TDMA Systems





Communications Transmission Analysis for the ESA OTS and EUTELSAT ECS Satellite Systems

Carried out the transmission analysis of the QPSK/TDMA systems for the OTS and ECS satellite communications systems during a two year period. This included :

  • Development of comprehensive computer simulation models of QPSK/TDMA transmission via non-linear earth station and satellite, including the effects of co-channel and adjacent-channel interference and adjacent-channel multipath.
  • Evaluation of the effects of burst-mode transmission on satellite TWTA amplifiers, including helix-cathode supply circuit impedance variations (and resulting am/pm conversion variations) as a function of TDMA frame rate.
  • Optimisation of modulator and demodulator cover filters to minimise adjacent-channel interference into carrier and clock recovery circuits.
  • Investigation of adjacent channel multipath effects, which can cause severe problems during inter-burst guard time gaps on adjacent TDMA transponders. This work resulted in the ECS satellite channel spacing specifications being changed.
  • Optimisation of the pulse shaping filters for the Eutelsat ECS TDMA system. Satellite IMUX and OMUX filter optimisation for the Eutelsat ECS TDMA system.
  • Investigation of anti hang-up techniques for burst-mode demodulators, including the use of quenched filters.
  • Study of carrier and clock recovery techniques for continuous-mode and burst-mode modems at 60 and 180 MBit/s.
  • Acceptance testing and performance evaluation of 60 and 180 MBit/s QPSK/TDMA modems and 2 kW Ku-Band HPAs.

Some Papers produced on the OTS and ECS Transmission Design

Some of the papers produced include:

  • Back-to-Back Performance of Pulse-Shaping Filters.
  • Effect of Satellite TWTA on Telephony Distortion. Spectrum Spreading.
  • Determination of TWTA Saturation.
  • HPA Power Transfer Characteristics with a Modulated Carrier.
  • OTS and ECS Adjacent Channel Interference, Multipath and Distortion.
  • ECS Performance with Cosine Roll-Off Pulse Shaping Filters : Effect of Division of Power Law between Transmitter and Receiver.
  • ECS System : Optimum TWTA Operating Point for Different Pulse Shaping Filters.
  • Adjacent Channel Multipath in ECS.
  • Simulated E/No Values - Effect of Clock Phase offset and Demodulator Carrier Phase Offset.
  • In-Plant Acceptance Tests of High Speed (180 MBit/s) Digital Test Subsystem.
  • On-Site Acceptance Tests of High Speed (180 MBit/s) Digital Test Subsystem.
  • 60 MBit/s Station Loop Tests : Continuous Mode Performance.
  • Adjacent Channel Interference in the 60 MBit/s Digital Equipment.
  • Adjacent Channel Interference in the 180 MBit/s Digital Test Equipment.

Design of a Variable Data Rate High Speed Burst-mode QPSK Modem

The design of this modem was for a Government customer.

Design of a Hybrid TDMA system

Carried out the detailed design of a Hybrid TDMA system for a European PTT Administration.

Training Materials and Training for the INTELSAT 120 MBit/s TDM/DSI System

A large amount of work was carried out on the INTELSAT 120MBit/s TDMA/DSI system. See link here for details.

Technical Specifications and Design of a 2-way TDMA VSAT System

Preparation of detailed technical specifications and the design of critical elements of a 2-way TDMA VSAT system for a Government customer. This ranged from all of the processing and algorithms in the hub station to items such as the effects of phase noise on the acquisition performance of the VSAT terminals.