LTE RACH Msg3 Collision Resolution via DMRS Randomization
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Solution Overview
Problem
In LTE RACH procedures, the high probability of Msg3 collisions due to multiple devices using the same preamble and DMRS, leading to co-channel interference and unsuccessful decoding, results in repeated transmissions and resource wastage as UEs retry until the maximum number of retransmissions is reached.
Innovation Solution
Implementing DMRS randomization, MCS level indication for Msg3, and early termination of Msg3 transmission to reduce collision probability and prevent unnecessary retransmissions, where UEs generate unique DMRS sequences and adjust MCS levels based on network feedback, and the eNB triggers early termination of Msg3 transmission upon decoding failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple devices use the same preamble for RACH, then the probability of collision increases, but the system cannot distinguish between different devices
Solution Approach 1:
The patent segments the Msg3 transmission by assigning different DMRS sequences to different UEs. Even though multiple devices may use the same preamble, the DMRS sequence differentiation allows the eNB to distinguish between different UEs' Msg3 transmissions, resolving the collision problem while maintaining RACH efficiency.
Solution Approach 2:
The patent applies local quality by making the DMRS sequence specific to each UE based on its unique identifier (such as UE ID or C-RNTI). Each UE uses a locally generated DMRS sequence that is unique to it, allowing the eNB to differentiate between different UEs' signals in the same time-frequency resource.
2Device complexity
If DMRS sequence is fixed for all UEs, then the implementation is simple, but Msg3 collisions occur with high probability
Solution Approach 1:
The patent changes the DMRS sequence parameter based on UE-specific identifiers. Instead of using a fixed DMRS sequence for all UEs, the system dynamically selects or generates DMRS sequences based on UE ID, C-RNTI, or other UE-specific parameters, thereby reducing collision probability while maintaining manageable complexity.
3Reliability
If UEs retry Msg3 transmission multiple times, then the probability of successful transmission increases, but resource wastage increases
Solution Approach 1:
The patent implements feedback mechanisms where the eNB provides acknowledgment information about Msg3 reception. Based on this feedback, UEs can determine whether retransmission is necessary, avoiding unnecessary retransmissions and reducing energy consumption while maintaining transmission success rate.
4Device complexity
If the eNB waits for maximum retransmissions before taking action, then the procedure is simple, but time is wasted
Solution Approach 1:
The patent applies preliminary action by having the eNB prepare and send acknowledgment information or termination indications before the maximum retransmission limit is reached. This allows the system to take proactive measures to resolve collisions early, reducing time waste while maintaining controlled complexity through predefined protocols.
Data Source
AI summary
Methods and apparatus are provided for Msg3 collision resolutions. In one embodiment, the UE obtains a set of DMRS seeds and randomly selecting one to generate a DMRS sequence for the Msg3. The set of DMRS seeds is either generated based on a received cell-specific parameter or are received from the network. In another embodiment, the eNB, upon detecting the collision in Msg3, indicates a lowered MCS level for the Msg3 transmission in the RAR after the preamble detection. In another embodiment, the early termination of Msg3 transmission is used upon determining the collision of Msg3. In one embodiment, the eNB responds an ACK to a failed Msg3 to suspend the re-transmission of the Msg3. In another embodiment, the eNB sends a flag to cancel the mac-ContentionResolutionTimer and terminate the Msg3 transmission. The termination indication is either embedded in the acknowledgement signaling or sent through PDCCH signaling.