Transcript Document

WiMAX Range and Throughput Measurements
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•
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Goals
Principal Elements
Process
Path Loss Measurements
Experiment Application Design
Connection Evaluation Steps
NEC Sector Antenna Tilt
Range and Throughput Measurements
– Plan
– Results
– Summary
• Conclusions and Next Steps
• Authors: Manu Gosain, Tony Michel, Tom Cahill, Harry Mussman
Sponsored by the National Science Foundation
March 15, 2011
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Goals
• Validate base station installation and configuration process
– Provide comprehensive documentation
• Design an experiment to evaluate range and throughput
– Document for use by other sites in evaluating their expected range and
throughput
– Later: move to OMF/OML environment
• Evaluate range and throughput at BBN site
– Compare to known calculations, measurements
– Document for use by other sites in estimating their expected range
and throughput
Sponsored by the National Science Foundation
March 15, 2011
2
Principal Elements
• Base station kit (BTS)
– Utilizing NEC Profile C IDU and ODU
• Rooftop antennas
– NEC 120deg sector
– Commercial omnidirectional
• Anritsu spectrum analyzer, for measuring received power
• Linux laptop with Intel 6250 WiMAX modem, acting as a mobile station
(MS)
• BTS servers, including:
– ASN GW with WiMAX RF AggMgr (Case 1b)
– Test host
– I&M host
• Experiment application, running in:
– MS (measurement script)
– Test host (ping and iperf servers)
– I&M host (report script)
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March 15, 2011
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Process
• 1) Conduct power measurements using Anritsu spectrum analyzer
– Check for presence of Clearwire signal with Anritsu spectrum analyzer
• 2) Build and verify experiment application to conduct range and throughput
measurements
• 3) Decide on best down tilt for NEC sector antenna
– Estimate for electrical down tilt: 5deg
– Options for mechanical down tilt: 10deg, 6deg, 4deg, 2deg (selected 4deg)
• 4) Conduct range and throughput measurements near BBN Technologies location
in Cambridge, MA
– Focus on line-of-sight, outside only (gives best case)
– Keep nominal BTS configuration parameters
• Power set to +38dbm, the maximum allowed
– Options for base station antenna:
• NEC sector base station antenna (at 4deg mechanical down tilt)
• Omni-directional base station antenna
– Options for Linux laptop mobile station:
• Internal Intel 6250 WiMAX modem, and internal antenna
• External (USB-connected) 6250, with handheld omni-directional antenna
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1) Power Measurements
• Power measurements using Anritsu spectrum analyzer
– Measured with sector antenna, 6deg mechanical tilt
– Near antenna: -34dBm
– Point 41, 370ft: -59dBm (good signal)
– Point, 520ft: -50dBm (good signal)
– Point, 1190-ft: -79dBm (edge of coverage)
• Presence of Clearwire signal with Anritsu spectrum analyzer
– On roof (line of sight): -60dBm
– Point 47: -70dBm
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2) Experiment Application Design
Antenna:
Mobile Station (MS)
1) NEC sector
2) Omni
GREtunnel
Dell 1012 Netbook
DHCP
NEC Base
Station
(BTS)
WiMAX
modem/antenna:
BTS
ODU/IDU
1) USB-connected Intel
6250/external omni
2) internal Intel 6250/
internal
1) Range/throughput
experiment script
“tstats2”:
ASNGW
.bbn.dataplane.geni.net
“salamis”
Test host
I&M host
“black”
2) WiMAX AggMgr
service:
Record location
Scan/connect/chk RSSI
Get IP via DHCP
ping sequence
iperf sequence
Log results
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Monitor GRE tunnels
Collect BTS stats,
chk RSSI
Log results
March 15, 2011
public
Internet
3) Report script
“report”:
(manually gather logs
from MS and BTS)
Process logs
Generate location
summaries
Generate run summary
“argos”
4) Test
targets:
ping
iperf
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Connection Evaluation Steps
• Step 1) Verify WiMAX connection occurs
– See tunnel setup from BTS log
– Check Down Link (DL) RSSI at MS
– Check Up Link (UL) RSSI from BTS log
• Step 2) Verify MS get IP address via DHCP
– Sometimes fails if UL is poor
• Step 3) Do a sequence of ping tests between MS and Test Host “argos”
– Ping to argos, 10bytes, 10 times; check response within 1sec window; log
delays, % responses not within window (lost)
– Ping to argos, 108bytes, 10 times; check response within 1sec window; log
delays, % responses not within window (lost)
– Ping to argos, 1008bytes, 10 times; check response within 1sec window; log
delays, % responses not within window (lost)
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(continued)
• Step 4) Do a sequence of iperf tests between MS and Test Host “argos”
