LTE Frame Structure

LTE Downlink Frame Structure

• 1 subframe is 1 msec, each subframe is divided into 2 slots
• Number of OFDM symbols per slot depends on use of normal or extended cyclic prefix
• Figure shows the positions of PCFICH, PHICH, PDCCH and PDSCH channels
• Downlink reference and Cell specific reference symbols are also shown
• Example is only for 72 subcarriers, can be extended to entire transmission bandwidth
• PBCH bandwidth is reduced when extended CP is used, appropriate calculation shown in callout
• PDCCH space is divided into UE specific and common search areas

 

LTE Uplink Frame Structure

• Mostly same structure as downlink, no change in number of OFDM symbols or subframes
• Extra DFT step done for reducing PAPR issues
• Central OFDM symbol (3rd or 4th) used to transmit reference signal along with PUSCH transmission for channel estimation and coherent demodulation
• PUCCH area shown (for an example format), and is used to carry out of band UL information (CQI, ACK/NACK, PMI, RI) and is multiplexed for multiple UE based on ZC + cyclic shift.
• Extra reference symbols are required for PUCCH area for more robustness
• Resource allocation (in green) shown only for 1 UE but in principle will have multiple UE