A Dual-frequency L1/E5a Galileo Test Receiver

The date is fast approaching for the first Galileo signals to be broadcast from space. In anticipation of this event, NovAtel has undertaken various Galileo related projects over the past three years. Projects have included sample level software simulations sponsored by the European Space Agency (ESA) and a single frequency BOC(1,1) receiver prototype sponsored by the Canadian Space Agency (CSA). In October 2004, NovAtel was awarded a contract by the CSA to develop an L1/E5a dual-frequency Galileo Test Receiver. The Galileo Test Receiver will include a new FPGA based dual-mode Galileo/GPS L1/E5a receiver card. The new receiver card will be integrated into a modified version of NovAtel’s WAAS–G-II ground reference receiver. To aid in testing and evaluation, an L1/E5a Galileo transmitter is also being developed. The L1/E5a transmitter is based on an existing L1/L5 Signal Generator design. The final deliverable system will be suitable for both in-lab demonstrations and signal-inspace testing purposes. In this paper, the overall architecture of the Galileo Test Receiver will be discussed. An overview of the FPGA based dual-mode/dual-frequency receiver card will be ENC-GNSS 2005, 19-22 July 2005, Munich, Germany given. The initial performance results of the Galileo Test Receiver will also be presented. INTRODUCTION Receiver manufacturers are anxiously waiting for the moment when they can track the first Galileo signals sent from space. It is anticipated that once Galileo is operational, the vast majority of all user receivers sold will be both GPS and Galileo capable. User benefits from receiving signals from both constellations will include improved accuracy, reliability, and availability. Currently, GPS users may find the signal path to the satellite constellation significantly obstructed by buildings, trees, bridges or other forms of signal blockage.. With twice as many satellites visible in the sky, the probability will be much lower that signal blockage will interfere with the navigation solution. Applications that are currently marginal, or impossible, will become viable and cost effective for users. In the meantime, much work needs to be done to produce Galileo capable receivers. Multiple signal types, multiple frequencies and the new binary offset carrier (BOC) modulation scheme make the receiver design challenging. Initiating a prototype receiver design effort now, in advance of a finalized signal specification, will reduce the design risk in years to come. Since 2001, NovAtel has worked on several Galileo projects. These are: • Galileo Signal Validation Study (Spring 2001) • Galileo Phase B2 Users (Dec 2001 – June 2002) • Galileo Phase B2 GSS Receiver (July 2002) • Galileo/GPS Interoperability (July 2002 – October 2002) • Galileo Reference Receiver (October 2002 – April 2004) • Galileo BOC(1,1) Receiver (December 2003 – July 2004) A description of the Galileo BOC(1,1) Receiver is given in (Gerein et al., 2004). The receiver was based on software modifications to an existing card and a new FPGA. A transmitter was modified to broadcast a BOC(1,1) signal. This contract was sponsored by the Canadian Space Agency (CSA). Results for tracking of the BOC(1,1) signal were in line with expectations. In October 2004, NovAtel began work on a contract for the development of an L1/E5a Galileo prototype receiver. This contract is sponsored by the CSA under the Space Technology Development Program (STDP). Canada is a participating member of the European Space Agency. The CSA is the principle Canadian body involved in European satellite infrastructure programs and is the Canadian sponsor for NovAtel’s participation in both EGNOS & Galileo. This Galileo Test Receiver (GTR) will include a new hardware receiver card to track Galileo L1 and E5a signals, as well as an existing L1/L2 GPS card. This receiver will be capable of tracking the first Galileo signals in space. The enclosure for the GTR will be developed and allow future expansion to include cards to track E5b and E6 signals. The contract also includes the modification of a GPS L1/L5 signal transmitter to output Galileo signals. The Galileo Test Signal generator (GTS) can output one L1 and one E5a signal simultaneously. GALILEO TEST RECEIVER The GTR consists of an enclosure containing individual receiver cards. The receiver card dedicated to tracking Galileo signals is the Galileo L1/E5a receiver card shown in Figure 1. The Galileo L1/E5a receiver card is a dualmode (Galileo/GPS) and dual-frequency (L1/E5a) receiver. It is populated with an FPGA and can be configured to track up to 16 channels of any combination of Galileo L1, Galileo E5a, GPS L1, GPS L5, WAAS L1, or WAAS L5. The receiver includes digital pulse blanking on both frequencies to mitigate in-band pulsed interference. Both the FPGA and baseband processor can be reprogrammed with new firmware via the serial port interface. The ability to reprogram the receiver in the field is an attractive feature, considering the Galileo signal structure is still in flux. The design includes Galileo L1 civil signals defined as memory codes, with the design turn around time to implement new codes on the order of minutes. Figure 1: Galileo L1/E5a Receiver Card The GTR enclosure will initially contain two receiver cards, one Galileo L1/E5a receiver card (as described in the previous paragraph) and one receiver card dedicated to GPS L1/L2. The GPS receiver card in the GTR is the Euro-3M card, which was developed for the WAAS G-II receiver. The Euro-3M is based on NovAtel’s OEM4-G2 receivers and features several enhancements such as Signal Quality Monitoring (SQM), improvements to ENC-GNSS 2005, 19-22 July 2005, Munich, Germany NovAtel’s patented Multipath Estimating Delay Lock Loop (MEDLL), cross correlation detection (NovAtel’s patent pending SafeTrak®), bit synchronization check and the addition of L2 digital pulse blanking. The Euro-3M card will be used to determine the position and time solution during the Galileo System Test Bed version 2 (GSTV-V2) test campaign, when only one or two Galileo satellites will be in operation. The time solution will be provided to the Galileo L1/E5a card. A block diagram of the GTR is shown in Figure 2. The enclosure for the GTR will be a modification of the enclosure built for the NovAtel WAAS G-II. A photo of the front of the WAAS G-II is shown in Figure 3, and a top view in shown in Figure 4. The GTR consists of one Galileo L1/E5a card, one Euro-3M GPS L1/L2 receiver card, and an I/O Master card contained in an EIA standard 19-inch enclosed rack with an LCD on the front panel. I/O Master Power Card External Power 120/240 VAC