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LTE/EPC Fundamentals
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2
Agenda
LTE Overview
LTE/EPC Network Architecture
LTE/EPC Network Elements
LTE/EPC Mobility & Session Management
LTE/EPC Procedure
LTE/EPS overview
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3
Agenda
Air Interface Protocols
LTE Radio Channels
Transport Channels and Procedure
LTE Physical Channels and Procedure
LTE Radio Resource Management
MIMO for LTE
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LTE Overview
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5
Cellular Generations
There are different generations as far as mobile communication is concerned:
First Generation (1G)
Second Generation (2G)
2.5 Generation (2.5G)
Third Generation (3G)
E3G (4G)
Fifth Generation(5G)
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6
History and Future of Wireless
data rates
< 1 Gbps
mobility
GSM/IS95
AMPS
WCDMA/cdma2000HSPA LTE
802.11a/b/g
802.16a/d 802.16e
< 100 Mbps< 50 Mbps< 10 Mbps< 1 Mbps< 200 kbps
time
2010200520001990
HIGH
LOW
2G
3G 3G Enhacements 3G Evolution
802.11 802.11nWLAN Family
WiMAX Family
1G
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3GPP Releases & Features
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Main LTE Requirements
Peak data ratesof uplink/downlink 50/100 Mbps
Reduced Latency:
Enables round trip time
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What is new in LTE?
New radio transmission schemes:
OFDMA in downlink
SC-FDMA in uplink
MIMO Multiple Antenna Technology
New radio protocol architecture:
Complexity reduction
Focus on shared channel operation, no dedicated channels anymore
New network architecture: flat architecture:
More functionality in the base station (eNodeB)
Focus on packet switched domain
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What is new in LTE?
Important for Radio Planning: Frequency Reuse 1
No need for Frequency Planning
Importance of interference control
No need to define neighbour lists in LTE
LTE requires Physical Layer Cell Identity planning (504 physical layer cell IDs organised
into 168 groups of 3)
Additional areas need to be planned like PRACH parameters, PUCCH and PDCCHcapacity and UL Demodulation Reference Signal
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Reasons for changes
Time
Traffic
volume
New technology, interfaces,
protocols
Simple low-cost architecture,
seamless transition from old
technologies (smooth coexistence)
Quick time2market for new
chipsets
OFDM, MIMO, large
bandwidth, scalable PHY/RRM
Cooperation with chipset
vendors
Flat LTE/SAE, co-location and
migration concept
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Evolution Path to LTE
Operator migration paths to LTE
>90 % of world radio access market migrating to LTE
Enabling flat broadband architecture
TD-SCDMAGSM /
(E)GPRS
LTE
CDMA
I-HSPA
WCDMA /
HSPA
TD-LTE
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LTE/EPC Network Architecture
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LTE/SAE Key FeaturesEUTRAN
Evolved NodeB No RNC is provided anymore
The evolved Node Bs take over all radio management functionality.
This will make radio management faster and hopefully the network architecture simpler
IP transport layer EUTRAN exclusively uses IP as transport layer
UL/DL resource scheduling In UMTS physical resources are either shared or dedicated
Evolved Node B handles all physical resource via a scheduler and assigns themdynamically to users and channels
This provides greater flexibility than the older system
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LTE/SAE Key FeaturesEUTRAN
QoS awareness
The scheduler must handle and distinguish different quality of service classes
Otherwise real time services would not be possible via EUTRAN
The system provides the possibility for differentiated service
Self configuration
Currently under investigation
Possibility to let Evolved Node Bs configure themselves
It will not completely substitute the manual configuration and optimization.
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Evolution of Network Architecture
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Evolution of Network Architecture
GGSN
SGSN
RNC
Node B
(NB)
Direct tunnel
GGSN
SGSN
HSPA R7 HSPA R7 LTE R8
Node B + RNC
Functionality
Evolved
Node B
(eNB)
GGSN
SGSN
RNC
Node B
(NB)
HSPA R6
LTE
SAE GW
MME/SGSN
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LTE Network Architecture Evolution
Node B RNC SGSN GGSN
Internet
3GPP Rel 6 / HSPA
User plane
Control PlaneOriginal 3G architecture.
2 nodes in the RAN.
2 nodes in the PS Core Network.
Every Node introduces additional delay.
Common path for User plane and Control plane data.
Air interface based on WCDMA.RAN interfaces based on ATM.
Option for Iu-PS interface to be based on IP
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LTE Network Architecture Evolution
Direct tunnel
3GPP Rel 7 / HSPA
Internet
Node B RNC
SGSN
GGSN
User plane
Control Plane
Separated path for Control Plane and User Plane data in the PS Core Network.
Direct GTP tunnel from the GGSN to the RNC for User plane data: simplifies the CoreNetwork and reduces signaling.
First step towards a flat network Architecture.
30% core network OPEX and CAPEX savings with Direct Tunnel.
The SGSN still controls traffic plane handling, performs session and mobility management,and manages paging.
Still 2 nodes in the RAN.
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LTE Network Architecture Evolution
Direct tunnel
3GPP Rel 7 / Internet HSPA
Internet
Node B
SGSN
GGSN
Node B
(RNC Funct.)User plane
Control Plane
I-HSPA introduces the first true flat architecture to WCDMA.
Standardized in 3GPP Release 7 as Direct Tunnel with collapsed RNC.
Most part of the RNC functionalities are moved to the Node B.
Direct Tunnels runs now from the GGSN to the Node B.
Solution for cost-efficient broadband wireless access.
Improves the delay performance (less node in RAN).
Deployable with existing WCDMA base stations.
Transmission savings
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LTE Network Architecture Evolution
Direct tunnel
3GPP Rel 8 / LTE
Internet
Evolved Node B
MME
SAE GW
LTE takes the same Flat architecture from Internet HSPA.
Air interface based on OFDMA.
All-IP network.
New spectrum allocation (i.e 2600 MHz band)
Possibility to reuse spectrum (i.e. 900 MHZ)
User plane
Control Plane
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LTE Network Architecture Evolution - Summary
Node B RNC SGSN GGSNInternet
3GPP Rel 6 / HSPA
Direct tunnel
3GPP Rel 7 / HSPA
Internet
Node B RNC
SGSN
GGSN
Direct tunnel
3GPP Rel 7 / Internet HSPA
Internet
Node B
SGSN
GGSN
Node B
(RNC Funct.)
Direct tunnel
3GPP Rel 8 / LTE
Internet
Evolved Node B
MME
SAE GW
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Terminology
EPS
EPCEPC - Evolved Packet Core
eUTRAN eUTRAN - Evolved UTRAN
EPSEvolved Packet System
SAE - System Architecture Evolution
LTE - Long Term Evolution
IP Network
http://www.sonyericsson.com/spg.jsp?cc=gb&lc=en&ver=4000&template=pp1_loader&php=php1_10238&zone=pp&lm=pp1&pid=10238http://www.sonyericsson.com/spg.jsp?cc=se&lc=sv&ver=4000&template=pp1_loader&php=php1_10409&zone=pp&lm=pp1&pid=10409 -
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TerminologyInterfaces----Logical view
EPC
S1S1 S1
X2 X2
eNodeBeNodeB eNodeB
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LTE/SAE Network Architecture
GGSN => Packet Gateway
SGSN => Mobility server
BSC
RNC
SGSN/ MME
GGSN/ P/S-GW
GSM, WCDMA
IP networks
LTE
SAE
MME = Mobility Management Entity
P/S-GW = PDN/Serving gateway
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Overall EPS Architecture
Basic EPS entities & interfaces
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LTE/EPC Network Elements
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LTE/SAE Network Architecture Subsystems
LTE/SAE architecture is driven by the goal to optimize the system for packet
data transfer.
