Availability of the EGNOS service for land mobile user Pavel Kovář, Libor Seidl, František Vejražka Czech Technical University in Prague Faculty of Electrical Engineering

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Agenda Introduction - EGNOS EGNOS channel Mathematical model Results of experiments −experimental GNSS receiver −signal availability −message availability −service availability Conclusions

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS European augmentation system of the GPS and the GLONASS Services −Open (OS) - available this summer −Safety of Life (SoL) - available summer 2007 Designed for navigation −aviation enroute −precision approach −maritime Planned for land mobile navigation

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS Ranging signal Data −WAD corrections −Integrity information −Maintain EGNOS data up-to-date in user receiver  Age of messages cannot exceed defined thresholds

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS  Land mobile reception problem: Out-of-date messages due to satellite shadowing

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Study objectives Mathematical modeling of shadowing process Experiments with signal reception  model parameters Signal availability Message availability Investigation of the EGNOS availability for a land mobile user:

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS channel model Two states: Blocked LOS −Rayleigh fading Unblocked LOS −Rice fading Log-normal fading ,, Complex Gauss process Spectrum shaping Rayleigh fading Rice fading Block Unblock Block/Unblock process Channel input Channel output P(f) c 1/

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Mathematical model Block/unblock process −two-state Markov process −dependent on run distance −transition intensity matrix − partial intensity of LOS unblocking − partial intensity of LOS blocking Model parameters − determined experimentally for various environments

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Mathematical model - results Statistics of −message reception −reception of at least one message from N messages −antenna diversity reception

RESULTS OF EXPERIMENTS AND MODELING

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Aim of experiments EGNOS signal availability in various environments −Assessment of model parameters −Estimates of EGNOS message statistics by simulated run trough the shadowing environment EGNOS message availability Estimation of EGNOS service availability Requirement: Maximum possible elimination of the receiver acquisition delay

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Experimental GNSS receiver Software defined architecture

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Experimental GNSS receiver Signal processing Massive parallel correlation – equivalent correlators Cross-correlation function for all delay bins simultaneously Fast signal detection (response on EGNOS < 4ms) Fast acquisition for signal reception EGNOS message demodulation immediately after signal appeared I&Q Demodulator IF Parallel Correlator Noncoherent Integrator Peak Detection

Signal availability

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Signal availability - example Country Town Unblocked Blocked Distance [km] 148 Unblocked Blocked Distance [km] 148 PRN 120 IOR, Prague, Czech Republic, elevation 15 

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Signal availability measurement Country Town Unblocked Blocked Distance [km] 148 Unblocked Blocked Distance [km] 148 PRN 120 IOR Elevation 15 , Prague, Czech Republic

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Signal availability model parameters obtained by measurement PRN 120 IOR, Prague, Czech Republic, elevation 15  Environment  [m -1 ] [m -1 ] Visibility (  0 ) [%] Town sparsely built-up Town narrow streets Country

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Conformity of model and measurement Comparison of experimental (measured) and modeled distribution of unblocked and blocked distance Distance [m] PDF Unblocked Blocked Distance [m] PDF Measurement Model Measurement Model

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Conformity of model and measurement Probability of reception of at least one message from N ones Speed [m/s] Reception probability Model Simulated run NN

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Antenna diversity reception Excellent technique for improvement of reception of signals in time variable channel Problem with implementation due to the strong correlation of the EGNOS land mobile channels for practical separation of antennas

Message availability

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS message availability 0 Time [s] Correlator output Error Decoded message No Town – sparsely built-up area

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS message availability 0 Time [s] Correlator output Error Decoded message No Undulating country

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS message availability 0 Time [s] Correlator output Error Decoded message No Flat country

Service availability

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS service availability - requirements on message age Msg. No.218 Content Fast correction & Integrity Ionosphere grid data Tx period< 6 s< 300 s Max. age RTCA DO 229B 18 s* 12 s** 1200 s * Aircraft enroute nav.** Aircraft precision approach nav.

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS service availability - requirements on message age position meassurement maximum acceptable age of message FLAG NO FLAG position OK message age

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS service availability assessment Estimation of probability that age of given EGNOS message exceeds given value ~ probability that among last N messages no one was successfully received N= [(max. acceptable age)/(Tx period)]

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS service availability Example: Msg. No. 2 Sparsely built-up townUndulating country Flat Country Age [s] Probability Probability that message age exceeds given threshold

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS service availability Example: Msg. No. 2 Sparsely built-up townUndulating country Flat Country Age [s] Probability Probability that message age exceeds given threshold threshold 18 s (for aircraft enroute navigation!)

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS service availability Example: Msg. No. 18 Sparsely built-up areaUndulating country Flat Country Age [s] Probability Probability that message age exceeds given threshold

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, EGNOS service availability Example: Msg. No. 18 Sparsely built-up areaUndulating country Flat Country Age [s] Probability Probability that message age exceeds given threshold threshold 1200 s threshold 1200 s threshold 1200 s

Czech Technical University in Prague IEEE/ION PLANS 2006 San Diego, April 25-27, Conclusions Level of EGNOS service to land mobile users is limited due to shadowing. The model of the EGNOS channel for a land mobile users has been developed and validated. EGNOS channel coding is inconvenient for burst error channel. Convolutional code performance could be dramatically improved by implementation of the interleaving which would eliminate problem of messages ageing. Level of service strongly depends on environment. Requirements on EGNOS service have been defined for air navigation only by RTCA DO 229. Similar standard for land mobile users should be defined as soon as possible.

Thank you for your attention Pavel Kovář Libor Seidl František Vejražka Czech Technical University in Prague, Czech Republic