How to decide No of RBs required in UL or DL transmission ? What are the parameters should consider?

Question

For FDD 20MHZ, no of DL RB = 100 and no of UL RB = 100. But in TDD, different UD configurations having different no of DL and UL subframes and few special subframes. Hence how to calculate no of Dl RB and no of UL RB in case of TDD?

Answer 1

Hi sripathi,

Say examble UE having 1500 bytes of data to send and UE reported cqi as 15 (coresponding MCS is 28 (corrsponding TBS for this mcs is 26)), then we can map TBS and required bytes with no of RB's . there is a correponding mapping is available in 3gpp spec
36.213 (7.1.7.2.1)

no of RB's required for this examble is 17 .. Max of 12576 bits w can send (1572 bytes).

Comments

Hi Jaganathan,

As per specification TB size can get by mapping I_tbs index and NO.of RBs.... But how can we decide Rbs required before mapping to get tb size?

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Do reverse mapping sripathi, Say examble your requirement is 12000bits then you know 26 is tbs index , then you can search in the table which RBs and TBD will cross greater than or equal to 12000bits..

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For example:

I_tbs = 26, TB_size = 75376, As per specification no of Rbs = 100 ... can you pls explain how it calculated .. how the no of Rbs = 100 derived ?

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Hi,
 Programetical wise :
Take two dimention array arr[Tbs][No.of.rbs] = store all values.  traverse it till array[Tb][J] >= required no of bits. once condition met J is the no of RBs.

Theoritical wise already you can refer the spec.