European Space Agency

COBRA

Objectives


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The Thrane & Thrane BGAN terminal "Explorer 100/110" is the world's smallest and most lightweight [1 kg] mobile satellite device for voice and broadband data communication. The results from the COBRA project will pave the way for even more enhanced equipment in the future.

 

 

 

The project was initiated under the ARTES 3 program as early as 2002. At that time Nera SatCom had started their development of new satellite terminal products for the Inmarsat BGAN system. The BGAN system was designed to utilise the improvements introduced with the Inmarsat I-4 satellites. The system was introduced as commercial services in 2006. The BGAN network is compatible with the earthbound UMTS/IMT-2000 (3G) networks and is capable of extending the reach of 3G land mobile networks to areas where sufficient telecom infrastructure does not exist or cannot support content-rich applications.

The objective of the project was to develop technological building blocks for different terminal products. In 2005, the project was divided into two phases. Phase 1 was completed by Final Review June 2005. The main objective of Phase 2 is to develop solutions for power amplifiers with high efficiency to reduce weight and cost, increase battery usage time for portable equipment and reduce over-temperature problems.

Challenges

Phase 1 of the COBRA project is summarised as follows:

  • A TX RF ASIC was developed and successfully tested,
  • A BB- FPGA was developed and successfully tested,
  • An adaptive digital predistortion (ADPD) algorithm was developed, implemented and successfully tested using the APACM test board,
  • A test-board (the APACM board) was implemented.

The phase 2 of the COBRA project is divided into the following main activities:

  • Development of a new transmitter and receiver architecture for Inmarsat BGAN terminal products,
  • Development of a power amplifier non-linearity characterisation unit,
  • Design of a 5 Watt power amplifier with high efficiency,
  • Power amplifier linearization using adaptive digital predistortion (ADPD),
  • Development of efficient power supply for dynamic biasing,
  • Power Amplifiers with dynamic biasing,
  • Power amplifiers with envelope modulation i.e. the Envelope Extraction and Restoration principle (EER).

Benefits

The main goal of this project was to develop an efficient High Power Amplifier solution for terminal products in the Inmarsat BGAN system. The solutions with adaptive digital predistortion developed in this project have demonstrated that power amplifiers may be designed with significantly higher efficiency than the present state of the art in the satellite terminal industry. This will lead to the following benefits for the end user of such terminal products:

  • Increased battery use time,
  • Smaller size, lower weight and price,
  • Less problem with overtemperature i.e. increased robustness.

Features

The focus has been on increasing the power amplifier efficiency by investigating linearisation techniques, envelope extraction and restoration schemes using a class E amplifier and finally by dynamic biasing of a linear or near linear power amplifier.

Power Amplifier linearisation
The COBRA Architecture make possible Adaptive Digital Predistortion (ADPD) of the power amplifier. The architecture is shown in the block diagram below.


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The data in is mapped according to the given modulation scheme e.g. 16QAM and filtered through a pulse shaping filter. The transmitted signal and the feedback signal from the PA output are both fed into a unit that performs the calculation of the AM/AM and AM/PM pre-distortion characteristics. The pre-distortion non-linearity is the inverse of the PA non-linearity up to close to PA saturation level

A product prototype for Inmarsat BGAN user terminal products consisting of four circuit boards has been developed and successfully tested. To our knowledge this is the first time the Adaptive Digital Predistortion scheme has been implemented and made ready for industrialisation for satellite user terminals. The benefits of the ADPD scheme is higher efficiency, robustness with respect to changing AM/AM and AM/PM non-linearity and freedom from extensive calibration procedures in production of the PA subsystem. It was demonstrated that by using ADPD the total efficiency of the PA subsystem, including driver stages and power supply circuitry, may be increased from around 12% to about 30%. The figures are valid for the spectrally efficient 16QAM modulation scheme.

Dynamically Biased Power Amplifier (DBPA)
A complete solution for dynamic biasing of the PA has been implemented and successfully tested. The DBPA scheme developed and demonstrated in the COBRA project includes sophisticated procedures for dynamically controlling the bias voltages (VGS and VDS). It was demonstrated that the drain efficiency of the PA may be substantially increased by applying this principle.

Envelope Extraction and Restoration with Class E PA
A class E power amplifier prototype was developed. This was demonstrated and tested in a test bed where the so-called envelope extraction and restoration (EER) principle was implemented and successfully tested. The power added efficiency of the class E PA was around 80% over a fairly good dynamic range. The total efficiency of the implemented EER scheme was measured to be 43.5% with the pi/4-QPSK modulation scheme.

A 5 watt PA with ADPD
A 5 Watt PA for different BGAN classes of products has been implemented. With this PA and use of adaptive digital predistortion, a total efficiency of up to 35 % was achieved with the 16QAM modulation scheme. This is superior to earlier generation of products where an efficiency of about 12% was the state of the art.

Plan

The contract was signed in December 2002. Phase 1 was completed in June 2005. Phase 2 of the project, with increased HPA activities was started in March 2003. The total project was concluded in June 2007.

Current status

The project was successfully completed in June 2007.

Status date

Tuesday, November 8, 2011 - 11:56