38 research outputs found
Energy-efficient diversity combining for different access schemes in a multi-path dispersive channel
Dissertação para obtenção do Grau de Doutor em
Engenharia Electrotécnica e ComputadoresThe forthcoming generation of mobile communications, 5G, will settle a new standard for a larger bandwidth and better Quality of Service (QoS). With the exploding growth rate of user generated data, wireless
standards must cope with this growth and at the same time be energy efficient to avoid depleting the batteries of wireless devices. Besides these issues, in a broadband wireless setting QoS can be severely affected from a multipath dispersive channel and therefore be energy demanding.
Cross-layered architectures are a good choice to enhance the overall performance of a wireless system.
Examples of cross-layered Physical (PHY) - Medium Access Control (MAC) architectures are type-II Diversity Combining (DC) Hybrid-ARQ (H-ARQ) and Multi-user Detection (MUD) schemes. Cross-layered type-II DC H-ARQ schemes reuse failed packet transmissions to enhance data reception on posterior retransmissions; MUD schemes reuse data information from previously collided packets on posterior retransmissions to enhance data reception. For a multipath dispersive channel, a PHY layer analytical
model is proposed for Single-Carrier with Frequency Domain Equalization (SC-FDE) that supports DC H-ARQ and MUD. Based on this analytical model, three PHY-MAC protocols are proposed. A crosslayered Time Division Multiple Access (TDMA) scheme that uses DC H-ARQ is modeled and its performance is studied in this document; the performance analysis shows that the scheme performs better with DC and achieves a better energy efficiency at the cost of a higher delay. A novel cross-layered prefix-assisted Direct-Sequence Code Division Multiple Access (DS-CDMA) scheme is proposed and modeled in this document, it uses principles of DC and MUD. This protocol performs better by means
of additional retransmissions, achieving better energy efficiency, at the cost of higher redundancy from a code spreading gain. Finally, a novel cross-layered protocol H-ARQ Network Division Multiple Access (H-NDMA) is proposed and modeled, where the combination of DC H-ARQ and MUD is used with the intent of maximizing the system capacity with a lower delay; system results show that the proposed scheme achieves better energy efficiency and a better performance at the cost of a higher number of retransmissions.
A comparison of the three cross-layered protocols is made, using the PHY analytical model, under normalized conditions using the same amount of maximum redundancy. Results show that the H-NDMA protocol, in general, obtains the best results, achieving a good performance and a good energy efficiency
for a high channel load and low Signal-to-Noise Ratio (SNR). TDMA with DC H-ARQ achieves the best energy efficiency, although presenting the worst delay. Prefix-assisted DS-CDMA in the other hand shows good delay results but presents the worst throughput and energy efficiency
Time diversity solutions to cope with lost packets
A dissertation submitted to Departamento de Engenharia Electrotécnica of Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotécnica e de ComputadoresModern broadband wireless systems require high throughputs and can also have very high
Quality-of-Service (QoS) requirements, namely small error rates and short delays. A high spectral efficiency is needed to meet these requirements. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation.
An alternative to simple retransmission that can improve both power and spectral
efficiency is to combine the signals associated to different transmission attempts.
This thesis analyses two time diversity approaches to cope with lost packets that are
relatively similar at physical layer but handle different packet loss causes. The first is a lowcomplexity Diversity-Combining (DC) Automatic Repeat reQuest (ARQ) scheme employed in a Time Division Multiple Access (TDMA) architecture, adapted for channels dedicated to a single user. The second is a Network-assisted Diversity Multiple Access (NDMA) scheme, which is a multi-packet detection approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This thesis combines these techniques with Single Carrier with Frequency Division Equalizer (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems.
It proposes a new NDMA scheme capable of handling more Mobile Terminals (MTs)
than the user separation capacity of the receiver. This thesis also proposes a set of analytical tools that can be used to analyse and optimize the use of these two systems. These tools are then employed to compare both approaches in terms of error rate, throughput and delay performances, and taking the implementation complexity into consideration.
