DESIGN OF A SPECIFIC CDMA SYSTEM FOR AIR TRAFFIC CONTROL APPLICATIONS

UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA

UNIVERSIDAD POLITÉCNICA DE MADRID

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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

Outline

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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 …

1.- Motivation and objectives

Communication capacities

2010 2020

POTENTIAL NEW SYSTEMS

Communication strategiesEurocontrol

8,33 kHz + VDL2SATCOM

Communication needs

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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

1.- Main goal of the project: flexible simulation tool

CDMAStandard Tx

Aeronauticalchannel +

interferences

CDMA Advanced receivers

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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

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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

FDD. Frequency Division Duplex

No such limitation.

Pay attention to the assigned bands of both links

Data transmission GuardKey

disadvantage

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Further considerations regarding the spreading factor in TDD /FDD and aeronautical channel delay spread.

Typical delay spread En route: 33 sec.Arrival, parking: 7 sec.Taxi: 0.7 secCDMA symbol length TDD (16 chips/Symbol)=4.16 sec (indoor applications) FDD (256 chips/Symbol)=66.6 sec (outdoor applications)

ConclusionsTDD suffers strong ISI (performance degradation). This point may be compensated by the use of advanced MultiUser DetectorsFDD 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.

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Our proposal for the ‘C’ band. UMTS-FDD.

Topics covered in our research MRC detector. SingleUser detector Adaptive implementation to follow channel variationsAdaptive beamforming

Several antennas at the ground stations Tx beamforming (Downlink) Rx beamforming (Uplink)

Increase SNR (or coverage) Reduce intra and inter-cell interferences

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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).

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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 solveVDL’s use the same channels for all the sectorsCDMA 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

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Analog Communications Envelope Detector

Original

SIR=10 dB

SIR=0 dB

Demonstration: Interference on Voice Channels

SIR=20 dB

Received Samples with Interference (Ratio is given at the output)

Received Samples with Interference (Ratio is given at the output)

Received Samples with Interference (Ratio is given at the output)

Received Samples as Recorded (without Interference)

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2.- VHF band: coexistence with legacy narrowband systems: Our proposal

Minimize interference by the combination of two techniques CDMA transmit beamforming to eliminate interferenceof no co-located victim Transmit a CDMA modified spectrum with spectral nulls in some specific channels

New codes design

CDMA 1

CDMA 2

Victim 1 no suffering interference by spatial filtering Victim 2

Suffering interference by spatial filtering

Freq.CDMA 2

Victim 2

Interference eliminated by frequency filtering

CDMA 2

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3.- Deployment in two steps

VHFAM, VDL

Current state

C bandCDMA

VHFAM, VDL

First step

C bandCDMA

VHFAM, VDL

CDMA

Second step

‘C’ Band: WCDMA- FDDVHF: IS-95 like FDD (new codes)

Exploit: spatial dimension !!