1,232 research outputs found
Optimisation of Mobile Communication Networks - OMCO NET
The mini conference âOptimisation of Mobile Communication Networksâ focuses on advanced methods for search and optimisation applied to wireless communication networks. It is sponsored by Research & Enterprise Fund Southampton Solent University.
The conference strives to widen knowledge on advanced search methods capable of optimisation of wireless communications networks. The aim is to provide a forum for exchange of recent knowledge, new ideas and trends in this progressive and challenging area. The conference will popularise new successful approaches on resolving hard tasks such as minimisation of transmit power, cooperative and optimal routing
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Laboratory and field trials evaluation of transmit delay Diversity applied to DVB-T/H networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The requirements for future DVB-T/H networks demand that broadcasters design and
deploy networks that provide ubiquitous reception in challenging indoors and other
obstructed situations. It is essential that such networks are designed cost-effectively and with minimized environmental impact. The use of transmit diversity techniques with
multiple antennas have long been proposed to improve the performance and capacity of
wireless systems. Transmit diversity exploits the scattering effect inherent in the channel by means of transmitting multiple signals in a controlled manner from spatially separated antennas, allowing independently faded signals to arrive at the receiver and improves the chances of decoding a signal of acceptable quality. Transmit diversity can complement receive diversity by adding an additional diversity gain and in situations where receiver diversity is not practical, transmit diversity alone delivers a comparable amount of diversity gain. Transmit Delay Diversity (DD) can be applied to systems employing the
DVB standard without receiver equipment modifications. Although transmit DD can
provide a gain in NLOS situations, it can introduce degradation in LOS situation. The aim of this thesis is to investigate the effectiveness in real-word applications of novel diversity techniques for broadcast transmitter networks. Tests involved laboratory experiments using a wireless MIMO channel emulator and the deployment of a field measurement campaign dedicated to driving, indoor and rooftop reception. The relationship between the diversity gain, the propagation environment and several parameters such as the transmit antenna separation, the receiver speed and the Forward Error Correction Codes (FEC) configuration are investigated. Results includes the effect of real-word parameter usually not modeled in the software simulation analysis, such as antenna radiation patterns and mutual coupling, scattering vegetation impact, non-Gaussian noise sources and receiver implementation. Moreover, a practical analysis of the effectiveness of experimental techniques to mitigate the loss due to transmit DD loss in rooftop reception is presented. The results of this thesis confirmed, completed and extended the existing predictions with real word measurement results
Physical and Link Layer Implications in Vehicle Ad Hoc Networks
Vehicle Ad hoc Networks (V ANET) have been proposed to provide safety on the
road and deliver road traffic information and route guidance to drivers along with
commercial applications. However the challenges facing V ANET are numerous. Nodes
move at high speeds, road side units and basestations are scarce, the topology is
constrained by the road geometry and changes rapidly, and the number of nodes peaks
suddenly in traffic jams. In this thesis we investigate the physical and link layers of
V ANET and propose methods to achieve high data rates and high throughput.
For the physical layer, we examine the use of Vertical BLAST (VB LAST) systems
as they provide higher capacities than single antenna systems in rich fading
environments. To study the applicability of VB LAST to VANET, a channel model was
developed and verified using measurement data available in the literature. For no to
medium line of sight, VBLAST systems provide high data rates. However the
performance drops as the line of sight strength increases due to the correlation between
the antennas. Moreover, the performance of VBLAST with training based channel
estimation drops as the speed increases since the channel response changes rapidly. To
update the channel state information matrix at the receiver, a channel tracking algorithm
for flat fading channels was developed. The algorithm updates the channel matrix thus
reducing the mean square error of the estimation and improving the bit error rate (BER).
The analysis of VBLAST-OFDM systems showed they experience an error floor due to
inter-carrier interference (lCI) which increases with speed, number of antennas
transmitting and number of subcarriers used. The update algorithm was extended to
VBLAST -OFDM systems and it showed improvements in BER performance but still
experienced an error floor. An algorithm to equalise the ICI contribution of adjacent
subcarriers was then developed and evaluated. The ICI equalisation algorithm reduces
the error floor in BER as more subcarriers are equalised at the expense of more
hardware complexity.
The connectivity of V ANET was investigated and it was found that for single lane
roads, car densities of 7 cars per communication range are sufficient to achieve high
connectivity within the city whereas 12 cars per communication range are required for
highways. Multilane roads require higher densities since cars tend to cluster in groups.
