D-MIMO AP Calibration in TDD Without Handshake Timeslots

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Solution Overview

Problem

Existing D-MIMO networks operating in TDD mode require dedicated handshake timeslots for phase calibration, which consumes radio resources, disrupts user-plane data flow, and incurs delays, especially in large-scale deployments.

Innovation Solution

A method for transmitting and receiving calibration reference signals between APs in D-MIMO networks in TDD mode without dedicated handshake timeslots, allowing phase difference estimation by exchanging reference signals during normal UL and DL timeslots while refraining from user data transmission or reception.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If dedicated handshake timeslots are used for phase calibration between APs, then phase alignment can be performed, but radio resources are consumed and user-plane data flow is disrupted

Engineering Contradiction:

Improvephase alignmentVSAvoidradio resource utilization

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent combines phase calibration operations with normal data transmission timeslots. Instead of separating calibration into dedicated handshake timeslots, the system performs calibration during regular UL/DL timeslots by having APs transmit calibration reference signals while refraining from user data transmission only during calibration portions of those timeslots. This merging eliminates the need for dedicated calibration resources and maintains continuous radio resource utilization.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent implements periodic calibration within the TDD frame structure. APs perform calibration periodically by transmitting calibration reference signals in specific timeslots according to a configured pattern. The network can adjust the periodicity and timing of these calibration actions to balance between maintaining phase alignment and preserving data transmission productivity.

Inventive Principle:

Principle #19Periodic action

2Measurement precision

If dedicated handshake timeslots are allocated for calibration, then phase difference estimation is possible, but latency increases and data transmission is interrupted

Engineering Contradiction:

Improvephase difference estimationVSAvoidcalibration delay

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent performs calibration actions in advance during timeslots before actual data transmission begins. By pre-transmitting calibration reference signals and estimating phase differences during available timeslots, the system prepares alignment information beforehand, eliminating the need to wait for dedicated calibration timeslots after data transmission is needed, thus reducing overall latency.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent maintains continuous calibration activity within the TDD cycle by performing phase difference estimation during timeslots that would otherwise be idle or by utilizing portions of data transmission timeslots. This continuous approach ensures phase alignment is always current without creating gaps or interruptions in the overall system operation, thereby reducing latency compared to batch calibration approaches.

Inventive Principle:

Principle #20Continuity of useful action

3Productivity

If calibration reference signals are transmitted during normal UL/DL timeslots, then radio resource utilization is improved, but interference with user data transmission may occur

Engineering Contradiction:

Improveradio resource utilizationVSAvoidsignal interference

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent segments each timeslot into distinct portions: calibration reference signal transmission portions and user data transmission portions. Within each UL/DL timeslot, the system identifies and separates the time intervals allocated for calibration signals from those allocated for user data, preventing overlap and interference. This segmentation allows both functions to coexist in the same timeslot without mutual interference.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different transmission characteristics to calibration reference signals versus user data signals within the same timeslot. Calibration signals use specific parameters (such as known sequence, particular power levels, or frequency allocation) that distinguish them from user data, allowing receiving APs to easily identify and separate calibration signals from data signals, thereby preventing interference between the two types of transmission.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20260012384A1Calibration between access points in a distributed multiple-input multiple-output network operating in time-division duplexing mode

Publication Date: 2026.01.08 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Techniques for transmitting and/or receiving calibration reference signals between APs in a D-MIMO network operating in TDD mode. A method includes transmitting, by a first AP and towards a second AP, a first calibration reference signal in a first uplink timeslot whilst the first AP refrains from receiving user data in the first uplink timeslot when transmitting the first calibration reference signal. Additionally or alternatively the method includes receiving, by a third AP and from a fourth AP, a second calibration reference signal in a first downlink timeslot whilst the third AP refrains from transmitting user data in the first downlink timeslot when receiving the second calibration reference signal.