# Analysis on Target Detection and Classification in LTE Based Passive Forward Scattering Radar
## 1 Introduction  
The advantages of Forward Scattering Radar (FSR) have created a 'comeback' interest in the system in the past decade. This is followed by active research throughout the world from Universities, Research Institutes and Industries [1; 2; 3; 4]. The main difference between the FSR and the traditional radar is that the operational mode of the FSR corresponds to the case where the bistatic angle is near \(180^{\circ}\). The key difference of the FSR in contrast to its monostatic and bistatic counterparts is that it utilizes the effect of electromagnetic waves, shadowing a target rather than reflecting from the target. The FSR system exhibits some special characteristics such as: enhanced target radar cross sections, not effected by stealth techniques for radar signal reduction, long coherent intervals of the receiving signal, absence of signal fluctuations and simple hardware [1; 2]. In other important areas of the radar system, passive radar has become very crucial and much research has been published comprising theoretical and practical applications with rapid developments. The passive radar system is made up of a receiver without the co-located transmitter. Hence, one factor that makes passive radar interesting is the possibility of utilizing an illuminator of opportunity, which can reduce the cost of a radar system due to the no expenses needed to be paid for a transmitter system. The basis of not having a dedicated transmitter leads to the system being practically invisibleto surveillance. To date, many illuminators of opportunity have been employed by many sources such as: Television Broadcasting [5], FM radio [6], Digital Video and Audio Broadcasting (DAB) [7], satellites [8; 9], Global Systems for Mobile communications (GSM) [10] and Long Term Evolution (LTE) [11]. The receiver circuit for conventional PBR using the heterodyne concept requires a reference signal from direct transmission for synchronization. The signal is then down converted to the base band. Target detection is evaluated by analyzing the ambiguity function of the received signal. Alternatively, this paper proves that by having hybrid operation between the FSR technique and conventional passive radar is beneficial due to: (i) a simple FS receiver circuit; (ii) significant improvement in radar cross section (RCS) at the forward scatter main lobe (FSML); (iii) passive FSR does not require direct signal from the base station and (iv) target detection scheme based on signal envelope is straight forward without complicated signal pre-processing step. Furthermore, the classification capability in passive FSR increases the effectiveness of the system [1; 12]. The interesting feature in passive FSR, which is the sharp rise of the FS RCS, can increase the sensitivity of the system, making it robust to \"Stealth\" technology. This effect which exists within the FSML can only be seen within a specific condition in the Mie region and the optical region [13]. Several researches have been carried out studying the feasibility of using passive radar with the FSR mode. In the meantime, studies on using GPS signals as a passive radar system have been demonstrated in [14; 15] by using GPS L1 and GPS L5 respectively for air target detection. Passive radar to detect ground targets by using the GPS signal is explained in [16] with positive experimental results. Despite the possibility of using GPS as passive radar, however, the proposed radar system is limited to the signal availability due to satellite movement, signal blockage by buildings or trees and difficulty in tracking the satellite position. A research using GSM as a signal source and utilizing the forward scatter geometry for target detection is explained in [17]. However, the proposed system deployed a conventional passive radar receiver mechanism by using two antennas; one for reference and the other one to receive signals from a target. Recent publications on passive forward scatter radar have introduced a new algorithm for signal detection, which is for air target detection.