This work lays the foundations for full-duplex (FD) extremely large (XL) holographic multiple-input multiple-output (MIMO) communication systems to achieve seamless integration of reconfigurable holographic surfaces (RHS) and FD capabilities, enabling ultra-high-capacity, low-latency, and energy-efficient wireless communications. We consider the problem of sum-rate maximization by jointly designing the digital beamformers, holographic beamformer, and holographic combiner at the FD base station to jointly suppress self-interference (SI) and cross-interference. However, this results in a highly non-convex problem, for which a novel alternating optimization combining the minorization-maximization principle and the gradient ascent method is proposed. Simulation results demonstrate that the proposed method almost doubles the spectral efficiency compared to a half-duplex (HD) system.

Reflective Intelligent Surface (RIS)-assisted Ultra-Massive MIMO (Um-MIMO) systems in the terahertz (THz) spectrum are gaining attention for surpassing current wireless system limitations. However, limited diffraction at these frequen-cies typically results in low-rank Um-MIMO channels, completely reducing the potential for spatial multiplexing gains. In this work, we aim at promoting a new research direction towards the strategies for achieving high-rank Um-MIMO for RIS-assisted THz communications. The maximum achievable spatial multiplexing gain over the RIS-assisted channel is analyzed, and the optimal antennas and RIS elements placement strategy is proposed for achieving extremely high-rank Um-MIMO channels. Simulation results demonstrate that while conventional Um-MIMO THz systems display low-rank, the proposed approach enables achieving a rank on the order of hundreds for the Um-MIMO THz systems.

In this paper, a novel robust beamforming for an intelligent reflecting surface (IRS) assisted FD system is presented. Since perfect channel state information (CSI) is often challenging to acquire in practice, we consider the case of imperfect CSI and adopt a statistically robust beamforming approach to maximize the ergodic weighted sum rate (WSR). We also analyze the achievable WSR of an IRS-assisted FD with imperfect CSI, for which the lower and the upper bounds are derived. The ergodic WSR maximization problem is tackled based on the expected Weighted Minimum Mean Squared Error (WMMSE), which is guaranteed to converge to a local optimum. The effectiveness of the proposed design is investigated with extensive simulation results. It is shown that our robust design achieves significant performance gain compared to the naive beamforming approaches and considerably outperforms the robust Half-Duplex (HD) system.

The reliability of command and control (C2) operation of the UAV is one of the crucial aspects for the success of UAV applications beyond 5G wireless networks. In this paper, we focus on the short-packet communication to maximize the coverage range of reliable UAV control. We quantify the reliability performance of the C2 transmission from a multi-antenna ground control station (GCS), which also leverages maximal-ratio transmission beamforming, by deriving the closed-form expression for the average block error rate (BLER). To obtain additional insights, we also derive the asymptotic expression of the average BLER in the high-transmit power regime and subsequently analyze the possible UAV configuration space to find the optimum altitude. Based on the derived average BLER, we formulate a joint optimization problem to maximize the range up to which a UAV can be reliably controlled from a GCS. The solution to this problem leads to the optimal resource allocation parameters including blocklength and transmit power while exploiting the vertical degrees of freedom for UAV placement. Finally, we present numerical and simulation results to corroborate the analysis and to provide various useful design insights.

Proliferating applications of unmanned aerial vehicles (UAVs) impose new service requirements, leading to several challenges. One of the crucial challenges in this vein is to facilitate the autonomous navigation of UAVs. Concretely, the UAV needs to individually process the visual data and subsequently plan its trajectories. Since the UAV has limited onboard storage constraints, its computational capabilities are often restricted and it may not be viable to process the data locally for trajectory planning. Alternatively, the UAV can send the visual inputs to the ground controller which, in turn, feeds back the command and control signals to the UAV for its safe navigation. However, this process may introduce some delays, which is not desirable for autonomous UAVs’ safe and reliable navigation. Thus, it is essential to devise techniques and approaches that can potentially offer low-latency solutions for planning the UAV’s flight. To this end, this paper analyzes a multi-access edge computing aided UAV and aims to minimize the latency of the task processing. More specifically, we propose an offloading strategy for a UAV by optimally designing the offloading parameter, local computational resources, and altitude of the UAV. The numerical and simulation results are presented to offer various design insights, and the benefits of the proposed strategy are also illustrated in contrast to the other baseline approaches.

