Composite RACH Preamble for Millimeter-Wave Beamforming
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Next-generation mm-wave cellular communication systems face challenges in achieving fast and robust initial access due to the tradeoff between latency and coverage, as directional beamforming requires a large number of beams, increasing acquisition time and latency, and existing solutions struggle to align beams optimally with user equipment locations.
Innovation Solution
The use of a single composite RACH preamble that signals multiple best downlink transmit beams and their relative weights allows the base station to calculate an optimal beamformer, enabling efficient and robust initial access by transmitting these beams during their respective opportunities, thereby optimizing beamforming during the initial access phase without the need for further beam refinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If directional beamforming with multiple transmit beams is used to overcome path loss, then coverage is improved, but acquisition time and latency increase
Solution Approach 1:
The base station performs preliminary beamforming training by transmitting synchronization signal blocks (SSBs) on multiple predefined transmit beams before the random access procedure. The UE measures these beams in advance and identifies the best beams, so that when the RACH preamble is transmitted, the base station can immediately determine the optimal beam without requiring extensive search during the access procedure itself.
Solution Approach 2:
The patent introduces an intermediate beam identification mechanism where the UE selects and indicates its preferred transmit beams through the RACH preamble transmission. The base station uses this intermediate information (the selected beam index carried in the preamble) to quickly determine the optimal beam for subsequent communication, avoiding the need to test all beams sequentially.
2Reliability
If the number of transmit beams is increased to align with exact UE location, then acquisition probability is improved, but acquisition time increases linearly
Solution Approach 1:
The patent segments the beam search space into two phases: (1) a coarse search phase where the UE measures multiple SSBs on different beams and identifies the best ones, and (2) a fine access phase where the UE transmits the RACH preamble on the identified best beam. This segmentation allows the system to handle a large number of beams without linearly increasing acquisition time, as the heavy lifting is done in parallel during SSB measurement rather than sequentially during access.
Solution Approach 2:
The base station transmits more SSBs on multiple beams than strictly necessary for minimum coverage, allowing the UE to measure and identify the best beams among a larger set. This excessive action in the SSB transmission phase enables faster convergence during the actual access phase, as the UE already has measurements to guide its preamble transmission.
3Reliability
If narrower beams are used to achieve high beamforming gains, then link quality is improved, but the number of beam directions increases
Solution Approach 1:
The base station performs preliminary beamforming training by transmitting synchronization signal blocks (SSBs) on multiple predefined transmit beams before the random access procedure. The UE measures these beams in advance and identifies the best beams, so that when the RACH preamble is transmitted, the base station can immediately determine the optimal beam without requiring extensive search during the access procedure itself.
Data Source
AI summary
A millimeter-wave wireless multiple antenna system (80) and method (100) are provided in which a UE (120) uses a multi-antenna subsystem (81) to identify a plurality of m strongest transmit beams (122) from the base station (110) based on power measurements of a plurality of synchronization signal blocks (SSBs) transmitted on a corresponding plurality of transmit beams by the base station (110), and to generate a composite uplink random access channel (RACH) preamble (123) that is sent (124) to the base station (110) to identify the plurality of m strongest transmit beams and relative weights for each of the plurality of m strongest transmit beams which are used by the base station (112) to generate an optimal downlink transmit beam for use in sending a RACH response to the UE (120).