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Power Saving Mechanisms Simulation in Wireless Networked Office Environment

This presentation delves into preliminary simulation results analyzing power-saving mechanisms impacting wireless networking for high-quality multimedia data transfer and real-time communication in an office setting. The study examines the performance and effects of APSD (Automatic Power Save Delivery) in a scenario involving multiple applications with specific bandwidth requirements and user activities. Insights on network topology, traffic patterns, simulation parameters, performance comparisons, and the impact of data aggregation are discussed. Future works include extending the simulation for PSMP (Power Saving Multi-Poll) and enhancing MAC functions for efficient data transmission.

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Power Saving Mechanisms Simulation in Wireless Networked Office Environment

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  1. [Preliminary Simulation Results on Power Saving] Date: 2009-11-19 Authors: Slide 1

  2. Abstract • This presentation reports the preliminary results of our simulations of existing power saving mechanisms. • The scenario simulated is taken from IEEE 802 Doc 09/0161r02, Usage Model 2d: Wireless Networking for Office. • The performance and effect of APSD have been examined. Slide 2

  3. Simulation Scenario* Pre-Conditions: Office with people engaged in high quality/high revenue services that involve video and voice interaction with client and transferring large volumes of multimedia data. A single AP serves 5 people. The office comprises 5 – 500 people. Application: Multiple applications run at the same time. High definition compressed video uses something like an Blu-ray codec. Voice is standard definition quality using a codec like G729. Aggregate bandwidth requirement is 5 simultaneous video streams per AP. Voice requirements are: ~50Kbps, Jitter <30msec. Delay <30msec. 1.0E-1 PER. Environment: Mostly not Line of sight within a single office. People walking around the office. There is potentially unmanageable interference from neighboring offices within 100 feet (horizontally) or adjacent floors (vertically) when in 2.4 / 5 GHz. AP density is more than 1 AP per 40m X 40m Traffic Conditions (per AP): 2 WLAN video streams 2 WVoIP streams Up to 5 best effort data streams The best effort data traffic can take up to 20% of the available bandwidth with saturated offered load. Use Case: Users run different applications during the day and may start each application at different time. A typical sequence is starting up a voice call, adding video sending/receiving multi-media data and discussing this over the voice/video link The duration of such a use case is typically one hour. Up to three of these “sessions” per AP may be going on in parallel. * This was taken from Doc 09/0161r02, Usage Model 2d: Wireless Networking for Office Slide 3

  4. Network Topology Slide 4

  5. Traffic Pattern Slide 5

  6. Simulation Parameters The simulation runs on ns2 platform. Slide 6

  7. Performance without Aggregation Note the data here are average numbers over 4 VoIP sessions, 2 Video sessions and 2 TCP sessions. Slide 7

  8. 802.11n Capacity with Video traffic Contention Window PLCP Header Video Frame SIFS DIFS Ack 34 µs 67 µs (min average) 28 µs 16 µs 32 µs Time 1. Video Frame = (Data + IP header + MAC header)/DataRate ( 1500 + 20 + 28 ) * 8 / 500 = 24.768 µs 2. Require Bandwidth = Application Load * Frame Start Interval / Video Frame 50 * (34+67+28+24.768+16+32) / 24 = 420.315 Mbps 3. Number of Video uplink sessions = Bandwidth * Utilization / Require Bandwidth 500 * 0.8 / 420.315 = 1.05 Reference: IEEE 802.11-07/2704r00, Efficiency of VoIP on 802.11n Slide 8

  9. Data Aggregation • In order to support the given traffic load, Aggregated MSDU is used. • In the results after this slide, four video MSDUs are aggregated into one A-MSDU. • VoIP and TCP packets are not aggregated. Slide 9

  10. STA 1 (VoIP only) STA 2 (VoIP only) STA 3 (VoIP, TCP) STA 4 (VoIP, Video) STA 5 (VoIP, Video) APSD Power Saving Effect Slide 10

  11. STA 1 (VoIP only) STA 2 (VoIP only) STA 3 (VoIP, TCP) STA 4 (VoIP, Video) VoIP Traffic Delay with and w/o APSD Note: Jitter for VoIP traffic with APSD is < 2 µs, and <0.1 µs without APSD Slide 11

  12. Uplink w/o APSD Downlink w/o APSD Uplink w/ APSD Downlink w/ APSD Video Traffic Performance Slide 12

  13. APSD’s effect on TCP throughput STA3 (VoIP, TCP) STA5 (Video, TCP) Note: all TCP traffic is uplink traffic Slide 13

  14. VoIP Video TCP Delay Comparison for all Traffic Types Note: 1) the data here are average numbers over 4 VoIP sessions, 2 Video sessions and 2 TCP sessions. 2) there is no data collected for downlink TCP traffic so the data is not available. Slide 14

  15. Summary and Future Works • Summary • A single stream of 500Mbps cannot support the given traffic load. Aggregation gets the job done. • APSD allows STAs sleep >95% of the time for VoIP traffic in this specific scenario; • APSD increases the delay for downlink VoIP traffic (from <1ms to ~10ms), but still within the requirement (<30ms). • APSD slightly increases the delay for video traffic when it is running in the AP. • TCP delay is >20% larger, and throughput is about 10% lower when APSD is running. • Future work • Run the simulation for PSMP (simulator is ready) • Develop module to support direct links so that STA to STA traffic can be simulated. • Support multiple streams (receivers) • Enhanced MAC functions needed. Slide 15

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