ION Technical Content
GPS Pseudolite Signal Design
| Abstract: | Pseudolites (PLs), ground-based satellites transmitting GPS-like signals, are becoming increasingly useful for a variety of applications, including differential GPS correction broadcasting and aircraft precision approach - Category I, II and III. PLs have the capability to augment the GPS constellation, providing better geometry for greater positioning accuracy, reliability, availability, continuity, and integrity monitoring. In addition they can be used to speed up integer ambiguity resolution in differential carrier phase applications, due to the large geometry change possible with the PL signal. However the use of PLs is not without its problems, the most notable being the “near-far problem”. This problem occurs due to the large dynamic range between a PL and a user, in contrast with the approximately constant distance of the GPS satellites from the user. Within some range, a PL signal can be orders of magnitude more powerful than the GPS satellite signal, and thus jam a user’s receiver. The paper discusses the design of a PL signal to mitigate the near-far problem using CDMA methods. The use of longer pseudo random (PR) code at C/A code rate, as well as the use of faster code (P-Code rate) is explored. Longer codes are formulated by concatenation of length- 1023 Gold codes, scrambled by a ‘Switching Sequence’. By applying selected switching sequences one can achieve signal-to- interference level improvements of up to 6 dB. Application of P-Code rate sequences shows even larger improvements, from 23 dB. |
| Published in: |
Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994) September 20 - 23, 1994 Salt Palace Convention Center Salt Lake City, UT |
| Pages: | 1375 - 1382 |
| Cite this article: | Ndili, Awele, "GPS Pseudolite Signal Design," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 1375-1382. |
| Full Paper: |
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