Abstract-In this paper, we analyze the outage probability and diversity order of opportunistic relay selection in a scenario based on decode and forward and where the available channel state information (CSI) is outdated. The study is conducted analytically by obtaining a closed-form expression for the outage probability, which is dened as the probability that the instantaneous capacity is below a target value. We derive high-SNR approximations for the outage probability. By doing so, we demonstrate that the diversity order of the system is reduced to 1 when CSI is outdated, being this behavior independent of the level of CSI accuracy. A physical explanation for this extreme loss of diversity is provided along with numerical results to support the analytical study.

Machine-to-Machine (M2M) communications are positioned to be one of the fastest growing technology segments in the next decade. Sensor and actuator networks connect communication machines and devices so that they automatically transmit information, serving the growing demand for environmental data acquisition. The IEEE 802.11ah Task Group (TGah) is working on a new standard to address the particular requirements of M2M networks: a large number of power-constrained stations, a long transmission range, small and infrequent data messages, low data rates and a non-critical delay. This paper explores the key features of this new standard, especially those related to the reduction of energy consumption in the medium access control layer. Given these requirements, a performance assessment of IEEE 802.11ah in four common M2M scenarios such as agriculture monitoring, smart metering, industrial automation and animal monitoring is presented. networks because of the growing but still reduced number of devices and light traffic requirements. Simultaneously, the 3rd Generation Partnership Project (3GPP) is working towards supporting M2M applications on 4G broadband mobile networks, such as UMTS and LTE, with the goal of natively embedding M2M communications in the upcoming 5G systems.

The continuous development and improvement of low-power wireless communication technologies is enabling the emergence of many new applications in the field of the Internet of Things (IoT). One of the main areas of research within the Smart City context is smart health, which engages novel IoT initiatives to improve both quality and access to health care and smart services in general. In this paper we present CUIDATS, an IoT hybrid monitoring system for health care environments which integrates RFID and WSN technologies in a single platform providing location, status, and tracking of patients and assets. After its performance validation in a suitable testbed, CUIDATS has been deployed and evaluated with a high degree of success in a real hospital.

Low-Power Wide Area Networks (LPWANs) have arisen as a promising communication technology for supporting Internet of Things (IoT) services due to their low power operation, wide coverage range, low cost and scalability. However, most LPWAN solutions like SIGFOX™or LoRaWAN™rely on star topology networks, where stations (STAs) transmit directly to the gateway (GW), which often leads to rapid battery depletion in STAs located far from it.In this work, we analyze the impact on LPWANs energy consumption of multi-hop communication in the uplink, allowing STAs to transmit data packets in lower power levels and higher data rates to closer parent STAs, reducing their energy consumption consequently. To that aim, we introduce the Distance-Ring Exponential Stations Generator (DRESG) framework 1 , designed to evaluate the performance of the so-called optimal-hop routing model, which establishes optimal routing connections in terms of energy efficiency, aiming to balance the consumption among all the STAs in the network. Results show that enabling such multi-hop connections entails higher network lifetimes, reducing significantly the bottleneck consumption in LPWANs with up to thousands of STAs. These results lead to foresee multi-hop communication in the uplink as a promising routing alternative for extending the lifetime of LPWAN deployments.transmission technologies, such as IEEE 802.15.4-based low-rate wireless personal area networks (e.g., Zigbee), or Bluetooth (formerly standardized as IEEE 802.15.1), provide very low power consumption, which is a critical requirement as things are usually battery-driven devices expected to remain operative up to years.However, these technologies were designed for short-range scenarios (about 100 meters), such as rooms or small buildings, having important limitations in typical IoT deployments requiring wide coverage areas. On the other hand, cellular networks are able to provide ubiquitousness and extensive coverage range (from 1 to 15 km in urban areas). Nonetheless, even though future mobile networks are intended to support machine-to-machine (M2M) services, their operational cost, high power consumption and lack of scalability for massive amount of devices remain major constraints [4].Low-Power Wide Area Networks (LPWANs) have arisen as a promising complementary communication technology for IoT. LPWANs are wireless wide area networks designed for achieving large coverage ranges, extending end devices battery lifetime and reducing the operational cost of traditional cellular networks.They are characterized by exploiting the sub-1GHz unlicensed, industrial, scientific and medical (ISM) frequency band, and by sporadically transmitting small packets at low data rates, which leads to achieving very low receptor sensitivities. Therefore, LPWANs are expected to be completely suitable for supporting IoT services, which commonly require low data throughput communications and large coverage ranges.Most LPWANs like SIGFOX™ [5] or LoRaWAN™[6] are built following a star topology, where end devic...

RSS-based localization is considered a low-complexity algorithm with respect to other range techniques such as TOA or AOA. The accuracy of RSS methods depends on the suitability of the propagation models used for the actual propagation conditions. In indoor environments, in particular, it is very difficult to obtain a good propagation model. For that reason, we present a cooperative localization algorithm that dynamically estimates the path loss exponent by using RSS measurements. Since the energy consumption is a key point in sensor networks, we propose a node selection mechanism to limit the number of neighbours of a given node that are used for positioning purposes. Moreover, the selection mechanism is also useful to discard bad links that could negatively affect the performance accuracy. As a result, we derive a practical solution tailored to the strict requirements of sensor networks in terms of complexity, size and cost. We present results based on both computer simulations and real experiments with the Crossbow MICA2 motes showing that the proposed scheme offers a good trade-off in terms of position accuracy and energy efficiency.