379 research outputs found
Interference Alignment for Cognitive Radio Communications and Networks: A Survey
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Interference alignment (IA) is an innovative wireless transmission strategy that has shown to be a promising technique for achieving optimal capacity scaling of a multiuser interference channel at asymptotically high-signal-to-noise ratio (SNR). Transmitters exploit the availability of multiple signaling dimensions in order to align their mutual interference at the receivers. Most of the research has focused on developing algorithms for determining alignment solutions as well as proving interference alignment’s theoretical ability to achieve the maximum degrees of freedom in a wireless network. Cognitive radio, on the other hand, is a technique used to improve the utilization of the radio spectrum by opportunistically sensing and accessing unused licensed frequency spectrum, without causing harmful interference to the licensed users. With the increased deployment of wireless services, the possibility of detecting unused frequency spectrum becomes diminished. Thus, the concept of introducing interference alignment in cognitive radio has become a very attractive proposition. This paper provides a survey of the implementation of IA in cognitive radio under the main research paradigms, along with a summary and analysis of results under each system model.Peer reviewe
INTERFERENCE MANAGEMENT IN LTE SYSTEM AND BEYOUND
The key challenges to high throughput in cellular wireless communication system are interference, mobility and bandwidth limitation. Mobility has never been a problem until recently, bandwidth has been constantly improved upon through the evolutions in cellular wireless communication system but interference has been a constant limitation to any improvement that may have resulted from such evolution. The fundamental challenge to a system designer or a researcher is how to achieve high data rate in motion (high speed) in a cellular system that is intrinsically interference-limited.
Multi-antenna is the solution to data on the move and the capacity of multi-antenna system has been demonstrated to increase proportionally with increase in the number of antennas at both transmitter and receiver for point-to-point communications and multi-user environment. However, the capacity gain in both uplink and downlink is limited in a multi-user environment like cellular system by interference, the number of antennas at the base station, complexity and space constraint particularly for a mobile terminal.
This challenge in the downlink provided the motivation to investigate successive interference cancellation (SIC) as an interference management tool LTE system and beyond. The Simulation revealed that ordered successive interference (OSIC) out performs non-ordered successive interference cancellation (NSIC) and the additional complexity is justified based on the associated gain in BER performance of OSIC. The major drawback of OSIC is that it is not efficient in network environment employing power control or power allocation. Additional interference management techniques will be required to fully manage the interference.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format
Energy efficiency and interference management in long term evolution-advanced networks.
Doctoral Degree. University of KwaZulu-Natal, Durban.Cellular networks are continuously undergoing fast extraordinary evolution to overcome
technological challenges. The fourth generation (4G) or Long Term Evolution-Advanced
(LTE-Advanced) networks offer improvements in performance through increase in network density,
while allowing self-organisation and self-healing. The LTE-Advanced architecture is heterogeneous,
consisting of different radio access technologies (RATs), such as macrocell, smallcells, cooperative
relay nodes (RNs), having various capabilities, and coexisting in the same geographical coverage
area. These network improvements come with different challenges that affect users’ quality of
service (QoS) and network performance. These challenges include; interference management, high
energy consumption and poor coverage of marginal users. Hence, developing mitigation schemes for
these identified challenges is the focus of this thesis.
The exponential growth of mobile broadband data usage and poor networks’ performance along
the cell edges, result in a large increase of the energy consumption for both base stations (BSs) and
users. This due to improper RN placement or deployment that creates severe inter-cell and intracell
interferences in the networks. It is therefore, necessary to investigate appropriate RN placement
techniques which offer efficient coverage extension while reducing energy consumption and mitigating
interference in LTE-Advanced femtocell networks. This work proposes energy efficient and optimal
RN placement (EEORNP) algorithm based on greedy algorithm to assure improved and effective
coverage extension. The performance of the proposed algorithm is investigated in terms of coverage
percentage and number of RN needed to cover marginalised users and found to outperform other RN
placement schemes.
Transceiver design has gained importance as one of the effective tools of interference
management. Centralised transceiver design techniques have been used to improve network
performance for LTE-Advanced networks in terms of mean square error (MSE), bit error rate (BER)
and sum-rate. The centralised transceiver design techniques are not effective and computationally
feasible for distributed cooperative heterogeneous networks, the systems considered in this thesis.
This work proposes decentralised transceivers design based on the least-square (LS) and minimum MSE (MMSE) pilot-aided channel estimations for interference management in uplink
LTE-Advanced femtocell networks. The decentralised transceiver algorithms are designed for the
femtocells, the macrocell user equipments (MUEs), RNs and the cell edge macrocell UEs (CUEs) in
the half-duplex cooperative relaying systems. The BER performances of the proposed algorithms
with the effect of channel estimation are investigated.
Finally, the EE optimisation is investigated in half-duplex multi-user multiple-input
multiple-output (MU-MIMO) relay systems. The EE optimisation is divided into sub-optimal EE
problems due to the distributed architecture of the MU-MIMO relay systems. The decentralised
approach is employed to design the transceivers such as MUEs, CUEs, RN and femtocells for the
different sub-optimal EE problems. The EE objective functions are formulated as convex
optimisation problems subject to the QoS and transmit powers constraints in case of perfect channel
state information (CSI). The non-convexity of the formulated EE optimisation problems is
surmounted by introducing the EE parameter substractive function into each proposed algorithms.
