7,603 research outputs found
Resource allocation for NOMA wireless systems
Power-domain non-orthogonal multiple access (NOMA) has been widely recognized as
a promising candidate for the next generation of wireless communication systems. By
applying superposition coding at the transmitter and successive interference cancellation
at the receiver, NOMA allows multiple users to access the same time-frequency resource
in power domain. This way, NOMA not only increases the system’s spectral and energy
efficiencies, but also supports more users when compared with the conventional orthogonal
multiple access (OMA). Meanwhile, improved user fairness can be achieved by NOMA.
Nonetheless, the promised advantages of NOMA cannot be realized without proper
resource allocation. The main resources in wireless communication systems include time,
frequency, space, code and power. In NOMA systems, multiple users are accommodated
in each time/frequency/code resource block (RB), forming a NOMA cluster. As a result,
how to group the users into NOMA clusters and allocate the power is of significance. A
large number of studies have been carried out for developing efficient power allocation
(PA) algorithms in single-input single-output (SISO) scenarios with fixed user clustering.
To fully reap the gain of NOMA, the design of joint PA and user clustering is required.
Moreover, the study of PA under multiple-input multiple-output (MIMO) systems still
remains at an incipient stage. In this dissertation, we develop novel algorithms to allocate
resource for both SISO-NOMA and MIMO-NOMA systems.
More specifically, Chapter 2 compares the system capacity of MIMO-NOMA with
MIMO-OMA. It is proved analytically that MIMO-NOMA outperforms MIMO-OMA in terms of both sum channel capacity and ergodic sum capacity when there are multiple
users in a cluster. Furthermore, it is demonstrated that the more users are admitted to
a cluster, the lower is the achieved sum rate, which illustrates the tradeoff between the
sum rate and maximum number of admitted users.
Chapter 3 addresses the PA problem for a general multi-cluster multi-user MIMONOMA
system to maximize the system energy efficiency (EE). First, a closed-form solution
is derived for the corresponding sum rate (SE) maximization problem. Then, the EE
maximization problem is solved by applying non-convex fractional programming.
Chapter 4 investigates the energy-efficient joint user-RB association and PA problem
for an uplink hybrid NOMA-OMA system. The considered problem requires to jointly
optimize the user clustering, channel assignment and power allocation. To address this
hard problem, a many-to-one bipartite graph is first constructed considering the users
and RBs as the two sets of nodes. Based on swap matching, a joint user-RB association
and power allocation scheme is proposed, which converges within a limited number of
iterations. Moreover, for the power allocation under a given user-RB association, a low complexity
optimal PA algorithm is proposed.
Furthermore, Chapter 5 focuses on securing the confidential information of massive
MIMO-NOMA networks by exploiting artificial noise (AN). An uplink training scheme is
first proposed, and on this basis, the base station precodes the confidential information
and injects the AN. Following this, the ergodic secrecy rate is derived for downlink transmission.
Additionally, PA algorithms are proposed to maximize the SE and EE of the
system.
Finally, conclusions are drawn and possible extensions to resource allocation in NOMA
systems are discussed in Chapter 6
Holographic thermalization with a chemical potential in Gauss-Bonnet gravity
Holographic thermalization is studied in the framework of
Einstein-Maxwell-Gauss-Bonnet gravity. We use the two-point correlation
function and expectation value of Wilson loop, which are dual to the
renormalized geodesic length and minimal area surface in the bulk, to probe the
thermalization. The numeric result shows that larger the Gauss-Bonnet
coefficient is, shorter the thermalization time is, and larger the charge is,
longer the thermalization time is, which implies that the Gauss-Bonnet
coefficient can accelerate the thermalization while the charge has an opposite
effect. In addition, we obtain the functions with respect to the thermalization
time for both the thermalization probes at a fixed charge and Gauss-Bonnet
coefficient, and on the basis of these functions, we obtain the thermalization
velocity, which shows that the thermalization process is non-monotonic. At the
middle and later periods of the thermalization process, we find that there is a
phase transition point, which divides the thermalization into an acceleration
phase and a deceleration phase. We also study the effect of the charge and
Gauss-Bonnet coefficient on the phase transition point.Comment: 23 pages, many figures,footnote 4 is modified. arXiv admin note:
substantial text overlap with arXiv:1305.484
Inflation Taxation and Welfare with Externalities and Leisure
This paper examines how inflation taxation a ects resource allocation and welfare in a neoclassical growth model with leisure, a production externality and money in the utility function. Switching from consumption taxation to inflation taxation to finance government spending reduces real money balances relative to income, but increases consumption, labor, capital and output. The net welfare effect of this switch depends crucially on the strength of the externality and on the elasticity of intertemporal substitution: While it is always negative without the externality, it is likely to be positive with a strong externality and elastic intertemporal substitution.
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