Open Loop MIMO Precoding for High Doppler LTE-A Uplink
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Solution Overview
Problem
Conventional LTE systems face challenges in supporting high Doppler fading and fast-moving user equipment (UEs) due to rapid channel changes in the uplink direction, limiting the effectiveness of existing MIMO transmission schemes.
Innovation Solution
A precoding scheme that switches precoding matrices for each OFDM symbol and a new downlink control message format allowing for open-loop MIMO modes, enabling flexible transmission schemes based on context-sensitive interpretation of control elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SIMO or closed loop MIMO transmission schemes are used in LTE systems, then system complexity is kept manageable, but communication performance deteriorates for high Doppler speeds and fast-moving UEs due to rapid channel changes
Solution Approach 1:
The patent applies dynamics by making the precoding matrix selection adaptive and time-varying. Instead of using fixed or slowly changing precoding matrices, the system dynamically selects different precoding matrices from a codebook for each OFDM symbol or resource block based on current channel conditions. This allows the transmission scheme to adapt to rapid channel changes caused by high Doppler speeds, improving communication reliability without requiring complex real-time channel feedback.
Solution Approach 2:
The patent changes the parameter of precoding matrix selection from static to dynamic. By varying the precoding matrix indices across different time-frequency resources and allowing UE to select from multiple candidate matrices, the system transforms a rigid transmission scheme into a flexible one that can track rapid channel variations. This parameter change enables the system to maintain performance under high mobility conditions while keeping implementation complexity manageable through codebook-based approaches.
2Adaptability or versatility
If different precoding matrices are applied to each OFDM symbol to handle rapid channel changes, then adaptability to high Doppler speeds is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-defining codebooks of precoding matrices at both the UE and base station. These codebooks contain multiple candidate precoding matrices that can be directly selected based on channel conditions. By preparing these matrices in advance rather than computing them in real-time, the system achieves rapid adaptation to channel changes while keeping processing complexity low. The UE simply needs to select appropriate indices from the pre-defined codebooks rather than performing complex matrix computations.
Solution Approach 2:
The patent uses copying by having the base station and UE both store identical precoding matrix codebooks. Instead of transmitting or computing complex precoding matrices dynamically, the system copies the same set of predefined matrices at both ends and selects from these copies based on channel conditions. This approach simplifies processing while maintaining adaptability, as both parties have ready access to the same candidate matrices without requiring complex real-time generation or exchange of matrix data.
3Ease of operation
If a unified downlink control message format is used for multiple transmission schemes, then ease of operation is improved, but measurement precision deteriorates due to context-sensitive interpretation requirements
Solution Approach 1:
The patent introduces an intermediary control element within the downlink control message that acts as a dispatcher or indicator. This control element specifies which transmission scheme is being used and provides context information that tells the UE how to interpret the remaining parameters in the message. By inserting this intermediary indicator, the system maintains a unified message format for ease of operation while ensuring precise interpretation through the context-providing control element that disambiguates parameter meanings based on the selected transmission scheme.
Data Source
AI summary
A precoding scheme to accommodate user equipment (UEs) having higher Doppler speeds. In such transmission schemes, a different precoding matrix is applied to each orthogonal frequency division multiplex (OFDM) symbol in the transmission stream. Additionally, a downlink control message format is defined to handle assignment of multiple different transmission schemes using the same message format. The downlink control message format includes a control element in one of the message fields along with a set of parameters specifically applicable to the assigned transmission scheme. Based on the value of this control element, the UE sets the specific transmission scheme and determines a set of interpretation rules uniquely associated with that transmission scheme. Using the interpretation rules, the UE is able to read the set of parameters as applied to the selected transmission scheme.