The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, wherein like reference numerals designate corresponding parts in the various drawings, and wherein:
In order to better understand the present invention, a description of a wireless local area network (WLAN) according to an example embodiment of the present invention is provided. Then, a call setup is described with respect to the example WLAN, followed by a handoff process performed within the example WLAN.
As discussed in the Background of the Invention section, APs in conventional WLANs each transmit on one of a plurality of channels, with neighboring APs typically transmitting on different channels to reduce outer-cell interference, or interference received at a local AP from a neighboring cell (e.g., from a neighbor AP and/or mobile devices being served by a neighbor AP). APs in conventional WLANs also typically have different machine access code (MAC) addresses and different basic service set identifiers (BSSIDs). As will now be described in greater detail, WLANs according to example embodiments of the present invention include APs which communicate over the same channel and with the same MAC address and BSSID such that, from the perspective of a mobile device within the WLAN, all of the APs are the same.
The APs 105, 110 and 115 each communicate on the same channel (i.e., frequency range or bandwidth) and are assigned the same MAC address and the same BSSID. As will now be described, the uniformity of the APs 105, 110 and 115 within the WLAN 100 allows handoff support to be “offloaded” from mobile devices being served by the APs 105/110/115 to the master controller 125.
An example of call setup will now be described with reference to
In order to facilitate handoffs of mobile devices (e.g., mobile device 530) from a first AP (e.g., AP 105) to a second AP (e.g., AP 110) within the WLAN 100, the MC 125 defines a lower connection strength threshold and a higher connection strength threshold for each AP within the WLAN 100. Referring to
As shown in
In the example embodiment of
In step S300 of
As discussed above, within the process of
In step S330 of
In the example embodiment of
The AP 105 remains in step S325 and continues to serve the mobile device 530. Referring to
In step S410 of
In step S430, the MC 125 receives the report from the AP 110 and determines whether another AP is serving the mobile device 530. Because the AP 105 is already serving the mobile device 530, the MC 125 determines to take no action and does not authorize the AP 110 to establish a connection with the mobile device 530.
In step S435 of
In step S450 of
In step S455 of
In step S470, the MC 125 receives the lowered connection status report from the AP 105 and analyzes the active set for the mobile device 530 to determine whether another AP is available to serve the mobile device 530. Because the MC 125 added the AP 110 to the mobile device's 530 active set in step S450, the MC 125 determines that a handoff of the mobile device 530 from the AP 105 to the AP 110 is available. Accordingly, in step S475, the MC 125 sends handoff instructions to the AP 105 and the AP 110.
In step S480, the AP 105 receives the handoff instructions from the MC 125 and stops serving, or attempting to serve, the mobile device 530. In step S485, the AP 110 receives the handoff instructions from the MC 125 and begins serving the mobile device 530.
While not illustrated in
Further, as will be appreciated with respect to the handoff process of
As discussed above, each AP within the WLAN system 100 of
In order to reduce interference within the WLAN system 100, the MC 125 configures the APs within the WLAN system 100, as well as corresponding served mobile devices 530, to use time division in accordance with a point coordination function (PCF) mode. The PCF mode is a well-known polling protocol which partitions potential interferers into different time slots. Thus, the MC 125 configures each of its APs to poll potentially intersecting or interfering mobile devices during different time slots. The time slot partitioning of communication within the WLAN system 100 will now be described with respect to
In the example embodiment of
Table 1 (below) illustrates an example polling schedule for the mobile terminals T1 through T4.
As shown in Table 1, the example polling schedule includes three (3) time slots. The three time slots repeat in succession such that each mobile device is polled and can access its serving AP at a given interval (e.g., at every third time slot). In time slot 1, mobile device T1 is polled by AP 105 while AP 110 is in “standby” mode. Because mobile device T1 is in the intersecting portion of the entry level boundary regions for AP 105 and AP 110, when the mobile device T1 is polled, the AP 110 cannot poll mobile devices without interfering with the polling of the mobile device T1. Accordingly, AP 110 remains in standby during time slot 1. In time slot 2, AP 105 remains in standby while AP 110 polls mobile device T2. In time slot 3, AP 105 polls mobile device T3 and AP 110 polls mobile device T4. Both mobile devices T3 and T4 are capable of simultaneous polling in time slot 3 because they are each positioned in non-intersecting portions of the entry level boundary regions of AP 105 and AP 110, respectively. In other words, because mobile devices T3 and T4 are non-intersecting, the mobile devices T3 and T4 can be simultaneously polled without interfering with each other. Simultaneous polling of non-intersecting mobile devices is desirable to reduce the number of required time slots.
