Long TermEvolution. Beyond 3G. OVERVIEW. LTE targets Network architecture LTE Physicallayer LTE Access tecniques MIMO Channels LTE Advanced. LTE TARGETs. Packet-Domain-Services only (e.g. VoIP) upon LTE, TCP/IP- based layers
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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
+ Includes methods for contrasting distortion due to multipath:
+ New access method scheme:
- up to 20 MHz for high data rates
- less than 5 MHz for migration from 2G technologies
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!!!
Cyclic prefix duration linked with highest degree of delay spread
Possible interference within a CP of two symbols
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
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)
PRB is the smallest element for resource allocation contains 12 consecutives subcarriers for 1 slot duration
Resource element 1 subcarrier for each symbol period
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
Definition of a time-varying channel response for each antenna:
When an antenna is transmitting her references, the others are idle.
Once the channel matrix is known, data are transmitted simultaneously.
LTE admitted configurations:
- UL: 1x1 ,1x2
-DL: 1x1, 1x2, 2x2, 4x2
MIMO techniques in LTE:
Two way to work:
eNodeBapplies a pre-codification on the transmittedsignal, accordingto the UE channelperception.
RI, PMI, CQI
Usedwhen the feedback rate istoo low and/or the feedback overheadistooheavy.
Manydifferentantennastransmit the samesignal. At the receiver, the spatialdiversityisexploitedbyusingcombiningtechniques.
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.
The eNodeBuses the antenna beamsaswellasan antenna array.
Access scheme for UL different requirements for power consumption!!
OFDMA isaffectedby a high PAPR (PeaktoAveragePowerRatio). Thisfacthas a negative influence on the poweramplifierdevelopment.
Assigning group of frequencies with good propagation conditions for UL UE
The subcarrierbandwidthisrelatedto the Doppler effectwhen the mobile velocityisabout 250 Km/h
° Physical Downlink Shared Channel (PDSCH)
- data and multimedia transport
- very high data rates supported
- BPSK, 16 QAM, 64 QAM
° Physical Downlink Control Channel (PDCCH)
° Common Control Physical Channel (CCPCH)
- Link adaptation
- Suitable for using beamforming
- Discontinuous receiving/ power saving
° Physical Uplink Shared Channel (PUSCH)
° Physical Uplink Control Channel (PUCCH)
° Uplink Shared channel (UL-SCH)
° Random Access Channel (RACH)