Intermodulation Cancellation in Distributed Antenna Systems
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Solution Overview
Problem
Distributed antenna systems (DAS) face interference from intermodulation byproducts due to limited transmitter/receiver isolation, which degrade the signal-to-interference and noise ratio (SINR) as the number of remote units increases, leading to unwanted noise in the receive band.
Innovation Solution
Implementing an intermodulation canceler in the head-end unit that applies a frequency-dependent transfer function to uplink signals to cancel, reduce, or eliminate unwanted intermodulation byproducts by using a processing device to apply a calculated transfer function that adjusts gain and phase, thereby isolating the undesired noise from the desired signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the number of remote units in a DAS is increased to extend wireless coverage, then the coverage area is improved, but the signal-to-interference and noise ratio (SINR) deteriorates due to accumulated intermodulation byproducts
Solution Approach 1:
The patent measures the intermodulation byproducts that naturally accumulate in the DAS and uses these harmful signals themselves to create cancellation signals. By injecting reference signals and measuring the actual byproducts, the system converts the harmful intermodulation into useful cancellation information that improves SINR while maintaining expanded coverage
2Reliability
If transmitter/receiver isolation is improved to reduce intermodulation byproducts, then the SINR is improved, but the device complexity increases due to additional isolation components
Solution Approach 1:
The patent introduces an intermediary signal processing system that measures and characterizes the intermodulation byproducts, then uses this information to generate cancellation signals. This intermediary measurement and processing approach avoids the need for complex physical isolation components while achieving the same SINR improvement goal
3Object-generated harmful factors
If duplexer isolation is increased to separate uplink and downlink signals, then the intermodulation byproducts are reduced, but the loss of useful signal increases due to insertion loss
Solution Approach 1:
The patent extracts and separates only the harmful intermodulation byproducts from the useful signals by measuring them with reference signals. The cancellation system then removes only the extracted byproduct components without affecting the useful uplink and downlink signals, avoiding the energy loss that would result from using duplexer isolation on all signals
Data Source
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AI summary
One embodiment is directed to a distributed antenna system (DAS) comprising a plurality of nodes, including a head-end unit and a plurality of remote units that are communicatively coupled to the head-end unit. The head-end unit is configured to receive uplink received signals from remote units that wirelessly transceive signals in a coverage area. The head-end unit is configured to sum two or more of the uplink received signals to produce a summed uplink received signal. At least one of the nodes of the DAS includes a processing device configured to determine a transfer function and apply the transfer function to signals in the DAS to cancel, reduce, attenuate, or eliminate intermodulation byproducts in the summed uplink received signal.