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Thursday 19 January 2012

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

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