No circuit switched components New approach in the inter-connection between radio access network and core
network
IMS/PDN
EPC
eUTRAN
LTE-UE
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EPS Architecture - Subsystems
LTE or EUTRAN SAE or EPC
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LTE/SAE Network Elements
LTE-UE
Evolved UTRAN (E-UTRAN)
MME S10
S6a
Serving
Gateway
S1-U
S11
PDN
Gateway
PDN
Evolved Packet Core (EPC)
S1-MME PCRF
S7
Rx+
SGiS5/S8
Evolved
Node B
(eNB)
cell
X2
LTE-Uu
HSS
MME: Mobility Management Entity
PCRF:Policy & Charging Rule Function
SAE
Gateway
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Evolved Node B (eNB)
RNC is not a part of E-UTRAN
Completely removed from the architecture
eNB is the only one entity in E-UTRAN eNB main functions:
Serving cell (or several cells)
Provisioning of radio interface to UEs (eUu)
Physical layer (PHY) and Radio Resource Management (RRM)
Exchange of crucial cell-specific data to other base stations (eNBs) eNB
RNC
eNB
X2
RRM(bearer control, mobility control, scheduling, etc.)
ROHC (Robust Header Compression)
MME selection when no info provided from UE
User Plane data forwarding to SAE-GW
Transmission of messages coming from MME
(i.e. broadcast, paging, NAS)
Ciphering and integrity protection for the air interface
Collection and evaluation of the measurements
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X2 interface
Newly introduced E-UTRAN interface
Inter eNB interface
X2 main functions: Provisioning of inter eNB direct connection
Handover (HO) coordination without EPC involvement
Data packets buffered or coming from SAE-GW to the source
eNB are forwarded to the target eNB
Improved HO performance (e.g. delay, packet loss ratio)
Load balancing Exchange of Load Indicator (LI) messages between eNBs to
adjust RRM parameters and/or manage Inter Cell Interference
Cancellation (ICIC)
X2 interface is not required
Inter eNB HO can be managed by MME
Source eNB target eNB tunnel is established using MME
eNB
eNB
X2
eNB
X2
X2
( )
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Evolved
Node B
(eNB)
MME
Serving
Gateway
S1-U
S1-MME
S11
HSS
S6a
MME Functions
Non-Access-Stratum (NAS)
Security (Authentication,
integrity Protection)
Idle State Mobility Handling
Tracking Area updates
Radio Security Control
Trigger and distribution of
Paging Messages to eNB
Roaming Control (S6a interfaceto HSS)
Inter-CN Node Signaling
(S10 interface), allows efficient
inter-MME tracking area updates
and attaches
Signalling coordination for
SAE Bearer Setup/Release
Subscriber attach/detach
Control plane NE in EPC
Mobility Management Entity (MME)
It is a pure signaling entity inside the EPC.
SAE uses tracking areas to track the position of idle UEs. The basicprinciple is identical to location or routing areas from 2G/3G.
MME handles attaches and detaches to the SAE system, as well astracking area updates
Therefore it possesses an interface towards the HSS (homesubscriber server) which stores the subscription relevant informationand the currently assigned MME in its permanent data base.
A second functionality of the MME is the signaling coordination tosetup transport bearers (SAE bearers) through the EPC for a UE.
MMEs can be interconnected via the S10 interface
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Evolved
Node B
(eNB)
MME
Serving SAE
Gateway
S1-U
S1-MME
S5/S8
PDN
Gateway
S11
S6a
Serving SAE Gateway
The serving gateway is a network element that manages the userdata path (SAE bearers) within EPC.
It therefore connects via the S1-U interface towards eNB andreceives uplink packet data from here and transmits downlinkpacket data on it.
Thus the serving gateway is some kind of distribution and packetdata anchoring function within EPC.
It relays the packet data within EPC via the S5/S8 interface to orfrom the PDN gateway.
A serving gateway is controlled by one or more MMEs via S11interface.
Local mobility anchor point:
Switching the user plane path to a
new eNB in case of Handover
Idle Mode Packet Buffering and
notification to MME
Packet Routing/Forwardingbetween eNB, PDN GW and SGSN
Lawful Interception support
Serving Gateway Functions
Mobility anchoring for inter-3GPP
mobility. This is sometimes referred
to as the 3GPP Anchor function
k k ( ) SA G
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Packet Data Network (PDN) SAE Gateway
The PDN gateway provides the connection between EPC and anumber of external data networks.
Thus it is comparable to GGSN in 2G/3G networks.
A major functionality provided by a PDN gateway is the QoScoordination between the external PDN and EPC.
Therefore the PDN gateway can be connected via S7 to a PCRF(Policy and Charging Rule Function).
MME
Serving
Gateway
S5/S8
PDN SAE
Gateway
PDNSGi
PCRF
S7 Rx+
S11
S6a
Policy Enforcement (PCEF)
Per User based Packet Filtering (i.e.
deep packet inspection)
Charging & Lawful Interception support
PDN Gateway Functions
IP Address Allocation for UE
Packet Routing/Forwarding betweenServing GW and external Data Network
Mobility anchor for mobility between
3GPP access systems and non-3GPP
access systems. This is sometimes
referred to as the SAE Anchor function
Packet screening (firewall functionality)
P li d Ch i R l F i (PCRF)
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Policy and Charging Rule Function (PCRF)
The PCRF major functionality is the Quality of Service (QoS)coordination between the external PDN and EPC.
Therefore the PCRF is connected via Rx+ interface to theexternal Data network (PDN)
This function can be used to check and modify the QoSassociated with a SAE bearer setup from SAE or to request thesetup of a SAE bearer from the PDN.
This QoS management resembles the policy and chargingcontrol framework introduced for IMS with UMTS release 6.
MME
Serving
Gateway
S5/S8
PDN SAE
Gateway
PDNSGi
PCRF
S7 Rx+
S11
S6a
Charging Policy: determines how
packets should be accounted
QoS policy negotiation with PDN
PCRF: Policy & Charging Rule Function
H S b ib S (HSS)
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Home Subscriber Server (HSS)
The HSS is already introduced by UMTS release 5.
With LTE/SAE the HSS will get additionally data persubscriber for SAE mobility and service handling.
Some changes in the database as well as in the HSSprotocol (DIAMETER) will be necessary to enable HSS forLTE/SAE.
The HSS can be accessed by the MME via S6a interface.
Permanent and central subscriber
database
HSS Functions
Stores mobility and service data for
every subscriber
MME
HSS
S6a
Contains the Authentication Center
(AuC) functionality.
LTE R di I t f d th X2 I t f
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LTE Radio Interface and the X2 Interface
LTE-Uu
Air interface of EUTRAN
Based on OFDMA in downlink and SC-FDMA inuplink
FDD and TDD duplex methods
Scalable bandwidth 1.4MHz to currently 20 MHz
Data rates up to 100 Mbps in DL
MIMO (Multiple Input Multiple Output) is a major
component although optional.
X2
Inter eNB interface
Handover coordination without involving the EPC
X2AP: special signalling protocol
During HO, Source eNB can use the X2 interface toforward downlink packets still buffered or arrivingfrom the serving gateway to the target eNB.
This will avoid loss of a huge amount of packetsduring inter-eNB handover.
(E)-RRC User PDUs User PDUs
PDCP (ROHC = RFC 3095)
..
RLC
MAC
LTE-L1 (FDD/TDD-OFDMA/SC-FDMA)
TS 36.300
eNB
LTE-Uu
eNB
X2
User PDUs
GTP-U
UDP
IPL1/L2
TS 36.424
X2-UP
(User Plane)
X2-CP
(Control Plane)
X2-AP
SCTP
IPL1/L2TS 36.421
TS 36.422
TS 36.423
TS 36.421
TS 36.420[currently also in TS 36.30020]
X2 H d
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X2 Handover
EUTRAN & EPC t d ith S1 fl
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1
2
3
EUTRAN & EPC connected with S1-flex
Several cases
eNB 1Single S1-MME
Single S1-U
eNB 2 Single S1-MME
Multiple S1-US1Flex-U
eNB 3 Multiple S1-ME
S1Flex Single S1-U
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LTE/EPC Mobility & Session Management
LTE/SAE Mobility Areas
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LTE/SAE Mobility Areas
Two areas are defined for handling of mobility in LTE/SAE:
The Cell
identified by the Cell Identity. The format is not standardized yet.
Tracking Area (TA)
It is the successor of location and routing areas from 2G/3G.When a UE is attached to the network, the MME will know the UEs position on
tracking area level.
In case the UE has to be paged, this will be done in the full tracking area.
Tracking areas are identified by a Tracking Area Identity (TAI).
