MIMO Polarization Control for Legacy Interference

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Solution Overview

Problem

The introduction of a second transmit antenna port in MIMO capable communication systems causes interference for legacy user equipment, degrading communication quality due to non-orthogonal channel conditions, which existing MMSE receivers cannot fully suppress.

Innovation Solution

A method and arrangement that control the polarization state of signals from a MIMO capable radio base station by adjusting the relative phase between transmit antenna ports to provide orthogonal polarization states and interchanging these states to reduce interference, utilizing a precoder unit and polarization switch to alternate between vertical and horizontal polarizations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a second transmit antenna port is introduced in MIMO capable communication systems, then spectral efficiency and bitrates are improved, but interference for legacy user equipment increases

Engineering Contradiction:

Improvespectral efficiencyVSAvoidinterference for legacy user equipment

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the polarization parameter of the transmitted signals by controlling the relative phase between antenna ports to provide orthogonal polarization states (e.g., vertical and horizontal). This parameter change allows legacy user equipment to suppress interference through polarization filtering, resolving the contradiction between improved spectral efficiency and reduced interference for legacy devices

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces polarization control as an intermediary mechanism between the MIMO transmission system and legacy user equipment. By manipulating the polarization states of signals from different antenna ports, the system creates an intermediate layer that allows legacy devices to distinguish and suppress unwanted interference while maintaining compatibility with existing hardware

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If orthogonal channelization codes are used for second antenna port signals, then interference orthogonality is improved, but interference suppression fails in dispersive channels

Engineering Contradiction:

Improvecode orthogonalityVSAvoidinterference in dispersive channels

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent transitions from relying solely on code orthogonality to utilizing polarization orthogonality as the primary interference suppression mechanism. By controlling the relative phase between antenna ports to create orthogonal polarization states, the system maintains interference suppression effectiveness even in dispersive channels where code orthogonality degrades

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent adds the polarization dimension as an additional degree of freedom for interference suppression. Instead of relying only on the code domain, the system exploits the polarization domain to create orthogonal signal separations that are robust against channel dispersion, effectively moving the interference suppression mechanism to another dimension

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 suppresses interference experienced by legacy user equipment, resulting in a practical gain of 1-2 dB in signal-to-interference ratio, facilitating the introduction of MIMO capability in HSPA networks and reducing inter-cell interference.

Implementation Method 1

controlling a relative phase between transmitted signals from the first transmit antenna port and the second transmit antenna port to provide a predetermined pair of orthogonal polarization states

Methodology Applied

Scientific EffectPhase control:

Implementation Method 2

a polarization switch configured to interchange the polarization states of the first and second antenna ports, to provide transmitted polarized signals with alternating polarization states

Methodology Applied

Scientific EffectPolarization switching:

Data Source

PatentUS9559763B2Method and arrangement for polarization control in a communication system

Publication Date: 2017.01.31 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Controlling the polarization state of signals to be transmitted from a MIMO capable radio base station node to a plurality of user equipment, which radio base station node comprises a precoder unit connecting a first and a second virtual antenna port to a respective first and second transmit antenna port, by the steps of controlling a relative phase between transmitted signals from the first and second transmit antenna port to provide a predetermined pair of orthogonal polarization states for signals transmitted on the first and second virtual antenna ports, and interchanging the polarization states of the first and second virtual antenna ports, to provide transmitted polarized signals with alternating polarization states.