In this work we evaluate the security gap of a network composed of two legitimate nodes and one passive eavesdropper, all of them provided with multiple antennas. We consider that transmit antenna selection (TAS) along with frame scrambling is adopted at the transmitter node, while both legitimate and malicious receivers operate under the maximum ratio combining (MRC) protocol. By considering a quasi-static fading scenario, we evaluate (analytically and through numerical results) the security gap in terms of both outage probability and frame error rate (when using convolutional codes), showing that in both situations it is possible to achieve negative security gaps using a feasible number of antennas.

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Resumo-Este artigo analisa o impacto da interferência gerada por uma rede LoRaWAN coexistindo no mesmo ambiente que uma rede IEEE 802.15.4g de interesse. As simulações comparam o modo de múltiplos saltos, restrito ao dual-hop nessa análise, com um algoritmo cooperativo, ambos utilizando seleção de relays. Os resultados mostram que a modificação do protocolo de comunicação IEEE 802.15.4g visando suportar cooperação, especialmente em ambientes que sofrem interferências de outras redes, chega a transmitir de 4 a 20 vezes mais informação, para os parâmetros de rede aqui considerados, quando comparado com o método tradicional usando o modo dual-hop.

Along the last years, an increasing demand for mobile radio systems operating within buildings has been observed. Considering the complex structure of a building, an important problem for planning such systems is the prediction of propagation loss. An empirical prediction model to be used in the frequency range from 0.8 to 2.0 GHz is proposed in this paper. The basic parameters of this model were fixed in using a reasonable large data bank established from measurements published in the open literature. The model is quite simple and, in spite of its limitations, appears to be a powerful tool for planning indoor systems.

MultiUser (MU) MIMO schemes introduced to IEEE 802.11ac amendments can achieve high throughput by transmitting different data streams to multiple users simultaneously. However, it requires the user Channel State Information (CSI), which is not trivial to obtain in practice. Alternatively, the access point can balance the expected rate with the CSI processing overhead by choosing an appropriate number of transmitting and receiving antennas, as well as the number of users according to client channel and backlog. We propose the application of a user selection algorithm based on MU-MIMO theoretical properties and user omnidirectional SNR named PUMA (Presounding User and Mode selection Algorithm) and its application on a diversity scenario. We compare the data rate of the proposed scheme with traditional fixed-mode and exhaustive search user selection, and the equivalent effects on energy efficiency. Results show that the PUMA advantages are enhanced in a diversity scenario when client grouping causes dramatic changes in the sum rate. Besides, by using different diversity schemes on the same network configuration, we obtained different rates and consumption.