OFDM Beam Switching Power Shaping for ACLR Control
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Solution Overview
Problem
Existing beam change management techniques in wireless communication systems, particularly in 5G cellular systems, result in spectrum broadening and degraded adjacent channel leakage ratio (ACLR), leading to capacity loss and difficulty in meeting regulatory emission limits, especially in scenarios with frequent beam direction changes.
Innovation Solution
Temporarily adapting output power during transmission beam changes, such as setting it to zero or decreasing it to a lower level, using functions like linear or root raised cosine, to mitigate spectrum broadening and maintain ACLR, implemented in the cyclic prefix of OFDM symbols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If beam direction is changed frequently to serve many users with low latency, then system capacity and user service quality are improved, but spectrum broadening occurs and ACLR is degraded
Solution Approach 1:
The patent applies preliminary action by performing output power adaptation during the cyclic prefix period before the actual beam change takes effect. By preparing the power adaptation in advance during the guard interval, the system mitigates spectrum broadening before it occurs during the data transmission portion of the OFDM symbol, thus maintaining both high beam switching frequency and spectral containment.
Solution Approach 2:
The patent implements beforehand cushioning by temporarily reducing the output power during the cyclic prefix period before the beam change is fully executed. This power reduction acts as a cushion that prevents the abrupt beam transition from causing excessive spectrum broadening and ACLR degradation, while allowing the beam direction to change as needed for serving multiple users.
2Ease of operation
If beam direction is changed frequently, then user service quality is improved, but ACLR is degraded and regulatory emission limits are difficult to fulfill
Solution Approach 1:
The system performs output power adaptation during the cyclic prefix period before the beam change affects data transmission. This preliminary power adjustment prevents ACLR degradation from occurring during the useful signal portion, allowing frequent beam switching to maintain user service quality while complying with emission limits.
Solution Approach 2:
The cyclic prefix serves as an intermediary period where output power adaptation is applied. This intermediary mechanism allows the system to transition between beam directions while using the guard interval to mitigate harmful spectral effects, thus maintaining ease of operation for serving multiple users while preventing ACLR degradation.
3Object-generated harmful factors
If output power is temporarily adapted during beam change, then spectrum broadening is reduced, but additional signal processing is required
Solution Approach 1:
The patent applies local quality by restricting the output power adaptation to only the cyclic prefix portion of the OFDM symbol, rather than applying it to the entire symbol duration. This localized approach reduces spectrum broadening during the critical data transmission period while minimizing the additional processing burden to only the guard interval period.
Solution Approach 2:
The system applies partial action by implementing output power adaptation only during the cyclic prefix period rather than continuously. This partial application is sufficient to mitigate spectrum broadening caused by beam changes while avoiding the excessive processing complexity that would result from continuous power adaptation throughout the entire OFDM symbol.
4Object-generated harmful factors
If channel filtering is used to mitigate spectrum broadening in digital beamforming, then spectrum broadening is reduced, but it does not address the analog part in hybrid beamforming
Solution Approach 1:
The patent implements universality by applying output power adaptation during the cyclic prefix period, which is a mechanism that works for all beamforming types including analog, digital, and hybrid beamforming. Unlike channel filtering which is specific to digital beamforming, this power adaptation approach provides a unified solution that mitigates spectrum broadening across all beamforming architectures.
Solution Approach 2:
The system changes the output power parameter during the cyclic prefix period to mitigate spectrum broadening. This parameter change approach is universally applicable to analog, digital, and hybrid beamforming systems, unlike channel filtering which cannot be applied to the analog portion of hybrid beamforming. The power parameter adjustment provides a beamforming-type-agnostic solution.
Data Source
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AI summary
A transmission beam change method is disclosed for a wireless communication transmitter adapted to transmit an orthogonal frequency division multiplex (OFDM) signal using a transmission beam of a plurality of transmission beams available at the wireless communication transmitter. The method comprises temporarily adapting an output power during a transmission beam change from one transmission beam to another transmission beam. Typically, the transmission beam change is performed during a cyclic prefix (CP) of an OFDM symbol and the temporary adaptation is applied to only a part of the CP. Temporarily adapting the output power may comprise decreasing the output power to initiate the temporary adaptation and increasing the output power to terminate the temporary adaptation. For example, the temporary adaptation may be performed during all transmission beam changes or only when an occurrence frequency of transmission beam changes is higher than a threshold value. Corresponding arrangement, network node, baseband unit, wireless communication device and computer program product are also disclosed.