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Lunar Surface EVA 802.16 Radio Study

Lunar Surface EVA 802.16 Radio Study. Adam Schlesinger adam.m.schlesinger@nasa.gov NASA – Johnson Space Center October 13, 2008. Outline of Presentation. Goal and Method of Lunar Surface 802.16 Radio Study Geometrical Theory of Diffraction Flat Lunar Path Loss Ground Effects

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Lunar Surface EVA 802.16 Radio Study

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

  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. 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: • Characterize lunar surface propagation characteristics at 5.8 GHz and develop statistical channel models for performance evaluation and testing. • Study antenna patterns at 5.8 GHz for various antenna designs and various antenna placements on the EVA suit. • 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. • 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. Transmit Antenna Receive Antenna 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.

  5. Lunar Ground Effects • Interference between the direct and ground-reflected signals generates ripples in the antenna pattern 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

  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/R2. • For longer distances (> 500 m) the flat lunar path loss approaches 1/R4 which is more severe than free space path loss.

  7. Antenna Height Effects at 5.8 GHz

  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. 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. Crater Multipath Propagation at 5.8 GHz

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

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

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

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

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

  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. Path Loss Models at 5.8 GHz

  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:

  21. Maximum Lunar LOS Distance • Moon Radius: 1738 km

  22. 802.16 Variants • 802.16e – Mobile 802.16 • 802.16j – Multihop Relay Specification • 802.16m – Advanced Air Interface

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

  27. Lunar Scenario without 802.16j • 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 BS MS1 MS2

  28. Lunar Scenario with 802.16j • 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 BS MS1 RS MS2

  29. Increased Throughput • 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 BS 64-QAM 64-QAM RS MS1 MS2 16-QAM QPSK BPSK

  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. Future Work • 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. • 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. • Repeat all analysis and simulations at 2.4 GHz. • 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. 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

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