Planning and Optimisation for the Coexistence of Mobile and Wireless Networks Towards Long Term Evolution

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Publications

Experimental Characterization of Wearable Antennas and Circuits for RF Energy Harvesting in WBANs

Publication . Saraiva, Henrique Morais; Borges, Luís M.; Pinho, Pedro; Gonçalves, Ricardo; Chavez-Santiago, Raul; Barroca, Norberto; Tavares, Jorge; Gouveia, Paulo T.; Carvalho, Nuno Borges; Balasingham, Ilangko; Velez, Fernando J.; Loss, Caroline; Salvado, Rita

Field trials have been performed in Covilhã to identify the spectrum opportunities for radio frequency (RF) energy harvesting through power density measurements from 350 MHz to 3 GHz. Based on the identification of the most promising opportunities, a dual-band printed antenna was conceived, operating at GSM bands (900/1800), with gains of 1.8 and 2.06 dBi, and efficiency varying from 77.6 to 82%, for the highest and lowest operating frequency bands, respectively. In this paper, guidelines for the design of RF energy harvesting circuits and choice of textile materials for a wearable antenna are briefly discussed. Besides, we address the development and experimental characterization of three different prototypes of a five-stage Dickson voltage multiplier (with and without impedance matching circuit) responsible for RF energy harvesting. All the three prototypes (1, 2 and 3) can power supply the sensor node for RF received powers of 2 dBm, -3 dBm and -4 dBm, and conversion efficiencies of 6, 18 and 20%, respectively.

2014-05Conference object

Open access

A Double Stage Random Access Scheme for Decentralized Single Radio Cognitive Networks

Publication . Oliveira, Rodolfo; Borges, Luís M.; Velez, Fernando J.

This work proposes a new scheme to coordinate the medium access of single-radio unlicensed users in a decentralized cognitive radio network. The proposed solution is based on two different stages. Unlicensed users randomly define the medium access sequence during the first stage and part of the second one. Then the nodes simply transmit their packets according to the reserved sequence. The performance of the proposed scheme is theoretically characterized in terms of the throughput achieved by unlicensed users and validated through simulation. Since a random access mechanism is used in the both stages, we also compare the performance of our proposal with a pure Slotted Aloha access scheme and an improved version of it. By comparing their performance, we conclude that the proposed scheme exhibits significant gains in terms of the throughput achieved by unlicensed users, and it can be recommended as a viable solution for future decentralized single radio cognitive networks.

2013-08Conference object

Open access

Frame Capture and Reliability Based Decider Implementation in the MiXiM IEEE 802.15.4 Framework

Publication . Borges, Luís M.; Velez, Fernando J.; Barroca, Norberto; Lebres, António

The task of properly modelling the physical (PHY) layer constitutes the most challenging endeavor in wireless networks simulation. Unfortunately, today, the majority of the wireless sensor network (WSN) simulators consider a simple model for the PHY frame reception, which does not account for emerging research on the frame capture (FC) effect. In this paper, we present enhancements for the PHY layer model for the IEEE 802.15.4 standard employed in the MiXiM framework, to account for the FC effect within WSN-based simulations. These improvements are as follows: i) proposal of a formulation for the PHY layer packet reception based on a reliability concept, identified as the Enhanced Reliability Decision Algorithm, which guarantees the delivery of a packet received by the PHY layer to the medium access control (MAC) layer, with a certain value for the reliability (0.9 and 0.99); ii) different frame overlapping scenarios, and iii) different values for the thresholds to decide frame recovery. The work includes the description, implementation and performance evaluation of the proposed decision algorithm, jointly with the FC effect, in the MiXiM framework simulator, for basic MAC and scheduled channel polling (SCP) MAC protocols. Based on the simulation results, the proposed approach can significantly improve simulation accuracy and provide a PHY decision algorithm that guarantees, with a certain reliability, the delivery of frames to the MAC layer.

2014-03Journal article

Open access

A two-phase contention window control scheme for decentralized wireless networks

Publication . Borges, Luís M.; Velez, Fernando J.; Oliveira, Rodolfo

Most studies on performance of IEEE 802.11 distributed coordination function (DCF) have proved that the binary exponential backoff (BEB) algorithm suffers from low throughput, long transmission delays and low transmission reliability, for a high traffic load. In this paper, we propose a two-phase contention window (TPCW) access mechanism that enhances the aggregate throughput and transmission reliability while decreasing the medium access delay. In addition, this scheme aims at being computationally simple. This work characterizes the performance of the TPCW mechanism for different parameterization values. An analytical model is proposed for the TPCW access mechanism, which characterizes the frame transmission reliability, the total transmission delay and the aggregate throughput. The validity of our analytical model is verified through extensive simulations. By comparing the performance results, we conclude that the proposed scheme can significantly enhance IEEE 802.11 in terms of frame transmission reliability, total transmission delay and aggregate throughput.

2014-04Conference object

Open access

Cost/revenue performance in an IMT-Advanced scenario with Spectrum Aggregation over non-contiguous frequency bands

Publication . Acevedo Flores, Jessica Elizabeth; Velez, Fernando J.; Cabral, Orlando; Robalo, Daniel Luís Silveira; Holland, Oliver; Aghvami, A. Hamid; Meucci, Filippo; Mihovska, Albena Dimitrova; Prasad, Neeli R.; Prasad, Ramjee

This paper determines the cost/revenue performance of a mobile communication system in an IMT-Advanced scenario with integrated Common Radio Resource Management (iCRRM). The iCRRM performs classic CRRM functionalities jointly with Spectrum Aggregation (SA), being able to switch users between non-contiguous frequency bands. The SA scheduling is obtained with an optimized General Multi-Band Scheduling (GMBS) algorithm with the aim of cell throughput maximization. In particular, we investigate the dependence of the throughput on the cell coverage distance for the allocation of users over the 2 and 5 GHz bands for a single operator scenario under a constant average Signal to Interference-plus-Noise Ratio (SINR), for the same type of Radio Access Technology and both frequency bands. The operator has the availability of a non-shared 2 GHz band and has access to part (or all) of a shared frequency band at 5 GHz. An almost constant gain near 30 % was obtained with the proposed optimal solution compared to a system where users are first allocated in one of the two bands and later not able to handover between the bands. It is shown that the profit in percentage terms decreases as the cell radius increases. These results allow for evaluating the impact of the revenue from the channel in the total revenue and in the profit, defined as the difference between revenues and costs, in percentage. Maximum profits of about 1270, 585 and 240 % have been obtained for prices of 0.10, 0.05 and 0.025 €/MByte, respectively, when iCRRM is employed, while profits of 990, 440, and 170 % have been reached with no iCRRM, i.e., simple CRRM. Finally, an energy efficiency strategy is proposed and analyzed, showing that there is significant transmission power saving potential through the opportunistic reallocation scheme.

2014-05Conference object

Open access