27 research outputs found
Cognitive Orthogonal Precoder for Two-tiered Networks Deployment
In this work, the problem of cross-tier interference in a two-tiered
(macro-cell and cognitive small-cells) network, under the complete spectrum
sharing paradigm, is studied. A new orthogonal precoder transmit scheme for the
small base stations, called multi-user Vandermonde-subspace frequency division
multiplexing (MU-VFDM), is proposed. MU-VFDM allows several cognitive small
base stations to coexist with legacy macro-cell receivers, by nulling the
small- to macro-cell cross-tier interference, without any cooperation between
the two tiers. This cleverly designed cascaded precoder structure, not only
cancels the cross-tier interference, but avoids the co-tier interference for
the small-cell network. The achievable sum-rate of the small-cell network,
satisfying the interference cancelation requirements, is evaluated for perfect
and imperfect channel state information at the transmitter. Simulation results
for the cascaded MU-VFDM precoder show a comparable performance to that of
state-of-the-art dirty paper coding technique, for the case of a dense cellular
layout. Finally, a comparison between MU-VFDM and a standard complete spectrum
separation strategy is proposed. Promising gains in terms of achievable
sum-rate are shown for the two-tiered network w.r.t. the traditional bandwidth
management approach.Comment: 11 pages, 9 figures, accepted and to appear in IEEE Journal on
Selected Areas in Communications: Cognitive Radio Series, 2013. Copyright
transferred to IEE
A Distributed Approach to Interference Alignment in OFDM-based Two-tiered Networks
In this contribution, we consider a two-tiered network and focus on the
coexistence between the two tiers at physical layer. We target our efforts on a
long term evolution advanced (LTE-A) orthogonal frequency division multiple
access (OFDMA) macro-cell sharing the spectrum with a randomly deployed second
tier of small-cells. In such networks, high levels of co-channel interference
between the macro and small base stations (MBS/SBS) may largely limit the
potential spectral efficiency gains provided by the frequency reuse 1. To
address this issue, we propose a novel cognitive interference alignment based
scheme to protect the macro-cell from the cross-tier interference, while
mitigating the co-tier interference in the second tier. Remarkably, only local
channel state information (CSI) and autonomous operations are required in the
second tier, resulting in a completely self-organizing approach for the SBSs.
The optimal precoder that maximizes the spectral efficiency of the link between
each SBS and its served user equipment is found by means of a distributed
one-shot strategy. Numerical findings reveal non-negligible spectral efficiency
enhancements with respect to traditional time division multiple access
approaches at any signal to noise (SNR) regime. Additionally, the proposed
technique exhibits significant robustness to channel estimation errors,
achieving remarkable results for the imperfect CSI case and yielding consistent
performance enhancements to the network.Comment: 15 pages, 10 figures, accepted and to appear in IEEE Transactions on
Vehicular Technology Special Section: Self-Organizing Radio Networks, 2013.
Authors' final version. Copyright transferred to IEE
Vandermonde-subspace Frequency Division Multiplexing for Two-Tiered Cognitive Radio Networks
Vandermonde-subspace frequency division multiplexing (VFDM) is an overlay
spectrum sharing technique for cognitive radio. VFDM makes use of a precoder
based on a Vandermonde structure to transmit information over a secondary
system, while keeping an orthogonal frequency division multiplexing
(OFDM)-based primary system interference-free. To do so, VFDM exploits
frequency selectivity and the use of cyclic prefixes by the primary system.
