Shortened PRACH for Low-Latency Random Access
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing random access procedures in LTE networks introduce latency due to the fixed length of the preamble and the need for UEs to wait for PRACH opportunities, which limits the benefits of shorter TTI transmissions and is resource inefficient.
Innovation Solution
The introduction of a shortened Physical Random Access Channel (sPRACH) with dynamic scheduling, allowing for shorter preamble sequences and flexible resource allocation, enabling contention-free and contention-based low-latency random access procedures without affecting legacy devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a fixed-length preamble is used in the random access procedure, then the structure is simple and reliable, but the latency is increased and the benefits of shorter TTI transmissions are not maximized
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed-length preamble to a variable-length preamble structure. The preamble length is dynamically adjusted based on the TTI length and random access procedure requirements, allowing the system to optimize latency while maintaining structural simplicity through standardized length configurations rather than complex adaptive coding.
2Productivity
If UEs wait for PRACH opportunities to transmit random access preambles, then the channel access is controlled and collisions are reduced, but the latency is increased and resource efficiency is reduced
Solution Approach 1:
The patent applies preliminary action by enabling UEs to transmit random access preambles at any time rather than waiting for scheduled PRACH opportunities. The network performs preliminary actions by configuring sPRACH resources and sending downlink control information that grants UE access rights, allowing immediate transmission without waiting for periodic opportunities, thus reducing latency while maintaining collision control through network coordination.
3Loss of time
If a shortened PRACH with dynamic scheduling is introduced, then latency is reduced and resource efficiency is improved, but the system complexity increases and legacy device compatibility may be affected
Solution Approach 1:
The patent applies segmentation by dividing the random access channel into two separate channels: the legacy PRACH for traditional operation and the shortened PRACH (sPRACH) for low-latency operations. This segmentation allows the system to introduce dynamic scheduling and shortened preambles without affecting legacy devices, as each channel maintains its own simplified or enhanced characteristics independently.
Solution Approach 2:
The patent uses downlink control information as an intermediary mechanism to manage the complexity of dynamic scheduling. The network sends downlink control information that indicates allocated sPRACH resources to UEs, serving as a mediator between the complex scheduling decisions and the simple UE transmission process. This intermediary approach abstracts the scheduling complexity from the UE while enabling efficient resource utilization.
4Productivity
If contention-based random access is used, then the procedure is simple to implement, but spectral efficiency is reduced due to guard periods and retransmissions
Solution Approach 1:
The patent applies dynamics by enabling flexible, dynamic allocation of sPRACH resources to UEs based on actual transmission needs rather than using fixed contention-based slots. The network dynamically assigns resources and preambles to UEs, allowing efficient utilization without the need for guard periods between contentions, thus improving spectral efficiency while managing complexity through network-coordinated dynamic scheduling.
Data Source
AI summary
Certain embodiments disclose a method in a wireless device. The wireless device receives a location of a time and/or frequency resource of a first Physical Random Access Channel (PRACH) from a network node. The wireless device receives a location of a time and/or frequency resource of a second PRACH. Furthermore, the wireless device transmits a first random access attempt via the first PRACH and transmits a second random access attempt via the second PRACH. The first PRACH and the second PRACH each have an associated preamble, and wherein the second PRACH preamble has a different length than the first PRACH preamble.