Company Experience

Recent Projects

Projects undertaken by Zelinda Ltd. include:

Non-Coherent 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.
Preliminary Results

Digital 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.

Inter-Spacecraft Ranging Module

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.

Experiment 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 Modulator 


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.