Uplink SRS-Based RTT Estimation for Mobile Positioning

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Solution Overview

Problem

Existing round trip time (RTT) estimation schemes in mobile communication systems require transmitting wideband signals in the downlink, increasing frequency resources and computational complexity at the user equipment (UE), and take longer to obtain RTT due to the need for sounding reference signals (SRS) and positioning reference signals (PRS).

Innovation Solution

A method for improved RTT estimation using a state-based signaling mechanism, where the base station determines a wideband signal configuration and generates Downlink Control Information (DCI) scrambled with a radio network temporary identifier (RNTI) based on the UE's state. The method involves transmitting the DCI to the UE, receiving an uplink synchronization message and a wideband signal impulse response, and estimating RTT from the time of arrival and sampling rate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If wideband signals are transmitted in the downlink for RTT estimation, then positioning accuracy is improved, but frequency resources and computational complexity at the UE increase

Engineering Contradiction:

Improvepositioning accuracyVSAvoidcomputational complexity at UE

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent inverts the traditional RTT estimation approach by having the UE transmit wideband uplink signals (SRS) instead of the base station transmitting wideband downlink signals (PRS). The base station then estimates RTT by processing the uplink signals from multiple UEs simultaneously. This inversion reduces downlink wideband signal transmission requirements while maintaining positioning accuracy through sophisticated base station-side processing of uplink signals.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent makes the base station's signal processing capability serve multiple functions: it processes uplink signals for both RTT estimation and channel quality assessment simultaneously. The same received uplink signals are used for positioning purposes and for evaluating channel conditions, eliminating the need for separate dedicated positioning reference signals in the downlink.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If SRS and PRS are transmitted for RTT estimation, then positioning information is obtained, but the time needed to obtain RTT increases

Engineering Contradiction:

Improvepositioning informationVSAvoidtime needed to obtain RTT

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent merges the RTT estimation function with existing uplink signaling procedures. Instead of requiring separate downlink PRS transmission and uplink SRS transmission in different time slots, the base station estimates RTT directly from the uplink SRS signals that UEs transmit for other purposes (channel sounding). This combining of functions eliminates the need for dedicated bidirectional positioning signal exchanges.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent enables the base station to derive positioning information from uplink signals that UEs transmit for their own operational needs (channel quality assessment, uplink synchronization). The base station performs self-service RTT estimation using signals already present in the uplink, without requiring additional signaling overhead or coordination for dedicated positioning measurements.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If downlink wideband signals are transmitted for RTT estimation, then RTT can be measured, but frequency resources are increased

Engineering Contradiction:

ImproveRTT measurementVSAvoidfrequency resources

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentEP4543106A1System and a method for improved round trip time estimation

Publication Date: 2025.04.23 EURECOM

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AI summary

There is provided a method of positioning a user equipment (1) implemented in a communication system (100) comprising at least the user equipment and a base station (2), the method comprising the following steps implemented at the base station (2): - Generating (506, 512) a DCI scrambled with a type of RNTI, the RNTI type depending on the RRC state of the user equipment, the generated DCI being configured to trigger a Round Trip Time (RTT) procedure; - Transmitting (506, 512) the generated DCI to the User Equipment (1). An uplink synchronisation procedure (e.g. RACH procedure) is initiated by the user equipment (1) in response to the receipt of the generated DCI, the user equipment sending the uplink synchronisation signal (e.g. RACH preamble) and a wideband signal (e.g. aperiodic SRS) next to the uplink synchronisation signal, in the same time slot, the method estimating (1302) the round trip time RTT between the base station (2) and the user equipment (1) from the time of arrival estimated from said wideband signal impulse response and the sampling rate of communication system.