On Low Complexity Detection for QAM Isomorphic Constellations

Despite of the known gap from the Shannon's capacity, several standards are still employing QAM or star shape constellations, mainly due to the existing low complexity detectors. In this paper, we investigate the low complexity detection for a family of QAM isomorphic constellations. These constellations are known to perform very close to the peak-power limited capacity, outperforming the DVB-S2X standard constellations. The proposed strategy is to first remap the received signals to the QAM constellation using the existing isomorphism and then break the log likelihood ratio computations to two one dimensional PAM constellations. Gains larger than 0.6 dB with respect to QAM can be obtained over the peak power limited channels without any increase in detection complexity. Our scheme also provides a systematic way to design constellations with low complexity one dimensional detectors. Several open problems are discussed at the end of the paper.Comment: Submitted to IEEE GLOBECOM 201

Unified Satellite and Terrestrial ACM Design

First step towards integrating satellite and terrestrial standards at the physical layer is to design a unified packet frame structure, and in particular, a unified adaptive coding and modulation (ACM) scheme without substantial loss in either of the systems. In this paper we introduce a methodology to design such a set of modulation and coding (MODCOD) combinations. In the first step, we design a set of base MODCODs for the AWGN channel. Then, for any other given channel model, we build a new set of MODCODs through a suitable transformation of the base MODCODs. We mainly focus on two types of channels: (a) non-linear satellite channels, and (b) AWGN channels with fading. We compare our results with latest digital video broadcasting standards, namely, DVB-T2 and DVB-S2X

Limites práticos de segurança da distribuição de chaves quânticas de variáveis contínuas

Discrete Modulation Continuous Variable Quantum Key Distribution (DM-CV-QKD) systems are very attractive for modern quantum cryptography, since they manage to surpass all Gaussian modulation (GM) system’s disadvantages while maintaining the advantages of using CVs. Nonetheless, DM-CV-QKD is still underdeveloped, with a very limited study of large constellations. This work intends to increase the knowledge on DM-CV-QKD systems considering large constellations, namely M-symbol Amplitude Phase Shift Keying (M-APSK) irregular and regular constellations. As such, a complete DM-CV-QKD system was implemented, con sidering collective attacks and reverse reconciliation under the realistic scenario, assuming Bob detains the knowledge of his detector’s noise. Tight security bounds were obtained considering M-APSK constellations and GM, both for the mutual information between Bob and Alice and the Holevo bound between Bob and Eve. M-APSK constellations with binomial distribution can approximate GM’s results for the secret key rate. Without the consideration of the finite size effects (FSEs), the regular constellation 256-APSK (reg. 32) with binomial distribution achieves 242.9 km, only less 7.2 km than GM for a secret key rate of 10¯⁶ photons per symbol. Considering FSEs, 256-APSK (reg. 32) achieves 96.4% of GM’s maximum transmission distance (2.3 times more than 4-PSK), and 78.4% of GM’s maximum compatible excess noise (10.2 times more than 4-PSK). Additionally, larger constellations allow the use of higher values of modulation variance in a practical implementation, i.e., we are no longer subjected to the sub-one limit for the mean number of photons per symbol. The information reconciliation step considering a binary symmetric channel, the sum-product algorithm and multi-edge type low den sity parity check matrices, constructed from the progressive edge growth algorithm, allowed the correction of keys up to 18 km. The consideration of multidimensional reconciliation allows 256-APSK (reg. 32) to reconcile keys up to 55 km. Privacy amplification was carried out considering the application of fast Fourier transforms to the Toeplitz extractor, being unable of extracting keys for more than, approximately, 49 km, almost haft the theoretical value, and for excess noises larger than 0.16 SNU, like the theoretical value.Os sistemas de distribuição de chaves quânticas com variáveis contínuas e modulação discreta (DM-CV-QKD) são muito atrativos para a criptografia quântica moderna, pois conseguem superar todas as desvantagens do sistema com modulação Gaussiana (GM) enquanto mantêm as vantagens do uso de CVs. No entanto, DM-CV-QKD ainda está subdesenvolvida, sendo o estudo de grandes constelações muito reduzido. Este trabalho pretende aumentar o conhecimento sobre os sistemas DM-CV-QKD com constelações grandes, nomeadamente as do tipo M-symbol Amplitude Phase Shift Keying (M-APSK) irregulares e regulares. Com isto, foi simulado um sistema DM-CV-QKD completo, considerando ataques coletivos e reconciliação reversa tendo em conta o cenário realista, assumindo que o Bob co nhece o ruído de seu detetor. Os limites de segurança foram obtidos considerando constelações M-APSK e GM, tanto para a informação mútua entre o Bob e a Alice, quanto para o limite de Holevo entre o Bob e a Eve. As constelações M-APSK com distribuição binomial aproximam-se à GM quanto à taxa de chave secreta. Sem considerar o efeito de tamanho finito (FSE), a constelação regular 256-APSK (reg. 32) com distribuição binomial atinge 242.9 km, apenas menos 7.2 km do que GM para uma taxa de chave secreta de 10¯⁶ fotões por símbolo. Considerando FSEs, a 256-APSK (reg. 32) atinge 96.4% da distância máxima de transmissão para GM (2.3 vezes mais que a 4-PSK), e 78.4% do valor máximo de excesso de ruído compatível para GM (10.2 vezes mais do que a 4-PSK). Adicionalmente, grandes constelações permitem o uso de valores mais altos de variância de modulação em implementações práticas, pelo que deixa de ser necessário um número de fotões por símbolo abaixo de um. A etapa de reconciliação de informação considerou um canal binário simétrico, o algoritmo soma-produto e matrizes multi-edge type low density parity check, construídas a partir do algoritmo progressive edge growth, permitindo a correção de chaves até 18 km. A consideração de reconciliação multidimensional permite que a 256-APSK (reg. 32) reconcilie chaves até 55 km. A amplificação de privacidade foi realizada considerando a aplicação de transformadas de Fourier rápidas ao extrator de Toeplitz, mostrando-se incapaz de extrair chaves para mais de, aproximadamente, 49 km, quase metade do valor teórico, e para excesso de ruído superior a 0.16 SNU, semelhante ao valor teórico.Mestrado em Engenharia Físic

