Uplink SRS Multiplexing for MIMO CSI Acquisition
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Solution Overview
Problem
In large-scale Multiple-Input Multiple-Output (MIMO) wireless communication systems, acquiring Channel State Information (CSI) for User Equipment (UE) is challenging due to high system overhead and feedback channel overload, especially when using reciprocal channels to estimate downlink CSI from uplink Sounding Reference Signals (SRS).
Innovation Solution
The method involves allocating radio resources for SRS using multiplexing patterns among UEs and neighboring Base Stations (BSs) through Time-Division Multiplexing (TDM), Frequency-Division Multiplexing (FDM), or Code-Division Multiplexing (CDM) to reduce inter-cell interference and optimize resource utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference pilots are sent in the downlink to obtain CSI, then the BS can acquire accurate CSI, but the system overhead becomes very large due to the large number of antennas
Solution Approach 1:
Instead of transmitting reference pilots from the BS to UEs in the downlink to obtain CSI, the patent inverts the approach by having UEs transmit Sounding Reference Signals (SRS) to the BS in the uplink. The BS then uses channel reciprocity to estimate downlink CSI from these uplink SRS transmissions. This inversion dramatically reduces the reference signal overhead from tens to hundreds of downlink pilots to just a few uplink SRS resources.
Solution Approach 2:
The patent introduces channel reciprocity as an intermediary mechanism that allows the BS to infer downlink CSI from uplink SRS measurements. By using the reciprocal property of wireless channels in TDD systems, the BS can obtain downlink channel state information without directly transmitting downlink reference pilots, thus reducing overhead while maintaining measurement accuracy.
2Measurement precision
If more bits are used to quantize CSI accurately, then the CSI precision is improved, but the feedback channel becomes overloaded
Solution Approach 1:
The patent extracts the CSI measurement process from the downlink feedback path and relocates it to the uplink measurement path. By having the BS measure uplink SRS signals directly, the system eliminates the need for UEs to quantize and feed back high-dimensional CSI matrices, thereby dramatically reducing feedback channel load while the BS maintains full-precision CSI measurements.
3Productivity
If SRS resources are shared among multiple UEs and BSs, then resource utilization is improved, but inter-cell interference increases
Solution Approach 1:
The patent segments SRS resources in the time and frequency domains to serve multiple UEs and BSs simultaneously. By dividing the available SRS resources into different time slots and frequency subbands, and by assigning different cyclic shifts and orthogonal covers to different UEs, the system enables resource sharing while maintaining orthogonality and minimizing inter-cell interference through structured resource partitioning.
Data Source
AI summary
This invention presents a method for uplink SRS transmission in MU-MIMO wireless communication systems comprising the BS reserving resources for SRS transmission and multiplexing the reserved resources among neighboring cells and among multiple UEs allocated to the same SRS transmission resource; the BS estimating the CQI of each UE through the uplink channel; and the BS allocating the same resource to a group of UEs to transmit uplink SRSs based on the estimated CQI and the QoS requirement.