Demodulation chain. From GHz to Gbyte. The requirements of the 26 GHz frequency band, impose some new constraints in the complete demodulation chain: A wider bandwidth is required and much higher data rates and new modulation schemes are used. Down conversion (1 of 5).
The requirements of the 26 GHz frequency band, impose some new constraints in the complete demodulation chain:
The critical requirements were:
With the former requirements in mind, two different downconversion schemes were selected:
Frequency plan for the first proposed design
Frequency plan for the second proposed design
Trade-off of two frequency plans
DOWN CONVERTER CONCLUSION
The final IF centre frequency was selected to be 1550 MHz with a bandwidth of 600 MHz.
The required filters were selected from COTS suppliers and the characteristics of each filter were determined.
The group delay variation, gain, noise figure and phase noise showed that using COTs components it is feasible to produce the required down converter.
IF FREQUENCY & Bandwidth
To cover the full range of IFs, and cope with the present IFMS functionalities, while adding the requirements in the 26 GHz band, 3 different IF and sampling schemes were proposed:
IF FREQUENCY AND SAMPLING SCHEME
The IF frequency that can be used in the high rate modem is constrained by theory:
Candidate sampling schemes for Wide band mode
Narrow Band Sampling Scheme
Proposal to retain high sampling rate used in wide band mode:
Medium Band IF of 420 – 640 MHz sampling scheme
DEMODULATOR ARCHITECTURE (1 of 2)
Key features of the proposed demodulator architecture are:
Narrow band demodulator
Wide band demodulator
The proposed Hardware Architecture consists of 3 FPGAs Virtex-5 devices, Flash memory, additional RAM, and peripheral chips (Ethernet line driver etc). FPGA assignments are shown below.
Due to the higher data rate (up to 400 Mb/s) and to the existing limitations in the maximum data rate that can be sent from the ground station to the control centre it is required to perform a feasibility activity to analyse the available Gigabit networks and to find the best communications configuration.
The first task is to assess the desired traffic profiles (for all foreseen missions):
• traffic type (stream vs. files)
• peak and average throughput (taking into account pass duration)
• maximum delivery time depending on current mission phase
• desired QoS and redundancy/back-up
The networking requirements must be derived from this information.
Gigabit Network solutions for Cebreros to Darmstadt.
In Cebreros, ESOC currently uses Telefonica. Telefonica is able to provide an end to end connection between Cebreros and Darmstadt, with bandwidths 155Mb/s, 622 Mb/s, or 2Gb/s. As an example, approximate costs (depending on the location) for a 155Mb/s connections from Madrid to Germany are:
NASA/JPL is already installing a 155 Mbps connection between some of their stations and Goldstone.
A likely candidate for the S&F system was identified, with 24 TB storage.