Effective capacity analysis of NOMA with transceiver hardware and SIC imperfections

In this paper, we study the performance of the non-orthogonal multiple access (NOMA) networks. By considering two practical factors of residual hardware impairments (RHIs) and imperfect serial interference cancellation (ipSIC), we adopt effective capacity as a metric to characterize the effects of latency on the performance of NOMA networks and derive the analytical expressions of the effective capacity for the near user (NU) and the far user (FU). For further insights, we provide asymptotic analysis by invoking high signal-to-noise ratio (SNR) slope and high SNR power offset. Numerous analytical and simulated results have shown that: (1) The effective capacities of NU and FU are positively proportional to the SNR at low SNR, while at high SNR, the effective capacities approach to the constants; (2) Comparing the two users of the considered NOMA network, the effective capacity of NU shows pronounced advantages under the requirements of low quality of service. (3) RHIs are detrimental to the effective capacities of both NU and FU, especially for the high SNR regime. (4) The effective capacity of NU is limited by ipSIC.     

Physical layer secrecy analysis of HS-UAV NOMA network with spatially random eavesdroppers

This work investigates the physical layer secrecy performance of a hybrid satellite/unmanned aerial vehicle (HS-UAV) terrestrial non-orthogonal multiple access (NOMA) network, where one satellite source intends to make communication with destination users via a UAV relay using NOMA protocol in the existence of spatially random eavesdroppers. All the destination users randomly distributed on the ground comply with a homogeneous Poisson point process in the basis of stochastic geometry. Adopting Shadowed-Rician fading in satellite-to-UAV and satellite-to-eavesdroppers links while Rayleigh fading in both UAV-to-users and UAV-to-eavesdroppers links, the theoretical expressions for the secrecy outage probability (SOP) of the paired NOMA users are obtained based on the distance-determined path-loss. Also, the asymptotic behaviors of SOP expressions at high signal-to-noise ratio (SNR) regime are analyzed and the system throughputs of the paired NOMA users are examined for gaining further realization of the network. Moreover, numerical results are contrasted with simulation to validate the theoretical analysis. Investigation of this work shows the comparison of SOP performance for the far and near user, pointing out the SOP performance of the network depends on the channel fading, UAV coverage airspace, distribution of eavesdroppers and some other key parameters.     

Enhancing the physical layer security of artificial noise-aided half-duplex cooperative NOMA systems

The objective of this paper is to propose techniques for enhancing the physical layer security (PLS) performance of half-duplex cooperative non-orthogonal multiple access (HD-CNOMA) network in the presence of an external passive eavesdropper. We propose an artificial noise (AN)-aided framework and derive approximate analytical expressions for the secrecy outage probabilities (SOPs) of the downlink users. It is demonstrated that the proposed AN-aided framework significantly reduces the SOPs of the users and completely resolves the zero-diversity order problem, which is prevalent in HD-CNOMA network without AN. To further enhance the PLS performance, we determine optimal power allocation coefficients (OPACs) for the downlink users at the base station (BS) that minimizes the system SOP (SSOP) of the AN-aided HD-CNOMA network. With the help of extensive numerical and simulation investigations, it is shown that the proposed OPAC leads to significant reduction of the SSOP, while lowering the SOPs of the users, compared to random/equal setting of the PACs.     

Rate analysis of ZF receiver for uplink cell-free massive MIMO systems with D2D communications

This paper proposes a transmission structure of zero forcing (ZF) receiver for uplink cell-free massive multiple-input multiple-output (MIMO) systems with device-to-device (D2D) communications, followed by a rate analysis. We assumed that D2D users (DUEs) can utilize orthogonal radio resources to improve the efficiency of the scarce utilization or repurpose the time–frequency-spectrum resources currently used by the cell-free users (CFUEs). Assuming that the imperfect channel state information (CSI) is realizable, after that, the use-and-forget bounding technique is then used to respectively obtain the closed-form expressions of the CFUEs and DUEs, which provide the lower bounds on the ergodic approximate realizable rate of both communication links. First, we calculate the minimum-mean-square error (MMSE) estimation for all channels. Then, the derived results of the achievable uplink sum rate provide us with a tool that enables us to explain how some important parameters, such as the number of access points (APs)/CFUEs, each AP/CFUE/antenna, and the density of DUEs, affect system performance, highlighting the significance of cooperation between cell-free massive MIMO and D2D communication.     

A novel model and behavior analysis for a swarm of multi-agent systems with finite velocity

Inspired by the fact that in most existing swarm models of multi-agent systems the velocity of an agent can be infinite,which is not in accordance with the real applications, we propose a novel swarm model of multi-agent systems where the velocity of an agent is finite. The Lyapunov function method and LaSalle’s invariance principle are employed to show that by using the proposed model all of the agents eventually enter into a bounded region around the swarm center and finally tend to a stationary state. Numerical simulations are provided to demonstrate the effectiveness of the theoretical results.