Precoding Vector Pattern Signaling in Lean-Carrier Systems
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Solution Overview
Problem
In wireless communication systems, especially in LTE, the lack of reliable channel state information (CSI) leads to inefficient transmission due to outdated or incorrect precoder information, particularly in high-speed scenarios or when lean carriers are used, where CRS is not present in majority of downlink subframes, causing potential destructive interference.
Innovation Solution
Implementing an extended transmission mode where precoders applied to data vary frequently across time-frequency resources, while DMRS precoding remains constant, creating a frequency-selective variation that appears random, allowing robustness against outdated or incorrect CSI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If precoding is applied based on channel state information in a lean-carrier system, then spatial multiplexing performance is improved, but transmission reliability deteriorates when CSI is outdated or incorrect
Solution Approach 1:
The patent applies dynamics by making the precoding configuration adaptable to channel conditions. The system dynamically selects between two precoding modes: when CSI is reliable, it uses precoding configured based on CSI feedback; when CSI is outdated, it switches to a different precoding configuration that does not rely on accurate CSI. This dynamic adaptation resolves the contradiction by allowing the system to maintain spatial multiplexing performance when possible while ensuring transmission reliability when CSI quality degrades.
Solution Approach 2:
The patent changes the precoding parameter configuration based on CSI reliability assessment. The network node determines whether CSI is outdated and accordingly changes the precoding matrix indicator (PMI) configuration sent to the user equipment. This parameter change allows the system to transition between different transmission modes, maintaining both productivity and reliability under varying channel conditions.
2Use of energy by moving object
If demodulation reference signals are used for channel estimation, then coverage gain is achieved, but transmission efficiency deteriorates when common reference signals are removed
Solution Approach 1:
The patent segments the reference signal functionality by separating demodulation reference signals (DMRS) from common reference signals (CRS). DMRS are user-specific and transmitted only when needed for data transmission, while CRS are removed to save energy. This segmentation allows the system to achieve coverage gain through DMRS-based beamforming without the continuous energy consumption of CRS, while maintaining transmission efficiency through targeted, user-specific reference signals.
Solution Approach 2:
The system uses user-specific demodulation reference signals that are self-contained and do not require common reference signals for operation. Each user's DMRS carries the necessary channel estimation information specifically for that user's data transmission, making the system self-sufficient and eliminating the need for always-on CRS, thereby improving both energy efficiency and maintaining transmission productivity.
3Reliability
If precoders vary frequently across time-frequency resources, then robustness against outdated CSI is improved, but system complexity increases
Solution Approach 1:
The patent implements periodic action by having the network node periodically assess CSI reliability and periodically update precoding configurations. Rather than continuously varying precoders in a complex manner, the system uses periodic updates triggered by CSI freshness evaluation. This periodic approach provides robustness against outdated CSI while maintaining manageable system complexity through structured, time-based updates rather than continuous complex adaptation.
Solution Approach 2:
The system dynamically adjusts precoding based on assessed CSI reliability, but uses a controlled dynamic approach rather than uncontrolled variation. The network node determines whether CSI is outdated and only changes precoding configuration when necessary, using predefined precoding matrices from codebooks. This controlled dynamics provides robustness while limiting complexity growth through structured decision-making and predefined options.
Data Source
AI summary
In a system using spatial precoding, in the event that reliable channel state information is unavailable, a transmitting node uses an extended transmission mode, in which the precoders applied to data within each of several groups of time-frequency resources vary according to frequency. The extended transmission mode creates a frequency-selective variation in precoders, which may appear to be random, while using DMRS-based transmission. This variation is achieved by applying different precoders to the resource elements carrying data, using a pattern of precoder variation that is known to the receiving device. The precoding applied to DMRS within a given group of time-frequency resources is held constant—thus, the varying precoders within a given group of time-frequency resources are only applied to data elements, not to the DMRS resource elements.