Transcript Long Term Evolution - Gabriele Falciasecca

Long Term Evolution
Beyond 3G
OVERVIEW
 LTE targets
 Network architecture
 LTE Physical layer
 LTE Access tecniques
 MIMO
 Channels
 LTE Advanced
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 UL @20MHz bandwidth

Reduced delay/latency  user-plane latency<5ms

Improved spectrum efficiency  up to 200 active users in a cell @5MHz 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
LTE TARGETs
Network Architecture
Network Architecture – E-UTRAN
 User Equipment
 Evolved Node B (eNB) Functionalities:
1)
resource management (allocation and HO)
2)
admission control
3)
application of negotiated UL QoS
4)
cell information broadcast
5)
ciphering/deciphering of user and control plane data
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
Network Architecture
Evolved Packet Core
 Serving Gateway  Functionalities:
1)
routing and forwarding user data packets
2)
acts as mobility anchor for the user plane during inter-eNB
handovers and for mobility between LTE and other 3GPP
3)
for idle state UEs, terminates the DL data path and triggers
paging when DL data arrives for the UE
4)
performs replication of the user traffic in case of lawful
interception.
Network Architecture
Evolved Packet Core
 Packet Data Network Gateway  Functionalities:
1)
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
2)
performs policy enforcement, packet filtering for each user,
charging support, lawful Interception and packet screening
3)
acst as the anchor for mobility between 3GPP and non-3GPP
technologies (WiMAX)
LTE PHY Layer
+ Includes methods for contrasting distortion due to multipath:
a)
OFDM
b) MIMO
+ New access method scheme:
a)
OFDMA
b) SC-FDMA
Multipath effects
 ISI induced by multipath  time-domain effect of multipath
 Frequency selectivity  frequency-domain effect of multipath
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
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!!!
Orthogonal Frequency Division Multiplexing
Cyclic prefix duration linked with highest degree of delay spread
FTT PERIOD
Possible interference within a CP of two symbols
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
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:
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
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
Multiple Input – Multiple Output
 MIMO CHANNEL
Definition of a time-varying channel response for each antenna:
h11 t ,  

H t ,    
h t ,  
 NR 1
h1NT t ,  


hNR NT t ,  
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.
Multiple Input – Multiple Output
 Advantages:
1)
Higher data rate  more than one flow simultaneously
2)
Spatial diversity  taking advantage from multiple paths 
multipath as a resource
-
Disadvantages:
1)
Complexity
LTE admitted configurations:
- UL: 1x1 ,1x2
-DL: 1x1, 1x2, 2x2, 4x2
Multiple Input – Multiple Output
MIMO techniques in LTE:
1)
SU-MIMO
2)
Transmit diversity
3)
Closed loop rank 1
4)
MU- MIMO
5)
Beamforming
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
-
RI: rank indicator
PMI: Precoding Matrix Indicator
CQI: Channel Quality Indicator
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
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.
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.
Single Carrier FDMA
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
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
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
1)
Reference signals for channel response estimation (CIR)
2)
Synchronization signals for network timing
TRANSPORT CHANNELS
1)
Broadcast channel (BCH)
2)
Downlink Shared channel (DL-SCH)
- Link adaptation
- Suitable for using beamforming
- Discontinuous receiving/ power saving
1)
Paging channel (PGH)
2)
Multicast channel (MCH)
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)
UL SIGNALS
 Random Access Preamble  transmitted by UE when cell
searching starts
 Reference signal
CHANNEL MAPPING
DOWNLINK
UPLINK
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