1. 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

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

3. Specification Interval
Month 2002
doc.: IEEE /xxxr0
May 2003
Schedule Element in D4.0
Section 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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