On the Derivation of Optimal Partial Successive Interference Cancellation

The necessity of accurate channel estimation for Successive and Parallel Interference Cancellation is well known. Iterative channel estimation and channel decoding (for instance by means of the Expectation-Maximization algorithm) is particularly important for these multiuser detection schemes in the presence of time varying channels, where a high density of pilots is necessary to track the channel. This paper designs a method to analytically derive a weighting factor $\alpha$, necessary to improve the efficiency of interference cancellation in the presence of poor channel estimates. Moreover, this weighting factor effectively mitigates the presence of incorrect decisions at the output of the channel decoder. The analysis provides insight into the properties of such interference cancellation scheme and the proposed approach significantly increases the effectiveness of Successive Interference Cancellation under the presence of channel estimation errors, which leads to gains of up to 3 dB.Comment: IEEE GLOBECOM 201

Frameless ALOHA with Reliability-Latency Guarantees

One of the novelties brought by 5G is that wireless system design has increasingly turned its focus on guaranteeing reliability and latency. This shifts the design objective of random access protocols from throughput optimization towards constraints based on reliability and latency. For this purpose, we use frameless ALOHA, which relies on successive interference cancellation (SIC), and derive its exact finite-length analysis of the statistics of the unresolved users (reliability) as a function of the contention period length (latency). The presented analysis can be used to derive the reliability-latency guarantees. We also optimize the scheme parameters in order to maximize the reliability within a given latency. Our approach represents an important step towards the general area of design and analysis of access protocols with reliability-latency guarantees.Comment: Accepted for presentation at IEEE Globecom 201

Detection and Combining Techniques for Asynchronous Random Access with Time Diversity

Asynchronous random access (RA) protocols are particularly attractive for their simplicity and avoidance of tight synchronization requirements. Recent enhancements have shown that the use of successive interference cancellation (SIC) can largely boost the performance of these schemes. A further step forward in the performance can be attained when diversity combining techniques are applied. In order to enable combining, the detection and association of the packets to their transmitters has to be done prior to decoding. We present a solution to this problem, that articulates into two phases. Non-coherent soft-correlation as well as interference-aware soft-correlation are used for packet detection. We evaluate the detection capabilities of both solutions via numerical simulations. We also evaluate numerically the spectral efficiency achieved by the proposed approach, highlighting its benefits.Comment: 6 pages, 7 figures. Work has been submitted to the 11th International ITG Conference on Systems, Communications and Coding 201

From 5G to 6G: Has the Time for Modern Random Access Come?

This short paper proposes the use of modern random access for IoT applications in 6G. A short overview of recent advances in uncoordinated medium access is provided, highlighting the gains that can be achieved by leveraging smart protocol design intertwined with advanced signal processing techniques at the receiver. The authors' vision on the benefits such schemes can yield for beyond-5G systems is presented, with the aim to trigger further discussion.Comment: 2 pages, 1 figure, presented at 6G Summit, Levi, Finland, 201

Trace-metaldynamics in response of increase CO₂ and iron availability in a coastal mesocosm experiment

A mesocosm experiment was performed in the Raunefjord (Norway) to study changes in dissolved Cu (dCu) and Fe (dFe), and in the elemental composition of particles during an Emiliania huxleyi dominated bloom. The CO2 treatments consisted of present (LC; 390 ppmV) and predicted levels (HC; 900 ppmV) and iron conditions were created with the addition of the siderophore desferoxamine B (DFB). Our results showed the DFB addition enhanced the solubility of Fe in this fjord environment. Initially, dFe was comparable among treatments but after the addition, the HC and/or +DFB treatments presented higher levels and finally, the only ones maintaining high dFe were the +DFB treatments. Unlike dCu presented indistinguishable levels in all mesocosms over time. Particulate metals were normalised to P and Al to evaluate the relative influence of biotic and abiotic sources. The Fe:P ratios decreased with time and compared to published phytoplankton ratios suggest Fe storage. On the other hand, Fe:Al ratios were relatively closer to the crustal ratios suggesting that the abiotic source was more important for this metal. Trends for other metals will be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Reliability-Latency Performance of Frameless ALOHA with and without Feedback

This paper presents a finite length analysis of multislot type frameless ALOHA based on a dynamic programming approach. The analysis is exact, but its evaluation is only feasible for moderate number of users due to the computational complexity. The analysis is then extended to derive continuous approximations of its key parameters, which, apart from providing an insight into the decoding process, make it possible to estimate the packet error rate with very low computational complexity. Finally, a feedback scheme is presented in which the slot access scheme is dynamically adapted according to the approximate analysis in order to minimize the packet error rate. The results indicate that the introduction of feedback can substantially improve the performance of frameless ALOH

