2,630 research outputs found
Energy Efficient Beamforming Design for MISO Non-Orthogonal Multiple Access Systems
When considering the future generation wireless networks, non-orthogonal
multiple access (NOMA) represents a viable multiple access technique for
improving the spectral efficiency. The basic performance of NOMA is often
enhanced using downlink beamforming and power allocation techniques. Although
downlink beamforming has been previously studied with different performance
criteria, such as sum-rate and max-min rate, it has not been studied in the
multiuser, multiple-input single-output (MISO) case, particularly with the
energy efficiency criteria. In this paper, we investigate the design of an
energy efficient beamforming technique for downlink transmission in the context
of a multiuser MISO-NOMA system. In particular, this beamforming design is
formulated as a global energy efficiency (GEE) maximization problem with
minimum user rate requirements and transmit power constraints. By using the
sequential convex approximation (SCA) technique and the Dinkelbach's algorithm
to handle the non-convex nature of the GEE-Max problem, we propose two novel
algorithms for solving the downlink beamforming problem for the MISO-NOMA
system. Our evaluation of the proposed algorithms shows that they offer similar
optimal designs and are effective in offering substantial energy efficiencies
compared to the designs based on conventional methods.Comment: Accepted at IEEE Transaction on Communicatio
Spectral-Energy Efficiency Trade-off-based Beamforming Design for MISO Non-Orthogonal Multiple Access Systems
Energy efficiency (EE) and spectral efficiency (SE) are two of the key
performance metrics in future wireless networks, covering both design and
operational requirements. For previous conventional resource allocation
techniques, these two performance metrics have been considered in isolation,
resulting in severe performance degradation in either of these metrics.
Motivated by this problem, in this paper, we propose a novel beamforming design
that jointly considers the trade-off between the two performance metrics in a
multiple-input single-output non-orthogonal multiple access system. In
particular, we formulate a joint SE-EE based design as a multi-objective
optimization (MOO) problem to achieve a good tradeoff between the two
performance metrics. However, this MOO problem is not mathematically tractable
and, thus, it is difficult to determine a feasible solution due to the
conflicting objectives, where both need to be simultaneously optimized. To
overcome this issue, we exploit a priori articulation scheme combined with the
weighted sum approach. Using this, we reformulate the original MOO problem as a
conventional single objective optimization (SOO) problem. In doing so, we
develop an iterative algorithm to solve this non-convex SOO problem using the
sequential convex approximation technique. Simulation results are provided to
demonstrate the advantages and effectiveness of the proposed approach over the
available beamforming designs.Comment: Accepted in IEEE TWC, June 202
Beamforming Techniques for Non-Orthogonal Multiple Access in 5G Cellular Networks
In this paper, we develop various beamforming techniques for downlink
transmission for multiple-input single-output (MISO) non-orthogonal multiple
access (NOMA) systems. First, a beamforming approach with perfect channel state
information (CSI) is investigated to provide the required quality of service
(QoS) for all users. Taylor series approximation and semidefinite relaxation
(SDR) techniques are employed to reformulate the original non-convex power
minimization problem to a tractable one. Further, a fairness-based beamforming
approach is proposed through a max-min formulation to maintain fairness between
users. Next, we consider a robust scheme by incorporating channel
uncertainties, where the transmit power is minimized while satisfying the
outage probability requirement at each user. Through exploiting the SDR
approach, the original non-convex problem is reformulated in a linear matrix
inequality (LMI) form to obtain the optimal solution. Numerical results
demonstrate that the robust scheme can achieve better performance compared to
the non-robust scheme in terms of the rate satisfaction ratio. Further,
simulation results confirm that NOMA consumes a little over half transmit power
needed by OMA for the same data rate requirements. Hence, NOMA has the
potential to significantly improve the system performance in terms of transmit
power consumption in future 5G networks and beyond.Comment: accepted to publish in IEEE Transactions on Vehicular Technolog
A High-Diversity Transceiver Design for MISO Broadcast Channels
In this paper, the outage behavior and diversity order of the mixture
transceiver architecture for multiple-input single-output broadcast channels
are analyzed. The mixture scheme groups users with closely-aligned channels and
applies superposition coding and successive interference cancellation decoding
to each group composed of users with closely-aligned channels, while applying
zero-forcing beamforming across semi-orthogonal user groups. In order to enable
such analysis, closed-form lower bounds on the achievable rates of a general
multiple-input single-output broadcast channel with superposition coding and
successive interference cancellation are newly derived. By employing
channel-adaptive user grouping and proper power allocation, which ensures that
the channel subspaces of user groups have angle larger than a certain
threshold, it is shown that the mixture transceiver architecture achieves full
diversity order in multiple-input single-output broadcast channels and
opportunistically increases the multiplexing gain while achieving full
diversity order. Furthermore, the achieved full diversity order is the same as
that of the single-user maximum ratio transmit beamforming. Hence, the mixture
scheme can provide reliable communication under channel fading for
ultra-reliable low latency communication. Numerical results validate our
analysis and show the outage superiority of the mixture scheme over
conventional transceiver designs for multiple-input single-output broadcast
channels.Comment: The inner region is evaluated. The single-group SIC performance is
evaluate
Energy-efficiency for MISO-OFDMA based user-relay assisted cellular networks
The concept of improving energy-efficiency (EE) without sacrificing the service quality has become important nowadays. The combination of orthogonal frequency-division multiple-access (OFDMA) multi-antenna transmission technology and relaying is one of the key technologies to deliver the promise of reliable and high-data-rate coverage in the most cost-effective manner. In this paper, EE is studied for the downlink multiple-input single-output (MISO)-OFDMA based user-relay assisted cellular networks. EE maximization is formulated for decode and forward (DF) relaying scheme with the consideration of both transmit and circuit power consumption as well as the data rate requirements for the mobile users. The quality of-service (QoS)-constrained EE maximization, which is defined for multi-carrier, multi-user, multi-relay and multi-antenna networks, is a non-convex and combinatorial problem so it is hard to tackle. To solve this difficult problem, a radio resource management (RRM) algorithm that solves the subcarrier allocation, mode selection and power allocation separately is proposed. The efficiency of the proposed algorithm is demonstrated by numerical results for different system parameter
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