Repositório Institucional da Universidade de Aveiro
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Prefilter bandwidth effects in sequential symbol synchronizers based on clock sampling
No full textThis work studies the prefilter bandwidth effects on the symbol synchronizer based on clock sampling.
The prefilter bandwidth B is changed between three values, namely B1=∞∞∞ (infinite), B2=2.tx and B3=1.tx, where tx is the transmission rate.
We use also the sequential symbol synchronizer based on clock sampling, with the variant discrete and continuous. Each variant has two versions which are the
manual and the automatic.
The objective is to study the prefilter bandwidth with the four symbol synchronizers and to evaluate their output jitter UIRMS (Unit Interval Root Mean Square) versus input SNR (Signal to Noise Ratio)
Radio-over-fiber as the enabler for joint processing of spatially separated radio signals
No full textAn overview of the FUTON project is presented, with emphasis on the optical link design for radio-over-fiber communication and virtual-MIMO functionalities between multiple remote antenna units and a centralized processing site
Symbol phase synchronizers tested with different input sequences
No full textThis work study four symbol phase synchronizers namely the analog, hybrid, combinational and sequential.These four synchronizers will be tested with three different input sequences (deterministic and pseudo random). The sequences are the deterministic P1=21 (one and zero dasia1-0psila), the deterministic P2=22 (two ones and two zeros dasia11-00psila) and the pseudo random P7=27-1. The objective is to study the four synchronizers and to evaluate their jitter UI-RMS (Unit Interval Root Mean Squared) versus input SNR (Signal- Noise Ratio), when the input sequence changes between P1, P2 and P7
Symbol synchronizers based on filter with Phase Lock Loop
No full textThis work study the symbol synchronizer based on a filter followed of a carrier PLL (Phase Lock Loop).
The filter is a bandpass filter, centered in an equal frequency to the data transmission rate.
We will present four symbol synchronizers, the filter is equal for all them, but the PLL can be one of four types, namely the analog, the hybrid, the combinational and the sequential.
The main objective is to study the four symbol synchronizers and to obtain their jitter noise curves
Pre-equalization technique for interference cancellation in the UMTS-TDD downlink channel
No full textThis paper proposes a technique aiming to simplify the mobile terminals by transferring as much as possible the complex operations to the base station. A pre-equalization technique is proposed for the downlink channel of UMTS TDD, which allows the use of simpler receiver schemes in the mobile unit. After the mathematical background, simulation results obtained in typical scenarios, using statistical channel models, are presented to demonstrate the performance of the proposed method. Several levels of correlation between the propagation channels that can be considered to exist between the different base station antenna array elements and the desired mobile unit were considered. The results have shown that that significant performance gains can be achieved in high multiple access interference (MAI) environment
Metrics for Optimal Relay Selection in Cooperative Wireless Networks
No full textA key design issue in relay based cooperative wireless networks is the metrics used for relay selection. Internal operational parameters and network sensing parameters are two categories recently considered as decision factors for cooperation strategies. We focus on the impact of these potential sensing parameters as indicators of the effective cooperation, from the perspective of the network layer, namely: movement, medium access delay and medium delay ratio. Simulation results indicate a strong correlation between network performance and the proposed cooperative metrics. Novel solutions for cooperation should take these metrics into consideration in order to provide better network performance
Community Building over Neighborhood Wireless Mesh Networks
No full textThe fourth generation (4G) network paradigm has long been sought. A user-centric vision for such "always best connected" next-generation 4G networks is neighborhood wireless mesh networks (WMNs). In this context, the vision for the formation of WMNs reflects the trade-off between the immediate self-interest of the user, and the user's need for social contacts. Notably, users would be required to pool their resources in order to support the creation and operation of the underlying communication network (participating at all physical, access, and network layers), but also for the service provision on top of it. We argue that the design of communities suitable for this environment will encourage users to participate, enable trustworthy network creation, and provide a social layer, which can be exploited in order to design cross-layer incentive mechanisms that will further encourage users to share their resources and cooperate at lower layers
Air quality management in Portugal: example of needs and available tools
No full textThe Framework Directive (FWD) and the proposed Daughter Directives are the newest legislative instruments concerning a new political strategy and air quality management approach for Europe. Additionally, the member countries of the United Nations Economic Commission for Europe have included the concepts of critical load and level for planning air pollution abatement strategies and as a base of international agreements concerning limitation of the emissions of air pollutants. These concepts imply an accurate knowledge about pollutants deposition fluxes. The paper describes the main needs and the tools available to define a strategy of air quality management in Portugal. Two study cases are presented: (1) extensive monitoring plan to assess the impact of an urban incinerator plant; and (2) contribution to a methodology to estimate critical levels for a coastal region in Portugal. These different approaches allowed illustrating the complexity of the implementation of an air pollution management strategy
A Hybrid formulation in the stress analysis of curved pipes
No full textDescribes a hybrid formulation solution based on variational techniques, where
unknown functions are combined with a set of Fourier trigonometric expansions. The unknown
functions refer to the toroidal shell distortion in the longitudinal direction when the shell is
submitted to generalised in-plane forces in the linear-elastic stress field. This set of functions is
solved from a system of differential equations, having calculated the eigenvalues and
corresponding eigenvectors in the complex field from the system equations matrix. For this
purpose the MAPLE1 mathematical solver was used. This module led to an analytical solution,
which is exact for each Fourier term used in the global solution. The final results agree very well
with finite element method or other solutions obtained using a total expansion of trigonometric
functions in the longitudinal and meridional directions