1. Lunar Surface EVA 802.16 Radio Study Adam Schlesinger adam.m.schlesinger@nasa.gov NASA – Johnson Space Center October 13, 2008

2. 2 Outline of Presentation Goal and Method of Lunar Surface 802.16 Radio Study Geometrical Theory of Diffraction Flat Lunar Path Loss –Ground Effects –Antenna Effects Lunar Crater Path Loss –Multipath –Delay Spread 802.16d Physical Layer Model and Analysis Variants of 802.16 –802.16j Future Work Questions

3. 3 Lunar Surface 802.16 Radio Study Goal: –To determine the feasibility of using IEEE 802.16 (WiMAX) as the communication protocol for lunar surface extra-vehicular activity (EVA) communications. Method: 1.Characterize lunar surface propagation characteristics at 5.8 GHz and develop statistical channel models for performance evaluation and testing. 2.Study antenna patterns at 5.8 GHz for various antenna designs and various antenna placements on the EVA suit. 3.Develop and implement a Matlab physical-layer (PHY) model for 802.16d and simulate the performance of 802.16d in Matlab using standard statistical wireless channel models at 5.8 GHz. 4.Combine the results of the lunar surface propagation study, the antenna study, and the Matlab PHY model to simulate and evaluate the performance of 802.16d on the lunar surface at 5.8 GHz.

4. 4 Geometrical Theory of Diffraction (GTD) Computational electromagnetic technique suitable for predicting the dominant effects of reflections and diffractions in large three-dimensional environments, such as the lunar surface N is the total number of reflections M is the total number of diffractions. Receive Antenna Transmit Antenna

5. 5 Lunar Ground Effects 5.8 GHz Dipole Antenna in Free Space 5.8 GHz Dipole Antenna 2 m above Flat Lunar Surface ε=3.0, σ=0.0001 S/m Interference between the direct and ground-reflected signals generates ripples in the antenna pattern

6. 6 Flat Lunar Surface Path Loss at 5.8 GHz The flat lunar path loss for short distances (< 500 m) resembles free space path loss which is proportional to 1/R 2. For longer distances (> 500 m) the flat lunar path loss approaches 1/R 4 which is more severe than free space path loss.

7. 7 Antenna Height Effects at 5.8 GHz

8. 8 Lunar Crater Scenario The flat lunar surface environment is replaced by a 3-D crater environment. Simulations were again computed using GTD to model reflections and diffractions from the 3-D crater terrain. Crater is modeled after Meteor Crater in Arizona which is 1200 m in diameter and 170 m deep.

9. 9 Multipath Propagation Reflections and diffractions of a transmitted signal generate multiple copies of the transmission at the receiver with different delays, polarizations, and attenuations. The resulting received signal is a superposition of the direct-path, reflected-path, and diffracted-path components, which results in signal distortion, fading, and delay spread which are a major concerns for high data rate wireless systems. Path loss, fading and delay spread can be significantly different in a line-of-sight (LOS) versus a non-line-of-sight (NLOS) environment.

10. 10 Crater Multipath Propagation at 5.8 GHz

11. 11 Delay Spread Delay spread is the time difference between the first and last arrival of the same signal with significant energy at the receiver. Delay spread can cause intersymbol interference (ISI), which is often the most limiting performance factor for wireless communication systems. To mitigate the effects of ISI, the transmitted symbol interval should be much longer than the channel delay spread.

12. 12 Crater Delay Spread at 5.8 GHz Max Delay Spread: 2 μsMax Delay Spread: 276 ns

13. 13 MATLAB IEEE 802.16-2004 (802.16d) Physical Layer Model

14. 14 MATLAB IEEE 802.16-2004 (802.16d) Physical Layer Model Variable Parameters Variable Parameters: –Carrier Frequency –Modulation Scheme –Channel Bandwidth –Data Rate –Transmit Power –Transmit and Receive Antenna Heights –Transmit and Receive Antenna Gains –Distance between Transmit and Receive Antennas –Path Loss Model

15. 15 MATLAB IEEE 802.16-2004 (802.16d) Physical Layer Model

16. 16 IEEE 802.16-2004 (802.16d) OFDM Bit Error Rate Performance

17. 17 IEEE 802.16-2004 (802.16d) OFDM Symbol Error Rate Performance

18. 18 Path Loss Models Free Space Path Loss Flat Lunar Path Loss Suburban Path Loss –Modified Hata-Okumura Model for 3 terrain types Type A – Hilly terrain with moderate-to-heavy tree densities Type B – Hilly terrain with light tree densities or flat terrain with moderate-to-heavy tree densities Type C – Flat terrain with light tree densities –Corrects for frequencies out of 500-1500 MHz range –Corrects for Tx-to-Rx distances less than 1 km –Corrects for antenna heights less than 30 m

