Blind phase noise estimation for CO-OFDM transmissions

In this paper, we discuss in detail the performance of different blind phase noise estimation schemes for coherent optical orthogonal frequency-division multiplexing transmissions. We first derive a general model of such systems with phase noise. Based on this model, the phase cycle slip probability in blind phase noise estimation is calculated. For blind phase tracking, we present and discuss the implementation of feedback loop and digital phase tracking. We then analyze in detail the performance of a decision-direct-free blind scheme, in which only three test phases are required for phase noise compensation. We show that the decision-direct-free blind scheme is transparent to QAM formats, and can provide a similar performance to the conventional blind phase search employing 16 test phases. We also propose two novel cost functions to further reduce the complexity of this scheme

Turbo Decoding and Detection for Wireless Applications

A historical perspective of turbo coding and turbo transceivers inspired by the generic turbo principles is provided, as it evolved from Shannon’s visionary predictions. More specifically, we commence by discussing the turbo principles, which have been shown to be capable of performing close to Shannon’s capacity limit. We continue by reviewing the classic maximum a posteriori probability decoder. These discussions are followed by studying the effect of a range of system parameters in a systematic fashion, in order to gauge their performance ramifications. In the second part of this treatise, we focus our attention on the family of iterative receivers designed for wireless communication systems, which were partly inspired by the invention of turbo codes. More specifically, the family of iteratively detected joint coding and modulation schemes, turbo equalization, concatenated spacetime and channel coding arrangements, as well as multi-user detection and three-stage multimedia systems are highlighted

Review of Recent Trends

This work was partially supported by the European Regional Development Fund (FEDER), through the Regional Operational Programme of Centre (CENTRO 2020) of the Portugal 2020 framework, through projects SOCA (CENTRO-01-0145-FEDER-000010) and ORCIP (CENTRO-01-0145-FEDER-022141). Fernando P. Guiomar acknowledges a fellowship from “la Caixa” Foundation (ID100010434), code LCF/BQ/PR20/11770015. Houda Harkat acknowledges the financial support of the Programmatic Financing of the CTS R&D Unit (UIDP/00066/2020).MIMO-OFDM is a key technology and a strong candidate for 5G telecommunication systems. In the literature, there is no convenient survey study that rounds up all the necessary points to be investigated concerning such systems. The current deeper review paper inspects and interprets the state of the art and addresses several research axes related to MIMO-OFDM systems. Two topics have received special attention: MIMO waveforms and MIMO-OFDM channel estimation. The existing MIMO hardware and software innovations, in addition to the MIMO-OFDM equalization techniques, are discussed concisely. In the literature, only a few authors have discussed the MIMO channel estimation and modeling problems for a variety of MIMO systems. However, to the best of our knowledge, there has been until now no review paper specifically discussing the recent works concerning channel estimation and the equalization process for MIMO-OFDM systems. Hence, the current work focuses on analyzing the recently used algorithms in the field, which could be a rich reference for researchers. Moreover, some research perspectives are identified.publishersversionpublishe

Two-tier channel estimation aided near-capacity MIMO transceivers relying on norm-based joint transmit and receive antenna selection

We propose a norm-based joint transmit and receive antenna selection (NBJTRAS) aided near-capacity multiple-input multiple-output (MIMO) system relying on the assistance of a novel two-tier channel estimation scheme. Specifically, a rough estimate of the full MIMO channel is first generated using a low-complexity, low-training-overhead minimum mean square error based channel estimator, which relies on reusing a modest number of radio frequency (RF) chains. NBJTRAS is then carried out based on this initial full MIMO channel estimate. The NBJTRAS aided MIMO system is capable of significantly outperforming conventional MIMO systems equipped with the same modest number of RF chains, while dispensing with the idealised simplifying assumption of having perfectly known channel state information (CSI). Moreover, the initial subset channel estimate associated with the selected subset MIMO channel matrix is then used for activating a powerful semi-blind joint channel estimation and turbo detector-decoder, in which the channel estimate is refined by a novel block-of-bits selection based soft-decision aided channel estimator (BBSB-SDACE) embedded in the iterative detection and decoding process. The joint channel estimation and turbo detection-decoding scheme operating with the aid of the proposed BBSB-SDACE channel estimator is capable of approaching the performance of the near-capacity maximumlikelihood (ML) turbo transceiver associated with perfect CSI. This is achieved without increasing the complexity of the ML turbo detection and decoding process

