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

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
1.- Motivation and objectives
Communication strategies
Eurocontrol
8,33 kHz + VDL2 SATCOM
Communication needs
POTENTIAL NEW SYSTEMS
Communication capacities
2010
2020
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. CDMA standard transmitters to obtain representative results
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. Available bandwidth: 60 MHz, from 5.090 to 5.150 GHz.
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 to 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: 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. Large coverage (around 300 Km). Ideal for en route scenario.
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. Interference of NB over CDMA is not a big deal
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. Minimize interference by the combination of two techniques
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. VHF: IS-95 like FDD (new codes) Exploit: spatial dimension !!
3.- Deployment in two steps
C band
CDMA
VHF
AM, VDL
First step
C band
CDMA
VHF
AM, VDL
Second step
VHF
AM, VDL
Current state
‘C’ Band: WCDMA- FDD
VHF: IS-95 like FDD (new codes)
Exploit: spatial dimension !!