Base Station Subframe Coordination for Interference Reduction

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Solution Overview

Problem

In heterogeneous cellular networks, downlink transmissions from low power base stations can be severely interfered by macro base stations, leading to difficulties in extending the range of low power base stations and achieving desirable user equipment coverage, as existing solutions like Almost Blank Subframes reduce macro base station capacity.

Innovation Solution

A method where a first base station defines subframes to avoid interfering with downlink radio channels of a second base station in an extended range, receiving interference indications from the second base station to adjust further downlink transmissions and minimize interference, allowing for increased capacity while reducing harmful interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If macro base stations use high downlink power to provide coverage, then coverage area is improved, but interference to low power base stations in extended range increases

Engineering Contradiction:

Improvecoverage areaVSAvoidinterference to low power base station

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The time domain is segmented into different subframes. Macro base stations transmit in certain subframes while avoiding transmission in other subframes when low power base stations need to serve users in extended range. This segmentation allows both coverage and interference reduction by dividing the transmission timeline into exclusive periods for different base station types.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Macro base stations employ periodic transmission patterns where they alternate between active transmission subframes and silent subframes. This periodic action ensures that during periods when low power base stations are serving extended range users, the macro base stations refrain from transmitting, thereby reducing interference while maintaining coverage during other periods.

Inventive Principle:

Principle #19Periodic action

2Area of stationary object

If low power base stations extend their range to serve more users, then user coverage is improved, but downlink transmission reliability decreases due to interference

Engineering Contradiction:

Improveservice areaVSAvoiddownlink transmission reliability

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The patent introduces an intermediary mechanism where the network controller coordinates between macro and low power base stations. The controller identifies subframes where interference should be avoided and signals this information to low power base stations, enabling them to reliably serve users in extended range without harmful interference from macro base stations during critical transmission periods.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system implements feedback mechanisms where the network controller monitors interference conditions and adjusts transmission schedules accordingly. Information about interfering subframes is fed back to low power base stations, allowing them to adapt their transmission timing to avoid interference while maintaining service area coverage and reliability.

Inventive Principle:

Principle #23Feedback

3Object-affected harmful factors

If Almost Blank Subframes are used to reduce interference, then interference to low power base stations is reduced, but macro base station capacity decreases

Engineering Contradiction:

Improveinterference to low power base stationVSAvoidmacro base station capacity

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

Instead of applying Almost Blank Subframes uniformly across all macro base station transmissions, the patent applies the principle locally by identifying specific subframes where interference to particular low power base stations occurs. Macro base stations then selectively avoid transmission only in those specific interfering subframes while maintaining full capacity in non-interfering subframes, thus reducing interference without unnecessarily sacrificing overall capacity.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS8879492B2Methods and arrangements for handling a downlink transmission in a cellular network

Publication Date: 2014.11.04 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A method in a first base station (105) for handling a downlink transmission is provided. The first base station (105) serves a first user equipment (120). The first base station (105) defines a subframe in which the first base station (105) is to avoid interfering a downlink radio channel between a second base station (115) and a second user equipment (125). The second user equipment (125) is located in an extended range of the second base station (120). The first base station (105) performs, in the defined subframe, a downlink transmission to the first user equipment (120). The first base station (105) receives, from the second base station (115), an indication of an interference caused by the performed downlink transmission on the downlink radio channel. The first base station (105) adjusts a further downlink transmission to be performed by the first base station (105) based on the indication.