Partial Sub-Frame Data Transmission in LTE Unlicensed Carriers
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Solution Overview
Problem
In LTE systems, the restrictions on Clear Channel Assessment (CCA) timing and duration limit the opportunities for data transmission on unlicensed carriers, leading to reduced spectral efficiency and increased interference, as existing solutions either restrict CCA to sub-frame boundaries or require lengthy preambles, disadvantage LTE devices compared to other technologies.
Innovation Solution
A method and apparatus that allow channel assessment and data transmission to start earlier than the next sub-frame boundary after a successful CCA, with a control message transmitted in a subsequent sub-frame to indicate the starting time and characteristics of the data transmission, enabling more frequent channel access while maintaining high spectral efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CCA timing is restricted to sub-frame boundaries, then LTE transmission timing is simplified, but the number of transmission opportunities is reduced and spectral efficiency decreases
Solution Approach 1:
The patent segments the sub-frame structure by introducing a partial sub-frame concept that allows data transmission to start at intermediate points (e.g., after a certain number of OFDM symbols) rather than requiring complete sub-frames. This segmentation enables multiple transmission opportunities within a single sub-frame boundary period, thereby improving spectral efficiency while maintaining manageable timing control through defined start positions.
2Productivity
If CCA duration is limited to 3 symbols, then sub-frame boundary alignment is maintained, but transmission opportunities are further restricted
Solution Approach 1:
The patent applies preliminary action by performing CCA assessment during the early portion of a sub-frame (within the first few OFDM symbols) and preparing transmission resources in advance. When CCA succeeds, data transmission can immediately start at a predetermined partial sub-frame position without waiting for the next sub-frame boundary, thus increasing channel access frequency and reducing idle waiting time.
3Reliability
If DCI is transmitted in the same sub-frame as data, then control information is available timely, but control information cannot be determined at sub-frame start whether CCA will succeed
Solution Approach 1:
The patent transmits control information (DCI) in advance in the sub-frame where CCA is performed, before data transmission actually occurs in a later partial sub-frame. This preliminary transmission of control information ensures that receivers have the necessary decoding parameters ready before data arrives, maintaining reliability while allowing flexible timing between control and data transmission.
4Reliability
If preamble transmission is used to grab channel, then channel occupation is secured, but spectral efficiency is reduced and interference to other systems increases
Solution Approach 1:
The patent extracts and removes the traditional preamble transmission element from the protocol. Instead of transmitting separate preamble symbols to grab the channel, the system relies on successful CCA assessment followed by direct data transmission at predefined partial sub-frame positions. This extraction eliminates the spectral efficiency penalty and interference caused by preambles while maintaining channel occupation through proper CCA-based access control.
Data Source
AI summary
A transmitting device performs a channel assessment in a previous sub-frame in an unlicensed carrier. After a successful channel assessment, the transmitting device starts a data transmission. The transmitting device transmits a control message for indicating the data transmission in (E)PDCCH. The control message may include the starting time of the data transmission and/or at least one transmission characteristic in the previous sub-frame. The transmission device may transmit an initial control message for indicating a potential data transmission being started in the sub-frame in which the initial control message is transmitting. Method and apparatus enable (E)CCA to take place at any time, and data transmission to start earlier than the next sub-frame boundary after a successful completion of (E)CCA, thus improving the data transmission capacity, especially in circumstances when the maximum length of transmission is constrained.