LTE Concept and Applications

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...

If SRS and PUCCH format 2/2a/2b messages coincide in same subframe, UE shall not transmit SRS. If SRS and PUCCH format 1/1a/1b (ACK/NACK and/or +SR) coincide in same subframe, UE shall transmit SRS iff simultaneousSRSACKNACK is true.   If SRS and PUSCH RARG (Random Access Response Grant) coincide in same subframe SRS will be dropped. If SRS and retransmission of same transport block (as a part of contention based Random access procedure),  coincide in the same subframe SRS will be dropped. If SR and CQI/PMI/RI coincide in same sub-frame, CQI/PMI/RI will be dropped only if UE send SR (which is triggered by BSR) otherwise CQI/PMI/RI will be reported by UE on the same subframe. If CQI/PMI and RI is configured on same subframe and coincide, MAC will schedule RI on that subframe     and hence UE will report RI on that subframe instead of CQI/PMI (One possible reason could be Periodicity of RI is always greater than equal to CQI/PMI. Which means eNB wi...