Nonlinear Distortion Discovery in Active OFDM Carriers
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Solution Overview
Problem
Conventional digital transmission systems, particularly those using DOCSIS 3.1 and OFDM technology, face challenges in detecting and locating nonlinear distortion caused by amplifiers and other sources, which resembles random noise and is difficult to discern from other signal impairments, leading to performance degradation and diagnostic complexities.
Innovation Solution
A digital transmission system that includes a transmitter, receiver, and diagnostic unit capable of demodulating OFDM signals, creating ideal signals, calculating error vectors, and cross-correlating them to determine nonlinear distortion levels, allowing for remote diagnostic testing without interrupting service.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM signals with high crest factor are transmitted to utilize wide bandwidth, then data transmission capacity is improved, but nonlinear distortion in amplifiers increases and becomes difficult to detect
Solution Approach 1:
The patent introduces a diagnostic signal as an intermediary carrier wave that is superimposed on the OFDM signal. This diagnostic carrier operates at a different frequency and allows separation of distortion measurement from normal data transmission, enabling accurate nonlinear distortion detection without interrupting service.
Solution Approach 2:
The diagnostic carrier is transmitted periodically alongside the OFDM signal, allowing continuous monitoring of nonlinear distortion while maintaining normal data transmission. This periodic injection enables ongoing system health assessment without affecting productivity.
2Measurement precision
If conventional test equipment is used to measure nonlinear distortion, then measurement capability is provided, but the distortion resembles random noise and cannot be easily discerned from other signal impairments
Solution Approach 1:
A dedicated diagnostic carrier wave serves as an intermediary reference signal that is clearly distinguishable from random noise and other impairments. By modulating this known carrier and comparing its received state against the transmitted state, nonlinear distortion can be precisely measured and differentiated from other signal degradations.
Solution Approach 2:
The diagnostic carrier is assigned a distinct frequency 'color' that differentiates it from the OFDM data carriers and random noise. This frequency separation allows selective filtering and analysis, enabling the measurement equipment to isolate and measure distortion affecting the diagnostic carrier without being confused by other signal components.
3Ease of operation
If diagnostic testing is performed on in-service carriers, then remote diagnostic capability is achieved, but the test signal may interfere with normal data transmission
Solution Approach 1:
The signal spectrum is segmented into distinct frequency regions: one for OFDM data carriers and another for the diagnostic carrier. This frequency division allows both data transmission and diagnostic testing to occur simultaneously without mutual interference, enabling remote diagnostics on in-service carriers while maintaining normal operations.
Solution Approach 2:
The diagnostic carrier acts as an intermediary element that carries measurement information without disrupting the primary data transmission function. By using this separate carrier, the system can perform remote diagnostics while the OFDM data carriers continue to transmit user data without interference.
Data Source
AI summary
A digital transmission system includes a transmitter configured to transmit an orthogonal frequency division multiplexing (OFDM) signal along a signal path, a receiver for receiving the OFDM signal from the transmitter and extracting OFDM symbols from the received OFDM signal, and a diagnostic unit configured to (i) demodulate the received OFDM signal to create an ideal signal, (ii) compare the received OFDM signal with the ideal signal to calculate an error signal, (iii) cross-correlate the error signal with the ideal signal, and (iv) determine a level nonlinear distortion from one of the transmitter and the signal path based on the correlation of the error signal with the ideal signal.