SUPL support for mobile devices

ABSTRACT Conventional Global Positioning System (GPS) receivers operate we ll in open-sky environmen ts. But their performance degrades in urban canyons, indoors and underground due to multipath, foliage, dissipation, etc. To overcome such situations, several enhancements have been suggested such as Assisted GPS (A-GPS). Using this approach, orbital parameters including ephemeris and almanac along with reference time and coarse location information are provided to GPS receivers to assist in acquisition of weak signals. To test A-GPS enabled receivers high- end simulators are used, which are not affordable by many academic institutions. This paper presents an economical A-GPS supplement for inexpensive simulators which operates on application layer. Particularly proposed solution is integrated with National Instruments (NI) GPS Simulation Toolkit and implemented using NIs Labview environment. This A-GPS support works for J2ME and Android platforms. The communication between the simulato r and the receiver is in accordance with the Secure User Plane Location (SUPL) protocol encapsulated with Radio Resource Location Protocol (RRLP) applies to Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) cellular networks. 1. INTRODUCTION The widespread use of Global Positioning Systems (GPS) and other existing and emerging Global Navigation Satellite Systems (GNSS) has significantly influenced Location Based Services (LBS) in cellular networks. The Enhanced-911 (E-911) regulation mandated by the US Federal Communications Commission (FCC) [1] proliferate the need for accurate LBS. According to E-911, the wireless network operators should provide accurate location information (accuracy of 50 to 150 m) of the mobile caller to the emergency service responders. Conventional GPS receivers incorporated in mobile devices provide excellent LB S (accuracy of 5 to 10m) in open sky environments when the receiver is in direct line of sight with the satellites. But, the GPS receivers performance deteriorates in so-called weak signal conditions such as urban canyons, indoors and underground due to tall buildings and foliage. Weak signals are both attenuated by structures and subjected to multipath degradation resulting in essential errors or signal loss. One of the enhancements to over come above mentioned problem is the Assisted GPS concept where an external reference server having direct-line of sight access to satellites provides assistance to the mobile device exploiting terrestrial links. Assistance includes data such as satellite orbital parameters, reference time and coarse location if available. A-GPS typically reduces Time to First Fix (TTFF) and improves sensitivity, i.e. allows for the acquisition of weaker GPS signals. It also helps to save battery power. The invention of A-GPS technology widely improved LBS in the cellular in dustry. Consequently, testing of A-GPS methods has become critical prior to their real-time usage in any cellular network. A number of simulators (e.g. Spirent, Aeroflex, Agilent Technologies and ETS Lindgren) for the purpose of testing these receivers are available in the market which are very expensive and are not affordable for many academic ins titutions and small businesses. This paper extends ideas in [2] which reported the developm ent of an affordable Assisted GPS (A-GPS) Simulator using Secure User Plane Location (SUPL) [3] arch itecture. SUPL is a user plane standard that relies on Internet Protocol (IP) [4] based data delivery channels to transmit assistance data making use of the existing control plane protocols for LBS positioning. Thus implementation of SUPL architecture remains infrastructure independent unlike the control plane protocols which widely depend on network infrastructure. This paper demonstrates the transmission of aiding data generated by A-GPS Simulator to handheld devices with different Operating Systems (OS) and also to a laptop PC where a GNSS receiver [5] is located. The hybr id GNSS receiver uses this A-GPS support for much faster position calculation.