AP) (120) which includes a Probe Request Receiver (141) and a RSSI Inspector (142). The Probe Request Receiver (141) is used to forward probe request messages received from the mobile device (110) to the RSSI Inspector (142). While for RSSI Inspector (142), it includes a Signal Strength Capture (143) and a Signal Strength Transmitter (144). The Signal Strength Capture (143) is used to check mobile device's signal strength at neighbor APs (120) whereas Signal Strength Transmitter (144) is used to send the mobile device's signal strength to the Next AP Selector (140).

FIGS. 5(a-b) show a flowchart of a method to reduce MAC layer handoff latency as performed by the system (100) according to an embodiment of the present invention. Initially, the mobile device (110) connects to the access point (120) as in step 310. When the mobile device (110) sends data to the access point (120) as in step 311 , the access point (120) forwards its Received Signal Strength Indication (RSSI) to the access controller (130) through IEEE 802.1 1 Frame Information. If the RSSI of mobile device (110) is less than a first Threshold, the RSSI Collector (133) collects the RSSI of the mobile device (110) for certain period and checks the changes in RSSI as in decision 312 and step 313. If RSSI of the mobile device (110) is greater than the first Threshold, the method returns to step 311.

Continue with step 314, if RSSI pattern continuously decreasing until it becomes less than a second Threshold, the RSSI Change Checker (131) informs the centralized neighbor graph (CNG) (136) on the status of the mobile device (110) as in step 315. Otherwise, the method returns to decision 312. Based on the mobile device' status, CNG (136) sends the neighbor AP channels to the mobile device 110) as in step 316. The neighbor AP channels are determined from the stored neighbor list in the CNG (136), wherein the stored neighbor list includes a list of address of the AP and the addresses of the neighbor APs. Thereon, the mobile device (110) broadcasts a probe request message to neighbor AP channels for certain times as in step 317 upon receiving the neighbor AP list. The probe request message includes an Action No Acknowledgement message in its sub-type field of the message frame.

In step 318, the neighbors APs (120) transmit the mobile device's signal strength to the access controller (130). Next in step 319, the access controller (130) checks whether all neighbor APs have sent mobile device's as in step 318 and decision 320. If all neighbor APs (120) have sent the RSSI, step 322 will take place where the access controller (130) will check the capacity and availability of the neighbor APs (120). Otherwise, mobile device's signal strength will be re-transmitted for certain times till the re-transmissions reach the maximum capacity as in step 321. If there is no response from the Neighbor APs (120), the method returns to step 316. In step 323, access controller (130) calculates the average of collected RSSI of the mobile device (110) provided by the neighbor APs (120). In step 324, the next access point (120) is selected based on the highest average signal strength with available capacity. Thereon, the access controller (130) informs the mobile device (110) the next access point (120) as in step (325). When the RSSI is less than the handoff Threshold as in step 326, the mobile device (110) roams to the selected next access point (120) as in step 327.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specifications are words of description rather than limitation and various changes may be made without departing from the scope of the invention.

Claims

1. A system to reduce media access control (MAC) layer handoff latency comprising:

a) at least one mobile device (110) connected to an access point (120), b) at least two access points (120), and

c) an access controller connected to the at least two access point (120); wherein the system is characterized in that:

d) the at least one mobile device (110) includes an AP Channel Receiver (111);

e) the access controller (130) includes a Next AP Selector (140); and f) each access point (120) includes a Received Signal Strength Inspector (142).

2. The system as claimed in Claim 1 , wherein the AP's Channel Receiver (111) includes:

a) a Next AP's Channel Receiver (112) for receiving the next AP's address and channel for the mobile device (110) to associate and authenticate; and

b) a Neighbor AP Channels List Receiver (113) for receiving the list of all neighbor AP channel for the mobile device (110) to broadcast probe request message.

3. The system as claimed in Claim 1 , wherein the Next AP Selector (140) includes: a) a Mobile Device Signal Strength Collector (137) for determining the signal strength of the mobile device (110) from all neighbour APs (120) ; b) a Next AP Manager (139) for checking the available capacity of neighbor APs (120) and detects candidate APs (120); and

c) a Next AP decision Maker (138) for selecting the next access point's address and channel.

4. The system as claimed in Claim 1 , wherein the Received Signal Strength Inspector (142) includes: a) a Signal Strength Capture (143) for checking mobile device's signal strength at neighbor APs (120); and

b) a Signal Strength Transmitter (144) for sending the mobile device's signal strength to the Next AP Selector (140).

5. A method to reduce media access control (MAC) layer handoff latency is characterized by the steps of: a) connecting a mobile device (110) to an access point (120);

b) sending data to the access point (120) from the mobile device (110);

c) collecting the received signal strength indication of the mobile device

( 10) for certain period by RSSI Collector (133) of an access controller (130) if the RSSI of mobile device (110) is less than a first Threshold; d) informing the centralized neighbor graph (CNG) (136) on the status of the mobile device by the RSSI Change Checker (131) if RSSI pattern continuously decreasing until it becomes less than a second Threshold; e) sending the neighbor AP channels to the mobile device (110) by the CNG (136);

f) broadcasting a probe request message to neighbor AP channels by the mobile device ( 10);

g) transmitting the mobile device's signal strength to the access controller

(130) by the neighbors APs (120);

h) checking whether all neighbor APs have sent mobile device's by the access controller (130);

i) checking the capacity and availability of the neighbor APs (120) by the access controller (130) if all neighbor APs have sent mobile device's signal strength;

j) calculating the average of collected RSSI of the mobile device (110) by the access controller (130);

k) selecting the next access point (120) based on the highest average signal strength with available capacity;

I) informing the mobile device (110) of the next access point (120) by the access controller (130); and

m) roaming to the selected next access point (120) by the mobile device

(110) if the RSSI is less than a handoff Threshold.

6. The method as claimed in claim 5, wherein step (b) includes forwarding the Received Signal Strength Indication (RSSI) to the access controller (130) through IEEE 802.1 1 Frame Information by the access point (120).

7. The method as claimed in claim 5, wherein if not all neighbor APs have sent mobile device's signal strength, re-transmitting mobile device's signal strength for certain times till the re-transmissions reach the maximum capacity.

8. The method as claimed in claim 5, wherein the probe request message includes an Action No Acknowledgement message in its sub-type field of the message frame.