GPS Observability and Availability for Various Antenna Locations on the Human Body

This paper quantifies the effects of placing GPS antennas on the body and seeks to understand the effect in four environments: open skies, under tree canopies, urban canyons and indoor. GPS antennas are placed on the top of the head, right shoulder, chest pocket, left and right front pant pockets, right forefoot and left heel. For the right pant pocket antenna, the antenna was reversed, so the sensing element was between the ground plane and the skin. A reference trajectory for each data collection test was obtained using ultra-tightly coupled postprocessed GPS/INS. The subject wore a small backpack to carry the GPS receivers, laptops, batteries and reference solution system. Tracking performance is discussed using six metrics: (1) percentage of observations available, (2) HDOP, (3) C/No, (4) absolute position, (5) residuals and (6) fault detection with exclusion (FDE). Several conclusions are made about the ability of receivers to provide different levels of performance. INTRODUCTION Pedestrian navigation applications using GPS are increasingly common. The desire to locate people using GPS technology at any time and in any environment has gained popularity with widespread applications. Applications of pedestrian navigation include mobile phone navigation, health and activity monitoring, athletic training, consensual tracking (e.g. elderly and children), recreational users, first responders and military personnel. GPS receivers are commercially available in watch and pod forms, and applications where GPS receivers are located in shoes, glasses and jackets are being developed (Mexperts 2006, DIGINFO TV 2010, McClure 2010). The result of such broad applications is the placement of GPS antennas on and around the human body. The impact of the body and the location of the antenna for high sensitivity GPS is therefore relevant. This paper seeks to understand the effect of the GPS antenna’s location on the body, and, in particular, quantify the discrepancy between an antenna located on the top of the head and other common locations around the body.