DL MIMO Channel Estimation Using UE Antenna Switching
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Solution Overview
Problem
In wireless communications, base stations face challenges in accurately estimating multiple-input, multiple-output (MIMO) channels due to UE devices having fewer transmit antennas than receive antennas, limiting the assessment of all downlink MIMO layers, which restricts the transmission of information to fewer layers than supported.
Innovation Solution
The base station determines the number of supported downlink MIMO layers and receive chains capable for uplink reference signals, configuring the UE to transmit these signals over some or all receive chains, and generates channel information using uplink and downlink reference signals, including additional transmissions over physical uplink channels to estimate the channel state and select a suitable precoding matrix.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the UE uses antenna switching to transmit uplink reference signals over a subset of Rx chains, then the device complexity is reduced, but the measurement precision of the DL MIMO channel deteriorates
Solution Approach 1:
The patent transitions from spatial domain limitations (physical antenna constraints) to temporal domain solutions by utilizing multiple time instances for channel estimation. The base station collects channel state information across different time slots and combines measurements from multiple dimensions (spatial + temporal) to achieve complete channel knowledge despite limited simultaneous transmit antennas.
Solution Approach 2:
The base station performs preliminary channel sounding by transmitting downlink reference signals before actual data transmission. The UE measures these signals and reports channel state information in advance, allowing the base station to pre-determine precoding matrices and transmission parameters based on the collected channel measurements from multiple time instances.
2Measurement precision
If the base station transmits downlink reference signals over multiple antenna chains, then the channel estimation accuracy is improved, but the use of energy increases
Solution Approach 1:
The base station transmits downlink reference signals over multiple antenna chains exceeding the minimum required for full-rank channel estimation. This excessive action ensures that even when the UE can only transmit feedback over L antenna chains, the base station has collected sufficient channel information from N≥L antenna chains to accurately estimate all DL MIMO layers.
Solution Approach 2:
The system uses the UE's own received signal measurements to generate channel state information feedback. The UE self-evaluates the quality of downlink reference signals received from multiple antenna chains and autonomously computes and reports channel metrics, reducing the need for additional base station transmission energy while maintaining estimation accuracy.
3Loss of information
If the UE reports channel state information for all supported DL MIMO layers, then the information completeness is improved, but the loss of time in feedback transmission increases
Solution Approach 1:
The patent combines multiple pieces of information into a unified channel state information feedback report. The UE aggregates channel measurements from downlink reference signals received over multiple antenna chains and time instances, then consolidates this information into a single comprehensive feedback message containing channel quality indicators, precoding matrix indicators, and rank indicators for all N DL MIMO layers.
Solution Approach 2:
The channel state information feedback process operates continuously across multiple time instances rather than as discrete separate measurements. The base station continuously transmits downlink reference signals and the UE continuously reports channel state information, maintaining an ongoing feedback loop that provides up-to-date channel knowledge without requiring repeated complete measurement cycles.
Data Source
AI summary
To control transmissions to a user equipment (UE) over a downlink (DL) multiple-input, multiple-output (MIMO) channel, a base station determining that the UE is configured to support N DL MIMO layers and transmit reference signals over L antenna chains (852). In response to determining that L<N (870), the base station generates channel information for the DL MIMO channel using (i) L uplink reference signals, each transmitted by the UE over a respective one of the L antenna chains (880), and (ii) one or more additional transmissions received from the UE (882). The base station transmits data streams over the DL MIMO channel in accordance with the generated channel information.