Alain SIBILLE Stéphane Laboratoire Electronique-Informatique ENSTA, 32 Bd Victor, Paris cedex 15, France * Now at THALES Communications, Colombes, France INTERSECTOR CORRELATIONS FOR SWITCHED BEAMS DIVERSITY PERFORMANCE EVALUATION

Outline  context and motivation  antennas  intersector correlations: theory  computations assuming a model scenario  comparison with experimental results  angular vs. spatial diversity  conclusion

Context and motivation  GENERAL CONTEXT: low-complexity beam-switched smart antennas for terminals, HIPERLAN 2 access points etc …  MOTIVATION: an attempt to quantify the potential benefit brought by beam- switched antennas prior to any experiment, intended for optimal antenna design.  PARTICULAR CONTEXT: experimental channel measurement campaigns and antenna design carried out within the European ADAMO project ( ).

Antennas 6 monopoles circular array 4 patches planar array

6 BSSA circular array 13 monopoles array Antennas

Intersector correlations : theory Hi Hj Wideband intersector correlation: with i j r ij is a measure of the diversity performance of a switched beams antenna for wideband radio link (single or multiple carriers)

Discrete multipath channel model: f( t ): receiver filter CIR A il : path transmittance (D i : receiver antenna radiation pattern) t l : path delay g l : CIR of environment+ emitter : Fourier transform of Intersector correlations : theory

Di,j: radiation patterns P(  ): angular power spectrum for omni receiver antenna Assuming perfect averaging of small-scale fading: Continuous approximation of the discrete sum (scenario averaging): Intersector correlation: Intersector correlations : theory

The channel correlation contains the term: Intersector correlations : theory Extension to polarisation-dependent propagation generalize is somewhat related to Continuous approximation:

Computations assuming a V-V model scenario  c  6 BSSA array  4 patches array  c

Complex vs. Amplitude-only correlations (Phase behavior)  13 monopoles array Computations assuming a V-V model scenario

Comparison with experimental results (ADAMO campaign 1, IMST indoor measurements)  3 rooms: small, library, hall  6 beams antenna at ceiling level  omnidirectional radiator at desk level  5.2 GHz, 120° MHz BW  31 locations, small-scale fading averaging every /10  6 monopoles array and 4 patches array library small office

 c (°)  (°)  =60°  =120°  =180° model: CAMPAIGN 1 (6 monopoles array) small office library hall Comparison with experimental results (ADAMO campaign 1, IMST measurements)

ADDITIONAL SPATIAL DIVERSITY  6 monopoles array d / Computations assuming a V-V model scenario

INTERSECTOR CORRELATION: model vs. Experiment (ADAMO campaign 1) 60°120°180°  d/ 6Monop exp Monop model Patches exp Patches model Comparison with experimental results expected on account of the Tx-Rx LOS tilt in elevation

Angular vs. spatial diversity  spatial diversity = spatial filtering of faded signals  angular diversity = angular filtering of incoming waves  IS THERE A FUNDAMENTAL DIFFERENCE BETWEEN BOTH ? IS THE DISTINCTION BETWEEN ANGULAR AND SPATIAL DIVERSITY SO CLEAR IN PRACTICAL ARRAYS ?

ROLE OF THE PHASE CENTER Angular vs. spatial diversity 6 points in angular space, used to locally equate to zero the phase differential « local » phase center for a given (  ) direction

ROLE OF THE PHASE CENTER A SIMPLE INTERPRETATION: sectored arrays also exhibit spatial diversity due to sector dependent position of the phase center 6 MONOPOLES ARRAY Angular vs. spatial diversity

13 MONOPOLES ARRAY ROLE OF THE PHASE CENTER Angular vs. spatial diversity

Conclusion  A simple tool has been proposed to evaluate the diversity performance of beam- switched antennas: intersector correlations assuming a model scenario  Comparison with indoor propagation channel measurements is favorable, on condition of the presence of extra spatial diversity  Evidence of hybrid spatial angular diversity in beam-switched circular arrays due to non central position of the phase center.  Perspective: evaluation of correlations for MIMO antennas

Acknowledgements The authors are grateful to J. Kunisch, M. Schneider, J. Pamp, E. Zollinger, A. Winkelman and M. Gehrt of IMST for supplying CIR measurements