The table below provides some of the specifications of the
LTE Physical Layer.
|
Transmission BW
|
1.25 MHz
|
2.5MHz
|
5MHz
|
10 MHz
|
15 MHz
|
20 MHz
|
|
|
Slot Duration
|
0.5
ms
|
||||||
|
Sub Carrier Spacing
|
15
KHz
|
||||||
|
Sampling Freq
|
1.92 MHz
|
3.84 MHz
|
7.68 MHz
|
15.36 MHz
|
23.04 MHz
|
30.72 MHz
|
|
|
FFT Size
|
128
|
256
|
512
|
1024
|
1536
|
2048
|
|
|
CP Length usec
|
Short
|
5.21x1, 4.69/9 x 6
|
5.21x1, 4.69/9 x 6
|
5.21x1, 4.69/9 x 6
|
5.21x1, 4.69/9 x 6
|
5.21x1, 4.69/9 x 6
|
5.21x1, 4.69/9 x 6
|
|
Long
|
16.67
|
16.67
|
16.67
|
16.67
|
16.67
|
16.67
|
|
Transmission BW: LTE supports varying bandwidth from 1.25
MHz to 20 MHz, allowing the operators to utilize BW chunks available. The
operator can use chunks of 1.25 MHz at different frequencies rather than a 5
mHz(which is required in UMTS).
The Radio Frame of 10ms is divided into 10 sub frames of 1
ms each. Each sub frame has two slots of 0.5ms each.
Sub carrier spacing: It is difference in the center frequency
of two adjacent sub carriers.
T-FFT: This is one FFT period and is equal to 66.667 us.
FFT size: This is the size of the FFT employed in the IFFT
and FFT.
Sampling Frequency: With the FFT size of 128, this means 128
samples are taken in each FFT period. Therefore, sampling frequency = 128/66.667
us = 1.92 MHz. Note that this is half of 3.84 MHz, which is the chip rate in
UMTs). Sampling frequency for other BW sizes can be calculated likewise.
Cyclic Prefix Length: Length of the prefix attached to each
OFDM symbol before transmission is 4.69 us or 16.67 us depending on
Short/extended prefix in use.
Ts: This is the unit of time in LTE and is equal to
1/(1500x2048) = 0.52086 us. Every time
duration is expressed in terms of Ts.