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Contents 1 Communications Subsystem Preliminary Design Review Notes 2 What will be covered 3 Notes 3.1 Design choices made 3.1.1 Transceiver 3.1.1.1 Discussion 3.1.2 Modulation 3.1.2.1 Discussion 3.1.3 Demodulation 3.1.3.1 Discussion 3.1.4 Error coder 3.1.4.1 Discussion 3.1.5 Communication Protocols 3.1.5.1 Discussion 3.2 Interfaces for the subsystem 3.3 Preliminary mass and subsystem dimensions 3.4 Preliminary power consumption figures 3.5 Subsystem progress since Design Review 2 3.6 Critical Issues 3.7 Timeframe for completion 3.8 Financial situation

Communications Subsystem Preliminary Design Review Notes

The design review will be on 6th April at 1300GMT

What will be covered

• Design Choices made(and the rationale for these).
• Interfaces for your subsystem(INPUTS and OUTPUTS for your subsystem).
• Preliminary mass and subsystem dimensions
• Preliminary power consumption figures
• Subsystem progress since Design Review 2
• Critical issues(Problems encountered or that need to be resolved)
• Timeframe for completion of subsystem
• Financial situation

Notes

Design choices made

Transceiver

We have decided to use the Yaesu VX-3R. ==

Discussion

It fits the power and space budgets, operates on the required bands, is reasonably popular (so reasonably easily available), isn't too expensive (new: ~$200), schematics available.

Modulation

We will use a PSK modulation scheme for the downlink.

Discussion

Following on from the previous design review, provided that PSK is correctly received with a coherent detector, it provides the lowest error rate for a given SNR, of the main binary modulation schemes.

Demodulation

We will use FSK for demodulation.

Discussion

FSK is very simple to demodulate and the extra performance of PSK is not needed on the uplink, as the uplink will use a high powered ground station, so will have high received SNR.

Error coder

We will use a turbo coding system.

Discussion

Turbo coding is very simple to implement - usually just a couple of flip-flops and some and/or gates, but with a trellis decoder at the ground station, can allow almost the shannon channel capacity (maximum theoretical capacity limit of a channel) to be reached.

Communication Protocols

We will provide two communication systems to CDH: A reliable protocol (SRTP), and an unreliable protocol (SUTP).

Discussion

The requirements for Payload data differ from all the other types of data (telemetry, beacon, acknowledgments etc...), so we need to different protocols to send the different classes of data.

Interfaces for the subsystem

Template:SEDSAT-2_Interface_Communications

Preliminary mass and subsystem dimensions

• Transceiver, 40 x 80 x 20 mm, 70g (approx)
• Main board, 80 x 80 x 10mm, 50g (approx)
• Antenna, 50 x 50 x 15mm, 100g (approx)

Preliminary power consumption figures

• power to transceiver, 200mA @ 3.3V (average)
• power to main board: 40mA @ 3.3V

Subsystem progress since Design Review 2

Progress:

• Finalized the high-level subsystem design (see design decisions above)
• Begun a Java prototype-implementation of the MCU, have completed a transmitter multiplexer and work is underway on a sliding window protocol, part of the SRTP.
• Design of the SRTP and SUTP protocols underway
• Channel modelling underway
• Orbital modelling
• Have set up a MCU development environment - dev board, software, additional dev board parts (RTC, I2C-interface modules)

Critical Issues

• We're not getting enough work done! Too many exams etc!

Timeframe for completion

TBD

Financial situation

Have been relying on "donation" from team members so far to purchase parts, and this may be sufficient to cover parts costs. We are also hoping to get the whole team to IAC'08, for this we are looking at team sponsorship opportunities.