Dear community friends, today I want to share with you information about the LTE frame structure.
There are two types of LTE frame structures.
LTE frame structure type 1
The duration of each frame is 10 ms and includes 20 timeslots, where the duration of each timeslot is 0.5 ms. A subframe consists of two adjacent timeslots, and the duration is 1 ms.
LTE frame structure type 2
Radio frame structure 2 is used in TDD mode. The TDD frame structure introduces the concept of special subframes.
The special subframe includes a DwPTS (downlink pilot timeslot), a GP (protection period), and an UpPTS (uplink pilot timeslot).
The length of each part of a special subframe is configurable, but the total duration is fixed at 1 ms.
Uplink-downlink subframe configuration and special slot assignment
The LTE-TDD frame structure is characterized by uplink-downlink conversion.
The subframes for uplink-downlink conversion are called special subframes (DwPTS, GP, and UpPTS).
The uplink-downlink slot assignment and special subframe configuration need to be planned.
UpPTS mainly carries RACH and sounding RS.
The short RACH is configurable and occupies one OFDM symbol.
The SRS must exist and occupies one OFDM symbol.
CP Classification and Scenario
Generally, Normal CP is configured.
For MBSFN, Extended CP is configured.
Extended CP may be configured for the cell with a larger radius like a wide coverage scenario.
CP is used to overcome ISI and CI caused by multipath delay spread.
Large cell radius = Multi-path delay spread, which is also related to the environment.
CP essentially sacrifices resource utilization to ensure performance.
LTE Physical Resource Concept
RE (Resource Element)
Minimum granularity of physical layer resources
Time-domain: one OFDM symbol, frequency domain: one subcarrier.
RB (Resource block)
Minimum unit of resource allocation for physical layer data transmission.
Time domain: 1 time-fault; frequency domain: 12 consecutive subcarriers.
CCE (Control Channel Element)
Resource unit of the control channel
1CCE=36 REs
1CCE =9REGs (1REG =4 REs)
TTI (Transmission Interval)
Basic time-domain unit for data transmission scheduling at the physical layer
1TTI = 1 subframe = 2 timeslots
1TTI = 14 DFDM symbols (Normal CP)
1 TTI = 12 OFDM symbols (Extended CP)
Resource grid structure
Relationship between channel BW and RB
That's all I want to share about the LTE frame structure. I'll share the LTE physical channel in the next article.
Welcome to read and comment!
