## 3 Proposed Resilment MFMC Receiver  
The use of MFMC receivers in various GNSS applications is very common nowadays. MFMC improves availability and continuity while also adding redundancy to the system. However, traditional MFMC receivers are not intelligent enough to minimize positioning errors in the event of massive jamming incidents. In this manuscript, the authors propose a resilient MFMC receiver prototype that would not only benefit from traditional MFMC receivers but also improve the overall resiliency of the system by exploiting frequency diversity. The proposed resilient MFMC receiver monitors the quality of the available signal in every epoch and prepares a pass/fail criterion for each of the GNSS signals to be included for the subsequent PVT computation. The objective of the proposed MFMC prototype is to detect jamming on any GNSS signals, exclude the impacted signal(s) from subsequent PVT computation, and perhaps notify the end-user about the identified abnormalities. For example, if the system detects jamming on the GPS L1 signal, all GPS L1 pseudo-range measurements for that epoch will be omitted from the PVT computation as long as it has one GNSS signal that has the jamming-free status. In this case, the system first identifies those \(N\) number of GNSS signals with jamming-free status so that it satisfies \(N\geq 1\). In the case when there are no GNSS signals with jamming-free status (i.e., in the case when \(N<1\)), the proposed resilient MFMC receiver falls back to a traditional GNSS receiver accepting all GNSS signals for PVT computation. This is to ensure that the proposed MFMC receiver makes the best use of multiple constellations and multiple frequencies in the case of simultaneous jamming on all of its received frequencies. The proposed resilient MFMC receiver consists of several processing blocks, some of which are common in traditional receivers. The digitized raw GNSS samples from the front-end are processed by a signal processing chain that includes signal acquisition, code and carrier tracking, jamming detection and exclusion, and a navigation processing unit to provide a PVT solution. The working principle of the proposed resilient MFMC receiver concept is depicted in Figure 5. In the case of a single frequency jamming event either on the L1/E1/B1 or L5/E5 bands, a jamming event is detected on those impacted GNSS signals, as per Equation (1). The proposed resilient MFMC receiver excludes all jamming-induced GNSS signals from PVT computation for the entire duration of the jamming event since it has the possibility to switch to other jamming-free GNSS signals (i.e., in both of the mentioned single-frequency jamming cases, there always exists \(N\) number of jamming-free  
Figure 4: Frequency spectrum of the L1 jammer (**left**) and the L5 wideband jammer (**right**). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **L1 Jammer** & **L5 Wideband Jammer** \\ \hline Center frequency (MHz) & 1564.74 & 1195.30 \\ Bandwidth (MHz) & 28.20 & 200 \\ Impacted GNSS signals & L1/E1/B1 & Lower L-band \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Jamming signal parameters. GNSS signals that satisfies \(N\geq 1\)). In the case of simultaneous multi-frequency jamming on all of its received GNSS signals, there is no available jamming-free signal for PVT computation (in the case when \(N<1\)). In this extreme multi-frequency jamming scenario, the proposed MFMC receiver then accepts all jamming-induced signals to be used in the PVT computation and notifies the end-user about the detected multi-signal jamming incident. As an efficient countermeasure, the receiver might seek an interference mitigation solution either internally within the receiver via receiver signal processing algorithms such as adaptive notch filters or externally by integrating an Inertial Measurement Unit (IMU) with sensor fusion [25; 26; 27].