Browsing by Author "Caldeirinha, Rafael F. S."
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- A 2D ray-tracing based model for wave propagation through forests at micro-and millimeter wave frequenciesPublication . Leonor, Nuno R.; Sanchez, Manuel Garcia; Fernandes, Telmo; Caldeirinha, Rafael F. S.This paper proposes the extension of a 2-D ray-tracing-based model for radiowave propagation in the presence of trees and vegetation areas to include real-sized trees and outdoor forest scenarios. The original propagation model proved to be suitable to characterize the electromagnetic behavior in the presence of indoor tree formation scenarios, despite some limitations found when applied to real-sized trees. In addition, the original propagation model requires the prior knowledge of the trees’ re-radiation function to extract the relevant propagation input parameters, which is not always possible to obtain in outdoor scenarios. Therefore, an empirical method to extract the relevant input propagation parameters based on simple measurements is proposed. The performance of the proposed propagation model extension is extensively assessed in both the line-of-trees and tree formation scenarios, including various (and mixed) species, both in- and out-of-leaf foliation states, and at three signal frequencies. Finally, depending on the type of scenario, a benchmark between the proposed propagation model and both the radiative energy transfer (RET) and discrete RET (dRET) models, for line-of-trees and tree formation, respectively, is presented.
- 3-D Mechanically Tunable Square Slot FSSPublication . Ferreira, David; Cuinas, Inigo; Caldeirinha, Rafael F. S.; Fernandes, TelmoWe introduce an innovative 3-D mechanically tunable frequency selective surface (FSS), which is inspired by the classical flat square slot FSS. The proposal improves the performance of classical 2-D FSS designs, and it also represents a novel method of achieving mechanical frequency tuning, despite other 3-D designs that consist of a collection of stacked 3-D layers exist. In our proposal, the rotation of an inner element provides tuning capability to the squared cell structure, consisting of metallic grids with a movable inner element. An aluminum prototype was built, which can be tuned from 2.4 to 4 GHz, and also compared its measured performance and numerical simulations. Some characteristics of the proposed structure are the rejection level at main polarization, up to 20 dB, and the maximum frequency sweep of approximately 50% of the fundamental frequency. The prototype showed a stable frequency response for angles of incidence up to 45°. Since results are in good agreement with simulations, we provide parametric equations to design 3-D structures at desired frequencies.
- All-digital reconfigurable STDCC radar baseband implementation in FPGAPublication . Duarte, Luís; Ribeiro, Carlos; Alves, Luís N.; Caldeirinha, Rafael F. S.This paper reports the architecture of an all-digital Swept Time-Delay Cross-Correlator (STDCC) baseband. Until recently, the sliding correlator technique has been mainly em-ployed for sounding the radio propagation channel. However, recent benchmarks have shown promising results in target detection context when compared to commercially available solutions. STDCC takes advantage of the sliding correlation properties of Pseudo-Noise (PN) sequences. Therefore, this paper presents the baseband generation for this new radar technique with on-the-fly sequence tuning using a Field-Programmable Gate Array (FPGA). The reconfigurable STDCC radar baseband generates both PN sequences digitally and requires a low-cost ADC to acquire the time dilated result. At the end, the proposed architecture is evaluated regarding resource usage efficiency and then the radar performance will be discussed in terms of the all-digital PN sequence spectrum and the real-time slide correlation. Our analysis confirmed a strong correlation between both sequence length and sampling frequency with radar detectable distance.
- Characterization of wireless propagation through traditional Iberian brick wallsPublication . Ferreira, David; Caldeirinha, Rafael F. S.; Fernandes, Telmo R.; Cuinas, InigoThis paper presents the wireless transmission properties for brick walls with different thicknesses and facade finish coatings. The ceramic hollowed bricks under study are traditionally employed in the Iberian residential construction, where the 11, 15 and 20 cm thicknesses are most common in indoor and outdoor walls. For each brick dimension, three different prototypes were manufactured varying in the type of wall finish, i.e.: naked brick, smooth painted plaster and rough painted plaster. The prototypes were measured in an anechoic chamber at frequencies ranging from 680MHz up to 10GHz. Results demonstrate that the brick wall internal heterogeneity, as well as the type of finish, significantly influence the frequency response of the walls.
- Electronically Reconfigurable FSS-Inspired Transmitarray for 2-D BeamsteeringPublication . Reis, João R.; Caldeirinha, Rafael F. S.; Hammoudeh, Akram; Copner, NigelA novel electronically reconfigurable transmitarray (TA) with 2-D beamsteering capability is presented in this communication. The proposed structure, inspired on frequency selective surfaces loaded with varactor diodes, allows the phase range of each TA element to be individually controlled enabling an automated steering of the main lobe of an original antenna pattern, in both elevation and azimuth planes (2-D beamsteering). This has been demonstrated on a 5 × 5 unit-cell stacked structure with active feeding, coupled to the aperture of a standard gain horn antenna. A complete electromagnetic study using CST Microwave Studio is presented to evaluate and characterize the TA elements and the effect the proposed feeding network has on the structure's behavior. Following initial simulations, a prototype of the active TA has been characterized. Automated antenna beamsteering with ranges up to Az = 28° and El = 26° and 1° of angular resolution, is achieved by means of electromagnetic simulations and validated against experimental results at 5.2 GHz.
