Support for Dynamic Channel Selection (DCS) in 802.11v January 2003 IEEE 802.11-03/100r1 May 2005 doc: IEEE 802.11-05/xxx1r0 Support for Dynamic Channel Selection (DCS) in 802.11v Joe Kwak, Marian Rudolf (InterDigital) Submission Kwak, Rudolf

Introduction Proposed goal of Dynamic Channel Selection for 802.11v “Change the operating channel (and/or band) for the entire BSS during live system operation” Channel change should be done seamlessly with no loss of connectivity both when idle and in a session The channel change should be done in a bandwidth efficient manner Channel change should not require manual user intervention Benefits of Dynamic Channel Selection Dynamic Channel Selection can be used for: Channel escape in the presence of external interference Channel selection optimization purposes Right setting of an AP’s operating channel is one key tool to increase effective throughput for a BSS (> factor 2-3) Cooperation between APs is not required for DCS to be efficient APs can independently observe interference levels and choose best channel Kwak, Rudolf Submission

DCS illustration Throughput Kwak, Rudolf Submission

DCS illustration Interference Throughput Kwak, Rudolf Submission

DCS illustration Interference Throughput Kwak, Rudolf Submission

DCS illustration Interference Throughput Kwak, Rudolf Submission

What we can and cannot do today Today, any 802.11 AP can change its channel AP will simply stop Tx on old channel and switch to new channel Associated STAs in the BSS will re-select a “new” BSS, i.e. they may or may not choose the old AP on the new channel or choose another BSS altogether Cons: Service interruption for all STAs currently in a session Cons: AP has no mean of knowing where the STA will end-up Cons: STA cannot request a channel change or indicate their preferred channel to the AP 802.11h DFS service (see annex) Primarily motivated by regulatory requirements in the 5GHz bands Goal is to stop Tx on interfered channel, not to ensure a smooth transition of the BSS (AP and all associated STAs) to the new frequency Cons: AP has no means of knowing if STA can/will follow or not Cons: After channel change, AP does not know who did / did not follow Cons: STA cannot request/suggest a channel change or indicate their preferred channel to the AP Kwak, Rudolf Submission

Shortcomings summarized AP has no mean of knowing if STA can/will follow or not AP does not even know if STA received the channel change notification Will result in service interruption / loss of connectivity for some STA Would the AP really change channel had he known its only STA would not follow? After channel change, AP does not immediately know who did follow and who did not This forces AP to try sending packets to STA that are no longer there Exponential backoff poor spectrum efficiency AP cannot release resources (802.11e) allocated to STA who did not follow STA cannot request / suggest a channel change or preferred channel to AP Interference experienced by STA is different than interference experienced by AP Measurement reporting is not enough as interference can arise suddenly Relying solely on AP to detect interference problems at STA would imply huge signaling overhead due to need for high frequency of measurement reports DCS needs to ensure that All STAs are aware of the intention of the AP to change the channel The AP knows, prior to making the channel change, which STA(s) will follow on new channel Had the AP decided to go forward with the channel change, AP knows which STA have followed on the new channel STA can suggest a channel change Kwak, Rudolf Submission

802.11v DCS Procedure (AP initiated) AP sends channel change intention message indicating its intention to change channel to channel X at time Y. Reason and measurements can be appended STAs send Channel Change Response message indicating whether or not it can/will follow the AP on its new channel If AP decides to change channel, it sends channel change notification, which confirms channel change STA X sends the AP a channel change executed message after it has changed channel Kwak, Rudolf Submission

802.11v DCS Procedure (STA initiated) The station sends change channel suggestion to its AP Upon reception of this message, If AP has multiple STAs, it will send Channel Change Intention message to other STAs indicating its intention to change channel to channel X at time Y If AP decides to go forward with channel change, AP sends Channel Change notification message Kwak, Rudolf Submission

802.11h DFS Background Kwak, Rudolf Submission

802.11h DFS Services Association of STAs with an AP in a BSS based on the STAs’ supported channels. Quieting the current channel so it can be tested for the presence of radar with less interference from other STAs. Testing channels for radar before using a channel and while operating in a channel. Discontinuing operations after detecting radar in the current channel to avoid interference with radar. Detecting radar in the current and other channels based on regulatory requirements. Requesting and reporting of measurements in the current and other channels. Selecting and advertising a new channel to assist the migration of a BSS or independent BSS (IBSS) after radar is detected. Source: IEEE Std 802.11h-2003 Kwak, Rudolf Submission

802.11h DFS Signaling (1/2) Supported Channel capabilities The Supported Channels element contains a list of channel in which a STA is capable of operating. “Supported channel” IE is added to Association/Re-association Request frame “Channel Switch Announcement” IE Used by an AP in a BSS to advertise when it is changing to a new channel and the channel number of the new channel, optionally, enforce stop of Tx on the current channel until switching time “Channel Switch Announcement” IE can be attached to the Beacon or Probe response frame or sent by itself as Channel Switch Announcement action frame (particularly IBSS case) Kwak, Rudolf Submission

802.11h DFS Signaling (2/2) Measurements Request/Report action frames Measurement Request contains measurement type and configuration (i.e. periodic, once), like 11k Measurement Report can be used to alert other STAs about presence of radar Quieting the current channel The Quiet element defines an interval during which no transmission shall occur in the current channel This interval may be used to assist in making channel measurements without interference from other STAs in the BSS or IBSS. Quiet IE attached to the beacon or probe response frames IBSS DFS element It contains information for DFS operation in an IBSS. Kwak, Rudolf Submission

BSS Operation AP can configure the quiet interval for measurement purposes AP detects radar signals on its own or via a measurement report from the STA AP sends channel switch announcement in the beacon or probe response frame Can be sent few times to make sure PS STAs received it Cannel switching may take up to several hundred of ms’s Kwak, Rudolf Submission

IBSS Operation DFS owner STA detects radar signals on its own or via a measurement report from other STA DFS owner STA sends channel switch announcement frame to all STA in the IBSS Other STAs are not mandated to switch channel However, they are mandated to cease transmission on current channel If other STA detects radar and did not receive channel switch announcement frame for DFS recovery interval STA starts the DFS owner recovery procedure to determine a new DFS owner for the IBSS Kwak, Rudolf Submission