# NextGen ADS-B Software-Defined Reception with Enhanced Techniques
## 2 Literature Review  
The 1090 MHz Mode Select (S) transponder is required for aircraft that fly at 18,000 feet and higher and is the standard throughout much of the world. A Mode S transponder's 1090 MHz Extended Squitter connection is also employed to transmit ADS-B signals. By taking into account that ADS-B has been conceptualized as a development of Mode S, the technical literature has dealt with the subject of insight into how the performance of ADS-B technology can be affected by the modern surveillance systems functioning in the same 1090 MHz frequency channel [4; 5; 6]. On the one hand, critical concerns like the potential weaknesses and their probable causes, as well as their possible downsides on the Air Traffic Control (ATC) operating state of the ADS-B technology have been explored [7]. On the other hand, considering the fact ADS-B messages volume is increasing constantly since there is an increment trend in the number of aircraft installed with ADS-B facilities [8; 9]. Besides, the quantity of ground stations supplied with ADS-B instruments is rising and it facilitates receiving surveillance air traffic messages and making accessible an enormous number of ADS-B data generated by the field for the research society [10]. Prior studies and findings on the evaluation of enhanced receipt methods in the occurrence of interference are described in [11; 12] by [PERSON]. The results are demonstrated in various received power signal levels versus the probability of corrected messages captured by the receiver. Subsequent guidelines in the RTCA related to enhanced reception designs, in [13] present two developed decoding methods that have been put under trial and assessed based on Bit Error Rate (BER) versus Signal-to-Noise Ratio (SNR). In comparison to the standard technique, simulation outcomes demonstrate that the exploitation of multiple samples is able to improve the decoding mechanism. Furthermore, another study of the implementation of matched digital filters for preamble pulse detection in conjunction with a multilevel threshold detection for decoding with mean input was conducted [14]. Apart from that, an N-confidence error correction algorithm has been offered by [15], based on the matched filter decoding scheme for enhancing ADS-B performance in weak signals, however, all trials were done in Simulink. In [16], further improvement in ADS-B performance has been achieved by combining enhanced techniques with antenna arrays to mitigate the receiver sensitivity. Moreover, other studies and works have been carried out based on the multi-channel receivers' technique [17; 18; 19; 20]. The researchers aimed to use signal separation techniques to find out solutions for decoding overlapped Mode S frames. Furthermore, cross-correlation is one of the often-used techniques for preamble detection. Cross-correlation detection is carried out in the potentially valid signal sequence to locate the highest value that meets the cross-correlation threshold. The start of the data block may be where the maximum value is located. The research's result is demonstrated in the probability of preamble detection versus SNR [21]. Nonetheless, a comprehensive study of ADS-B enhanced detection techniques was done in the work [22]. The researchers developed a simulation environment to model an operational scenario by generating ADS-B frames and Mode A/C interfering signals. The result is shown in signal power against preamble detection. Ultimately, measurement-based evaluation of extended squitter detection likelihood in actual scenarios has been conducted by [23], to be more specific, this study was limited to air-to-ground stations, and it is done based on the RTCA-enhanced methods through receivers. The flexibility and modularity feature of Software Defined Radio (SDR) facilitates the assessment and testing of innovative ADS-B receiver advancements to be done quickly.