7. From 3G to 4G…
UTRAN in 3G,
E-UTRAN in 4G
CN in 3G, EPC in
4G
NodeB in 3G,
E-NodeB in 4G
No RNC as in 3G
RNC tasks perform
by eNodeB and
EPC
9. Evolved UTRAN (E-UTRAN)
eNodeB :
Directly connected to the Core via S1 interface
No RNC as in WCDMA
eNodeBs interconnected via X2 interface
Handovers are handled by eNodeBs it self, communicating via X2
interface
This is an intelligent Node
Evolved Packet Core (EPC)
Supports only packet switched domain only
Mobility Management Entity (MME) :
Control Plane Node of the EPC
handling connection/release of bearers to a terminal
handling of IDLE to ACTIVE Transition
handling of security keys
10. Serving Gateway(S-GW) :
User plane node which connects EPC to E-UTRAN
Acts as a mobility anchor when Terminals move between eNodeBs
Mobility Anchor for other 3GPP technologies (GSM,HSPA)
Collecting information for charging purposes
Packet Data Network Gateway (P-GW) :
Connects EPC to the Internet
Allocation of the IP address for a specific terminal
QoS handling
Home Subscriber Service (HSS) :
A database containing subscriber information
13. ISI – Inter Symbol Interference
Time domain :
Data Rate ISI
14. Time Spreading (Freq. Selective
Fading)
• When an impulse is transmitted , how
does the average power received by Power Delay Profile
Mobile
vary as a function of time delay ζ ?
Freq. Selective Fading : Ts < ζ0
Non Freq. Selective Fading : Ts > ζ0
15. 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
16. • 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).
OFDM Modulation OFDM demodulation
17. Single carrier transmission Vs OFDM
Transmission
: Single Carrier
1 0 1 Transmission
1
: OFDM Transmission
0
1
t
19. Why “Orthogonal” ?
Subcarriers “Orthogonal” in the time domain
In OFDM, Subcarriers are overlapped in Frequency
domain while maintaining orthogonality in time domain
21. OFDM Symbol
• Generated by Multiplexing several overlapping
subcarriers and a Cyclic Prefix (CP).
CP Modulated Subcarriers
• Cyclic Prefix added to the beginning of the OFDM
symbol in order to eliminate IBI
• At the Receiver CP is removed and only the information
bearing part is further processed .
22. OFDM as a Multiple Access Scheme
(OFDMA)
OFDMA : In each OFDM symbol interval, Different
subsets of the overall set of available subcarriers are
used for transmission to different terminals.
24. Main Transmission Techniques
Spatial Diversity : Signal copies are transmitted at
multiple antennas or received at more than one antenna
.
Spatial Multiplexing : Transmit independent and
separately encoded data streams over different antennas
25. Why MIMO?
Significant increase in Spectral efficiency and data
rates - Spatial Multiplexing
High QoS - Spatial diversity
Wide Coverage - Spatial diversity
28. SC – FDMA (DFTS-OFDM)
Why not Multi Carrier OFDM in Uplink ?
One of the main drawbacks in OFDM : Large instantaneous
power variations in the Transmitting signal
This leads to High Peak-to-Average-Power Ratio (PAPR) in
the Power Amplifier.
Power Amplifier Efficiency
Power Amplifier Cost
Hence Multicarrier OFDM is not a Viable solution for Low
power Mobiles
29. In OFDM, each subcarrier carries information relating
to one specific Symbol
In SC-FDMA, each subcarrier contains information of
All Transmitted symbols.
Hence no need of transmitting with High Power. Signal
energy is distributed among sub carriers.
30. User Multiplexing in SC-FDMA
Localized Transmission : Distributed Transmission :
User 1 User 2 User 3 User 1 User 2 User 3
35. 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
36. Physical Resource Block (PRB) allocation is done by the
scheduling function in eNodeB
PRB is the smallest element of resource allocation
assigned by the base station scheduler.
38. Channel dependent Scheduling and Rate adaptation :
Depending on the channel conditions, time – frequency resources
are allocated to users by the scheduler
Scheduling decisions taken once every 1ms with frequency
domain granularity of 180 kHz.
Scheduler allocates resources depending on the Channel State
Information(CSI) provided by the UE
39. Inter Cell interference Coordination (ICIC) :
In LTE, Frequency Reuse Factor equals to one (full spectrum
availability at each Cell)
This leads to high performance degradation specially the Users in
cell edge.
ICIC reduce ICI at cell edge applying certain restrictions on
resource assignment.
Adaptive Fractional Frequency Reuse
Coordination:
3
1
2
Inner Region
Outer Region
40. Multicast / Broadcast Single frequency Network
(MBSFN)
As Identical information is transmitted from transmitters (time aligned),
UEs in Cell edge can utilize received power of several surrounding
cells to detect / decode broadcasted data.
42. Extended Multi Antenna Transmission :
DL Spatial Multiplexing has been expanded to support up to 8
transmission Layers.
Heterogeneous Deployments :
Ex : Pico Cell placed inside a Macro Cell
44. References :
. “4G LTE/LTE-Advanced for Mobile Broadband” by Erik
Dhalman, Stefan Parkvall, Johan Skold
“Overview of the 3GPP Long Term Evolution Physical Layer ”
by Jim Zyren, Dr.Wes McCoy
“Wireless Communication” by Andrea Goldsmith
EPC : Evolved Packet CoreSAE : System Architecture Evolution
SAE : System Architecture EvolutionSome of the RNC functions in UMTS have been brought to the eNodeB and some of the functions to the MME.One eNodeB can be connected to multiple MMEs/S-GW for the purpose of load sharingS1 –c: S1 control for MME ; S1- u : S1 user for S-GW
PCRF : Policy and charging rules Function : Responsible for QoS handling and charging
Multipath propagation
When data rate increases ISI also increases.
Multi path intensity profile
-. Cross Correlation of AWGN is an impulse response. What is the meaning of this?-. Spaced freq. Correlation function is generated by cross correlating two carriers which are separated by Delta(f)-. Disadv. Of single carrier transmission??
-. Symbol periods are now longer compared to single carrier. but bits are txd parallel in order to achieve the desired data rate. -. As Ts is high ISI can completely be removed from the system.-. Depending on the channel condition each subcarrier can be modulated using different modulation schemes (QPSK, 16QAM, 64 QAM etc..)
-. Each OFDM symbol is a liner combination of instantaneous signals on each of the subcarriers in the channel.
- Multi carrier systems with non overlapping sub carriers :- Spectrally inefficient
Frequency Selective fading is not an issue for Subcarriers (𝐵𝑊𝑠𝑢𝑏𝑐𝑎𝑟𝑟𝑖𝑒𝑟 < 𝐵𝑊𝐶𝑜h𝑒𝑟𝑒𝑛𝑐𝑒)Frequency Selective fading is not an issue for Subcarriers (〖𝐵𝑊〗_𝑠𝑢𝑏𝑐𝑎𝑟𝑟𝑖𝑒𝑟 < 〖𝐵𝑊〗_𝐶𝑜ℎ𝑒𝑟𝑒𝑛𝑐𝑒)
One Resource Grid per antenna.
QoS : Beam forming
PAR : Peak to Average Power RatioDFTS-OFDM : DFT-Spread-OFDM
Target : Lower PAPR and Use the benefit of OFDM transmission using multiple carriers.