Junctions and turns have lower connectivity than straight roads due to disconnections at
the turns. Although higher densities improve the connectivity and, hence, the
performance of the network layer, it leads to poor performance at the link layer. The
IEEE 802.11 p MAC layer standard under development for V ANET uses a variant of
Carrier Sense Multiple Access (CSMA). 802.11 protocols were analysed
mathematically and via simulations and the results prove the saturation throughput of
the basic access method drops as the number of nodes increases thus yielding very low
throughput in congested areas. RTS/CTS access provides higher throughput but it
applies only to unicast transmissions. To overcome the limitations of 802.11 protocols,
we designed a protocol known as SOFT MAC which combines Space, Orthogonal
Frequency and Time multiple access techniques. In SOFT MAC the road is divided into
cells and each cell is allocated a unique group of subcarriers. Within a cell, nodes share
the available subcarriers using a combination of TDMA and CSMA. The throughput
analysis of SOFT MAC showed it has superior throughput compared to the basic access
and similar to the RTS/CTS access of 802.11
A Mobile Wireless Channel State Recognition Algorihm: Introduction, Definition, and Verification - Sensing for Cognitive Environmental Awareness
This research includes mobile wireless systems limited by time and frequency dispersive channels. A blind mobile wireless channel (MWC) state recognition (CSR) algorithm that detects hidden coherent nonselective and noncoherent selective processes is verified. Because the algorithm is blind, it releases capacity based on current channel state that traditionally is fixed and reserved for channel gain estimation and distortion mitigation. The CSR algorithm enables cognitive communication system control including signal processing, resource allocation/deallocation, or distortion mitigation selections based on channel coherence states. MWC coherent and noncoherent states, ergodicity, stationarity, uncorrelated scattering, and Markov processes are assumed for each time block. Furthermore, a hidden Markov model (HMM) is utilized to represent the statistical relationships between hidden dispersive processes and observed receive waveform processes. First-order and second-order statistical extracted features support state hard decisions which are combined in order to increase the accuracy of channel state estimates. This research effort has architected, designed, and verified a blind statistical feature recognition algorithm capable of detecting coherent nonselective, single time selective, single frequency selective, or dual selective noncoherent states. A MWC coherence state model (CSM) was designed to represent these hidden dispersive processes. Extracted statistical features are input into a parallel set of trained HMMs that compute state sequence conditional likelihoods. Hard state decisions are combined to produce a single most likely channel state estimate for each time block. To verify the CSR algorithm performance, combinations of hidden state sequences are applied to the CSR algorithm and verified against input hidden state sequences. State sequence recognition accuracy sensitivity was found to be above 99% while specificity was determined to be above 98% averaged across all features, states, and sequences. While these results establish the feasibility of a MWC blind CSR algorithm, optimal configuration requires future research to further improve performance including: 1) characterizing the range of input signal configurations, 2) waveform feature block size reduction, 3) HMM parameter tracking, 4) HMM computational complexity and latency reduction, 5) feature soft decision combining, 6) recursive implementation, 7) interfacing with state based mobile wireless communication control processes, and 8) extension to wired or wireless waveform recognition
Adaptive Communications for Next Generation Broadband Wireless Access Systems
Un dels aspectes claus en el disseny i gestiĂł de les xarxes sense fils d'accĂ©s de banda ampla Ă©s l'Ășs eficient dels recursos radio. Des del punt de vista de l'operador, l'ample de banda Ă©s un bĂ© escĂ s i preuat que sÂŽha d'explotar i gestionar de la forma mĂ©s eficient possible tot garantint la qualitat del servei que es vol proporcionar. Per altra banda, des del punt de vista del usuari, la qualitat del servei ofert ha de ser comparable al de les xarxes fixes, requerint aixĂ un baix retard i una baixa pĂšrdua de paquets per cadascun dels fluxos de dades entre la xarxa i l'usuari. Durant els darrers anys sÂŽhan desenvolupat nombroses tĂšcniques i algoritmes amb l'objectiu d'incrementar l'eficiĂšncia espectral. Entre aquestes tĂšcniques destaca l'Ășs de mĂșltiples antenes al transmissor i al receptor amb l'objectiu de transmetre diferents fluxos de dades simultaneament sense necessitat d'augmentar