The authors consider the robust Tomlinson–Harashima precoding (THP) for downlink multiuser multiple-input
multiple-output orthogonal frequency-division multiplexing systems with quantised feedback. The authors discuss vector
channel feedback strategies in the frequency and time domains, and develop a robust version of THP that takes into account
of error statistics of the channel state information, that consists of the optimal feedforward filters, feedback filters and the
receive filters. Feedback techniques are developed to exploit the spatial correlations in realistic 3GPP channel models by
applying dimension reduction and scalar-quantisation. Extensive simulations results are provided to demonstrate the
performance of the proposed robust THP design as well as the channel feedback scheme.
A novel quality-of-service (QoS) differentiation framework for optical burst switching networks is introduced. Two different methods are provided and subsequently validated. Particularly, both methods aim at using controlled loops as deflection routes, which assures an upper bounded number of hops from source to destination. This yields a 2-fold outcome. First, the insufficient offset time problematic of standard deflection routing under just-enough-time is solved. Second, excessively long delays owing to uncontrolled deflections are avoided. In both methods, the number of allowed loops is proposed as a QoS metric, giving support for class differentiation. This applies to a scenario with heterogeneous traffic demands, each one with different latency and burst loss requirements. The benefits of each proposal are quantified and further compared with existent alternatives by simulations.
Optical burst switching architectures without buffering capabilities are sensitive to burst congestion. The existence of a few highly congested links may seriously aggravate the network throughput. Proper
network routing may help in congestion reduction. The authors focus on adaptive routing strategies to be applied in labelled OBS networks, that is, with explicit routing paths. In particular, two isolated alternative routing algorithms that aim at network performance improvement because of reactive route selection are studied. Moreover, a nonlinear optimisation method for multi-path source-based routing, which aims at proactive congestion reduction is proposed. Comparative performance results are provided and some implementation issues are discussed.
Loss-free schemes are defined to ensure successful packet/burst transmissions in optical packet/burst
switching networks. To this end, they rely on a collision-free routing and wavelength assignment (CF-RWA)
scheme combined with simple contention resolution mechanisms that guarantee the absence of losses in
intermediate links. Here, the CF-RWA problem is studied. In particular, by using graph theory, the problem of
finding CF-RWA schemes that minimise the number of wavelengths to serve a given traffic matrix is set. The
problem is simplified when it is formulated by using pre-defined sets of non-colliding paths. Within this
framework, the problem is shown to be equivalent to finding a given vertex-set colouring of the so-called
restriction digraph. Here, two heuristic algorithms are proposed to obtain such vertex-set colourings. One of
them provides a suitable CF-RWA without having to solve the minimisation problem. By way of example, the
proposed method is applied to the NSFNet and the EON network providing quasi-optimal results.