These EE parameters are updated using the Dinkelbach’s algorithm. The EE optimisation of the
proposed algorithms is achieved after finding the optimal transceivers where the unknown
interference terms in the transmit signals are designed with the zero-forcing (ZF) assumption and
estimation errors are added to improve the EE performances. With the aid of simulation results, the
performance of the proposed decentralised schemes are derived in terms of average EE evaluation
and found to be better than existing algorithms
Achieving Large Multiplexing Gain in Distributed Antenna Systems via Cooperation with pCell Technology
In this paper we present pCellTM technology, the first commercial-grade
wireless system that employs cooperation between distributed transceiver
stations to create concurrent data links to multiple users in the same
spectrum. First we analyze the per-user signal-to-interference-plus-noise ratio
(SINR) employing a geometrical spatial channel model to define volumes in space
of coherent signal around user antennas (or personal cells, i.e., pCells). Then
we describe the system architecture consisting of a general-purpose-processor
(GPP) based software-defined radio (SDR) wireless platform implementing a
real-time LTE protocol stack to communicate with off-the-shelf LTE devices.
Finally we present experimental results demonstrating up to 16 concurrent
spatial channels for an aggregate average spectral efficiency of 59.3 bps/Hz in
the downlink and 27.5 bps/Hz in the uplink, providing data rates of 200 Mbps
downlink and 25 Mbps uplink in 5 MHz of TDD spectrum.Comment: IEEE Asilomar Conference on Signals, Systems, and Computers, Nov.
8-11th 2015, Pacific Grove, CA, US
Approaching universal frequency reuse through base station cooperation
Base Station (BS) architectures are a promising cellular wireless solution to mitigate
the interference issues and to avoid the high frequency reuse factors implemented
in conventional systems. Combined with block transmission techniques, such as Orthogonal
Frequency-Division Multiplexing (OFDM) for the downlink and Single-Carrier with
Frequency-Domain Equalization (SC-FDE) for the uplink, these systems provide a significant
performance improvement to the overall system. Block transmission techniques are
suitable for broadband wireless communication systems, which have to deal with strongly
frequency-selective fading channels and are able to provide high bit rates despite the channel
adversities. In BS cooperation schemes users in adjacent cells share the same physical
channel and the signals received by each BS are sent to a Central Processing Unit (CPU)
that combines the different signals and performs the user detections and/or separation,
which can be regarded as a Multi-User Detection (MUD) technique. The work presented
in this thesis is focused on the study of uplink transmissions in BS cooperations systems,
considering single carrier block transmission schemes and iterative receivers based on the
Iterative-Block Decision Feedback Equalization (IB-DFE) concept, which combined with
the employment of Cyclic Prefix (CP)-assisted block transmission techniques are appropriate
to scenarios with strongly time-dispersive channels. Furthermore, the impact of the
sampling and quantization applied to the received signals from each Mobile Terminal (MT)
to the corresponding BS is studied, with the achievement of the spectral characterization
of the quantization noise. This thesis also provides a conventional analytical model for the
BER (Bit Error Rate) performance complemented with an approach to improve its results.
Finally, this thesis addresses the contextualization of BS cooperation schemes in clustered
C-RAN (Centralized-Radio Access Network)-type solutions.As arquitecturas BS cooperation são uma solução promissora de redes celulares sem
fios para atenuar o problema da interferência e evitar os factores de reuso elevados, que
se encontram implementados nos sistemas convencionais. Combinadas com técnicas de
transmissão por blocos, como o OFDM para o downlink e o SC-FDE no uplink, estes
sistemas fornecem uma melhoria significativa no desempenho geral do sistema. Técnicas
de transmissão por blocos são adequadas para sistemas de comunicações de banda larga
sem fios, que têm que lidar com canais que possuem um forte desvanescimento selectivo
na frequência e são capazes de fornecer ligações com taxas de transmissão altas apesar
das adversidades do canal. Em esquemas BS cooperation os terminais móveis situados em
células adjacentes partilham o mesmo canal físico e os sinais recebidos em cada estação
de base são enviados para uma Unidade Central de Processamento (CPU) que combina
os diferentes sinais recebidos associados a um dado utilizador e realiza a detecção e/ou
separação do mesmo, sendo esta considerada uma técnica de Detecção Multi-Utilizador
(MUD). O trabalho apresentado nesta tese concentra o seu estudo no uplink de transmissões
em sistemas BS cooperation, considerando transmissões em bloco de esquemas monoportadoras
e receptores iterativos baseados no conceito B-DFE, em que quando combinados
com a implementação de técnicas de transmissao por blocos assistidas por prefixos cíclicos
(CP) são apropriados a cenários com canais fortemente dispersivos no tempo. Além disso, é
estudado o impacto do processo de amostragem e quantização aplicados aos sinais recebidos
de cada terminal móvel para a estação de base, com a obtenção da caracterização espectral
do ruído de quantização. Esta tese também fornece um modelo analítico convencional para
a computação do desempenho da taxa de erros de bit (BER), com um método melhorado
para o mesmo. Por último, esta tese visa a contextualização dos sistemas BS cooperation
em soluções do tipo C-RAN
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