LTE Concept and Applications

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...

Rank Indication is one of the important input to eNB , in selection of the transmission layer in downlink data transmission. Even though the system is configured in transmission mode 3 (or open loop spatial multiplexing) for a particular UE and if the same UE report the Rank Indication value 1 to eNB, eNB will start sending the data in Tx diversity mode to UE . If UE report Rank Indication 2 , eNB will start sending the downlink data in MIMO mode (Transmission Mode 3). Why we need this RI in LTE concept? When UE experience bad SNR and it would be difficult (error prone) to decode transmitted downlink data  it gives early warning to eNB by stating Rank Indication value as 1. When UE experience good SNR it pass this information to eNB by indicating rank value as 2. Because of this reason, you might have observed that some time data transmitted by eNB is in Tx diversity mode, though MIMO was configured and hence you may have observed less downlink throughput than expected ...

Well, we had discussed about uplink channel state information  Difference between SRS and DMRS by reference signals (SRS and DMRS). Now to achieve 1Gbps or more downlink speed in LTE with effective resource utilization of full bandwidth available,   CQI PMI RI and many more parameter play very important role. So what are CQI, PMI and RI in LTE? CQI (Channel Quality Indicator) , reported by UE to eNB. UE indicates modulation scheme and coding scheme to eNB , if used I would be able to demodulate and decode the transmitted downlink   data with maximum block error rate 10%. To predict the downlink channel condition, CQI feedback by the UE is an input. CQI reporting can be based on PMI and RI. Higher the CQI value (from 0 to 15) reported by UE, higher the modulation scheme (from QPSK to 64QAM ) and higher the coding rate will be used by eNB to achieve higher efficiency.  PMI (Precoding Matrix Indicator) , UE indicates to eNB , which precoding ma...

There are two types of reference signals used in LTE uplink, to estimate uplink channel quality. Which allow eNB to take smart decisions for resource allocation for uplink transmission, link adaptation and to decode transmitted data from UE . So to take first smart decision by eNB Sounding Reference Signal  (SRS) is being used. SRS is being transmitted by UE on the last symbol of subframe (in which subframe will come to know later). This SRS report the channel quality of over all bandwidth and using this information eNB assign the resource (to UE for uplink transmission )has better channel quality comparing to  other bandwidth  region. So is SRS optional in LTE? Yes. SRS is configurable and infact we do not need SRS at all in case eNB assign all resource block or full bandwidth or have no choice. Now on the basis of configuration and node wise there are two types of SRS (refer 36.211), cell specific (Common SRS) and UE specific (Dedicated SRS).  eNB...