Inside GNSS Media & Research

MAY-JUN 2018

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54 Inside GNSS M A Y / J U N E 2 0 1 8 WORKING PAPERS Navigation Satellite System (GNSS) due to its coverage and its ease of use, i.e., the user is not required to install any kind of infrastructure. However, GNSS chipsets are power hungr y devices, incurring a considerable decrease of the IoT sensor battery lifetime, an aspect that vendors are trying to tackle with the development of low-powered GNSS chipsets. Furthermore, as we will see in the next section, the performance of GNSS receivers is jeopardized in chal- lenging environments such as indoor, light-indoor, or urban scenarios (G. Seco-Granados et alia). Current GNSS IoT positioning solu- tions compute the so-called Position, Velocity, and Time (PVT) on the sensor itself, hence requiring a certain amount of computational resources (i.e., CPU and RAM) and thus consuming a cer- tain amount of power. This is further aggravated by the increase of data (e.g., signals from multiple GNSS constella- tions) to be processed and the complex- ity of the GNSS signal processing tech- niques to be applied. is article sheds some light on the challenges of current IoT positioning sensors and proposes the use of a cloud-based GNSS positioning approach, in which the computational tasks typically carried out on-chip are migrated to a cloud ser ver with the objective of enhancing the sensor's bat- tery lifetime without compromising the performance (V. Lucas-Sabola et alia, 2016). e processing of GNSS signals in remote servers was initially proposed in the 1990s to reduce power consumption and economic cost of positioning sen- sors (A. Brown and R. Silva). Nowadays, the high-scalability and low-cost offered by cloud computing services make them the perfect choice for implementation of remote GNSS signal processing. ese services require less energy than GNSS modules (J. Liu et alia; V. Lucas-Sabola et alia, 2017). IoT Positioning Sensors IoT positioning solutions can be divided into three main groups: those based on GNSS, those based on non-GNSS, and those combining both GNSS and non- GNSS technologies in a hybrid manner. Outdoor IoT positioning typically relies on the use of GNSS modules that are in charge of capturing the GNSS sig- nal transmitted by the satellites from one or multiple constellations such as Global Positioning System (GPS), Gali- leo, GLONASS, or BeiDou and applying the necessary signal processing tech- niques in order to obtain the PVT. Even though GNSS were originally designed for outdoor environments, novel tech- niques are designed to boost the perfor- mance in indoor scenarios, including the exploitation of distributed Receivers of Opportunity (RoO) located in close- by locations in a cloud-based GNSS framework (J. A. GarcĂ­a-Molina et alia) and the implementation of advanced GNSS signal processing techniques. On the other hand, indoor IoT positioning usually relies on non-GNSS technologies namely 4G/Long Term Evolution (LTE), Wireless Local Area Network (WLAN), L o w- Po w e r W i d e -A r e a N e t w o r k (LPWAN), Ultra-Wide-Band (UWF), or Inertial Navigation Systems (INS). Eventua lly, IoT positioning sensors may perform on-chip hybrid position- ing using a combination of GNSS and non-GNSS technologies at the expense of higher power consumption and cost (G. De Angelis et alia). An IoT positioning sensor is typi- cally composed of a MicroController Unit (MCU), a reception/transmis- sion Radio-Frequency (RF) front-end (so-called communication module), an antenna, the respective positioning module, memory and the power sup- ply (i.e., battery). e MCU is the brain of the sensor, an integrated circuit that includes one or more CPUs and a low capacity RAM able to perform basic computational tasks. e communica- tion module (includes reception and transmission front-end) receives the requests and transfers the data or infor- mation to a central node. e position- ing module varies depending on the technology used (e.g., GNSS, INS, LTE). In this article we only focus on GNSS- based solutions. e positioning module of a GNSS- based IoT positioning sensor is a GNSS module, as depicted in Figure 1 (a), which is in charge of capturing and condition- ing the GNSS signals of interest with its own RF front-end (usually included in the GNSS module) and processing them to compute the position. Positioning data is oen delivered by means of the National Marine Electronics Association FIGURE 1 (a) Conventional GNSS IoT positioning sensor; (b) Cloud GNSS IoT sensor

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