UL BWP Switching for Reliable 5G Random Access
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Solution Overview
Problem
In 5G NR systems, UEs autonomously switching between normal and supplementary uplink bandwidth parts without notifying the base station can result in missed uplink transmissions, such as Sounding Reference Signal (SRS), Physical Uplink Shared Channel (PUSCH), or Physical Uplink Control Channel (PUCCH), leading to communication gaps.
Innovation Solution
The UE suspends transmissions on a new UL BWP until the base station acknowledges the switch, and the base station monitors potential transmissions on multiple UL BWPs to ensure detection, with the UE optionally notifying the base station of the switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the UE autonomously switches between UL BWPs without notifying the base station, then the switching speed and responsiveness are improved, but the base station may miss uplink transmissions resulting in communication reliability deterioration
Solution Approach 1:
The base station monitors multiple UL BWPs to detect uplink transmissions from the UE after autonomous switching. This feedback mechanism allows the base station to become aware of the UE's BWP switch through detection of transmissions on the new BWP, resolving the contradiction by maintaining reliability while preserving autonomous switching speed
Solution Approach 2:
The base station pre-configures multiple UL BWPs for the UE and proactively monitors these BWPs for potential transmissions. By preparing monitoring resources in advance for multiple BWPs, the base station can quickly detect autonomous switching without waiting for UE notification, thus maintaining both switching speed and communication reliability
2Reliability
If the UE notifies the base station of every BWP switch, then the base station awareness and transmission reliability are improved, but the signaling overhead and system complexity increase
Solution Approach 1:
The UE autonomously determines when to switch BWPs and the base station autonomously monitors the configured BWPs for transmissions. This self-service approach eliminates the need for explicit notification signaling, reducing system complexity while maintaining reliability through autonomous detection capabilities
Solution Approach 2:
Instead of UE-initiated notifications, the base station receives feedback about BWP switching through detection of uplink transmissions on monitored BWPs. This feedback mechanism provides base station awareness without requiring additional signaling complexity
3Reliability
If the base station monitors multiple UL BWPs for potential transmissions, then the detection capability and reliability are improved, but the base station processing load and energy consumption increase
Solution Approach 1:
The base station uses a universal monitoring approach where the same detection mechanisms are applied across multiple UL BWPs. By configuring the UE with multiple BWPs that can serve different functions (normal uplink, supplementary uplink, fallback), the base station monitors these BWPs using standardized procedures, improving detection capability while managing energy consumption through efficient resource allocation
Data Source
AI summary
A user equipment, UE, switches between UL BWPs to perform a random access procedure. A base station transmits a configuration specifying multiple UL BWPs on a NUL carrier and a SUL carrier (802). Because the base station selects the configuration for the UE, the base station is aware of the UL BWP which the UE will select as the active UL BWP as well as the UL BWP to which the UE will switch if the UE lacks RACH resources or if the UE decides to switch the between the NUL and SUL carriers. The base station attempts (804) to detect transmission from the UE on the active UL BWP as well as the initial UL BWP of the same NUL (or SUL) carrier.