4G mobile communication is a global technology. Therefore, it is essential to enforce confidentiality between mobile users and their networks. This paper presents a Group Security Authentication and Key Agreement Protocol Built by Elliptic Curve Diffie Hellman Key Exchange (GSAKA-ECDHKE) to overcome and address the LTE networks Evolved Packet System Authentication and Key Agreement Protocol (EPS-AKA) protocol flaws and vulnerabilities. GSAKA-ECDHKE is presented for 4G mobile military group communications to provide security, confidentiality, and privacy while the users and networks authenticate. By embedding the Group Commander (GC) role in the EPS-AKA protocol to control the member authentication in the group. GSAKA-ECDHKE protocol is based on Elliptic Curve Diffie Hellman Key Exchange (ECDHKE) and hash function to generate and share secret Elliptic Curve (EC) key to encrypt and protect the routing authentication parameters. The Automated Validation of Internet Security Protocols and Applications (AVISPA) tool is used for security analysis and formal verification. AVISPA demonstrated that GSAKA-ECDHKE had overcome various known security attacks such as Man In The Middle (MITM), replay attacks, and Denial of Services (DoS) attacks, satisfying the evaluated security requirements. Additionally, the suggested protocol provides the lowest communication overheads compared to the existing group-based AKA protocols.

In cognitive radio networks (CRNs), secondary users (SUs) transmission requests are fulfilled via the use of portions of the licensed bandwidth dedicated to primary users (PUs). Meanwhile, through spectrum sharing of dynamic spectrum access (DSA), the PUs gain either financial benefits or cooperative communications. Due to the fact that the spectrum bandwidth resources are restricted hence; the dynamic allocation requests have become the focus of attention in recent years. Therefore, the dynamic channel reservation (DCR) in CRNs has a significant influence on improving network performance via the adjustment of the optimal number of reserved channels. Also, the centralized control (central controller) with a software-defined network (SDN) can be employed effectively to manage configuration, simplify the complexities, and develop dynamic coordination between the users in the network. In this paper, two algorithms of DCR are investigated to determine the optimal number of reserved channels based on SU retainability or SU channel availability while taking into consideration PU’s channel availability minimum limit in both cases. Performance metrics in both cases indicate the enhancement in system quality of service (QoS). Moreover, the results show a significant reduction in SU cost function and network unserviceable probability ( $Q_{s}$ ), while meeting the QoS requirements of PU through a minor inconsiderable impact on its channel availability and throughput compared to other previous models. In this paper, a proposed DCR algorithm is designed for selecting one of the two modes of operation depending on the incoming traffic requests to attain better performance characteristics.

A unidirectional Visible Light Communication (VLC) system has the potential to serve as an Indoor Positioning System (IPS). However, it is important to note that many existing VLC IPS setups rely on keeping LED lights switched on, which can lead to energy wastage when indoor lighting is unnecessary during daylight hours. Additionally, most indoor Visible Light Positioning (VLP) research has focused on 2D localization, assuming a fixed receiver height. This approach tends to overlook the positional inaccuracies that can arise due to variations in height. In this paper, to address these concerns, a 3D IPS is proposed. This system employs multiple transmitters and a single receiver, utilizing a Dark Light Visible Light Communication (DL-VLC) system. This innovative approach ensures the functionality of IPSs even when LEDs are turned "OFF" resulting in more efficient energy usage. The results of the investigation indicate that the positioning error remains within approximately 3 cm when the receiver is positioned at a height of 2.4 m, assuming standard room dimensions, which is in a fair agreement with previously published work.

In wireless networks, there are two prominent challenges. The first challenge is ensuring that users have opportunities to access channels and request new services. The second challenge is maintaining connections for data flows. These challenges are compounded by the occurrence of channel failures, which often occur due to characteristics of radio transmission such as signal attenuation, signal blockage or device and power outages. Channel failures can significantly impact the effectiveness of both the primary and secondary networks. Therefore, it becomes crucial to prioritize retainability which denotes the need to maintain uninterrupted user connections even during network disruptions. This paper proposes an analytical model that evaluates performance of cognitive radio networks in the context of random channel failure rates. Additionally, the dynamic channel reservation (DCR) scheme is introduced. It can be integrated into dynamic spectrum access (DSA) strategies. This integration aims to give priority to existing services over requests from users to provide cognitive networks with more opportunities to allocate idle channels or maintain their current services. Moreover, the cost functions for both the primary user (PU) and the secondary user (SU) are calculated. This calculation considers the failure rate specifically in either reserved channels (RCN) or non-reserved channels (N-RCN) to meet different performance requirements. The results show a decrease in the SUs cost function, which guarantees that the quality of service (QoS) requirements for the PU are fulfilled. Importantly, this reduction in SU cost leads to an enhancement in SU channel availability or throughput when compared to previous models.

In this paper, we propose an underlay cognitive radio (CR) system that includes subscribers, termed secondary users (SUs), which are designed to coexist with the spectrum owners, termed primary users (PUs). The suggested network includes the PUs system and the SUs system. The coexistence between them is achieved by using a novel dynamic spectrum co-access multicarrier-based cognitive radio (DSCA-MC-CR) technique. The proposal uses a quadrature phase shift keying (QPSK) modulation technique within the orthogonal frequency-division multiplexing (OFDM) scheme that maximizes the system data rate and prevents data inter-symbol interference (ISI). The proposed CR transmitter station (TX) and the CR receiver node (RX) can use an advanced smart antenna system, i.e., a multiple-input and multiple-output (MIMO) system that provides high immunity against channel impairments and provides a high data rate through its different combining techniques. The proposed CR system is applicable to coexist within different existing communication applications like fifth-generation (5G) applications, emergence applications like the Internet of Things (IoT), narrow-band (NB) applications, and wide-band (WB) applications. The coexistence between the PUs system and the SUs system is based on using power donation from the SUs system to improve the quality of the PU signal-to-interference-and-noise ratios (SINRs). The green communication concept achieved in this proposal is compared with similar DSCA proposals from the literature. The simulations of the proposed technique show enhancement in the PUs system throughput and data rate along with the better performance of the SUs system.

Advances in microwave technology and telecommunications have led to compact circuits, reduction of costs, masses and losses. The integration between microwave devices and components are considered a trend for microwave applications. The substrate integrated waveguide (SIW) technology has a great agreement with this trend in these applications. In this paper an integration of $-3 \mathrm{~dB}$ SIW directional coupler operating from 8.31 to 9.67 GHz with 90 degree phase shift at output ports and two series (E-plane) tee junctions operating from 8.8 to 12 GHz with 180 degree phase shift at output ports have been designed to feed 4-array of wideband hybrid slots including rectangular and ring shape slots with phase shifted signals. The wideband arrays consist of 64 rings and 16 rectangular slots distributed equally for the four arrays. The proposed integrated system has been designed and implemented using Roggers 4350 of $\varepsilon_{\mathrm{r}}=3.6, \tan \delta=0.004$ and thickness $h_{R}=1.5 \mathrm{~mm}$. The proposed integrated system has been simulated using HFSS simulator. The SIW system has an agreement between simulated and measured results. The SIW system introduces $S_{11}=-51 \mathrm{~dB}$, gain of 7.5 dB, radiation efficiency of 81.1% and fractional bandwidth of 15.7% for airborne insight, observation and surveillance (AISR) applications.