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Conference Paper
Fraction Sample Effect Compensation Technique for Acquisition of Weak C/A Code Modulated GPS Signals
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- Authors
- Uzair Ahmad, Wan Sik Choi
- Issue Date
- 2009-11
- Citation
- International Symposium on GPS/GNSS 2009, pp.1-8
- Language
- English
- Type
- Conference Paper
- Abstract
- High sensitivity GPS receivers can enable a variety of Location Based Services (LBS) targeting the places where people spend most of their time. This paper presents a novel algorithm for acquisition of weak GPS L1 signals using coherent integration of pre-consolidated chunks of received signal.Several approaches have been proposed to acquire and track weak signals which employ variants of coherent integration techniques. The length of coherent integration period is limited by data bit edge position because the processing gain can become void should the bit edge position is not taken into account. Long coherent integration also requires finer frequency search grid making it computationally prohibitive. The results of such integrations are incoherently added multiple times to achieve a predefined autocorrelation peak power. However, the processing gain from incoherent integrations is limited due to squaring loss. The bit reversal effect mitigation is achieved by estimating the bit edge positions. Then all or a selected subset of possible navigation data message bit combinations are superimposed on the coherent integration results to remove the bit reversal effect from results. This approach requires enormous memory and processing overhead.The proposed algorithm deals with sample fraction problem that degrades the coherent integration gain. This problem can occurs when the sampling frequency of Analog to Digital Converter (ADC) renders fraction sample in one millisecond which is the code period of C/A code. For normal signal strength case, the sample fraction effect is negligible. However in case of long integration intervals, which is required for weak signal acquisition, the sample fraction causes degradation or total depletion of the integration gain. This happens because the sample fraction causes the code phase estimates to drift away. A simple algorithm is devised to control this drift by selecting appropriate chunks of input signal for integration. This adjustment is a function of sample fraction magnitude and can be compensated in acquisition algorithm without changing the ADC.
- KSP Keywords
- Analog to digital converter(ADC), C/A Code, Coherent integration gain, Data Message, Edge position, High Sensitivity, Input signal, Location-Based Services, Long Coherent Integration, Navigation data, Novel algorithm