MIMO Precoder Polarization Control for Legacy Interference
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Solution Overview
Problem
Legacy user equipment in MIMO capable communication systems experience interference from secondary antenna port transmissions, which degrades communication quality due to non-orthogonal channel conditions, even with advanced receivers like MMSE.
Innovation Solution
A method and apparatus for controlling the polarization state of signals transmitted from a MIMO capable radio base station, using a precoder unit to adjust the relative phase between virtual antenna ports and interchanging polarization states to provide either vertical or horizontal polarization, thereby reducing interference for legacy user equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a second transmit antenna port is introduced for MIMO capability, then spectral efficiency and bitrates are improved, but interference for legacy user equipment increases
Solution Approach 1:
The patent changes the polarization parameter of the transmitted signals by controlling the relative phase between signals on the first and second antenna ports. By setting specific phase relationships (0°, 90°, 180°, or 270°), the system creates orthogonal polarization states that allow legacy user equipment to suppress interference from the second antenna port, thus resolving the contradiction between improved spectral efficiency and reduced interference for legacy devices
2Reliability
If orthogonal channelization codes are used for second antenna port signals, then interference orthogonality is improved, but interference suppression fails in dispersive channels
Solution Approach 1:
The patent transitions from relying solely on code-domain orthogonality to utilizing polarization-domain orthogonality. By controlling the relative phase between antenna ports to create orthogonal polarization states, the system adds a spatial dimension to interference suppression that remains effective even in dispersive channels where code orthogonality degrades
3Ease of operation
If MMSE receiver is used for legacy user equipment, then signal processing capability is improved, but complete interference suppression is still not achieved
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring the transmit system to create orthogonal polarization states before the signal reaches the receiver. This proactive measure ensures that interference from the second antenna port is inherently orthogonal to the desired signal, allowing legacy user equipment with MMSE receivers to achieve complete or near-complete interference suppression without requiring complex post-processing
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 by up to 1-2 dB, facilitating the introduction of MIMO capability in HSPA networks and improving signal-to-interference ratio, while allowing coordination of transmit polarization between cells to further reduce inter-cell interference.
Implementation Method 1
controlling, for legacy signals transmitted on the first and the second virtual antenna ports, a relative phase between legacy signals to be transmitted from the first transmit antenna port and the second transmit antenna port to provide one polarization state
Implementation Method 2
interchanging the polarization state of the legacy signals transmitted from the first transmit antenna port and the second transmit antenna port, for the legacy signals transmitted on the first and second virtual antenna ports, to provide transmitted legacy signals from the first transmit antenna port and the second antenna port with alternating polarization states
Data Source
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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 (S10) 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 (S20) the polarization states of the first and second virtual antenna ports, to provide transmitted polarized signals with alternating polarization states.