Ambient backscatter communication (AmBC) technology can potentially offer spectral- and energy-efficient solutions for future wireless systems. This paper proposes a novel design to facilitate the spectrum sharing between a secondary system and a primary system based on the AmBC technique in intelligent reflective surface (IRS)-assisted unmanned aerial vehicle (UAV) networks. In particular, an IRS-aided UAV cooperatively relays the transmission from a terrestrial primary source node to a user equipment on the ground. On the other hand, leveraging on the AmBC technology, a terrestrial secondary node transmits its information to a terrestrial secondary receiver by modulating and backscattering the ambient relayed radio frequency (RF) signals from the UAV-IRS. The performance of such a system setup is analyzed by deriving the expressions of outage probability and ergodic spectral efficiency. Finally, we present the numerical results to provide useful insights into the system design and also validate the derived theoretical results using Monte Carlo simulations.

The evolution of 5G wireless networks poses significant research challenges such as securing the user data, maintaining certain latency and reliability requirements etc. However, it can be challenging to simultaneously meet these performance requisites, which may lead to resort to a trade-off among different metrics. This paper investigates the secrecy-reliability performance trade-off (SRPT) for non-orthogonal multiple access (NOMA)-based millimeter wave (mmWave) networks. Herein, we consider two end-users, namely primary and secondary, which are served by an mmWave base station using downlink NOMA. Besides, a passive eavesdropper lying in the vicinity of these end-users attempts to intercept their legitimate message signals. For this set-up, we derive the closed-form expressions of the outage probability (OP) of a targeted end-user and intercept probability (IP) of the eavesdropper to analyze the SRPT of the system. We further propose a low-complexity average channel state information (CSI)-based power allocation strategy to improve the reliability of a targeted user while maintaining its information secrecy. Moreover, we obtain the condition under which NOMA guarantees superior secrecy performance than that of orthogonal multiple access (OMA) scheme. We corroborate our theoretical analysis via simulation results presented in terms of IP and OP.

Terahertz (THz) communication is a promising technique for chip-to-chip communication and wireless personal area networks. In this paper, we present an experimental study and design to realize such THz communication systems. We develop two different chip sets for on-off-keying (OOK) modulation based THz transceivers which include carrier generators, modulators, THz amplifiers, and baseband amplifiers. Specifically, the first chip set integrates the circuit blocks for the OOK modulation without the THz amplifier for short-range communication. In addition, the second chip set design includes the THz amplifier modules to extend the coverage of transmission. For these two chip sets, we experimentally demonstrate the feasibility of the wireless communication at THz frequency bands and assess performance using the bit error rate (BER) analysis. We estimate the BER by calculating the signal-to-noise ratio (SNR) based on the eye diagram and compare with actual BER measurements and Monte Carlo simulations. We also address the impact of the distance, the transmit power, and the data rate for the proposed THz transceivers based on the link budget analysis, and confirm the accuracy of the derived BER expression.

In this paper, we consider an overlay cognitive satellite-terrestrial relay network comprising a primary satellite source-receiver pair and a secondary transmitter-receiver pair on the ground while taking into account the practical relay transceiver hardware impairments. Herein, a primary satellite source communicates with its terrestrial user by utilizing both direct and relay links, using an amplify-and-forward based cooperative communication technique. Considering distortion noises in relay signal processing, we obtain new closed-form expressions for the outage probability of primary satellite network and secondary terrestrial network and explicitly derive the asymptotic outage behaviour for primary network by adopting pertinent heterogeneous fading models. Both primary and secondary networks satisfy their quality-of-service criteria for the low data rate requirements only. However, for the high data rate requirements, a ceiling effect is shown to occur which eventually makes the spectrum sharing infeasible.

In this paper, we analyze the performance of simultaneous wireless information and power transfer (SWIPT) in two-way relay systems with an active direct link under Nakagami-m fading environment. We consider a three-node based cooperative relaying system consisting of two source nodes and a battery-enabled relay node. Herein, one round of information exchange between source nodes can be accomplished in three time phases. Relay node relies on amplify-and-forward (AF) operation to broadcast the signals, while the destination nodes utilize maximal-ratio combining (MRC) technique to make use of both the direct and relay links. Moreover, the relay node harvests energy from the radio-frequency (RF) signals in the first two phases using power-splitting (PS) approach and then utilizes the harvested energy for information processing and broadcasting the received signals in the third phase. For the considered setup, we proficiently derive accurate expressions for the outage probability (OP), system throughput, and energy efficiency. Numerical results enlighten the importance of considering direct link with MRC in the SWIPT-enabled two-way relay systems.

