Wireless Control Unit Path Delay Compensation in Cell-Free MIMO
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Solution Overview
Problem
In cell-free massive MIMO systems, the variation in cable lengths between the BBU and APs leads to differences in transmission/reception timing, increasing costs due to the need for precision time protocol (PTP) and optical time-domain reflectometer (OTDR) measurements, especially when dealing with multiple APs.
Innovation Solution
A wireless control unit that transmits control signals to analog sections to transition to a loopback mode, observes delay times using an internal clock, counts clock cycles, calculates path delays, and adjusts downlink signal timings to compensate for these delays without requiring digital circuitry or manual settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PTP and OTDR are used to measure and compensate path delays, then transmission/reception timing synchronization is improved, but cost increases
Solution Approach 1:
The analog section performs self-measurement of path delay by automatically detecting the timing difference between receiving the downlink signal and transmitting the uplink signal, eliminating the need for external measurement equipment like OTDR or complex digital circuitry for PTP synchronization
Solution Approach 2:
The patent replaces complex digital timing synchronization systems (PTP requiring digital circuitry) and manual measurement tools (OTDR) with a simpler analog-based timing adjustment mechanism that uses the existing radio frequency signals and analog circuitry to achieve synchronization
2Measurement precision
If manual settings are used for path delay compensation, then timing synchronization is achieved, but operation complexity increases
Solution Approach 1:
The analog section automatically measures its own path delay by detecting the timing difference between receiving the downlink signal and transmitting the uplink signal, eliminating the need for manual measurement and configuration operations
Solution Approach 2:
The system uses feedback from the timing difference detection to automatically adjust the transmission timing of the uplink signal, creating a closed-loop synchronization mechanism that eliminates manual intervention
Data Source
AI summary
A wireless control unit transmits to a plurality of analog sections a control signal for performing control so as to cause the plurality of analog sections to transition to a loopback mode, transmits to the plurality of analog sections an observation signal for observing delay times, calculates, for each of the plurality of analog sections, a path delay based on the number of clocks generated from when the observation signal is transmitted to when the observation signal is received, and transmits to the plurality of analog sections a control signal for canceling the loopback mode of the plurality of analog sections. In addition, the wireless control unit transmits a downlink signal at a timing calculated for each of the plurality of analog sections according to the path delay.