COGNITIVE RADIO TRANSCEIVER DESIGN FOR ENERGY EFFICIENT DATA TRANSMISSION

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Publications

IEEE 802.15.4 MAC layer performance enhancement by employing RTS/CTS combined with packet concatenation

Publication . Barroca, Norberto; Borges, Luís M.; Velez, Fernando J.; Chatzimisios, Periklis

IEEE 802.15.4 Medium Access Control (MAC) layer does not include the Request-To-Send/Clear-To-Send (RTS/CTS) handshake mechanism, in order to overcome the hidden node problem that affects Wireless Sensor Networks (WSNs). In this paper we propose and analyse the use of RTS/CTS in IEEE 802.15.4 for the nonbeacon-enable mode. The proposed solution shows that by considering the RTS/CTS mechanism combined with packet concatenation we improve the network performance in terms of maximum throughput, minimum delay and bandwidth effciency. In IEEE 802.15.4 with RTS/CTS, the backoff procedure process is not repeated for each data packet sent unlike the basic access mode of IEEE 802.15.4, but only for each RTS/CTS set. Therefore, the channel utilization is maximized by decreasing the deferral time period before transmitting a data packet. Our work introduces an analytical model capable of accounting the retransmission delay and the maximum number of backoff stages. The successful validation of our analytical model is carried out by comparison against simulation results by using the OMNeT++ simulator.

2014-06Conference object

Open access

Extending the LTE-Sim Simulator with Multi-Band Scheduling Algorithms for Carrier Aggregation in LTE-Advanced Scenarios

Publication . Robalo, Daniel; Velez, Fernando J.; Paulo, Rui R.; Piro, Giuseppe

Carrier Aggregation (CA) has been proposed by 3GPP LTE-Advanced to meet or even exceed IMT-Advanced systems enhanced peak data rates requirements. In its rationale, multiple Component Carriers (CC) can be flexibly aggregated so that user equipment can access a total bandwidth of up to 100 MHz. As each CC has the same structure as the one from LTE R8, CA does not require notable changes in the LTE physical layer structure. Nevertheless, the way radio resources are allocated to mobile users in CA scenarios is still an hot research topic and the availability of an open source tool modelling such kind of feature is highly demanded in both academia and industry contexts. The present contribution is three-folded. First, it presents an open source and freeware extension of the well-known LTE-Sim simulator, which implements CA functionalities. Second, it also proposes an implementation of multi-band scheduling strategies able to optimally distribute radio resource among mobile users in the presence of multiple CCs and strict Quality of Service (QoS) constraints. Third, computer simulations have been also carried out to demonstrate the effectiveness of the aforementioned contributions. In particular, simulation results show the capacity improvements achieved by the proposed Enhanced Multi Scheduler against systems without CA, considering values of the bandwidth per component carrier of 5 and 20 MHz, in terms of average cell packet loss, delay, goodput and spectral efficiency.

2015-05Conference object

Open access

LTE radio and network planning: Basic coverage and interference constraints

Publication . Velez, Fernando J.; Robalo, Daniel; Acevedo Flores, Jessica

In the cellular planning process, the UL and DL the values from carrier-to-noise-plus-interference ratio (CNIR) from/at the mobile station are very important parameters. From a detailed analysis of its variation with the coverage and reuse distances for different values of the Chanel Quality Indicator (CQI) and given empirical propagation models, an evaluation of the possible range for the reuse pattern is performed for the DL. By considering the CQI and reference CNIR requirements recommended by 3GPP, DL peak bit rates along with the Transport Block Size (TBS) assumed for single stream and bandwidth of 5 MHz, physical and supported throughputs are analysed. These formulations shows the clear decrease of the supported throughput for the longest coverage distances in the LTE 2.6 GHz band, a behaviour that is not so clear at 800 MHz, and gives useful indications to the optimization of the use of different frequency bands in the optimization of carrier aggregation between two different bands in LTE-A scenarios.

2015-11Conference object

Open access

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

Experimental Characterization of WSNs Applied to Swarms of Aquatic Surface Drones

Publication . Velez, Fernando J.; Nadziejko, Aleksandra K. N.; Christensen, Andersen; Oliveira, Sancho; Rodrigues, Tiago; Costa, Vasco; Duarte, Miguel; Silva, Fernando; Gomes, Jorge

ANCAD project aims at developing technologies and communication protocols for swarms of aquatic inexpensive surface drones. The goal is to perform maritime tasks such as sea border patrolling or environmental monitoring, keeping the cost of the drones low. The exchange of information within the swarm is essential for the success of the mission. The most recent solution for control and communications within the current prototypes are supported by Raspberry Pi 2 and XBee-PRO S1 allowing for low power consumption while expanding the range of transmission. Field trial results enabled to verify the potential of the proposed solution, in terms of coverage range and multi-hop capabilities, in actual maritime scenarios.

2015-09Conference object

Open access