Multicore fibers (MCFs) are one of the main technological enablers for space-division multiplexing. In principle, MCFs could scale the fiber capacity by a factor equal to the number of cores, but in practice such increase is hindered by transmission impairments due to the inter-core crosstalk between adjacent lit cores. The entity of such crosstalk depends on the number of cores and on their disposition within the fiber cladding, and also on the baud rate and modulation format used for transmission. As first MCF applications are expected over point-to-point systems, in this paper we concentrate on the resource allocation over a single link. Specifically, we study the Baud rate, Modulation format, Core and Spectrum Assignment problem in a multicore flexi-grid link, considering distance-adaptive reaches for different baud rates, modulation formats, and crosstalk impairments. We show that the problem is NP-hard and provide two integer linear programs, as well as heuristic approaches to solve it over large/practical traffic instances. Our problem formulations incorporate modeling of the exact inter-core crosstalk contributions depending on the number of lit neighbor cores. Numerical results are provided in a high-spatial-efficiency 19-core fiber considering different transmission impairment conditions.

This work considers a Poisson noise channel with an amplitude constraint. It is well-known that the capacity-achieving input distribution for this channel is discrete with finitely many points. We sharpen this result by introducing upper and lower bounds on the number of mass points. Concretely, an upper bound of order $\mathsf {A}\log ^{2}(\mathsf {A})$ and a lower bound of order $\sqrt { \mathsf {A}}$ are established where $\mathsf {A}$ is the constraint on the input amplitude. In addition, along the way, we show several other properties of the capacity and capacity-achieving distribution. For example, it is shown that the capacity is equal to $- \log P_{Y^\star }(0)$ where $P_{Y^\star }$ is the optimal output distribution. Moreover, an upper bound on the values of the probability masses of the capacity-achieving distribution and a lower bound on the probability of the largest mass point are established. Furthermore, on the per-symbol basis, a nonvanishing lower bound on the probability of error for detecting the capacity-achieving distribution is established under the maximum a posteriori rule.

The behavior of exponential backoff (EB) has challenged researchers ever since its introduction, but only approximate and partial results have been produced up to this date. This paper presents accurate results about the effect of protocol parameters on throughput and delay, assuming queues in saturation. Among the manifold results, we first introduce a simple model that provides close-form results for the approximated model known as “decoupling assumption.” Since the latter fails to provide well approximated results in many cases, we also introduce a Markovian model able to trade the precision of the results with complexity even with an infinite number of users, enabling us to get definite throughput results, such as 0.3706 with binary EB, and 0.4303 with an optimized base. Analytical considerations allow to derive the tail of the access-delay distribution, found to be slowly decreasing and with no variance as the number of users goes to infinity. Taking into account the overall performance, preliminary results seem to indicate that the exponential base b=1.35 is more appealing than the standard value b=2.

In optical transmission systems based on high-order modulations, the impact on system performance of Wiener phase noise affecting the received carrier phase can be relevant. To make less severe phase noise effects, solutions based on the use of known pilot symbols, that aid carrier phase recovery, have been recently introduced. This letter proposes a pilot-aided demodulation scheme where the memory of phase noise is dealt with by a trellis-based demodulation algorithm. The benefits in terms of achievable information rate and bit error rate compared to adversary schemes are demonstrated by computer simulations for strong phase noise with 4-ary quadrature amplitude modulation (4-QAM) and 16-QAM.

The Kalman filter is proposed here to track the phase noise introduced by independent transmit and receive oscillators in multiple-input multiple-output transmission. To take advantage of pilot symbols that are transmitted before and after the time instant where one wants to estimate the vector of phases, a forward-backward Kalman filter is proposed. To reduce the complexity of the Kalman filter, suboptimal methods are introduced and their performance is compared to that of the full complexity Kalman filter by computer simulation.

This paper studies the secrecy capacity of an n-dimensional Gaussian wiretap channel under a peak power constraint. This work determines the largest peak power constraint ${\overline{\mathsf{R}}}_n$, such that an input distribution uniformly distributed on a single sphere is optimal; this regime is termed the low-amplitude regime. The asymptotic value of ${\overline{\mathsf{R}}}_n$ as n goes to infinity is completely characterized as a function of noise variance at both receivers. Moreover, the secrecy capacity is also characterized in a form amenable to computation. Several numerical examples are provided, such as the example of the secrecy-capacity-achieving distribution beyond the low-amplitude regime. Furthermore, for the scalar case $(n=1)$, we show that the secrecy-capacity-achieving input distribution is discrete with finitely many points at most at the order of $\frac{{\mathsf{R}}^2}{{\sigma }_1^2}$, where ${\sigma }_1^2$ is the variance of the Gaussian noise over the legitimate channel.