Finally, it is shown that both approaches represent viable solutions for future broadband wireless communications complementing each other.Fundação para a Ciência e Tecnologia - PhD grant(SFRH/BD/41515/2007); CTS multi-annual funding project PEst-OE/EEI/UI0066/2011, IT
pluri-annual funding project PEst-OE/EEI/LA0008/2011, U-BOAT project PTDC/EEATEL/
67066/2006, MPSat project PTDC/EEA-TEL/099074/2008 and OPPORTUNISTICCR
project PTDC/EEA-TEL/115981/200
High performance faster-than-nyquist signaling
AbstractIn a wireless broadband context, multi-path dispersive channels can severely affectdata communication of Mobile Terminals (MTs) uplink.Single Carrier withFrequency-Domain Equalization (SC-FDE) has been proposed to deal with highlydispersive channels for the uplink of broadband wireless systems. However, currentsystems rely on older assumptions of the Nyquist theorem and assume that a systemneeds a minimum bandwidth 2Wper MT. Faster-Than-Nyquist (FTN) assumesthat it is possible to employ a bandwidth as low as 0.802 of the original Nyquistbandwidth with minimum loss - despite this, the current literature has only proposedcomplex receivers for a simple characterization of the wireless channel. Furthermore,the uplink of SC-FDE can be severely affected by a deep-fade and or poor channelconditions; to cope with such difficulties Diversity Combining (DC) Hybrid ARQ(H-ARQ) is a viable technique, since it combines the several packet copies sent bya MT to create reliable packet symbols at the receiver.In this thesis we consider the use of FTN signaling for the uplink of broadbandwireless systems employing SC-FDE based on the Iterative Block with DecisionFeedback Equalization (IB-DFE) receiver with a simple scheduled access HybridAutomatic Repeat reQuest (H-ARQ) specially designed taking into account thecharacteristics of FTN signals. This approach achieves a better performance thanNyquist signaling by taking advantage of the additional bandwidth employed of aroot-raised cosine pulse for additional diversity.Alongside a Packet Error Rate (PER) analytical model, simulation results show that this receiver presents a better performance when compared with a regular system,with higher system throughputs and a lower Energy per Useful Packet (EPUP)
QoS in LEO satellite networks with multipacket reception
Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaLow Earth Orbit (LEO) satellite networks can improve terrestrial wireless networks to
allow global broadband services for Mobile Terminals (MT), regardless of the users' location.
In this context, hybrid telecommunication systems combining satellites with Long
Term Evolution (LTE) networks, like the LightSquared technology, are intended to provide
ubiquitous high-speed services.
This dissertation analyses the performance of a random access protocol that uses Hybrid
Network-assisted Diversity Multiple Access (H-NDMA), for a LEO satellite system
network, named by Satellite Random NDMA (SR-NDMA). The protocol also considers
a Single Carrier-Frequency Domain Equalization (SC-FDE) scheme for the uplink transmission
and a Multipacket Reception (MPR) receiver. In this scenario, the transmission
of data packets between MTs and the Base Station (BS) is made through random access
and schedule access slots, organized into super-frames with the duration of a Round Trip
Time (RTT).
A SR-NDMA simulator is implemented to measure the system performance in matters
of throughput, energy consumption, system delay and also the protocol capacity to
meet Quality of Service (QoS) requirements. A set of simulations tests were made with a
random Poisson process tra c generation to validate the analytical model. The capacity
to ful l the QoS requirements of a real-time tra c class was also tested.FCT/MEC: MPSat - PTDC/EEA-TEL/099074/2008,
OPPORTUNISTIC CR - PTDC/EEA-TEL/115981/2009, Femtocells - PTDC/EEA-TEL/120666/2010
e ADIN - PTDC/EEI-TEL/2990/201
A random access MAC protocol for MPR satellite networks
Dissertação apresentada para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadores, pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaRandom access approaches for Low Earth Orbit (LEO) satellite networks are usually incompatible
with the Quality of Service (QoS) requirements of multimedia tra c, especially when hand-held devices must operate with very low power.
Cross-Layered optimization architectures, combined with Multipacket Reception (MPR)schemes are a good choice to enhance the overall performance of a wireless system. Hybrid
Network-assisted Diversity Multiple Access (H-NDMA) protocol, exhibits high energy e ciency, with MPR capability, but its use with satellites is limited by the high round trip time. This protocol was adapted to satellites, in Satellite-NDMA, but it required a pre-reservation mechanism that introduces a signi cant delay.
This dissertation proposes a random access protocol that uses H-NDMA, for Low Earth Orbit (LEO) satellite networks, named Satellite Random-NDMA (SR-NDMA). The protocol addresses the problem inherent to satellite networks (large round trip time and signi cant energy consumption) de ning a hybrid approach with an initial random access plus possible additional scheduled retransmissions. An MPR receiver combines the multiple copies received, gradually reducing the error rate. Analytical performance models are proposed for the throughput, delay, jitter and energy e ciency considering nite queues at the terminals. It is also addressed the energy e ciency optimization, where the system
parameters are calculated to guarantee the QoS requirements.
