1. [Preliminary Simulation Results on Power Saving]
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Slide 1 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.
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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
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4. Network Topology
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5. Traffic Pattern Slide 5 Flow No. STAs (Source/Sink)
Source Location (meters)
Sink Location (meters)
Channel Model
Application (Forward Traffic / Backward Traffic)
Application Load (Mbps) (Forward / Backward)
Rate Distribution (Forward / Backward)
MSDU Size (B) (Forward / Backward)
Max. Delay (ms) (Forward / Backward)
Max. PLR (Forward / Backward) 1
AP / STA1
(0,0)
(0,5) C
VoIP / VoIP
0.008 / 0.008
UDP / UDP
20/ 20
30 / 30
5% / 5% 2
AP / STA2
(-10,-10) 3
AP/ STA3
(5,0) 4
STA3/ AP
Local file transfer
Max. 1Gbps
TCP
300
INF
N/A 5
AP/ STA 4
(-7,7) 6
STA 4/ AP
Blu-ray/ control channel
50.00 / 0.06
Constant, UDP / Constant UDP
1500 / 64
20 / 100
 10^-7 / 10^-2 7
STA 5/ AP
(10,5) 8
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6. Simulation Parameters
Bit rate for DATA packets
500 Mbps
Bit rate for RTS/CTS/ACK
6 Mbps
aCWmin 31
aCWmax
1024
PLCPDataRate
A Slot Time
9 us
SIFS
16 us
DIFS
34 us
PreambleLength
144 bits
PLCPHeaderLength
48 bits
MAC header
224 bits
IP header
160 bits
DATA packet
Payload size + MAC header + IP header=Payload size+ 384 bits
RTS
CTS, ACK
112 bits
AC 3 for VoIP traffic
PF 2, AIFS 2, CW_MIN 7, CW_MAX 15
AC 2 for Video traffic
PF 2, AIFS 2, CW_MIN 15, CW_MAX 31
AC 0 for Video Best effort traffic
PF 2, AIFS 7, CW_MIN 31, CW_MAX 1023
The simulation runs on ns2 platform.
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7. Performance without Aggregation
Network Performance with APSD
Delay (ms)
Throughput (Kbps)
Packet Loss (%)
Uplink
Downlink
VoIP
0.361
10.622 8
Video
0.661
19,298 60
60.23
TCP
18.668
N/A
Network Performance without APSD
Delay (ms)
Throughput (Kbps)
Packet Loss (%)
Uplink
Downlink
VoIP
0.375
0.351 8
Video
0.619
19,907 60
59.06
TCP
22.137
N/A
1,068.31
Note the data here are average numbers over 4 VoIP sessions, 2 Video sessions and 2 TCP sessions.
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8. 802.11n Capacity with Video traffic
Contention
Window
PLCP
Header
Video
Frame
DIFS
SIFS
Ack
34 µs
67 µs
(min average)
28 µs
16 µs
32 µs
Time
1. Video Frame = (Data + IP header + MAC header)/DataRate
( ) * / = µs
2. Require Bandwidth = Application Load * Frame Start Interval / Video Frame
50 * ( ) / 24 = Mbps
3. Number of Video uplink sessions = Bandwidth * Utilization / Require Bandwidth
* / = 1.05
Reference: IEEE /2704r00, Efficiency of VoIP on n
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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. APSD Power Saving Effect
STA 1
(VoIP only)
STA 2
STA 3
(VoIP, TCP)
STA 4
(VoIP, Video)
STA 5
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11. VoIP Traffic Delay with and w/o APSD
STA 1
(VoIP only)
STA 2
STA 3
(VoIP, TCP)
STA 4
(VoIP, Video)
Note: Jitter for VoIP traffic with APSD is < 2 µs, and <0.1 µs without APSD
Slide 11

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

13. APSD’s effect on TCP throughput
STA3
(VoIP, TCP)
STA5
(Video, TCP)
Note: all TCP traffic is uplink traffic
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14. Delay Comparison for all Traffic Types
VoIP
Video
TCP
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.
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15. Summary and Future Works
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.
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