LTE/SAE Mobility Areas
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LTE/SAE Mobility Areas
Tracking Areas
S-eNBTAI3
TAI3 TAI3TAI3
TAI3TAI3
TAI3
MME
HSS
eNB
TAI2
TAI2TAI2
TAI2
TAI2
TAI2
TAI2
TAI2
TAI1
TAI1TAI1
TAI1
TAI1eNB 1 2
MME
3
Cell Identity
Tracking Area
Tracking Areas Overlapping
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Tracking Areas Overlapping
S-eNBTAI3
TAI3TAI3
TAI3
TAI3TAI3
TAI3
MME
HSS
eNB
TAI2
TAI2 TAI2TAI2
TAI2
TAI2
TAI2
TAI2
TAI1-2TAI1
TAI1
TAI1 eNB 1 2
MME
3
Cell Identity
1.- Tracking areas are allowed to overlap:
one cell can belong to multiple trackingareas
TAI1-2
2.- UE is told by the network to be in several
tracking areas simultaneously.Gain: when the UE enters a new cell, it checkswhich tracking areas the new cell is part of. Ifthis TA is on UEs TA list, then no tracking areaupdate is necessary.
Tracking Areas: Use of S1 flex Interface
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Tracking Areas: Use of S1-flex Interface
TAI1-2
S-eNBTAI2
TAI2TAI2
TAI3
TAI3TAI3TAI3
MME
HSS
eNB
TAI2
TAI2TAI2
TAI2
TAI2
TAI2
TAI2
TAI2
TAI1
TAI1
TAI1
eNB
S-MME
TAI1-2 MME
Pooling:several MME
handle the
same
tracking area
Cell Identity
321
1 2 3
UE Identifications
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UE Identifications
IMSI: International Mobile Subscriber Identity
S-TMSI: SAE Temporary Mobile Subscriber Identity
C-RNTI: Cell Radio Network Temporary Identity
S1-AP UE ID: S1 Application Protocol User Equipment Identity
UE Identifications: IMSI
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UE Identifications: IMSI
IMSI:International Mobile Subscriber Identity.
Used in SAE to uniquely identify a subscriber world-wide.
Its structure is kept in form of MCC+MNC+MSIN:MCC: mobile country code
MNC: mobile network codeMSIN: mobile subscriber identification number
A subscriber can use the same IMSI for 2G, 3G and SAE access.
MME uses the IMSI to locate the HSS holding the subscribers permanentregistration data for tracking area updates and attaches.
IMSI
MCC MNC MSIN
3 digits 2 digits 10 digits
UE Identification: S TMSI
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UE Identification: S-TMSI
S-TMSI:
SAE Temporary Mobile Subscriber Identity
Itis dynamically allocated by the serving MME (S-MME).
Its main purpose is to avoid usage of IMSI on air.
Internally the allocating MME can translate S-TMSI into IMSI and vice versa.
Whether the S-TMSI is unique per MME.
In case the S1flex interface option is used, then the eNB must select the right MME for
a UE. This is done by using some bits of the S-TMSI to identify the serving MME of the
UE. This identifier might be a unique MME ID or a form of MME color code. Under
investigation
S-TMSI
MME-ID or
MME color code
32 bits
UE Identifications: C RNTI
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UE Identifications: C-RNTI
C-RNTI:
Cell Radio Network Temporary Identity
C-RNTI is allocated by the eNB serving a UE when it is in active mode(RRC_CONNECTED)
This is a temporary identity for the user only valid within the serving cell of
the UE.
It is exclusively used for radio management procedures.
X-RNTI identifications under investigation.
UE Identifications Summary
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UE Identifications Summary
IMSI International Mobile Subscriber Identity
S-TMSI S-Temporary Mobile Subscriber Identity
C-RNTI Cell Radio Network Temporary Identity
S-MME Serving MME
S-eNB Serving E-Node B
TAI Tracking Area Identity (MCC+MNC+TAC)
S-TMSI
MME-ID or
MME color code
C-RNTI
eNB S1-AP UE-ID | MME S1-AP UE-ID
MCC
IMSI
MNC MSIN
S-eNBTAI2
TAI2TAI2
TAI3
TAI3TAI3
TAI3
MME
HSS
eNB
TAI2
TAI2TAI2
TAI2
TAI2
TAI2
TAI2
TAI2
TAI1
TAI1TAI1
TAI1
TAI1
eNB
1 2
S-MME
32
Cell IdentityMME Identity
3
1
Terminology for 3G & LTE: Connection & Mobility Management
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Terminology for 3G & LTE: Connection & Mobility Management
3G LTEConnection Management
GPRS Attached EMM Registered
PDP Context EPS Bearer
Radio Access Bearer Radio Bearer + S1 Bearer
Mobility Management
Location Area Not Relevant (no CS core)
Routing Area Tracking Area
Handovers (DCH) and Cell
reselections (PCH) when RRC
connected
Handover when RRC
connected
RNC hides mobility from corenetwork
Core Network sees everyhandover
LTE Mobility & Connection States
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LTE Mobility & Connection States
There are two sets of states defined for the UE based on the information held by
the MME.
These are:
- EPS* Mobility Management (EMM) states
- EPS* Connection Management (ECM) states
*EPS: Evolved Packet System
EPS Mobility Management (EMM) states
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EPS Mobility Management (EMM) states
EMM-DEREGISTERED:
In this state the MME holds no valid location information about the UE
MME may keep some UE context when the UE moves to this state (e.g. to avoid the needfor Authentication and Key Agreement (AKA) during every attach procedure)
Successful Attach and Tracking Area Update (TAU) procedures lead to transition to EMM-
REGISTERED
EMM-REGISTERED:In this state the MME holds location information for the UE at least to the accuracy of a
tracking area
In this state the UE performs TAU procedures, responds to paging messages and performs
the service request procedure if there is uplink data to be sent.
EPS Mobility Management (EMM) states
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EPS Mobility Management (EMM) states
EMM
deregistered
EMM
registered
Attach
Detach
EPS Connection Management (ECM) and LTE Radio Resource Control
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States
UE and MME enter ECM-CONNECTED state when the signalling connection is established
between UE and MME
UE and E-UTRAN enter RRC-CONNECTED state when the signalling connection is
established between UE and E-UTRAN
RRC IdleRRC
Connected
ECM IdleECM
Connected
EPS Connection Management (ECM) states
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EPS Connection Management (ECM) states
ECM-IDLE:
In this state there is no NAS signalling connection between the UE and the network andthere is no context for the UE held in the E-UTRAN.
The location of the UE is known to within the accuracy of a tracking area
Mobility is managed by tracking area updates.
ECM-CONNECTED:
In this state there is a signalling connection between the UE and the MME which is
provided in the form of a Radio Resource Control (RRC) connection between the UE and the
E-UTRAN and an S1 connection for the UE between the E-UTRAN and the MME.
The location of the UE is known to within the accuracy of a cell.Mobility is managed by handovers.
RRC States
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RRC States
RRC_IDLE: No signalling connection between the UE and the E-UTRAN, i.e. PLMN
Selection.
UE Receives system information and listens for Paging. Mobility based on Cell Re-selection performed by UE. No RRC context stored in the eNB. RACH procedure used on RRC connection establishment
RRC_CONNECTED: UE has an E-UTRAN RRC connection. UE has context in E-UTRAN (C-RNTI allocated). E-UTRAN knows the cell which the UE belongs to. Network can transmit and/or receive data to/from UE. Mobility based on handovers UE reports neighbour cell measurements
EPS Connection Management
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EPS Connection Management
ECM Connected= RRC Connected + S1 Connection
eNB
MME
UE
RRC Connection S1 Connection
ECM Connected
EMM & ECM States Transitions
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EMM & ECM States Transitions
EMM_Deregistered
ECM_Idle
Power On
Registration (Attach)
EMM_Registered
ECM_Connected
Allocate C-RNTI, S_TMSI
Allocate IP addresses
Authentication
Establish security context
Release RRC connection
Release C-RNTI
Configure DRX for paging
EMM_Registered
ECM_Idle
Release due to
Inactivity
Establish RRC Connection
Allocate C-RNTI
New TrafficDeregistration (Detach)
Change PLMN
Release C-RNTI, S-TMSI
Release IP addresses
Timeout of Periodic TA
Update
Release S-TMSI
Release IP addresses
EMM & ECM States Summary
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EMM & ECM States Summary
EMM_Deregistered
ECM_Idle
Network Context:
no context exists
Allocated IDs:
IMSI
UE Position:
unknown tonetwork
Mobility:
PLMN/cell
selection
UE Radio Activity:none
EMM_Registered
ECM_Connected
Network Context:
all info for ongoing
transmission/recepti
on
Allocated IDs:
IMSI, S-TMSI per
TAI1 or several IP
addresses
C-RNTI
UE Position:
known on cell level
Mobility:
NW controlled
handover
EMM_Registered
ECM_Idle
Network Context:
security keys
enable fast
transition to
ECM_CONNECTED
Allocated IDs:IMSI, S-TMSI per
TAI
1or several IP
addresses
UE Position:
known on TA level
(TA list)
Mobility:
cell reselection
LTE/SAE Bearer
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/
The main function of every mobile radio telecommunication network is to
provide subscribers with transport bearers for their user data.
