Abstract

Cubesat project in Qatar University has been divided into sub-projects that involve designing the different subsystems. This sub-project tackles the communication subsystem, where the system design requirements and components were set, and the Low-Earth-Orbit channel model following the rician distribution was developed, as well as formulizing an energy optimization algorithm to achieve transmitting from the satellite with high data rates with minimal energy losses. The developed algorithms were tested by simulation since the hardware implementation that complies to cubesat requirements didn’t take place so far because of the shortage in equipment. USRP devices were used in terms of hardware as a proof of concept only..

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ObjectivesThis phase of the project is focused on designing and modelling the onboard communication subsystem of Qubesat. This major objective can be subdivided into the following specific thrusts:1) Achieving High data rate and low power communications system with the baseband design and prototyping.2) Understanding and modelling the LEO wireless channel characteristics.

ConclusionThe objectives of designing a communication subsystem for Qubesat were theoretically achieved. The developed energy minimization algorithm can be applied by the coming groups on the Rician channel model to simulate the real case. Moreover, a LEO channel model was developed, where the Rician model was adopted since it accounts for both Line-of-Sight and reflected components. For the hardware implementation part, the USRP platform was used to demonstrate transmitting on a 2.4-GHz channel using QPSK modulation, and a picture was successfully transmitted between the two devices, which corresponds to the real life application of the satellite.

Design of an Energy Efficient Communication System for Qatar University CubesatAbdulrahman Alassi, Ahmed Al-Mashhadani and Ahmed Khan

Supervised by: Dr. Tamer Khattab and Dr. Ahmed Massoud

Acknowledgments

To our supervisors and the department’s technical engineers for their continuous support and guidance

throughout the year.

Constellation diagrams for transmitter, unequalized and equalized received signals for the developed Rician Channel Simulink model. As well as the BER Vs. SNR curve for the model, showing the inverse proportionality between them

Testing the effect on the received image for different SNR and resulting BER values. The picture to the left is received with 7% error, while the picture to the right is received with 0% error.

Results

Energy Minimization Algorithm For Transmission Scheduling and the developed Simulink model for testing it using an AWGN channel. The table shows the test results with the selected thresholds of T1 = 1 dB and T2 = 3 dB. It also shows the tradeoff between the BER and the number of received symbols for a set of SNR values.

Es/No (dB)

Reciever BER (Simulation)

Received Symbols

RS Per 3 Rotations

0 0 0 01 0.05068 2303905 69117152 0.02357 2303905 69117153 0.03136 11519905 345597154 0.00526 11519905 345597155 0.00057 11519905 345597156 0.00005 11519905 34559715

-20 -10 0 10 20 30 40

BER Vs. SNR (dB)

SNR (dB)

BER

The experimental setup for testing the USRP devices. One of the laptops has the transmitting blocks whereas the other one has the receiving blocks

Decoded data at the receiver side of the USRP devices network. It can be extended to include any kind of data

Future WorkFor the communications subsystem, the coming groups have to continue working on the following: integrating the Rician channel model to the energy optimization Simulink file and getting the threshold values based on that, as well as trying to update the mathematical formulization of the problem. Also, in terms of hardware, they have to work on getting a functional board from a specialized manufacturer that complies with the cubesat standards. Eventually, the coming groups have to coordinate with their partners who will be working in other groups on developing and enhancing other subsystems to integrate the whole thing into one functional system.