4,242 research outputs found
Impact of User Pairing on 5G Non-Orthogonal Multiple Access
Non-orthogonal multiple access (NOMA) represents a paradigm shift from
conventional orthogonal multiple access (MA) concepts, and has been recognized
as one of the key enabling technologies for 5G systems. In this paper, the
impact of user pairing on the performance of two NOMA systems, NOMA with fixed
power allocation (F-NOMA) and cognitive radio inspired NOMA (CR-NOMA), is
characterized. For FNOMA, both analytical and numerical results are provided to
demonstrate that F-NOMA can offer a larger sum rate than orthogonal MA, and the
performance gain of F-NOMA over conventional MA can be further enlarged by
selecting users whose channel conditions are more distinctive. For CR-NOMA, the
quality of service (QoS) for users with the poorer channel condition can be
guaranteed since the transmit power allocated to other users is constrained
following the concept of cognitive radio networks. Because of this constraint,
CR-NOMA has different behavior compared to F-NOMA. For example, for the user
with the best channel condition, CR-NOMA prefers to pair it with the user with
the second best channel condition, whereas the user with the worst channel
condition is preferred by F-NOMA
A General MIMO Framework for NOMA Downlink and Uplink Transmission Based on Signal Alignment
The application of multiple-input multiple-output (MIMO) techniques to
non-orthogonal multiple access (NOMA) systems is important to enhance the
performance gains of NOMA. In this paper, a novel MIMO-NOMA framework for
downlink and uplink transmission is proposed by applying the concept of signal
alignment. By using stochastic geometry, closed-form analytical results are
developed to facilitate the performance evaluation of the proposed framework
for randomly deployed users and interferers. The impact of different power
allocation strategies, such as fixed power allocation and cognitive radio
inspired power allocation, on the performance of MIMO-NOMA is also
investigated. Computer simulation results are provided to demonstrate the
performance of the proposed framework and the accuracy of the developed
analytical results
The Application of MIMO to Non-Orthogonal Multiple Access
This paper considers the application of multiple-input multiple-output (MIMO)
techniques to non-orthogonal multiple access (NOMA) systems. A new design of
precoding and detection matrices for MIMO-NOMA is proposed and its performance
is analyzed for the case with a fixed set of power allocation coefficients. To
further improve the performance gap between MIMO-NOMA and conventional
orthogonal multiple access schemes, user pairing is applied to NOMA and its
impact on the system performance is characterized. More sophisticated choices
of power allocation coefficients are also proposed to meet various quality of
service requirements. Finally computer simulation results are provided to
facilitate the performance evaluation of MIMO-NOMA and also demonstrate the
accuracy of the developed analytical results
A Two-Phase Power Allocation Scheme for CRNs Employing NOMA
In this paper, we consider the power allocation (PA) problem in cognitive
radio networks (CRNs) employing nonorthogonal multiple access (NOMA) technique.
Specifically, we aim to maximize the number of admitted secondary users (SUs)
and their throughput, without violating the interference tolerance threshold of
the primary users (PUs). This problem is divided into a two-phase PA process:
a) maximizing the number of admitted SUs; b) maximizing the minimum throughput
among the admitted SUs. To address the first phase, we apply a sequential and
iterative PA algorithm, which fully exploits the characteristics of the
NOMA-based system. Following this, the second phase is shown to be quasiconvex
and is optimally solved via the bisection method. Furthermore, we prove the
existence of a unique solution for the second phase and propose another PA
algorithm, which is also optimal and significantly reduces the complexity in
contrast with the bisection method. Simulation results verify the effectiveness
of the proposed two-phase PA scheme
Secrecy outage probability of a NOMA scheme and impact imperfect channel state information in underlay cooperative cognitive networks
Security performance and the impact of imperfect channel state information (CSI) in underlay cooperative cognitive networks (UCCN) is investigated in this paper. In the proposed scheme, relay R uses non-orthogonal multiple access (NOMA) technology to transfer messages e1, e2 from the source node S to User 1 (U-1) and User 2 (U-2), respectively. An eavesdropper (E) is also proposed to wiretap the messages of U-1 and U-2. The transmission's security performance in the proposed system was analyzed and performed over Rayleigh fading channels. Through numerical analysis, the results showed that the proposed system's secrecy performance became more efficient when the eavesdropper node E was farther away from the source node S and the intermediate cooperative relay R. The secrecy performance of U-1 was also compared to the secrecy performance of U-2. Finally, the simulation results matched the Monte Carlo simulations well.Web of Science203art. no. 89
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