# NextGen ADS-B Software-Defined Reception with Enhanced Techniques
## 6 Discussion  
The principal goal of this work is to design, develop, and implement an ADS-B software application capable of ADS-B signal reception by deploying advanced algorithms during pulse detection, bit detection, and error correction toward certifiable SDAM and capable of a receiving, decoding, and tracking aircraft information in long-distance ranges with high integrity and robustness. In the meantime, the ADS-B Apps should be not only easily integrated with the airplane but also minimize the size, weight, power, and cost.  
Prior to applying the ADS-B reception algorithm in the digital domain, it is completely necessary to have an acceptable RF signal level since setting manual Gain may lead to either saturation in case of the high-power input signal and high gain setting, or loss of data in case of the low-power input signal and low gain setting. While the aim of slow attack AGC activation and applying proper settings is to prevent the above-mentioned circumstances and issues. Proper setting of AGC parameter brings about optimum gain setting according to input signal strength level. Besides, it is crucial to make AGC activated in ADS-B In since signal strength varies based on distance, transmitted signal power, and type of antenna. Furthermore, it is necessary to take into consideration that the slow attack AGC is not the same as digital gain which merely increases the gain of both signal and noise by multiplying the setting factor, and the overall signal-to-noise ratio remains the same. Whereas the slow attack AGC and gain adjustment applied prior to A/D and to the analog signal, thus it enhances quantization error and signal-to-noise ratio (SNR).  
In this research, leading-edge pulse detection is used to detect and validate the preamble pulses. Two major factors of accuracy and real-time processing play pivotal roles. Therefore, it is necessary to accomplish accuracy criteria and to consider processing time. As discussed earlier, the leading-edge and multiple amplitude samples algorithms are preferred to cross-correlation and the central sampling approaches. The reason is having high accuracy and robustness to the interference and overlapping phenomenon. In this method, applying a higher sampling rate may lead to improving the accuracy of pulse detection, however, it brings about a higher processing load and may cause data loss.  
Apart from pulse detection, the enhanced bit detection algorithm is deployed to detect bits and score each bit's confidence level. The confidence declaration is computed based on the sample position within the pulse and given higher weightage to center samples.  
Figure 19: Number of correctly decoded messages per second during flight test.  
In addition, low-confidence bits are used as possible candidates for error correction if the error syndrome value is nonzero.  
Although taking the diverse advantage of antenna array enhances ADS-B receiver sensitivity, in practice installation of more antennas in the aircraft, particularly in small ones is not feasible. In this research, a DME antenna is used in the flight test to validate system performance and behaviors in the operational environment.