Configurable RAR Window Length for Low Latency Random Access
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Solution Overview
Problem
In wireless communications, particularly in New Radio (NR), the existing Random Access Response (RAR) window length is not suitable for low latency applications due to its impact on random access latency and beam correspondence, as it restricts the transmission of new PRACH preambles until the end of the RAR window, which can be too long, especially when beam correspondence is not established.
Innovation Solution
Configuring the RAR window length as a fraction or multiple of a slot, with the smallest length being less than a slot duration, allowing for faster power ramping and reducing latency, and enabling more efficient beam-sweeping procedures by allowing PRACH preamble retransmissions within a shorter timeframe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RAR window length is configured to be long to ensure reliable RAR reception and accommodate network processing time, then the reliability of RAR reception is improved, but the random access latency increases significantly
Solution Approach 1:
The patent applies dynamics by making the RAR window length configurable and adaptable rather than fixed. The network can dynamically adjust the RAR window length based on actual network conditions, processing capabilities, and service requirements. This allows the system to optimize between reliability and latency by selecting appropriate window lengths (e.g., 1, 2, or 3 slots) rather than being constrained to a long fixed window, thus resolving the contradiction between ensuring reliable reception and minimizing access latency.
2Reliability
If the RAR window length is extended to accommodate power ramping procedures and beam-sweeping retransmissions, then the completeness of random access procedure is improved, but the overall access time increases
Solution Approach 1:
The patent enables dynamic configuration of RAR window length to match the actual needs of power ramping and beam-sweeping procedures. Rather than always using a long window, the network can configure shorter windows (1-3 slots) when conditions permit, allowing devices to perform necessary retransmissions more quickly. This dynamic approach maintains procedure completeness while reducing overall access duration by adapting the window length to current network and device states.
Solution Approach 2:
The patent changes the parameter of RAR window length from a fixed value to a configurable parameter that can be adjusted based on network conditions, device capabilities, and service requirements. By allowing the window length parameter to vary (configured as 1, 2, or 3 slots), the system can optimize the balance between completing necessary procedures like power ramping and minimizing access duration, directly resolving the contradiction.
3Reliability
If the RAR window length is increased to support beam-sweeping PRACH preamble retransmissions, then the coverage and reliability are improved, but the latency for low latency applications deteriorates
Solution Approach 1:
The patent applies dynamics by enabling the network to configure the RAR window length adaptively based on whether beam-sweeping is required and the urgency of the access. For low-latency applications where beam-sweeping may not be necessary or can be performed more efficiently, the network can configure shorter RAR windows (1-3 slots), allowing devices to proceed with retransmissions sooner. This dynamic configuration maintains reliability for beam-sweeping when needed while reducing latency for time-critical applications.
Solution Approach 2:
The patent changes the RAR window length parameter from a fixed long duration to a configurable parameter with multiple possible values (1, 2, or 3 slots). This parameter change allows the system to optimize for low-latency applications by selecting shorter window lengths when beam-sweeping can be performed efficiently or is not required, thereby reducing the time devices must wait before retransmitting preambles while maintaining sufficient reliability.
Data Source
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AI summary
A method, system and apparatus are disclosed. In one embodiment, A wireless device (WD) configured to communicate with a network node is provided. The wireless device includes a radio interface and processing circuitry configured to: implement a Random Access Response, RAR, window, and receive a RAR using the implemented RAR window. A time length of the RAR window being configurable to correspond to a fraction or multiple of a slot in the frame.