Offsetting Downlink Interference in DAS Uplink Paths
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Solution Overview
Problem
In distributed antenna systems (DAS), unwanted downlink interference signals generated by non-linearities in power amplifiers leak into the uplink path, degrading wireless communications signals and requiring costly high-isolation RF filters to mitigate.
Innovation Solution
An interference signal offset circuit is introduced in the remote antenna unit (RAU), comprising an offset signal generation circuit and a signal summing circuit to generate and combine uplink interference offset signals with uplink communications signals, effectively offsetting unwanted downlink interference products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-isolation RF filters are used to block downlink interference products from leaking into the uplink path, then uplink signal quality is improved, but system cost and device complexity increase
Solution Approach 1:
The patent generates interference offset signals that replicate the characteristics of the unwanted downlink interference products (including intermodulation and harmonic products). These offset signals are intentionally designed to have the same frequency and amplitude characteristics as the harmful interference, but with opposite phase. When combined with the uplink signal, they cancel out the interference through destructive interference, converting the harmful interference into a beneficial cancellation effect.
Solution Approach 2:
The system proactively generates and applies interference offset signals before the uplink signal is transmitted through the power amplifier. By pre-calculating the expected interference products based on the downlink signal characteristics and applying their opposites to the uplink path, the system prevents interference degradation before it occurs, rather than attempting to filter it out after the fact.
2Object-affected harmful factors
If high-isolation RF filters are deployed to prevent interference product leakage, then interference suppression is improved, but device complexity and implementation difficulty increase
Solution Approach 1:
The patent replaces the mechanical/passive approach of using physical RF filters with an active electronic signal processing approach. Instead of relying on complex filter hardware to block interference frequencies, the system uses digital signal processing to generate and inject cancellation signals. This substitution of active electronic control for passive mechanical filtering simplifies the hardware architecture while achieving equivalent or superior interference suppression.
Solution Approach 2:
The interference offset circuit acts as an intermediary between the downlink and uplink paths. Rather than directly blocking interference between these paths with complex filters, the circuit mediates by generating intermediate cancellation signals that represent the interference characteristics. These intermediary offset signals are then combined with the uplink signal to achieve clean transmission, simplifying the overall system architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances signal quality by suppressing unwanted interference, providing flexibility in implementation without the need for high-cost RF filters, thereby improving uplink signal integrity and reducing costs.
Implementation Method 1
One or more interference products (e.g., intermodulation or harmonic product(s)) of the downlink wireless communications signals can be generated in the downlink path and leak over to the uplink path, thus interfering with the uplink wireless communications signals
Data Source
AI summary
Offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (DAS) is disclosed. In this regard, in one example, an interference signal offset circuit is provided in an RAU to offset interference products leaked from a downlink path to an uplink path. An offset signal generation circuit is configured to generate at least one uplink interference offset signal based on the interference products leaked from the downlink path. A signal summing circuit is configured to combine the at least one uplink interference offset signal with an uplink signal received on the uplink path, thus offsetting the interference products in the uplink signal. By providing the interference signal offset circuit in the RAU to offset the interference products on the uplink path, it is possible to provide more implementation flexibility for the RAU without degrading the uplink signal.