Uplink Control Information Transmission in Low Latency Wireless
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Solution Overview
Problem
Legacy LTE wireless communication systems face challenges in achieving low latency due to the limitations of traditional transmission time intervals (TTIs), which hinder efficient communication of uplink control information (UCI) and increase latency as demand for mobile broadband access grows.
Innovation Solution
The proposed method involves assigning resource allocations for user equipment (UEs) to transmit UCI using a two-symbol TTI, where one symbol is dedicated to a demodulation reference signal (DMRS) and the other for data, allowing for frequency hopping and reduced DMRS overhead, with resources assigned based on a decimation factor to support orthogonal transmissions and increased UCI payload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional 1 millisecond subframe TTI is used in legacy LTE, then system compatibility and existing infrastructure are maintained, but latency is high and low-latency communication requirements cannot be met
Solution Approach 1:
The patent segments the traditional 1 millisecond subframe TTI into shorter transmission time intervals by dividing subframes into multiple slots, where each slot can independently carry data. This segmentation enables flexible TTI lengths (e.g., 2 slots per TTI) to be configured, thereby reducing latency while maintaining compatibility with existing LTE infrastructure through configurable parameters.
2Measurement precision
If more frequency resources are allocated for DMRS in shorter TTI, then channel estimation accuracy is improved, but overhead increases and spectral efficiency decreases
Solution Approach 1:
The patent applies partial action by allocating DMRS resources selectively rather than uniformly across all subcarriers. Specifically, DMRS is transmitted only on a subset of subcarriers (e.g., every fourth subcarrier with decimation factor K=4) where channel estimation is most critical, thereby maintaining adequate channel estimation accuracy while significantly reducing overall DMRS overhead and freeing up resources for data transmission.
3Reliability
If frequency hopping is implemented for UCI transmission, then robustness against frequency-selective fading is improved, but spectral efficiency may be reduced due to resource fragmentation
Solution Approach 1:
The patent resolves the contradiction by transitioning from single-frequency transmission to multi-frequency transmission across time dimensions. UCI is transmitted on one set of physical resource blocks (PRBs) in one slot and on different PRBs in another slot through frequency hopping. This dimensional approach provides frequency diversity for robustness while the configurable hopping pattern allows optimization of spectral efficiency based on channel conditions.
4Reliability
If decimation factor is increased for frequency resource assignment, then orthogonality among multiple UEs is maintained, but available frequency resources for each UE are reduced
Solution Approach 1:
The patent applies dynamics by making the decimation factor configurable rather than fixed. The network can dynamically adjust the decimation factor K based on the number of active UEs, channel conditions, and traffic requirements. When few UEs are active, a smaller K (e.g., K=2) allocates more resources per UE. When many UEs are active, a larger K (e.g., K=4) maintains orthogonality. This dynamic adjustment resolves the contradiction between maintaining orthogonality and providing sufficient resources.
Data Source
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AI summary
Various aspects described herein relate to communicating uplink control information (UCI) in low-latency communications. A resource assignment is received from an access point to transmit over a first symbol and a second symbol that comprise a first TTI, wherein the resource assignment includes, at least for the first symbol, an indication of one or more consecutive frequency resources in a system bandwidth based on a decimation factor. A reference signal is transmitted in the first TTI over the first symbol and a data signal indicating UCI over the second symbol according to the resource assignment.