March 2006 doc.: IEEE 802.11-06/xxxr0 March 2006 Clarification on OM149: Some PSMP-enabled STAs may miss PSMP frame and remain awake for the entire PSMP sequence duration Harkirat Singh, Huai-Rong Shao and Chiu Ngo {har.singh, hr.shao, chiu.ngo}@samsung.com Samsung Electronics March 9, 2006 Harkirat, et al., Samsung Electronics

A typical PSMP sequence March 2006 A typical PSMP sequence PSMP frame includes multiple STA info frames: TSID STA ID DLT Start offset DLT Duration ULT Start offset ULT Duration 8 bits 16 bits 11 bits 10 bits STA info field format The ULT and DLT Start offsets are specified relative to the end of the PSMP frame (pg. 61-62 P802.11n-D0.02) The ULT and DLT durations specify Up Link and Down Link transmission periods Harkirat, et al., Samsung Electronics

March 2006 PSMP sequence error Some PSMP-enabled STAs may miss PSMP frame and remain awake for the entire PSMP sequence duration STA2 failed to receive the PSMP frame. The channel remains idle for this duration – no UL transmissions. STA2 remains awake during the entire PSMP sequence. This leads to: Waste of energy resources. Possibility of collisions caused by power-save legacy devices. Real-time applications may not meet the dead-line. Harkirat, et al., Samsung Electronics

March 2006 PSMP recovery (Without PSMP recovery) No UL transmissions (With PSMP recovery) (Time) Modify PSMP schedule of the currently scheduled STA only (STA2 in this figure) NO CHANGE in PSMP schedule of other STAs (STA3 & STA4 in this figure) Harkirat, et al., Samsung Electronics

Previous slide details March 2006 Previous slide details The AP takes control of the channel if the channel remains idle for a PIFS duration from the start of an ULT duration. The AP generates PSMP-recovery frame that includes modified ULT and/or DLT for the currently scheduled STA, but NO CHANGE of ULTs and/or DLTs for other STAs scheduled later in the PSMP sequence. No PSMP-recovery will be performed if the currently ULT duration is shorter than the total time of PSMP-recovery frame plus PIFS. Other STAs can be benefited, such as STA3/4 in the previous slide: If STA3/4 missed the original PSMP frame, STA3/4 must be awake. Hence, it can obtain its schedule from the PSMP-recovery frame which is the same schedule as in the original PSMP frame. If STA3/4 received the original PSMP frame, STA3/4 must be sleeping. Therefore, the schedule remains unchanged. Harkirat, et al., Samsung Electronics

March 2006 Changes suggested to the current draft (P802.11n-D0.02.pdf) to support the PSMP recovery Section 9.18.1.2: Up Link Transmission Suggested addition at the end of the above section (page 86): “The AP may gain control of the channel whenever the channel remains idle for a PIFS time from the start of an ULT duration. The AP may transmit a PSMP-recovery frame if the currently scheduled ULT duration is longer than the total time of PSMP-recovery frame plus PIFS. The PSMP-recovery frame will modify the schedule of the currently scheduled STA only. The schedule of other STAs will remain unchanged. The PSMP-recovery frame may include: (a) a modified ULT (and/or DLT) for the currently scheduled STA by adjusting the time remaining after PIFS and PSMP-recovery frame and (b) unmodified ULTs (and/or DLTs) for other STAs being originally scheduled after this ULT in the PSMP sequence. The ULT (or DLT) Start Offset is specified relative to the end of the PSMP-recovery frame to compensate for the time already lapsed. If the currently scheduled ULT duration is shorter than the total time of PSMP-recovery frame plus PIFS, no PSMP-recovery frame will be transmitted.” Harkirat, et al., Samsung Electronics

March 2006 Remarks PSMP-recovery does not change the scheduling of the PSMP sequence specified in the original PSMP frame. PSMP-recovery does not influence any other parts in the current draft (P802.11n-D0.02.pdf). PSMP-recovery is completely optional. Harkirat, et al., Samsung Electronics

March 2006 Thankyou! Harkirat, et al., Samsung Electronics

March 2006 Backup Harkirat, et al., Samsung Electronics

How offsets are calculated? March 2006 How offsets are calculated? ULT offset is specified from here After PSMP-recovery frame transmission, this much time is already lapsed New offset is specified from here (Time) Harkirat, et al., Samsung Electronics