Asynchronous HARQ for LTE-U Uplink Channel Access
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing LTE uplink scheduling with synchronous Hybrid Automatic Repeat Request (HARQ) schemes fail to function effectively in LTE-U deployments using Listen-Before-Talk (LBT) over unlicensed spectrum due to unpredictable latency and interference from other devices like Wi-Fi, leading to sub-optimal channel access and interference issues.
Innovation Solution
The implementation of contention-based uplink channel access and medium reservation techniques, including Listen Before Talk (LBT) mechanisms and reservation signals, to ensure fair access to unlicensed spectrum, mitigate interference, and allow asynchronous HARQ operations, enabling LTE devices to transmit data over shared channels while minimizing interference with other devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous HARQ schemes are used in LTE uplink, then reliable data transmission is achieved, but the system fails to function effectively in unlicensed spectrum due to unpredictable latency and interference
Solution Approach 1:
The patent transitions from synchronous HARQ to asynchronous HARQ operations, allowing the system to dynamically adapt to variable channel conditions in unlicensed spectrum. The UE can perform LBT and transmit data at different times based on channel availability, rather than following fixed synchronous timing, thus maintaining reliability while adapting to dynamic environment.
Solution Approach 2:
The patent changes the timing parameters of HARQ operations from fixed synchronous intervals to variable asynchronous intervals. The round-trip time (RTT) and retransmission timing are adjusted based on actual channel conditions and LBT outcomes, enabling effective operation in unlicensed spectrum while maintaining transmission reliability.
2Ease of operation
If Listen-Before-Talk (LBT) is employed at both eNB and UE, then fair channel access is achieved, but existing LTE uplink scheduling with synchronous HARQ does not work
Solution Approach 1:
The patent implements preliminary LBT actions before data transmission and before HARQ retransmissions. The UE performs LBT checks at each transmission opportunity, and the eNB performs LBT before sending HARQ acknowledgments or retransmissions. This preliminary action ensures fair channel access while maintaining scheduling functionality through asynchronous operations.
Solution Approach 2:
The patent introduces asynchronous HARQ as an intermediary mechanism that bridges the gap between LBT-based fair access and reliable data transmission. The asynchronous timing allows LBT to succeed without rigid synchronous constraints, while HARQ provides the reliability mechanism needed for effective communication.
3Quantity of substance
If LTE devices transmit over shared unlicensed spectrum, then additional radio spectrum is utilized, but interference with Wi-Fi and other devices increases
Solution Approach 1:
The patent applies preliminary anti-action through LBT mechanisms that detect and avoid interference before transmission occurs. By listening to the channel before transmitting and deferring when other devices are active, LTE devices reduce harmful interference to Wi-Fi and other unlicensed spectrum users while still utilizing the available spectrum resources.
Solution Approach 2:
The patent implements periodic LBT checks and transmissions rather than continuous transmission. This periodic action allows other devices like Wi-Fi to access the channel periodically, reducing overall interference levels while LTE devices still utilize the shared spectrum effectively for data transmission.
4Ease of operation
If contention-based uplink channel access is implemented, then fair medium access is ensured, but channel access timing becomes unpredictable
Solution Approach 1:
The patent uses feedback mechanisms where the eNB provides uplink grants and HARQ acknowledgments that inform UEs about channel access timing and retransmission opportunities. This feedback allows UEs to adjust their LBT and transmission timing, managing the unpredictable nature of contention-based access while maintaining fair medium access for all devices.
Data Source
AI summary
A mobile device transmits data over a shared spectrum in an uplink channel to a base station in a contention-based access scheme. The mobile device obtains data to be wirelessly transmitted over the shared spectrum in the uplink channel to the base station. The uplink channel is formatted with a frame/subframe structure with a predetermined timing. The mobile device determines whether the shared spectrum is free for transmission according to a listen before transmit procedure. When the shared spectrum is free for transmission, the mobile device contends with other mobile device to gain access to the uplink channel. After gaining access to the uplink channel, the mobile device transmits the data over the shared spectrum in the uplink channel to the base station.