Signal Processing Aspects of HAP Antenna (UoY)

Transcription

1 Signal Processing Aspects of HAP Antenna (UoY) WP3.3: Steerable antenna technology: Signal processing aspects Presenter: Yuriy Zakharov (UoY) 1 Participants of WP3.3 UoY: HAP antenna POLITO: Ground terminal antenna EUCON: Implementation aspects 2

2 Contributions to WP3.3: WP Leader: Yuriy Zakharov (UoY) Contributors: George White, Yuriy Zakharov, Zhengyi Xu, Jie Liu, Ben Weaver (UoY), Emanuela Falletti, Daniele Borio, Luigi Rega, Fabrizio Sellone, Marco Urso (POLITO), L. Lo Presti, F. Daneshgaran (EUCON) Editors: Marina Mondin (POLITO), Tomaz Javornik (JSI) 3 Overview of presentation Cellular communications from HAPs (conventional beamforming) Planar antenna array Vertical linear antenna array Adaptive beamforming Hardware-efficient adaptive beamforming an FPGA implementation Conclusions 4

3 Cellular communications from HAP: Scenario 5 Cellular communications from HAP: Array of aperture antennas (benchmark) We use as a benchmark the design from the paper: Optimising an array of antennas for cellular coverage from high altitude platforms by J.Thornton et al. in IEEE Trans. Wireless Comm., This design is based on: 121 aperture (complicated) antennas (with beams of ~5 deg.) Frequency reuse - 4. The coverage performance: SIR > 17dB for 95% of the coverage area. Our target: To achieve at least the same coverage performance with 121 omnidirectional (simple) antenna elements. As a result, the HAP antenna payload is significantly reduced. 6

4 Cellular communications from HAP: Planar antenna array optimisation Circularisation of HAP footprints achieved by back-transformation from spatial mask to element weights Z. Xu, G. White, and Y. Zakharov, Optimization of beampattern of High Altitude Platform antenna using conventional beamforming, IEE Proc. Communications, to appear, Cellular communications from HAP: Planar antenna array optimisation (results) Coverage performance similar to 121 aperture antennas is achieved with 424 antenna elements: ~ 3.5 omnidirectional elements / cell 1 aperture antenna / cell. Lighter, more compact HAP payload (?) 8

5 Cellular communications from HAP: Ring-shaped cells M. Nofal et al. A novel cellular structure for stratospheric platform mobile communications (2002) Ring-shaped cells No rotational motion monitoring is needed TDMA techniques can be implemented Arbitrary frequency reuse plan Rectangular planar array is used to implement the ringshaped cellular configuration large number of antenna elements and high complexity 9 Cellular communications from HAP: Vertical linear antenna array Z. Xu, Y. Zakharov, and G. White, Vertical antenna array and spectral reuse for ringshaped cellular coverage from High Altitude Platform, Conf. LAPC,

6 Cellular communications from HAP: Vertical linear antenna array (beampattern) Power (db) Y Distance (km) X Distance (km) Cellular communications from HAP: Vertical linear antenna array (results) Hamming weights: 171 omnidirectional elements allow better coverage performance than 121 aperture antennas. Semidefinite Programming (SDP): 121 omnidirectional elements allow better coverage performance than 121 aperture antennas. Z. Xu, Y. Zakharov, and G. White, SDP optimisation of antenna array for cellular communications from HAPs, submitted to Electronics Letters,

7 Cellular communications from HAP: Coverage performance aperture antennas 121 VA (SDP) 171 VA (SDP) 0.95 Coverage PA 171 VA (Hamming) SIR (db) 13 Adaptive beamforming Array topologies for HAP based smart antennas G.White, Y.Zakharov, and J. Thornton, WPMC 2005 Channel allocation method for adaptive beamforming from HAPs Capanina report, 2006 SINR balancing for HAP-user downlink Capanina report, 2006 Data communications to trains from HAPs G.White and Y.Zakharov, IEEE Trans. Veh. Techn., to appear, 2006 Robust beamforming 14

8 FPGA implementation of adaptive beamforming 15 FPGA implementation of adaptive beamforming: DCD algorithm Weight vector Adaptive Capon beamforming: w 1 R c h = where Rh = c H 1 H c R c c h = N x N sample correlation matrix Steering vector DCD (dichotomous coordinate descent) algorithm: Fixed-point algorithm No multiplication or division Fast convergence Large systems Y. Zakharov and T. Tozer, Multiplication-free iterative algorithm for LS problem, Electronics Letters,

9 FPGA implementation of adaptive beamforming: Matlab vs FPGA 1) Linear antenna array of 64 elements; 2) 128 x 128 system of equations is solved 17 FPGA implementation of adaptive beamforming: Design parameters - 1 XC2VP30 FPGA Virtex-II Pro Platform FPGA element Total available Total used DCD usage Correlation usage Other usage Slices (18%) 767 (5.6%) 1336 (9.8%) 345 (2.5%) Slice Flip-flops (3.6%) 233 (0.9%) 516 (1.9%) 226 (0.8%) Slice LUTs (14%) 1049 (3.8%) 2389 (8.7%) 489 (1.8%) Block RAMs (49%) 2 (1.5%) 32 (24%) 33 (24%) Multipliers (2.2%) 0 (0%) 3 (2.2%) 0 (0%) J. Liu, B.Weaver, G.White, and Y. Zakharov, An FPGA-based MVDR beamformer using dichotomous coordinate descent iterations, ICC 2007, submitted. 18

10 FPGA implementation of adaptive beamforming: Design parameters DCD blocks can be implemented in parallel in one FPGA chip: 16 parallel beamformers or Increasing the update rate by 16 times (10 khz for 64-element antenna) Antenna elements Update time (ms) Update rate (khz) Deliverables: Deliverables and Milestones D17: Report on adaptive beamforming algorithms for advanced antenna types for aerial platform and ground terminals, delivered Jan. 31 st D28: Detailed design of adaptive beamforming algorithms for ground terminals and aerial platform antennas, delivered July 31 st Milestones: M0127: Possible Approaches for the Signal Processing Aspects of the HAP Antennas, completed 3 rd December M0095: Beamforming algorithms and implementation aspects for ground terminals and aerial platforms specified, completed 28 th September

11 Conclusions Vertical linear antenna arrays may provide better HAP coverage performance with lower implementation complexity and HAP payload weight than previously proposed methods. Hardware-efficient FPGA beamforming can be implemented using DCD algorithm, with greatly reduced slice count compared to any other method. The idea of smart antennas on HAPs provides a wealth of new possibilities in coverage optimisation and interference mitigation: Opens up new research areas Possibility of HAP smart antenna demonstrator 21