- Enabling spatial diversity and beamsteering with reduced RF-chains using reconfigurable transmitarraysPublication . João R. Reis; Caldeirinha, Rafael F. S.; Fernandes, Telmo R.; Hammoudeh, AkramThis manuscript introduces a new vision on the implementation of spatial diversity with beamsteering capability, by suppressing the typical beamforming networks of antenna phased arrays and replace them by Reconfigurable Transmitar- rays. Consequently, the radio frequency components, i.e. RF- chains that compose such systems, were replaced by a device with the capability to perform two-dimensional beamsteering relying on single antenna source, hence reducing the number of associated RF hardware in comparison with traditional phased array systems. By spatially distributing side-by-side more than one device, spatial diversity with beamsteering is enabled with an estimated reduction of 1:8 in the number of associated RF-chains. This new concept clearly demonstrates its merit by directly reducing the implementation costs„ RF-chain components and increasing the energy efficiency, specially in larger systems.
- Input parameter extraction method for point scatterer formulation in vegetation media at millimetre-wave frequenciesPublication . Leonor, Nuno R.; Caldeirinha, Rafael F. S.; Sánchez, Manuel García; Fernandes, TelmoAn empirical method to extract the relevant point scatterer formulation input parameters for appropriate radio coverage simulation in vegetation areas, is proposed. While the original propagation model would require the prior knowledge of the complete tree(s) re-radiation function(s) to extract the relevant propagation input parameters, the empirical method proposed herein is based only on two simple measurements. Re-radiation measurements of several specimens of Thuja pelicata and Ficus benjamina trees at two frequencies have been used to validate the proposed simplified extraction method. The proposed empirical model was then used to characterise the propagation phenomena of various trees arranged in four different scenarios. Subsequently, directional spectra measurements performed inside an anechoic chamber at both 20 and 62.4 GHz were used to assess the empirical model performance, while predicting the received signal level arriving from various directions. A relatively good overall model performance when applied to tree formations was obtained which, coupled with the simplified parameter extraction proposed, makes it suitable to be integrated in commercial simulation platforms and/or as input data to other propagation models that may require the prior knowledge of the individual tree re-radiation functions.
- A mm Wave solution to provide wireless Augmented Reality in classroomsPublication . Gomes, Rodolfo; Sismeiro, Luis; Ribeiro, Carlos; Sanchez, Manuel G.; Hammoudeh, Akram; Caldeirinha, Rafael F. S.This paper presents a very high throughput wireless data transmission solution for Augmented Reality (AR) Head Mounted Devices (HMDs) in the 60 GHz band. Its feasibility is assessed in an Orthogonal Frequency Division Multiplexing (OFDM) downlink communication towards five User Equipment (UE) devices, placed at different locations inside an indoor classroom environment scenario. Key Performance Indicators (KPIs) as Error Vector Magnitude (EVM), Signal-to-Noise Ratio (SNR), and path loss are considered for Quality of Service (QoS) assessment. Experimental results demonstrate the reliability of the proposed mmWave system, where a data rate of 312.5 Mbps is achieved over distances of 1, 2.4 and 4.1 m, regardless the UE position.
- Simplified RET model derived from path loss and directional spectrum measurements in vegetation media at 11.2 and 20 GHzPublication . Caldeirinha, Rafael F. S.; Fernandes, Telmo; Richter, Jürgen; Al-Nuaimi, Miqdad O.This study presents a simplified radiative energy transfer (RET) model derived from path loss and directional spectrum measurements in vegetation media at 11 and 20 GHz. Thus, a simplified extraction procedure for the inputs parameters based on the method foreseen by the international telecommunications union - recommendation (ITU-R) P.833-8, however for isolated vegetation volumes, is proposed. Results for specific measurements aimed at the extraction of the RET model parameters are subsequently presented and discussed. The extraction method relies on a limited set of propagation measurements to find and optimise the RET input parameters. Specific measurements of the received signal directional profile are used to show the applicability of the method. This parameter evaluation method is tested and assessed based on the received signal directional profile measurements performed in Populous trees at 11.2 and 20 GHz.
- Towards 5G : performance evaluation of 60 GHz UWB OFDM communications under both channel and RF impairmentsPublication . Gomes, Rodolfo; Hammoudeh, Akram; Caldeirinha, Rafael F. S.; Al-Daher, Zaid; Fernandes, Telmo; Reis, JoãoDetailed analysis on the impact of RF and channel impairments on the performance of Ultra-Wideband (UWB) wireless Orthogonal Frequency Division Multiplexing (OFDM) systems based on the IEEE 802.15.3c standard, for high data-rate applications using the 60 GHz millimetre frequency band is presented in this paper. This frequency band, due to the large available bandwidth is very attractive for future and 5G wireless communication systems. The usage of OFDM at millimetre-wave (mmWaves) frequencies is severely affected by non-linearities of the Radio Frequency (RF) front-ends. The impact of impairments is evaluated, in terms of some of the most important key performance indicators, including spectral efficiency, power efficiency, required coding overhead and system complexity, Out-Of-Band Emissions (OOBEs), Bit Error Rate (BER) target and Peak Signal-to-Noise Ratio (PSNR). Additionally, joint distortion effects of coexisting Phase-Noise (PN), mixer IQ imbalances and Power Amplifier (PA) non-linearities, on the performance degradation of a mmWave radio transceiver, combined with various multipath fading channels, are investigated. Subsequently, the power efficiency of the system is evaluated by estimating values of the PA Output-Power-Backoff (OBO) needed to meet the requirements for the Transmit Spectrum Mask (TSM) and BER target. Finally, a comparison of the system overall performance between uncoded and coded OFDM systems combined with Quadrature Amplitude Modulations (16 and 64 QAM) and its maximum operable range are evaluated by transmitting a Full HD uncompressed video frame under five different RF impairment conditions over a typical LOS kiosk 60 GHz IEEE channel model.