# Calculate the number of bits per PRB

Hi Experts.

I am a bit confused about what does Target Code Rate and Spectral Efficiency mean here.

If I want to calculate the number of bits per PRB for, let’s say MSC index 1, should I use Target Code Rate or Spectral Efficiency?

If you want to calculate number of coded bits per prb, then you only use Qm.

If you want to calculate number of information bits per PRB, then you use Qm and Code rate both.

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Hi @shanjaffry ,

Some information now days look confuse to use, because they are not put unit on the explanation.

But let me try here to inform you the unit on each of it, hope getting clear on it

Qm : total information can carry by 1 RE [b/RE]

Code Rate : useful information carry (bit) / total information carry (bit), (1024 bit, in this table) [b/b]

Spectral Efficiency : useful information carry (bit) / time (s) / spectral frequency (Hz) [b/s/Hz], (so in this table : SE : Qm * Code Rate /1024)

So the table actually to make simplicity in a complexity of calculation of throughputs, because there will be another *factor effecting throughput calculation.

If I want to calculate the number of bits per PRB for, let’s say MSC index 1, should I use Target Code Rate or Spectral Efficiency?

If LTE in simplicity in 1 second time :

Total Information Can Carry
1 PRB / s = 12 * 7 * 2 = 168 * 2 = 336 b/s

Useful Information
1 PRB / s = 12 * 7 * 2 * (120/1024) = 168 * 2 * 0.117188 = 39.375 b/s

Hope this clear to you.

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Here SE is actual information bits per RE, for example MCS:0 —> SE = 2 * 120 / 1024 = 0.2344.