Sunday, 2 November 2014

Peak Data rate calculation in LTE.


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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