Schedule Element Synchronization and Simplification May 2003 Schedule Element Synchronization and Simplification Amjad Soomro, Javier del Prado, Sai Shankar, Zhun Zhong and Atul Garg Philips . . . Soomro et. al. Philips

Outline Current Draft Specifications Issues Proposed Fixes Conclusions Month 2002 doc.: IEEE 802.11-02/xxxr0 May 2003 Outline Current Draft Specifications Issues Proposed Fixes Conclusions Soomro et. al. Philips John Doe, His Company

Specification Interval Month 2002 doc.: IEEE 802.11-02/xxxr0 May 2003 Schedule Element in D4.0 Section 7.3.2.19 Schedule Element 1 4 4 2 2 2 Element ID Length Min Service Interval Max Service Interval Minimum TXOP Interval Maximum TXOP Interval Specification Interval Soomro et. al. Philips John Doe, His Company

Min & Max Service Interval in D4.0 May 2003 Min & Max Service Interval in D4.0 The Min Service Interval specifies the minimum of: a) the minimum time in units of microseconds between the start of successful successive QoS(+)CF-Poll that is sent to a non-AP QSTA for uplink or direct link transmissions, and; b) the minimum time between successive successful TXOP downstream transmissions to a non-AP The Max Service Interval specifies the maximum of: a) the maximum time in units of microseconds between the start of scheduled successive QoS(+)CF-Poll that is sent to a non-AP QSTA for uplink or direct link transmissions, and; b) the maximum time between successive scheduled TXOP downstream transmissions to a non-AP Soomro et. al. Philips

Min & Max TXOP Duration in D4.0 May 2003 Min & Max TXOP Duration in D4.0 The Minimum TXOP Duration field is 2 octets long and contains an unsigned integer that specifies the minimum TXOP duration in units of microseconds that is allocated to this non-AP QSTA. The Maximum TXOP Duration field is 2 octets long and contains an unsigned interger that specifies the maximum TXOP duration in units of microseconds that is allocated to this non-AP QSTA. Soomro et. al. Philips

Issues in D4.0 HC services QSTA with bursts of downlink frames /TXOPS May 2003 Issues in D4.0 HC services QSTA with bursts of downlink frames /TXOPS To maximize power saving, chain of downlink frames/TXOPs could be grouped together when mean data rates are significant fraction of PHY data rate Max TXOP size of ~8ms may fragment channel allocation while reducing the potential to save power. Ambiguity in start/end of a service period If the response for the first frame in the service period is lost, the QAP and non-AP QSTA may become unsynchronized. Soomro et. al. Philips

Proposed Schedule Element Fixes May 2003 Proposed Schedule Element Fixes Proposed Schedule Element Frame Format Add one bit in QoS Control Field Last Bit: Indicates the this is the last downlink frame/TXOP in this service period Element ID Length Start Time Service Interval Max Service Duration Specification Interval 4 1 2 Octets: 1 Soomro et. al. Philips

May 2003 Definitions Start Time: The Start Time field shall be set equal to the low order four bytes of the TSF timer value at the start of the first service period, expressed in units of microseconds. Service Interval: The Service Interval shall be set equal to the time between two successive service periods, expressed in units of microseconds. Max Service Duration: The Max Service Duration shall be set equal to the maximum duration of a service period, expressed in units of 8 microseconds. Specification Interval: Same as in D4.0. Soomro et. al. Philips

May 2003 Definitions Service Period What: A service period is contiguous time during which a set of one or more downlink frames and/or one or more polled TXOPs are granted to a QSTA. Beginning: A Service Period starts at regular intervals of time specified in ‘Service Interval’ field. The first service period starts when low order 4 bytes of the TSF time equals the value specified in ‘Start Time’ field. End: A service period ends after 1) time duration specified in ‘Max Service Duration’ field; or 2) if it receives a frame with ‘Last’ bit set in QoS Control Field during a service period. Soomro et. al. Philips

Definitions May 2003 Max Service Duration Beacons Start Time Service Period TBTT TBTT TBTT TBTT TBTT TBTT Schedule Element Reception Service Interval Service Interval Soomro et. al. Philips

On Last Bit Last bit separates May 2003 On Last Bit Last bit separates End of power-save data delivery End of service period Both mechanisms could overlap in time and overloading More bit cannot resolve ambiguity Soomro et. al. Philips

Truncated TSF Timer Value May 2003 Truncated TSF Timer Value Low order 4 bytes cover ~ 71 min Timer ambiguity due to wrap over could be simply resolved by using the nearest reference value, that is, choose the nearest absolute time value between future and past values Reduces implementation complexity Soomro et. al. Philips

Conclusions Simplified Schedule Element Synchronized Service Periods May 2003 Conclusions Simplified Schedule Element Synchronized Service Periods HC and QSTA unambiguously know the service period start time Better power saving Less channel fragmentation Multiple TXOPs allowed per Service Period Soomro et. al. Philips