8 research outputs found
Advanced interference management techniques for future generation cellular networks
The demand for mobile wireless network resources is constantly on the rise, pushing
for new communication technologies that are able to support unprecedented
rates. In this thesis we address the issue by considering advanced interference
management techniques to exploit the available resources more efficiently under
relaxed channel state information (CSI) assumptions. While the initial studies
focus on current half-duplex (HD) technology, we then move on to full-duplex
(FD) communication due to its inherent potential to improve spectral efficiency.
Work in this thesis is divided into four main parts as follows.
In the first part, we focus on the two-cell two-user-per-cell interference broadcast
channel (IBC) and consider the use of topological interference management
(TIM) to manage inter-cell interference in an alternating connectivity scenario.
Within this context we derive novel outer bounds on the achievable degrees of freedom
(DoF) for different system configurations, namely, single-input single-output
(SISO), multiple-input single-output (MISO) and multiple-input multiple-output
(MIMO) systems. Additionally, we propose new transmission schemes based on
joint coding across states that exploit global topological information at the transmitter
to increase achievable DoF. Results show that when a single state has a
probability of occurrence equal to one, the derived bounds are tight with up to
a twofold increase in achievable DoF for the best case scenario. Additionally,
when all alternating connectivity states are equiprobable: the SISO system gains
11/16 DoF, achieving 96:4% of the derived outer bound; while the MISO/MIMO
scenario has a gain of 1/2 DoF, achieving the outer bound itself.
In the second part, we consider a general G-cell K-user-per-cell MIMO IBC
and analyse the performance of linear interference alignment (IA) under imperfect
CSI. Having imperfect channel knowledge impacts the effectiveness of the IA
beamformers, and leads to a significant amount of residual leakage interference.
Understanding the extent of this impact is a fundamental step towards obtaining
a performance characterisation that is more relevant to practical scenarios. The
CSI error model used is highly versatile, allowing the error to be treated either
as a function of the signal-to-noise ratio (SNR) or as independent of it. Based
on this error model, we derive a novel upper bound on the asymptotic mean
sum rate loss and quantify the DoF loss due to imperfect CSI. Furthermore,
we propose a new version of the maximum signal-to-interference plus noise ratio
(Max-SINR) algorithm which takes into account statistical knowledge of the CSI
error in order to improve performance over the naive counterpart in the presence
of CSI mismatch.
In the third part, we shift our attention to FD systems and consider weighted
sum rate (WSR) maximisation for multi-user multi-cell networks where FD base-stations
(BSs) communicate with HD downlink (DL) and uplink (UL) users. Since
WSR problems are non-convex we transform them into weighted minimum mean
squared error (WMMSE) ones that are proven to converge. Our analysis is first
carried out for perfect CSI and then expanded to cater for imperfect CSI under
two types of error models, namely, a norm-bounded error model and a stochastic
error model. Additionally, we propose an algorithm that maximises the total DL
rate subject to each UL user achieving a desired target rate. Results show that
the use of FD BSs provides significant gains in achievable rate over the use of HD
BSs, with a gain of 1:92 for the best case scenario under perfect CSI. They also
demonstrate the robust performance of the imperfect CSI designs, and confirm
that FD outperforms HD even under CSI mismatch conditions.
Finally, the fourth part considers the use of linear IA to manage interference
in a multi-user multi-cell network with FD BSs and HD users under imperfect
CSI. The number of interference links present in such a system is considerably
greater than that present in the HD network counterpart; thus, understanding
the impact of residual leakage interference on performance is even more important
for FD enabled networks. Using the same generalised CSI error model from the
second part, we study the performance of IA by characterising the sum rate and
DoF losses incurred due to imperfect CSI. Additionally, we propose two novel IA
algorithms applicable to this network; the first one is based on minimising the
mean squared error (MMSE), while the second is based on Max-SINR. The proposed
algorithms exploit statistical knowledge of the CSI error variance in order
to improve performance. Moreover, they are shown to be equivalent under certain
conditions, even though the MMSE based one has lower computational complexity.
Furthermore for the multi-cell case, we also derive the proper condition for
IA feasibility
Competencia mediática: investigación sobre el grado de competencia de la ciudadanía en España
Producción CientíficaLa educación mediática no ha tenido un papel importante en los currículos escolares, en los planes de estudios universitarios, en los medios de comunicación y en la propia sociedad, a pesar de la fuerte presencia de la comunicación mediática en todos los ámbitos de nuestra vida personal y social. Este abandono de la educación mediática implica una ausencia de definiciones y de evaluaciones sobre el grado de competencia mediática de las personas. Un primer paso para la definición del concepto de competencia mediática se dio mediante el diseño del documento «Competencias en Comunicación Audiovisual», auspiciado por el CAC) y consensuado por un grupo de expertos españoles. El documento define los ámbitos de incidencia de esta competencia y las dimensiones que debe cumplir: el lenguaje, la tecnología, los procesos de producción y programación, la ideología y los valores, la recepción y las audiencias, y la dimensión estética.Departamento de Historia Moderna, Contemporánea y de América, Periodismo y Comunicación Audiovisual y Publicidad