Modulation, Coding, and Receiver Design for Gigabit mmWave Communication

While wireless communication has become an ubiquitous part of our daily life and the world around us, it has not been able yet to deliver the multi-gigabit throughput required for applications like high-definition video transmission or cellular backhaul communication. The throughput limitation of current wireless systems is mainly the result of a shortage of spectrum and the problem of congestion. Recent advancements in circuit design allow the realization of analog frontends for mmWave frequencies between 30GHz and 300GHz, making abundant unused spectrum accessible. However, the transition to mmWave carrier frequencies and GHz bandwidths comes with new challenges for wireless receiver design. Large variations of the channel conditions and high symbol rates require flexible but power-efficient receiver designs. This thesis investigates receiver algorithms and architectures that enable multi-gigabit mmWave communication. Using a system-level approach, the design options between low-power time-domain and power-hungry frequency-domain signal processing are explored. The system discussion is started with an analysis of the problem of parameter synchronization in mmWave systems and its impact on system design. The proposed synchronization architecture extends known synchronization techniques to provide greater flexibility regarding the operating environments and for system efficiency optimization. For frequency-selective environments, versatile single-carrier frequency domain equalization (SC-FDE) offers not only excellent channel equalization, but also the possibility to integrate additional baseband tasks without overhead. Hence, the high initial complexity of SC-FDE needs to be put in perspective to the complexity savings in the other parts of the baseband. Furthermore, an extension to the SC-FDE architecture is proposed that allows an adaptation of the equalization complexity by switching between a cyclic-prefix mode and a reduced block length overlap-save mode based on the delay spread. Approaching the problem of complexity adaptation from time-domain, a high-speed hardware architecture for the delayed decision feedback sequence estimation (DDFSE) algorithm is presented. DDFSE uses decision feedback to reduce the complexity of the sequence estimation and allows to set the system performance between the performance of full maximum-likelihood detection and pure decision feedback equalization. An implementation of the DDFSE architecture is demonstrated as part of an all-digital IEEE802.11ad baseband ASIC manufactured in 40nm CMOS. A flexible architecture for wideband mmWave receivers based on complex sub-sampling is presented. Complex sub-sampling combines the design advantages of sub-sampling receivers with the flexibility of direct-conversion receivers using a single passive component and a digital compensation scheme. Feasibility of the architecture is proven with a 16Gb/s hardware demonstrator. The demonstrator is used to explore the potential gain of non-equidistant constellations for high-throughput mmWave links. Specifically crafted amplitude phase-shift keying (APSK) modulation achieve 1dB average mutual information (AMI) advantage over quadrature amplitude modulation (QAM) in simulation and on the testbed hardware. The AMI advantage of APSK can be leveraged for a practical transmission using Polar codes which are trained specifically for the constellation