Virtual Beam Sweeping for Uniform PRACH Detection in Active Antennas
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Solution Overview
Problem
In LTE and NR active antenna systems, the narrow beams used for physical random access channels (PRACH) cause directional variations in signal power, leading to performance degradation, especially in scenarios with additive white Gaussian noise and high mobility, where beam changes can result in delayed initial attachment and poor preamble detection.
Innovation Solution
The implementation of virtual beam sweeping, where a virtual beam sweeping matrix V is applied to uplink signals to reduce directional beam variations, allowing for ubiquitous PRACH performance across all cell directions without relying on channel reciprocity or reported information from wireless devices, and is applicable to both LTE and NR systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If narrow beams are used for PRACH in active antenna systems, then beamforming gain is improved, but directional inequality causes ripple effect leading to signal power variation
Solution Approach 1:
The patent segments the beamforming process into two independent components: a beamforming matrix W that provides directional gain, and a virtual beam sweeping matrix V that fills directional gaps. This segmentation allows each matrix to specialize - W for gain and V for coverage uniformity - resolving the contradiction between beamforming gain and detection consistency.
Solution Approach 2:
The virtual beam sweeping matrix V acts as an intermediary between the narrow beams from matrix W and the final combined signal. It introduces intermediate virtual beams that fill the directional gaps, mediating the transition from high-gain narrow beams to uniform omnidirectional coverage without sacrificing the beamforming gain provided by W.
2Power
If beam management with narrow beams is implemented, then beamforming performance is improved, but beam changes during initial attachment cause delay and detection problems
Solution Approach 1:
The patent performs preliminary action by pre-calculating and applying the virtual beam sweeping matrix V in conjunction with the beamforming matrix W during the initial attachment process. This eliminates the need for sequential beam sweeping and measurement, as the virtual beam sweeping proactively fills directional gaps before preamble detection, preventing attachment delays.
Solution Approach 2:
The combined application of matrices W and V creates continuous useful action across all directions simultaneously, rather than sequentially switching between narrow beams. This continuity ensures that regardless of beam changes during initial attachment, there is always consistent coverage and detection capability in all directions, eliminating attachment delays.
3Shape
If conventional beam forming is used, then spatial patterns are created, but ripple effects cause probability of missed detection to vary by 1-2 dB in different directions
Solution Approach 1:
The patent applies local quality by making different parts of the beamforming system have different functions: matrix W provides high gain in specific directional sectors, while matrix V provides uniform coverage in the interstitial regions. This local specialization ensures that each region of the cell coverage area receives appropriate treatment - high gain where needed and uniform coverage in gaps - eliminating the ripple effect.
Solution Approach 2:
The patent merges the beamforming matrix W and virtual beam sweeping matrix V into a unified processing system where their effects are combined through matrix multiplication. This merging integrates the directional gain capability of W with the coverage uniformity of V, producing a composite beamforming solution that achieves both spatial patterning and detection probability uniformity.
Data Source
AI summary
A method and network node for virtual beam sweeping of signals received by antennas of the network node are provided. According to one aspect, a method includes determining elements of abeam forming matrix W. The method further includes determining elements of a virtual beam sweeping matrix V, the elements of the virtual beam sweeping matrix V being determined to form beams between beams formed by the beam forming matrix W. The method also includes applying the matrices V and W to uplink signals Sa received by antennas of the network node to produce received signals Sb in a beam space.