Data Units in LTE


This article shall speak about the different data units in LTE, the terms used for describing the amount of data. The basic data units in LTE are as below,
-->  Bits
--> Complex Symbols
--> Transport Block & Code Block
-->Resource Element Group

 Bits
The basic unit, in any digital communication system, a bit. Its a binary representation, in terms of 1 or 0. Even in LTE, the smallest data unit is a bit. The bits undergo various processing such as encoding, scrambling, modulation etc
Complex Symbols
A complex symbol, in LTE is nothing but a representation for a group of bits, when a bit or group of bits is digitally modulated using different modulation schemes such as QPSK, 16QAM or 64QAM, we get complex symbols. The symbols are complex numbers with different number of bits per symbol depending on the modulation scheme. Each complex symbol is mapped to a subcarrier in the LTE resource grid.
Transport Block & Code Block
A transport block is the main data unit in LTE physical layer. The physical layer gets the TB from MAC as payload, which the physical layer processes further to make it air worthy. The TB is nothing but a group of bits of length as per the LTE standard. The range of TB is 16 to 36696 bits for a 10MHz LTE system. The TB is divided into code blocks or CB, if the size of the TB is greater than or equal to 6144 bits. So there can be a maximum of 7 code blocks per TB for the largest TB size. A TB CRC is attached to the TB and if the TB is divided into more than 1 CB, then a CB CRC is attache to each of the CB.
Resource Element Group
A resource element group is a entity used in LTE downlink control channels. A REG consists of 4 subcarrier each. 9 REGs make a CCE or control channel element.

These are the basic data units used in LTE.

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