# GAE and OBE Enhanced Interference Mitigation Techniques in LDACS
## 2 Related Work  
Several interference mitigation techniques for LDACS are available in the literature; among these, most of the proposed schemes focus on mitigating DME interference. In 2011, [PERSON] et al. proposed two methods to detect and reduce DME interference. One of the methods takes advantage of the repetitive structure of the DME pulse, while the other utilizes the spectral shape of the DME signal. Simplicity is the advantage of this technique, but at the cost of losing a part of the desired signal due to pulse blanking [21]. In 2012, [PERSON] et al. proposed a mixed blanking technique (combination of pulse blanking and notch filter) mainly for the B2 band (1900 MHz). Though the technology has the advantage of operating in both time and frequency domain, it is more effective and safe for the B2 signal [22]. Further, [PERSON] et al. suggested a scheme that uses complementary code keying (CCK) to reduce DME interference. Though the CCK encoding has the advantage of better gain, it demands low phase distortion and a wideband channel. The acquisition  
Figure 2: Interference between DME and LDACS [16]. time is greater, which increases the latency of the system. Moreover, the modulation used here is not a power-efficient modulation [23]. In 2014, an iterative receiver design was proposed by [PERSON] et al. [24]. The design employs iterative decoding between the demodulator and decoder based on the turbo principle. Later, [PERSON] et al. proposed a block-based selective pulse blanking method, which mitigates DME interference with the employment of a designed fast filter bank [25]. Another DME mitigation method based on deformed pulse pair detection and its negation from the actual signal was proposed by [PERSON] et al. in 2016 [26]. Later, [PERSON] and [PERSON] introduced lattice signal sets to combat DME interference from aeronautical signals. The method uses precoding at the transmitter based on the lattice signal set, which modifies the shape of the DME signal spectrum; a simple clipping technique is then applied for DME mitigation [27]. The major drawback with the pulse blanking is the inter-carrier interference. A method that removes the inter-carrier interference was proposed by [PERSON] et al. [12]; the method is based on the decision-directed noise estimation. Even though this method removes inter-carrier interference, the cyclic prefix reduces the throughput of transmission and leads to wastage of power. In 2019, [PERSON] proposed LDACS-OFDM based on discrete wavelet transform (DWT) and increased sidelobe suppression [28]. The method utilizes the real nature of DME and the selective transmission of signal through the quadrature channel in the presence of DME. With the intelligence of the direct sequence spread spectrum to combine the inphase and quadrature phase, the method claims to perform DME free transmission. The computational complexity and resource requirement are the disadvantages of this method. In 2021, two methods named deep clipping and joint clipping blanking to reduce DME interference were proposed in [29]. Careful study of the existing interference mitigation techniques in LDACS exposes that there is a scope of DME mitigation in LDACS. In 2015, a linear finite impulse response equalizer was proposed to compensate for the inter-carrier interference caused due to pulse blanking in OFDM systems [30]. Besides this, some of the existing nonlinear estimators which are still not utilized in reducing impulsive noise (or DME) in LDACS are genie-aided estimator (GAE) and optimum Bayesian estimator (OBE), to the best of our knowledge. The GAE uses statistical description of the side information as the design parameters to attain lower bounds on the bit error at the receiver [31]. GAE is expected to show better performance than any other detector working without the side information. However, an explicit detail of the side information is needed to attain this lower bound performance.