Unlicensed Cellular Contention Window Adjustment via Terminal Feedback
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Solution Overview
Problem
In cellular radio networks operating in unlicensed frequency bands, existing contention window adjustment methods are inadequate for managing data collisions, particularly in scenarios where multiple base stations transmit simultaneously, leading to inefficient data transmission and potential packet loss.
Innovation Solution
A method is introduced where the base station determines a contention window size based on channel occupancy measurements from terminals, adjusting the window size by comparing signal strength or NACK feedback thresholds to minimize collisions and optimize transmission opportunities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple base stations transmit simultaneously in unlicensed bands, then bandwidth utilization is improved, but collision risk increases
Solution Approach 1:
The base station performs preliminary actions by determining a contention window size before transmission and selecting a random backoff counter within that window. This preliminary random selection prevents simultaneous transmission by ensuring that even if multiple base stations attempt to transmit at the same time, they will likely choose different backoff intervals, thus avoiding collisions while still utilizing the unlicensed band effectively
2Reliability
If contention window size is increased to reduce collisions, then collision avoidance is improved, but transmission delay increases
Solution Approach 1:
The base station dynamically adjusts the contention window size based on channel conditions and collision experience. When collisions are detected through NACK feedback or channel occupancy measurements, the contention window is increased to reduce future collisions. When the channel is clear, the window is decreased to minimize transmission delay. This dynamic adaptation resolves the contradiction by making the contention window flexible rather than fixed
Solution Approach 2:
The system uses feedback mechanisms where the base station monitors transmission outcomes (ACK/NACK signals) and channel occupancy measurements from terminals. Based on this feedback, the base station adjusts the contention window size adaptively. If collisions occur, the window increases to avoid future collisions; if the channel is clear, the window decreases to reduce delay. This feedback loop enables the system to optimize between collision avoidance and transmission delay in real-time
3Reliability
If random backoff selection is used within contention window, then collision probability is reduced, but transmission unpredictability increases
Solution Approach 1:
The base station changes the parameter of backoff counter selection from completely random to pseudo-random based on a hash function. The hash function takes the physical layer identifier as input and produces a deterministic yet distributed result that appears random. This resolves the contradiction by providing collision avoidance benefits of randomness while maintaining predictability and controllability through the deterministic hash function
Data Source
AI summary
A base station of a cellular radio communications network configured to operate in an unlicensed radio band, comprising a radio transceiver connected to an antenna, and a controller including a processor and a memory holding computer program code. The processor is configured to execute the computer program code to realize a machine for determining a size for a contention window, within which the base station may transmit data from the transceiver to a radio terminal operating in the network; receiving a signal from the terminal, comprising an indication of occupancy of a radio channel, as detected by the terminal; adjusting the contention window size dependent on the indication of occupancy of the radio channel; transmitting data to the terminal within the adjusted contention window.