GNSS data processing in 5G Mobile Phones
This article covers GNSS data processing steps used in 5G mobile phone. It also mentions GNSS architecture implemented in mobile phones.
Introduction: The term GNSS is the short form of Global Navigation Satellite System. It is used in various applications viz. navigation, mapping, surveying and time synchronization for wireless telecommunications and other systems. It is mainly used to determine device's location, velocity and time located on the ground or in the air. To estimate this information, GNSS devices utilize signals received from multiple satellites installed for GNSS use. The well known GNSS systems use across the world include GPS (US), GLONASS (Russia), GALILEO (European Union), BeiDou (China) etc. GNSS standards are developed and managed by various organizations such as IGS, GSA, IOB, ISO and ICAO.
The GNSS system architecture consists of three parts viz. space segment, control segment and user segment. The space segment is composed of constellation of satellites which transmit their location information and time stamp at which signals are transmitted from them. These signals are received by GNSS receivers on the earth. User segment is composed of one or many GNSS receivers. These receivers calculate their positions based on GNSS signals received from satellites. In addition to positions, receivers calculate their velocities and time stamp when the signals are received from satellites. The control segment is mainly used as monitoring and control station for the GNSS satellites. This segment takes care of adjustment of satellites orbits and their clocks. Moreover control segment generates and uploads useful navigation messages to satellites which are relayed back to users on the ground.
GNSS device architecture in 5G mobile phones consists of antenna, RF to baseband conversion, location engine and OS (Operating system). In general, GNSS receiver is composed of RF processing and baseband processing. The RF processing is carried out using RF down converter with the help of mixers and LOs. The baseband processing is carried out using DSP (Digital Signal Processor) and firmware. GNSS antenna receives GNSS signals from multiple satellites and provide the output to RF down converter which provides baseband output. The receiver is responsible to process GNSS signals and to calculate location of the device. The location engine processes other location data from WiFi gateways and cellular towers to determine more accurate and reliable location of the device. Operating System (OS) takes care of APIs and services required to access the GNSS data (Location, Altitude, Velocity and Time). GNSS chipset usually houses GNSS antenna, RF to baseband conversion and GNSS receiver in a single package. Samsung and Ericsson are the popular 5G mobile phone manufacturers. Different manufacturers implement GNSS device architectures in different ways.
GNSS signal codes : GNSS signals utilize various codes in order to modulate RF carrier wave transmitted by satellites. These codes help receivers distinguish different satellites, their positions and precise timings of their respective signal transmissions. Different codes are used by various GNSS systems across the world. C/A (Coarse/Acquisition) code and p-code (Precision code) are used by GPS satellite system operated by US government. L1C and L2C are used by GPS III satellites and are also compatible with Galileo and BeiDou. L5 code is recently introduced to be used in GPS III satellites. E1, E5a and E5b codes are used by European Galileo system. B1, B2 and B3 codes are used by Chinese BeiDou system. These signal codes are modulated onto the carrier wave using different data formats which depend on specific GNSS system and signal type used.
GNSS satellite systems use various data formats such as NMEA 0183, RINEX, BINEX, SP3 or GPX to transmit above signal codes which carry necessary information such as ephemeris, almanac data, time information and other useful data to calculate accurate positions. NMEA 0183 format is widely used in 5G mobile phones. Refer various GPS/NMEA sentences >> for more information.
GNSS data processing steps
GNSS data is received by GNSS antenna from GNSS satellites orbiting in the space. The received RF signal is down converted and translated to baseband information after necessary radio frequency processing. GNSS is implemented on both RF and baseband in 5G mobile phones. GNSS data processing in 5G mobile phones involve following steps as shown in the figure. Implementation of data processing on GNSS data varies with different manufacturers. The steps mentioned are generic functional modules implemented in a typical GNSS receiver.
GNSS signal acquisition : This block uses GNSS antenna and RF receiver to acquire
GNSS signals from satellites. It uses correlator in order to identify signal codes received.
GNSS signal tracking : It performs tracking of GNSS signals in order to maintain stable connection with the GNSS satellites. It monitors phase/frequency of received signals and adjust LO (Local Oscillator) of receiver to maintain locking.
GNSS signal demodulation : This block demodulates signals using DSP techniques to extract navigation data.
GNSS navigation data processing : This block processes navigation data and calculates location, velocity and time information of the device (or GNSS receiver). Navigation data helps to determine pseudoranges to different satellites and ToA (Time of Arrival) of GNSS signals from them.
GNSS location computation : This block uses pseudoranges and ToAs and least square algorithm to determine location, time and velocity of the device.
GNSS data fusion : This block uses location related data from other sources such as wifi routers and cellular towers to estimate more accurate and precise location of the device. This block combines location data derived using signals from GNSS satellites and other sources to provide best estimate.
There are various manufacturers of GNSS chipsets which include Qualcomm, Broadcom, Mediatek etc. 5G mobile phone manufacturers use these GNSS chipsets and integrate in their phone designs or can have their own proprietary GNSS chipset implementations.
Refer 5G Mobile phone architecture >> for internal modules of a generic 5G Cellular phone.