Peak data rate question!

Rox · 4G Newbie Joined: 31 Jul 2009 Posts: 1

Hi, I have been trying to obtain the theoretical peak data rate for LTE:

Asumming:
- 20 MHz (2100 useful subcarriers)
- 64-QAM (6 bits per subcarrier)
- Channel Coding Rate = 1
- 2x2 MIMO configuration/2 layers (doubles the rate)
- Normal CP (14 OFDM symbols per subframe)
- Assume that in every subframe an OFDM symbol is used for control purposes (so, only 13 OFDM symbols carry user data)
- A subframe is 1 ms long

So:

Rmax = 2 layers* 6 bits/subcarrier * 1200 subcarriers * (13 symbols / 1 ms)
Rmax = 187.2 Mbps

However, according to the 3GPP specs, the maximum data rate for the 2 x2 MIMO configuration is 172.8 Mbps [TR 25.912]

What am I doing wrong?

Junqueira · 4G Newbie Joined: 13 Aug 2009 Posts: 1

OK, I think you have the right expression.

The thing is that the DL FDD frame has 2 OFDM symbols for PDCCH.
Considering this you have:

(13 symbols per subframe/1 msec) * (6x2 bits per modulated subcarrier) * (1200 subcarrier for 20 MHz channel) * (3/42 as the % of the number of Reference Signals occupied to map the antennas in the MIMO2x2) = 172.8

---Not right---
(12 symbols per subframe/1 msec) * (6x2 bits per modulated subcarrier) * (1200 subcarrier for 20 MHz channel) = 172.8
----------------

This does consider code rate=1, 1 OFDM symbol minimum for PDCCH and the P-SCH, S-SCH, PBCH channel is not considered (would be 1% overhead)

regards

Tiago Junqueira
Msc
Portugal Telecom