4G Speeds

Now, let’s see an example for the calculation procedure for downlink(PDSCH):

1. refer to TS 36.213 Table 7.1.7.1-1

2. get I_TBS for using MCS value (Let’s assume MCS is 2. in this case, I_TBS is 1 )

5. go to row header ‘1’ which is I_TBS

    6. we would get 1800 (if the number of RB is 50 and I_TBS is 1)

Now, how these 1800 bits are obtained? What’s the formula behind this number? Have a look to the following set of Resource Blocks:

Source: http://www.ece.drexel.edu/walsh/Gwanmo-Nov11-2.pdf

For data, there are:

10 OFDM symbols per subframe x 12 subcarriers = 120 (we are counting the 6 Reference Signal symbols and excluding the PDCCH symbols)

Therefore,

120 symbols x 50 RBs x 2 bits/symbol (QPSK) = 12000 bits

For QPSK we know that the efficiency is 0.15 (approx.), so:

12000 x 0.15 = 1800 bits, as in table Table7.1.7.2.1 3GPP TS 36.312 for 50 RBs and I_TBS=1

Note that a more accurate way to do this calculation, which you can find in other sources as well, uses this approach:

Source: http://www.ece.drexel.edu/walsh/Gwanmo-Nov11-2.pdf

Here, we are considering:

Number of non-sync symbols per RB= 12×7 – 4 (RS symbols)=80 OFDM symbols per slot

80 non-sync symbols x 50 RBs x 2 bits/symbol x 0.0762 x 2 slots =1219 bits

1219 bits -24 bits for the CRC = 1195 bits 

The 0.0762 is the code rate, which is calculated from table 7.2.3-1: 4-bit CQI Table (3GPP document TS. 36.213):

The calculation procedure for uplink(PUSCH) is the same as the downlink: same steps as above except that you have to refer to 36.213 Table 8.6.1-1 at step 1.

Hope this was helpful!

Any feedback or comment on this post will be very welcomed! 🙂