Herein, a global view of VFDM is presented, including also practical aspects
such as linear receivers and the impact of channel estimation. We show that
VFDM provides a spectral efficiency increase of up to 1 bps/Hz over cognitive
radio systems based on unused band detection. We also present some key design
parameters for its future implementation and a feasible channel estimation
protocol. Finally we show that, even when some of the theoretical assumptions
are relaxed, VFDM provides non-negligible rates while protecting the primary
system.Comment: 9 pages, accepted for publication in IEEE Transactions on
Communication
Physical-Layer Transmission Cooperative Strategies for Heterogeneous Networks
The deployment of small cells within the boundaries of a macro-cell is considered to be an effective solution to cope with the current trend of higher data rates and improved system capacity. In the current heterogeneous configuration with the mass deployment of small cells, it is preferred that these two cell types coexist over the same spectrum, because acquiring additional spectrum licenses for small cells is difficult and expensive. However, the coexistence leads to cross-tier/inter-system interference. In this context, this contribution investigates interference alignment (IA) methods in order to mitigate the interference of macro-cell base station towards the small cell user terminals. More specifically, we design a diversity-oriented interference alignment scheme with space-frequency block codes (SFBC). The main motivation for joint interference alignment with SFBC is to allow the coexistence of two systems under minor inter-system information exchange. The small cells just need to know what space-frequency block code is used by the macro-cell system and no inter-system channels need to be exchanged, contrarily to other schemes recently proposed. Numerical results show that the proposed method achieves a performance close to the case where full-cooperation between the tiers is allowed
Joint IA and SFBC Macrocells and Small-Cells Coexistence under Minor Information Exchange
Thedeployment of small-cells within the boundaries of a macrocell is considered to be an effective solution to cope with the current
trend of higher data rates and improved system capacity. In the current heterogeneous configuration with the mass deployment of
small-cells, it is preferred that these two cell types will coexist over the same spectrum, because acquiring additional spectrum
licenses for small-cells is difficult and expensive. However, the coexistence leads to cross-tier/intersystem interference. In this
context, this contribution investigates interference alignment (IA) methods in order to mitigate the interference of macrocell base
station towards the small-cell user terminals.More specifically, we design a diversity-oriented interference alignment scheme with
space-frequency block codes (SFBCs).The main motivation for joint interference alignment with SFBC is to allow the coexistence
of two systems under minor intersysteminformation exchange.The small-cells just need to know what space-frequency block code
is used by the macrocell system and no intersystem channels need to be exchanged, contrarily to other schemes recently proposed.
Numerical results show that the proposed method achieves a performance close to the case where full cooperation between the
tiers is allowed
Implementação e avaliação no system generator de um sistema cooperativo para os futuros sistemas 5G
With the arrival of 5G it is expected the proliferation of services in the
different fields such as healthcare, utility applications, industrial automation,
4K streaming, that the former networks can not provide. Additionally,
the total number of wireless communication devices will escalate in such
a manner that the already scarce available frequency bandwidth won’t be
enough to pack the intended objectives. Cisco’s Annual Internet Report from
2018 predicts that by 2023 there will be nearly 30 billion devices capable of
wireless communication. Due to the exponential expiation of both services
and devices, the challenges upon both network data capacity and efficient
radio resourse use will be greater than ever, thus the urgency for solutions
is grand.
Both the capacity for wireless communications and spectral efficiency are
related to cell size and its users proximity to the access point. Thus,
shortening the distance between the transmitter and the receiver improves
both aspects of the network. This concept is what motivates the
implementation of heterogeneous networks, HetNets, that are composed
of many different small-cells, SCs, overlaid across the same coexisting
area of a conventional macro-cell, shortening the distance between the
cell users and its access point transceivers, granting a better coverage and
higher data rates. However, the HetNets potential does not come without
any challenges, as these networks suffer considerably from communication
interference between cells.
Although some interference management algorithms that allow coexistence
between cells have been proposed in recent years, most of them were
evaluated by software simulations and not implemented in real-time
platforms. Therefore, this master thesis aims to give the first step on the
implementation and evaluation of an interference mitigation technique in
hardware. Specifically, it is assumed a downlink scenario composed by a
macro-cell base station, a macro-cell primary user and a small cell user,
with the aim of implementing an algorithm that eliminates the downlink
interference that the base station may cause to the secondary users. The
study was carried out using the System Generator DSP tool, which is a tool
that generates code for hardware from schematics created in it. This tool
also offers a wide range of blocks that help the creation, and fundamentally,
the simulation and study of the system to be implemented, before being
translated into hardware. The results obtained in this work are a faithful
representation of the behavior of the implemented system, which can be
used for a future application for FPGA.Com a chegada do 5G, espera-se a proliferação de serviços nas mais diversas
áreas tal como assistência médica, automação industrial, transmissão em
4k, que não eram possíveis nas redes das gerações anteriores. Além deste
fenómeno, o número total de dispositivos capazes de conexões wireless
aumentará de tal maneira que a escassa largura de banda disponível não
será suficiente para abranger os objetivos pretendidos. O Relatório Anual
de 2018 sobre a Internet da Cisco prevê que até 2023 haverá quase 30
bilhões de dispositivos capazes de comunicação sem fio. Devido ao aumento
exponencial de serviços e dispositivos, os desafios sobre a capacidade de
dados da rede e o udo eficiente dos recursos de rádio serão maiores que
nunca. Por estes motivos, a necessidade de soluções para estas lacunas é
enorme.
