Adaptive HARQ Scheduling for Contention-Based Wireless Grants
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Solution Overview
Problem
In wireless communication systems, contention-based transmissions face challenges in correcting transmission errors due to interference from other user equipment, making it difficult to implement Hybrid Automatic Repeat Request (HARQ) protocol effectively, leading to increased access delay, signaling overhead, and negative impacts on throughput and latency.
Innovation Solution
A method and arrangement in a base station and user equipment that schedules contention-based grants with information indicating whether the grant should be used for initial transmission or retransmission, enabling adaptive HARQ retransmissions only when no collision is detected, and using state bit indicators or Contention Based-Radio Network Temporary Identifiers (CB-RNTIs to differentiate between initial and retransmission grants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If HARQ protocol is implemented for contention based transmissions, then transmission error correction capability is improved, but system performance deteriorates due to increased access delay and signaling overhead
Solution Approach 1:
The patent applies dynamics by making the HARQ process configurable and adaptive rather than fixed. The base station can dynamically enable or disable HARQ retransmissions based on collision detection outcomes, allowing the system to flexibly adjust between reliability and latency requirements for different transmission scenarios
Solution Approach 2:
The patent changes the parameter of retransmission behavior by introducing collision detection mechanisms that modify HARQ operation. When collisions are detected, the system changes parameters to prevent redundant retransmissions, thereby reducing access delay while maintaining error correction capability when applicable
2Reliability
If HARQ retransmissions are performed for contention based grants, then transmission reliability is improved, but resource wastage increases due to redundant retransmissions during collisions
Solution Approach 1:
The patent implements feedback through collision detection mechanisms that provide information to the base station about transmission conflicts. This feedback enables the base station to make informed decisions about whether to permit HARQ retransmissions, thereby avoiding resource wastage from redundant retransmissions during collisions while maintaining reliability when collisions are absent
Solution Approach 2:
The patent extracts the harmful element of redundant retransmissions by detecting collisions and preventing HARQ retransmissions in those specific cases. This selective removal of problematic retransmissions reduces resource wastage while preserving the beneficial retransmissions that occur during non-collision scenarios
3Ease of operation
If fixed retransmission timing is used for contention based transmissions, then scheduling simplicity is maintained, but collision probability increases leading to performance degradation
Solution Approach 1:
The patent applies dynamics by transitioning from fixed to flexible retransmission timing. The base station can dynamically adjust retransmission opportunities based on collision detection outcomes, maintaining scheduling simplicity through centralized control while reducing collision probability through adaptive timing adjustments
Data Source
AI summary
The present invention relates to a method and arrangement in base station for scheduling user equipments. The base station is adapted to schedule communication from user equipments by sending contention based grants comprising information indicating if the contention based grant should be used for initial transmission or for retransmission. If it is detected that data is not correctly received due to a collision, the information in a following contention based grant is set to indicate that said contention based grant is to be used for initial transmission, while if data is not correctly received, but no collision is detected, the information is set to indicate that the contention based grant is to be used for retransmission. Corresponding method and arrangement in a user equipment is described.