On the Application of the Baum-Welch Algorithm for Modeling the Land Mobile Satellite Channel

Accurate channel models are of high importance for the design of upcoming mobile satellite systems. Nowadays most of the models for the LMSC are based on Markov chains and rely on measurement data, rather than on pure theoretical considerations. A key problem lies in the determination of the model parameters out of the observed data. In this work we face the issue of state identification of the underlying Markov model whose model parameters are a priori unknown. This can be seen as a HMM problem. For finding the ML estimates of such model parameters the BW algorithm is adapted to the context of channel modeling. Numerical results on test data sequences reveal the capabilities of the proposed algorithm. Results on real measurement data are finally presented.Comment: IEEE Globecom 201

Reliability-Latency Performance of Frameless ALOHA with and without Feedback

This paper presents a finite length analysis of multislot type frameless ALOHA based on a dynamic programming approach. The analysis is exact, but its evaluation is only feasible for moderate number of users due to the computational complexity. The analysis is then extended to derive continuous approximations of its key parameters, which, apart from providing an insight into the decoding process, make it possible to estimate the packet error rate with very low computational complexity. Finally, a feedback scheme is presented in which the slot access scheme is dynamically adapted according to the approximate analysis in order to minimize the packet error rate. The results indicate that the introduction of feedback can substantially improve the performance of frameless ALOH

Irregular Invertible Bloom Look-Up Tables

We consider invertible Bloom lookup tables (IBLTs) which are probabilistic data structures that allow to store keyvalue pairs. An IBLT supports insertion and deletion of key-value pairs, as well as the recovery of all key-value pairs that have been inserted, as long as the number of key-value pairs stored in the IBLT does not exceed a certain number. The recovery operation on an IBLT can be represented as a peeling process on a bipartite graph. We present a density evolution analysis of IBLTs which allows to predict the maximum number of key-value pairs that can be inserted in the table so that recovery is still successful with high probability. This analysis holds for arbitrary irregular degree distributions and generalizes results in the literature. We complement our analysis by numerical simulations of our own IBLT design which allows to recover a larger number of keyvalue pairs as state-of-the-art IBLTs of same size

Barcelona, de las barracas a los polígonos

El barraquismo surge como respuesta a la incapacidad de ciertas clases sociales a acceder a una vivienda digna. Es una problemática que muchas ciudades sufren o han sufrido a lo largo de la historia y que en muchas de ellas han marcado su crecimiento y su configuración actual. Barcelona fue una de esas ciudades que sufrió el fenómeno del barraquismo y que actualmente vuelve a sufrirlo. Estos asentamientos empezaron a surgir a finales del s.XIX y perduraron durante gran parte del s.XX, llegando a su mayor auge entre 1920 -1950. Las grandes inmigraciones que sufrió la ciudad sumada a la escasez de vivienda, los elevados precios y la incapacidad de construcción de viviendas por falta de recursos, provocaron que empezaran a surgir asentamientos de barracas por varias zonas de la ciudad. La problemática de las barracas no se llegó a solucionar hasta los años 50-60, cuando se empezó una construcción masiva de polígonos residenciales que abastecían la demanda de vivienda. Sin embargo, la construcción rápida, sin urbanización y a bajo coste tuvo consecuencias en la calidad constructiva de las edificaciones y las condiciones de vida que ofrecían a sus residentes. Por estos motivos, el objetivo del trabajo consiste en mostrar el fenómeno del barraquismo en esta época de la ciudad de Barcelona y su posterior realojo en los polígonos de vivienda, para comparar la mejora de condiciones de vida que ofrecían y analizar si fue la mejor opción posible.The shantytown arises as a response to the inability of certain social classes to access decent housing. It is a problem that many cities suffer or have suffered throughout history and that in many of them have marked their growth and their current configuration. Barcelona was one of those cities that suffered from the phenomenon of squatting and is currently suffering again. These settlements emerged at the end of the 19th century and lasted for a large part of the 20th century, reaching their peak between 1920 and 1950. The large immigration that the city suffered, added to the shortage of housing, the high prices and the inability to build houses due to lack of resources, caused shanty towns to begin to emerge in various areas of the city. The problem of the shacks was not solved until the 1950s and 1960s, when the massive construction of residential estates that met the demand for housing began. However, rapid construction, without urbanization and at low cost, had consequences on the constructive quality of the buildings and the living conditions offered to its residents. For these reasons, the objective of the work is to show the phenomenon of shantytowns in this period of the city of Barcelona and its subsequent relocation to housing estates, to compare the improvement in living conditions that they offer and to analyze if it was the best option. possible