Projects:2014S1-13 S-band Communication for Small Satellite
The S-band radio frequency range is being increasingly explored as an option for communications onboard CubeSats. This project aims to develop a simulation of a communication system using GNURadio and determine what would be the best technology to implement the S-band transceiver.
- Aaron Hardman
- Daniel Dac Vien
- Dr Braden Phillips
- Dr Behnam Jamali
CubeSats have been in development since 1999, with the first successful CubeSat launch in 2003. Since that time, the majority of CubeSats have data rates of 9600 baud or less, utilising the amateur radio frequency band. Using the S-band ISM band (2.4 GHz - 2.5 GHz), it is hoped that the data rates of CubeSats can be increased, allowing them to be more effective and successful.
The project was broken up into three stages: a simulation stage, a realisation stage and an optimisation stage.
Simulation At this stage, using software, a simulation of the system would be established to try and find appropriate parameters for the simulation.
Realisation The simulation would be integrated with hardware at this stage, to try and obtain some data using hardware. Hardware-in-the-loop was explored as a potential way of completing this stage.
Optimisation This stage would focus on the technology that would be best used to implement the S-band transceiver. This stage would consider what is currently in use with CubeSats and compare the various microcontrollers, FPGAs and others.
GNURadio was chosen as the simulation software due to the fact that many SDR board manufacturers (Nuand, Ettus Research) offered support for GNURadio with their SDR boards. This would prove invaluable in integrating hardware into the system simulation. As such, GNURadio was chosen as the software to use for the simulation.
Nuand bladeRFx115 SDR Board
After the simulation stage, the next milestone for the project was to integrate an SDR board into the simulation. Although a number of options were explored, the SDR board chosen for this project was the Nuand bladeRFx115 SDR board.
At this stage the project is behind the planned schedule. The project initially planned to have a completed software simulation of the system and hardware components defined at this stage. Currently there is a simulation of the system in GNURadio but there are errors present. These errors are related to the testing of the BER of the signal. To circumvent this offline evaluation of the BER was attempted but when the test files became too large, i.e. in the size of MBs, GNURadio's live BER calculator was required. Unfortunately this brought about another error. When the team attempted to compare the two bit streams created in GNURadio synchronisation errors were encountered with these two streams; even if the streams were one bit out the BER calculation would be incorrect. The team has not as of yet been able to resolve this issue with the simulation and the creation of the team's own GNURadio module may be required to deal with the unsynchronised bit streams.
The team has been able to develop numerous test environments for the project. These test environments use GNURadio and a Matlab simulation has been started as well, however this Matlab simulation is in an early stage still and requires significant work. The GNURadio test environments include the one displayed below which is capable of testing GMSK, DQPSK and FSK modulation techniques and the effect that fading and noise will have on the system. The team has also been able to set up a test environment with hardware that allows students to send digitally modulated and FM data from one GNURadio computer to another. They are capable of encoding, sending and then decoding this data.
With respect to hardware the team has also not completely met the initial goals set out. Initially the team planned to have selected hardware to be used in the transceiver. Instead a definitive listing of potential hardware to be used and what hardware cannot be used has been produced. In addition to this the team has also been able to produce an in depth listing of the current hardware that is employed in CubeSats and the reasoning behind the choices that has been made.
At this stage there is no definitive data to suggest a modulation technique that can be used. The team has only been able to narrow it down to 3 potential schemes, GMSK DQPSK and FSK. Instead the team has been able to setup multiple test environments that only contain one small error that when fixed will ensure proper testing can be completed. From the small bit stream tests performed DQPSK was the best performing modulation technique, however the bit streams were too small to make this finding valid.
GNURadio Simulation System
Below is a picture of the system created in GNURadio to simulate the channel affects on our signal and how the bladeRFx115 has been integrated into the simulation.