Turbo-BLAST: Performance evaluation in correlated Rayleigh-Fading environment

Recent theoretical investigations of spatially correlated multitransmit and multireceive (MTMR) links show that not only independently and identically distributed links, but also spatially correlated links can offer linear capacity growth with increasing number of transmit and receive antennas. In this paper, we explore the suitability of the turbo-BLAST architecture in correlated Rayleigh-fading MTMR environments. In particular, for an MTMR system with a large number of receive antennas, a near optimal performance can be achieved by the turbo-BLAST architecture in spatially and temporarily correlated Rayleigh-fading environments. The performance of turbo-BLAST, in terms of both bit-error rate and spectral efficiency, is analyzed empirically in indoors and correlated outdoor environments.

Turbo-smt: Accelerating coupled sparse matrix-tensor factorizations by 200x

How can we correlate the neural activity in the human brain as it responds to typed words, with properties of these terms (like ‘edible’, ‘fits in hand’)? In short, we want to find latent variables, that jointly explain both the brain activity, as well as the behavioral responses. This is one of many settings of the Coupled Matrix-Tensor Factorization (CMTF) problem.

Can we accelerate any CMTF solver, so that it runs within a few minutes instead of tens of hours to a day, while maintaining good accuracy? We introduce Turbo-SMT, a meta-method capable of doing exactly that: it boosts the performance of any CMTF algorithm, by up to 200x, along with an up to 65 fold increase in sparsity, with comparable accuracy to the baseline.

We apply Turbo-SMT to BrainQ, a dataset consisting of a (nouns, brain voxels, human subjects) tensor and a (nouns, properties) matrix, with coupling along the nouns dimension. Turbo-SMT is able to find meaningful latent variables, as well as to predict brain activity with competitive accuracy.

On the performance of LDPC and turbo decoder architectures with unreliable memories

In this paper, we investigate the impact of faulty memory bit-cells on the performance of LDPC and Turbo channel decoders based on realistic memory failure models. Our study investigates the inherent error resilience of such codes to potential memory faults affecting the decoding process. We develop two mitigation mechanisms that reduce the impact of memory faults rather than correcting every single error. We show how protection of only few bit-cells is sufficient to deal with high defect rates. In addition, we show how the use of repair-iterations specifically helps mitigating the impact of faults that occur inside the decoder itself.

Detecção multiutilizador do domínio da frequência para sistemas DS-CDMA

Os Sinais de Espalhamento de Espectro de Sequência Directa exibem propriedades cicloestacionárias que implicam redundância entre componentes de frequência espaçadas por múltiplos da taxa de símbolo. Nesta tese, é apresentado um cancelador de interferência multiutilizador (Cancelador por translação na frequência - FSC) que tira partido desta propriedade. Este cancelador linear opera no domínio da frequência no sinal espalhado de tal forma que minimiza a interferência e ruído na saída (Critério do Mínimo Erro Quadrado Médio). Além de testado para o caso de antena única, são avaliadas as performances das configurações de antenas múltiplas para o caso de beamforming e canais espacialmente descorrelacionados considerando sistemas síncronos e sistemas com desalinhamento no tempo dos perfis de canais (ambos UMTS-TDD). Essas configurações divergiam na ordem da combinação temporal, combinação espacial e detecção multiutilizador. As configurações FSC foram avaliadas quando concatenadas com o PIC-2D. Os resultados das simulações mostram consideráveis melhorias nos resultados relativamente ao RAKE-2D convencional e PIC-2D. Foi atingida performance próximo ao RAKE de utilizador único quando o FSC foi avaliado concatenado com PIC-2D em quase todas as configurações. Todas as configurações foram avaliadas com modulação QPSK, 8-PSK e 16-QAM. Foi introduzida codificação Turbo e identificou-se as situações da vantagem de utilização do FSC antes do PIC-2D. As modulações 8-PSK e 16-QAM foram igualmente testadas com codificação.

Joint turbo equalization and cancelation of nonlinear distortion effects in MC-CDMA signals

In this paper, we consider low-PMEPR (Peak-to-Mean Envelope Power Ratio) MC-CDMA (Multicarrier Coded Division Multiple Access) schemes. We develop frequencydomain turbo equalizers combined with an iterative estimation and cancellation of nonlinear distortion effects. Our receivers have relatively low complexity, since they allow FFT-based (Fast Fourier Transform) implementations. The proposed turbo receivers allow significant performance improvements at low and moderate SNR (Signal-to-Noise Ratio), even when a low-PMEPR MC-CDMA transmission is intended.

Turbo equalization with cancellation of nonlinear distortion effects for CP-Assisted and Zero-Padded MC-CDMA signals

We consider MC-CDMA schemes, with reduced envelope fluctuations. Both CP-assisted (cyclic prefix) and ZP (zero-padded) MC-CDMA schemes are addressed. We develop turbo FDE (frequency-domain equalization) schemes, combined with cancelation of nonlinear distortion effects. The proposed turbo receivers allow significant performance improvements at low and moderate SNR, even when the transmitted signals have reduced envelope fluctuations.

"Entre a sala de aula e a viagem : o diário gráfico como auxiliar na aprendizagem dos códigos de expressão visual presentes nas disciplinas artísticas e no quotidiano"

Relatório da prática de ensino supervisionada, Mestrado em Ensino de Artes Visuais, Universidade de Lisboa, 2014