LTE - Physical Layer

2. Why LTE ?

3. Network Topology

4. Overall RAN Architecture
Logical
IP Packet
PDCP RLC MAC
Transport
PHY
 PDCP : Packet Data Convergence Protocol
 RLC : Radio Link Control
 MAC : Medium Access Control
 PHY : Physical Layer

5. Physical Layer
MAC Layer
Logical channels Transport channels Physical channels
Channel Mapping

6. Physical Layer
Physical Channels :
DL UL
PDSCH PUSCH
PBCH PUCCH
PMCH PRACH
PDCCH
PHICH
PCFICH

7. Generic Frame Structure
1 Frame (10 ms)
1 Slot (0.5 ms)
1 Sub Frame (1 ms)
7 OFDM symbols

8. Resource Grid 7 OFDM symbols
Time
F
R
E
q
R
E
S
O
U
R
C R
E E
S
B O
L U
O R
C C
K E
G
R
I
D
Resource Element

9. OFDM
Why ?

10. ISI – Inter Symbol Interference

11. Time Spreading (Freq. Selective
Fading)
 When an impulse is transmitted , how
Power Delay Profile
does the average power received by Mobile
vary as a function of time delay ζ ?
 Freq. Selective Fading : Ts < ζ0
 Non Freq. Selective Fading : Ts > ζ0

12. Power Delay Profile Spaced Freq.
Correlation function
FT
Inside Coherence BW channel passes all freq. components with
equal gain and linear phase
 Freq. Selective Fading : W > f0
 Non Freq. Selective Fading : W < f0

13.  Symbol rate not increased in order to achieve high
data rates.
 Instead of that Available BW breaks in to many
narrower subcarriers and modulate generated symbols
to these subcarriers.
 These subcarriers then combine linearly and transmit
(OFDM symbol).

14. : Single Carrier Transmission
1 0 1
1
: OFDM Transmission
0
1
t

15.  Cyclic Prefix added to the beginning of the OFDM
symbol in order to eliminate ISI
 ICI – Inter Carrier Interference has already been
removed by selecting subcarriers with Ts > ζ0