Network Node Intermodulation Handling via Power Scheduling
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Solution Overview
Problem
In wireless communication systems, passive intermodulation (PIM) products caused by nonlinear effects in radio frequency (RF) transmitters can lead to reduced signal-to-noise ratio (SNR) and decreased coverage due to interference between different frequency bands, especially in multi-operator FDD RBS sites, where third-order PIM products can fall into receive bands and cannot be filtered out, resulting in increased noise levels and reduced uplink SNR.
Innovation Solution
A method is implemented where a network node detects probable intermodulation interference by monitoring interference levels and scheduling an uplink transmission grant for affected stations, reducing TX signal power during specific time intervals to minimize PIM effects, allowing only necessary signals like pilots and synchronization signals to be transmitted at lower power, thereby reducing intermodulation interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple FDD downlink bands are transmitted simultaneously at full power, then network capacity and throughput are maximized, but third-order PIM products fall into receive bands causing SNR degradation and coverage reduction
Solution Approach 1:
The system implements periodic monitoring of uplink signal quality at the network node. When PIM interference is detected, the node periodically schedules reduced-power transmission time intervals (TTIs) for the affected downlink band, creating a cyclic pattern of normal and reduced-power transmissions that maintains acceptable SNR while preserving overall network capacity
Solution Approach 2:
The system dynamically adjusts the transmit power of the downlink band based on real-time detection of PIM interference conditions. The network node monitors uplink signal quality and adaptively schedules reduced-power TTIs only when interference is detected, allowing the system to transition between full-power and reduced-power states according to actual channel conditions
2Reliability
If reduced TX power is applied to downlink bands to eliminate PIM products, then uplink SNR improves, but network capacity and throughput decrease
Solution Approach 1:
Instead of continuously reducing transmit power across all TTIs, the system applies reduced power only to specific TTIs where PIM interference is detected. This partial application of the power reduction measure maintains network capacity during normal operation while providing sufficient interference mitigation when needed
Solution Approach 2:
The system changes the transmit power parameter dynamically based on detected interference conditions. By monitoring uplink signal quality and adjusting the downlink transmit power level accordingly, the system optimizes the balance between maintaining high network capacity and ensuring acceptable uplink SNR
3Object-affected harmful factors
If frequency filtering is applied to remove PIM products, then receive band interference is reduced, but PIM products cannot be filtered out when they are collocated with wanted signals
Solution Approach 1:
The system uses time-domain scheduling as an intermediary mechanism to separate wanted and unwanted signals. By scheduling reduced-power TTIs specifically for downlink bands that generate PIM interference, the system creates temporal separation between high-power transmission (which generates PIM) and uplink reception, avoiding the need for frequency filtering
4Object-affected harmful factors
If service technicians are sent to RBS sites to identify and replace PIM-causing elements, then the root cause of interference is eliminated, but service interruption time increases and network availability decreases
Solution Approach 1:
The network node performs self-diagnosis by monitoring uplink signal quality and automatically detecting PIM interference conditions. The system schedules reduced-power TTIs autonomously without requiring external intervention, enabling the network to self-correct the interference problem and maintain service continuity
Solution Approach 2:
The system implements a feedback loop where the network node continuously monitors uplink signal quality, detects PIM interference conditions, and automatically adjusts downlink transmit power accordingly. This closed-loop control enables real-time interference mitigation without requiring manual site visits
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 approach effectively reduces intermodulation interference by scheduling reduced TX power during affected time intervals, maintaining communication quality and capacity while minimizing the need for immediate site maintenance, thus addressing the issue of PIM-induced SNR degradation and coverage limitations.
Implementation Method 1
The purpose of a transmitter in a digital wireless communication system is to convert a digital low-frequency baseband signal into an RF signal while preserving the modulation, and thereby the baseband information
Implementation Method 2
distortion products caused by nonlinearities in the transmitter may fall into the receive band and raise the over-all receiver noise figure
Implementation Method 3
In order to reduce this effect, external cavity filters may be used in radio base stations (RBS) to filter out unwanted components outside wanted transmission band
Implementation Method 4
due to non-linear effects caused by for instance excitation of ferromagnetic materials or other physical properties, e.g. metal oxidation, mechanical disruptions, etc., passive intermodulation (PIM) products may be reflected back to or within the RBS site and fall into one of the operator's receive band and cause desensitization
Implementation Method 5
a radio receives and transmits information simultaneously, which may be performed according to frequency duplex division (FDD), i.e. the radio transmits on one frequency and receives on another frequency
Data Source
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Figure 5
AI summary
There is provided a method of handling interference caused by inter-modulation in a network node. The method comprises detecting an interference level on an uplink carrier frequency band for stations, and determining whether the interference level indicates probable inter-modulation interference. If the interference level indicates probable inter-modulation interference, the method proceeds with scheduling an uplink transmission grant for at least one of the stations. The uplink transmission grant is valid for a first transmission time interval. The uplink transmission grant is transmitted to the station. A transmit level on the downlink carrier frequency band is assigned at the first transmission time interval such that inter-modulation interference is reduced on the uplink carrier frequency band at the first transmission time interval. An uplink transmission from the station is received at the first transmission time interval. Further methods, computer programs, a network node and a network node site are also disclosed.