Synchronization of HCCA APs in OBSS January 2011 doc.: IEEE 802.11-08/0xxx January 2011 Synchronization of HCCA APs in OBSS Date: 2011, January Authors: Graham Smith, DSP Group Graham Smith, DSP Group

January 2011 doc.: IEEE 802.11-08/0xxx January 2011 Abstract As noted by several commenter's on 164, the HCCA TX OP Advertisement scheme suffers from inefficiency due to "gaps" caused when TSs go away or new TSs cannot be scheduled because of fragmented allocations. In addition, because the APs time clocks are not synchronized, there is a potential clock drift problem that causes the allocated time slots to also drift. The scheme was based upon the 11s scheme but in that case, there was a synchronization scheme. This presentation looks at the ‘drift problem’ and proposes to use the “adjust TSF to the fastest” scheme. This presentation addresses CIDs 1159 and 1254 in LB 170 Graham Smith, DSP Group Graham Smith, DSP Group

Drift TSF timer can have 0.01% error. January 2011 Drift TSF timer can have 0.01% error. Therefore worse case is 20us per Beacon (100TUs) OR 200us /second, 12ms per minute Therefore relative drift is significant Graham Smith, DSP Group

January 2011 The Drift Problem Graham Smith, DSP Group

Synchronize the Beacons January 2011 Synchronize the Beacons APs can synchronize their Beacon timing to the slowest clock. This is straight out of 11s. The basic mechanism is: Establish the relative offset of the TSFs by noting the advertised TSF in the other AP Beacon and comparing to own TSF. For each subsequent Beacon, measure the difference in the local TSF and the advertised TSF in the other AP (accounting for the offset) If difference is positive, say N, then ADD the difference, N, to the TSF. If listening to two Beacons, then take the higher result and add that Same as correcting on each one individually if they are seperated Graham Smith, DSP Group

January 2011 Simulations Permanent error as per timing error per Beacon Graham Smith, DSP Group

Proposal Add text along the lines as per this presentation January 2011 Proposal Add text along the lines as per this presentation Use 11s text with changes from ‘mesh STA’ to “HCCA AP” Graham Smith, DSP Group