Access Node Coverage Signaling for REDCAP Initial Access
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Solution Overview
Problem
Complexity reduction techniques in REDCAP UEs, such as reduced number of antennas and bandwidth, result in coverage degradation due to loss of frequency diversity and spatial multiplexing, necessitating methods for coverage enhancement during initial access.
Innovation Solution
An access node sends a coverage enhancement indicator prior to the UE achieving an RRC connected state, allowing the use of techniques like repetition in the time domain, frequency hopping, or lower MCS tables during the random access procedure to enhance coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If complexity reduction techniques are applied to REDCAP UEs (reduced antennas, bandwidth), then device complexity is reduced, but coverage is degraded
Solution Approach 1:
The network configures coverage enhancement parameters (MCS table, repetition factor, frequency hopping) in advance during initial access before the UE enters RRC connected state. This preliminary configuration ensures that UEs with reduced complexity can immediately utilize appropriate coverage enhancement techniques without requiring complex real-time adjustments, thereby maintaining reliability while keeping device complexity low.
Solution Approach 2:
The patent changes key transmission parameters including MCS table selection (using more robust tables), repetition factor (increasing number of transmissions), and frequency hopping patterns to enhance coverage. These parameter changes compensate for the reduced antenna count and bandwidth by using more reliable transmission modes, thus maintaining coverage reliability despite device complexity reduction.
2Device complexity
If smaller bandwidth is used for SSB, then frequency diversity is reduced, but device complexity is reduced
Solution Approach 1:
The network performs preliminary configuration of frequency hopping patterns and bandwidth parameters before the UE begins data transmission. This allows the UE to use simpler processing with smaller bandwidth while the network pre-arranges frequency diversity through hopping patterns, compensating for the reduced frequency diversity without increasing UE processing complexity.
Solution Approach 2:
The patent introduces frequency hopping as an additional dimension for achieving frequency diversity. Instead of relying solely on bandwidth for frequency diversity, the system uses time-domain frequency hopping to provide diversity across multiple frequency resources, effectively compensating for the reduced bandwidth while keeping UE processing complexity low.
3Device complexity
If fewer receive antennas are used, then spatial multiplexing is reduced, but device complexity is reduced
Solution Approach 1:
The patent changes the MCS table to use more robust modulation and coding schemes that are more resilient to reduced spatial diversity. By selecting appropriate MCS tables configured for coverage enhancement, the system compensates for the loss of spatial multiplexing capability, maintaining reliable communication despite using fewer antennas.
Solution Approach 2:
The network configures appropriate MCS tables and transmission parameters in advance during the random access procedure, before the UE enters connected mode. This preliminary configuration ensures that UEs with fewer antennas can immediately use robust transmission modes that compensate for reduced spatial multiplexing, maintaining reliability without requiring complex real-time antenna management.
4Reliability
If coverage enhancement techniques are used during RACH, then initial access reliability is improved, but signaling overhead is increased
Solution Approach 1:
The patent uses system information blocks (SIB) to convey multiple pieces of configuration information including coverage enhancement parameters, MCS tables, and random access parameters in a unified manner. This multi-functional signaling approach reduces overall signaling overhead by combining multiple configuration tasks into single messages, while still providing comprehensive coverage enhancement during initial access.
Solution Approach 2:
The network performs preliminary configuration of coverage enhancement parameters during the system information broadcast and random access response, before the actual data transmission begins. This preliminary signaling establishes the coverage enhancement mode early in the process, allowing subsequent transmissions to proceed efficiently without requiring continuous re-negotiation of parameters, thereby minimizing total signaling overhead while maintaining high initial access reliability.
Data Source
AI summary
A method implemented by an access node includes sending, by the access node to a user equipment (UE), an indicator indicating use of coverage enhancement technique, the indicator being sent prior to the UE achieving a radio resource control (RRC) connected state with the access node; receiving, by the access node from the UE, an uplink transmission in accordance with the indicator; and sending, by the access node to the UE, a contention resolution message in accordance with the indicator.