LTE Concept and Applications

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  J (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.   Process of finding UE location using PRS: The overall process of finding UE locations are based on three major steps. Step 1. UE receive PRS from cells (Reference cell and Neighbor cells)   Step 2. Based on received PRS...

In LTE or any other cellular radio network, UE report some sort of signal to base station for various decision making. It could be used for better downlink scheduling (using CSI), uplink scheduling (using SRS), cell selection , handover, cell reselection , calculation of uplink and downlink path loss for power control, multipath propagation, Uplink interference  and for location based services.  All of these achieved by parameter called RSRP, RSSI, RSRQ and RSTD. RSRP: RSRP Reference Signal Received Power is the average power received by UE from a single cell specific reference signal resource element spread over the full bandwidth. It is calculated by UE for cell selection, handover, cell reselection and for path loss calculation for power control. The power measurement is the energy of the OFDMA symbol excluding the energy of the cyclic prefix.  The measurement of RSRP may be based on energy of reference signal transmitted by antenna port 1 or 1 a...

DAI ( Downlink Assignment Index ) is an index, which is communicated to UE by eNB to prevent ACK/NACK reporting errors due to HARQ ACK/NAK bundling procedure performed by the UE. To understand how DAI works we need to learn how ACK/NAK reporting used to happen in LTE TDD. In LTE TDD, UE can send single ACK/NAK of multiple PDSCH sub frame in one bit for each code word CW0 and CW1. UE perform AND logical operation on each code word CW0 and CW1 (CRC Passed/Failed) of each PDSCH received and report the result in two bits (00, 01, 10, 11) on specific uplink subframe. Below is the table which shows that which all PDSCH subframes need to be bundled for reporting ACK/NAK on which Uplink subframe for each TDD UL DL configurations (Mentioned only for config 1 and config 2 in green color). For Example:            UL/DL Configuration 1: We can see that the k value for 2 nd subframe (Uplink) are 7,6 (according to Table 10.1.3.1-1 of s...