MOBNET GSM Positioning
The main objective of MOBNET is to locate isolated victims during natural disasters and situations of emergency such as earthquakes, hurricanes or large snowstorms. It will also help first responder services to find lost people in general. To that end, the use of European Global Navigation Satellite (EGNSS) systems (both Galileo early services and EGNOS) and Digital Cellular Technologies (DCT) will play the key role in these situations in which it is difficult, dangerous or even impossible to access the affected areas.
In MOBNET project, a drone carrying a mobile-BTS (Base Transceiver Station) will be flying around the disaster site. This mobile-BTS, for handling its normal functioning, uses different parameters. Some of them are related to the distance between the mobile phone and the mobile-BTS, so they could be used for the localization of victims (assuming that the victim is located in the vicinity of his or her mobile phone).
In the case of the GSM technology the two most relevant parameters, which could be used for positioning, are:
- The Timing Advance (TA) parameter that is used for synchronization, and gives an estimate of the propagation delay between the mobile phone and the serving BTS. By knowing the speed of the radio waves, which is equal to the speed of light, it is possible to directly obtain the distance between the UE and the BTS.
- The second parameter is the Received Signal Level (RXLEV), that gives an estimate of how strong is the BTS signal as received by the mobile phone. The relationship between the signal strength and the distance is not direct. The loss of signal strength depends on many factors. The GSM standard considers three possible scenarios, also called environments: urban, suburban and rural and provides models, which were created based on numerous and extensive measurement campaigns for each of those scenarios. By knowing the scenario, it is then possible to work out the distance from the signal strength.
The UMTS technology offers similar parameters that can be used for positioning: Propagation delay (PD), Received Signal Code Power (RSCP), and Received Signal Strength Indicator (RSSI). UMTS communication channels are much wider than in GSM so higher precision in the estimation of the propagation delay is possible. In consequence, the distance of the mobile phone from the BTS can also be known with higher accuracy.
The LTE technology offers two different types of Timing Advance (TA Type 1 and 2) andReference Signal Received Power (RSRP). The error of the estimated signal delay is half of that of the UMTS technology, so higher precision is possible. LTE has also a built-in mechanism for locating the mobile phones, for example during the emergency calls.
Using any of the mentioned parameters in a least squares (LS) or a Kalman filter algorithm the position of the victim’s mobile phone could be estimated. However, to perform this estimation, it is also necessary to know the position of the drone in each time instant. In MOBNET system, this global position will be accurately provided by the on-board EGNSS module. Thus, the developed MOBNET system will take advantage of the Galileo and EGNOS capabilities and will strengthen the position of European Industry in the field of security services. It will greatly facilitate their missions and the rescue of isolated victims.
- 3GPP TS 45.010 Technical Specification Group GSM/EDGE Radio Access Network; Radio subsystem synchronization.
- Ref: 3GPP TS 45.008 Technical Specification Group GSM/EDGE Radio Access Network; Radio subsystem link control.
- ETSI TS 125 215 Technical Specification Universal Mobile Telecommunications System (UMTS); Physical layer - Measurements (FDD).
- 3GPP TS 36.321 Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification.
- 3GPP TS 36.213 Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures.
- 3GPP TS 25.133 Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for support of radio resource management (FDD).