A Robust Threshold for Iterative Channel Estimation in OFDM Systems

A novel threshold computation method for pilot symbol assisted iterative channel estimation in OFDM systems is considered. As the bits are transmitted in packets, the proposed technique is based on calculating a particular threshold for each data packet in order to select the reliable decoder output symbols to improve the channel estimation performance. Iteratively, additional pilot symbols are established according to the threshold and the channel is re-estimated with the new pilots inserted to the known channel estimation pilot set. The proposed threshold calculation method for selecting additional pilots performs better than non-iterative channel estimation, no threshold and fixed threshold techniques in poor HF channel simulations

Digital Linearization of High Capacity and Spectrally Efficient Direct Detection Optical Transceivers

Metropolitan area networks are experiencing unprecedented traffic growth. The provision of information and entertainment supported by cloud services, broadband video and mobile technologies such as long-term evolution (LTE) and 5G are creating a rapidly increasing demand for bandwidth. Although wavelength division multiplexing (WDM) architectures have been introduced into metro transport networks to provide significant savings over single-channel systems, to cope with the ever-increasing traffic growth, it is urgently required to deploy higher data rates (100 Gb/s and beyond) for each WDM channel. In comparison to dual-polarization digital coherent transceivers, single-polarization and single photodiode-based direct-detection (DD) transceivers may be favourable for metropolitan, inter-data centre and access applications due to their use of a simple and low-cost optical hardware structure. Single sideband (SSB) quadrature amplitude modulation (QAM) subcarrier modulation (SCM) is a promising signal format to achieve high information spectral density (ISD). However, due to the nonlinear effect termed signal-signal beat interference (SSBI) caused by the square-law detection, the performance of such SSB SCM DD systems is severely degraded. Therefore, it is essential to develop effective and low-complexity linearization techniques to eliminate the SSBI penalty and improve the performance of such transceivers. Extensive studies on SSB SCM DD transceivers employing a number of novel digital linearization techniques to support high capacity (≥ 100 Gb/s per channel) and spectrally-efficient (net ISD > 2 b/s/Hz) WDM transmission covering metropolitan reach scenarios (up to 240 km) are described in detail in this thesis. Digital modulation formats that can be used in DD links and the corresponding transceiver configurations are firstly reviewed, from which the SSB SCM signalling format is identified as the most promising format to achieve high data rates and ISDs. Following this, technical details of the digital linearization approaches (iterative SSBI cancellation, single-stage linearization filter and simplified non-iterative SSBI cancellation, two-stage linearization filter, Kramers-Kronig scheme) considered in the thesis are presented. Their compensation performance in a dispersion pre-compensated (Tx-EDC) 112 Gb/s per channel 35 GHz-spaced WDM SSB 16-QAM Nyquist-SCM DD system transmitting over up to 240 km standard single-mode fibre (SSMF) is assessed. Net ISDs of up to 3.18 b/s/Hz are achieved. Moreover, we also show that, with the use of effective digital linearization techniques, further simplification of the DD transceivers can be realized by moving electronic dispersion compensation from the transmitter to the receiver without sacrificing performance. The optical ISD limit of SSB SCM DD system finally explored through experiments with higher-order modulation formats combined with effective digital linearization techniques. 168 Gb/s per channel WDM 64-QAM signals were successfully transmitted over 80 km, achieving a record net optical ISD of 4.54 b/s/Hz. Finally, areas for further research are identified

Compensation of fibre impairments in coherent optical systems

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 201