# ROAD Statistics-Based Noise Detection for DME Mitigation in LDACS
## 5 Results and Discussions  
This section exposes the advantages of ROAD statistics-based sensing over amplitude-based sensing in LDACS FL communication. The results obtained from the detailed analysis of threshold ROAD value-based sensing for different threshold values under different SNR conditions are distinctly presented. The section also discusses the performance of the proposed ROAD statistics-based nonlinear device (ROAD PB) in reducing DME interference when employed in OFDM-based LDACS communication. The discussion is based on the results obtained from the MATLAB simulation of the LDACS forward link communication prototype. The performance of the proposed method is compared with the conventional pulse blanking method which uses the amplitude of the received signal for the detection of DME interference. The nonlinear devices such as GAEPPA, GAEPPL, OBEPPA and OBEPPL are also included to compare the performance of ROAD PB. The mathematical model of the LDACS FL GS transmitter (Figure 3) and LDACS FL AS receiver (Figure 3) are developed as per the standards of the LDACS system for all the inner building blocks. At the transmitter side, random data of 91 bytes are generated by the data source and given as the input of RS coder (91,101) for external coding. Once external encoding is performed by the RS encoder, 6-bit zero padding is performed before passing through internal encoding by the convolutional encoder (171,133). The encoded bits from the output of convolutional code, with native coding rate half, are further interleaved (using permutation interleaver) and then mapped to symbols (using symbol mapper). The mapped symbols form complex values when they pass through the QPSK modulation block. The frame composer block forms the LDACS FL data/CC frame with proper insertion of pilot values (158), null values (728) and complex data values (2442) over a total of 3328 subcarriers. Further, the time domain composite waveform of this OFDM frame is generated by passing the frame through the IFFT block of length 64. The effect of the introduction of IFFT (windowing) is canceled by adding 16 cyclic prefix bits. Table 1 holds the OFDM system parameters used in this simulation study. To analyze the performance degradation of the LDACS FL AS receiver due to DME interference, the AWGN channel is considered. The BER variation of the received signal when passed through the AWGN channel without the influence of DME interference is obtained as shown in Figure 7. For the study of interference on LDACS, DME signals are generated by (3) for a duration \(\Delta t\) of 12 us as shown in Figure 8. The baseband DME pulse pairs are modulated to the relative carrier frequency of the channel to 0.5 MHz left and to 0.5 MHz right of the LDACS1 system bandwidth. A reduction in performance of the LDACS FL AS receiver can be observed when DME interference is allowed to affect the transmitted data. Figure 7 also shows how the existing simple noise reduction method (pulse blanking) improved the performance of the receiver. The threshold value used for the pulse blanking method is 0.3. Careful analysis of Figure 7 reveals the fact that the pulse blanking technique showed a significant improvement in the performance of the receiver at high SNR powers and a slight decrease at low SNR values. The reason for the reduction in performance of pulse blanking (at low SNR values) is the false detection caused due to the amplitude-based sensing and the resulting extra loss of data. It is possible to reduce this number of false detections by increasing the threshold value of detection. However, high threshold value can lead to an increase in missed detection and more interference power at the output of the receiver.