The proposed system's performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) receiver. Results show that the proposed system is energy e cient and can provide enough QoS to support services such as video telephony
Lightly synchronized Multipacket Reception in Machine-Type Communications Networks
Machine Type Communication (MTC) applications were designed to monitor and control
elements of our surroundings and environment. MTC applications have a different
set of requirements compared to the traditional communication devices, with Machine to
Machine (M2M) data being mostly short, asynchronous, bursty and sometimes requiring end-to-end delays below 1ms. With the growth of MTC, the new generation of mobile communications has to be able to present different types of services with very different requirements, i.e. the same network has to be capable of "supplying" connection to the user that just wants to download a video or use social media, allowing at the same time MTC that has completely different requirements, without deteriorating both experiences.
The challenges associated to the implementation of MTC require disruptive changes at
the Physical (PHY) and Medium Access Control (MAC) layers, that lead to a better use of the spectrum available. The orthogonality and synchronization requirements of the PHY layer of current Long Term Evolution Advanced (LTE-A) radio access network (based on glsofdm and Single Carrier Frequency Domain Equalization (SC-FDE)) are obstacles for this new 5th Generation (5G) architecture. Generalized Frequency Division Multiplexing (GFDM) and other modulation techniques were proposed as candidates for the 5G PHY layer, however they also suffer from visible degradation when the transmitter and receiver are not synchronized, leading to a poor performance when collisions occur in an asynchronous MAC layer. This dissertation addresses the requirements of M2M traffic at the MAC layer applying multipacket reception (MPR) techniques to handle the bursty nature of the traffic and synchronization tones and optimized back-off approaches to reduce the delay. It proposes a new MAC protocol and analyses its performance analytically considering an SC-FDE modulation. The models are validated using a system level cross-layer simulator developed in MATLAB, which implements the MAC protocol and applies PHY layer performance models. The results show that the MAC’s latency depends mainly on the number of users and the load of each user, and can be controlled using these two parameters
Serviços pós-4G em redes de satélite LEO com recepção multi-pacote e com handover
Dissertação para obtenção do Grau de Mestre em
Engenharia Electrotécnica e de ComputadoresUm pacote com erros, quer seja devido à existência de colisões ou ruído no canal, é normalmente descartado e necessita de ser retransmitido, levando a perdas de desempenho.
A junção do protocolo H-ARQ (Hybrid Automatic Retransmission reQuest) com técnicas de recepção multi-pacote e com diversidade temporal como o NDMA (Network Diversity Multiple Access), melhoram o desempenho, visto terem a capacidade de pedir
transmissões extra e combinar todos os sinais recebidos no mesmo período. Contudo, o
atraso provocado pelo tempo de ida e volta na comunicação com uma rede de satélites,
limita o número de retransmissões que possam ser pedidas pelos terminais para garantir
qualidade de serviço.
Esta tese considera o desenho de um protocolo híbrido que combina H-ARQ com NDMA
para redes satélites com tráfego atribuído a pedido. O protocolo S-NDMA (Satellite
NDMA) é apresentado, juntamente com modelos analíticos para o seu desempenho. É
analisada a sua eficiência energética, tendo em conta requisitos de qualidade de serviço
(QoS). O sistema é feito para satélites de órbita baixa (LEO) e com SC-FDE (Single-Carrier with Frequency Domain Equalization). É feita também uma comparação de desempenhos
deste esquema com H-NDMA (Hybrid-NDMA), mostrando que é eficiente em termos
energéticos e que cumpre requisitos de QoS para serviços exigentes como videochamadas.
São necessários vários satélites para cobrir uma vasta área do planeta. Como os satélites
estão em constante movimento, a zona de cobertura associada a cada satélite também se
desloca. Isto leva a uma necessidade do terminal móvel trocar constantemente de ligação para um novo satélite. Nesta dissertação são propostos dois esquemas para S-NDMA: o tradicional com interrupção temporária de ligação, e um novo com continuidade de ligação baseado em SIMO distribuído. São estudadas a viabilidade e desempenho dos dois esquemas, analisando-se a eficiência energética, o efeito de Doppler, o ponto óptimo de troca e o atraso no tempo na comunicação entre terminais móveis e satélites