15 research outputs found
Spatial modulation: theory to practice
Spatial modulation (SM) is a transmission technique proposed for multiple–input multiple–
output (MIMO) systems, where only one transmit antenna is active at a time, offering an increase
in the spectral efficiency equal to the base–two logarithm of the number of transmit
antennas. The activation of only one antenna at each time instance enhances the average bit
error ratio (ABER) as inter–channel interference (ICI) is avoided, and reduces hardware complexity,
algorithmic complexity and power consumption. Thus, SM is an ideal candidate for
large scale MIMO (tens and hundreds of antennas). The analytical ABER performance of SM
is studied and different frameworks are proposed in other works. However, these frameworks
have various limitations. Therefore, a closed–form analytical bound for the ABER performance
of SM over correlated and uncorrelated, Rayleigh, Rician and Nakagami–m channels is proposed
in this work. Furthermore, in spite of the low–complexity implementation of SM, there
is still potential for further reductions, by limiting the number of possible combinations by exploiting
the sphere decoder (SD) principle. However, existing SD algorithms do not consider
the basic and fundamental principle of SM, that at any given time, only one antenna is active.
Therefore, two modified SD algorithms tailored to SM are proposed. It is shown that the proposed
sphere decoder algorithms offer an optimal performance, with a significant reduction of
the computational complexity. Finally, the logarithmic increase in spectral efficiency offered
by SM and the requirement that the number of antennas must be a power of two would require
a large number of antennas. To overcome this limitation, two new MIMO modulation systems
generalised spatial modulation (GNSM) and variable generalised spatial modulation (VGSM)
are proposed, where the same symbol is transmitted simultaneously from more than one transmit
antenna at a time. Transmitting the same data symbol from more than one antenna reduces
the number of transmit antennas needed and retains the key advantages of SM.
In initial development simple channel models can be used, however, as the system develops it
should be tested on more realistic channels, which include the interactions between the environment
and antennas. Therefore, a full analysis of the ABER performance of SM over urban
channel measurements is carried out. The results using the urban measured channels confirm
the theoretical work done in the field of SM. Finally, for the first time, the performance of SM
is tested in a practical testbed, whereby the SM principle is validated
An intelligent approach to quality of service for MPEG-4 video transmission in IEEE 802.15.1
Nowadays, wireless connectivity is becoming ubiquitous spreading to companies and in domestic areas. IEEE 802.15.1 commonly known as Bluetooth is high-quality, high-security, high-speed and low-cost radio signal technology. This wireless technology allows a maximum access range of 100 meters yet needs power as low as 1mW. Regrettably, IEEE 802.15.1 has a very limited bandwidth. This limitation can become a real problem If the user wishes to transmit a large amount of data in a very short time. The version 1.2 which is used in this project could only carry a maximum download rate of 724Kbps and an upload rate of 54Kbps In its asynchronous mode. But video needs a very large bandwidth to be transmitted with a sufficient level of quality. Video transmission over IEEE 802.15.1 networks would therefore be difficult to achieve, due to the limited bandwidth. Hence, a solution to transmit digital video with a sufficient quality of picture to arrive at the receiving end is required. A hybrid scheme has been developed in this thesis, comprises of a fuzzy logic set of rules and an artificial neural network algorithms. MPEG-4 video compression has been used in this work to optimise the transmission. This research further utilises an ‘added-buffer’ to prevent excessive data loss of MPEG-4 video over IEEE 802.15.1transmission and subsequently increase picture quality. The neural-fuzzy scheme regulates the output rate of the added-buffer to ensure that MPEG-4 video stream conforms to the traffic conditions of the IEEE 802.15.1 channel during the transmission period, that is to send more data when the bandwidth is not fully used and keep the data in the buffers if the bandwidth is overused. Computer simulation results confirm that intelligence techniques and added-buffer do improve quality of picture, reduce data loss and communication delay, as compared with conventional MPEG video transmission over IEEE 802.15.1
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Error relilient video communications using high level M-QAM. Modelling and simulation of a comparative analysis of a dual-priority M-QAM transmission system for H.264/AVC video applications over band-limited and error-phone channels.
An experimental investigation of an M level (M = 16, 64 and 256) Quadrature Amplitude Modulation (QAM) transmission system suitable for video transmission is presented. The communication system is based on layered video coding and unequal error protection to make the video bitstream robust to channel errors. An implementation is described in which H.264 video is protected unequally by partitioning the compressed data into two layers of different visual importance. The partition scheme is based on a separation of the group of pictures (GoP) in the intra-coded frame (I-frame) and predictive coded frame (P frame). This partition scheme is then applied to split the H.264-coded video bitstream and is suitable for Constant Bit Rate (CBR) transmission. Unequal error protection is based on uniform and non-uniform M-QAM constellations in conjunction with different scenarios of splitting the transmitted symbol for protection of the more important information of the video data; different constellation arrangements are proposed and evaluated to increase the capacity of the high priority layer. The performance of the transmission system is evaluated under Additive White Gaussian Noise (AWGN) and Rayleigh fading conditions.
