Delivering the Outdoors Down a Cable: An RF Test Environment for Hybrid Systems

R.L. Maw, M.R. Jarvis, N.G.A. Graube, X. Long

Abstract:	Hybrid positioning systems capable of combining cellular timing measurements and Global Navigation Satellite System (GNSS) measurements offer the potential for significant benefits, including, improved power consumption, yield, accuracy and time to first fix. This is usually achieved by supplying the GNSS sub-system with frequency, time and position assistance, and offering an accurate fallback position. Enhanced-GPS (E-GPS) is one example of these hybrid systems. It tightly couples timing measurements and timing-based position estimates generated from cellular network signals with GNSS receivers in cellular telephones. One obstacle in the development of these hybrid systems has been access to controlled test environments covering moving as well as static scenarios. In this paper, we describe a test system capable of generating a realistic radio frequency (RF) environment containing both GSM and WCDMA networks contemporaneous to a full GPS constellation. The RF environment is responsive to user dynamics including both changes in cellular timings and cell visibility. The system is driven from a scriptable front end that orchestrates the different sub-systems and enables complex scenarios such as outdoor to indoor transitions, urban push to fix, and long drive tests to be executed. A key feature of the test system is that the cellular timing offsets are precisely measured with respect to the system GPS time. This enables the establishment of absolute time stamps for cellular events such as frame boundaries, providing a known truth against which measurements made by hybrid devices can be evaluated. Additionally, testing of server based assistance methods such as assisted GPS (A-GPS), both coarse and fine time aided, enhanced observed time difference (E-OTD) and observed time difference of arrival (OTDOA) is facilitated by the embedding of a serving mobile location centre (SMLC) that communicates with the device under test using the secure user plane for location (SUPL) protocol. One of the major challenges in building this system has been to organize the system in such a way that it may be used in a flexible yet straightforward manner. In this paper we describe how this has been achieved. Additionally, we illustrate the system’s capabilities using examples.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	2241 - 2247
Cite this article:	Maw, R.L., Jarvis, M.R., Graube, N.G.A., Long, X., "Delivering the Outdoors Down a Cable: An RF Test Environment for Hybrid Systems," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 2241-2247.
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