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DESIGN OF A SPECIFIC CDMA SYSTEM FOR AIR TRAFFIC CONTROL APPLICATIONS

UNIVERSIDAD POLITÉCNICA DE MADRID. UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA. DESIGN OF A SPECIFIC CDMA SYSTEM FOR AIR TRAFFIC CONTROL APPLICATIONS. Outline. 1.- Motivation and objectives 2.- Operational aspects 2.1.- Proposal for the TMA / taxiing scenarios: C band Duplex options

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DESIGN OF A SPECIFIC CDMA SYSTEM FOR AIR TRAFFIC CONTROL APPLICATIONS

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  1. UNIVERSIDAD POLITÉCNICA DE MADRID UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA DESIGN OF A SPECIFIC CDMA SYSTEM FOR AIR TRAFFIC CONTROL APPLICATIONS

  2. Outline • 1.- Motivation and objectives • 2.- Operational aspects • 2.1.- Proposal for the TMA / taxiing scenarios: C band • Duplex options • Topics covered • 2.2.- Proposal for the en route scenario: VHF band • Coexistence with legacy systems • Transmit Beamforming • Codes with arbitrary spectral nulls • 3.- Deployment in two steps

  3. Communication strategies Eurocontrol 8,33 kHz + VDL2SATCOM Communication capacities POTENTIAL NEW SYSTEMS Communication needs 2010 2020 1.- Motivation and objectives • New needs require new systems • CDMA technologies might complement current narrowband VHF transmissions. Main advantage: very mature and available technology • Two available bands: VHF and ‘C’ band. Global solution • Provide a flexible simulation tool to test different alternatives in realistic aeronautical environments • Contribute to EUROCONTROL initiatives, ad-hoc working groups …

  4. 1.- Main goal of the project: flexible simulation tool CDMA Standard Tx Aeronautical channel + interferences CDMA Advanced receivers • CDMA standard transmitters to obtain representative results • Aeronautical channel simulator: en route, TMA, Taxiing • Advanced CDMA receivers • MultiUser Detection covering also ISI increase • Doppler Correction. Adaptive implementation • Multiple antennas at the ground station: beamforming and spatial diversity

  5. 2.- Operational aspects. Proposal for the ‘C’ band • Very high attenuation: link budget analysis recommends coverage around 25 Km. Limited to TMA / Parking • Available bandwidth: 60 MHz, from 5.090 to 5.150 GHz. • WCDMA (5 MHz Bw) is the most suitable option. Larger bandwidth, larger gain. • Two duplex options: FDD vs TDD

  6. TDD. Time Division Duplex. • Extra time guard interval is required for time alignment of different users in uplink. Maximum time guard depends on the cell size. • To cover 25 Km, time guard should be 688 chips instead of the UMTS 96 chips. • 96 chips means 3.7 % efficiency loss per slot • 688 chips means 26.9 % efficiency loss per slot Data transmission Guard Key disadvantage • FDD. Frequency Division Duplex • No such limitation. • Pay attention to the assigned bands of both links

  7. Further considerations regarding the spreading factor in TDD /FDD and aeronautical channel delay spread. Typical delay spread • En route: 33 msec. • Arrival, parking: 7 msec. • Taxi: 0.7 msec CDMA symbol length • TDD (16 chips/Symbol)=4.16 msec (indoor applications) • FDD (256 chips/Symbol)=66.6 msec (outdoor applications) • Conclusions • TDD suffers strong ISI (performance degradation). This point may be compensated by the use of advanced MultiUser Detectors • FDD is more suitable for these scenarios. MultiUser Detectors are not realistic. The interference limitation behaviour may be reduced by using beamforming • We have simulated both systems. Evaluated pros & cons.

  8. Our proposal for the ‘C’ band. UMTS-FDD. Topics covered in our research • MRC detector. SingleUser detector • Adaptive implementation to follow channel variations • Adaptive beamforming • Several antennas at the ground stations • Tx beamforming (Downlink) • Rx beamforming (Uplink) • Increase SNR (or coverage) • Reduce intra and inter-cell interferences

  9. 2.- Operational aspects. Proposal for the VHF band • Large coverage (around 300 Km). Ideal for en route scenario. • FDD is mandatory with both links separated around 12 MHz (current technology provides enough isolation). • Main problem: mutual interference with existing narrowband systems. • Narrower band CDMA is recommendable: type IS-95 (or its Multicarrier version CDMA-2000).

  10. 2.- VHF band: coexistence with legacy narrowband systems: voice, VDLx • Interference of NB over CDMA is not a big deal • Interference of CDMA over VDL is easy to solve VDL’s use the same channels for all the sectors CDMA has to avoid these channels • Interference of CDMA over voice channels is the key issue • Voice channels use different frequencies per sector • The use of these channels is dynamic depending on the activity factor • It is mandatory to guarantee null degradation of these voice channels to allow the deployment of the new system

  11. Demonstration: Interference on Voice Channels Analog Communications Envelope Detector Received Samples as Recorded (without Interference) Original Received Samples with Interference (Ratio is given at the output) SIR=0 dB Received Samples with Interference (Ratio is given at the output) SIR=10 dB Received Samples with Interference (Ratio is given at the output) SIR=20 dB

  12. 2.- VHF band: coexistence with legacy narrowband systems: Our proposal • Minimize interference by the combination of two techniques • CDMA transmit beamforming to eliminate interference of no co-located victim • Transmit a CDMA modified spectrum with spectral nulls in some specific channels New codes design Victim 2 CDMA 2 CDMA 2 Freq. Victim 1 no suffering interference by spatial filtering Victim 2 Suffering interference by spatial filtering Interference eliminated by frequency filtering CDMA 1 CDMA 2

  13. C band CDMA C band CDMA VHF AM, VDL VHF AM, VDL VHF AM, VDL CDMA Current state First step Second step 3.- Deployment in two steps ‘C’ Band: WCDMA- FDD VHF: IS-95 like FDD (new codes) Exploit: spatial dimension !!

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