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A Sampling Interval Compensation Scheme for Improving the Gain of Long Coherent Integrations
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- Authors
- Uzair Ahmad, Wan Sik Choi
- Issue Date
- 2009-12
- Citation
- International Global Navigation Satellite Systems Society (IGNSS) 2009, pp.1-9
- Language
- English
- Type
- Conference Paper
- Abstract
- Software-based or post-processing GPS receivers perform a coherent integration in order to acquire the C/A code phase and estimate the Doppler shift on L1 carrier. Generally one millisecond, the duration of the C/A code, long integration is enough for acquisition. However, in weak signal environments, an extended coherent integration is required over a long record of received signal. The weaker the signal power the longer the data record is required to be treated coherently. There are several challenges in performing such coherent integrations. First of all, the computational requirements increase tremendously as the code phase search in longer data records needed to be performed on finer frequency steps. Secondly, the navigation data bit sign may reverse its sign in a 20 millisecond data record. The sign reversal, if not compensated, can decimate the coherent integration gain altogether. This paper establishes an interesting observation that such coherent integrations can still decimate the total gain even if there is no bit sign reversal or it is compensated properly.A comparative analysis of four different coherent integration methods is presented to show that the observation holds across different methods. A sampling interval compensation method is presented to remove the decimation out of coherent integration process. Experimental results show that the proposed method can effectively recover the loss induced by uncompensated coherent integrations.
- KSP Keywords
- C/A Code, Coherent integration gain, Comparative analysis, Compensation method, Compensation scheme, Computational requirements, Different methods, Doppler Shift, Integration method, Navigation data, Post-Processing