In circuit switched networks users get a fixed assigned portion of the networks
bandwidth.
In packet networks users get a bearer with a certain quality of service (QoS)
ranging from fixed guaranteed bandwidth down to best effort services without anyguarantee.
LTE/SAE is a packet oriented system
LTE/SAE
Bearer
PDN GW
UE
SAE Bearer Architecture
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SAE Bearerspans the complete network, from UE over EUTRAN and EPS up to the
connector of the external PDN.
The SAE bearer is associated with a quality of service (QoS) usually expressed by a label
or QoS Class Identifier (QCI).
cell
S1-U
LTE-Uu
S5PDN
Sgi
eNB Serving
Gateway
PDN
Gateway
End-to-End Service
SAE Bearer Service (EPS Bearer)External Bearer
Service
SAE Radio Bearer Service (SAE RB) SAE Access Bearer Service
Physical Radio Bearer Service S1 Physical Bearer Service
E-UTRAN EPC PDN
S5/S8 Bearer Service
SAE Bearer Establishment
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It can be establish by MME or P-GW
MME:
This happens typically during the attach procedure of an UE. Depending on theinformation coming from HSS, the MME will set up an initial SAE bearer, also known
as the default SAE bearer. This SAE bearer provides the initial connectivity of the UE
with its external data network.
PDN Gateway:
The external data network can request the setup of a SAE bearer by issuing thisrequest via PCRF to the PDN gateway. This request will include the quality of service
granted to the new bearer.
cell
S1-U
UE
S5PDN
Sgi
eNB
Serving
Gateway
PDN
Gateway
SAE Bearer Service (EPS Bearer)External Bearer
Service
MME
S1-MME
S11
QoS Class Indentifier (QCI) Table in 3GPP
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Q (Q )
GBR1
Guarantee Delay budget Loss rate ApplicationQCI
GBR
100 ms 1e-2 VoIP
2
GBR
150 ms 1e-3 Video call
3
GBR
300 ms 1e-6 Streaming
4
Non-GBR 100 ms 1e-6 IMS signalling5
Non-GBR 100 ms 1e-3 Interactive gaming6
Non-GBR 300 ms 1e-6TCP protocols :
browsing, email, filedownload
7
Non-GBR 300 ms 1e-68
Non-GBR 300 ms 1e-69
Priority
2
4
5
1
7
6
8
9
50 ms 1e-3 Real time gaming3
Operators can define more QCIs
Several bearers can be aggregated together if they have the same QCI
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LTE/EPC Procedures
Attach
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MMEHSS
PCRF
UE eNB new
MME
Serving
Gateway
(SGW)
PDN
Gateway
Attach Request
S-TMSI/IMSI,old TAI, IP address allocation
Authentication Request
Authentication Response
Update Location
Authentication Vector Request (IMSI)
Insert Subscriber Data
IMSI, subscription data = default APN, tracking area restrictions,
Insert Subscriber Data Ack
Update Location Ack
EMM_Deregistered
Authentication Vector Respond
RRC_Connected
ECM_Connected
Attach cont.
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Update Bearer Response
Update Bearer Request
IP/TEID of eNB for S1u
Attach Complete
IP/TEID of eNB for S1u
RB Est. Resp.
Includes Attach Complete
Create Def. Bearer Req.
MMEHSS
PCRF
UE eNB new
MME
Serving
Gateway
(SGW)
PDN
Gateway
S-TMSI, security info,
PDN address, ,IP/TEID
of SGW-S1u (only for eNB)
Create Def. Bearer Rsp.
IP/TEID of SGW-S1u,
PDN address, QoS,
Create Def. Bearer Rsp.
PDN address, IP/TEID of PDN GW,
QoS according PCRF
select SAE GW
Create Default Bearer Request
IMSI, RAT type, default QoS, PDN address info
IMSI, , IP/TEID of SGW-S5
Attach Accept
RB Est. Req.
Includes Attach Accept
UL/DL Packet Data via Default EPS Bearer
PCRF Interaction
EMM_Registered
ECM_Connected
S1 Release
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After attach UE is in EMM Registered state.
The default Bearer has been allocated (RRC connected + ECM connected) even it maynot transmit or receive data
If there is a longer period of inactivity by this UE, then we should free these admissioncontrol resources (RRC idle + ECM idle)
The trigger for this procedure can come from eNB or from MME.
RRC Connection Release
MME
S1 Release Request
causeUpdate Bearer Request
release of eNB S1u resources
Update Bearer Response
Serving
Gateway
(SGW)
PDN
Gateway
S1 Release Command
cause
S1 Release Complete
RRC Connection Release Ack
EMM_Registered
ECM_Connected
S1 Signalling Connection ReleaseEMM_Registered
ECM_Idle
Detach
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Can be triggered by UE or by MME.
During the detach procedure all SAE bearers with their associated tunnels andradio bearers will be deleted.
MME
NAS: Detach Accepted
Delete Bearer Request
Delete Bearer Response
EMM-Registered
Serving
Gateway
(SGW)
PDN
Gateway
NAS Detach Request
switch off flag Delete Bearer Request
Delete Bearer Response
PCRF
S1 Signalling Connection Release
RRC_Connected
ECM_Connected
EMM-Deregistered
RRC_Connected + ECM Idle
Note: Detach procedure initiated by UE.
Detach
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Note: Detach procedure initiated by MME.
MME
NAS: Detach Accepted
Delete Bearer Request
Delete Bearer Response
EMM-Registered
Serving
Gateway
(SGW)
PDN
Gateway
NAS Detach Requestswitch off flag
Delete Bearer Request
Delete Bearer Response
PCRF
S1 Signalling Connection Release
RRC_Connected
ECM_Connected
EMM-Deregistered
RRC_Connected + ECM Idle
Service Request
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From time to time a UE must switch from ECM_Idle to ECM_connected
The reasons for this might be UL data is available, UL signaling is pending (e.g.tracking area update, detach) or a paging from the network was received.
MMEServing
Gateway
(SGW)
PDN
Gateway
Paging
S-TMSI, TAI/TAI-list
Service Request
DL Packet DataDL Packet NotificationPaging
S-TMSI
S-TMSI, TAI, service type
Authentication Request
authentication challenge
Authentication Response
Authentication response
RRC_Idle+ ECM_Idle
ECM_Connected
RRC_Connected
Service Request
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MME
Initial Context Setup Req.
Update Bearer Request
eNB-S1 IP/TEID
Update Bearer Response
Serving
Gateway(SGW)
PDN
Gateway
SGW-S1 IP/TEID, QoSRB Establishment Req.
RB Establishment Rsp.
Initial Context Setup Rsp.
eNB-S1 IP/TEID, ..
Tracking Area Update (TAU)
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Tracking area (TA) is similar to Location/Routing area in 2G/3G .
Tracking Area Identity = MCC (Mobile Country Code), MNC (Mobile NetworkCode) and TAC (Tracking Area Code).
When UE is in ECM-Idle, MME knows UE location with Tracking Area accuracy.
