1. Long Term Evolution
Beyond 3G

2. OVERVIEW LTE targets Network architecture LTE Physical layer
LTE Access tecniques
MIMO
Channels
LTE Advanced

3. LTE TARGETs
Packet-Domain-Services only (e.g. VoIP) upon LTE, TCP/IP- based layers
Higher peak data rate/ user throughput  100 Mbps DL/50 Mbps bandwidth
Reduced delay/latency  user-plane latency<5ms
Improved spectrum efficiency  up to 200 active users in a bandwidth
Mobility  optimized for low-mobility (up to 15Km/h), supported with high performance for medium mobility (up to 120 Km/h), supported for high mobility (up to 500 Km/h)
Multimedia broadcast & multicast services
Spectrum flexibility
Multi-antennas configuration
Coverage  up to 30 Km

4. LTE TARGETs

5. Network Architecture

6. Network Architecture – E-UTRAN
User Equipment
Evolved Node B (eNB) Functionalities:
resource management (allocation and HO)
admission control
application of negotiated UL QoS
cell information broadcast
ciphering/deciphering of user and control plane data

7. Network Architecture Evolved Packet Core
Mobility Management Entity  key control-node for the LTE ac- cess-network.
Functionalities:
1) idle mode UE tracking and paging procedure including retransmissions
2) bearer activation/deactivation process and choice of the SGW for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN) node relocation
3) authentication of users : it checks the authorization of the UE to camp on the service provider’s Public Land Mobile Network (PLMN)
4) control plane function for mobility between LTE and 2G/3G access

8. Network Architecture Evolved Packet Core
Serving Gateway  Functionalities:
routing and forwarding user data packets
acts as mobility anchor for the user plane during inter-eNB handovers and for mobility between LTE and other 3GPP
for idle state UEs, terminates the DL data path and triggers paging when DL data arrives for the UE
performs replication of the user traffic in case of lawful interception.

9. Network Architecture Evolved Packet Core
Packet Data Network Gateway  Functionalities:
provides connectivity to the UE to external packet data networks (IP adresses..). A UE may have simultaneous connectivity with more than one PDN GW for accessing multiple PDNs
performs policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening
acst as the anchor for mobility between 3GPP and non-3GPP technologies (WiMAX)

10. LTE PHY Layer
+ Includes methods for contrasting distortion due to multipath:
OFDM
MIMO
+ New access method scheme:
OFDMA
SC-FDMA

11. Multipath effects
ISI induced by multipath  time-domain effect of multipath
Frequency selectivity  frequency-domain effect of multipath

12. Spectrum flexibility
Possibility for using all cellular bands (45o MHz, 800 MHz, 900 MHz, 1700 MHz, 1900 MHz, 2100MHz, 2600MHz)
Differently-sized spectrum allocations 
- up to 20 MHz for high data rates
- less than 5 MHz for migration from 2G technologies

13. Orthogonal Frequency Division Multiplexing
Eliminates ISI problems  simplification of channel equalization
OFDM breaks the bandwidth into multiple narrower QAM-modulated subcarriers (parallel data transmissions)  OFDM symbol is a linear combination of signals (each sub-carrier)
 VERY LONG SYMBOLS!!!

14. Orthogonal Frequency Division Multiplexing
Cyclic prefix duration linked with highest degree of delay spread
FTT PERIOD
Possible interference within a CP of two symbols

15. OFDM Problems
Zero ICI achieved if OFDM symbol is sampled exactly at its center f (14/45 KHz..)
 FFT is realized at baseband after down-conversion from RF

16. Orthogonal Frequency Division Multiple Access
Multiplexing scheme for LTE DL  more efficient in terms of LATENCY than classical packet oriented schemes (CSMA/CA)
Certain number of sub-carriers assigned to each user for a specific time interval  Physical Resource Block (time-frequency dimension)
FRAME STRUCTURE:
LTE FRAME DURATION 10ms diviso per 10 sub-frame
Ogni sub-frame è spezzato in 2 time slot
Ogni slot contiene 6/7 OFMD symbol a seconda del CP

17. Orthogonal Frequency Division Multiple Access
PRB is the smallest element for resource allocation  contains 12 consecutives subcarriers for 1 slot duration
Resource element  1 subcarrier for each symbol period

18. Orthogonal Frequency Division Multiple Access
CARRIER ESTIMATION
PHY preamble not used for carrier set
Use of reference signals transmitted in specific position (e.g. I and V OFDM symbols) every 6 sub-carriers
INTERPOLATION is used for estimation of other sub-carriers

19. Multiple Input – Multiple Output
MIMO CHANNEL
Definition of a time-varying channel response for each antenna:

20. Multiple Input – Multiple Output
In LTE each channel response is estimated thanks to pilot signals transmitted for each antenna
When an antenna is transmitting her references, the others are idle.
Once the channel matrix is known, data are transmitted simultaneously.

