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CELL ID METHOD<br />
This is the simplest of all positioning methods but the UE position is very coarse in that only the serving<br />
cell where the UE is located is provided. As E-UTRAN and MME are involved in the mobility management<br />
(e.g. tracking area update or paging) of UEs the serving base station and serving cell of the UE is always<br />
known especially when there is signaling between the E-SMLC and the UE to query the UE position.<br />
ENHANCED CELL ID‐BASED METHOD<br />
In this method the position obtained by the Cell ID method is enhanced through means of use of other UE<br />
or E-UTRAN measurements to estimate the UE position with better accuracy than the Cell ID method.<br />
The measurements used may be radio resource measurements or other measurements. The E-SMLC<br />
does not configure these measurements in the UE/E-UTRAN but only queries the UE/E-UTRAN for these<br />
measurements and obtains them if available in the UE/E-UTRAN.<br />
NETWORK ASSISTED GNSS METHODS<br />
In network assisted GNSS methods the network provides various assistance data to the UE that are<br />
equipped with radio receivers capable of receiving GNSS signals. The UEs use the assistance data<br />
provided by the network to help perform measurements. Examples of GNSS include: GPS, Modernized<br />
GPS, Galileo, GLONASS, Space Based Augmentation Systems (SBAS) and Quasi Zenith Satellite<br />
System (QZSS). Different GNSS can be used separately or in combination to determine the position of a<br />
UE.<br />
OTDOA METHOD<br />
The OTDOA method is a downlink terrestrial positioning method. In this method the UE performs<br />
measurements of downlink signals of neighbor E-UTRAN cells. This is a good backup method for<br />
positioning the UE when satellite signals are not strong enough (e.g. indoors or bad atmospheric<br />
conditions etc). The UE receives the downlink radio transmission of four or more neighbor cells, aided by<br />
downlink reference signal transmissions from those cells and measures the time difference of arrival of<br />
the radio frames of the measured neighbor cells relative to the serving cell. These UE measurements are<br />
then used either by the UE or by the E-SMLC to estimate the UE position using a trilateration technique.<br />
The E-UTRAN may combine two or more of the supported UE positioning methods and perform a hybrid<br />
positioning estimation to achieve a better positioning accuracy.<br />
The UE positioning protocol is an end-to-end protocol with terminations in the UE and the E-SMLC. This<br />
protocol is called the LTE Positioning Protocol (LPP). This is a transaction-oriented protocol with<br />
exchange of LPP messages between UE and E-SMLC where one or more messages realize each<br />
transaction. A transaction results in one activity or operation such as assistance data transfer, UE<br />
positioning capability transfer or position measurement/estimate exchange. There is a second UE<br />
positioning protocol, LPPa, with terminations in the E-UTRAN and E-SMLC that allows the exchange of<br />
information and measurements, which are useful for some specific positioning methods. Currently, the<br />
LPPa is used for the delivery of timing information that is resident only to the E-UTRAN and/or is semidynamically<br />
changing, which is required for the OTDOA positioning method. Apart from this the LPPa<br />
also supports the exchange of E-UTRAN assisted measurements that are used for the Enhanced Cell ID<br />
positioning method.<br />
www.4gamericas.org February 2011 Page 123
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