Ivo Sousa

Realistic mobility modeling of pedestrian traffic in wireless networks

In this paper a new pedestrian mobility model for outdoor scenarios is presented. It captures realistic features like moving-in-groups, conscious traveling and smart traveling. The routing algorithm proposed within the model works under a step by step approach, leading users to their destination while, at the same time, using more attractable streets from a pedestrian point of view. The model concept is perfectly generic and applicable to any pedestrian outdoor scenario, provided that the street database and pedestrian traffic information is available. The mobility model was validated using Lisbons downtown as a case study. The output shows a high correlation between simulated and real data, thus validating the approach.

Full-duplex relaying in MIMO-OFDM frequency-selective channels with optimal adaptive filtering

In-band full-duplex transmission allows a relay station to theoretically double its spectral efficiency by simultaneously receiving and transmitting in the same frequency band, when compared to the traditional half-duplex or out-of-band full-duplex counterpart. Consequently, the induced self-interference suffered by the relay may reach considerable power levels, which decreases the signal-to-interference-plus-noise ratio (SINR) in a decode-and-forward (DF) relay, leading to a degradation of the relay performance. This paper presents a technique to cope with the problem of self-interference in broadband multiple-input multiple-output (MIMO) relays. The proposed method uses a time-domain cancellation in a DF relay, where a replica of the interfering signal is created with the help of a recursive least squares (RLS) algorithm that estimates the interference frequency-selective channel. Its convergence mean time is shown to be negligible by simulation results, when compared to the length of a typical orthogonal-frequency division multiplexing (OFDM) sequences. Moreover, the bit-error-rate (BER) and the SINR in a OFDM transmission are evaluated, confirming that the proposed method extends significantly the range of self-interference power to which the relay is resilient to, when compared with other mitigation schemes.

A smart scheme for relay selection in cooperative wireless communication systems

The performance of multiple-input multiple-output systems using spatial multiplexing can be degraded when the spatial information channels are correlated. This work proposes a solution to this problem, which is based on a cooperative wireless communication system. Within the cooperative system, the relay is selected either randomly or using the smart selection scheme, a simple and distributed approach proposed herein. These relay selection schemes are evaluated for several situations within a small cell environment, using a simulator that generates frequency-selective channel realizations. The simulation results show that the smart selection scheme yields high capacity gains close to the theoretical maximum gain.

MIMO channel capacity spatial distribution in a microcell environment

In this paper the spatial distribution of the channel capacity of Multiple Input Multiple Output (MIMO) wireless systems within a microcell scenario is studied. Based on the capacity location dependency, made clear by realistic simulation results, a segmentation of the cell area into high and low capacity regions is proposed. The Base Station (BS) and Mobile Stations (MSs) inter-antenna spacing impact on these regions is also investigated. The results suggest the most efficient ways to enlarge the high capacity region, providing a framework to optimize the design and deployment of MIMO systems.

Location Error Spatial Distribution in Urban Wireless Cellular Networks

In this work the spatial distribution of the location error in wireless cellular networks operating in an urban outdoor environment is studied. We assume signal strength based positioning methods that avoid additional network hardware costs and handset modifications, while approaching FCC requirements for emergency positioning. In order to cope with the computational burden associated with the required spatial discrimination of our analysis, we developed an efficient simulator that is capable of analyzing a comprehensive class of cost efficient location algorithms based on the received signal strength measurements made periodically by the mobile terminals in GSM and UMTS systems. The simulation results show that the key factors to achieve positioning accuracy are line-of-sight and homogeneous distribution of base stations in the vicinity of the mobile terminals, leading to the conclusion that the positioning error is location dependent. This conclusion motivates a reliability analysis based on the spatial segmentation of the location process. In the same scenario we estimate the a posteriori location probabilities providing a framework for the further development of reliable methodologies for the tracking of mobile terminals.

Coexistence of DC and CSMA in SRD channel access and resilience to LTE interference: A simulator-based analysis: Coexistence of DC and CSMA in SRD channel access and resilience to LTE interference: A simulator-based analysis

