LAAS VDB Receiver Sensitivity Performance Analysis

O.K. Nyhus, E.F.C. LaBerge, T.A. Skidmore

Abstract:	This paper provides an in-depth analysis of the theoretical sensitivity performance of a Local Area Augmentation System (LAAS) Very High Frequency (VHF) Data Broadcast (VDB) avionics (airborne) receiver. The VDB is a critical element of the LAAS as well as the corresponding Ground Based Augmentation System (GBAS) developed by the International Civil Aviation Organization (ICAO). The VDB is used to transfer GPS (and GNSS) differential corrections, integrity, and final approach segment information from the LAAS (GBAS) ground facility to aircraft conducting approaches to the LAAS (GBAS) serviced airport. The VDB operates using Time Division Multiple Access (TDMA) for maximizing spectral capacity. The VDB modulation format is differential eight-phase shift keying (D8PSK), and employs a Reed-Solomon FEC (Forward Error Correcting) code. A scrambling code is also employed to avoid bias in the data string being transmitted. The receiver's sensitivity threshold definition is based on a system level requirement that dictates no more than one message failure per 1000 LAAS messages, for a message failure rate of 0.001. This performance is nominally specified in an additive white Gaussian noise channel. However, in operation, the VDB receiver must operate in a spectral environment which includes noise (interference) from numerous other sources, including co-channel and adjacent channel interference from other VDBs, ILS localizers, and VORs. Other potential sources of interference to the VDB include FM broadcast interference as well as the threat of emissions from emerging ultra wide band (UWB) devices. The primary factors determining receiver sensitivity are the type of modulation used and the demodulator's ability to correctly decode signals in the presence of noise. The paper also considers the FEC characteristics in terms of the number of erroneous bytes in a block of code that can be corrected. Practical limitations of the VDB receiver sensitivity are discussed in relation to the system link budget and planned LAAS service volume.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1758 - 1774
Cite this article:	Nyhus, O.K., LaBerge, E.F.C., Skidmore, T.A., "LAAS VDB Receiver Sensitivity Performance Analysis," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1758-1774.
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