Tracking Area Update (1/2)
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MMEHSS
eNB new
MMEMME
old
MME
new
Serving
Gateway
(SGW)
PDN
Gateway
Tracking Area Update Request
Context RequestS-TMSI/IMSI,old TAI, PDN (IP) address allocation
S-TMSI/IMSI,old TAI
Context Response
mobility/context data
Create Bearer Request
IMSI, bearer contexts
Context Acknowledge
S-TMSI/IMSI,old TAI
Update Bearer Request
new SGW-S5 IP/TEID
Create Bearer Response
new SGW-S1 IP/TEID
Update Bearer Response
PDN GW IP/TEID
old
Serving
Gateway
(SGW)UEEMM_Registered
RRC_Idle + ECM_Idle
RRC_Connected
ECM_Connected
Authentication / Security
Tracking Area Update cont
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MMEHSS
eNB new
MME MME
old
MME
new
Serving
Gateway
(SGW)
PDN
Gateway
Update Location
new MME identity, IMSI,
IMSI, cancellation type = update
Cancel Location Ack
Delete Bearer Request
TEID
Delete Bearer Response
Cancel Location
old
Serving
Gateway
(SGW)
Update Location Ack
Tracking Area Update Accept
new S-TMSI, TA/TA-list
Tracking Area Update Complete
EMM_Registered
RRC_Idle + ECM_Idle
Handover Procedure
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SAE GW
MME
SourceeNB
TargeteNB
SAE GW
MME
SAE GW
MME
SAE GW
MME
= Data in radio
= Signalling in radio
= GTP tunnel
= GTP signalling
= S1 signalling
= X2 signalling
Before handoverHandover
preparationRadio handover
Late path
switching
Note: Inter eNB Handover with X2 Interface and without CN Relocation
User plane switching in Handover
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Automatic Neighbor Relations
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1--UE reports neighbor cell signal including Physical Cell ID
1
24
3
2--Request for Global Cell ID reporting
3--UE reads Global Cell ID from BCH
4--UE reports Global Cell ID
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LTE Air Interface
LTE Design Performance Targets
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Scalable transmission bandwidth(up to 20 MHz)
Improved Spectrum Efficiency Downlink (DL) spectrum efficiency should be 2-4 times Release 6 HSDPA.
Downlink target assumes 2x2 MIMO for E-UTRA and single Tx antenna with Type 1
receiver HSDPA.
Uplink (UL) spectrum efficiency should be 2-3 times Release 6 HSUPA.
Uplink target assumes 1 Tx antenna and 2 Rx antennas for both E-UTRA and Release 6
HSUPA.
Coverage
Good performance up to 5 km
Slight degradation from 5 km to 30 km (up to 100 km not precluded)
Mobility
Optimized for low mobile speed (< 15 km/h)
Maintained mobility support up to 350 km/h (possibly up to 500 km/h)
LTE Design Performance Targets
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Advanced transmission schemes, multiple-antenna technologies
Inter-working with existing 3G and non-3GPP systems Interruption time of real-time or non-real-time service handover between E-UTRAN
and UTRAN/GERAN shall be less than 300 or 500 ms.
Air Interface Capabilities
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Bandwidth support
Flexible from 1.4 MHz to 20 MHz
Waveform
OFDM in Downlink
SC-FDM in Uplink
Duplexing mode
FDD: full-duplex (FD) and half-duplex (HD)
TDD
Modulation orders for data channels
Downlink: QPSK, 16-QAM, 64-QAM
Uplink: QPSK, 16-QAM, 64-QAM
MIMO support
Downlink: SU-MIMO and MU-MIMO (SDMA)
Uplink: SDMA
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Downlink Air Interface-OFDMA
Fast Fourier Transform
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Two characteristics define a signal:
Time domain:represents how long the symbol lasts on air
Frequency domain:represents the spectrum needed in terms of bandwidth
Fast Fourier Transform (FFT) and the Inverse Fast Fourier Transform (IFFT) allow to
move between time and frequency domain representation and it is a fundamental
block in an OFDMA system
OFDM signals are generated using the IFFT
OFDM Basics
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Transmits hundreds or even thousands of separately modulated radio signals using
orthogonal subcarriersspread across a wideband channel
Orthogonality:
The peak (centrefrequency) of one
subcarrier
intercepts the
nulls of theneighbouring
subcarriers
15 kHzin LTE: fixed
Total transmission bandwidth
OFDM Basics
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Data is sent in parallel across the set of subcarriers, each subcarrier only transports
a part of the whole transmission
The throughput is the sum of the data rates of each individual (or used) subcarriers
while the power is distributed to all subcarriers
FFT (Fast Fourier Transform) is used to create the orthogonal subcarriers. The
number of subcarriers is determined by the FFT size (by the bandwidth)
In LTE, these subcarriers are separated 15kHZ
Power
frequency
bandwidth
Multi-Path Propagation and Inter-Symbol Interference
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Inter Symbol Interference
BTS
Time 0 Ts
+
Time 0 Tt Ts+Tt
Tt
Multi-Path Propagation and the Guard Period
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2
time
TSYMBOLTime Domain
1
3
time
TSYMBOL
time
TSYMBOL
Tg
1
2
3
Guard Period (GP)
Guard Period (GP)
Guard Period (GP)
Propagation delay exceeding the Guard Period
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Multipath causes Inter Symbol Interference (ISI) which affects the subcarrier
orthogonality due to phase distortion
Solution to avoid ISI is to introduce a Guard Period (Tg) after the pulse
Tg needs to be long enough to capture all the delayed multipath signals
To make use of that Tg (no transmission) Cyclic Prefix is transmitted
12
34
time
TSYMBOLTime Domain
time
time
Tg
1
2
3
time
4
Obviously when the
delay spread of the
multi-path
environment is
greater than the
guard period
duration (Tg), then
we encounter inter-
symbol interference
(ISI)
Cyclic Prefix (CP) and Guard Time
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Consists in copying the last part of a symbol shape for a duration of guard-time andattaching it in front of the symbol
CP needs to be longer than the channel multipath delay spread.
A receiver typically uses the high correlation between the Cyclic Prefix (CP) and the lastpart of the following symbol to locate the start of the symbol and begin then with
decoding
2 CP options in LTE:
Normal CP:for small cells or with short multipath delay spread
Extended CP:designed for use with large cells or those with long delay profiles
t
total symbol time T(s)
Guard Time
T(g)
CP
T(g)Useful symbol time
T(b)
Note: CP represents an overhead
resulting in symbol rate reduction.
Having a CP reduces the
bandwidth efficiency but the
benefits in terms of minimizing the
ISI compensate for it
Last part of the next
Symbols is used as
Cyclic Prefic (CP)CP ratio = T(g)/T(b)
Cyclic Prefix
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In multi-path propagation environments the delayed versions of the signal arrive
with a time offset, so that the start of the symbol of the earliest path falls in the
cyclic prefixes of the delayed symbols.
As the CP is simply a repetition of the end of the symbol this is not a inter-
symbol interference and can be easily compensated by the following decoding
based on discrete Fourier transform.
CP
Ts
Symbol
Detection
Interval
CP
CP
SYMBOL
SYMBOL
SYMBOL
1
2
3
1
2
3
Multi-Carrier Modulation
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One solution is to use multiple carriers in parallel (Subcarriers).
This allows to increase the bit rate, but keeping the advantages of smaller
carriers with simple inter-symbol interference handling via cyclic prefix and/orcyclic suffix.
frequency
Serial-to-Parallel
ConverterFast Data
011001011100101001011101
011 001 011 100 101 001 011 101
Slow Data
Subcarriers
Guard Bands
OFDMA Symbol
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OFDMA is an extension of OFDM technique to allow multiple user transmissions
and it is used in other systems like Wi-Fi, DVB and WiMAX
OFDMA Symbol is the Time period occupied by the modulation symbols on all
subcarriers. Represents all the data being transferred in parallelat a point in time
OFDM symbol duration including CP is aprox. 71.4
s (*) Long duration when compared with 3.69s for
GSM and 0.26s for WCDMA allowing a good
CP duration
Robust for mobile radio channel with the
use of guard internal/cyclic prefix
Symbol length without considering CP:
66.67s (1/15kHz)
Subcarrier types
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Data subcarriers: used for data transmission
Reference Signals:
used for channel quality and signal strength estimates.
They dont occupy a whole subcarrier but they are periodically embedded in the
stream of data being carried on a data subcarrier.
Null subcarriers (no transmission/power):
DC (centre) subcarrier: 0Hz offset from the channels centre frequency
Guard subcarriers: Separate top and bottom subcarriers from any adjacent channel
interference and also limit the amount of interference caused by the channel.
Guard band size has an impact on the data throughput of the channel.