21. Multiple Input – Multiple Output
Advantages:
Higher data rate  more than one flow simultaneously
Spatial diversity  taking advantage from multiple paths  multipath as a resource
Disadvantages:
Complexity
LTE admitted configurations:
- UL: 1x1 ,1x2
-DL: 1x1, 1x2, 2x2, 4x2

22. Multiple Input – Multiple Output
MIMO techniques in LTE:
SU-MIMO
Transmit diversity
Closed loop rank 1
MU- MIMO
Beamforming

23. Single User MIMO Two way to work: Closed Loop Open Loop
CLOSED LOOP SU-MIMO
eNodeB applies a pre-codification on the transmitted signal, according to the UE channel perception. Tx Rx X
Y=WX
RI, PMI, CQI
RI: rank indicator
PMI: Precoding Matrix Indicator
CQI: Channel Quality Indicator

24. Single User MIMO OPEN LOOP SU-MIMO
Used when the feedback rate is too low and/or the feedback overhead is too heavy.
eNodeB applies a pre-coded cycling scheme to all the transmitted subcarriers . Tx Rx X
Y=WX

25. Other MIMO Techniques
Transmit diversity Many different antennas transmit the same signal. At the receiver, the spatial diversity is exploited by using combining techniques. Closed Loop Rank-1 The same as the closed loop with RI=1  this assumption reduces the riTx overhead. Multi User MIMO, MU-MIMO The eNodeB can Tx and Rx from more than one user by using the same time-frequency resource Need of orthogonal reference signals. BEAMFORMING The eNodeB uses the antenna beams as well as an antenna array.

26. Single Carrier FDMA
Access scheme for UL  different requirements for power consumption!! OFDMA is affected by a high PAPR (Peak to Average Power Ratio). This fact has a negative influence on the power amplifier development.

27. Single Carrier FDMA

28. Single Carrier FDMA 2 ways for mapping sub-carriers
Assigning group of frequencies with good propagation conditions for UL UE
The subcarrier bandwidth is related to the Doppler effect when the mobile velocity is about 250 Km/h

29. DL CHANNELS and SIGNALS
Physical channels: convey info from higher layers
° Physical Downlink Shared Channel (PDSCH) 
- data and multimedia transport
- very high data rates supported
- BPSK, 16 QAM, 64 QAM
° Physical Downlink Control Channel (PDCCH) 
Specific UE information
Only available modulation (QPSK)  robustness preferred

30. DL CHANNELS and SIGNALS
° Common Control Physical Channel (CCPCH) 
Cell wide control information
Only QPSK available
Transmitted as closed as the center frequency as possible
Physical signals: convey information used only in PHY layer
Reference signals for channel response estimation (CIR)
Synchronization signals for network timing

31. TRANSPORT CHANNELS Broadcast channel (BCH)
Downlink Shared channel (DL-SCH)
- Link adaptation
- Suitable for using beamforming
- Discontinuous receiving/ power saving
Paging channel (PGH)
Multicast channel (MCH)

32. UL CHANNELS ° Physical Uplink Shared Channel (PUSCH) 
BPSK, 16 QAM, 64 QAM
° Physical Uplink Control Channel (PUCCH) 
Convey channel quality information
ACK
Scheduling request
° Uplink Shared channel (UL-SCH)
° Random Access Channel (RACH)

33. UL SIGNALS
Random Access Preamble  transmitted by UE when cell searching starts
Reference signal

34. CHANNEL MAPPING
DOWNLINK
UPLINK

35. Beyond the future: LTE Advanced
Relay NodesUE
Dual TX antenna solutions for SU-MIMO and diversity MIMO
Scalable system bandwidth exceeding 20 MHz, Potentially up to 100 MHz
Local area optimization of air interfaceNomadic / Local Area network and mobility solutions
Flexible Spectrum Usage / Cognitive radio
Automatic and autonomous network configuration and operation
Enhanced precoding and forward error correction
Interference management and suppression
Asymmetric bandwidth assignment for FDD
Hybrid OFDMA and SC-FDMA in uplinkUL/DL inter eNB coordinated MIMO