Digital Equalization for Distributed Antenna Systems
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Solution Overview
Problem
Distributed Antenna Systems (DAS) with digital transport for downlink and uplink RF signals face unwanted distortion issues due to digitization, affecting signal quality across frequency bands.
Innovation Solution
A signal processing device with a finite impulse response (FIR) filter is used to equalize RF signals by determining a compensator parameter vector based on estimated system responses to frequency sweep test inputs, ensuring a flat frequency response across the band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital transport is used for downlink and uplink RF signals, then signal quality and stability are improved, but distortion is introduced into the RF signal
Solution Approach 1:
The patent measures the actual distortion characteristics of the digital transport system using frequency sweep signals, then uses this measured distortion information to design compensating filters that convert the harmful distortion into beneficial pre-equalization, eliminating the net distortion effect while maintaining digital transport benefits
Solution Approach 2:
The patent applies pre-equalization filtering to the transmitted RF signal before it enters the digital transport system, and post-equalization filtering to the received signal after digital transport. This preliminary and subsequent action compensates for distortion before it degrades signal quality and corrects any remaining distortion after transport
2Measurement precision
If frequency sweep signal testing is performed to estimate system response, then accurate distortion measurement is achieved, but measurement time is increased
Solution Approach 1:
The patent implements a two-stage measurement approach: first performing comprehensive frequency sweep measurements to establish the baseline system response and distortion characteristics, then using these pre-measured characteristics for ongoing system calibration and adaptation, reducing the need for repeated full-spectrum measurements
Solution Approach 2:
The patent focuses frequency sweep measurements on critical frequency bands where distortion is most likely to occur and where the system operates most frequently, rather than uniformly measuring all possible frequencies, thereby achieving sufficient measurement precision with reduced measurement time
Data Source
AI summary
Systems and methods for digitally equalizing a signal in a distributed antenna system are provided. In one embodiment, a signal processing device within a distributed antenna system comprises a signal path within a signal processing board, the signal path having an uncompensated distortion function of G(ω) with a system response represented by y(n); and a compensator coupled to the signal path, the compensator having a finite impulse response (FIR) filter with an impulse response function represented by H(ω), the compensator having an FIR filter parameter vector {right arrow over (h)} determined from an estimated system response y(n) of the signal path to an input comb signal x(n), wherein y(n) is estimated from interpolated measured output responses of the signal path to a plurality of frequency sweep signal test inputs.