Subcarrier Reservation for xDSL Modem Training Interference
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Solution Overview
Problem
The integration of new modems into Dynamic Spectrum Management (DSM) systems in xDSL networks causes interference and noise due to the training phase, which affects existing connections and reduces performance, especially during startup, as the DSM system takes time to adapt and may result in bit errors or lost connections.
Innovation Solution
Reserving a small group of subcarriers exclusively for the training phase of new modems joining the DSM group, allowing them to connect with reduced interference, using techniques like subcarrier masking or shaping, and dynamically managing these reserved subcarriers to minimize disruption to existing connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If new modems perform training phase over the whole frequency band, then they can calculate feasible data rate based on SNR measurements, but this causes interference to existing connections and results in bit errors
Solution Approach 1:
The frequency band is segmented into two parts: a first part reserved exclusively for training phase of new modems, and a second part for data transmission. This segmentation allows training signals to be isolated from data-carrying subcarriers, preventing interference to existing connections while enabling accurate SNR measurements for new modems.
Solution Approach 2:
Different quality requirements are applied to different parts of the frequency band. The first part (training subcarriers) is optimized for measurement accuracy with no data transmission, while the second part (data subcarriers) is optimized for data transmission with power spectral density constraints. This local quality differentiation resolves the contradiction between measurement needs and interference prevention.
2Adaptability or versatility
If DSM L3 controller adapts to new modems, then system performance improves, but this takes time and may result in lost connections
Solution Approach 1:
The system performs preliminary actions by reserving specific subcarriers for training before normal data transmission begins. This preliminary training phase allows the DSM L3 controller to adapt to new modems in advance, calculating feasible data rates and power spectral densities without disrupting existing connections, thereby maintaining connection stability during the adaptation process.
3Productivity
If idle data is sent over twisted-pair lines, then bandwidth utilization increases, but crosstalk interference is induced affecting other lines
Solution Approach 1:
Training signals are extracted and placed on dedicated subcarriers that are taken out from the data-carrying portion of the frequency band. This extraction ensures that training activities do not generate crosstalk interference on data transmission lines, while idle data can still be sent on the remaining subcarriers to maintain bandwidth utilization.
Data Source
Figure 1
AI summary
A method and a device for data processing are provided, wherein at least one subcarrier is reserved by a network component for a modem to get connected to the network component. Furthermore, a communication system is suggested comprising said device.