GNSS Data Processing in 5G Mobile Phones

This article delves into the GNSS (Global Navigation Satellite System) data processing steps employed within 5G mobile phones. It also outlines the GNSS architecture typically found in these devices.

Introduction

GNSS stands for Global Navigation Satellite System. It’s a technology used in a wide array of applications, including navigation, mapping, surveying, and time synchronization, especially crucial for wireless telecommunications. Its primary function is to pinpoint the location, velocity, and time of a device, whether it’s on the ground or in the air. GNSS achieves this by analyzing signals received from multiple satellites specifically designed for GNSS use.

Prominent GNSS systems used globally include GPS (United States), GLONASS (Russia), GALILEO (European Union), and BeiDou (China). Various organizations like IGS, GSA, IOB, ISO, and ICAO are responsible for developing and managing GNSS standards.

GNSS Architecture

The GNSS architecture is comprised of three main segments:

• Space Segment: This consists of a constellation of satellites. These satellites transmit their location information alongside a timestamp indicating when the signal was transmitted. GNSS receivers on Earth pick up these signals.

• User Segment: This segment includes one or more GNSS receivers. These receivers calculate their positions based on the signals received from the satellites. Additionally, they determine their velocities and the timestamp when the signals were received.

• Control Segment: This segment acts as a monitoring and control station for the GNSS satellites. It’s responsible for adjusting the satellites’ orbits and clocks. Furthermore, the control segment generates and uploads navigation messages to the satellites, which are then relayed back to users on the ground.

GNSS Device Architecture in 5G Mobile Phones

The GNSS device architecture within 5G mobile phones typically includes an antenna, RF to baseband conversion circuitry, a location engine, and the operating system (OS).

Generally, a GNSS receiver is split into RF processing and baseband processing components. The RF processing is handled by an RF down-converter using mixers and local oscillators (LOs). The baseband processing is performed using a Digital Signal Processor (DSP) and associated firmware.

The GNSS antenna receives signals from multiple satellites and feeds them to the RF down-converter, which then provides a baseband output. The receiver is then responsible for processing the GNSS signals and calculating the device’s location. The location engine augments this by processing location data from Wi-Fi gateways and cellular towers to improve the accuracy and reliability of the location data.

The Operating System (OS) provides the necessary APIs and services for applications to access GNSS data (Location, Altitude, Velocity, and Time).

A GNSS chipset often integrates the GNSS antenna, RF to baseband conversion circuitry, and the GNSS receiver into a single package. Samsung and Ericsson are well-known 5G mobile phone manufacturers. It’s worth noting that different manufacturers may implement GNSS device architectures in different ways.

GNSS Signal Codes

GNSS signals use various codes to modulate the RF carrier wave transmitted by the satellites. These codes enable receivers to distinguish between different satellites, their positions, and the precise timing of their signal transmissions. Different GNSS systems utilize different codes.

• GPS (US) uses C/A (Coarse/Acquisition) code and p-code (Precision code).
• GPS III satellites use L1C and L2C codes, which are also compatible with Galileo and BeiDou.
• L5 code is a newer addition for use in GPS III satellites.
• European Galileo system uses E1, E5a, and E5b codes.
• Chinese BeiDou system employs B1, B2, and B3 codes.

These signal codes are modulated onto the carrier wave using various data formats, depending on the specific GNSS system and signal type.

GNSS satellite systems use data formats such as NMEA 0183, RINEX, BINEX, SP3, or GPX to transmit the signal codes. These formats carry essential information like ephemeris, almanac data, time information, and other data required to calculate accurate positions. NMEA 0183 is a commonly used format in 5G mobile phones.

GNSS Data Processing Steps

GNSS data is received by the GNSS antenna from satellites orbiting in space. This RF signal is down-converted and translated to baseband information after undergoing the necessary radio frequency processing. GNSS is implemented on both the RF and baseband sections within 5G mobile phones.

GNSS data processing in 5G mobile phones involves the following steps (as depicted in the figure). While the specific implementation varies among manufacturers, the listed steps represent generic functional modules present in a typical GNSS receiver.

• GNSS signal acquisition: This block utilizes the GNSS antenna and RF receiver to acquire GNSS signals from satellites. It employs a correlator to identify the received signal codes.

• GNSS signal tracking: This function tracks the GNSS signals to maintain a stable connection with the satellites. It monitors the phase and frequency of the received signals and adjusts the local oscillator (LO) of the receiver to maintain signal lock.

• GNSS signal demodulation: This block uses DSP techniques to demodulate the signals and extract navigation data.

• GNSS navigation data processing: This block processes the navigation data and calculates the location, velocity, and time information of the device (or GNSS receiver). Navigation data helps determine pseudoranges to different satellites and the Time of Arrival (ToA) of GNSS signals from them.

• GNSS location computation: This block uses pseudoranges and ToAs along with a least-squares algorithm to determine the device’s location, time, and velocity.

• GNSS data fusion: This block incorporates location related data from other sources like Wi-Fi routers and cellular towers to estimate a more accurate and precise location for the device. It combines location data derived from GNSS satellite signals and other sources to provide the best possible estimate.

Several manufacturers produce GNSS chipsets, including Qualcomm, Broadcom, and Mediatek. 5G mobile phone manufacturers either use these GNSS chipsets and integrate them into their phone designs or develop their own proprietary GNSS chipset implementations.