4G/LTE - MCS

MCS for Retransmission

MCS for Retransmitted PDSCH

For retransmitted PDSCH (according to 36.213 Table 7.1.7.1-1),  MCS  is determined only by Qm and is not affected by RV.

• When Qm for the first transmission is 2, Retransmitted MCS become 29
• When Qm for the first transmission is 4, Retransmitted MCS become 30
• When Qm for the first transmission is 6, Retransmitted MCS become 31

MCS for Retransmitted PUSCH

For retransmitted PUSCH (according to 36.213 Table 8.6.1-1),  MCS  is determined only by RV and is not affected by Qm.

• When RV = 1, Retransmitted MCS become 29

• When RV = 2, Retransmitted MCS become 30

• When RV = 3, Retransmitted MCS become 31

Now let's look at a real life example, which might look more complicated and confusing but hopefully look more interesting :). This shows an example of what's happening during the initial process (RACH process) after you turn on your mobile phone.

Again, the log and background RB map is from Amarisoft LTE Network simulator. All the labels were put manually (If you roll over the mouse pointer onto each channel it shows some detailed information, but it would not show information on the exact contents. This is understandable.. because Physical channel by itself does not have any detailed knowledge on the contents).

In this example, you can see almost every cases that might happen in the real communication. You may ses SR and DCI 0 in response to SR and PUSCH retransmission due to CRC failure.

How can I figure out all the details printed on each labels shown above ? It came from the text based log as shown below. (The current log viewer does not show the MCS value for PUSCH, it show RV index as marked below)

It took me almost an hour to pul all the lables shown above based on the log below. However, this can be a good practice if you are at learning phase of LTE protocol.. or you HAVE TO go through this tedious process when you are in troubleshooting situation.