Retransmission Scheduling via Cyclic Shift Mapping
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Solution Overview
Problem
In wireless communication networks, contention-based access leads to collisions during retransmissions, reducing efficiency due to simultaneous user transmissions, which complicates demodulation and processing, especially in packet-switched environments where resource allocation is flexible and bursty.
Innovation Solution
A base station supports both contention-based and schedule-based channels, using a reference signal with cyclic shifts to facilitate retransmissions on the schedule-based channel, allowing the base station to determine the cyclic shift and schedule retransmissions even if data demodulation fails, thereby avoiding collisions and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If contention-based access is used to eliminate scheduling overhead, then communication link efficiency is improved, but collisions between user transmissions occur reducing reliability
Solution Approach 1:
The patent segments the retransmission process by introducing a dedicated retransmission channel separate from the initial contention-based access channel. This allows successful initial transmissions to continue using the efficient contention-based channel while isolating retransmissions to a controlled scheduled channel, preventing retransmission collisions from affecting overall system efficiency
Solution Approach 2:
The patent introduces an intermediary mechanism (the scheduled retransmission channel) that mediates between the contention-based access channel and the reliability requirements. When collisions occur on the contention channel, the intermediary scheduled channel provides a fallback path for retransmissions, ensuring reliability without compromising the efficiency of the primary contention-based access
2Speed
If multiple users transmit simultaneously on contention-based channel, then access speed is improved, but demodulation complexity increases due to collisions
Solution Approach 1:
The patent segments the transmission process into initial access and retransmission phases, with each phase using appropriate channel access methods. The initial access phase allows simultaneous transmissions for speed, while the retransmission phase uses scheduled access to reduce complexity, separating the functions of speed and complexity management
3Reliability
If scheduled access is used to control user transmissions, then collision avoidance is improved, but signaling overhead increases reducing efficiency
Solution Approach 1:
The patent applies local quality by using different access methods in different contexts: contention-based access for initial transmissions where speed is critical and collisions are acceptable, and scheduled access for retransmissions where reliability is critical. This localized application of access methods optimizes overall system performance by matching the right method to the right need
Data Source
AI summary
A base station supports a contention-based channel and a schedule-based channel. If too many mobile terminals simultaneously transmit on the contention-based channel, the base station schedules retransmissions to those terminals on the schedule-based channel. Supporting this, a terminal transmits a user transmission on the contention-based channel that includes both a data transmission and a reference signal. The terminal derives this reference signal by selecting one of a plurality of cyclic shifts (CSs). Correspondingly, the base station receives the user transmission and can determine the selected CS even if it is unable to demodulate the data transmission. The base station then determines a retransmission identifier (RTI) mapped to that CS, according to a mapping between CSs and RTIs, and sends scheduling information for any needed retransmission to the terminal by addressing that information to the RTI. Meanwhile, the terminal knows this mapping and monitors for scheduling information addressed to that RTI.