Section: New Results

Modelling and experimentations of interferences and other PHY effects

Participants : Nathalie Mitton, Valeria Loscri.

In the era of Internet of Things (IoT), the development of Wireless Sensor Networks (WSN) arises different challenges. Two of the main issues are electromagnetic interference and the lifetime of WSN nodes. In [48], we show and evaluate experimentally the relation between interference and energy consumption, which impacts the network lifetime. We present a platform based on commercially available low-cost hardware in order to evaluate the impact of electromagnetic interference in 2.4 GHz ISM band on energy consumption of WSN. The energy measurements are obtained separately from each electronic component in the node. Interference and energy measurements are conducted in an anechoic chamber and in an office-type lab environment. X-MAC protocol is chosen to manage the Radio Duty Cycle of the nodes and its energy performance is evaluated. The energy consumption transmitter nodes is analyzed particularly in this work. Moreover, this energy consumption has been quantified and differentiated according to the number of (re-)transmissions carried out by the transmitter as well as the number of ACK packets sent by the receiver for a single packet. Finally, we use a model of real battery to calculate the lifetime of the node for operation within different interference level zones. This study lays the basis for further design rules of communication protocols and development of WSNs.

In [49], we propose a WSN architecture for wild animal monitoring. The key requirements of the system are long range transmissions and low power consumption. Indeed, the animals could be spread over vast areas. Kruger National Park in South Africa (19485 km2) is the potential zone of implementation of the network. On the other hand, size and weight limitations of wearable devices must be respected, which limits the size and capacity of battery. Moreover, battery replacement is a difficult and expensive process. So, low energy consumption is essential to extend the network lifetime. Some animal tracking projects [3] use GSM to transmit collected data to insure the coverage over a large area. However, high energy consumption of GSM and lack of coverage of the deployment area do not meet the essential requirements of the application. LoRa technology provides both long range transmissions and low power operation. This technology could be an appropriate solution for PREDNET project. The contribution of this work is multiple: 1) we defined communication parameters of LoRa radio for PREDNET WSN; 2) we performed radio propagation simulation for chosen parameters to estimate the coverage area for both urban and wilderness (rural) scenarios; 3) we confirmed the propagation simulations with range tests; 4) we measured experimentally the Packet Error Rate (PER) of transmissions.

Terahertz frequency band is an emerging research area related to nano-scale communications. In this frequency range, specific features can provide the possibility to overcome the issues related to the spectrum scarcity and capacity limitation.

Apart high molecular absorption, and very high reflection loss that represent main phenomena in THz band, we can derive the characteristics of the channel affected by chirality effects occurring in the propagation medium, specifically , in the case where a Giant Optical Activity is present. This effect is typical of the so-called chiral-metamaterials in (4-10) THz band, and is of stimulating interest particularly for millimeter wireless communications.

In [51], [25], we analyze the behavior of specific parameters of a chiral-metamaterial, like the relative electrical permitivity, magnetic permeability and chirality coefficients, and from that we derive the channel behavior both for Line-of-Sight and No Line-of-Sight propagations. We notice the presence of spectral windows, due to peaks of resonance of chiral parameter.

Finally, performances of the chirality-affected channel have been assessed in terms of (i) channel capacity, (ii) propagation delay, and (iii) coherence band-width, for different distances.

Thanks to the exploitation of frequencies in the interval ranging from 0.06 to 10 THz, it is envisioned the possibility to overcome the issues related to the spectrum scarcity and capacity limitation. On the other hand, the design of new channel models, able to capture the inherent features of the phenomenons related with this specific field is of paramount importance. Very high molecular absorption, and very high reflection loss are peculiarities phenomenons that need to be included in these models. In [26], we present a full-wave propagation model of the electromagnetic field that propagates in the THz band both for Line-of-Sight and Non-Line-of-Sight propagation models. In the full-wave model, we also introduce the chirality effects occurring in the propagation medium, i.e., a chiral metamaterial.