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Projeto de investigação
Instituto de Telecomunicações
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Publicações
In-Band Full-duplex Residual Self-interference Approximation in Multi-tap Delay Fading Channels
Publication . Abusabah, Ayman T.; Irio, Luís; Oliveira, Rodolfo; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 Telecomunicações
Residual self-interference (SI) is primarily a key challenge when designing In-Band Full-duplex (IBFDX) wireless systems. Channel estimation errors are one of the major causes of the residual SI. The SI channel is composed by multiple fading taps which makes the characterization of the residual SI more challenging as multiple copies of the transmitted signal, with variable delays and gains, are eventually aggregated at the receiver. In this paper, we derive an approximation for the distribution of the residual SI power in multi-tap delay fading channels. In particular, we show that under specific conditions the multi-tap fading channel can be represented by a summation of non-identical independent gamma distributions. In a further step, we approximate the summation of the gamma distributions using the Welch-Satterthwaite equation, obtaining a closed form expression for the distribution of the residual SI power. The accuracy of the theoretical approach is evaluated through simulation results. The similarity comparison between simulated data and the proposed model indicates a high accuracy of the adopted approximation when considering low fading uncertainty associated to the taps and low estimation errors. On the other hand, the accuracy of the approximation slightly decreases for higher uncertainty fading scenarios and for higher estimation errors. However, as a final remark, we highlight that the results computed with the model are close to the simulated ones and for most of the applications the model's error can be negligible.
LoRaWAN Performance evaluation
Publication . Figueiredo, Tiago Afonso Antunes de; Bernardo, Luis
The Internet of Things (IoT) is expected to grow in the upcoming years. LoRaWAN is one
promising Low Power Wide Area Network (LPWAN) standard proposed for IoT widely
adopted across the world. It runs on unlicensed spectrum and was designed to carry
sporadic traffic.
This dissertation analyses the performance of LoRaWAN in extreme conditions, where
peak traffic loads occur in the network. It starts by evaluating the Network Simulator 3 (ns-
3) LoRaWAN module, identifying and correcting their implementation. In a second phase,
it evaluates the limitations of the class A LoRaWAN access protocol during synchronized
peaks of traffic, and proposes a new access algorithm to improve the reliability and reduce
the latency.
Simultaneous Wireless Information and Power Transfer in 5G communication
Publication . Rajaram, Akashkumar; Dinis, Rui; Jayakody, Dushantha
Green communication technology is expected to be widely adopted in future generation
networks to improve energy efficiency and reliability of wireless communication network.
Among the green communication technologies,simultaneous wireless information and
power transfer (SWIPT) is adopted for its flexible energy harvesting technology through
the radio frequency (RF) signa lthati sused for information transmission. Even though
existing SWIPT techniques are flexible and adoptable for the wireless communication
networks, the power and time resources of the signal need to be shared between infor-
mation transmission and RF energy harvesting, and this compromises the quality of the
signal. Therefore,SWIP Ttechniques need to be designed to allow an efficient resource
allocation for communication and energy harvesting.
The goal oft his thesisis to design SWIP Ttechniques that allow efficient,reliable and
secure joint communications and power transference. A problem associated to SWIPT
techniques combined with multi carrier signals is that the increased power requirements
inherent to energy harvesting purposes can exacerbate nonlinear distortion effects at the
transmitter. Therefore, we evaluate nonlinear distortion and present feasible solutions to
mitigate the impact of nonlinear distortion effects on the performance.Another goal of
the thesisis to take advantage of the energy harvesting signals in SWIP Ttechniques for
channel estimation and security purposes.Theperformance of these SWIPT techniques is
evaluated analytically, and those results are validated by simulations. It is shownthatthe
proposed SWIPT schemes can have excellent performance, out performing conventional
SWIPT schemes.
Portable Video Streaming Network
Publication . Santos, Júlio Martins; Bernardo, Luís
This dissertation addresses the challenge of developing a video call system
capable of supporting both Android mobile devices and fixed computers. Addi tionally, it analyses the quality of video achieved and its variation in the presence
of network bandwidth and packet loss constraints.
A prototype of a video call system was implemented using a web application
and the Web Real-Time Communication (WebRTC) library. Clients use WebRTC
to stream video over a Traversal Using Relays around NAT (TURN) relay server,
allowing them to send video to any terminal connected to the Internet. Signalling
was implemented using WebSockets and a Node.js server.
A quality testing prototype was also implemented, which supports sending
pre-recorded videos and capturing and storing video recordings at the sender and
receiver. The Video Multimethod Assessment Fusion (VMAF) metric was used as
the main video quality metric, based on the comparison between the transmitted
and received videos.
The quality of a video encoded using the open source video encoder VP8
was analysed in constrained network setups. The results measured the video
quality degradation and percentage of received frames, showing that the system
is resilient to some bandwidth strangulation and packet loss, although with a
noticeable video quality degradation.
Distribution of the Residual Self-Interference Power in In-Band Full-Duplex Wireless Systems
Publication . Irio, Luis; Oliveira, Rodolfo; DEE2010-A1 Telecomunicações; DEE - Departamento de Engenharia Electrotécnica e de Computadores; Institute of Electrical and Electronics Engineers (IEEE)
This paper derives the distribution of the residual self-interference (SI) power in an analog post-mixer canceler adopted in a wireless in-band full-duplex communication system. We focus on the amount of uncanceled SI power due to SI channel estimation errors. Closed form expressions are provided for the distribution of the residual SI power when Rician and Rayleigh fading SI channels are considered. Moreover, the distribution of the residual SI power is derived for low and high channel gain dynamics, by considering the cases when the SI channel gain is time-invariant and time-variant. While for time-invariant channels the residual SI power is exponentially distributed, for time-variant channels the exponential distribution is not a valid assumption. Instead, the distribution of the residual SI power can be approximated by a product distribution. Several Monte Carlo simulation results show the influence of the channel dynamics on the distribution of the residual SI power. Finally, the accuracy of the theoretical approach is assessed through the comparison of numerical and simulated results, which confirm its effectiveness.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UID/EEA/50008/2019