Tanto a capacidade da rede e o uso eficiente do espectro de frequências
estão relacionados ao tamanho da célula e à proximidade dos usuários com
o ponto de acesso da célula. Ao encurtar a distância entre o transmissor e
o recetor ocorre um melhoramento destes dois aspetos da rede. Este é o
principal conceito na implementação de redes heterogéneas, HetNets, que
são compostas por diversas células pequenas que coexistem na área de uma
macro célula convencional, diminuído a distância entre os utilizadores da
célula e os pontos de acesso, garantindo uma melhor cobertura e taxa de
dados mais elevadas. No entanto, o potencial das HatNets não vem sem
nenhum custo, pois estas redes sofrem consideravelmente de interferência
entre as células.
Embora nos últimos anos foram propostos alguns algoritmos que permitem
a coexistência das células, a maioria destes foi só testado em simulações
de software e não em plataformas em tempo real. Por esse motivo, esta
dissertação de mestrado visa dar o primeiro passo na implementação e
a avaliação de uma técnica de mitigação de interferência em hardware.
Mais especificamente no cenário de downlink entre uma estação base de
uma macro célula, um utilizador primário da macro célula e um utilizador
secundário de uma célula pequena, com o principal objetivo de cancelar a
interferência que a estação base possa fazer ao utilizador secundário. O
estudo foi realizado utilizando a ferramenta System Generator DSP, que é
uma ferramenta que gera código para hardware a partir de esquemáticos
criados na mesma. Esta ferramenta também oferece uma vasta gama de
blocos que ajudam a criação, e fundamentalmente, a simulação e o estudo do
sistema a implementar antes de ser traduzido para hardware. Os resultados
obtidos neste trabalho são uma fiel representação do comportamento do
sistema implementado. O quais podem ser utilizados para uma futura
aplicação para FPGA.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
Spectrum- and Energy-Efficient Radio Resource Allocation for Wireless Communications
Wireless communications has been evolved significantly over the last decade. During this period, higher quality of service (QoS) requirements have been proposed to support various services. In addition, due to the increasing number of wireless devices and transmission, the energy consumption of the wireless networks becomes a burden. Therefore, the energy efficiency is considered as important as spectrum efficiency for future wireless communications networks, and spectrum and energy efficiency have become essential research topics in wireless communications. Moreover, due to the exploding of number mobile devices, the limited radio resources have become more and more scarce. With large numbers of users and various QoS requirements, a lot of wireless communications networks and techniques have emerged and how to effectively manage the limited radio resources become much more important.
In this dissertation, we focus our research on spectrum- and energy-efficient resource allocation schemes in wireless communication networks. Recently, heterogeneous networks (HetNets) have been proposed and studied to improve the spectrum efficiency. In a two-tier heterogeneous network, small base stations reuse the same spectrum with macro base stations in order to support more transmission over the limited frequency bands. We design a cascaded precoding scheme considering both interference cancellation and power allocation for the two-tier heterogeneous network. Besides heterogeneous networks, as the fast development of intelligent transportation, we study the spectrum- and energy-efficient resource allocation in vehicular communication networks. The intelligent transportation and vehicular communications both have drawn much attention and are faced special wireless environment, which includes Doppler effects and severe uncertainties in channel estimation. A novel designed spectrum efficiency scheme is studied and verified. With consideration of energy efficiency, the device-to-device (D2D) enabled wireless network is an effective network structure to increase the usage of spectrum. From a device\u27s perspective, we design an energy-efficient resource allocation scheme in D2D communication networks. To improve the energy efficiency of wireless communication networks, energy harvesting technique is a powerful way. Recently, the simultaneous wireless information and power transfer (SWIPT) has been proposed as a promising energy harvesting method for wireless communication networks, based on which we derive an energy-efficient resource allocation scheme for SWIPT cooperative networks, which considers both the power and relay allocation.
In addition to the schemes derivation for spectrum- and energy-efficient resource allocation, simulation results and the proofs of the proposed propositions are provided for the completeness of this dissertation
Técnicas de transmissão e recepção para sistemas MIMO heterogéneos na banda das ondas milimétricas
Mestrado em Engenharia Eletrónica e TelecomunicaçõesCom o crescimento dos dispositivos de comunicações móveis e de serviços de banda larga, os requisitos do sistema tornam-se cada vez mais exigentes. O LTE-Advanced apresenta um melhoramento progressivo relativamente ao seu antecessor LTE, introduzindo redes heterogéneas, que têm vindo provar constituir uma solução sólida para melhorar tanto a capacidade, como a cobertura da rede.
Quanto à implementação do 5G, será necessário um salto disruptivo na tecnologia, que permita novas possibilidades, tal como a de conectar pessoas e coisas. Para tornar isso possível, é necessário investigar e testar novas tecnologias. MIMO massivo e comunicações em ondas milimétricas são algumas das tecnologias que têm vindo a demonstrar resultados com potencial, tais como o aumento da capacidade e da eficiência espectral.
