UL MIMO Retransmission Precoding Control in LTE
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Solution Overview
Problem
In LTE systems, the existing UL synchronous HARQ process is limited by the need for separate control signals for retransmissions, which increases resource consumption and limits the number of simultaneous HARQ processes due to the reliance on PHICH and PDCCH for changing transmission properties during retransmissions, especially in scenarios where only one of two transmitted codewords is successfully decoded.
Innovation Solution
The solution involves configuring the UE and eNB to independently determine and manage the precoding matrix for UL MIMO transmissions without a separate control signal, allowing for retransmissions to be handled based on previously used parameters, such as scrambling sequences and RS parameters, to optimize resource allocation and reduce overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate control signals (PDCCH/PHICH) are used for UL HARQ retransmissions to change transmission properties, then the reliability of retransmission control is improved, but the resource consumption and system complexity increase
Solution Approach 1:
The patent extracts the transmission property configuration from separate control signals (PDCCH/PHICH) and integrates it into the uplink data transmission itself. The UE determines precoding matrices and other transmission properties autonomously based on downlink channel estimates, eliminating the need for eNB to send separate control signals for retransmission property changes.
Solution Approach 2:
The UE performs self-service by autonomously determining its own transmission properties (precoding matrices, power allocation, etc.) for uplink MIMO retransmissions based on downlink channel state information. This self-determination mechanism eliminates dependency on continuous eNB control signaling for property management.
2Adaptability or versatility
If PHICH and PDCCH are used for changing transmission properties during retransmissions, then the adaptability of transmission control is improved, but the number of simultaneous HARQ processes is limited
Solution Approach 1:
The patent applies preliminary action by having the UE determine and store multiple precoding matrices in advance based on downlink channel estimates before uplink retransmissions occur. This pre-determination allows the UE to quickly switch between different transmission properties during retransmissions without waiting for control signals, thereby increasing the number of simultaneous HARQ processes.
3Measurement precision
If separate control signals are required for UL MIMO retransmissions, then the precision of transmission property control is improved, but the resource consumption increases
Solution Approach 1:
The patent makes the downlink channel state information serve multiple functions: it is used for both downlink reception optimization and uplink transmission property determination. This multi-functionality allows the UE to derive precoding matrices and other transmission properties from the same channel estimates used for downlink, eliminating the need for separate control signaling.
Data Source
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AI summary
A base station supporting uplink multiple input multiple output, UL MIMO, and configured to: receive, via the transceiver, a physical uplink shared channel, PUSCH, based on two transport blocks; transmit, via the transceiver, a hybrid automatic repeat request, HARQ, indicator for the PUSCH on a physical HARQ indicator channel, PHICH, and not detecting a physical downlink control channel, PDCCH; and in case that one of the two transport blocks, TB, is negatively acknowledged, receive, via the transceiver, retransmission of a negatively acknowledged TB by using a precoding matrix indicated by a precoding index 0 and a number of transmission layers equal to a number of layers corresponding to the negatively acknowledged TB, wherein at least one uplink demodulation reference signal, DMRS, resource is calculated according to a cyclic shift field for DMRS, and the number of layers corresponding to the negatively acknowledged transport block..