l'ample de banda. Per altra banda, la optimizaciĂł conjunta de la capa d'accĂ©s al medi i la capa fĂsica (fent Ășs de l'estat del canal per tal de gestionar de manera optima els recursos) tambĂ© permet incrementar sensiblement l'eficiĂšncia espectral del sistema.L'objectiu d'aquesta tesi Ă©s l'estudi i desenvolupament de noves tĂšcniques d'adaptaciĂł de l'enllaç i gestiĂł dels recursos rĂ dio aplicades sobre sistemes d'accĂ©s rĂ dio de propera generaciĂł (Beyond 3G). Els estudis realitzats parteixen de la premissa que el transmisor coneix (parcialment) l'estat del canal i que la transmissiĂł es realitza fent servir un esquema multiportadora amb mĂșltiples antenes al transmisor i al receptor. En aquesta tesi es presenten dues lĂnies d'investigaciĂł, la primera per casos d'una sola antenna a cada banda de l'enllaç, i la segona en cas de mĂșltiples antenes. En el cas d'una sola antena al transmissor i al receptor, un nou esquema d'assignaciĂł de recursos rĂ dio i prioritzaciĂł dels paquets (scheduling) Ă©s proposat i analitzat integrant totes dues funcions sobre una mateixa entitat (cross-layer). L'esquema proposat tĂ© com a principal caracterĂstica la seva baixa complexitat i que permet operar amb transmissions multimedia. Alhora, posteriors millores realitzades per l'autor sobre l'esquema proposat han permĂšs tambĂ© reduir els requeriments de senyalitzaciĂł i combinar de forma Ăłptima usuaris d'alta i baixa mobilitat sobre el mateix accĂ©s rĂ dio, millorant encara mĂ©s l'eficiĂšncia espectral del sistema. En cas d'enllaços amb mĂșltiples antenes es proposa un nou esquema que combina la selecciĂł del conjunt optim d'antenes transmissores amb la selecciĂł de la codificaciĂł espai- (frequĂšncia-) temps. Finalment es donen una sĂšrie de recomanacions per tal de combinar totes dues lĂnies d'investigaciĂł, aixĂ con un estat de l'art de les tĂšcniques proposades per altres autors que combinen en part la gestiĂł dels recursos rĂ dio i els esquemes de transmissiĂł amb mĂșltiples antenes.Uno de los aspectos claves en el diseño y gestiĂłn de las redes inalĂĄmbricas de banda ancha es el uso eficiente de los recursos radio. Desde el punto de vista del operador, el ancho de banda es un bien escaso y valioso que se debe explotar y gestionar de la forma mĂĄs eficiente posible sin afectar a la calidad del servicio ofrecido. Por otro lado, desde el punto de vista del usuario, la calidad del servicio ha de ser comparable al ofrecido por las redes fijas, requiriendo asĂ un bajo retardo y una baja tasa de perdida de paquetes para cada uno de los flujos de datos entre la red y el usuario. Durante los Ășltimos años el nĂșmero de tĂ©cnicas y algoritmos que tratan de incrementar la eficiencia espectral en dichas redes es bastante amplio. Entre estas tĂ©cnicas destaca el uso de mĂșltiples antenas en el transmisor y en el receptor con el objetivo de poder transmitir simultĂĄneamente diferentes flujos de datos sin necesidad de incrementar el ancho de banda. Por otro lado, la optimizaciĂłn conjunta de la capa de acceso al medio y la capa fĂsica (utilizando informaciĂłn de estado del canal para gestionar de manera Ăłptima los recursos) tambiĂ©n permite incrementar sensiblemente la eficiencia espectral del sistema.El objetivo de esta tesis es el estudio y desarrollo de nuevas tĂ©cnicas de adaptaciĂłn del enlace y la gestiĂłn de los recursos radio, y su posterior aplicaciĂłn sobre los sistemas de acceso radio de prĂłxima generaciĂłn (Beyond 3G). Los estudios realizados parten de la premisa de que el transmisor conoce (parcialmente) el estado del canal a la vez que se considera que la transmisiĂłn se realiza sobre un sistema de transmisiĂłn multiportadora con mĂșltiple antenas en el transmisor y el receptor. La tesis se centra sobre dos lĂneas de investigaciĂłn, la primera para casos de una Ășnica antena en cada lado del enlace, y la segunda en caso de mĂșltiples antenas en cada lado. Para el caso de una Ășnica antena en el transmisor y en el receptor, se ha desarrollado un nuevo esquema de asignaciĂłn de los recursos radio asĂ como de priorizaciĂłn de los paquetes de datos (scheduling) integrando ambas funciones sobre una misma entidad (cross-layer). El esquema propuesto tiene como principal caracterĂstica su bajo coste computacional a la vez que se puede aplicar en caso de transmisiones multimedia. Posteriores mejoras realizadas por el autor sobre el esquema propuesto han permitido tambiĂ©n reducir los requisitos de señalizaciĂłn asĂ como combinar de forma Ăłptima usuarios de alta y baja movilidad. Por otro lado, en caso de enlaces con mĂșltiples antenas en transmisiĂłn y recepciĂłn, se presenta un nuevo esquema de adaptaciĂłn en el cual se combina la selecciĂłn de la(s) antena(s) transmisora(s) con la selecciĂłn del esquema de codificaciĂłn espacio-(frecuencia-) tiempo. Para finalizar, se dan una serie de recomendaciones con el objetivo de combinar ambas lĂneas de