Blind Carrier Phase Recovery for General 2{\pi}/M-rotationally Symmetric Constellations

This paper introduces a novel blind carrier phase recovery estimator for general 2{\Pi}/M-rotationally symmetric constellations. This estimation method is a generalization of the non-data-aided (NDA) nonlinear Phase Metric Method (PMM) estimator already designed for general quadrature amplitude constellations. This unbiased estimator is seen here as a fourth order PMM then generalized to Mth order (Mth PMM) in such manner that it covers general 2{\Pi}/M-rotationally symmetric constellations such as PAM, QAM, PSK. Simulation results demonstrate the good performance of this Mth PMM estimation algorithm against competitive blind phase estimators already published for various modulation systems of practical interest.Comment: 14 pages, 12 figures, International Journal of Wireless & Mobile Networks (IJWMN

Pilot Decontamination in CMT-based Massive MIMO Networks

Pilot contamination problem in massive MIMO networks operating in time-division duplex (TDD) mode can limit their expected capacity to a great extent. This paper addresses this problem in cosine modulated multitone (CMT) based massive MIMO networks; taking advantage of their so-called blind equalization property. We extend and apply the blind equalization technique from single antenna case to multi-cellular massive MIMO systems and show that it can remove the channel estimation errors (due to pilot contamination effect) without any need for cooperation between different cells or transmission of additional training information. Our numerical results advocate the efficacy of the proposed blind technique in improving the channel estimation accuracy and removal of the residual channel estimation errors caused by the users of the other cells.Comment: Accepted in ISWCS 201

Filter Bank Multicarrier for Massive MIMO

This paper introduces filter bank multicarrier (FBMC) as a potential candidate in the application of massive MIMO communication. It also points out the advantages of FBMC over OFDM (orthogonal frequency division multiplexing) in the application of massive MIMO. The absence of cyclic prefix in FBMC increases the bandwidth efficiency. In addition, FBMC allows carrier aggregation straightforwardly. Self-equalization, a property of FBMC in massive MIMO that is introduced in this paper, has the impact of reducing (i) complexity; (ii) sensitivity to carrier frequency offset (CFO); (iii) peak-to-average power ratio (PAPR); (iv) system latency; and (v) increasing bandwidth efficiency. The numerical results that corroborate these claims are presented.Comment: 7 pages, 6 figure

Implementation of Carrier Phase Recovery Circuits for Optical Communication

Fiber-optic links form a vital part of our increasingly connected world, and as the number of Internet users and the network traffic increases, reducing the power dissipation of these links becomes more important. A considerable part of the total link power is dissipated in the digital signal processing (DSP) subsystems, which show a growing complexity as more advanced modulation formats are introduced. Since DSP designers can no longer take reduced power dissipation with each new CMOS process node for granted, the design of more efficient DSPalgorithms in conjunction with circuit implementation strategies focused on power efficiency is required.One part of the DSP for a coherent fiber-optic link is the carrier phase recovery (CPR) unit, which can account for a significant portion of the DSP power dissipation, especially for shorter links. A wide range of CPR algorithms is available, but reliable estimates of their power efficiency is missing, making accurate comparisons impossible. Furthermore, much of the current literature does not account for the limited precision arithmetic of the DSP.In this thesis, we develop circuit implementations based on a range of suggested CPR algorithms, focusing on power efficiency. These circuits allow us to contrast different CPR solutions based not only on power dissipation, but also on the quality of the phase estimation, including fixed-point arithmetic aspects. We also show how different parameter settings affect the power efficiency and the implementation penalty. Additionally, the thesis includes a description of our field-programmable gate-array fiber-emulation environment, which can be used to study rare phenomena in DSP implementations, or to reach very low bit-error rates. We use this environment to evaluate the cycle-slip probability of a CPR implementation

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

Optical fibre communication over a noisy partially coherent channel

As global IP traffic grows unceasingly, optical networks demand for technology upgrades in order to keep the feared “capacity crunch” away. The most celebrated technologies of coherent detection and wavelength-division multiplexing (WDM), widely deployed in long-haul links, are gaining ground in access networks, which is particularly challenging due to the shared-cost requirements, leading to denser channel spacings and the use of cheaper devices that tend to be noisier. In order to make the most of this technology combination, it is crucial to have a model of the channel that accurately describes all the present sources of noise. Traditionally, the most used model has been the additive white Gaussian noise (AWGN) channel, which, although only accounting for a linear contribution of complex noise and being insensitive to rotational phenomena, has shown its validity in numerous studies, as well as in commercial equipment. In this thesis, however, it is observed that the adoption of coherent detection and WDM, with lower-grade semiconductor lasers showing a moderate linewidth, yields scenarios where a phase-sensitive model becomes a must. The partially coherent AWGN (PCAWGN) channel is a popular choice that fulfils this need, but its high complexity due to non-trivial functions involved, deprives it from being suitable in high-speed digital circuits. The main goal of this thesis is to describe a reduced-complexity approximation in polar coordinates, accurate enough to find its applicability in modern systems. Furthermore, this works explores some possible end-to-end applications, like channel capacity estimation or symbol detection, assessing its performance by means of extensive simulations. Lastly, the emerging field of complex modulation of directly modulated lasers is revisited, with a special interest in how the proposed approximation can help to improve the performance of previously reported techniques, as well as proposing a new way to design spiral-shaped constellations aimed to maximise the channel capacity

Multidimensional Optimized Optical Modulation Formats

This chapter overviews the relatively large body of work (experimental and theoretical) on modulation formats for optical coherent links. It first gives basic definitions and performance metrics for modulation formats that are common in the literature. Then, the chapter discusses optimization of modulation formats in coded systems. It distinguishes between three cases, depending on the type of decoder employed, which pose quite different requirements on the choice of modulation format. The three cases are soft-decision decoding, hard-decision decoding, and iterative decoding, which loosely correspond to weak, medium, and strong coding, respectively. The chapter also discusses the realizations of the transmitter and transmission link properties and the receiver algorithms, including DSP and decoding. It further explains how to simply determine the transmitted symbol from the received 4D vector, without resorting to a full search of the Euclidean distances to all points in the whole constellation

Asymptotic Performance of the Pth Power-Law Phase Estimator

An expression for the true variance of the Pth powerlaw phase estimator, as the number of samples approaches infinity, is given. This expression is an extension to the linear approximation of Moeneclaey and de Jonghe [1] which is known to be inadequate in some practical systems. Our new expression covers general 2π/P-rotationally symmetric constellations that include those of PAM, QAM, PSK, Star M-QAM, MR-DPSK, and others. This expression also generalizes the known expressions for QAM and PSK. Additionally, our expression reduces to the Cramer-Rao bound given by Steendam and Moeneclaey [9], as SNR goes to zero. Monte Carlo simulations provide experimental verification of the theoretical expression for various constellations