– Repeat 3 times
– Use TCP
– Use -d for double connection, separating DL and UL measurements
– Throughput in Mb/s calculated from bytes transmitted within 60sec interval
– Print throughput in Mb/s to log
– TCP parameters:
• use Nagle’s algorithm
• window size and segment size per OS: 16kB
• depth read/write buffer in socket, default: 8kB
• max segment size: 1408B (MTU size) - 40B = 1368B
– Use of TCP gives conservative result, but typical of many applications
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3) NEC Sector Antenna Tilt
• WiMAX antennas typically have a built-in electrical
(down) tilt, and a variable mechanical (down) tilt
• Estimate for electrical tilt on NEC sector antenna,
per specs: 5deg
• Options tried for mechanical (down) tilt: 10deg,
6deg, 4deg, 2deg
– Too much down tilt “buries” the signals close to
the base station, and shortens range
– Too little tilt creates a blank spot near base
station
– There is always a blank spot very near the base
station (and within the building) caused by
shadow of the building
• Chosen for mechanical tilt: 4deg
– Throughput measurements showed range at
4deg to be higher than at 2deg or 6deg
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4) Measurements Plan
• Focus on line-of-sight, outside only (gives best case)
– Points 41 through 48, in a straight line at center of 120deg sector pattern
– Optional points 1 through 7, in orthogonal direction (with point 7 obstructed by
building), to verify expected 360deg omni coverage
• Keep nominal BTS configuration parameters
– Power set to +38dbm, the maximum allowed
• Options for base station antenna:
– NEC sector base station antenna (at 4deg mechanical down tilt), approx 90ft high
– Omni-directional base station antenna, approx 90ft high
– Expect sector to work better than omni antenna within 120deg sector pattern,
since has higher gain
• Options for Linux laptop mobile station (MS):
– External (USB-connected) 6250, with handheld large omni-directional antenna
– Internal Intel 6250 WiMAX modem, and internal antenna
– Expect large omni antenna to work better than internal antenna
– Expect packet loss and throughput to vary from moment-to-moment, due to MS
position and multi-path propagation
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(continued)
• For each option combination:
– A) BS sector, MS omni antennas
– B) BS sector, MS internal antennas
– C) BS omni, MS omni antennas
– D) BS omni, MS internal antennas
• For each point:
– 41 – 48
– option for C): 41 – 48 and 1 – 7
• Plot vs distance (mi) from base station to mobile station:
– DL RSSI (db)
– UL RSSI (db)
– 1008byte pings, the % of responses not within window (lost)
– DL iperf throughput, min and max over three attempts (Mb/s)
– UL iperf throughput, min and max over three attempts (Mb/s)
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Neighborhood of
BBN Technologies, Cambridge, MA
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Photo of BBN base station and
Concord Ave measurement points 41 - 48
BBN
Base
Station
0
41
42
43
44
45
46
47
48
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0
(0 mi,
90 ft up)
BBN
Base
Station
Antenna
41
(0.058 mi)
Center
Parking
Lot
42
(0.085 mi)
Social
Security
Entrance
43
(0.090 mi)
NE
FawcettConcord
44
(0.097 mi)
SE
FawcettConcord
45
(0.153 mi)
T (Bus)
Stop
46
(0.200 mi)
S
WheelerConcord
47
(0.221 mi)
West edge
rotary
48
(0.254 mi)
East edge
rotary
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Photo of BBN base station and
Fawcett St measurement points 1 - 7
7
6
5
4
3
BBN
Base
Station
0
2
1
0
(0 mi,
90 ft up)
BBN
Base
Station
Antenna
1
(0.040 mi)
Parking
Lot
2
(0.080 mi)
Fawcett
St
3
(0.110 mi)
Fawcett
St
4
(0.140 mi)
Fawcett
St
5
(0.180 mi)
Fawcett
St
6
(0.220 mi)
Fawcett
St
7
(0.230 mi)
Fawcett
St
(obstructed
)
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-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
-80
DLRSSI
-90
-90
ULRSSI
14
14
12
12
10
10
8
8
6
6
4
4
2
2
Ping % lost
0
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0
0.05
0.1
0.15
0.2
0.25
0.3
ULRSSI (db)
-30
iperf UL Thru'put
(Mb/s)
iperf DL Thru'put (Mb/s)
DLRSSI (db)
A) Measurements results for
BS with sector, MS with external omni antennas
DLMax
ULMin
DLMin
ULMax
100
80
60
40
20
0
Distance from BTS to MS (mi)
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March 15, 2011
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-30
-50
-50
-70
-70
DLRSSI
-90
-90
16
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
Ping % lost
ULRSSI (db)
-30
0
0
0.05
0.1
0.15
0.2
0.25
0
0.05
0.1
0.15
0.2
0.25
0.3
ULRSSI
iperf UL Thru'put
(Mb/s)
iperf DL Thru'put (Mb/s)
DLRSSI (db)
B) Measurements results for
BS with sector, MS with internal antennas
DLMax
DLMin
ULMax
ULMin
120
100