Guard (no power)
DC (no
power)
data
Guard (no power)
OFDMA Parameters
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Channel bandwidth:Bandwidths ranging from 1.4 MHz to 20 MHz
Data subcarriers:They vary with the bandwidth
72 for 1.4MHz to 1200 for 20MHz
OFDMA Parameters
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Frame duration: 10ms created from slots and subframes
Subframe duration (TTI): 1 ms (composed of 2x0.5ms slots)
Subcarrier spacing: Fixed to 15kHz (7.5 kHz defined for MBMS)
Sampling Rate: Varies with the bandwidth but always factor ormultiple of 3.84 to ensure compatibility with WCDMA by using common clocking
Frame Duration
Subcarrier Spacing
Sampling Rate (MHz)
Data Subcarriers
Symbols/slot
CP length
1.4MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz
10 ms
15 kHz
Normal CP=7, extended CP=6
Normal CP=4.69/5.12 sec, extended CP= 16.67sec
1.92 3.84 7.68 15.36 23.04 30.72
72 180 300 600 900 1200
10ms
Peak-to-Average Power Ratio in OFDMA
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The transmitted power is the sum of the powers of all the subcarriers
Due to large number of subcarriers, the peak to average power ratio (PAPR) tends
to have a large range
The higher the peaks, the greater the range of power levels over which the power
amplifier is required to work
Having a UE with such a PA that works over a big range of powers would be
expensive
Not best suited for use with mobile (battery-powered) devices
OFDM Wrap-up
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High spectral efficiency and little interference between channels
Robust in multi-path environments thanks to Cyclic Prefix
Frequency domain scheduling offer high potential for throughput gain
Severe High PAPR (Peak to Average Power Ratio)
Small subcarrier spacing makes it more sensitive to frequency offset (subcarriers may interfere
each others)
Pros:
Cons:
OFDMA Operation:
Total channel bandwidth
Transmitted frequency spectrum:
S/P IFFT CP
Modulation
mapping e.g.
QPSK
symbols
Transmitter structure Receiver structure
P/S FFTCP
Re-
moval
Modulation
mapping e.g.
QPSK
symbols
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Downlink Air Interface-SC-FDMA
SC-FDMA in Uplink
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115
Single Carrier Frequency Division Multiple Access: Transmission
technique used for Uplink
Variant of OFDM that reduces the PAPR: Combines the PAR of single-carrier system with the multipath resistance and
flexible subcarrier frequency allocation offered by OFDM
It can reduce the PAPR between 69dB compared to OFDMA
Reduced PAPR means lower RF hardware requirements (power
amplifier) SC-FDMA
OFDMA
SC-FDMA and OFDMA Comparison
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OFDMA transmits data in parallel across multiple subcarriers
SC-FDMA transmits data in series employing multiple subcarriers
In the example:
OFDMA: 6 modulation symbols (01,10,11,01,10 and 10) are transmitted per OFDMA
symbol, one on each subcarrier
SC-FDMA: 6 modulation symbols are transmitted per SC-FDMA symbol using all
subcarriers per modulation symbol. The duration of each modulation symbol is 1/6thof
the modulation symbol in OFDMA
OFDMA SC-FDMA
SC-FDMA and OFDMA Comparison
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SC-FDMA Operation
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The parallel transmission of multiple symbols in OFDMA creates high PAR
SC-FDMA avoids this by additional processing before the IFFT: modulation symbols
are presented to FFT. The output represents the frequency components of the
modulation symbols.
Subcarriers created by this process have a set amplitudethat should remain nearly
constant between one SC-FDMA symbol and the next for a given modulation
scheme which results in little difference between the peak power and the average
power radiated on a channel
Rx
Uplink Air Interface Technology-SC-FDMA
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User multiplexing in frequency domain, a user is allocated different bandwidths(multiples of 180kHz)
In OFDMA the user multiplexing is in sub-carrier domain: user is allocated Resource
Blocks
One user is always continuous in frequency
Smallest uplink bandwidth, 12 subcarriers: 180 kHz
same for OFDMA in downlink
Largest uplink bandwidth: 20 MHz
same for OFDMA in downlink
Terminals are required to be able to receive & transmit up to 20 MHz, depending on the
frequency band though
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Physical Layer
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Physical Layer Structure and Channels
Introduction
d h b b f l
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It provides the basic bit transmission functionality over air
LTE physical layer based on OFDMA downlink and SC-FDMA in uplink direction
This is the same for both FDD and TDD mode of operation
No need of RNC like functional element
Everything radio related can be terminated in the eNodeB
System is reuse 1, single frequency network operation is feasible
No frequency planning required
There are no dedicated physical (neither transport) channelsanymore, as all
resource mapping is dynamically driven by the scheduler
Frame Structure (FDD)
FDD F ( l ll d T 1 F ) i b h li k d
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FDD Frame structure (also called Type 1 Frame) is common to both uplink and
downlink.
Divided into 20 x 0.5ms slots
Structure has been designed to facilitate short round trip time
- Frame duration =10 ms (same as UMTS)
- FDD: 10 ms radio frame for UL and 10 ms radio frame for DL
- Radio frame includes 10 subframes- 1 Subframe represents a Transmission Time Interval (TTI)
- Each subframes includes two slots- 1 slot = 7 (normal CP) or 6 symbols (extended CP)
10 ms frame
0.5 ms slot
s0 s1 s2 s3 s4 s5 s6 s7s
18
s19..
SF0
1 ms sub-frame
SF1 SF2 SF9..
sy4sy0 sy1 sy2 sy3 sy5 sy6
0.5 ms slot
SF3SF1 SF2 SF3 SF9
SF: SubFrame
s: slot
Sy: symbol
Frame Structure (FDD)
LTE Ti D i i i d
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LTE Time Domain is organized as:
Frame (10 ms)
Subframe (1 ms) Slot (0.5 ms)
Symbol (duration depending on configuration)
Radio Frame has 2 structures:
Type 1 (FS1) for FDD DL/UL
Type 2 (FS2) for TDD FS1 is considered ithis presentation
Frequency Domain Organization
LTE DL/UL i i t f f l th l b i t d
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LTE DL/UL air interface waveforms use several orthogonal subcarriers to send
user traffic data, Reference Signals (Pilots), and Control Information.
f: Subcarrier spacing DC Subcarrier: Direct Current subcarrier at center of frequency band
Number of DL or UL Resource Blocks (groups of subcarriers)
Number of subcarriers within a Resource Block
Normal and Extended Cyclic Prefix
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Normal Cyclic Prefix
160 Ts 144 Ts
2048 Ts
Ts = 1/30720 ms
Cyclic Prefix
144 Ts 144 Ts 144 Ts 144 Ts 144 Ts
2048 Ts 2048 Ts 2048 Ts 2048 Ts 2048 Ts 2048 Ts
7 2048 Ts
+ 6 144 Ts
+ 1 160 Ts
15360 Ts = 0.5 ms
Main Body
512 Ts 512 Ts
2048 Ts
Ts = 1/30720 ms
Cyclic Prefix
512 Ts 512 Ts 512 Ts 512 Ts
2048 Ts 2048 Ts 2048 Ts 2048 Ts 2048 Ts
6 2048 Ts
+ 6 512 Ts
15360 Ts = 0.5 ms
Main Body
Extended Cyclic Prefix
Resource Block
Ph i l R Bl k R Bl k (PRB RB)
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Physical Resource Block or Resource Block (PRB or RB):
12 subcarriers in frequency domain (180kHz) x 1 slot period in time domain (0.5ms)
Capacity allocation is based on Resource Blocks
Resource
Element
Note: Although 3GPP definition of RB refers to
0.5ms, in some cases it is possible to found that RBrefers to 12 subcarriers in frequency domain and
1ms in time domain. In particular, since the
scheduler in the eNodeB works on TTI basis (1ms)
RBs are considered to last 1ms in time domain. They
can also be known as scheduling resource blocks
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
Subcarrier 1
Subcarrier 12
180KHz
1 slot 1 slot
1 ms subframe
Resource Element
Theoretical minimum capacity allocation unit
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Theoretical minimum capacity allocation unit
Equivalent to one subcarrier x one symbol period
72 or 84 Resource Elements per Resource Block
Each Resource Element can accommodate 1 modulation symbol, e.g. 2 bits for
QPSK, 4 bits for 16QAM and 6 bits for 64 QAM
Modulation symbol rate per Resource Block is 144 ksps or 168 ksps
Case 1: Normal Cyclic Prefix Case 2: Extended Cyclic Prefix
7 symbols = 0.5 ms 6 symbols = 0.5 ms
12subcarriers=180kHz
Resource Element
12subcarriers=180kHz
Frequ
encyDomain
12subcarriers=180kHz
Time Domain Time Domain
Resource Grid Definition-Ul/DL
Resource Element (RE)
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Resource Element (RE)
One element in the time/frequency resource grid.
