WiMAX Range and Throughput Measurements
•
•
•
•
•
•
•
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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
1
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
3
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
Sponsored by the National Science Foundation
March 15, 2011
4
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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March 15, 2011
5
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
Sponsored by the National Science Foundation
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
6
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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March 15, 2011
7
(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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March 15, 2011
8
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
Sponsored by the National Science Foundation
March 15, 2011
9
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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March 15, 2011
10
(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)
Sponsored by the National Science Foundation
March 15, 2011
11
Neighborhood of
BBN Technologies, Cambridge, MA
Sponsored by the National Science Foundation
March 15, 2011
12
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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March 15, 2011
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
13
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
)
Sponsored by the National Science Foundation
March 15, 2011
14
-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)
Sponsored by the National Science Foundation
March 15, 2011
15
-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
16
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)
Sponsored by the National Science Foundation
March 15, 2011
17
-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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March 15, 2011
18
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)
Sponsored by the National Science Foundation
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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March 15, 2011
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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March 15, 2011
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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March 15, 2011
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