Performance Evaluation of L2C Data/Pilot Combined Carrier Tracking Kannan Muthuraman 1 , Richard Klukas 2 and Gérard Lachapelle 1 1 Position, Location And Navigation (PLAN) Group, Department of Geomatics Engineering, University of Calgary, Canada 2 School of Engineering, University of British Columbia Okanagan, Canada BIOGRAPHY Kannan Muthuraman is a PhD student in the Department of Geomatics Engineering, University of Calgary. He received his B.E. in Electronics and Communication Engineering from the College of Engineering, Guindy, Anna University, Chennai, India in 2006. His research interests include GNSS software receiver design for modernized signals. (kmuthura@ucalgary.ca ) Prof. Richard Klukas is an Assistant Professor in the Faculty of Applied Science, University of British Columbia Okanagan. His research interests include wireless location, high sensitivity and assisted GPS. He also has industrial experience with Nortel and Cell-Loc Inc., (richard.klukas@ubc.ca ) Prof. Gérard Lachapelle holds a CRC/iCORE Chair in Wireless Location in the Department of Geomatics Engineering at the University of Calgary, where he also heads the PLAN Group. He has been involved with GPS developments and applications since 1980. More information is available at http://plan.geomatics.ucalgary.ca ABSTRACT Inclusion of the pilot channel in addition to the navigation data channel is considered one of the major changes in GNSS modernization. A pilot channel undergoes similar path delays and shifts as a data channel, thus making data/pilot combined tracking attractive. This combination is often not straight forward for carrier phase tracking due to the presence of data bits on the data channel. In addition, the inherent advantages of a pure PLL are often lost in such a combination. Two novel methods to combine the data/pilot channels effectively without compromising the advantages gained by using a pure PLL are proposed. These two methods are evaluated in comparison with architectures already available in literature. Results indicate that the proposed algorithms perform closer to a PLL in terms of minimum required /ܥ ଴ to maintain lock with the added advantage of reduced tracking jitter. INTRODUCTION The current constellation of GPS is being modernized at L2 (L2-Civilian) and L5 frequencies. Apart from the usage of codes with improved correlation properties as compared to the legacy GPS L1 C/A signal, both L2C and L5 include a data-less channel (pilot) in addition to the data channel. The inclusion of a pilot channel allows a pure Phase Locked Loop (PLL) for carrier phase tracking. Normally, the phase discriminator used in a pure PLL has an extended linear region over ሾെ ,ߨ൅ߨሿ, thus avoiding the േ ߨambiguity due to phase wrapping in a Costas loop. Further, a pure PLL has an improved tracking threshold of 6 dB in comparison with the Costas loop (Kaplan 2006). The absence of data bits on the pilot channel allows longer coherent integration times, an important aspect of weak signal tracking. The focus of this paper is L2C signals. The L2C signal carries the data and pilot channels in a chip-by-chip time multiplexed fashion. The data channel carries a moderate length code (CM) of length 10,230 chips and the pilot channel carries a long length code (CL) which is of length 75 ൈ 10230 ൌ 767250chips. The codes are clocked at 511.5 kHz, thus the time multiplexed code is at 1.023 MHz. A unique property of the L2C data channel is the alignment of the data bits (20 ms) with the CM code period. After CM acquisition, the data bit boundaries are known within a fraction of a chip length and this avoids the need for a separate bit synchronization algorithm. Further, synchronization between the CM and CL code reduces the search space for CL acquisition to 75 distinct possibilities. Standard tracking architectures for L2C, often assume a zero padded local code generator as described by Tran & Hegarty (2003) to account for the time multiplexed nature of the received signal. This causes a 3 dB loss since the power in the pilot channel is neglected while tracking the data channel and vice versa. However, this avoids the cross correlation noise between the data and pilot channels. The same is assumed in this work for acquiring and tracking the L2C signal. By standard tracking architecture, a normal PLL + DLL with respective error ION GNSS 2008, Session B4, Savannah, Georgia, 16-19 September 2008 1/9