LTE Radio Frames

LTE Radio Frame:                                          Reference: 3G

• Air Interface For 3G LTE.
• Manage the different types of information that needs to be carried between the eNodeB and the User Equipment.
• The frame structures for LTE differ between the Time Division Duplex, TDD and the Frequency Division Duplex, FDD
• Two adjacent slots constitute a sub-frame of length 1 ms
• There are two types of LTE frame structure:

• Type 1:   used for the LTE FDD mode systems.
• Type 2:   used for the LTE TDD systems.

Type 1 LTE Frame Structure

• The basic type 1 LTE frame has an overall length of 10 ms.
• This is then divided into a total of 20 individual slots. 
• LTE Sub-frames then consist of two slots - in other words there are ten LTE sub-frames within a frame.

Type 1 LTE Frame Structure

Type 2 LTE Frame Structure

• The frame structure for the type 2 frames used on LTE TDD.
• The 10 ms frame comprises two half frames, each 5 ms long.



Type 2 LTE Frame Structure

• The LTE half-frames are further split into five sub-frames, each 1ms long.

• The sub-frames may be divided into
• Standard sub-frames or
• Special sub-frames.

The special sub-frames consist of three fields;

• DwPTS - Downlink Pilot Time Slot
• GP - Guard Period
• UpPTS - Uplink Pilot Time Stot.

The fields are individually configurable in terms of length, although the total length of all three together must be 1ms.

LTE TDD sub-frame positions:

• Possible to dynamically change the up and down-link balance.
• Characteristics to meet the load conditions.
• A total of seven up / down-link configurations have been set.
• These use either 5 ms or 10 ms switch periodicity.
• In the case of the 5ms switch point periodicity, a special sub-frame exists in both half frames.
• In the case of the 10 ms periodicity, the special sub-frame exists in the first half frame only.
• Sub-frames 0 and 5 as well as DwPTS are always reserved for the down-link.
• UpPTS and the sub-frame immediately following the special sub-frame are always reserved for the up-link transmission.

Uplink-downlink configuration	Downlink to uplink switch periodicity	Subframe number
Slot No		0	1	2	3	4	5	6	7	8	9
0	5 ms	D	S	U	U	U	D	S	U	U	U
1	5 ms	D	S	U	U	D	D	S	U	U	D
2	5 ms	D	S	U	D	D	D	S	U	D	D
3	10 ms	D	S	U	U	U	D	D	D	D	D
4	10 ms	D	S	U	U	D	D	D	D	D	D
5	10 ms	D	S	U	D	D	D	D	D	D	D
6	5 ms	D	S	U	U	U	D	S	U	U	D

Where:
    D is a sub-frame for down-link transmission
    S is a "special" sub-frame used for a guard time
    U is a sub-frame for up-link transmission

Uplink / Downlink subframe configurations for LTE TDD