Physical Layer Parameter - DL, FDD
Followings would be a quick cheatsheet if you are DSP engineer or FPGA engineer working in LTE PHY.
Channel Bandwidth (Mhz) |
1.4
|
3
|
5
|
10
|
15
|
20
|
Frame Duration (ms) |
10
|
10
|
10
|
10
|
10
|
10
|
Sub carrier spacing (Khz) |
15
|
15
|
15
|
15
|
15
|
15
|
Sampling Frequency (Mhz) |
1.92
|
3.84
|
7.68
|
15.36
|
23.04
|
30.72
|
FFT Size |
128
|
256
|
512
|
1024
|
1536
|
2048
|
Occupied Subcarriers (including DC) |
73
|
181
|
301
|
601
|
901
|
1201
|
Guard Subcarriers |
55
|
75
|
211
|
423
|
635
|
847
|
Number of Resource Blocks |
6
|
15
|
25
|
50
|
75
|
100
|
Occupied Channel Bandwith (Mhz) |
1.095
|
2.715
|
4.515
|
9.015
|
13.515
|
18.015
|
DL Bandwidth Efficiency |
78.2%
|
90%
|
90%
|
90%
|
90%
|
90%
|
OFDM Symbols for Subframe (for Short CP) |
7
|
7
|
7
|
7
|
7
|
7
|
CP Length for Short CP (in us) |
5.2 for the first symbol/4.69 for other symbols
|
Let's get into further details for some of the important parameters.
< Sampling Time >
- 20 Mhz BW Case : 1 sec / 30.72 Mhz = 1,000,000 us/30,720,000 Hz = 0.0326 us = 32.6 ns
- 15 Mhz BW Case : 1 sec / 23.04 Mhz = 1,000,000 us/23,040,000 Hz = 0.0434 us = 43.4 ns
- 10 Mhz BW Case : 1 sec / 15.36 Mhz = 1,000,000 us/15,360,000 Hz = 0.0652 us = 65.2 ns
- 5 Mhz BW Case : 1 sec / 7.68 Mhz = 1,000,000 us/7,680,000 Hz = 0.1302 us = 130.2 ns
- 3 Mhz BW Case : 1 sec / 3.84 Mhz = 1,000,000 us/3,840,000 Hz = 0.2604 us = 260.4 ns
- 1.4 Mhz BW Case : 1 sec / 1.92 Mhz = 1,000,000 us/1,920,000 Hz = 0.5208 us = 520.8 ns
< Number of Samples for each CP and OFDM Symbol >
Following illustration shows the number of samples in each CP and OFDM symbols for 20Mhz case. I will calculate the number of samples for other BW case by taking the ratio of FFT site of 20 Mhz and the FFT size of other BW.

In short, I will list up the value of A,B,C,D for each system BW.

Followings are A,B,C values for each BW
- 15 Mhz BW Case :
- A = 160 x (FFT size for 15 Mhz/FFT size for 20 Mhz) = 160 x (1536/2048) = 120
- B = 144 x (FFT size for 15 Mhz/FFT size for 20 Mhz) = 144 x (1536/2048) = 108
- C = 2048 x (FFT size for 15 Mhz/FFT size for 20 Mhz) = 2048 x (1536/2048) = 1536
- 10 Mhz BW Case :
- A = 160 x (FFT size for 10 Mhz/FFT size for 20 Mhz) = 160 x (1024/2048) = 80
- B = 144 x (FFT size for 10 Mhz/FFT size for 20 Mhz) = 144 x (1024/2048) = 72
- C = 2048 x (FFT size for 10 Mhz/FFT size for 20 Mhz) = 2048 x (1024/2048) = 1024
- 5 Mhz BW Case :
- A = 160 x (FFT size for 5 Mhz/FFT size for 20 Mhz) = 160 x (512/2048) = 40
- B = 144 x (FFT size for 5 Mhz/FFT size for 20 Mhz) = 144 x (512/2048) = 36
- C = 2048 x (FFT size for 5 Mhz/FFT size for 20 Mhz) = 2048 x (512/2048) = 512
- 3 Mhz BW Case :
- A = 160 x (FFT size for 3 Mhz/FFT size for 20 Mhz) = 160 x (256/2048) = 20
- B = 144 x (FFT size for 3 Mhz/FFT size for 20 Mhz) = 144 x (256/2048) = 18
- C = 2048 x (FFT size for 3 Mhz/FFT size for 20 Mhz) = 2048 x (256/2048) = 256
- 1.4 Mhz BW Case :
- A = 160 x (FFT size for 1.4 Mhz/FFT size for 20 Mhz) = 160 x (128/2048) = 10
- B = 144 x (FFT size for 1.4 Mhz/FFT size for 20 Mhz) = 144 x (128/2048) = 9
- C = 2048 x (FFT size for 1.4 Mhz/FFT size for 20 Mhz) = 2048 x (128/2048) = 128
< BandWidth/Guardband Width >

- 20 Mhz BW Case :
- A = Occupied Subcarriers (including DC) x 15 Khz = 1201 x 15 Khz = 18015 Khz = 18.015 Mhz
- B = Occupied Subcarriers (including DC) = 1201
- C + D = Guard Subcarriers = 847
- 15 Mhz BW Case :
- A = Occupied Subcarriers (including DC) x 15 Khz = 901 x 15 Khz = 13515 Khz = 13.515 Mhz
- B = Occupied Subcarriers (including DC) = 901
- C + D = Guard Subcarriers = 635
- 10 Mhz BW Case :
- A = Occupied Subcarriers (including DC) x 15 Khz = 601 x 15 Khz = 9015 Khz = 9.015 Mhz
- B = Occupied Subcarriers (including DC) = 601
- C + D = Guard Subcarriers = 423
- 5 Mhz BW Case :
- A = Occupied Subcarriers (including DC) x 15 Khz = 301 x 15 Khz = 4515 Khz = 4.515 Mhz
- B = Occupied Subcarriers (including DC) = 301
- C + D = Guard Subcarriers = 211
- 3 Mhz BW Case :
- A = Occupied Subcarriers (including DC) x 15 Khz = 151 x 15 Khz = 2265 Khz = 2.265 Mhz
- B = Occupied Subcarriers (including DC) = 151
- C + D = Guard Subcarriers = 105
- 1.4 Mhz BW Case :
- A = Occupied Subcarriers (including DC) x 15 Khz = 76 x 15 Khz = 1140 Khz = 1.140 Mhz
- B = Occupied Subcarriers (including DC) = 76
- C + D = Guard Subcarriers = 52
|
|