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【资料名称】:Satellite Signal Acquisition Tracking and Data Demodulation
【作者】:Phillip W. Ward
NAVWARD GPS Consulting
John W. Betz and Christopher J. Hegarty
The MITRE Corporation
【语言】:英
【页数】:89
【格式】:pdf
【发表时间】:2003
【摘要或目录】:In practice, a GPS receiver must first replicate the PRN code that is transmitted by
the SV being acquired by the receiver; then it must shift the phase of the replica code
until it correlates with the SV PRN code. When cross-correlating the transmitted
PRN code with a replica code, the same correlation properties occur that occurs for
the mathematical autocorrelation process for a given PRN code. As will be seen in
this chapter, the mechanics of the receiver correlation process are very different
from the autocorrelation process because only selected points of the correlation
envelope are found and examined by the receiver. When the phase of the GPS
receiver replica code matches the phase of the incoming SV code, there is maximum
correlation. When the phase of the replica code is offset by more than 1 chip on
either side of the incoming SV code, there is minimum correlation. This is indeed the
manner in which a GPS receiver detects the SV signal when acquiring or tracking the
SV signal in the code phase dimension. It is important to understand that the GPS
receiver must also detect the SV in the carrier phase dimension by replicating the
carrier frequency plus Doppler (and usually eventually obtains carrier phase lock
with the SV signal by this means). Thus, the GPS signal acquisition and tracking
process is a two-dimensional (code and carrier) signal replication process. |
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