|
|
|
|
|
|
Also, there may be retransmission in case transmission is erroneous; which would further lower the effective data rate. Actual transmission quality of medium in the field is not known, so losses due to retransmissions can only be guessed. What about rest of the factors ? Let us start accounting for various factors that we mentioned and see how it affects data rate value.
L1/L2 control signaling and reference symbols
Out of 14 (normal CP) resource elements of a subframe per subcarrier (refer fig 1.3.3), first 1-4 OFDM symbols goes for downlink control signaling (PDCCH/PCFICH/PHICH) [36.211:6.7]. Also, there are two downlink reference symbols or signals in each resource block in a subframe [36.300:5.1.4] - one of which comes within first symbols. Considering case of only first OFDM symbol being used for control signaling, remaining resource elements would be (12 x 7 x 2 - 12 - 6 = ) 150. The corresponding data rate would be NRB . 150 . Qm kbps. For 20 MHz/110 RBs, the value is 99 Mbps !
|
| A Subframe (1 ms) |
| 1st Slot |
2nd Slot |
| 1 |
2 |
3 |
4 |
5 |
6 |
7 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
| | |
Subcarriers
(1..12) |
| |
|
Control signaling |
|
|
Reference symbols |
|
Fig 1.3.3
So percentage loss in data rate due to L1/L2 control signaling and reference symbols is (110.8 - 99)/110.8 = 10.6 % !
Now let us account for data added due to PHY processing, assuming all resource elements other than L1/L2 control signaling & reference symbols are used for user data i.e. tranport channel, DTCH.
|
|
|
|
|
|
|
|
|
|
|
