11 research outputs found
Outage performance analysis of non-orthogonal multiple access systems with RF energy harvesting
Non-orthogonal multiple access (NOMA) has drawn enormous attention from the research community as a promising technology for future wireless communications with increasing demands of capacity and throughput. Especially, in the light of fifth-generation (5G) communication where multiple internet-of-things (IoT) devices are connected, the application of NOMA to indoor wireless networks has become more interesting to study. In view of this, we investigate the NOMA technique in energy harvesting (EH) half-duplex (HD) decode-and-forward (DF) power-splitting relaying (PSR) networks over indoor scenarios which are characterized by log-normal fading channels. The system performance of such networks is evaluated in terms of outage probability (OP) and total throughput for delay-limited transmission mode whose expressions are derived herein. In general, we can see in details how different system parameters affect such networks thanks to the results from Monte Carlo simulations. For illustrating the accuracy of our analytical results, we plot them along with the theoretical ones for comparison
UxNB-Enabled Cell-Free Massive MIMO with HAPS-Assisted Sub-THz Backhauling
In this paper, we propose a cell-free scheme for unmanned aerial vehicle
(UAV) base stations (BSs) to manage the severe intercell interference between
terrestrial users and UAV-BSs of neighboring cells. Since the cell-free scheme
requires enormous bandwidth for backhauling, we propose to use the
sub-terahertz (sub-THz) band for the backhaul links between UAV-BSs and central
processing unit (CPU). Also, because the sub-THz band requires a reliable
line-of-sight link, we propose to use a high altitude platform station (HAPS)
as a CPU. At the first time-slot of the proposed scheme, users send their
messages to UAVs at the sub-6 GHz band. The UAVs then apply match-filtering and
power allocation. At the second time-slot, at each UAV, orthogonal resource
blocks are allocated for each user at the sub-THz band, and the signals are
sent to the HAPS after analog beamforming. In the HAPS receiver, after analog
beamforming, the message of each user is decoded. We formulate an optimization
problem that maximizes the minimum signal-to-interference-plus-noise ratio of
users by finding the optimum allocated power as well as the optimum locations
of UAVs. Simulation results demonstrate the superiority of the proposed scheme
compared with aerial cellular and terrestrial cell-free baseline schemes.Comment: 32 pages, 13 figure
Transmission Scheme, Detection and Power Allocation for Uplink User Cooperation with NOMA and RSMA
In this paper, we propose two novel
cooperative-non-orthogonal-multiple-access (C-NOMA) and
cooperative-rate-splitting-multiple-access (C-RSMA) schemes for uplink user
cooperation. At the first mini-slot of these schemes, each user transmits its
signal and receives the transmitted signal of the other user in full-duplex
mode, and at the second mini-slot, each user relays the other user's message
with amplify-and-forward (AF) protocol. At both schemes, to achieve better
spectral efficiency, users transmit signals in the non-orthogonal mode in both
mini-slots. In C-RSMA, we also apply the rate-splitting method in which the
message of each user is divided into two streams. In the proposed detection
schemes for C-NOMA and C-RSMA, we apply a combination of
maximum-ratio-combining (MRC) and successive-interference-cancellation (SIC).
Then, we derive the achievable rates for C-NOMA and C-RSMA, and formulate two
optimization problems to maximize the minimum rate of two users by considering
the proportional fairness coefficient. We propose two power allocation
algorithms based on successive-convex-approximation (SCA) and
geometric-programming (GP) to solve these non-convex problems. Next, we derive
the asymptotic outage probability of the proposed C-NOMA and C-RSMA schemes,
and prove that they achieve diversity order of two. Finally, the
above-mentioned performance is confirmed by simulations.Comment: 32 pages, 13 figure
Performance analysis of Multi-Phase cooperative NOMA systems under passive eavesdropping
A key feature of the non-orthogonal multiple access (NOMA) technique is that users with better channel conditions have prior knowledge about the information of other weak users. Given this prior knowledge, the idea that a strong user can serve as a relay node for other weak users in order to improve their performance, is known as cooperative NOMA. In this paper, we study the physical layer security of such a cooperative NOMA system. In order to reduce the complexity of the analytical process, the considered system in this paper has three users, in which the performance of the weaker users are enhanced by the stronger users. Given that there is an eavesdropper in the system that can hear all the transmissions, we study the secrecy performance of all the users. More specifically, we make an attempt to derive the ergodic secrecy capacity (ESC) and secrecy outage probability (SOP) of all the users. Due to the intractable nature of the exact analysis for the weak users, we provide the closed form expressions of the ESC and SOP for these users at the high SNR regime, while providing the exact analysis for the strongest user. Targeting on the optimality, we further reveal that better secrecy performance of the system is achievable through an appropriate power control mechanism. Finally, based on the analytical methodology of the three-user cooperative system, we provide insightful observations on the performance (in terms of ESC and SOP) of a multi-phase cooperative NOMA system with N users at the high SNR regime. Through rigorous numerical simulations, we verify the correctness of our analytical derivations under different practical scenarios while providing evidence of achieving optimal secrecy performance with the proposed power control scheme.acceptedVersionPeer reviewe