In this paper, we investigate the performance of a spectrum sharing decode-and-forward multiple-relay network (SSDMN) with direct link under the joint impact of two practical and detrimental imperfections, called transceiver hardware impairments (HIs) and channel estimation errors (CEEs). Here, we consider the hardware distortions induced by all the non-ideal secondary nodes and residual interferences originating from imperfect channel estimations. By taking these imperfections into account, we derive an exact closed-form expression for the outage probability of the considered SSDMN employing selection cooperation over independent and non-identical Rayleigh fading channels. We identify three important ceiling effects invoked by HIs, namely relay cooperation ceiling (RCC), direct link ceiling (DLC), and overall system ceiling. Specifically, we highlight the impact of these prevailing effects on the system's performance and provide some useful insights about the tolerable level of HIs while designing the practical systems for a given rate requirement. We also illustrate that a potential direct link and a relaying link can, respectively, partially compensate for the incurred performance losses due to RCC and DLC effects. Moreover, we investigate the asymptotic behavior of outage probability to highlight the impact of HIs and CEEs on the achievable diversity and coding gains.

In this paper, we analyze the performance of a cognitive amplify-and-forward multi-relay network (CAFMRN) with direct link under the joint impact of transceiver hardware impairments (HIs) and channel estimation errors (CEEs). Herein, we consider hardware distortions induced by all the non-ideal secondary nodes and residual interferences originating from imperfect channel estimations. Taking these imperfections into account, we derive a new closed-form expression for the outage probability of the considered CAFMRN employing selection cooperation over independent and non-identical Rayleigh fading channels. Furthermore, we derive an asymptotic outage behavior to assess achievable diversity order. We illustrate that HIs may invoke ceiling effects into the system, namely relay cooperation ceiling (RCC) and overall system ceiling (OSC). Specifically, we showcase that the RCC ceases the full cooperation, whereas, the OSC may further aggravate the system outage performance under a high-rate requirement. By modeling the CEEs as decreasing function of signal-to-noise-ratio, we demonstrate that CEEs pose critical impact on the coding gain only and not on the diversity gain of the system. Finally, numerical and simulation results are presented to validate our theoretical findings.

In this paper, we investigate the secrecy performance of an underlay cognitive decode-and- forward relay network (CDRN) by exploiting an active direct link in the presence of primary user's (PU's) interference. Herein, a secondary user (SU) transmitter strives to maintain a secure communication link with a legitimate SU receiver in presence of a passive eavesdropper. On account of system's viability, we consider the presence of a PU transmitter as well as a PU receiver, wherein the secondary transmissions satisfy the fading- averaged interference constraints at the PU receiver. Specifically, we focus on utilizing the interference from primary transmission as a jamming signal for ameliorating the secrecy performance of secondary network. We derive closed-form expressions of secrecy outage probability for the secondary network with and without PU's interference. Numerical and simulation results validate our analysis and reveal the secrecy performance improvement of considered CDRN.

This study investigates the performance of a cognitive relay sharing system (CRSS) wherein two primary users (PUs) exchange the information bidirectionally. The overall transmission in CRSS takes place using an amplify‐and‐forward‐based multiple access broadcast protocol. Herein, besides assisting the transmission of secondary users, the relay also provides an aid for the bidirectional communication between PUs. In addition, the secondary system employs an opportunistic user scheduling with multiple destinations to further ameliorate the performance of secondary network. Here, by considering Nakagami‐ m fading channels, the authors derive novel closed‐form expressions of outage probability (OP) and average error probability for both primary and secondary systems. Based on the derived expressions of OP, the authors also quantify the average system throughput. With bidirectional primary communications, the proposed CRSS offers higher spectral efficiency and incentivises the secondary communication through multiuser diversity. Finally, numerical and simulation results are provided for the validation of the theoretical analysis.

In this paper, we investigate the outage performance of a decode-and-forward (DF) underlay cognitive two-way relay system with direct link using time division broadcast protocol in the presence of primary user's interference. Herein, relying on the practicability and low-complexity of statistical channel state information (CSI), the secondary transmissions satisfy the fading-averaged interference constraints at the primary receiver. We study an efficient link utilization scheme that can exploit both direct and relay links with appropriate combining methods to improve the performance of secondary users. Considering Nakagami-m fading channels, we derive a tight closed-form expression of outage probability for the secondary communications. We further perform the asymptotic high signal-to-interference noise ratio (SINR) analysis to gain more insight. We quantify the implications of primary user's interference on the secondary system performance and present several useful insights. With the proposed scheme, secondary system is shown to harness full diversity as long as the primary interference remains limited otherwise outage floor phenomenon occurs. Numerical and simulation results corroborate our theoretical developments.