80
60
40
20
0
0.3
Distance from BTS to MS (mi)
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March 15, 2011
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Ping % lost
-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
-80
-90
-90
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
0
0.05
0.1
0.15
0.2
0.25
0
0.05
0.1
0.15
0.2
0.25
ULRSSI (db)
-30
DLRSSI
ULRSSI
iperf UL Thru'put
(Mb/s)
iperf DL Thru'put (Mb/s)
DLRSSI (db)
C) Measurements results for
BS with omni, MS with external omni antennas
DLMax
DLMin
ULMax
ULMin
0.3
100
80
60
40
20
0
0.3
Distance from BTS to MS (mi)
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March 15, 2011
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-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
-80
-90
-90
12
12
10
10
8
8
6
6
4
4
2
2
0
0
0
0.05
0.1
0
0.05
0.1
0.15
0.2
0.25
0.3
0.15
0.2
0.25
0.3
ULRSSI (db)
-30
DLRSSI
ULRSSI
iperf UL Thru'put
(Mb/s)
iperf DL Thru'put (Mb/s)
DLRSSI (db)
C2) Measurements results for
BS with omni, MS with external omni antennas
DLMax
DLMin
ULMax
ULMin
Ping % lost
100
50
0
Distance from BTS to MS (mi)
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ULRSSI (db)
-30
-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
-80
DLRSSI
-90
-90
ULRSSI
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0
0.05
0.1
0.15
0.2
0.25
0.3
iperf UL Thru'put
(Mb/s)
iperf DL Thru'put (Mb/s)
DLRSSI (db)
D) Measurements results for
BS with omni, MS with internal antennas
DLMax
DLMin
ULMax
ULMin
Ping % lost
100
80
60
40
20
0
Distance from BTS to MS (mi)
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March 15, 2011
19
Measurements Summary
• RSSIs
– DL RSSIs varies from -30db for a strong signal point, down to -64db for a weak
signal point; below that, the connection fails
– UL RSSIs remained more constant, often close to -75db for a wide range of
points. Is this due to automatic WiMAX UL transmit power adjustments?
• Ping loss (1008bytes)
– Measured delays are relatively constant (80 – 100ms) until link is about to fail
– For 1008byte pings, the % of responses not within window (lost) increases
quickly as link is about to fail; otherwise 0%
– Good measure of overall connection quality
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March 15, 2011
20
(continued)
• iperf Throughput
– Use of TCP gives conservative result, but is typical of many applications
– Use of TCP results in significant variations over the 3 runs, due to packet
losses and retransmissions; need to consider both min and max
– As link gets poorer, the throughput eventually falls to zero
– DL throughput is typically better than UL throughput, following WiMAX
convention
– Best case DL throughput is over 10Mb/s
– Best case UL throughput is approximately 1 Mb/s
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March 15, 2011
21
(continued)
• Range:
– Best range (to point 48, 0.254mi) seen with BS sector antenna and MS
handheld large omni antenna
– Range is worse, as expected, with BS sector antenna and MS internal antenna
– Worst range (to point 46, 0.2mi) seen with BS omni antenna and MS handheld
large omni antenna
– However, range is better with BS omni antenna and MS internal antenna;
why?
– Expected packet loss and throughput to vary from moment-to-moment, due to
MS position and multi-path propagation, but not directly verified
– Range at points 1 - 7 comparable to range at points 41 – 47 verifies expected
360deg omni coverage
– Signal gone at point 7 obstructed by building
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22
Conclusions and Next Steps
• Current measurements give range of approximately 0.25mi
– How does this range compare with others?
– What might be done to improve range?
• Other reported ranges:
– Textbook gives calculated range of 0.6mi
– Clearwire plots indicate their BS’s are approx 0.5mi apart
– Univ Colorado plan calculates range up to 0.75mi
– But, commercial services operate at higher power, and include diversity at BS
and sometimes diversity at MS
– NYU Poly measurements?
– UCLA measurements?
– Univ Wisconsin measurements?
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23
(continued)
• Consider to improve range:
– Fix some mistake in BTS parameters
– Modify BTS parameters to improve range by forcing reduced rate
– Add diversity at BS (requires an extra ODU and an extra antenna)
– Use vehicular omni antenna at MS (includes ground plane)
– Add diversity at MS?
– Tune up TCP and/or WiMAX parameters to improve throughput, e.g., reduce
iperf buffer length so packets fit within MTU
– Turn ON ARQ or HARQ
– Utilize for UDP traffic, and accept more lost packets
– Can we get to 0.6mi?
• Expected to reduce range:
– Use of MSs indoors
– Leaves on trees starting in spring
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