Software Defined Radios
The SCaN Testbed will consist of three reconfigurable and reprogrammable Software Defined Radio (SDR) transceivers/transponders:
JPL SDR: S-Band and L-Band (GPS)
S-band (duplex) microwave Radio Frequency (RF) links directly
with the ground, (also referred to as the Near Earth Network
Software Defined Radio Software
Each SDR will have an Operating Environment (OE) which provides a software infrastructure (including an operating system), command processing, interact with hardware, and configure the SDR. All three OEs comply with the STRS Standard. SDR must run waveforms which implement the capability of the radio and generate the RF signal that will be transmitted. The OE does not actually generate or receive signals or perform communication functions. That is done by loadable waveforms which use the resources provided by the hardware platform and OE to communicate, network, or keep time (or anything else the experimenter wishes to do).
Radio Frequency (RF) Subsystem
The RF subsystem enables the SDRs to transmit/receive RF signals from the SN and NEN, and receive GPS signals, through one of five antennas (3 fixed, 2 movable).
The Radio Frequency (RF) Subsystem is comprised of:
Traveling Wave Tube Amplifier (TWTA)
The RF Subsystem interfaces with the Avionics Subsystem, the
Flight Enclosure, the Antenna Pointing Subsystem, and the three
SDRs. The Mission Operations tab further details RF communication
The Antenna Pointing System (APS) allows the Ka-Band High
Gain Antenna (HGA) and S-Band Medium Gain Antenna(MGA) to be
moved to track TDRSS (or other experimenter selected targets).
The antenna pointing may be done in either open loop or closed
loop mode. In the former, the antennas are pointed according
to a pre-computed track profile. In closed loop mode, the tracking
algorithm uses signal strength information from the Ka-band
radio to point the Ka-band HGA more accurately to the Ka-band
source. The ISS is sufficiently large and flexible that open
loop pointing of the Ka-band antenna may have pointing errors
reducing the maximum data rate that can be carried. The gimbaled
antennas are locked for launch and deployed on-orbit.
As shown in Figure 8, the APS consists of: