Biblio

Global Navigation Satellite System (GNSS) jamming is an evolving technology where new modulations are progressively introduced in order to reduce the impact of interference mitigation techniques such as Adaptive Notch Filters (ANFs). The Standardisation of GNSS Threat reporting and Receiver testing through International Knowledge Exchange, Experimentation and Exploitation (STRIKE3) project recently described a new class of jamming signals, called tick signals, where a basic frequency tick is hopped over a large frequency range. In this way, discontinuities are introduced in the instantaneous frequency of the jamming signals. These discontinuities reduce the effectiveness of ANFs, which unable to track the jamming signal. This paper analyses the effectiveness of interference mitigation techniques with respect to frequency-hopped tick jamming signals. ANFs and Robust Interference Mitigation (RIM) techniques are analysed. From the analysis, it emerges that, despite the presence of frequency discontinuities, ANFs provide some margin against tick signals. However, frequency discontinuities prevent ANFs to remove all the jamming components and receiver operations are denied for moderate Jamming to Noise power ratio (J/N) values, RIM techniques are not affected by the presence of frequency discontinuities and significantly higher jamming power are sustained by the receiver when this type of techniques is adopted.

Military reconnaissance in 1999 has paved the way to establish its own, self-reliant and indigenous navigation system. The strategic necessity has been accomplished in 2013 by launching seven satellites in Geo-orbit and underlying Network control center in Bangalore and a new NavIC control center at Lucknow, later in 2016. ISTRAC is one of the premier and amenable center to track the Indian as well as external network satellite launch vehicle and provide house-keeping and inertial navigation (INC) data to launch control center in real time and to project team in off-line. Over the ISTRAC Launch network, Simple Network Management Protocol (SNMP) was disabled due to security and bandwidth reasons. The cons of SNMP comprise security risks that are normal trait whenever applied as an open standard. There is "security through obscurity" linked with any slight-used communications standard in SNMP. Detailed messages are being sent between devices, not just miniature pre-set codes. These cons in the SNMP are found in majority applications and more bandwidth seizure is another contention. Due to the above pros and cones in SNMP in form of open source, available network monitoring system (NMS) could not be employed for link monitoring and immediate decision making in ISTRAC network. The situation has made requisitions to evolve an in-house network monitoring system (NMS). It was evolved for real-time network monitoring as well as communication link performance explication. The evolved system has the feature of Internet control message protocol (ICMP) based link monitoring, 24/7 monitoring of all the nodes, GUI based real-time link status, Summary and individual link statistics on the GUI. It also identifies total downtime and generates summary reports. It does identification for out of order or looped packets, Email and SMS alert to Prime and Redundant system which one is down and repeat alert if the link is failed for more than 30 minutes. It has easy file based configuration and no application restart required. Generation of daily and monthly link status, offline link analysis plot of any day, less consumption of system resources are add-on features. It is fully secured in-house development, calculates total data flow over a network and co-relate data vs link percentage.

With the rapid development of radio detection and wireless communication, narrowband radio-frequency interference (NB-RFI) is a serious threat for GNSS-R (global navigation satellite systems - reflectometry) receivers. However, interferometric GNSS-R (iGNSS-R) is more prone to the NB-RFIs than conventional GNSS-R (cGNSS-R), due to wider bandwidth and unclean replica. Therefore, there is strong demand of detecting and mitigating NB-RFIs for GNSS-R receivers, especially iGNSS-R receivers. Hence, focusing on working with high sampling rate and simplifying the fixed-point implementation on FPGA, this paper proposes a system design exploiting cascading IIR band-stop filters (BSFs) to suppress NB-RFIs. Furthermore, IIR BSF compared with IIR notch filter (NF) and IIR band-pass filter (BPF) is the merely choice that is able to mitigate both white narrowband interference (WNBI) and continuous wave interference (CWI) well. Finally, validation and evaluation are conducted, and then it is indicated that the system design can detect NB-RFIs and suppress WNBI and CWI effectively, which improves the signal-to-noise ratio (SNR) of the Delay-Doppler map (DDM).