Small Spacecraft Electric Propulsion (SSEP) Technology Suite
Signal Combiner for Wideband Communication (LEW-TOPS-113)
A frequency division multiplexer combined with an analog-to-digital converter increases efficiency
Innovators at NASA's Glenn Research Center have devised an efficient new method of combining primary and secondary signals with minimal loss and noise. Exploiting non-traditional uses of frequency domain multiplexers and analog-to-digital converters (ADC), Glenn's secondary signal combiner uses a frequency multiplexer in the analog domain and wideband ADC to combine electromagnetic signals (primarily MHz to GHz) with extremely low loss for both signals thereby reducing noise. With its ability to reduce system noise, this novel signal combiner delivers the best opportunity to receive a desired signal not easily distinguished from background noise. While Glenn's new technology will form part of the front-end for a new software-defined radio in ground stations, it is also poised to be an important piece in telecommunications devices, including cell phones, Wi-Fi, hot spots, satellites, and future wireless technologies.
Through low-loss signal combination, Glenn is leading the way to optimize radio transmission remotely during self-checking routines. Glenn's signal combiner offers a simple method to minimize signal loss significantly when combining two signals. Using conventional combiners in bit-error-rate testing results in a loss of 3 to 4 dB per band, and with a directional coupler the secondary signal experiences losses of 10 dB or more. Moreover, during signal measurements, the additional components must be placed and later removed to prevent any impact to the measurement, making for a cumbersome process. Glenn's solution is to combine the primary and secondary signals in the frequency domain through the use of a frequency division diplexer/multiplexer in combination with a wideband ADC. The multiplexer selects one or more bands in the frequency domain, and the ADC performs a non-linear conversion to digital domain by folding out-of-band signals in with the primary signal. NASA makes use of subsampling a given band within the ADC bandwidth to fold it into another band of interest, effectively frequency-shifting them to a common frequency bandwidth. Glenn's breakthrough method has two significant advantages over the conventional use of a power combiner or directional coupler in bit-error-rate testing: 1) it combines signal and noise (secondary signal) with very low loss, and 2) it enables the selection of the desired signal-to-noise ratio with no need for the later cumbersome removal of components. This streamlined process allows for invaluable in-situ or installed measurement. Glenn's novel technology has great potential for satellite, telecommunications, and wireless industries, especially with respect to equipment testing, measurement, calibration, and check-out.
- Efficient: Offers low distortion and improved bit-error-rate, thereby maximizing data throughput given the available spectrum
- Reduced noise: Less than 1 dB insertion loss for each frequency band
- Cost-saving: Requires very few components for effective transmission and testing
- Versatile: Can be configured to enable self-calibration, or to include a bit-rate-tester into the hardware
- Communications satellites
- Wireless communications
- Military communications
- Signal processing
- Ground stations
- Software-defined radios