ADS-B Data Link

What is ADS-B data link?
As introduced in the Simple Explanation of What is ADS-B, ADS-B relies on communication equipment to transmit the aircraft's own ADS-B information to other aircrafts and ground stations. This communication link is known as the ADS-B data link.


How many tyeps of data link does ADS-B utilize?
Three. 1090ES,Universal Access Transceiver (UAT) and VDL M4.


What are the advantages and disadvantages of the three ADS-B data links?
1090, frequency is 1090MHz
Advantages: The 1090 MHz ADS-B communication equipment utilized on board air carrier aircraft typically is the Mode S transponder. Originally designed for Secondary Surveillance Radar (SSR), Mode S transponders are already installed on most air carrier aircraft. This means that the cost of modifying air carriers to support ADS-B is relatively low. In many cases, it only requires upgrading the software of the existing transponder, provided it's not an outdated version. This software update enables the Mode S transponder to also transmit ADS-B data, ensuring compliance with ADS-B regulations without the need for significant hardware modifications or replacements.
Disadvantages: The 1090 MHz frequency is indeed heavily utilized by various aviation systems, including Secondary Surveillance Radar (SSR), Traffic Collision Avoidance System (TCAS), and Multilateration (MLAT). This high level of utilization results in significant congestion on the 1090 MHz frequency band, it’s like having numerous vehicles trying to navigate the same road simultaneously. This congestion can potentially lead to interference and signal collisions, impacting the effectiveness and reliability of these systems. As a result, airspace authorities and regulatory bodies often face challenges in managing the allocation and usage of the 1090 MHz frequency band to ensure optimal performance and safety for all users.
UAT, frequency is 978MHz
Advantages: This data link is designed specifically for ADS-B transmission in the United States. One of the advantages of UAT is its allocation of sufficient bandwidth, which helps mitigate congestion and interference issues commonly associated with the heavily utilized 1090 MHz frequency band.
Disadvantages: The implementation of UAT communication equipment on aircrafts can introduce additional costs and complexities to ADS-B adoption, particularly in regions where UAT is utilized alongside 1090 MHz ADS-B. In the United States, where both 1090MHz ADS-B and UAT are utilized, the ADS-R (Automatic Dependent Surveillance – Rebroadcast) technology is implemented to facilitate communication between aircraft equipped with different ADS-B technologies. ADS-R rebroadcasts ADS-B information from one data link (e.g., 1090 MHz ADS-B) to another (e.g., UAT ADS-B), enabling aircrafts to "see" each other despite using different communication systems. While ADS-R helps address compatibility issues between 1090 MHz ADS-B and UAT ADS-B, it adds complexity to the overall ADS-B infrastructure and may require additional equipment and configuration adjustments. It’s like you need an interpreter for two persons who speak English and Chinese to talk to each other. 
Almost no one is using this anymore.


Which datalink should ADS-B use?
The short answer is 1090ES ADS-B. A simple reason is, as mentioned above in 1090ES advantages, 1090ES is the cheap and easy solution. The decision to utilize the UAT data link for general aviation (GA) in the United States is influenced by the congested nature of the 1090 MHz frequency band. With a high volume of both air carrier and GA aircraft, as well as numerous radar installations, the 1090 MHz frequency can become crowded, leading to potential interference and congestion issues. But other countries don’t have this congestion in 1090MHz band yet.

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