This article investigates the performance of a wireless-powered reconfigurable intelligent surface (RIS)-assisted cognitive-radio (CR)-nonorthogonal multiple access (NOMA) network with hardware impairments (HIs). In the secondary network, the secondary source harvests its energy wirelessly from the multiantenna power beacon for its operation. The secondary source operates in underlay mode to communicate with the near user through a direct link, and the far user is served with the help of RIS, under the multiantenna primary user constraint. The performance of the considered system is analyzed using different assumptions of blocklengths, HIs, and successive interference cancellation (SIC). In other words, we have considered the infinite blocklength (IBL) and finite blocklength (FBL) transmission under the practical constraints of HI and imperfect SIC. We have derived the novel closed-form expression for the outage probability (OP) and system throughput for the IBL transmission. In contrast, for the FBL transmission, we have derived the closed-form expression for the average block error rate (ABLER), goodput, latency, and reliability. The asymptotic analysis for the OP and ABLER is also presented in two different power-setting scenarios: 1) when the transmit power of the power beacon goes to infinity and 2) when the maximum interference constraint of the primary network goes to infinity. Monte Carlo simulations are performed to verify the analytical results. Numerical results indicate the superior performance of the combination of RIS and NOMA in the considered system over RIS-assisted orthogonal multiple access (OMA) schemes. The impact of other parameters, such as the number of antennas at the power beacon, the number of antennas at the primary user, the number of RIS elements, time-splitting factor, HIs, blocklength, and imperfect SIC on the system performance, is also examined.

Unmanned aerial vehicles (UAVs) have emerged as a specular technology that can assist the terrestrial base stations. However, the battery limitation of UAV inhibits the system performance by decreasing the overall lifespan of coverage provided by the UAV, driving the necessity of replacement and recharging. Thus, the energy-depleted UAV must be returned to a charging station and be replaced by a fully charged UAV to increase the service span. Therefore, this paper presents a novel framework of UAV replacement to maintain coverage continuity in a UAV-assisted wireless communication system when a serving UAV runs out of energy. Our objective during this replacement process is to maximize the minimum achievable throughput to the UAV-served ground users by jointly optimizing the three-dimensional (3D) multi-UAV trajectory and resources allocated to the users from the individual UAVs. The formulated problem is non-convex for which an efficient algorithm based on successive convex approximation and alternating optimization is proposed. Numerical results provide insights into the UAV trajectories and the effectiveness of the proposed scheme compared to the existing benchmark schemes.

Abstract Coordinated Multi‐Point (CoMP) transmission in Cloud Radio Access Network (CRAN) requires a large amount of data transmission and processing within a coherence time window. Hence, CoMP transmission puts a lot of burden on the central processor and back‐haul unit. Also, establishing CoMP for high‐mobility users is challenging due to small coherence window and large beamforming overhead over mm‐Wave transmission. This paper proposes a two‐layer CRAN architecture with intelligent mm‐Wave and micro‐Wave allocation. A dual connectivity framework has been introduced to increase the coverage of high‐mobility users. Further, it is shown that the proposed scenario reduces the load on the central processor and central back‐haul. To avoid unnecessary handoffs, a mobility management algorithm is also proposed, which can provide seamless connectivity to the users irrespective of their velocity. Further, through simulation results, it is shown that the proposed network outperforms the existing CRAN framework.

In this study, bit error rate (BER) performance of multiple input multiple output (MIMO) systems employing transmit antenna selection with maximal ratio combining (TAS/MRC) and orthogonal space time block codes (OSTBC) is analysed and compared. Analysis has been done for several modulation schemes in equicorrelated Rayleigh fading channels. Novel infinite series expressions for BER of TAS/MRC are proposed in this work. The authors observe that the existing literature on performance analysis of TAS/MRC in correlated channels implicitly or explicitly assume no correlation on the transmitter side. In this work the authors overcome this shortcoming. An alternate closed‐form expression for BER performance of OSTBC MIMO systems is derived. This closed‐form expression is computationally efficient than existing expressions. Monte Carlo simulations were performed to validate the analytical results. It has been observed that TAS/MRC outperforms OSTBC in terms of BER performance in equicorrelated Rayleigh fading channel. As a case study, performance comparison of cognitive radio (CR) links employing OSTBC and TAS/MRC MIMO systems is investigated in order to show the usefulness of the present analytical study. Even though TAS is the optimum transmit antenna technique in terms of BER performance, OSTBC seems to be a promising alternative for more realistic scenarios in CR systems.