Multi-stage transmit power control for femto cell interference mitigation

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Solution Overview

Problem

Femto cells deployed on different carrier frequencies from neighboring macro cells cause interference with macro network users, affecting voice call quality and leading to call drops, as their beacon transmissions on macro frequencies attract access terminals and induce interference.

Innovation Solution

Implementing a multi-stage transmit power control scheme for femto cells, which includes network listen-based power calibration, mobile-assisted range tuning, and active mobile protection, to adjust transmit power based on signal strength and messages from access terminals, ensuring adequate coverage while minimizing interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If femto cell transmits beacons on macro cell carrier frequencies to attract access terminals, then femto cell discovery and coverage are improved, but interference to macro network users increases causing call quality degradation and call drops

Engineering Contradiction:

Improvefemto cell discovery capabilityVSAvoidinterference to macro network users

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the transmit power of beacon signals based on detected macro user presence. When macro users are detected in the vicinity, the femto cell reduces or mutes beacon transmit power on macro frequencies, thereby reducing interference while maintaining the ability to provide coverage when no macro users are present.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system implements dynamic transmit power control where the beacon power level is not fixed but changes in real-time based on environmental conditions (presence of macro users). This dynamic adjustment allows the system to adapt between two states: high power for discovery when safe, and low/muted power when macro users are present, resolving the contradiction between discovery capability and interference prevention.

Inventive Principle:

Principle #15Dynamics

2Area of stationary object

If femto cell uses high transmit power to provide adequate coverage, then coverage area is improved, but interference to macro network users increases

Engineering Contradiction:

Improvefemto cell coverage areaVSAvoidinterference to macro network users

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The patent changes the transmit power parameter dynamically based on macro user detection. When no macro users are detected, the femto cell uses high transmit power to provide adequate coverage area. When macro users are detected, the system reduces transmit power to minimize interference, thus adapting the coverage area parameter based on external conditions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The system introduces an intermediary mechanism (macro user detection and control logic) that mediates between the need for high power (coverage) and the need to prevent interference. This intermediary layer allows the system to intelligently select power levels, providing coverage when safe and preventing interference when macro users are present.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If femto cell transmits continuously to maintain coverage, then service availability is improved, but interference duration and impact increase

Engineering Contradiction:

Improveservice availabilityVSAvoidinterference duration

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent implements periodic monitoring of macro user presence and adjusts beacon transmission accordingly. Instead of continuous high-power transmission, the system periodically checks for macro users and adjusts power levels in response, creating an on-demand transmission pattern that maintains service availability when safe while reducing interference duration when macro users are present.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system transitions from static continuous transmission to dynamic conditional transmission. The beacon transmission duration and continuity are adjusted in real-time based on macro user detection, allowing the system to maintain reliability when no macro users are present while limiting interference duration when macro users are detected.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS9055541B2Multi-stage transmit power control scheme for access point

Publication Date: 2015.06.09 QUALCOMM INC

AI summary

Transmit power for an access point is controlled based on information received by the access point. For example, an access point may employ one or more algorithms that use messages received from nearby access terminals to maintain an acceptable tradeoff between providing an adequate coverage area for access point transmissions and mitigating interference that these transmissions cause at nearby access terminals. Here, the access point may employ a network listen-based algorithm upon initialization of the access terminal to provide preliminary transmit power control until sufficient information is collected for another transmit power control algorithm (e.g., an access terminal assisted algorithm). Also, the access terminal may employ an active access terminal protection scheme to mitigate interference the access point may otherwise cause to a nearby access terminal that is in active communication with another access point.