Simulation results showed that in noisy channels the decoded video can be improved by assigning a larger portion of the video data to the enhancement layer in conjunction with non-uniform constellation arrangements; in better channel conditions the quality of the received video can be improved by assigning more bits in the high priority channel and using uniform constellations. The aforementioned varying conditions can make the video transmission more successful over error-prone channels. Further techniques were developed to combat various channel impairments by considering channel coding methods suitable for layered video coding applications. It is shown that a combination of non-uniform M-QAM and forward error correction (FEC) will yield a better performance. Additionally, antenna diversity techniques are examined and introduced to the transmission system that can offer a significant improvement in the quality of service of mobile video communication systems in environments that can be modelled by a Rayleigh fading channel
Variable Rate Transmission Over Noisy Channels
Hybrid automatic repeat request transmission (hybrid ARQ) schemes aim to provide
system reliability for transmissions over noisy channels while still maintaining a reasonably
high throughput efficiency by combining retransmissions of automatic repeat
requests with forward error correction (FEC) coding methods. In type-II hybrid ARQ
schemes, the additional parity information required by channel codes to achieve forward
error correction is provided only when errors have been detected. Hence, the
available bits are partitioned into segments, some of which are sent to the receiver immediately,
others are held back and only transmitted upon the detection of errors. This
scheme raises two questions. Firstly, how should the available bits be ordered for optimal
partitioning into consecutive segments? Secondly, how large should the individual
segments be?
This thesis aims to provide an answer to both of these questions for the transmission
of convolutional and Turbo Codes over additive white Gaussian noise (AWGN),
inter-symbol interference (ISI) and Rayleigh channels. Firstly, the ordering of bits is
investigated by simulating the transmission of packets split into segments with a size of
1 bit and finding the critical number of bits, i.e. the number of bits where the output of
the decoder is error-free. This approach provides a maximum, practical performance
limit over a range of signal-to-noise levels. With these practical performance limits, the
attention is turned to the size of the individual segments, since packets of 1 bit cause
an intolerable overhead and delay. An adaptive, hybrid ARQ system is investigated,
in which the transmitter uses the number of bits sent to the receiver and the receiver
decoding results to adjust the size of the first, initial, packet and subsequent segments
to the conditions of a stationary channel
Performance evaluation of a 40 GHz broadband cellular system
Doutoramento em Engenharia ElectrónicaO trabalho apresentado nesta tese enquadra-se na área das comunicações móveis celulares e tem subjacente a utilização de um protótipo de um sistema de comunicações móveis de banda larga desenvolvido no âmbito do projecto Europeu SAMBA. Este protótipo apresenta como principais características inovadoras as taxas de transmissão, a frequência de operação, a mobilidade e os protocolos de handover rádio. Inicialmente são descritos aspectos relacionados com a evolução das comunicações móveis ao longo do tempo e apresentados conceitos teóricos fundamentais para compreender o comportamento do canal rádio móvel e os mecanismos de propagação. São identificados os tipos de desvanecimento e descritos os vários parâmetros que permitem caracterizar o canal rádio. A descrição do impacto do desvanecimento e as formas de o mitigar são apresentadas para contextualizar o trabalho desenvolvido em termos da especificação do protótipo e as opções escolhidas. As características globais do protótipo são apresentadas o que inclui a descrição do interface rádio, da arquitectura, dos módulos de RF, dos módulos de processamento de banda base, protocolos e algoritmo de transferência rádio. O protótipo foi avaliado em vários cenários com diferentes características. No cenário exterior foi analisada uma rua urbana típica do tipo canyon. Em termos de configuração do sistema foram consideradas e analisadas várias alturas da Estação Base, anglos de inclinação das antenas, várias velocidades da Terminal Móvel, operação com e sem linha de vista e a penetração do sinal rádio em ruas transversais. No cenário interior foram realizados testes similares e medidas relativas às transferências que só foram executadas para este cenário por questões logísticas. Numa primeira abordagem foi analisada a cobertura oferecida por cada célula e posteriormente activada a funcionalidade de transferência. Foram também efectuados estudos com uma única Estação Base cobrindo toda a área. Em termos de caracterização do canal rádio em banda larga são apresentadas medidas da resposta impulsiva para dois cenários interiores e complementados por outros estudos via simulação utilizando uma ferramenta de ray tracing. Nas medidas foi utilizado um método de medição do canal no domínio da frequência. A relação entre o Espalhamento do Atraso e a Banda de Coerência em diferentes cenários foi analisada em detalhe e feita a verificação em termos da violação do limite teórico de Fleury. Como consequência dos tópicos abordados, esta tese apresenta um estudo abrangente de aspectos relacionados com o comportamento do canal rádio na faixa dos 40 GHz e a análise das opções técnicas do protótipo em termos do seu desempenho no âmbito dos sistemas de comunicações móveis 4G.The work presented in this thesis addresses the area of mobile cellular broadband communications and encompasses the utilization of a prototype developed in the framework of the European project SAMBA. This prototype has as main innovative characteristics the transmission rates, the frequency band of operation, the mobility and