Generally, in order to increase the bandwidth used by the WLAN system 100 and to reduce “standby” or idle times, the fewest number of time slots for the polling schedule (e.g., of Table 1) should be used. Accordingly, Table 1 represents a relatively simple optimized polling schedule for the two APs 105/110 and four mobile devices T1-T4 illustrated in the example embodiment of
An example of a polling optimization process will now be described with respect to
In the example embodiment of
In step S800 of
Next, the MC 125 defines matrix criteria in step S805. The matrix criteria includes a set of assumptions for establishing rows and columns in a table format. The table format conforms with a merging algorithm, which will be described below. The merging algorithm collapses or reduces a number of columns within the initially established matrix into an “optimized” form. Once established, the matrix criteria is used to generate an initial “merging matrix”, which will be described in greater detail later with respect to step S815 of
One row is allocated to each of the APs 105 through 125. The row allocations do not change during the subsequent merging process (steps S820 through S825 of
One column is initially allocated to each mobile device T1 through T12. The initial column allocations may change during the subsequent merging process, such that after the merging process, columns are not necessarily associated with individual mobile devices;
A cell intersecting a mobile device's column and a row allocated to an AP serving the mobile device is assigned the ID Number of the mobile device (from step S800);
A cell intersecting with a mobile device's column and a row allocated to an AP, other than the AP serving the mobile device, having an entry level boundary region within which the mobile device is positioned is assigned a value of “1”; and
A cell intersecting with a mobile device's column and a row allocated to an AP which does not include the mobile device within its entry level boundary region is assigned a value of “0”.
In step S810 of
[1, ID Number], [ID Number, 1] or [ID Number, ID Number] does not transform and columns X and Y do not merge.
Once the MC 125 has assigned unique ID numbers for each of the plurality of mobile devices T1 through T12 (step S800) and defined matrix criteria (step S805) and merging criteria (step S810), the MC 125 is ready to generate and optimize the merging matrix.
In step S815 of
The merging matrix of Table 3 is “un-optimized” such that each of columns 1 through 12 correspond to mobile devices T1 through T12, respectively. In other words, if one were to simply use Table 3 as a polling schedule, twelve (12) time slots would be required to poll each of mobile devices T1 through T12, with each column corresponding to a time slot. Accordingly, it will be appreciated that such a tactic is inefficient if merges (i.e., column reductions) are possible. Rows 1 through 5 correspond with APs 105 through 125, respectively. However, unlike the columns 1 through 12, rows 1 through 5 correspond with APs 105 through 125 throughout the subsequent merging process.
In step S820, the MC 125 evaluates the initial merging matrix generated in step S815 to determine whether one or more column merges are possible. If each cell in a first column satisfies the merging criteria, as above described, for a transformation, with each cell in the same row of a second column, then a merge is considered to be possible. In other words, if the conditions [ID Number, 1] and [1, ID Number] do not occur in any pair of cells belonging to the same rows in the first and second columns, then the first and second columns may merge. Alternatively, if one or more of the conditions [ID Number, 1] and [1, ID Number] occur in any pair of cells belonging to the same rows in the first and second columns, then the first and second columns may not merge.
As will now be described, column merges will be described as being performed “from left to right”. In other words, a first available pair of mergeable columns will be assumed to include the two left-most columns for which merging is possible, wherein “left-most” means that a higher of two mergeable columns is minimized (e.g., such that a column merge of columns 4 and 5 is “left” compared to a column merge of 3 and 11, etc.). However, it is understood that the merging process may be performed in alternative ways, such as “from right to left”, or even at random. Accordingly, applying the merging criteria defined in step S810, the MC 125 determines that a merging of columns 1 and 2 may be performed, and the process advances to step S825.
