
256 Chapter 10
GPS Modulation
Option Overview
Option Overview
This real-time personality simulates GPS satellite transmissions for single channel receiver
testing. The following list shows some of the features for building a basic signal:
• P code generation at 10.23 Mcps with the standard GPS 10.23 Mcps reference
• C/A code generation at 1.023 Mcps with the standard GPS 10.23 Mcps reference
• navigation data output at 50 bps using PN9, PN15, a fixed 4-bit pattern, user file, or
default data (TLM mode) for encoding with the C/A code
• three selectable ranging codes: C/A, P, or C/A+P
• satellite ID range of 1 to 32 with an additional range of 33 to 37 for other uses
• three selectable data modes that include a TLM mode, which uses a formatted handover
word (HOW) and telemetry (TLM) word (refer to “Data Modes and Subframe Structures”
on page 258 for more information)
• simulated doppler shifting with a 250 kHz range
• selectable internal or external chip clock reference source
A basic signal setup is provided when the signal generator is preset using factory-defined
attributes (C/A ranging code, satellite ID of 1, zero doppler shift, and the Raw data mode
using PN9 data with the standard 10.23 Mcps reference clock). These attributes are available
when Normal is selected using the
Preset Normal User softkey. Refer to the Key and Data Field
Reference for more information.
The satellite ID numbers operate according to the GPS standards; they match the
pseudorandom numbers (PN) that are used to generate the C/A and P codes and they also
dictate the amount of chip delay.
More advanced features are available for modifying the basic signal to match your testing
needs. The following is a list of some of these features:
• P code power adjustment (
−40 to 0 dB)
• adjustable chip clock reference (1 kcps to 12.5 Mcps)
• selectable I/Q phase
• selectable filters and the ability to create user-defined filters using the ESG features
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