DigitalGlobe engineers modeled the complete communications system for their newest satellite in Simulink and performed extensive simulations to ensure reliable performance at 1200 Mbps data rates.
The end-to-end Simulink model included an amplifier, an 8-PSK modulator and demodulator, an encoder and decoder, filters, equalizers, and the space-to-ground channel, modeled as additive white Gaussian noise.
The encoding and decoding components were modeled using Reed-Solomon encoding and decoding blocks from Communications Toolbox™.
The engineers used Communications Toolbox to model the receiver’s adaptive equalizers using an LMS algorithm running in decision-directed mode.
They used the Filter Design and Analysis app in Signal Processing Toolbox™ to design and calibrate the system’s Butterworth filter. They modeled the amplifier and other RF components using RF Blockset™ and RF Toolbox™. They used the models to evaluate how RF effects affected baseband data rates. The models also enable them to trade off filter bandwidths with equalizer complexity.
To verify that the system had a bit-error rate of less than 10-6, they ran simulations in Simulink in which 10 million bits were transmitted. Additional simulations were used to analyze effects due to distortion, the environment, and the satellite’s elevation.
Using DSP System Toolbox™ and Communications Toolbox, the team conducted spectral analysis, and produced eye diagrams, vector scatter plots, and constellation plots to visualize simulation results and analyze system behavior.
DigitalGlobe has completed development of the communications system for WorldView-3, achieving the target data rate of 1200 Mbps. The team is currently using Simulink to model and simulate the WorldView-4 communications system.