19. 19 Path Loss Models at 5.8 GHz

20. 20 Maximum Radio Separation Maximum achievable Tx-to-Rx distances to guarantee a BER of 10 -5 with 0 dB of margin for a channel bandwidth of 5 MHz and a 1/16 cyclic prefix ratio: Maximum Distance Between Tx and Rx (km) Modulation Scheme: Raw Data Rate (Mbps): Free Space Path Loss Flat Lunar Path Loss Suburban Path Loss (Type C) BPSK – ½2.03294114.863.660.38 QPSK – ½4.06588210.813.120.34 QPSK – ¾6.0988246.252.370.28 16-QAM – ½8.1317655.572.240.27 16-QAM – ¾12.1976473.411.750.23 64-QAM – 2/316.2635292.151.390.19 64-QAM – ¾18.2964711.811.280.18

21. 21 Maximum Lunar LOS Distance Moon Radius: 1738 km Transmit Antenna Height (m) Maximum LOS Distance (km) 11.86 22.64 54.17 105.90 208.34 3010.21 4011.79 5013.18

22. 22 802.16 Variants I.802.16e – Mobile 802.16 II.802.16j – Multihop Relay Specification III.802.16m – Advanced Air Interface

23. 23 802.16j Overview The goal of 802.16j is to develop a relay mode based on IEEE 802.16e by adding Relay Stations to gain: –Extended Coverage –Increased Throughput

24. 24 Radios in an 802.16j System Mobile Station (MS) –802.16e MS can be used Multihop Relay (MR) Base Station (BS) –New 802.16e BS with MR functionality Relay Station (RS) –Similar to BS but with less complexity –Can be fixed, nomadic or mobile

25. 25 Relay vs. Mesh 802.16j is a relay protocol, not a mesh protocol Relay –Tree-based architecture with BS at one end –Routing from MS to BS by RS Mesh –Each node can communicate with each other –Routing From MS to BS by MS

26. 26 Relay vs. Mesh Relay: Mesh: BS MS1 RS1 MS2 BS MS1 RS2 MS2 MS3

27. 27 Lunar Scenario without 802.16j BSMS1 MS2 MS1 has direct line-of-sight communication with the BS –Can communicate with all elements that can also communicate with the BS MS2 is shadowed by the crater –Limited or no communication with BS –MS1 and MS2 cannot communicate

28. 28 Lunar Scenario with 802.16j BSMS1 MS2 MS1 has direct line-of-sight communication with the BS –Can communicate with all elements that can also communicate with the BS MS2 can communicate to the BS by way of the RS –MS1 and MS2 can communicate RS

29. 29 Increased Throughput 64-QAM 16-QAM QPSK BPSK BS MS1MS2 RS MS1 and MS2 are the same distance away from the BS MS1 can only communicate using BPSK, the least efficient modulation scheme The RS reduces transmit distances through hops and allows MS2 to communicate using a more efficient modulation scheme –Increases the link data rate –Can decrease transmit power

30. 30 Issues with 802.16j for Lunar Surface Increased Latency –Each hop induces more latency No MS-RS-MS Communication –Although it was discussed during the initial 802.16j task group meetings, there is no current plan to implement MS-RS-MS capability –All communication must involve a BS No Fault Tolerance –If a BS fails, each RS and MS that can only communicate with the failed BS becomes unusable

31. 31 Future Work 1.Conduct extensive field testing of Nortel 802.16d base station and subscriber station radios that only operate only at 5.8 GHz, and use the results to validate the 802.16d Matlab PHY model. 2.Use the lunar surface channel models and antenna patterns along with the EB PROPSim Channel Simulator and the Nortel 802.16d radios to simulate and evaluate performance of 802.16d on the lunar surface at 5.8 GHz. 3.Repeat all analysis and simulations at 2.4 GHz. 4.Complete similar analysis and simulations for variants of 802.16, including 802.16e and 802.16j at both 2.4 and 5.8 GHz.

32. 32 802.16 Study Summary Completed a path loss analysis for a flat lunar surface and both LOS and NLOS lunar crater scenarios using GTD. Created a physical layer model of 802.16d, with a wide range of configurable input parameters, that was used determine the performance of 802.16 under different conditions. Usable data rates and allowable transmit distances are two major issues with 802.16. Variants of 802.16, such as 802.16j, are currently being developed and would extend coverage and enhance throughput of the lunar surface network. However, these variants are still immature and need to be further evaluated. 802.16 is a promising protocol, but more work is required in order to make a final decision on whether it is fully suitable for lunar surface EVA communications.

33. Questions? Adam Schlesinger adam.m.schlesinger@nasa.gov