LBT Design for Uplink LAA in Unlicensed Bands
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Solution Overview
Problem
The challenge in implementing Listen Before Talk (LBT) for uplink Licensed Assisted Access (LAA) in unlicensed bands is ensuring fair coexistence with existing systems like WiFi, while maintaining efficient data transmission and compliance with regulatory requirements.
Innovation Solution
The proposed solution involves each User Equipment (UE) performing LBT by determining if the unlicensed frequency band is clear, using parameters provided by the eNB, and implementing a backoff procedure if the channel is occupied. This allows for simultaneous channel access among UEs and adherence to ETSI regulations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LBT procedure is implemented for uplink transmission in unlicensed band, then fair coexistence with WiFi and compliance with regulations is improved, but transmission delay and channel access time increase
Solution Approach 1:
The eNB performs downlink LBT and transmits a group common PDCCH order to trigger uplink LBT at a specific time, preparing UEs in advance for channel access. This preliminary scheduling approach reduces uncertainty and optimizes the timing of LBT execution, balancing coexistence requirements with transmission efficiency
Solution Approach 2:
The system dynamically adjusts LBT parameters including contention window size, backoff counter, and random backoff value based on channel conditions and traffic requirements. This dynamic adaptation allows the system to optimize between aggressive channel access (when channel is clear) and conservative access (when channel is busy), reducing unnecessary delays while maintaining fair coexistence
2Adaptability or versatility
If each UE performs independent LBT for uplink transmission, then channel access flexibility is improved, but transmission efficiency and resource utilization decrease
Solution Approach 1:
Multiple UEs are grouped and scheduled together via group common PDCCH orders, merging their LBT procedures into a coordinated process. The eNB transmits a single scheduling command that triggers simultaneous or near-simultaneous LBT execution across multiple UEs, reducing redundant sensing operations and improving overall resource utilization while maintaining individual UE flexibility
Solution Approach 2:
The eNB provides feedback through PDCCH orders indicating whether UEs should proceed with uplink transmission based on LBT results. This feedback mechanism allows the eNB to coordinate channel access across multiple UEs, optimizing transmission efficiency by preventing unnecessary LBT executions when channel conditions are unfavorable, while still allowing individual UEs to adapt to local channel conditions
3Reliability
If LBT with backoff procedure is implemented, then coexistence with other unlicensed band users is improved, but small packet transmission efficiency decreases
Solution Approach 1:
The system dynamically changes LBT parameters such as contention window size and backoff counter values based on packet size, traffic type, and channel conditions. For small packets, the system uses optimized parameter sets that minimize backoff duration and sensing time, reducing the overhead impact on transmission efficiency while still providing adequate coexistence protection through regulated LBT procedures
Data Source
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AI summary
Techniques for mobile communication in an unlicensed frequency band are discussed. One example apparatus implementing such techniques includes a processor, transmitter circuitry, and receiver circuitry. The processor is configured to determine, for one or more user equipments (UEs), a set of listen before talk (LBT) parameters associated with an unlicensed frequency band; and determine at least one uplink grant in the unlicensed frequency band for at least one of the one or more UEs. The transmitter circuitry is configured to transmit the set of LBT parameters and the at least one uplink grant. The receiver circuitry is configured to receive transmissions over resources associated with the at least one uplink grant.