One subcarrier in one OFDM/LFDM symbol for DL/UL. Often used for Control channel
resource assignment.
Resource Block (RB)
Minimum scheduling size for DL/UL data channels
Physical Resource Block (PRB) [180 kHz x 0.5 ms]
Virtual Resource Block (VRB) [180 kHz x 0.5 ms in virtual frequency domain]
Localized VRB
Distributed VRB
Resource Block Group (RBG)
Group of Resource Blocks
Size of RBG depends on the system bandwidth in the cell
Modulation Schemes for LTE/EUTRAN
Each OFDM symbol even within a resource block can have a different
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Each OFDM symbol even within a resource block can have a differentmodulation scheme.
EUTRAN defines the following options: QPSK, 16QAM, 64QAM.
Not every physical channel will be allowed to use any modulation scheme:Control channels to be using mainly QPSK.
In general it is the scheduler that decides which form to use depending oncarrier quality feedback information from the UE.
b0 b1
QPSK
Im
Re10
11
00
01
b0 b1b2b3
16QAM
Im
Re
0000
1111
Im
Re
64QAM
b0 b1b2b3 b4 b5
LTE Frequency Variants in 3GPPFDD
T t l [MH ] U li k [MH ] D li k [MH ] E rope Japan Americas
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1
2
3
4
5
7
8
9
6
2x25
2x75
2x60
2x60
2x70
2x45
2x35
2x35
2x10
824-849
1710-1785
1850-1910
1920-1980
2500-2570
1710-1755
880-915
1749.9-1784.9
830-840
Total [MHz] Uplink [MHz]
869-894
1805-1880
1930-1990
2110-2170
2620-2690
2110-2155
925-960
1844.9-1879.9
875-885
Downlink [MHz]
10 2x60 1710-1770 2110-2170
11 2x25 1427.9-1452.9 1475.9-1500.9
1800
2600900
US AWS
UMTS core
US PCS
US 850
Japan 800
Japan 1700
Japan 1500
Extended AWS
Europe Japan Americas
788-798 758-768
777-787 746-756
UHF (TV)
US700
2x10
2x1013
12 2x18 698-716 728-746
14
790-820 832-862?2x30?xx
US700
US700
LTE Frequency Variants - TDD
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33
34
35
36
1x60
1x15
1x20
1x60
1850-1910
2010-2025
1900-1920
1930-1990
37
38
1x20
1x50
1910-1930
2570-2620
Total
Spectrum Frequency (MHz)
UMTS TDD1
UMTS TDD2
US PCS
US PCS
US PCS
Euro middle gap 2600
39
40
1x40
1x100
1880-1920
2300-2400
China TDD
2.3 TDD
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LTE Radio Interface LTE States
LTE Radio Interface LTE States
LTE DETACHED
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LTE_DETACHED
Used @ power up when the mobile terminal is not known to the network.
Before any further communication, the mobile terminal need to register with the
network using the random-access procedure.
LTE_ACTIVE
Mobile terminal is active with transmitting and receiving data.
IN_SYNC
Uplink is synchronized with eNodeB
OUT_SYNC
Uplink is not synchronized with eNodeB.
Mobile terminal needs to perform a random-access procedure to restore uplink
synchronization.
LTE Radio Interface LTE States
LTE IDLE
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LTE_IDLE
Low activity state to reduce battery consumption.
The only uplink transmission activity that may take place is random access to move
to LTE_ACTIVE.
In the downlink, the mobile terminal can periodically wake up in order to be paged
for incoming calls
The network knows at least the group of cells in which paging of the mobile
terminal is to be done.
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Downlink Physical Signals and Channels
Downlink Physical Signals and Channels
Downlink Physical Signals
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Downlink Physical Signals
Reference Signals
Synchronisation Signals
Downlink Physical Channels
Physical Broadcast Channel (PBCH)
Physical Downlink Shared Channel (PDSCH)
Physical Downlink Control Channel (PDCCH)
Physical Control Format Indicator Channel (PCFICH)
Physical Hybrid-ARQ Indicator Channel (PHICH)
Physical Multicast Channel (PMCH)
DL Physical Channels
PBCH:
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PBCH:
To broadcast the MIB (Master Information Block), RACH parameters
PDSCH:
Carries user data, paging data, SIBs (cell status, cell IDs, allowed services)
PMCH:
For multicast traffic as MBMS services
PHICH:
Carries H-ARQ Ack/Nack messages from eNB to UE in response to UL transmission
PCFICH:
Carries details of PDCCH format (e.g.# of symbols)
PDCCH:
Carries the DCI (DL control information): schedule uplink resources on the PUSCH or
downlink resources on the PDSCH. Alternatively, DCI transmits TPC commands for
UL
Note:There are no dedicated channels in LTE, neither in UL nor DL
DL Channelization Hierarchy
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PCCH BCCH CCCH DCCH DTCH MCCH MTCH
PCH BCH DL-SCH MCH
DL-RS SCH PCFICH PBCH PHICH PDSCH PDCCH PMCH
Dedicated & ControlCommon Control
Downlink
Logical Channels
Downlink
Transport Channels
DownlinkPhysical Channels
Paging
System
Broadcast
MBSFN
Reference Signals: OFDMA Channel Estimation
Channel estimation in LTE is based on reference signals (like CPICH functionality in
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g ( y
WCDMA)
Reference signals position in time domain is fixed (0 and 4 for Type 1 Frame)
whereas in frequency domain it depends on the Cell ID In case more than one antenna is used (e.g. MIMO) the Resource elements
allocated to reference signals on one antenna are DTX on the other antennas
Reference signals are modulated to identify the cell to which they belong.
Antenna 1 Antenna 2
sub
carriers
symbols 6 symbols
subcarriers
Synchronization Signals (PSS & SSS)
PSS and SSS Functions
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PSS and SSS Functions
Frequency and Time synchronization
Carrier frequency determination
OFDM symbol/subframe/frame timing determination
Physical Layer Cell ID determination
Determine 1 out of 504possibilities
PSS and SSS resource allocationTime: subframe0 and 5 of every Frame
Frequency: middle of bandwidth (6 RBs = 1.08 MHz)
Synchronization Signals (PSS & SSS)
Primary Synchronization Signals (PSS)
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y y g ( )
Assists subframe timing determination
Provides a unique Cell ID index (0, 1, or 2) within a Cell ID group
Secondary Synchronization Signals (SSS)
Assists frame timing determination
M-sequences with scrambling and different concatenation methods for SF0 and SF5)
Provides a unique Cell ID group number among 168 possible Cell ID groups
Synchronization Signals allocation (DL)
Synchronization signals:
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Transmitted during the 1stand 11thslots within a
radio frame
Occupy the central 62 Subcarriers (around the DC
subcarrier) to facilitate the cell search
5 Subcarriers above and 5 Subcarriers below the
synch. Signals are reserved and transmitted as DTx
Synchronisation Signal can indicate 504 (168 x 3)
CellID different values and from those one can
determine the location of cell specific reference
symbols
Physical Broadcast Channel (PBCH)
PBCH Function
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Carries the primary Broadcast Transport Channel
Carries the Master Information Block (MIB), which includes:
Overall DL transmission bandwidth
PHICH configuration in the cell
System Frame Number
Number of transmit antennas (implicit)
Transmitted in
Time: subframe 0 in every frame
4 OFDM symbols in the second slot of corresponding subframe
Frequency: middle 1.08 MHz (6 RBs)
Physical Broadcast Channel (PBCH)
TTI = 40 ms
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Transmitted in 4 bursts at a very low data rate
Same information is repeated in 4 subframes
Every 10 ms burst is self-decodable
CRC check uniquely determines the 40 ms PBCH TTI boundary
Last 2 bits of SFN is not transmitted
Physical Control Format Indicator Channel (PCFICH)
Carries the Control Format Indicator (CFI)
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( )
Signals the number of OFDM symbols of PDCCH:
1, 2, or 3 OFDM symbols for system bandwidth > 10 RBs
2, 3, or 4 OFDM symbols for system bandwidth > 6-10 RBs
Control and data do not occur in same OFDM symbol
Transmitted in:
Time: 1st OFDM symbol of all subframes
Frequency: spanning the entire system band4 REGs -> 16 REs
Mapping depends on Cell ID
PCFICH in Multiple Antenna configuration
1 Tx: PCFICH is transmitted as is
2Tx, 4Tx: PCFICH transmission uses Alamouti Code
Physical Downlink Control Channel (PDCCH)
Used for:
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DL/UL resource assignments
Multi-user Transmit Power Control (TPC) commands
Paging indicators
CCEs are the building blocks for transmitting PDCCH
1 CCE = 9 REGs (36 REs) = 72 bits
The control region consists of a set of CCEs, numbered
from 0 to N_CCE for each subframe
The control region is confined to 3 or 4 (maximum)
OFDM symbols per subframe (depending on system
bandwidth)
A PDCCH is an aggregation of contiguous CCEs
(1,2,4,8)
Necessary for different PDCCH formats and coding rate
protections
Effective supported PDCCH aggregation levels need to
result in code rate < 0.75
Physical Downlink Shared Channel (PDSCH)
Transmits DL packet data
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One Transport Block transmission per UEs code word per subframe
A common MCS per code word per UE across all allocated RBs
Independent MCS for two code words per UE
7 PDSCH Tx modes
Mapping to Resource Blocks (RBs)
Mapping for a particular transmit antenna port shall be in increasing order of:
First the frequency index,
Then the time index, starting with the first slot ina subframe.
