Estimating Secondary Channel SRS via Primary CIR for Beamforming
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Solution Overview
Problem
In LTE networks employing carrier aggregation, eNodeBs typically do not have uplink channels associated with secondary RF channels, making it difficult to determine downlink beamforming weights for these channels, as they rely on uplink sounding reference signals (SRS) which are only available for primary RF channels.
Innovation Solution
The method involves estimating an uplink SRS for secondary RF channels by using either the instantaneous channel impulse response (CIR) from the primary channel or a long-term-average CIR, based on the difference in channel quality indicators (CQIs) between primary and secondary channels, to determine downlink beamforming weights for secondary RF channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carrier aggregation is deployed to increase network capacity, then network capacity is improved, but the ability to determine downlink beamforming weights for secondary channels deteriorates because uplink channels are not available for secondary RF channels
Solution Approach 1:
The patent copies the uplink SRS signal from the primary RF channel to estimate the uplink channel characteristics for secondary RF channels. By using the channel impulse response obtained from the primary channel's SRS, the system creates a proxy representation of the secondary channel's uplink characteristics, enabling beamforming weight determination without direct uplink measurements on secondary channels.
Solution Approach 2:
The patent introduces the primary RF channel's uplink SRS as an intermediary to indirectly obtain channel information for secondary RF channels. The channel impulse response from the primary channel serves as a mediator that allows the eNodeB to infer secondary channel characteristics through reciprocity assumptions, bypassing the need for direct uplink channels on secondary frequencies.
2Measurement precision
If uplink SRS is used to determine downlink beamforming weights, then beamforming accuracy is improved, but the applicability to secondary channels deteriorates because uplink channels do not exist for secondary RF channels
Solution Approach 1:
The patent makes the primary channel's uplink SRS serve multiple functions: it not only determines beamforming weights for the primary channel but also provides channel estimates for secondary channels. This multi-functional use of the primary channel's uplink signal extends the applicability of uplink measurements across multiple downlink channels without requiring separate uplink channels for each frequency.
Solution Approach 2:
The patent merges the channel estimation functions for primary and secondary channels into a single process using the primary channel's SRS. By combining the use of one uplink measurement to serve multiple downlink channels, the system achieves both measurement precision and broad channel applicability through a unified estimation approach.
Data Source
AI summary
A method, system, and medium are provided for approximating an uplink sounding reference signal for a secondary radio-frequency channel associated with an eNodeB in a long-term-evolution (LTE) network deploying carrier aggregation. This is useful when the eNodeB does not have an uplink channel associated with the secondary RF channel. The approximated uplink sounding reference signal is utilized by the eNodeB to determine downlink beamforming weights for the secondary RF channel.