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WiMAX Range and Throughput Measurements

This study aims to validate base station setup and assess range and throughput on the WiMAX network using a NEC sector antenna. The process involves power measurements, antenna tilt adjustments, and connection evaluations. Results are compared to known data for accuracy.

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WiMAX Range and Throughput Measurements

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  1. WiMAX Range and Throughput Measurements • 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

  2. 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

  3. 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)

  4. 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

  5. 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

  6. 2) Experiment Application Design Antenna: 1) NEC sector 2) Omni Mobile Station (MS) Dell 1012 Netbook GREtunnel DHCP public Internet NEC Base Station (BTS) BTS ODU/IDU ASNGW “salamis” .bbn.dataplane.geni.net WiMAX modem/antenna: 1) USB-connected Intel 6250/external omni 2) internal Intel 6250/ internal Test host “argos” I&M host “black” 2) WiMAX AggMgr service: Monitor GRE tunnels Collect BTS stats, chk RSSI Log results 4) Test targets: ping iperf 3) Report script “report”: (manually gather logs from MS and BTS) Process logs Generate location summaries Generate run summary 1) Range/throughput experiment script “tstats2”: Record location Scan/connect/chk RSSI Get IP via DHCP ping sequence iperf sequence Log results

  7. 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)

  8. (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

  9. 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

  10. 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

  11. (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)

  12. Neighborhood ofBBN Technologies, Cambridge, MA

  13. Photo of BBN base station and Concord Ave measurement points 41 - 48 BBN Base Station 0 41 42 43 44 45 46 47 48

  14. Photo of BBN base station and Fawcett St measurement points 1 - 7 7 6 5 BBN Base Station 0 4 3 2 1

  15. A) Measurements results for BS with sector, MS with external omni antennas

  16. B) Measurements results for BS with sector, MS with internal antennas

  17. C) Measurements results for BS with omni, MS with external omni antennas

  18. C2) Measurements results for BS with omni, MS with external omni antennas

  19. D) Measurements results for BS with omni, MS with internal antennas

  20. 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

  21. (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

  22. (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

  23. 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?

  24. (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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