Estudio de mercado .1 Análisis de demanda

L-DACS 2 is the second of two proposed communications links for aeronautical use in the L band. This system is based heavily on the proposed AMACS technology along with the physical layer from GSM and UAT adapted to the L-band. The assessment of this technology is based mainly upon the proposed system specification16. In places where the L-DACS 2 specification was found to be incomplete or unclear, the AMACS description document17 is referenced.

L-DACS 2 uses the modified version of the basic AMACS frame structure. Each frame is divided into 5 sections: two forward link sections (UP1 and UP2), two reserve link Class of Service (CoS) sections (CoS1 and CoS2), and a log on section (LoG2). The specification declares that the beginning of each frame is

aligned with a UTC second. A framing message transmitted in the beginning of UP1 can be used to adjust the length of each of these sections within a frame.

The UP1 and UP2 sections are used by the ground to transmit data, acknowledgements, or reservation grants to aircraft. In the CoS1 section, each aircraft has dedicated timeslots allocated to request slots for data or send acknowledgements. Slots are granted for data in the CoS2 section. Unused slots in the CoS2 section are available for use via random access.

Figure 17. L-DACS 2 Frame Structure

5.4.3.1 Air/Ground Communications Criteria

L-DACS 2 is designed for aeronautical use and thus long range communications. The specification states that guard times are based on a range of 200 NM between the aircraft and ground station. This rates L- DACS 2 as green for all the air/ground criteria.

Air/Ground Communications

Taxi / Surface Takeoff / Landing / Terminal

En Route 5.4.3.2 Data Transmission Criteria

L-DACS 2 supports addressed air/ground messaging with a local address assigned to the aircraft upon log on. The local address is used for all message exchanges from that point. The addressing criterion is rated as green.

The repetition rate of L-DACS 2 is limited. The 1 second frame length combined with the division between the forward and reverse link sections creates a situation where access to the channel is restricted, thus data messages would need to be queued until an appropriate section. The length of the frame would need to be greatly reduced, by more than an order of magnitude, to enable consistently spaced 20 Hz access rates. For this reason L-DACS 2 receives a red rating for repetition rate.

The raw data rate of L-DACS 2 is 270.833 kbps. This easily supports the command and control and ATS relay traffic, but is not sufficient for the inclusion of surveillance traffic.

Data Transmission

Addressing Repetition Rate Command/Control

C&C and ATS C&C, ATS, and Surveillance

5.4.3.3 Mobility Criteria

L-DACS 2 is designed with soft handoff mechanisms and receives a green rating for the handoff criteria. It supports closed loop dynamic power control on the aircraft side, but uses a fixed modulation and coding. The aircraft does passive scanning of nearby ground stations on other frequencies and performs a handoff as appropriate, qualifying for a green rating for the active QoS retuning.

Mobility

Handoff

Dynamic Power Control Adaptive Modulation Rates

Active QoS Retuning 5.4.3.4 Security Criteria

Like L-DACS 1, L-DACS 2 does not mention any encryption or hashing algorithms in the specification and receives a red rating for confidentiality and integrity. It supports dynamic power control and frequency allocation for a rating of yellow for availability.

Security

Confidentiality Integrity Availability 5.4.3.5 Traffic QoS Criteria

The L-DACS 2 specification does not specifically mention cross-carrier distribution. However, it does include methods for a ground station to request an aircraft to handoff. If the request includes a retune, this mechanism could be used to implement this feature. Since some modification likely would be needed on the ground side, the criteria is rated as yellow.

The specification for L-DACS 2 indicates the use of priority in the range of 0-3; however, in the messages the priority field is specified in the range of 0-14. Although the specification has some conflict on priority, it is included and receives a green rating.

L-DACS 2 does not support traffic classes or selectable reliability and receives a yellow rating for these two criteria. The original AMACS specification did include guaranteed and best effort traffic classes, but these seem to have been removed in L-DACS 2 as the use of the CoS1 and CoS2 reverse link sections have been changed, although parts of the documentation still have references to the these two traffic classes.

The TDMA nature of L-DACS 2 inherently supports dynamic bandwidth allocation yielding a green rating for this criteria. No mention of any RF statistics reporting could be found in the specification.

Traffic QoS

Cross-Carrier Distribution Priority

Classes Reliability/ARQ

Dynamic Bandwidth Allocation RF Statistics Reporting

5.4.3.6 Standardization and Certification Criteria

L-DACS 2 is not a commercially available system. Like L-DACS 1, this technology is still in the development phase. It is rated as yellow for the TRL. It is designed as an aeronautical link yielding a green rating for certification risk.

No issues were identified for L-DACS 2 in the area of robustness, determinism, or link layer compatibility therefore these criteria are rated green.

Standardization and Certification

Technology Readiness Level Certification Risk

Robustness Determinism Link Layer Compatibility 5.4.3.7 Waveform Criteria

L-DACS 2 is a TDD system with TDMA multiplexing for the forward and reverse link. This yields a green rating for the duplexing and forward link multiplexing criteria, but a yellow rating for the reverse link multiplexing. It uses GMSK for both the forward and reverse link modulation yielding a green rating for these criteria.

Waveform

Duplexing

Forward Link Multiplexing Reverse Link Multiplexing Forward Link Modulation Reverse Link Modulation