LTE physical layer

LTE physical layer-Brief Description

1. LTE Physical layer Frame Structure, Resource Block

2. OFDMA Orthogonal Frequency Division Multiple Access: In LTE OFDMA Divide MHz bandwidth into Subcarriers and Each subcarriers having 15KHz bandwidth Ex-1MHz is Having 1000KHz 5 MHZ Subcarrier-15KHz

3. Frame Structure 1RB=180 KHZ 0.5 MS Subframe- 1 MS 1 Frame Time FREQUENCY 1 Resource block is having 12 Subcarriers and Each Subcarriers having 15KHz bandwidth. 1 Resource block is having 180 KHz. bandwidth. 12 Sub*15KHz = 180 KHz. 1 Frame is Having 10 Subframe. 1 Subframe having 2 slots/ 1 Subframe=1 Ms. Each slot is 0.5 Ms. Each Slots having 7 OFDMA Symbols. Each OFDMA Symbols is 71.2 Micro/Sec.

4. Resource Element:- RE is the Smallest Unit made by 1 RE = 1OFDM Symbols/1 Subcarriers. Total 84 Resource element in LTE. 1 Slot-0.5 MS 71.2 71.2 71.2 71.2 71.2 71.2 71.2 OFDMA Symbols 1 Subcarrier RE RE

5. How to calculate resource block in Channel Bandwidth:- For 1.4 MHz. 1.4 MHz= 1400 KHz Formula:- Guardband =B.W-( Nref . DeltaF-DeltaF )/2 = 1400/180=7 Nref =Delta=180 KHz =1400-(7*(180)-180)/2 =320/2 =160 Guard band =1400-320 =1080/180=6 RB. For 3 MHz. 3 MHz= 3000 KHz Formula:- Guardband =B.W-( Nref . DeltaF-DeltaF )/2 = 3000/180=16 Nref =Delta=180 KHz =3000-(16*(180)-180)/2 =300/2 =150 Guard band =3000-300 =2700/180=15 RB. 1080 160 160 150 150 2700

6. There are two types of LTE frame structure: Type 1:   FDD mode frame Structure. Type 2:   TDD mode frame structure. Type-1:FDD Frame Structure As LTE FDD is full duplex system, means both the downlink and uplink transmission happens at the same time at different frequencies.

7. Type-2:TDD Frame Structure: In TDD, the transmission is divided into time domain, means at one moment of time either downlink subframe is transmitted or uplink. As one can see in above image, one frame is divided into 10 subframes (1ms each), and that subframe can be either downlink, uplink or special subframe.

8. Now the question comes, who decides the sequence of these subframes. That has been defined by 3GPP with the name TDD Frame Configurations. There are fixed patterns of these configurations and network operator can choose out of these defined patters. There are total 7 TDD configurations as shown below: