APEXX: Algorithms for Pre-distortion and Equalization of tX and rX terminals

Objectives

Satellite communication data traffic rates are growing. In the scope of obtaining higher data rates, the increase of the spectral efficiency and the use of higher bandwidth is mandatory. Future systems will also implement multi-carrier operation.

In the frame of this study, some key technologies for on-ground processing techniques to minimize non-linear effects in multi-carrier operation mode are investigated. Pre-distortion and equalization algorithms will be analysed and evaluated by software simulations. The end-to-end system simulation will be performed with a DVB-S2 system and representative channel impairments caused by IMUX, OMUX and HPAs.

The study will survey and analyse the performance of different techniques for on-ground pre-distortion and equalization. The techniques will be benchmarked using different mission scenarios for single and multi-carrier broadcasting. The scenarios applied will include present state and predicted future demands of the end-to-end system requirements for increased data rates and bandwidth.

The study will define realistic mission scenarios (respecting requirements of the near future), survey existing algorithms, compare algorithms for on-ground pre-distortion and equalization and select a set of promising techniques to be evaluated in more detail for the defined scenarios (task 1+2). The selected algorithms will be added to a already existing software environment (TOPCOM++) which realises a DVB-S2 system. The software is adapted for end-to-end simulations respecting non-linear effects in the channel. The simulation results will be evaluated by the study team and will draw conclusions for future development work (task 3+4).

Figure: Distortion of a 32APSK modulated carrier (exemplary)

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Features

The project will not develop hardware. The pre-distortion and equalization techniques are evaluated in numerical simulations. The project will use the Topcom++ Software tool from ESA, which will be extended by adequate models of IMUX, TWTA, OMUX and filters for this investigation. The algorithms for pre-distortion and equalization will be implemented as C++ subroutines.

Figure: Simulation chain with models (exemplary)

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Project Plan

In the first 2-3 month of the project, the future mission scenarios to which the techniques shall apply will be defined (task 2). A survey of the state-of-the art algorithms for on-ground pre-distortion and equalization techniques will be performed and an analysis of the candidate algorithms will be performed with respect to the mission requirements (task 1). This initial analysis process will be closed with a baseline review (BDR), at which a set of algorithms will be selected for more detailed analysis.

In a consecutive task 3, a simulation environment (Topcom++) will be adapted to the project and the selected algorithms will be added to the software. A test plan will be established and a test readiness review of the tool will be held at CDR. In task 4 this tool will be used to analyse the performance of the algorithms within different mission scenarios and detailed evaluation and conclusions will be done.

Challenges

The keywords of the APEXX project are:

• Improvement of the spectral efficiency in satellite broadcasting/broadband communication,
• Non-linear effects characterization of the transmission channel,
• Novel pre-distortion and equalization techniques for satellite multi-carrier systems,
• Multi-gateway scenarios.

Benefits

To increase the data rates of today’s satellite communication, new technologies have to be applied in the near future to fulfil these demands.

Pre-distortion and equalization are state-of-the art techniques to counteract non-linearities in the transmission channel, especially if multi-carrier systems instead of single-carrier systems will be used.

The study will survey the latest research results with respect to on-ground pre-distortion and equalization techniques and evaluate their performance within future mission scenarios and requirements of future broadcasting systems. The conclusions of this study will support decisions for a development of an operational system (hardware) in the near future.

Current Status (dated: 06 Mar 2013)

The CDR (Critical Design Review) milestone has been achieved on January 2013 by validating the software tools (done with TopCom++) for the case of single carrier transmission. Now, the last WP is started to evaluate the proposed multi-carrier predistortion and equalization techniques for dual and three carriers configurations.

The end of the project is currently planned for June 2013.