LTE Concept and Applications

SR (Scheduling Request) is a request of scheduling radio resource for uplink transmission by the UE to the eNB. UE send SR on PUCCH when regular BSR (Buffer status report) is triggered and UE does not have radio resource to transmit this BSR to eNB.  To send this SR, UE must be configured with SR periodicity. If PUCCH resource is not configured for SR, UE start RA (Random Access) procedure. Since PUCCH resource is limited, SR periodicity should not be very less (short periodicity leads to fast resource allocation). If we fix short periodicity for SR, UE may not utilize the PUCCH for SR transmission allocated each time (UE may not have data to transmit in uplink always).   There must be a tradeoff between PUCCH load and SR periodicity.  UE always keep track of SR transmission on PUCCH. After reaching the maximum number of SR transmission (SR Max) and UE has not been allocated any radio resource for uplink transmission, it releases PUCCH resource for SR and s...

What are different PUCCH formats and PUCCH Mixed Mode in LTE? We should know what all PUCCH formats are available in LTE or LTE-A, before exploring PUCCH Mixed Mode. Basically PUCCH formats are of two types Format 1 and Format 2 (Format 3 is introduced in LTE advance release 10, which uses modulation scheme QPSK and number of bits used as 48 per subframe).   PUCCH Format 1 (Rel 8): Format Type Control Information Modulation Scheme No. of bits / Subframe 1 SR (Scheduling Request) Not Applicable Not Applicable 1a HARQ ACK/NACK BPSK 1 bit 1b HARQ ACK/NACK (for MIMO) QPSK 2 bits PUCCH Format 2: Format Type Control Information Modulation Scheme No. of bits / Subframe 2 CSI (Channel State Info.) QPSK 20 bits 2a CSI+HARQ ACK/NACK QPSK+BPSK 21 bits 2b CSI+HARQ ACK/NACK (for MIMO) QPSK + B...