Transcript of Long Term Evolution Beyond 3G. OVERVIEW LTE targets Network architecture LTE Physical layer LTE...
- Slide 1
- Long Term Evolution Beyond 3G
- Slide 2
- OVERVIEW LTE targets Network architecture LTE Physical layer
LTE Access tecniques MIMO Channels LTE Advanced
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- 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
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- LTE TARGETs
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- Network Architecture
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- 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
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- 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 providers Public Land Mobile Network (PLMN) 4)
control plane function for mobility between LTE and 2G/3G
access
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- 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.
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- 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)
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- LTE PHY Layer + Includes methods for contrasting distortion due
to multipath: a) OFDM b) MIMO + New access method scheme: a) OFDMA
b) SC-FDMA
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- Multipath effects ISI induced by multipath time-domain effect
of multipath Frequency selectivity frequency-domain effect of
multipath
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- 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
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- 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!!!
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- Orthogonal Frequency Division Multiplexing Cyclic prefix
duration linked with highest degree of delay spread Possible
interference within a CP of two symbols FTT PERIOD
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- 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
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- 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:
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- Orthogonal Frequency Division Multiple Access Resource element
1 subcarrier for each symbol period PRB is the smallest element for
resource allocation contains 12 consecutives subcarriers for 1 slot
duration
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- 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
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- Multiple Input Multiple Output MIMO CHANNEL Definition of a
time-varying channel response for each antenna:
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- 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.
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- 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
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- Multiple Input Multiple Output MIMO techniques in LTE: 1)
SU-MIMO 2) Transmit diversity 3) Closed loop rank 1 4) MU- MIMO 5)
Beamforming
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- 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
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- 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
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- 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.
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- 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.
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- Single Carrier FDMA
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- 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
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- 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
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- 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
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- 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)
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- 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)
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- UL SIGNALS Random Access Preamble transmitted by UE when cell
searching starts Reference signal
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- CHANNEL MAPPING DOWNLINK UPLINK
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- Beyond the future: LTE Advanced Relay NodesUERelay NodesUE Dual
TX antenna solutions for SU-MIMO and diversity MIMO Dual TX antenna
solutions for SU-MIMO and diversity MIMO Scalable system bandwidth
exceeding 20 MHz, Potentially up to 100 MHz Scalable system
bandwidth exceeding 20 MHz, Potentially up to 100 MHz Local area
optimization of air interfaceNomadic / Local Area network and
mobility solutions Local area optimization of air interfaceNomadic
/ Local Area network and mobility solutions Flexible Spectrum Usage
/ Cognitive radio Flexible Spectrum UsageCognitive radio Automatic
and autonomous network configuration and operation Automatic and
autonomous network configuration and operation Enhanced precoding
and forward error correction Enhanced precoding and forward error
correction Interference management and suppression Interference
management and suppression Asymmetric bandwidth assignment for FDD
Asymmetric bandwidth assignment for FDD Hybrid OFDMA and SC-FDMA in
uplinkUL/DL inter eNB coordinated MIMO Hybrid OFDMA and SC-FDMA in
uplinkUL/DL inter eNB coordinated MIMO