LDACS1 frame structure

This page describes LDACS1 frame structure used for resource access and communicaion between Aircraft stations and ground station for air traffic control. LDACS1 is the L band Digital Aeronautical Communication System in FDD configurations at the Airport and also during the travel path of flight from the source to the destination.

As we know OFDM frames are formed using OFDM symbols. Depending upon MAC data frame to be transmitted different types of frames are generated. They are data segment, dedicated control segment and random access frame. LDACS1 uses OFDMA-TDMA for transmissions from Aircraft Stations(ASs) to the Ground Station(GS).

LDACS1 tile structure

In OFDM all the subcarriers of the entire symbol is assigned to one signal user (i.e. subscriber). In OFDMA, total subscribers are divided into subchannels or group of subcarriers (either contiguous or distributed) . These are assigned to multiple users or subscribers or Aircraft Stations. In LDACS1, two users have been assigned subcarriers in one single FFT across one time symbol. Here minimum one tile structure is assigned to the Aircraft Station. One tile is made of 6 symbols across time axis and 25 subcarriers across frequency axis. Refer OFDM vs OFDMA for difference between OFDM and OFDMA.

LDACS1 frame structure

Figure-2 depicts LDACS1 frame structure used by Aircraft Stations(ASs) to the Ground Station(GS) in LDACS1. As shown, LDCAS1 frame is made of superframe, multiframes and tiles. Each tile is of duration 0.72ms. One superframe will be of the duration of 240ms. This superframe consists of Random Access subframe of duration 6.72ms and four multiframes of duration 58.32ms each.

The data carried on the reverse link is in the form of PHY-PDU provided by the MAC sublayer. The size of RL PHY-PDU vary based on different frames and tiles.

One RA PHY-PDU mapped to one RA subframe as shown. Each multiframe is composed of Dedicated Control Segment and Data Segment.

LDACS(L Band Digital Aeronautical Communication System) RELATED LINKS

Following links covers LDACS1 and LDACS2 Physical layers, LDACS1 and LDACS2 frame structures and provide difference between LDACS1 and LDACS2.
Difference between LDACS1 versus LDACS2
LDACS1 frame structure
LDACS2 frame structure
LDACS1 physical layer
LDACS2 physical layer
Air Traffic Management

frame structure of other Wireless standards

•  WiMAX physical layer Frame Structure as per 802.16d and 802.16e standards
•  WiMAX MAC layer Frame Structure as per OFDM 802.16d standard
•  Zigbee RF4CE Frame Structure
•  Zigbee physical layer Frame Structure
•  Zigbee MAC layer Frame Structure
•  GPRS Frame Structure
•  GPS Frame Structure
•  LTE Frame Structure
•  TD-SCDMA Frame Structure
•  UMTS Frame Structure
•  SONET Frame Structure
•  SDH Frame Structure
•  802.11ac PHY Frame Structure
•  802.11ac MAC layer Frame Structure
•  WLAN Frame Structure as per 802.11a,11b,11n,11ac standards
•  AMPS Frame Structure
•  Ethernet Frame Structure
•  VLAN Frame Structure
•  GSM Frame Structure

RF and Wireless Terminologies