In S825, the MC 125 performs the merging of two columns of the initial merging matrix. The merging of step S825 is performed as shown below in Table 4 (below).
As shown in Table 4 (above), columns 1 and 2 are merged to a resultant column 2 in accordance with the merging criteria established in step S810. Table 5 (below) illustrates the merging matrix after performing the above-described “first iteration” of the merging step S825.
After the merging step S825, the process returns to step S820. To simplify the description of the iterative merging process of
Accordingly, after step S820 determines that another merge is available, the process advances to a second iteration of step S825. In the second iteration of the merging step S825, columns 2 and 4 from Table 5 merge to a resultant column 3. In addition, because column 4 is merged into the resultant column 3, column 3 from Table 5 is “bumped up” to a resultant column 4. Further, in the second iteration of the merging step S825, the two left-most columns (i.e., columns 2 and 3) do not merge because [201, 1] for row #2 does not meet the merging criteria defined above in step S810, and as such, step S820 would not determine that a merge of columns 2 and 3 is possible. Table 6 (below) illustrates the merging matrix after performing the second iteration of the merging step S825.
In a third iteration of the merging step S825, columns 4 and 5 from Table 6 merge to a resultant column 5 (e.g., because a merge with column 3 and either of columns 4 or 5 is not possible). Accordingly, because column 4 is merged into resultant column 3, column 3 from Table 6 is “bumped up” to a resultant column 4. Table 7 (below) illustrates the merging matrix after performing the third iteration of the merging step S825.
Hereinafter, iterations four through seven of the merging step S825 will be illustrated in the forms of resultant merging matrixes in Tables 8 through 11, respectively, for the sake of brevity, without a further description thereof. The column merges shown below in Tables 8 through 11 will be readily apparent in view of the description above.
After achieving the merging matrix illustrated above in Table 11 in the seventh iteration of the merging step S825, the process returns to step S820 and the MC 125 determines that no additional merges are possible (e.g., because no pair of columns meet the merging criteria in each respective rows). The process of
Table 12 (above) illustrates an optimized polling schedule for the example embodiment of
The merging matrix illustrated in Table 12 may be interpreted as a polling schedule by treating each column as a time slot and treating rows 1 through 5 as APs 105 through 125, respectively. Accordingly, Table 12 may be alternatively presented in a more descriptive fashion as shown in Table 13 (below).
Accordingly, referring to Table 13 (above), during time slot 1, AP 105 polls mobile device T1, AP 110 polls mobile device T2, AP 115 polls mobile device T11 and AP 120 polls mobile device T4. In time slot 2, AP 105 polls mobile device T6, AP 115 polls mobile device T3 and AP 125 polls mobile device T5. In time slot 3, AP 110 polls mobile device T7. In time slot 4, AP 105 polls mobile device T9, AP 120 polls mobile device T8 and AP 125 polls mobile device T10. In time slot 5, AP 120 polls mobile device T12.
Thus, the APs 105 through 125 transition through time slots 1 through 5 and poll mobile devices T1 through T12 in accordance with Table 13 repeatedly until the MC 125 updates the polling schedule. In an example, the MC 125 updates the polling schedule (1) if one or more of the mobile devices T1 through T12 is dropped, (2) if one or more of the mobile devices T1 through T12 is handed off to a different AP, (3) if a new mobile device is added to the WLAN or (4) if one or more of the mobile devices T1 through T12 moves to a new position which affects the polling schedule (e.g., from a position intersecting with one set of entry level boundary regions to a position intersecting with a different set of entry level boundary regions, etc.).
Example embodiments of the present invention being thus described, it will be obvious that the same may be varied in many ways. For example, while generally above-described with respect to 802.11 WLANs, it is understood that other example embodiments of the present invention may be applied to WLANs operating in accordance with any wireless communication protocol (e.g., Bluetooth, 802.16, etc.). Such variations are not to be regarded as a departure from the spirit and scope of the exemplary embodiments of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the invention.
Number | Date | Country | Kind |
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200610108067.2 | Jul 2006 | CN | national |