LTE-A Reference Signal Design for Time Tracking in CoMP
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Solution Overview
Problem
Current communication systems, particularly in LTE Rel-11 and beyond, face challenges with time tracking due to the limitations of common reference signals (CRS), as they may not be present or appropriate in all subframes or carriers, especially in scenarios like CoMP transmission, leading to compromised performance in UE-RS and CSI-RS based time tracking.
Innovation Solution
The solution involves enhancing reference signal design by restricting the number of resource blocks allocated to a UE for downlink assignments, utilizing precoding resource block groups, and configuring multiple CSI-RS ports to improve time tracking, especially in scenarios where CRS is unavailable or inappropriate, by leveraging UE-RS and CSI-RS for coherent combining and increased density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If common reference signals (CRS) are used for time tracking, then time tracking can be performed in traditional LTE systems, but CRS may not be present or appropriate in all subframes or carriers (e.g., in CoMP transmission scenarios), leading to compromised performance
Solution Approach 1:
The patent introduces UE-specific reference signals (UE-RS) and channel state information reference signals (CSI-RS) as intermediary elements to replace CRS for time tracking purposes. These new reference signals are specifically designed to be present in scenarios where CRS is unavailable, such as CoMP transmissions, thereby maintaining time tracking reliability across diverse transmission scenarios.
Solution Approach 2:
The patent changes the fundamental parameter of which reference signal is used for time tracking - transitioning from CRS-based time tracking to UE-RS and CSI-RS based time tracking. This parameter change enables the system to adapt to different transmission scenarios including CoMP, where the new reference signals are specifically designed to be available while CRS may not be appropriate.
2Measurement precision
If UE-RS and CSI-RS are used for time tracking without adequate resource allocation, then resource efficiency is maintained, but time tracking accuracy and reliability are compromised
Solution Approach 1:
The patent establishes minimum resource allocation parameters for UE-RS and CSI-RS to ensure adequate signal density for time tracking. By defining that resource blocks allocated for downlink assignments should be greater than or equal to two, and by configuring multiple CSI-RS ports, the system ensures sufficient reference signal density to achieve accurate time tracking while maintaining resource efficiency through optimized allocation rules.
3Reliability
If multiple CSI-RS ports are configured to improve time tracking, then time tracking reliability is enhanced, but system complexity increases
Solution Approach 1:
The patent configures multiple CSI-RS ports to serve dual purposes: enabling coherent combining for improved time tracking reliability and supporting multi-antenna transmissions. This multi-functionality approach allows the same reference signal structure to achieve multiple objectives, thereby enhancing time tracking reliability without proportionally increasing system complexity.
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AI summary
Time tracking in current communication systems may be traditionally based on common reference signals (CRS). However, in certain communication systems, CRS-based time tracking may be impossible to implement due to an absence of CRS in certain subframes or carriers. CRS-based time tracking may also be inappropriate to implement in certain communication systems such as a coordinated multipoint (CoMP) system where control and data may arrive from different cells, and therefore, a UE may assume a wrong cell for CRS-based time tracking. Accordingly, methods, apparatuses, and computer program products for wireless communication are provided in which additional UE specific reference signals (UE-RS) and/or channel state information reference signals (CSI-RS) are made available to the UE so that the UE may have improved channel estimation and/or time tracking performance.