Positioning Reference Signal (PRS) is taken into consideration in one of the LTE release 9 features to determine the location of User Equipment (UE) based on radio access network information. Now you might be thinking that what is the necessity of PRS, if we have a GPS technology already built in smartphones and in other cellular equipment. Just think of it (GPS may not be accurate always and GPS services may not be available all around the geographical areas , also the accuracy of functioning GPS depends on money you have paid for the services and the quality of GPS device). The end user application of this PRS feature could be supporting location based services which can be navigation (direction to hotel etc.), emergency call etc. Follow the blog for more detail:
http://lte-question.blogspot.in/2014/09/PRSLTE.html
http://lte-question.blogspot.in/2014/09/PRSLTE.html
Hi Abhishek,
I think you explained in very well - PRS type of position calculation is a complementary to GPS and to cell ID based localization as defined in the standard. In my opinion everything depends on the application for localization services and the QoS for the position that need to be calculated. And additionally GPS is not always having "good signal" e.g. in buildings and tunnels - this is where PRS (i.e. the cellular network based reference signals) may be of help to actually get the location. GPS may be also complemented with PRS (not as alternative) using both signals to calculate precise position.
Best,
Marcin
BTW very nice blog.
Thanks for valuable input Marcin. I was wondering how eNB actually calculate the latitude and longitude of UE . I am very curious to know that, can you please give some idea about that.
Thanks a lot.
BR,
Abhishek
Hi,
Quite nice discussion :)
As far as I know, eNB only provides its own parameters (e.g. cell info, PRS info, antenna cell geolocation) for OTDOA (observed time difference of arrival) calculation (i.e. measurements based on PRS) to E-SMLC (enhanced serving mobile location center), which is actually the node performing UE position calculation. And this is because individual eNB cannot calculate the position since it doesn't have enough information - i.e. from multiple cells. Therefore we need a more central node that gathers all the info from multiple eNBs and calculate the position.
The options are:
a) UE based positioning: UE calculation of position (i.e. it measures its own position based on cells' antennas geolocation and PRS measurements - i.e. OTDOAs) - and sending the calculated position over LPP protocol to E-SMLC.
b) UE assisted positioning: UE performs measurements of OTDOA and sends them over LPP to E-SMLC that performs the calculation of UE position. All depends on the UE capabilites and the necessity of the application.
Furthermore for PRS ideally we have 4 PRS cells (but at least 3) and for each we calculate the OTDOA and based on the calculated times and the GEO-location of the cell antennas the UE position is calculated.
Regarding the details of the protocols and the parameters please take a look on: a) 3GPP TS 36.455 "LTE Positioning Protocol A (LPPa)" which deals with protocol used for sending messages between eNB and E-SMLC.
b) 3GPP TS 36.355 "LTE Positioning Protocol" which deals with protocol used for sending messages between UE and E-SMLC.
A nice whitepaper regarding PRS and Location services is provided by Qualcomm under this link: http://blog.3g4g.co.uk/2014/07/observed-time-difference-of-arrival.html
Best,
Marcin
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