In 4G LTE, the duration of a frame is 10 milliseconds (ms), and each frame is divided into 10 subframes, making the duration of a subframe 1 ms.

The duration and structure of OFDM symbols within a frame and subframe depend on the cyclic prefix (CP) used, which can be normal or extended.

The use of a normal or extended cyclic prefix affects the number of OFDM symbols per subframe and the symbol length, with the choice between them typically based on the specific requirements of the network environment, such as the need to mitigate inter-symbol interference in scenarios with significant multipath propagation.

Normal Cyclic Prefix:

Each subframe (1 ms) consists of 14 OFDM symbols in the time domain. The length of each OFDM symbol, including the cyclic prefix, is approximately 71.4 microseconds (µs) for normal CP.

Extended Cyclic Prefix:

Each subframe with an extended cyclic prefix consists of 12 OFDM symbols to accommodate a longer cyclic prefix, which helps in environments with large delay spreads. The length of each OFDM symbol, including the cyclic prefix, is longer than in the normal CP configuration, approximately 83.3 microseconds (µs) for extended CP.

Further Readings

• LTE Downlink Frame Structure
• LTE Uplink Frame Structure