Home Satellite TV Receivers

By Cyril Iskander Signal Processing Consultant, formerly with Averna

Digital radio is rapidly establishing a foothold in the market, placing new demands on receiver manufacturers. Today's receivers must support XM, Sirius, Digital Audio Broadcasting (DAB), HD Radio, Radio Data System (RDS), Global Positioning System (GPS) protocols, and a wide variety of other broadcast and navigation standards. To test their receivers, manufacturers often require several costly hardware platforms, one for each standard supported. This test setup is not only expensive; it is also inconvenient for the engineers, who must configure multiple test environments and switch between them to test different protocols.

The Averna Universal Receiver Test (URT) platform is a software-defined radio frequency (RF) signal source that lets manufacturers test their devices against a range of standards using a single, integrated platform. Engineers can easily update the URT to support additional protocols as testing needs change or new standards emerge.

We wrote, debugged, optimized, and tested the core URT algorithms for the XM and Sirius standards in MATLAB®. This workflow enabled us to verify our design before deploying it to an FPGA. We used our MATLAB simulation results to verify the FPGA implementation, giving us confidence in our production hardware.

Challenges of the Initial URT Development Process

Averna developed an early version of the XM and Sirius Toolkits for the URT platform in C and C++. Although the toolkits worked well, the development process was arduous, and toolkit functionality was limited. For example, the C and C++ implementation could generate the two satellite beams and one terrestrial beam in the Sirius band individually but was not fast enough to generate all three simultaneously. Similarly, it could not simultaneously generate the six beams required by the XM standard (Figure 1).

Figure 1. The Sirius and XM frequency bands.

These limitations were minor, however, compared with the difficulties we faced in developing these URT toolkits in C and C++. We had to test our algorithms on the hardware, which meant slow and costly iterations. After writing a new algorithm or altering an existing one, we had to compile the code, deploy it to the hardware, and then check the results with a spectral analyzer. Slow development iterations made it difficult to find the optimal combination of parameters to maximize performance. Further, debugging the software as it ran in real time was exceptionally difficult. Developing a solution that worked well enough took so long that it left little time to refine and optimize the design.

Developing and Optimizing Algorithms in MATLAB

The key to accelerating development was to design, debug, and optimize our algorithms in MATLAB before implementing them in hardware. We could then use the MATLAB simulation results as a reference to verify the FPGA implementation.

The Sirius and XM multibeam generators that we were creating required similar modulation components, including differential quadrature phase-shift keying (DQPSK) and coded orthogonal frequency division multiplexing (COFDM) schemes. Both generators also required similar filtering, waveform generation, and upconversion components. Using built-in functions in MATLAB, Communications System Toolbox™, and Signal Processing Toolbox™ we quickly developed algorithms for these components without having to code in C. As we developed the algorithms and tested new ideas, we created power spectral density plots in MATLAB to visualize the intermediate results and the final output.

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