IAB RACH Resource Overlap Handling for Millimeter Wave Access
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Solution Overview
Problem
Current random access channel (RACH) procedures are not suitable for integrated access and backhaul (IAB) systems, particularly in millimeter wave deployments, due to severe path losses and interference challenges, which affect the initial access and beamforming processes between access WTRUs and backhaul nodes.
Innovation Solution
The system configures and manages random access channel resources dynamically, allowing access WTRUs to receive an overlap indication of available resources from IAB nodes, enabling them to select appropriate resources for PRACH transmission, perform beam failure recovery, and adjust timing advance values for reliable communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current RACH procedures are used in IAB systems, then initial access can be performed, but severe path losses and interference in millimeter wave deployments degrade reliability and coverage
Solution Approach 1:
The system performs preliminary configuration of RACH resources and provides overlap indications to WTRUs before actual PRACH transmission occurs. This allows WTRUs to pre-know which resources are available and avoid collisions with IAB node transmissions, thereby improving access reliability in the presence of severe path loss
Solution Approach 2:
The RACH resources are segmented into overlapping and non-overlapping portions. By dividing the resource space and providing clear indications to WTRUs about which segments are available, the system enables reliable access despite the harmful effects of millimeter wave propagation
2Productivity
If RACH resources are configured for both access WTRUs and IAB nodes, then resource utilization increases, but resource overlap causes interference and access failures
Solution Approach 1:
The system implements feedback mechanisms where IAB nodes provide overlap indications to WTRUs regarding RACH resource availability. This feedback loop enables WTRUs to select appropriate resources that avoid interference with IAB node transmissions, maintaining high resource utilization while eliminating harmful interference effects
Solution Approach 2:
The RACH resource allocation is made dynamic through time-varying overlap indications. The system can adaptively inform WTRUs about which resources are currently available for PRACH transmission, allowing flexible resource utilization that avoids interference while maximizing spectral efficiency
3Area of stationary object
If beamforming is used to overcome path loss, then coverage is improved, but beam alignment complexity and timing synchronization difficulties increase
Solution Approach 1:
The system performs preliminary beam alignment and establishes timing relationships before WTRUs attempt PRACH transmission. By pre-configuring beam directions and timing advance values, the system reduces the complexity of real-time beam alignment while maintaining wide coverage area through coordinated beamforming
Solution Approach 2:
The system uses reference signals and synchronization signals as intermediaries to facilitate beam alignment between WTRUs and IAB nodes. These intermediary signals enable WTRUs to determine appropriate beam directions and timing advance values without requiring complex direct beam searching, thereby reducing alignment complexity while preserving coverage
Data Source
AI summary
In an integrated access and backhaul (IAB) system, an access WTRU may receive a random access channel (RACH) occasion (RO) configuration comprising one or more RO resources from a first integrated access backhaul (IAB) node. The access WTRU may receive an indication that one or more of the configured RO resources have an overlap with one or more IAB node RO resources. The access WTRU may monitor and receive the ROI indicating the configured RO resources that overlap with the one or more IAB node RO resources. Based on the received ROI and the configured RO resources, the access WTRU may determine one or more RO resources available for PRACH transmission. The access WTRU may select an RO resource from the available RO resources for PRACH transmission. The access WTRU may send a first PRACH transmission to the first IAB node using the selected RO resource.