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Projeto de investigação
New RAN TEchniques for 5G UltrA-dense Mobile networks
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Publicações
The Importance of Repetitions in Ultra-Dense NB-IoT Networks
Publication . Abu Sabah, Ayman T.; Rahman, Md Arifur; Oliveira, Rodolfo; Flizikowski, Adam; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 Telecomunicações; Institute of Electrical and Electronics Engineers (IEEE)
This letter investigates the influence of the number of repetitions adopted in the NB-IoT standard to increase cellular coverage. We characterize the SINR in both uplink and downlink channels of ultra-dense networks, which is then used to derive the coverage probability and the NB-IoT’s capacity. The performance results show the effectiveness of the number of repetitions to reduce the block error rate for different densities of transmitters.
Interference Distribution for Directional Beamforming Mobile Networks
Publication . Abusabah, Ayman T.; Oliveira, Rodolfo; DEE - Departamento de Engenharia Electrotécnica e de Computadores; Institute of Electrical and Electronics Engineers (IEEE)
In this paper, we model the aggregate interference power in directional beamforming mobile networks. The work considers the random waypoint model to describe the mobility of the nodes and adopts directional beamforming for communication. The major contribution of this paper is the statistical characterization of the aggregate interference caused by directional beamforming transmissions of mobile interferers to a given node positioned at a reference point. The analysis assumes Rayleigh and Rician small-scale fading channels, a distance-based path-loss large-scale fading model, and a three gain levels sectored antenna model. The quality of the proposed approximations has been confirmed through various simulations for different mobility scenarios, channel conditions, and beamforming parameters, highlighting the effect of directional communications along with mobility on aggregate interference. To demonstrate the practical application of the work, we use two different estimators for the interference characterization. The results confirm the effectiveness of the estimators even when adopting a small set of samples.
Increasing Reliability on UAV Fading Scenarios
Publication . Viana, Joseanne; Madeira, João; Nidhi; Sebastião, Pedro; Cercas, Francisco; Mihovska, Albena; Dinis, Rui; Faculdade de Ciências e Tecnologia (FCT); DEE - Departamento de Engenharia Electrotécnica e de Computadores; Institute of Electrical and Electronics Engineers (IEEE)
Unmanned aerial vehicles (UAVs) are the next technology to be incorporated into a telecommunications network to improve command and control on a large scale in both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. However, there is still room for improvement in terms of reliability. This paper investigates Constant Packet Combining (CPC) and Adaptive Packet Combining (APC) techniques applied to Unmanned Aerial Vehicle (UAV) communication in the presence of large-scale fading, where the channels are subject to sudden degradation for long periods due to obstructions. We use Single Carrier (SC) Frequency Domain Equalization (FDE) combined with the Iterative Block Decision-Feedback Equalizer (IB-DFE) to handle command and control messages mapped for UAV use cases. We present closed-form equations for the equalization design as well as the performance parameters such as Bit Error Rate (BER), the Packet Error Rate (PER), the throughput, the retransmissions amount, the goodput (the transmission rate without the retransmissions quantity), and the outage probability. Then, we analyze the system performance using correlated, independent, and equal channels. There is a trade-off between the overall available power, throughput, and reliability. For instance, more retransmissions result in higher reliability, power consumption and lower goodputs (effective data rates). CPC validates the transmission system and confirms the improvement of BER and PER parameters without energy efficiency optimization. APC is appealing because it can reduce the number of retransmissions for all channels used with the advantage of meeting energy efficiency requirements by adapting the overall power to the scenario experienced by the UAV.
Self-interference in Multi-tap Channels for Full-Duplex Wireless Systems
Publication . Sabah, Ayman T. Abu; Oliveira, Rodolfo; Irio, Luis; 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 residual SI. Consequently, a deeper understanding of the impact of the channel effects on the residual SI becomes indispensable. In this paper, we investigate the influence of multiple taps on the residual SI power of IBFDX systems. We first formulate the effect of having independent taps on the residual SI power mathematically. The derivations take into account the amount of interference cancellation on each tap by considering phase and amplitude estimation coefficients. We conclude that the increase in the number of taps always leads to an additive effect of the residual power. Such findings are shown mathematically and also reported in different results obtained by simulation. Finally, we compare the distribution of the residual SI power with different known distributions, concluding that Weibull and Gamma distributions are the closest ones in terms of accuracy. In-Band Full-Duplex communication Residual self-interference Independent fading taps channel.
A Scalable LDPC Coding Scheme for Adaptive HARQ Techniques
Publication . Madeira, João; Viana, Joseanne; Guerreiro, João; Dinis, Rui; DEE - Departamento de Engenharia Electrotécnica e de Computadores; DEE2010-A1 Telecomunicações; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias
In wireless communication systems, the achievable data rates are always dependent on the characteristics of the wireless channel. Although a system is designed for an expected channel link quality, the channel may deteriorate for certain periods of time due to the changing nature of the propagation environment. A weak channel may lead to transmission errors, which can be corrected by employing Hybrid Automatic Repeat Requests (HARQ). In particular, type II HARQ protocols have become an appealing option since they only involve the transmission of additional parity bits, instead of repeating the original transmission. These additional parity bits can be obtained by puncturing a low rate channel code. However, finding an optimum pattern of puncturing for a specific code is non-trivial. In this work, we propose a retransmission scheme that considers various Low-Density Parity-Check (LDPC) codes of different rates that can be concatenated to perform the encoding and decoding operations, resulting in a lower encoding overhead for successful transmissions, while maintaining efficient decoding. We show that this technique can maintain high throughput and goodput, and a low outage probability, even when the received signal power is suddenly reduced due to the loss of the Line-of-sight (LOS) component.
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Entidade financiadora
European Commission
Programa de financiamento
H2020
Número da atribuição
813391