Beam-Based Random Access Using BRS-Guided Beam Selection
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Solution Overview
Problem
In beam-based radio-access systems, network nodes face challenges in selecting the appropriate beam for transmitting random-access responses and detecting preambles due to unknown uplink and downlink reception conditions, leading to increased complexity, latency, and interference.
Innovation Solution
Wireless devices and network nodes utilize beam-specific reference signals (BRS) to determine a preferred downlink beam, allowing the network to transmit random-access responses in the same beam, thereby improving coverage and reducing the need for calibrated RF chains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If beam-based random access is implemented without beam-specific reference signals, then device complexity is reduced, but random-access coverage and reliability deteriorate due to unknown uplink and downlink reception conditions
Solution Approach 1:
The network node transmits beam-specific reference signals (BRS) before the random access procedure to enable the wireless device to measure and determine the preferred downlink beam in advance. This preliminary beam measurement allows the device to select an appropriate random access resource that corresponds to the best beam, ensuring reliable random access without requiring complex beam management during the access procedure itself.
2Reliability
If the network node searches for preambles in all beams, then detection reliability is improved, but latency and processing complexity increase
Solution Approach 1:
The patent segments the random access resources (preambles, time slots, frequency resources) into multiple groups, where each group is associated with a specific downlink beam. The wireless device selects a resource from the group corresponding to its preferred beam, and the network node only needs to search for preambles in the specific beam associated with that resource group. This segmentation dramatically reduces the search space compared to searching all beams, thereby reducing latency and processing complexity while maintaining reliable detection.
Solution Approach 2:
The selection of random access resources by the wireless device provides implicit feedback to the network node about the preferred downlink beam. By monitoring which resource group the device selects and detecting the preamble in the corresponding beam, the network node can efficiently identify the best beam without exhaustive searching, reducing both latency and complexity while maintaining detection reliability.
3Strength
If multiple beams are used for sector coverage, then signal strength and beamforming gain are improved, but the number of beams and system complexity increase
Solution Approach 1:
The patent creates a universal mapping relationship between downlink beams and random access resources that applies across all beams in the sector. Each random access resource is designed to work with a specific beam, and the mapping rules are standardized so that the same resource selection logic applies regardless of which beam is preferred. This universal approach allows the system to manage multiple beams efficiently without requiring separate complex management mechanisms for each beam, thereby maintaining beamforming gain while controlling system complexity.
Data Source
AI summary
A method in a wireless device for performing random access to a network node. The method comprises receiving a set of downlink beam-specific reference signals, BRS, from the network node, and determining a preferred BRS based on the received signal power for each BRS. The method also comprises selecting, based on the preferred BRS, a random-access resource to be used for transmitting a random-access attempt to the network node, as well as using the selected random-access resource when transmitting a random-access attempt to the network node, whereby the selection of random-access resource indicates to the network node which downlink beam is preferred by the wireless device to be used for downlink transmissions.