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Number of bits per resource element depend on modulation scheme. LTE use three modulation schemes for traffic channels: QPSK, 16QAM, and 64QAM. Below table lists down the rates for each modulation.
| QPSK |
2 |
30 |
| 16QAM |
4 |
60 |
| 64QAM |
6 |
90 |
Table 1.3.1
Data rate per resource block
A resource block is 12 subcarriers, 0.5 ms slot i.e. a grid of 7 x 12 resource elements (continuing case of normal CP). So data rate for resource block would be (number of subcarriers per resource block) x 7 x (modulation order) / 0.5 ms bps. For 64 QAM, the value is 1008 kbps.
Maximum data rate with maximum bandwidth
LTE specifies bandwidth from 1 MHz/6 RBs till 20 MHz/110 RBs [36.211:6.2.1]. So taking case of 110 RBs, maximum data rate for 64 QAM and normal CP would be 110.88 Mbps. The formula is NRB . NSC per RB . Nresource elements per subcarrier per slot . Qm / 0.5 kbps that is:
NRB . 168 . Qm kbps
The data rate that we deduced above is "PHY data rate". In addition to actual User information (application data or IP packets), the data would contain protocol signaling, phy signaling, error detection & correction bits, and reference symbols. User data is only a part of whole chunk, so effective or actual user data rate would be smaller than above data rate (refer diagram below).
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User data
(x bits)
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Protocol
Stack
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Physical signals
(y bits)
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Fig 1.3.2
Percentage loss or overhead would be (y-x)/x.
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