What is a resource block and resource element in LTE?

Question

How the capacity depends upon these resource blocks and how large it is ?

Answer 1

A Resource Block (RB) is a time- and frequency resource that occupies 12 subcarriers (12x15 kHz = 180 kHz) and one slot
(= 0.5 ms). RBs are allocated in pairs by the scheduler (then referred to as Scheduling Blocks).

12 subcarriers á 15 kHz = 180 kHz in frequency domain and one slot (0.5 ms) in time domain

Comments

well explained.

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Well, there is a statement above MAC scheduler allocates resource in RB pair. where it is mentioned and why ? Can you please provide some detail about scheduler ?

Answer 2

Resource Element = Covered by 1 sub carrier and one symbol period i.e 1 Symbol
Resource Block = Covered by 12 Subcarriers and 6 or 7 symbols(Based on Cyclic prefix)

We can calculate the capacity if we know the Bandwidth allocated,Modulation scheme used and Cyclic Prefix type.
Consider
Bandwidth Allocated = 5MHz
Modulation Scheme = QPSK(2 its per symbol)
Cyclic prefix used = Normal Cyclic Prefix (7 symbols in a slot)

Capacity = No of bits transferred in a sub frame / Duration of the Subframe(i.e 1milli sec)

Calculation No of Bits transferred in a Subframe

Total number of Resource block in a slot = Bandwidth / (Each subcarrier bandwidth * no of subcarriers in a Resource Block)
Bandwidth = 5Mhz
Each sub carrier width = 15Khz
No of sub carriers in a Resource Block = 12 (As 12 Subcarrier is 1 Resource block )

Calculation of total no of resource blocks in 5MHz Bandwidth

so Resource block in one slot = 5 Mhz / (15 KHz *12 ) = 27.77 (But used RBs will be 25 for 5MHz bandwidth)
so Total Resource block in one subframe = 2 * Resource blocks in a slot = 50 RBs

Calculation of total no of symbols/Resource Elements in 5MHz Bandwidth
Total no of symbols / Resource Elements = 50 * no of symbols(REs) in a Resource block
No of symbols(REs) in a resource block = 12 subcarrier * 7 symbols = 84 symbols(REs)
Total symbols(REs ) in 50 Resource blocks = 50 * 84 = 4200 Resource Elements.

****Calculation of total no of bits sent in 5MHz Bandwidth in one subframe ****

In one symbol we can send no of bits at a time which depends on the modulation scheme (like BPSK,QPSK ,64QAM
BPSK - 1 bit,QPSK - 2 bit ,64 QAM - 6bits in a Symbol/ Resource elements
We will consider QPSK Scheme so in one symbol 2bits we can send.
So 1 Symbol = 2 bits.

So total no of Bits sent in a subframe = 2 * 4200 = 8400 bits.

So capacity = 8400 / 1ms = 8.4 MBPS

So capacity in 5MHz Bandwidth with QPSK Modulation with normal cyclic Prefix is 8.4MBPS.

if Modulation scheme is BPSK, 1 bits in a symbol = 1 * 4200 / 1ms = 4.2 MBPS
if Modulation scheme is 64QAM , 6 bits in a symbol = 6 * 4200 / 1ms = 25.2 MBPS.

Comments

No of symbols is 7/6 but REs are 84.Please be clear with ur answer.http://www.sharetechnote.com/html/FrameStructure_DL.html

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Thank you sahu.
can you explain down link channel allocation in resource block?like PHICH,and7 other channels.

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Its very old thread, will you like to ask fresh question?

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thank you

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Very helpful. Thanks!

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very helpful... i need help in resource block allocation in matlab. can you help me

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I don't have idea about MATLAB to simulate these things, Search for online resource you may get it.

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Well explained Mr Sahu