1. Performance of Smart Antennas and PCF
20 September 2018
Performance of Smart Antennas and PCF
Vinayak Nandikal
Courtesy: Nokia Research Center
Vinayak Nandikal

2. 20 September 2018
20 September 2018
Introduction
IEEE will be an important method for providing high rate low mobility data services
While existing capacity may seem high, particularly for IEEE802.11a, the enterprise environment may experience capacity limits
Antenna technologies offer a means to boast IEEE capacity without changing the existing PHYs
Vinayak Nandikal
Vinayak Nandikal

3. 20 September 2018
20 September 2018
What is a SMART Antenna? AP
STA
Antenna that adjusts its beam pattern based upon the
channel and interference between AP and STA
Vinayak Nandikal
Vinayak Nandikal

4. Approach to Model Performance
20 September 2018
20 September 2018
Approach to Model Performance
Measure channel using a channel sounder to determine
Multipath power profile as a function of time
Signal-to-interference ratio
Simulate PHY to obtain PER information as a function of channel measurements and the number of packets delivered as a function of time
Use PER, number of packets delivered by the PHY as a function of time and models of real-time traffic to examine delay and throughput using a PHY with and without smart antennas
PCF is used for delivery of audio and video packets
Vinayak Nandikal
Vinayak Nandikal

5. PHY Simulation Parameters
20 September 2018
20 September 2018
PHY Simulation Parameters
Vinayak Nandikal
Vinayak Nandikal

6. PHY Channel Sounder Approach
20 September 2018
20 September 2018
PHY Channel Sounder Approach
127 chip pn sequence is transmitted at 5.3 GHz with a bandpass bandwidth of 30 MHz
A 32 element array with 0.5 wavelength space is used to downconvert the transmitted pn sequence
Snap shots of the delay spread are written to memory and stored on a hard disk
For further information see:
Jarmo Kivinen, Timo O. Korhonen, Pauli Aikio, Ralf Gruber,
Pertti Vainikainen, and Sven-Gustav Häggman,
IEEE Transactions on Instrumentation and Measurement,
vol. 48, no. 1, pp , 1999.
Vinayak Nandikal
Vinayak Nandikal

7. Smart Antenna Operation (5GHz)
20 September 2018
20 September 2018
Smart Antenna Operation (5GHz) RF
A/D
FFT
Antenna Combining
Weight
Calculation
Decoding
STA
OFDM Symbol Index
Subcarrier
Uplink Operation
D/A RF
IFFT
Antenna Weighting
Coding &
Modulation
STA
Downlink Operation
Vinayak Nandikal
Vinayak Nandikal

8. 20 September 2018
20 September 2018
Channel Correlation 50
100
150
200
250
300
350
400
450
0.93
0.94
0.95
0.96
0.97
0.98
0.99 1
time [ms]
amplitude correlation coefficient
average over TX positions
Ruoholahti
Heikkiläntie
Airport
Airport 2
The figure to the right shows the correlation coefficient for different measurement environments
For smart antenna operation, the AP needs the ability to probe the channel between any STA and AP
Note: Ruholahti and Heikkiläntie are Nokia office buildings
Vinayak Nandikal
Vinayak Nandikal

9. MAC Simulation Parameters
20 September 2018
20 September 2018
MAC Simulation Parameters
Vinayak Nandikal
Vinayak Nandikal

10. Traffic Model: All traffic measured in data-units/slot-time
20 September 2018
20 September 2018
Traffic Model:
All traffic measured in data-units/slot-time
1 data-unit takes 1 slot-time for transmission
Max traffic in network = 1.0
Audio and video traffic originates from “calls” made by the user
Calls are Poisson distributed; once placed, each call generates periodic packet traffic
Mean inter-call-arrival-time controls load on the network
Vinayak Nandikal
Vinayak Nandikal

11. Traffic Model (cont.): Real-time traffic load = 20 September 2018
20 September 2018
Traffic Model (cont.):
Real-time traffic load =
apkt_sz: audio packet size
vpkt_sz: video packet size
int_call_arvl_time: mean intercall arrival time (8:1 ratio between audio and video calls)
int_apkt_arvl_time, int_vpkt_arvl_time: arrival time between audio packets and video packets respectively
acalls, vcalls: number of audio anc video calls respectively
Vinayak Nandikal
Vinayak Nandikal

12. Throughput & Latency Curves: Audio Packets
20 September 2018
Throughput & Latency Curves: Audio Packets
Packets/Seconds
Packets/Second
Normalized Througput
PCF Latencies
0.5 1
1.5 2
2.5
x 10 4 10 -4 -3 -2 -1
No SDMA
3-channel SDMA
DCF:PCF = 1:1
Audio Packets
0.1
0.2
0.3
0.4
0.6
0.7
0.8
0.9
DCF:PCF = 1:1
Vinayak Nandikal

13. Throughput & Latency Curves: Audio Packets
20 September 2018
Throughput & Latency Curves: Audio Packets
Packets/Seconds
Packets/Second
Normalized Throughput
PCF Latencies 1 2 3 4
x 10 10 -4 -3 -2 -1
No SDMA
3-channel SDMA
DCF:PCF = 1:3
Audio Packets
0.5
1.5
2.5
3.5
0.1
0.2
0.3
0.4
0.6
0.7
0.8
0.9
Aduio Packets
Vinayak Nandikal

14. Throughput & Latency Curves: Video Packets
20 September 2018
Throughput & Latency Curves: Video Packets
Packets/Seconds
Packets/Second
Normalized Throughput
PCF Latencies
100
200
300
400
500 10 -4 -3 -2 -1
No SDMA
3-channel SDMA
DCF:PCF = 1:1
Video Packets
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 1
Vinayak Nandikal

15. Throughput & Latency Curves: Video Packets
20 September 2018
Throughput & Latency Curves: Video Packets
Packets/Seconds
Packets/Second
Normalized Throughput
PCF Latencies
200
400
600
800 10 -4 -3 -2 -1
No SDMA
3-channel SDMA
DCF:PCF = 1:3
Video Packets
100
300
500
700
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 1
Vinayak Nandikal

16. New Control Frame Subtypes for Smart Antennas
20 September 2018
New Control Frame Subtypes for Smart Antennas
AP to STA
A message requesting the STA to transmit a preamble (null frame) for channel estimation
Channel Id Request
STA to AP
A response to the above request
Channel Id Response
Duration RA TA
FCS
Message Fields
Frame
Control
Vinayak Nandikal

17. Remove Polling Dependence
20 September 2018
Remove Polling Dependence
The existing standards reads,
"During each CFP, the PC shall issue polls to a subset of the STAs on the polling list in order by ascending AID value".
Vinayak Nandikal

18. 20 September 2018
20 September 2018
Conclusions
Particularly in a large enterprise environment, smart antennas can help boast capacity
Wireless office replacement for "wired" Ethernet
Public service networks such as airports
Changes to the existing MAC are minor to enable antenna technologies in IEEE802.11a networks
SDMA is not for all WLANS
Multiple antennas cost additional money for the AP that may not be required in homes and small businesses
Vinayak Nandikal
Vinayak Nandikal