TDRSS SIMULATOR (TSIM)
OVERVIEW
 The RT Logic TDRSS Simulator (TSIM) generates all the spread spectrum signals used by the NASA Tracking and Data Relay Satellite System (TDRSS). The TSIM was built for NASA as an economical alternative to the TDRSS User RF Test Set (TURFTS) in order to test payloads and transponders that will access TDRSS while orbiting. RT Logic can easily modify the basic TSIM for other applications.

As a fully integrated system (typically rack-mounted), the TSIM comes with a Graphical User Interface (GUI) for easy configuration. Ethernet control is also provided.
ARTICTURE
 The TSIM receives command data and generates the TDRSS spread spectrum forward link signal. The forward link signal contains the command data modulo-2 added to a command PN sequence and a ranging PN sequence. The two PN sequences are modulated in an unbalanced QPSK format. The TSIM receives the return link RF signal, and despreads and demodulates either the Mode 1 or Mode 2 return link PN codes. The return link signal is modulated in a staggered QPSK format known as SQPN, and allows data to be placed on both the I and Q phases. The TSIM recovers this data, and outputs data and clock for both I and Q streams. Epochs from the forward and return links are used for range measurements. A Doppler simulator allows any Doppler profile to be easily simulated.
MODULAR,
DIGITAL
IMPLEMENTA-
TION
 The TSIM is implemented using the RT Logic Telemetrix® architecture and is comprised of Dynamic Digital Processors, which support the full range of IF and baseband processing, signal modulation, demodulation, and digital front-end functions. This configurable high-speed digital technology offers many performance advantages over analog and nonconfigurable digital systems. The modularity and configurability of RT Logic’s architecture permits easy tailoring of the basic TSIM to meet specific customer requirements.
SPECS
Simulates the TDRSS Forward Link And Return Link

S-Band Single Access (SSA) And Multiple Access (MA), Data Group 1, Mode 1 And 2 (Spread Spectrum Signals) Supported

User Codes 1 To 85 For NASA, NASDA, And ESA

Designed To Meet The Space Network User Guide (SNUG) Specifications

Forward Link
  • 100 bps To 300 kbps Command Data Rate
  • I Channel: Command Data And Command PN, Convolutional Encoding
  • Q Channel: Range PN, 1/10 Power Of I Channel, Epoch Output
  • PN Chip Rate Proportional To Carrier, UQPSK Modulation
  • Doppler Simulation, Custom Profiles, 0.1 Hz Resolution
 Return Link
  • 2200 To 2300 MHz, +/- 4 kHz And 70 Hz/sec For Acquisition
  • Acquisition Within 20 Sec
  • Mode 1 Or Mode 2 PN Codes, Rate Proportional To Carrier, Epoch Output
  • 100 bps To 300 kbps I Or Q Data Rate, Independent Rates, Variable I:Q Power Ratios
  • NRZ-L, M, Or S Format Conversions, Viterbi Decoding
  • Output I And Q Data And Clocks
  • SQPN Modulation
Performs Range Measurement Using Spread Spectrum Codes

Loopback Capability For Testing both Forward And Return Links

FPGA And Software-Based Design Allows Customization For Specific Applications