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).
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.
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
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• Zigbee MAC layer Frame Structure
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• 802.11ac PHY Frame Structure
• 802.11ac MAC layer Frame Structure
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• VLAN Frame Structure
• GSM Frame Structure