Physical HARQ Indicator Channel (PHICH)
Used for ACK/NAK of UL-SCH transmissions
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Transmitted in:
Time
Normal duration: 1stOFDM symbol
Extended duration: Over 2 or 3 OFDM symbols
Frequency
Spanning all system bandwidth
Mapping depending on Cell ID
FDM multiplexed with other DL control channels
Support of CDM multiplexing of multiple PHICHs
DL Physical Channels Allocation
PBCH:
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Occupies the central 72 subcarriers across 4 symbols
Transmitted during second slot of each 10 ms radio frame on all
antennas
PCFICH:
Can be transmitted during the first 3 symbols of
each TTI
Occupies up to 16 RE per TTI
PHICH:
Normal CP: Tx during 1stsymbol of each TTI
Extended CP: Tx during first 3 symbols of each TTI
Each PHCIH group occupies 12 RE
PDCCH:
Occupies the RE left from PCFICH and PHICH within the first 3
symbols of each TTI
Minimum number of symbols are occupied. If PDCCH data is small
then it only occupies the 1st symbol
PDSCH:
Is allocated the RE not used by signals or other physical channels
RB
DL Reference Signals: 1 TxAntenna
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DL Reference Signals transmitted on 2 OFDM symbols every slot
6 subcarrier spacing
DL Reference Signals: 2 Tx Antenna
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DL Reference Signals: 4 Tx Antenna
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153
Overheads Normal CP Extended CP
1 TX Antenna 4.76% 5.56%
2 TX Antenna 9.52% 11.11%
4 TX Antenna 14.29% 15.87%
7Downlink TransmissionAn Example
Example of Frame Structure Type 1 (extended CP) transmission
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154
lDL Scheduled Operation Overview
1.UE reports CQI(Channel Quality Indicator),
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PMI(Precoding Matrix Index), and RI (Rank
Indicator) in PUCCH (or PUSCH if there is UL
traffic).
2.Scheduler at eNodeB dynamically allocates
resources to UE:UE readsPCFICH every
subframe to discover the number of OFDM
symbols occupied by PDCCH.UE readsPDCCH to discover Tx Modeand assigned
resources (PR BandMCS).
3.eNodeB sends user data in PDSCH.
4.UE attempts to decode the received packet
and sends ACK/NACK using PUCCH(or PUSCH
if there is UL traffic).
Uplink Physical Signals and Channels
Uplink Physical Signals
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Demodulation Signals:
Used for channel estimation in the eNodeB receiver to demodulate control and data
channels Located in the 4thsymbol (normal CP) of each slot and spans the same bandwidth as
the allocated uplink data
Sounding Reference Signals:
Provides uplink channel quality estimation as basis for the UL scheduling decisions -
> similar in use as the CQI in DL
Sent in different parts of the bandwidth where no uplink data transmission isavailable.
Not part of first NSNs implementations (UL channel aware scheduler in RL30)
Uplink Physical Channels
Physical Uplink Shared Channel (PUSCH) Physical Uplink Control Channel (PUCCH)
Physical Random Access Channel (PRACH)
UL Physical Channels
PUSCH: Physical Uplink Shared Channel
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Intended for the user data (carries traffic for multiple UEs)
PUCCH: Physical Uplink Control Channel
Carries H-ARQ Ack/Nack indications, uplink scheduling request, CQIs and MIMO
feedback
If control data is sent when traffic data is being transmitted, UE multiplexes both
streams together
If there is only control data to be sent the UE uses Resources Elements at the edges
of the channel with higher power PRACH: Physical Random Access Channel
For Random Access attempts. PDCCH indicates the Resource elements for PRACH
use
PBCH contains a list of allowed preambles (max. 64 per cell in Type 1 frame) and
the required length of the preamble
UL Channelization Hierarchy
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No dedicated transport channels: Focus on shared transport channels.
E-UTRA Uplink Reference Signals
Two types of E-UTRA/LTE Uplink Reference Signals:
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Demodulation reference signal
Associated with transmission of PUSCH or PUCCH
Purpose: Channel estimation for Uplink coherent demodulation/detection of the
Uplink control and data channels
Transmitted in time/frequency depending on the channel type (PUSCH/PUCCH),
format, and cyclic prefix type
Sounding reference signal
Not associated with transmission of PUSCH or PUCCH
Purpose: Uplink channel quality estimation feedback to the Uplink scheduler (for
Channel Dependent Scheduling) at the eNodeB
Transmitted in time/frequency depending on the SRS bandwidth and the SRS
bandwidth configuration (some rules apply if there is overlap with PUSCH andPUCCH)
OFDMA versus SC-FDMA
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Physical Uplink Shared Channel (PUSCH)
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Physical Uplink Control Channel (PUCCH)
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Sounding Reference Signals (SRS)
SRS shall be transmitted on the last symbol of the subframe.
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PUSCH:
The mapping to resource elements only considers those not
used for transmission of reference signals.
PUCCH Format 1 (SR) / 1a / 1b (HARQ-ACK):
When ACK/NAK and SRS are to be transmitted in SRS cell-
specific subframes:
If higher-layer parameter Simultaneous-AN-and-SRS is TRUE => Use
shortened PUCCH format.
Else UE shall not transmit SRS.
PUCCH Format 2 / 2a / 2b (CQI):
UE shall not transmit SRS whenever SRS and PUCCH 2 / 2a / 2b
coincide.
SRS multiplexing:
Done with CDM when there is one SRS bandwidth, and
FDM/CDM when there are multiple SRS bandwidths.
PRACH
The preamble format determines the length of the
Cyclic Prefix and Sequence
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Cyclic Prefix and Sequence.
FDD has 4 preamble formats (for different cell sizes).
16 PRACH configurations are possible.
Each configuration defines slot positions within a frame
(for different bandwidths).
Each random access preamble occupies a bandwidth
corresponding to 6 consecutive RBs.
is the starting RB for the PRACH.
PRACH6
-110RBs
6RBs
SequenceCP
Tcp Tseq FDD Specific RACH format
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MIMO
MIMO
MIMO stands for Multiple Input Multiple Output. It is a key technology to increase a channels capacity by using multiple transmitter
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y gy p y y g pand receiver antennas.
The propagation channel is the air interface, so that transmission antennas are
handled as input to the channel, whereas receiver antennas are the output of it. The very basic ideas behind MIMO have been established already 1970 , but have
not been used in radio communication until 1990. MIMO is currently used in 802.11n, 802.16d/e to increase the channel capacity.
Air Interface
Transmission antennas (inputs)
Reception antennas (outputs)
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THANK YOU