1 frame = 10 subframe = 10ms
1 subframe = 2 slots = 0.5ms
1 slot = 12 sub carriers & 7 symbols
&& 1 slot = Resource Block
Therefore 1RB = 12 x 7 = 84 Resource Elements
Bandwidth of 1 Resource Block = 180 Khz
Bandwidth of 1 Sub Carrier = 15 Khz (spacing)
Total RB Calculation:
10% of the total bandwidth is reserved for guard band.
Eg. 20Mhz = 18Mhz usable = 18Mhz / 180Khz = 100RB and so on.
Total Subcarrier Calculation
10% of the total bandwidth is reserved for guard band.
Eg. 20Mhz = 18Mhz usable = 18Mhz /
15Khz = 1200 subcarriers
Data Rate Calculation:
Some Parameters to be considered:
Ø
Cyclic prefix
Ø
Available Resource
Ø
Modulation and coding scheme
Ø
MIMO
Example:
20 Mhz channel bandwidth, normal CP & 4x4 MIMO
1.
Calculate the number of RE in a subframe with
20Mhz channel Bandwidth =
12 subcarriers x 7
symbols x 100 RB x 2 slots = 16800 RE’s per subframe.
Each RE carry a
modulation symbol.
2.
Assume 64QAM modulation & no coding, 1
modulation symbol will carry 6bits. Therefore, total bits in a subframe (1ms)
= 16800 modulation symbols x
6bits/modulation symbol = 100800bits
Data rate = 100800bits/ms =
100.8Mbps
3.
With 4x4 MIMO, peak data rate = 4x100.8 =
403Mbps
4.
Estimating 25% overhead such as PDCCH, reference
signal, sync signal, PBCH & some coding we get,
= 403Mbps x 0.75 =
302Mbps
For more accurate
calculation refer to 3GPP specification 36.2.3
Modulation Scheme and coding table
0-9 MCS – QPSK – 2bit
10-16 MCS – 16QAM – 4bit
17-28 MCS – 64QAM – 6bit
29, 30 & 31 are reserved with 2, 4 & 6 bit respectively.
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