Position-location capabilities are being installed in both code-division-multiple-access (CDMA) and Global System for Mobile Communications (GSM) networks. In the US, these capabilities are mandated by such policies as the Federal Communications Commission's (FCC's) E911 Phase II. For manufacturers seeking to evaluate the performance of position-location functions in CDMA handsets, the CDMA Position Location Test System (PLTS) from Spirent Communications (Eatontown, NJ) has been available for about a year. The PLTS has recently been integrated with Spirent's C2K-ATS CDMA2000 Automatic Test system (see figure) to fully characterize the performance of CDMA handsets.
Handset manufacturers are now developing GSM and wideband CDMA (WCDMA) mobile devices that include position location. In the US, the driver is again E911 and in Europe a similar initiative (E112) will soon be requiring location capabilities to be included in handsets. Commercial location-based services (LBS) are the other big drivers of location technology, with market forecasts ranging from $10 billion to $100 billion by the end of this decade. For these handset manufacturers, and the operators that buy their products, Spirent is adding location capabilities to its recently announced U-ATS Universal Mobile Telecommunications System (UMTS) Automatic Test System.
Like the integrated PLTS/C2K-ATS system, the U-ATS is intended to be a complete test bed for the evaluation of WCDMA mobile device performance. The system incorporates a commercially available one-box radio test set to supply the call processing required to execute a wide range of physical layer transmitter (Tx) and receiver (Rx) parametric tests. A new advanced WCDMA network emulator from Spirent will shortly add advanced protocol control and multi-sector Node B emulation. Rx performance is characterized under impaired downlink conditions created by an RF channel emulator and interference emulator. TestDrive test-application software automates all aspects of test execution, including test suites for 3GPP Terminal Conformance test specifications, such as 34.121.
A key handset-based location technology whose popularity is expected to grow for both GSM and WCDMA networks is Assisted GPS (A-GPS). With A-GPS, assistance data is sent through the Radio Access Network. The data includes ephemeris, clock information and differential corrections. Compared with unassisted GPS, A-GPS enhances accuracy, integrity, time-to-first-fix and increases battery life. Measurements are always made in the handset, although position can be calculated in the handset ("MS-based") or in a Serving Mobile Location Center ("MS-assisted"). Recent sensitivity-enhancement techniques now allow satisfactory indoor operation.
To test the performance of GSM and WCDMA handsets that employ this technology, Spirent is integrating its GSS5060 GPS simulator into U-ATS to provide signals from up to 12 Global Positioning System (GPS) satellites. The GSS5060 models the GPS constellation in real time, including atmospheric and multipath effects and terrain obscuration. A commercial SMLC will provide assistance data to the handset and, for MS-assisted handsets, calculate the handset's location. A unique "virtual receiver" capability in the GSS5060 allows the GPS constellation to be modeled at two different locations simultaneously, one for the GPS reference Rx and one for the handset. The GPS reference Rx is modeled in software and the output data passed directly to the SMLC.
In the US, GSM operators initially selected E-OTD as the location technology for their E911 Phase II implementations. In recent months, a series of announcements has left only one major GSM operator, T-Mobile, publicly committed to following through on E-OTD deployment. With its unique range of signal-generator platforms and system-integration expertise, Spirent is also well positioned to offer performance test solutions for E-OTD capable handsets. Spirent Communications, 541 Industrial Way West, Eatontown, NJ 07724; (732) 544-8700, FAX: (732) 544-8347, Internet: www.spirentcom.com.