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Physical Layer Parameter - DL, FDD

Followings would be a quick cheatsheet if you are DSP engineer or FPGA engineer working in LTE PHY.

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

• 20 Mhz BW Case :
• A = 160
• B = 144
• C = 2048

• 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