The "FRAME"

Lets discuss the LTE frame structure. Depending upon TDD/FDD , there are two types of frame structures.


Frame structure 1 : 
Let me start with FDD, as I am more familiar with FDD systems and yet to work on any TDD system

Smallest slot here is called as Tslot = 15360Tb = 0.5ms. Two consecutive slot is a subframe. Each slot has some OFDM symbols and cyclic prefixes.Every frame will have 10 subframes i.e 10ms.

The diagram shows one frame structure. In these systems , the uplink and downlink systems are separated in the frequency domain each with 10 sub frames.

Every slot will have 6 symbols in case of Normal cyclic prefixes and 5 in case of extended cyclic prefixes. 

Frame Structure 2 : 

Here is frame is 10ms and consists of two sub frames of 5ms each. These 5ms subframes are further divided into smaller frames of 1ms. Each of these smaller sub frames have three fields.

Every subframe will have following fields.

a. DwPTS - Downlink Pilot TimeSlot - Normal downlink channel with 3-12 OFDM symbols.
b. UpPTS - Uplink Pilot TimeSlot - Normal uplink channel with 1 or 2 OFDM sysmbols.
c. GP Field - Guard Period - It has remaining symbols!

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LTE :PRB : The actual transmission!

To begin with, Lets start with Physical resource blocks.. Before we move into what to transmit and how to transmit, Let's look at the actual transmission..

The physical channel: means of actual transmission , is made of multiple resource blocks and resource elements.. A resource element is one single carrier over single OFDM symbol. 
Resource block is the smallest portion of the resource that can be allocated.

Here are the different channels for uplink and downlink

Downlink Physical Channels

There are six different types of downlink physical channels.
1. Physical Downlink Control Channel : PDCCH - It contains information regarding transport format and resource allocation.

2. Physical Downlink Shared Channel : PDSCH - It contains information user data and signalling.

3. Physical Downlink Broadcast Channel : PDBCH - It carries system information

4. Physical Multicast Channel : PMCH - multicast or broadcast information is carried.

5. Physical Hybrid ARQ Indicator Channel : PHICH - It carries ACK/NAKs associated with data transmission

6. Physical Control Format Indicator Channel : PCFICH -  Indicates number of OFDM symbols used.


Uplink Physical Channels 

There are just three different uplink channels.

1. Physical Uplink Control Channel : PUCCH - It carries ACK/NAK information along with the CQI 

2. Physical Uplink Shared Channel : PUSCH - It is similar to PDSCH - It carries user data along with some signalling.

3. Physical Random Access Channel - PRACH - It has the random access permeable sent by UE.

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