RA-RNTI Calculation for Coverage Enhanced LTE UEs
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Solution Overview
Problem
The existing method of calculating RA-RNTI for Low Complexity (LC) and Coverage Enhanced (CE) UEs in LTE networks can lead to increased contention probability due to overlapping RA response windows, causing UEs with different coverage enhancement levels to search for the same RA-RNTI for different RAR time/frequency resources, resulting in reduced network performance.
Innovation Solution
The solution involves defining and configuring Coverage Enhanced Physical Random Access Channel (PRACH) resource sets with unique Configuration Indices (CE PCI) for each coverage level, allowing UEs to calculate RA-RNTI based on a starting subframe number assigned to their PRACH resource set, thereby distributing preamble transmissions according to UE CE levels and alleviating contention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the existing RA-RNTI calculation method is used for LC and CE UEs, then the RA response window can be established, but different RA response windows may have overlapping RA-RNTIs causing increased contention probability
Solution Approach 1:
The patent segments the RA-RNTI calculation by introducing a coverage enhancement level-specific offset parameter. UEs with different CE levels (CE level 0, 1, 2, 3) are assigned different offsets, which segment the overall RA-RNTI space into separate ranges for each coverage level. This prevents overlap between RA response windows of different CE levels while maintaining the original RA-RNTI calculation structure for each individual level.
Solution Approach 2:
The patent applies local quality by making the RA-RNTI calculation adaptive to the specific coverage enhancement level of each UE. Instead of using a uniform calculation method for all UEs, the system applies different offset values locally based on the UE's CE level, ensuring that each UE group operates in its own dedicated RA-RNTI range without interfering with other groups.
2Reliability
If time repetitions are used for RAR transmission to enhance coverage, then coverage enhancement is achieved, but RA response windows may overlap causing UEs to search for the same RA-RNTI on different time/frequency resources
Solution Approach 1:
The patent segments the RA-RNTI identification space by introducing CE level-specific offsets. This ensures that UEs at different coverage enhancement levels, even when using time repetitions, will calculate and search for different RA-RNTI values. The segmentation prevents the loss of identification accuracy that would occur if multiple CE levels used the same RA-RNTI calculation method.
3Device complexity
If a single RA-RNTI calculation method is used for all UEs, then the calculation is simple, but UEs with different coverage enhancement levels experience performance degradation due to RA-RNTI overlap
Solution Approach 1:
The patent applies local quality by introducing coverage enhancement level-specific parameters into the RA-RNTI calculation. Each UE determines its CE level and applies the corresponding offset, maintaining simplicity at the individual UE level while improving overall network performance through differentiated treatment of different UE groups.
Solution Approach 2:
The patent changes the RA-RNTI calculation parameters by introducing an additional offset parameter that varies based on coverage enhancement level. This parameter change allows the system to maintain the original simple calculation structure while adding differentiation capability to prevent RA-RNTI overlap and improve network performance.
Data Source
AI summary
Embodiments herein may relate to a method performed by a network node (115). The network node defines one or more parameters of a Coverage Enhanced Physical random access channel Configuration Index, CE PCI, for one or more Physical Random Access Channel, PRACH, resource sets, each of the one or more PRACH resource sets is associated with a coverage level whereby a different CE PCI is defined for each coverage level. The network node configures the one or more PRACH resource sets in a broadcast message. Furthermore, the network node assigns a starting subframe number to a PRACH resource set used by a UE, (110), and calculates a Random Access Radio Network Temporary Identifier, RA-RNTI, using the assigned starting subframe number.