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Top1. Introduction
The development of information and communication technologies (ICT) is expected to meet the growing demands of users to be continuously and uninterruptedly connected with everyone and everything. Today’s wireless communication networks (WCNs) face a number of serious issues, such as the rapid increase in traffic volume, significant changes in the type of network traffic, the constantly growing number of highly mobile users and, as a result of this need for network access and connectivity, a demand for lower latency. These problems, along with the lack of communication resources, a complex signal and interference environment, the need to process large amounts of data, complicated synchronization, etc., give rise to the need to develop new and effective methods for solving them. WCNs are becoming heterogeneous, ultra-dense, resource-constrained, low power, intelligent, and self-organizing. They must efficiently use the telecommunications infrastructure and provide an excellent service, together with an extremely important element: secure communication.
Security and privacy provisioning are a major concern in current and future wireless communication systems. Over the last decade, physical layer security (PLS) has received significant research attention as a means of protecting networks from unauthorized access. PLS makes use of the physical properties of the transmission medium and the types of line coding, multiplexing and modulation implemented, in order to improve the quality of the signal at the intended receiver, while simultaneously reducing information leakage to an attacker. In essence, PLS employs the mathematical principles of communications theory as an alternative to using computationally complex algorithms to provide confidentiality. Consequently, PLS has become an attractive solution for resource-limited applications.
Despite its numerous advantages, PLS is still vulnerable to certain malicious user interventions. Two commonly used attacks that can be launched against security at the physical layer are jamming and eavesdropping. Due to the broadcast nature of their interface, wireless systems are especially at risk from these types of intrusion, which facilitate the interception of legitimate communication exchange by a third party and are known as an eavesdropping attack. In the case of a jamming attack, the jammer, taking advantage of the open wireless medium, can send signals, which interfere with the legitimate transmission.
The effect of a jamming attack is twofold: on one hand, the intentional interference caused by the jammer significantly decreases the quality of service, due to the adverse effect on the performance parameters, such as bit error rate (BER) and packet delivery ratio (PDR). On the other hand, the signal sent by a jammer occupies parts of the frequency band, which may prevent legitimate access to the wireless channel. Hence, jamming attacks may result in Denial-of-Service (DoS) at the physical layer. While different types of jamming attacks have been studied in the literature (Amin, 2016; Muraleedharan, 2006; Mpitziopoulos, 2009; Zou, 2016). narrowband jamming is more commonly encountered than the wideband version, due to its better energy efficiency.
In this article, a method to overcome high-power narrowband jamming attacks at the physical layer is proposed. The method involves the use of a first-order notch adaptive filter with complex coefficients. Since the filter’s operational bandwidth and central frequency are tunable in an adaptive manner, the proposed technique can be used against narrowband jamming whose frequency varies rapidly over time across the spectrum. The efficiency of adaptive complex filtering is experimentally studied in the presence of high-power narrowband jamming.
The rest of the paper is organized as follows: in Section 2 a brief overview of the available jamming mitigation methods based on adaptive filtering is given. Section 3 presents the proposed adaptive complex notch filter. In Section 4, simulation results are presented, and Section 5 concludes the paper.