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Air traffic control systems
Published in Mike Tooley, David Wyatt, Aircraft Communications and Navigation Systems, 2017
The Mode S method extends the information already described above for enhanced surveillance. Extended squitter (ES) messages include aircraft position and other status information. The advantage of using ES is that the infrastructure exists via Mode S ground stations and TCAS- equipped aircraft. Note that Mode S provides only unidirectional communications.
Automatic Dependent Surveillance Broadcast (ADS-B)
Published in Busyairah Syd Ali, Aircraft Surveillance Systems, 2017
Mode S technology has two types of squitter, a short (56 bit) DF11 acquisition squitter and the extended (112 bit) DF17 squitter. The squitter is a reply format transmission without being interrogated by another means such as radar. The downlink format (DF) and uplink format (UF) are the two functional components of Mode S. UF is a specific interrogation originating from SSR or other aircraft requesting specific information from the aircraft. DF is the reply from the aircraft to the UF interrogation. The DF17 extended squitter is similar to elementary and enhanced surveillance (explained in Chapter 2) except that it does not need interrogation, i.e. it simply “broadcasts”. The DF17 extended squitter includes the airborne position (BDS 0, 5), surface position (BDS 0, 6), extended squitter status (BDS 0, 7), identity and category (BDS 0, 8) as well as airborne velocity (BDS 0, 9). Binary Data Store (BDS) is a register within the transponder maintaining avionics data in 256 different 56 bit wide registers. It can be loaded with information and read out by the ground system. Each register contains the data payload of a particular Mode S reply or extended squitter. The BDS registers are also known as Ground Initiated Comm B (GICB) registers (ICAO, 2004c). The registers that are not updated within a fixed period are cleared by the transponder. Registers are identified by a two digit hex number. For example, BDS 05h (or also represented as BDS 0, 5) is the position squitter (Selex System Integration, 2013). In addition to the 56 bits, the Mode S short acquisition squitter includes: 8 bit CONTROL24 bit ICAO aircraft address24 bit PARITY. 1090ES includes an additional 56 bits data field used to carry ADS-B information. Table 4.7 presents the 1090ES ADS-B message type DF17, register and broadcast rate of each register. Figure 4.4 presents the data format.
Estimation of aircraft distances using transponder signal strength information
Published in Cogent Engineering, 2018
The algorithm described here processes Basic Mode S, Extended Mode S, and Mode C data output by a 1090 MHz tuner/demodulator combination hosted by a Raspberry Pi single-board computer running a modified version of the open-source software dump1090 (Sanfilippo & Robb, 2014). These data consist of eight closely chronologically-spaced values of relative signal strength for each transponder transmission that is received. Generally, these transmissions are received every few seconds; the interval between transmissions is, however, irregular and dependent on the frequency of interrogations from ground-based secondary surveillance radar stations and of uninterrogated Mode S DF17 squitter transmissions. These eight values constitute a signal strength vector that may be combined into a single scalar quantity that can, in turn, be used to represent the signal strength in the manner described below. A detailed flowchart of the distance estimation process is depicted in Figure 1.