investigaciĂłn, asĂ como un estado del arte de las tĂ©cnicas propuestas por otros autores que combinan en parte la gestiĂłn de los recursos radio y los esquemas de transmisiĂłn con mĂșltiples antenas.In Broadband Wireless Access systems the efficient use of the resources is crucial from many points of views. From the operator point of view, the bandwidth is a scarce, valuable, and expensive resource which must be exploited in an efficient manner while the Quality of Service (QoS) provided to the users is guaranteed. On the other hand, a tight delay and link quality constraints are imposed on each data flow hence the user experiences the same quality as in fixed networks. During the last few years many techniques have been developed in order to increase the spectral efficiency and the throughput. Among them, the use of multiple antennas at the transmitter and the receiver (exploiting spatial multiplexing) with the joint optimization of the medium access control layer and the physical layer parameters.In this Ph.D. thesis, different adaptive techniques for B3G multicarrier wireless systems are developed and proposed focusing on the SS-MC-MA and the OFDM(A) (IEEE 802.16a/e/m standards) communication schemes. The research lines emphasize into the adaptation of the transmission having (Partial) knowledge of the Channel State Information for both; single antenna and multiple antenna links. For single antenna links, the implementation of a joint resource allocation and scheduling strategy by including adaptive modulation and coding is investigated. A low complexity resource allocation and scheduling algorithm is proposed with the objective to cope with real- and/or non-real- time requirements and constraints. A special attention is also devoted in reducing the required signalling. However, for multiple antenna links, the performance of a proposed adaptive transmit antenna selection scheme jointly with space-time block coding selection is investigated and compared with conventional structures. In this research line, mainly two optimizations criteria are proposed for spatial link adaptation, one based on the minimum error rate for fixed throughput, and the second focused on the maximisation of the rate for fixed error rate. Finally, some indications are given on how to include the spatial adaptation into the investigated and proposed resource allocation and scheduling process developed for single antenna transmission
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Advanced Techniques for High-Throughput Cellular Communications
The next generation wireless communication systems require ubiquitous high-throughput mobile connectivity under a range of challenging network settings (urban versus rural, high device density, mobility, etc). To improve the performance of the system, the physical layer design is of great importance. The previous research on improving the physical layer properties includes: a) highly directional transmissions that can enhance the throughput and spatial reuse; b) enhanced MIMO that can eliminate
contention, enabling linear increase of capacity with number of antennas; c) mmWave technologies which operate on GHz bandwidth to over substantially higher throughput; d) better cooperative spectrum sharing with cognitive radios; e) better multiple access method which can mitigate multiuser interference and allow more multi-users.
This dissertation addresses several techniques in the physical layer design of the next generation wireless communication systems. In chapter two, an orthogonal frequency division with code division multiple access (OFDM-CDMA) systems is proposed and a polyphase code is used to improve multiple access performance and make the OFDM signal satisfy the peak to average ratio (PAPR) constraint. Chapter three studies the I/Q imbalance for direct down converter. For wideband transmitter and receiver that use direct conversion for I/Q sampling, the I/Q imbalance becomes a critical issue. With higher I/Q imbalance, there will be higher degradation in quadrature amplitude modulation, which degrades the throughput tremendously. Chapter four investigate a problem of spectrum sharing for cognitive wideband communication. An energy-efficient sub-Nyquist sampling algorithm is developed for optimal sampling and spectrum sensing. In chapter ve, we study the channel estimation of millimeter wave full-dimensional MIMO communication. The problem is formulated as an atomic-norm minimization problem and algorithms are derived for the channel estimation in different situations.
In this thesis, mathematical optimization is applied as the main approach to analyze and solve the problems in the physical layer of wireless communication so that the high-throughput is achieved. The algorithms are derived along with the theoretical analysis, which are validated with numerical results
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