Air Force

Pre-distortion filter for multi-GHz data transmission

Improved signal quality for ultra wideband radio

Communications

As data-rate requirements necessary to support the wireless transmission of high-quality information increase, so does the need for high bandwidth communications systems to support the receiving of this information. One method proposed to enable these high data-rates is to increase wireless bandwidths to multi-gigahertz (GHz). Such a bandwidth can theoretically support much higher data-rates than traditional kilohertz (kHz) to megahertz (MHz) signals, while maintaining realistic modulation schemes that require only moderate signal-to-noise ratios. However, existing microwave frequency components are not designed with the intention of supporting multiple GHz of instantaneous bandwidth. Even though these components may support wide bandwidths, their magnitude and phase response is non-linear. While a narrow-band may approach linear operation through an analog component, the wideband nature of a multi-GHz transmission means that some signal components may experience frequency-selective fading that differs significantly from other frequency components across the same instantaneous signal bandwidth. This results in distortion of the transmission and data loss.

Pre-distortion of a transmitted radio frequency is an accepted technique and is necessary when compression of a waveform within a high-power amplifier (PA) causes distortions in the signal. Because some amount of this distortion is dependent on the input signal power, temperature stability, and PA specifications, given enough information a portion of the distortion can be modeled.

Air Force researchers have extended the use of pre-distortion techniques from not only the non-linear effects of PA compression, but also to the wideband non-linear effects exhibited by analog upconversion components.

The novel system models the steady-state magnitude response of the analog upconversion to determine the non-linear effects introduced on the transmission, through the sounding of the analog components. It uses a finite impulse response filter, whose magnitude response is the inversion of the steady-state magnitude response of the analog upconversion chain, derived using existing mean error minimization techniques.

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