No entanto, devido às características da propagação de ondas milimétricas, a existência de cenários com redes heterogéneas ultradensas é uma possibilidade. Ao se considerar cenários ultradensos com um número massivo de utilizadores, o sistema fica limitado devido à interferência, mesmo operando na banda das ondas milimétricas. Como tal, é de extrema importância o desenvolvimento de técnicas que mitiguem essa interferência.
Nesta dissertação, propõe-se uma arquitetura de baixa complexidade para um transmissor e um recetor a operarem no sentido ascendente, numa rede heterogénea ultradensa. Nesta arquitetura são aplicadas tecnologias como MIMO massivo, ondas milimétricas e técnicas de beamforming, com o intuito de mitigar a interferência entre células. Usando a probabilidade de erro de bit como métrica de performance, os resultados mostram que a arquitetura proposta consegue remover a interferência eficientemente, alcançando resultados próximos de uma arquitetura completamente digital.With the constant increase of mobile communication devices and broadband services, the system requirements are getting more demanding. Long Term Evolution (LTE) Advanced comes as a progressive enhancement to its predecessor LTE, introducing heterogeneous networks (HetNets), which have proven to be great solutions to improve both capacity and coverage. As for 5G, it takes more of a disruptive step, enabling new possibilities, such as connecting people and things. To enable such a step, new technologies and techniques need to be researched and tested. Massive Multiple-Input Multiple-Output (MIMO) and millimeter wave (mmWave) communications are two of such technologies, as they show promising results such as increased capacity and spectral efficiency. However, due to the mmWave propagation constraints, the existence of ultra-dense HetNet scenarios may be a possibility. When considering ultra-dense scenarios with a massive number of users, the system becomes interference-limited, even using mmWave band. As such, the design of interference mitigation techniques that deal with both inter and intra-tier interference are of the utmost importance.
In this dissertation, a low complexity analog-digital hybrid architecture for both the transmitter and receiver in the uplink scenario is proposed. It is designed for an ultra-dense heterogeneous system and employing massive MIMO, mmWave and beamforming techniques in order to mitigate both intra- and inter-tier interference. Considering the Bit Error Rate (BER) as the performance metric, the results show that the proposed architecture efficiently removes both inter- and intra-tier interferences, achieving a result close to its fully digital counterpart
Transmission Cooperative Strategies for MIMO-OFDM Heterogeneous Networks
Mobile traffic in cellular networks is increasing
exponentially, mainly due to the use of data intensive services
like video. One way to cope with these demands is to
reduce the cell-size by deploying small-cells along the
coverage area of the current macro-cell system. The deployment
of small-cells significantly improves indoor coverage.
Nevertheless, as additional spectrum licenses are
difficult and expensive to acquire it is expected that the
macro and small-cells will coexist under the same spectrum.
The coexistence of the two systems results in crosstier/
inter-system interference. In this context, we design
several interference alignment based techniques for the
downlink of heterogeneous networks, in order to cancel the
interference generated from macro-cell at small-cell user
terminals. More specifically, in this contribution we design
interference alignment methods under different levels of
inter-system coordination and the constraint that the performance
of macro-cell system is kept close to the case
where small-cell system is switched-off. Numerical results
demonstrate that the proposed methods achieve close to
the optimal performance with low overhea
Recommended from our members
A composite approach to self-sustainable transmissions : rethinking OFDM
This paper proposes two novel strategies to extend the battery life of an orthogonal frequency division multiplexing (OFDM) receiver, by exploiting the concept of wireless power transfer (WPT). First a new receiver architecture is devised that does not discard the cyclic prefix (CP), but instead, exploits it to extract power from the received signal, realizing a WPT between the transmitter and the receiver. Subsequently, a flexible composite transmit strategy is designed, in which the OFDM transmitter transmits to the receiver two independent signals coexisting in the same band. It is shown that, by means of this approach, the transmitter can arbitrarily increase the power concentrated within the CP at the OFDM receiver, without increasing the redundancy of the transmission. The feasibility conditions for the self-sustainability of the transmission are derived, in terms of power consumption at the receiver, for both legacy and composite transmission. Numerical findings show that, under reasonable conditions, the amount of power carried in the CP could be made sufficient to decode the information symbols, making the transmission fully self-sustainable. The potential of the proposed approach is confirmed by the encouraging results obtained when the full self-sustainability constraint is relaxed, and partially self-sustainable OFDM transmissions are analyzed