Comlab's research topics cover a broad range of topics in the field of digital communications and networks. In particular, our current efforts are focused on four main research fields:

  • Avanced modulation and signal processing for coherent optical communications systems

Coherent detection enabled a new generation of 100 Gb/s transceivers using the DP-QPSK modulation format that is compatible with the legacy infrastructure installed for 10-Gb/s links. The natural next step is 400 Gb/s, whose transceiver architecture is still under discussion in standardization bodies. The reach limitations of future 400-Gb/s systems have been addressed in several ways, from advanced FEC techniques to the power-hungry nonlinear compensation using digital back-propagation. Another way to improve the link capacity and/or reach is contellation shaping. While this can be achieved using a constellation with unequally spaced points (geometric shaping), it is considered more practical to use a set of equally spaced points with unequal probability [probabilistic shaping (PS). In this research line we investigate shaping, coding and signal processing algorithms for future coherent optical communications systems. Collaborators/supporters: BrPhotonics, CPqD, Idea!.

  • Avanced modulation and signal processing for optical systems with mode multiplexing

Space-Division Multiplexing (SDM) has been accepted as the only transmission technique able to cope with the exponential traffic growth experienced in several segments of data networks, especially in inter and intra data center interconnects. Besides parallel transmission of signals in bundles of single-mode fibers (SMFs), multicore fibers (MCFs) and multimode fibers (MMFs) are important candidate technologies for the SDM transmission media. Signals conveyed by MCFs with uncoupled cores are easy to couple and switch, but require careful crosstalk management. On the other hand, MMFs use typically multiple-input multiple-output (MIMO) processing to separate the signals multiplexed over the multiple orthogonal modes. The complexity of such MIMO equalizers is specially challenging in mode-multiplexed systems with large differential mode delays (DMD) and low or intermediate mode-coupling levels. In this research field we develop a suite of signal processing techniques tailored for mode-multiplexing systems. Collaborators/supporters: Aston University (UK), FAPESP.

  • Fronthaul architectures for the support of 5G networks

The 5th generation of mobile communications systems promises to offer unprecedented connectivity among users and devices, providing completely new services and paving the way the Internet of Things (IoT). This new mobile paradigm will require significant technological advances, both in the wireless infrastructure as well as in the transport network that supports it. In this context, the architecture of the future Radio Access Network (RAN) is under intense debate. One possibility is to have a fully centralized RAN (C-RAN), where the Remote Radio Head (RRH) is a simple device that, in the uplink, collects the waveforms received from the wireless channel before sending them transparently (i.e., without decoding) to a centralized Baseband Unit (BBU), and, in the downlink, follows the reverse path. However, several other functional splits are possible, with the intent of distributing the signal processing tasks between the RRH and the BBU. While a fully distributed RAN alleviates the traffic requirements imposed on the fronthaul links, a fully centralized architecture enables inter-site coordination (in particular collaborative signal processing techniques, RAN virtualization, etc.) potentially leading to operational cost savings. In this research field we investigate optical fronthaul architectures for a cost-effective C-RAN. Collaborators/supporters: KTH (Sweeden), University of Brasilia.

  • Networking technologies for future optical networks with space-division multiplexing

For almost three decades, wavelength-division multiplexing (WDM) has been the key technology for supporting the exponentially increasing data traffic in core optical networks. To date, network upgrades have been mainly based on activation of additional wavelength channels within a single fiber. However, the capacity of single-mode fibers (SMFs) is limited. As the routed throughput exceeds the capacity of a single SMF provided by the entire spectrum, the deployment of space-division multiplexing (SDM) - either in multiple SMFs, multi-core fibers (MCFs), or multi-mode fibers (MMFs) - is inevitable [1]–[4]. While utilizing spatial channels, to keep the complexity of SDM switching nodes at an acceptable level, one approach proposed is the wavelength switching (WS) of spatial superchannels. On the other hand, the sustained exponential increase in data rates shall render the fine granularity and flexibility provided by wavelength channels less essential. A promising option may be to replace wavelength switching (WS) with spatial switching (SS), which allocates a spectral superchannel individually for a source-destination pair. When implemented for full-spectrum in uncoupled spatial channels, SS can substantially reduce the complexity of a networking node. This research line studies viable switching architectures for smoothly evolving the network towards space-division multiplexing in terrestrial and submarine networks. Collaborators: Stanford University (USA), FAPESP.

A simulation tool for space-division multiplexing elastic optical networks

About Space-D

This software is a custom discrete event-driven simulator for Space-division Multiplexed Elastic Optical Networks (SDM-EON) with support to uncoupled channels that are represented by single-mode multi-core fibers as the links of the network.

The dynamics of the system is represented by the event chaining. The events are associated with the snapshot system actions that indicate state transitions and can trigger other events that will be executed in the future.

The events are connection requests to connect source-destination pairs of nodes in the network. The network is managed by the Control Plane, which checks if there are enough resources to accomodate all requirements before to install each connection request in the network.

This project was supported by CNPq and by FAPESP grant 2015/04382-0.