High Speed LORAN-C Data Communications June 2001 Update

Ben Peterson, Ken Dykstra, Peter Swaszek and James M. Boyer

Abstract:	This paper is a status report in an ongoing project to develop methods for transmitting GPS Wide Area Augmentation System (WAAS) data over LORAN. The project is being funded by the Federal Aviation Administration under their program to determine what potential benefits LORAN-C might provide to the National Airspace System. In order to minimize the impact on legacy navigation receivers, present efforts are focused on maintaining the present one millisecond spacing between pulses and leaving the leading edge of the pulse unchanged. Intrapulse Frequency Modulation (IFM) with a somewhat longer pulse is being used to increase the pulse energy used for modulation, while at the same time minimizing the spectrum spreading and making the phase shifts more easily accomplished in a narrowband transmitter. The signal specification for attenuation at the 500-microsecond point of the pulse will be met. The modulation involves two 4-phase state symbols per pulse for four bits per pulse. The full WAAS message of 250 bits will be transmitted in one second. In earlier efforts, seven pulses per group were modulated for a raw data rate in excess of 500 bits per second and rate ½ convolutional forward error correction utilized. The bits were interleaved in order to minimize the effects of the burst nature of bit errors. After extensive simulations, it was determined that better performance would result from using Reed Solomon block encoding. Present tests are being done modulating six pulses per group. The 250-bit message is encoded into 32 of the 54 bytes transmitted in 18 groups with 22 bytes for forward error correction. For 18 groups per message a Group Repetition Interval (GRI) of 55,550 usec or less for a single rate transmitter or modulating all unblanked groups of both rates of a dual rate transmitter is required. The status of testing with the LORAN Support Unit transmitter and plans for testing in Alaska in late summer/early fall are presented. Recent flight trials were conducted utilizing an aircraft from Ohio University. The results from these trials are presented.
Published in:	Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001) June 11 - 13, 2001 Albuquerque, NM
Pages:	530 - 546
Cite this article:	Peterson, Ben, Dykstra, Ken, Swaszek, Peter, Boyer, James M., "High Speed LORAN-C Data Communications June 2001 Update," Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, June 2001, pp. 530-546.
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