the radio handover protocols. Initially are described aspects related with the historical evolution of the mobile communications and presented fundamental theoretical concepts to understand the behaviour of the radio channel and the propagation mechanisms. The different types of fading are identified as well as the various parameters that allow the characterisation of the radio channel. The fading impact and its mitigation techniques are presented to contextualise the work developed in terms of the specification of the features implemented in the prototype and the options available. The global characteristic of the prototype are presented namely the radio interface, the architecture, the RF modules, the baseband modules, protocols and the algorithm for the radio handover. The prototype was evaluated in various scenarios with different characteristics. In the outdoor scenario a canyon type street was analysed. Several heights of the Base Station, antenna tilting angles, Mobile Terminal velocities, operation in line-of-sight and non line-of-sight and the penetration of the signal in a transversal street. In the indoor scenario similar measurements were performed. The handover feature was analysed just for this scenario due to logistic reasons. In a first phase the coverage provided by each Base Station was analysed and subsequently activated the handover functionality. Studies using a single Base Station to cover the whole pavilion were also performed. In terms of broadband analysis, channel impulse response measurements were performed using a frequency domain technique in two scenarios and complemented by others analysed only using a ray tracing simulation tool. The relationship between the radio channel Delay Spread and the Coherence Bandwidth was analysed in different scenarios and the possible violation of the Fleury lower bond checked. As a consequence of the several topics covered in this thesis, a deep study of the aspects related with the behaviour of the radio channel in the 40 GHz band and the performance of the technical options implemented in the prototype is presented in the framework of 4G mobile communication systems
Design and performance evaluation of Wireless Multi-Protocol Label Switching (WMPLS)
Scope and Method of Study: The research presented in this document focuses on the design of a new protocol for high-speed wireless data communications. The primary goal of this new design is to overcome the limitations of its predecessors, while minimizing the needed resources and maximizing throughput and efficiency in its operations. Another important goal of the study is to provide a homogeneous protocol for wired and wireless networks in order to provide complete interoperability for overlay models and other protocols that can be designed on the basis of this work. The performance evaluation part of this document shows the areas in which improvement has been achieved over previous protocol implementations, and it also shows the areas in which further research is needed in order to improve the performance at least to the levels set by previous protocols.Findings and Conclusions: This study shows that a native wireless design and implementation of the Multi-Protocol Label Switching (MPLS) protocol provides improvements in the field of wireless data communications, providing a homogeneous platform for voice and data communication networks. The research is open for further improvements and modifications for services not contemplated in this document, and continuous developments should be conducted in order to obtain a working prototype of this proposal
Using embedded hardware monitor cores in critical computer systems
The integration of FPGA devices in many different architectures and services
makes monitoring and real time detection of errors an important concern in FPGA
system design. A monitor is a tool, or a set of tools, that facilitate analytic
measurements in observing a given system. The goal of these observations is
usually the performance analysis and optimisation, or the surveillance of the system.
However, System-on-Chip (SoC) based designs leave few points to attach external
tools such as logic analysers. Thus, an embedded error detection core that allows
observation of critical system nodes (such as processor cores and buses) should
enforce the operation of the FPGA-based system, in order to prevent system
failures. The core should not interfere with system performance and must ensure
timely detection of errors.
This thesis is an investigation onto how a robust hardware-monitoring module
can be efficiently integrated in a target PCI board (with FPGA-based application processing
features) which is part of a critical computing system. [Continues.
Adaptive Error Control Schemes For Supporting Quality Of Service In Wireless Atm Networks
This thesis deals with the error control problems, which is one of the major issues
for supporting quality of service (QoS) in wireless ATM (W A TM). Generally in
wireless communication, error is induced by impairment prone wireless links. As a
method of quality of service based error control, the design and performance
evaluation of a retransmission based error control scheme is proposed to overcome
wireless channel impairments for multimedia traffic support over wireless A TM
networks. The purpose of the proposed error control scheme is to provide error-free
services to the higher layers by either correcting the errors in a packet or
recovering corrupted packets by retransmission in a wireless link.
From the perspective of error control, multimedia traffic can be divided into two
types: loss-sensitive traffic and delay-sensitive traffic. To support all these traffic
over W ATM networks, we propose two approaches for error control. One
approach is to utilize the reliable AAL protocol, which are referd to as AALXl and AALX2, as the end-to-end error control, based on our knowledge-based selectivereject
automatic repeat request (KSRARQ) scheme, and adaptive header protection
with KSRARQ scheme for loss-sensitive and delay-sensitive traffic, respectively