Front-loaded RACH Preamble for Beam Refinement
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Solution Overview
Problem
In wireless communications, user equipment (UE) may experience difficulties in transmitting the third message of a random access channel (RACH) procedure due to limited transmit power, leading to failed access attempts when far from the base station, especially in scenarios where maximum permissible exposure limits constrain transmission power.
Innovation Solution
The UE transmits a preamble and/or reference signal with the third message to enhance beam gain and channel estimation at the base station, allowing for improved coverage without increasing transmit power, by using front-loaded transmission techniques based on reference signal received power measurements and exposure conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the UE transmits the third message with limited transmit power due to maximum permissible exposure limits, then the UE can maintain safe exposure levels, but the transmission may fail when the UE is located too far from the base station
Solution Approach 1:
The UE transmits a preamble and/or reference signal before the third message to enable the base station to perform beam refinement and channel estimation in advance. This preliminary action allows the base station to optimize its receive beamforming before the actual data transmission, compensating for the limited transmit power of the third message and improving the likelihood of successful reception even when the UE is far from the base station.
2Reliability
If the UE increases transmit power to improve coverage, then the RACH procedure success rate improves, but the maximum permissible exposure limits are violated
Solution Approach 1:
The transmission is segmented into multiple components: a preamble/reference signal transmission phase and a third message transmission phase. The preamble and reference signal are transmitted first to enable beam refinement, while the third message is transmitted subsequently with controlled power levels that comply with maximum permissible exposure limits. This segmentation allows the system to achieve reliable communication without violating safety constraints.
3Device complexity
If the base station uses fixed receive beam configuration, then the system complexity is reduced, but the channel estimation accuracy decreases when the UE is far from the base station
Solution Approach 1:
The base station performs beam refinement and channel estimation using the preamble and reference signal transmitted by the UE before the third message. This preliminary action enables the base station to calculate accurate channel state information and optimize its receive beamforming weights in advance, significantly improving channel estimation accuracy for distant UEs without requiring complex real-time beam switching during the actual data transmission.
Data Source
AI summary
Methods, systems, and devices for wireless communications are described. For instance, a user equipment (UE) may transmit a first message of a RACH procedure to a base station. The UE may receive a second message of the RACH procedure from the base station based on the first message. The UE may transmit a preamble, a reference signal, or both and a third message of the RACH procedure to the base station based on the second message. The UE may transmit the preamble, the reference signal, or both before transmission of the third message. In some cases, the UE may receive control signaling that indicates whether to transmit the preamble, the reference signal, both, or neither with the third message. Additionally or alternatively, the control signaling may indicate a resource for the preamble, the reference signal, or both and a resource for the third message.