Funding information Instituto de Telecomunicações; Fundação para a Ciência e a Tecnologia (FCT), Grant/Award Number: UID/EEA/50008/2013 Abstract The foreseen increased use of short-range devices (SRDs) will boost the competition for radio channel access in license-exempt frequency bands. Therefore, it is important to find out the most efficient SRD configurations in terms of their performance in high-contention scenarios; moreover, it is crucial to ensure that SRD networks do not impair the radio systems that operate in neighboring licensed spectrum, and vice versa. This paper addresses the previous issues by simulating a building automation application scenario, where 2 channel access mechanisms, namely duty cycling (DC) and carrier sense multiple access (CSMA), are evaluated independently and in coexisting scenarios, and, also, in the presence of a Long-Term Evolution (LTE) user equipment. The CSMA protocol analysis shows that very high or very low transmission powers decrease its performance, and thus, either this parameter has to be calibrated or the gateways location has to be adjusted; for the DC protocol, its performance is only affected by the number of gateways within the SRD network, which should be as high as possible. Regarding the coexistence of the DC and CSMA schemes, the results show that CSMA-based SRDs can successfully operate in the presence of a significant number of DC-based SRDs, whereas the contrary is not true. Lastly, it is proven that an LTE user equipment may harm the SRD network, although this effect can be mitigated by adjusting the SRDs transmission power; furthermore, the SRDs interference on LTE systems is found to be negligible.

QoE-Aware Scheduling Algorithm for Adaptive HTTP Video Delivery in Wireless Networks

In the last years, the video content consumed by mobile users has increased exponentially. Since mobile network capacity cannot be increased as fast as required, it is crucial to develop intelligent schedulers that allocate radio resources very efficiently and are able to provide a high Quality of Experience (QoE) to most of the users. This paper proposes a new and effective scheduling solution—the Maximum Buffer Filling (MBF) algorithm—which aims to increase the number of satisfied users in video streaming services provided by wireless networks. The MBF algorithm uses the current buffer level at the client side and the radio channel conditions, which are reported to the network by the client, as well as the bitrate of the requested video segment. The proposed scheduling strategy can also fulfill different satisfaction criteria, since it can be tuned to maximize the numbers of users with high QoE levels or to minimize the number of users with low QoE levels. A simulation framework was developed, considering a Long Term Evolution (LTE) scenario, in order to assess the performance of the proposed scheduling scheme and to compare it with other well-known scheduling solutions. The results show the superior performance achieved by the proposed technique, in terms of the number of satisfied and unsatisfied users.

An Efficient Visibility Prediction Framework for Free-Space Optical Systems

Free-Space Optical (FSO) systems are greatly affected by fog conditions, which cause very high attenuation over considerable amounts of time. Therefore, some models have been adopted by the designers of FSO links, which take into account visibility values in order to compute the attenuation due to fog. However, the visibility distribution for an FSO link site may not be available. In this paper we propose a simple but reliable framework that estimates the visibility distribution and has a single statistical input: the number of foggy hours per year. The proposed tool is evaluated using real visibility data from a large variety of sites with different climates within the Portuguese territory. The results show that the predicted visibility distributions considerably agree with the real data for all sites, as well as they are robust for cases where the available fog statistics are not the most accurate, proving that the simple metric proposed herein is an easy-to-use, valid and robust tool to take into account when designing FSO systems.

Full-duplex MIMO and PLNC for the Y-network

This paper considers a multi-way wireless network with three terminals which want to exchange or share data with the help of a relay: each terminal has some information that wants to transmit to the other two. The traditional way of doing this exchange either involves time-domain multiplexing (TDMA) or dedicated frequency-domain disjoint channels, at the expense of high bandwidth inefficiency. With the advent of network coding, and later physical-layer network coding, it became possible to reduce the number of time slots required to exchange the information between all the terminals. Moreover, using multiple-input multiple-output (MIMO) terminals and relays, the time-usage efficiency can be further boosted by transferring the burden from the time-domain to the spatial-domain via spatial multiplexing. This paper proposes the concatenation of the aforementioned techniques along with loopback interference cancellation, which recently became a central topic for the next generation of the physical-layer of wireless communications. The paper shows a protocol and techniques that allow all the information exchange between terminals to be reduced from the 6 time-slots, required in traditional TDMA, to one time-slot only, provided that the information packets are not too short. The error performance of this system is shown by means of simulation using MIMO Rayleigh fading channels.

Enhancing MIMO channel capacity through the use of cooperation in realistic microcell environments

This paper considers the use of a cooperative wireless communication system in order to enhance Multiple-Input Multiple-Output (MIMO) channel capacity. Within the cooperative system, a relay is selected by exploiting the MIMO spatial multiplexing feature in a simple and distributed approach, aiming at selecting the partner which yields the best MIMO capacity. The study is performed for a realistic microcellular environment and it is envisioned for technology that is already available on the market, i.e., the performance of the MIMO system is assessed using a simulator with a real Manhattan-like test scenario, with realistic radio propagation models that make use of Long Term Evolution (LTE) and Bluetooth technologies and with a realistic pedestrian mobility model. The simulation results show that the cooperative system accomplishes the goal of improving the overall MIMO channel capacity in microcell environments.