1. doc.: IEEE 802.11-00/269
Submissio
n
Performance of Smart AntennasPerformance of Smart Antennas
and PCFand PCF
Vinayak NandikalVinayak Nandikal
Courtesy: Nokia Research CenterCourtesy: Nokia Research Center
2. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
Introduction
⢠IEEE802.11 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
IEEE802.11 capacity without changing the existing
PHYs
3. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
What is a SMART Antenna?
AP
G S WG S W
P D E
G S WG S W
G S WG S W
G S WG S W
D X 2 0 0
STA
STA
Antenna that adjusts its beam pattern based upon the
channel and interference between AP and STA
4. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
Approach to Model Performance
⢠Measure channel using a channel sounder to
determine
â Multipath power profile as a function of time
â 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
5. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
PHY Simulation Parameters
DOCUMENTTYPE 1 (1)
TypeUnitOrDepartmentHere
TypeYourNameHere TypeDateHere
Parameter Value
Data Rate 12 Mbps/channel
Packet LossRate 10-2
Channel Model experimental
Number of Antenna
Elements
4
Adjacent BSSInterference
Level
varying
Center Frequency 5.3 GHz
6. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
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. 39-44, 1999.
7. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
Smart Antenna Operation (5GHz)
RF A/D FFT
RF A/D FFT
RF A/D FFT
AntennaCombining
Weight
Calculation
[ ] [ ] [ ]pkxkwpky n
N
n
n
,,
1
*
â=
=
Decoding
[ ]pkx ,1
[ ]pkx ,2
[ ]pkxN ,
[ ]kw
STA
[ ]kH1
[ ]kH2
[ ]kHN
[ ]kc
STA
[ ]kH1
[ ]kH2
[ ]kHN
OFDM Symbol IndexSubcarrier
D/A RF
D/A RF
D/A RF
IFFT
IFFT
IFFT
AntennaWeighting
Coding &
Modulation
[ ]kH1
[ ]kH2
[ ]kHN
STA
STA
Uplink Operation
Downlink Operation
8. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
Channel Correlation
⢠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
0 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]
amplitudecorrelationcoefficient
average over TX positions
Ruoholahti
Heikkilä ntie
Airport
Airport 2
Note: Ruholahti and Heikkiläntie are Nokia office buildings
9. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
MAC Simulation Parameters
DOCUMENTTYPE 1 (1)
TypeUnitOrDepartmentHere
TypeYourNameHere TypeDateHere
Parameter Value
Speech Packet Size 640 bits
Video Packet Size 3.8 kb
CFP 1.5 ms
Packet Buffer Lifetime Audio: 5 ms
Video: 100 ms
CFPRepetition Interval 3 ms
Average # of Speech STAs 10/30 users
Average# of Video STAs 10/30 users
10. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
Traffic Model:
⢠All traffic measured in data-units/slot-time
â 1 data-unit takes 1 slot-time for transmission
â Max traffic in network = 1.0
⢠Audio and video traffic originates from âcallsâ 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
11. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
Traffic Model (cont.):
⢠Real-time traffic load =






+
+
+ vcallsacalls
vcalls
x
timearvlvpkt
szvpkt
vcallsacalls
acalls
x
timearvlapkt
szapkt
X
timearvlcall
durncall
___
_
___
_
___
_
intint
int
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
16. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
New Control Frame Subtypes for
Smart Antennas
⢠AP to STA
â A message requesting the STA to transmit a
preamble (null frame) for channel estimation
â Channel Id Request
⢠STA to AP
â A response to the above request
â Channel Id Response
Duration RA TA FCS
Message Fields Frame
Control
17. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
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".
18. March 31, 2015
Vinayak NandikalSlid
doc.: IEEE 802.11-00/269
Submissio
n
Conclusions
⢠Particularly in a large enterprise environment, smart
antennas can help boast capacity
â Wireless office replacement for "wired" Ethernet
â 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
â Multiple antennas cost additional money for the
AP that may not be required in homes and small
businesses
