The open nature of radio propagation enables ubiquitous wireless communication. This allows for seamless data transmission. However, unauthorized users may pose a threat to the security of the data being transmitted to authorized users. This gives rise to network vulnerabilities such as hacking, eavesdropping, and jamming of the transmitted information. Physical layer security (PLS) has been identified as one of the promising security approaches to safeguard the transmission from eavesdroppers in a wireless network. It is an alternative to the computationally demanding and complex cryptographic algorithms and techniques. PLS has continually received exponential research interest owing to the possibility of exploiting the characteristics of the wireless channel. One of the main characteristics includes the random nature of the transmission channel. The aforesaid nature makes it possible for confidential and authentic signal transmission between the sender and the receiver in the physical layer. We start by introducing the basic theories of PLS, including the wiretap channel, information-theoretic security, and a brief discussion of the cryptography security technique. Furthermore, an overview of multiple-input multiple-output (MIMO) communication is provided. The main focus of our review is based on the existing key-less PLS optimization techniques, their limitations, and challenges. The paper also looks into the promising key research areas in addressing these shortfalls. Lastly, a comprehensive overview of some of the recent PLS research in 5G and 6G technologies of wireless communication networks is provided.
With the advancement of solid-state devices for lighting, illumination is on the verge of being completely restructured. This revolution comes with numerous advantages and viable opportunities that can transform the world of wireless communications for the better. Solid-state LEDs are rapidly replacing the contemporary incandescent and fluorescent lamps. In addition to their high energy efficiency, LEDs are desirable for their low heat generation, long lifespan, and their capability to switch on and off at an extremely high rate. The ability of switching between different levels of luminous intensity at such a rate has enabled the inception of a new communication technology referred to as visible light communication (VLC). With this technology, the LED lamps are additionally being used for data transmission. This paper provides a tutorial and a survey of VLC in terms of the design, development, and evaluation techniques as well as current challenges and their envisioned solutions. The focus of this paper is mainly directed towards an indoor setup. An overview of VLC, theory of illumination, system receivers, system architecture, and ongoing developments are provided. We further provide some baseline simulation results to give a technical background on the performance of VLC systems. Moreover, we provide the potential of incorporating VLC techniques in the current and upcoming technologies such as fifth-generation (5G), beyond fifth-generation (B5G) wireless communication trends including sixth-generation (6G), and intelligent reflective surfaces (IRSs) among others.
This treatise presents a framework for the optimisation of a colour-based optical spatial modulation for visible light communication (VLC). The focus is particularly on the conflicting interests between illuminance and signal transmission. The system under consideration is configured with a non-lineof-sight (NLoS) model, based on the joint use of colour shift keying (CSK) and optical spatial modulation (OSM) with intensity modulation and direct detection (IM/DD). With the adaptation of the aforementioned optical techniques and convex optimisation, the design and development of a colour-based optical wireless system is carried out. Firstly, an optimisation problem with the intention of minimising the total luminous intensities of the light emitting diode (LED) arrays subject to the transmitting LED array's optical power budget, minimum required illuminance level, LED-user channel conditions and latency intolerant users' (LITUs) quality-of-service (QoS) target constraints is defined. Secondly, a coordinated algorithm for the selection of a transmitting LED array, maintenance of a particular illuminance and signal-to-interferenceplus noise ratio (SINR) levels during symbol transmission is designed. Lastly, through computer simulations, a numerical analysis is carried out to demonstrate and evaluate the performance of the algorithm. During the transmission of all symbols, the proposed framework is capable of satisfying the SINR target for LITUs while reducing the optical power by approximately 20% to 25% and 20% to 75% for transmitting and non-transmitting LED arrays, respectively. Additionally, provided that the required illuminance level is specified within the standardised levels of 300 lux to 1500 lux, the proposed system can provide adequate illuminance as per the users' requirement at all points where either a LITU or a latency tolerant user (LTU) is located at any given instance. However, fair SINR levels are not guaranteed at the points where the LTUs are positioned. On the other hand, the algorithm disposes low illuminance levels ranging from 100 lux to 250 lux at locations towards the room boundaries where there are no users. The proposed system is able to achieve data rates of 5 Mbps to 25 Mbps using commercially-off-the-shelf LEDs.
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