DSL Transmitter Phantom Channel Selection for Crosstalk Reduction
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Solution Overview
Problem
High-frequency signal transmission over twisted metallic pairs in DSL networks is hindered by crosstalk, particularly Far End Cross Talk (FEXT), which increases with frequency, and additional interference from phantom modes, making it difficult to maintain effective data transmission without physical access to interfering modes.
Innovation Solution
The method involves selecting a subset of phantom channels based on cross-talk coupling to transmit signals in multiple modes, including differential and phantom modes, optimizing signal transmission to maximize data rate and reduce errors by exploiting orthogonal phantom channels and using multiple access techniques like FDMA or CDMA to create a unified composite channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high frequency signals are transmitted over twisted metallic pairs to increase bandwidth, then data transmission capacity is improved, but crosstalk interference increases significantly
Solution Approach 1:
The patent converts the harmful crosstalk effect into a beneficial signal by transmitting the same data over multiple pairs and using signal processing at the receiver to combine the direct signal with crosstalk-induced signals constructively, thereby improving signal strength and bandwidth while mitigating interference
Solution Approach 2:
The patent merges multiple transmission paths (direct path and crosstalk paths through different wire pairs) into a unified communication channel, allowing signals to arrive through multiple routes and be combined at the receiver to achieve diversity gain and improved transmission reliability
2Reliability
If vectoring technology is used to compensate for crosstalk effects, then signal quality is improved, but system complexity increases due to required signal processing
Solution Approach 1:
The patent performs preliminary characterization of the crosstalk coupling between pairs during system setup or training phases, storing this information for later use in signal combination, thereby avoiding real-time complex processing during data transmission
Solution Approach 2:
The patent uses feedback from signal quality measurements to adjust the combining weights and phases of signals from different paths, continuously optimizing the reception to maintain high signal quality while adapting to changing channel conditions
3Productivity
If multiple pairs are used to transmit signals to improve bandwidth, then data rate is increased, but phantom mode interference is introduced
Solution Approach 1:
The patent applies different signal processing techniques to different pairs based on their individual characteristics and coupling relationships, optimizing each pair's contribution while minimizing phantom mode interference through selective signal combination
Solution Approach 2:
The patent transforms the problem by moving from single-pair differential mode transmission to multi-pair transmission utilizing both differential and phantom modes, adding a new dimension to the signal space and enabling higher data rates through increased degrees of freedom
Data Source
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AI summary
A transmitter device 16 for transmitting data to a plurality of receiver devices 51, 52, 53, each of which is connected to the transmitter device via at least one respective pair of wires 21, 22, 23, each receiver device being operable to receive signals detected as a change over time in the potential difference across the local ends of each respective pair of wires extending between the receiver device and the transmitter device, the transmitter device being operable to transmit signals onto the wires extending between the transmitter device and the plurality of receiver devices in a plurality of different modes, over a plurality of different channels, the different modes including phantom and differential modes and the different channels including a first set of phantom channels, the transmitter comprising a phantom channel selector 1690 for selecting a second set of one or more phantom channels from the first set, the second set being a proper subset of the first set comprising one or more of the phantom channels of the first set, the selection being made in dependence upon the cross-talk coupling between the phantom channels of the first set and the reception of signals at each of the receivers detected as a change over time in the potential difference across the local ends of the respective pair of wires extending between the respective receiver device and the transmitter device; and a connector 1670 for connecting the selected phantom channels to the transmitter such that the transmitter is able to transmit signals from the transmitter onto the phantom channel or channels of the second set of phantom channels.