Projects undertaken by Zelinda Ltd. include:
2-Way Doppler Experiment
The KaTE Deep-Space Transponder (see below) is now flying on ESA's Smart-1
mission to the moon. Zelinda Ltd. has been carrying out an experiment to
compare the results obtained by using simultaneous non-coherent range rate
measurements on the uplink and downlink signals with the traditional
coherent method of range-rate measurement. Using the non-coherent method
also enables the frequency of the on-board TCXO to be measured.
Processing Unit for Deep Space Transponder
Design of a Digital Processing unit for a Deep Space Transponder. The
transponder operates with X-Band uplink and simultaneous X-Band and Ka-Band
downlink signals. The unit interfaces with the 12 MHz final IF
frequency of the receiver and uses digital processing techniques to acquire
and tract the signal. A digital ASIC (designed using VHDL) is used to
demodulator the carrier, and recover the ranging signals at baseband.
The telecommand subcarrier is demodulated and the telecommand data stream
is recovered. The unit also produces IF outputs (at around 16 MHz) to
the X-Band and Ka-Band exciters. Digital techniques, using NCOs,
enable a coherent or non-coherent carrier frequency to be used. Phase
modulation is also performed digitally, the modulation indices for the
telemetry and ranging channels can be set independently for the X-Band and
Ka-Band signals. Apart from digital modulation and demodulation, the
unit also provides general control and monitoring functions for the
transponder via an interface to the spacecraft data handling system.
The design includes a custom designed ASIC and a microprocessor using
the standard 1750 instruction set.
Design of a digital processing unit to perform inter-spacecraft range and
range-rate measurements using spread-spectrum techniques. This unit
is integrated into a spread spectrum transponders at both ends of an
inter-spacecraft communications link. The unit measures the range and
range-rate between the spacecraft as well as providing signal processing
functions for the transmitted signal, including convolutional
encoding, spread-code generation, signal spreading, and digital filtering
and provides a serial digital interface for on-board mode control and
housekeeping data functions. The design is based on a
radiation-tolerant FPGA, designed using the VHDL design language, which
provides the signal processing and logic functionality. The design
also uses ADCs and DACs sampled at up to 36 MHz to provide the analogue
input and output signals, together with various other interface
circuits. Software written in C++ to run on a PC platform was
developed for simulation and evaluation of many aspects of the design.
Data Processing Software
Zelinda is developing software to provide a database of telemetry from the
KaTE experiment which is to be flown on ESA's SMART1 mission to the
moon. The software provides facilities to interface via FTP to a
data-distribution system in order to obtain the experiment data and
provides facilities for archiving, searching, processing, and graphically
displaying both raw and processed data. The software makes extensive
use of commercially available software and extends its capabilities with
software modules written in VBA and C++.
SRRC OQPSK Demodualtor and
Zelinda won the contract to
develop a prototype Bandwidth Efficient modulator and demodulator for use with the Meteosat
Second Generation (MSG) Data Collection Service (DCS). The DCS allows Users to
collect environmental data from sensors at remote locations on the Earth
and to transmit that data via the DCS UHF to L-band transponder to be
received at a central facility.
A characteristic of the METEOSAT series satellites is that they are
spin stabilised. The satellite
communications antennas for L Band and for UHF are consequently
electronically de-spun (EDA).
The EDA causes phase and amplitude ripple to be introduced onto the
DCP signals. SRRC SQPSK
(square root raised cosine offset Quadrature phase shift keying) modulation scheme was selected for
DCP transmissions because of its tolerant to the effects of the EDA.