Overview and Basics of LTE
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Transcript of Overview and Basics of LTE
Discontent is the first step in the progress of a man or a nation. -Oscar Wilde
Why LTE ?
Less number of components so less cost,low latency and complexity.
End user perspective: Support for high end multimedia services
High data rates fast downloading capabilities
Support for multicast and broadcast services
Low latency and high reliability Global roaming between different radio access technologies
Support for DVB-H
Network provider perspective: Scalable bandwidth results in high flexibility (1.4 –20mhz)
Easy upgrade from existing technologies High spectral efficiency (3-4 times HSPA)
High ARPU(average revenue per user) ALL IP network
Requirements
Simple architecture in terms of number of components, low cost ,latency and complexity.
Down->OFDMA (384 kbps), UP->SC-FDMA (86 kbps)
2 operating modes: FDD and TDD User plane latency (UE->BS) < 5ms and control plane <100ms (idle->active)
Seamless mobility (prepared handoff’s) QOS directly evolved from HSPA+ ALL IP network Spectrum utilization: 1.4 Mhz to 20 Mhz
Requirements
Frequency Bands
BW Comparison:
Block Diagram
Functionality of All the Components in LTE
eNobeB: Radio resource management: Radio bearer control,Radio admission control,Scheduling, radio resource allocation (UL and DL),paging message forwarding , ROHC (user plane encryption) and Ciphering (PDCP)
EPC and enB have a many-many mapping to support redundancy,load sharing and avoiding congestion.
MME: Mobility management Entity
Tracking and maintenance of UE position Inter MME handovers pre-ordained Inter 3GPP handovers AS (UE-enB) and NAS(UE-MME) security Controls NAS signaling Consults HSS on 6a then chooses SGW and PDNGW accordingly (establishes a bearer between UE and PDNGW)
S-GW:
Routing and forwarding user data to PGW through S5 (GTP/PMIP based)
Provides user plane tunneling and inter eNB handovers through s1u
Inter 3GPP mobility through s1a (SGW-SGSN)
Lawful interception and accounting
Provides local mobility
PDN GW:
It is UE’s default router Provides user plane mobility and inter 3GPP handoff by acting as HA
Allocates IP address during default EPS bearer setup
QOS is here in the DL Enforces DL data rate ensuring that user is not crossing the subscription levels
S7 to PCRF S5 to SWGW(GTP/PMIP/Both) Provides global mobility
HSS:Home Subscriber Service
Stores subscription info (User info,Authentication and authorization )
S6a interface to MME for ciphering and auth (Mutual auth and integrity check)
1 or more HSS as per the number of subscribers
PCRF
Policy control decision and flow based charging
Contacts IMS for dynamic QOS and charging related service through “rx reference point”
Controls service data flows and IP bearer
Redundancy
When the UE powers up and attaches to the network eNB performs a load balancing algorithm to choose MME from MME pool
Then similarly MME selects SGW from SGW pool
By the we can achieve high fault tolerance and low congestion
This can be implemented using MME identifiers (MMEC,MMEGI,MMEI and GUMMEI)
Protocol Stack
Radio Resource Control (RRC)
Medium Access Control(MAC)
Transport channels
Physical layer
Contr
ol
/ M
easure
ments
Layer 3
Logical channelsLayer 2
Layer 1
Layers Functionality:
PDCP sublayer (terminated in eNB on the network side) performs ROHC, ciphering and integrity protection;
MAC- Mapping between logical channels and transport channels;
Multiplexing/demultiplexing of RLC PDUs belonging to one or different radio bearers into/from transport blocks (TB) delivered to/from the physical layer on transport channels;
MAC (Contd…):
MAC: - Traffic volume measurement reporting;- Error correction through HARQ;- Priority handling between logical channels of one UE;
- Priority handling between UEs by means of dynamic scheduling;
- Transport format selection;- Padding.
RLC sub layer: Transfer of upper layer PDUs supporting AM or UM;
TM data transfer; Error Correction through ARQ (CRC check provided by the physical layer, in other words no CRC needed at RLC level);
Segmentation according to the size of the TB: only if an RLC SDU does not fit entirely into the TB then the RLC SDU is segmented into variable sized RLC PDUs, which do not include any padding;
RLC (Contd…..)
Re-segmentation of PDUs that need to be retransmitted: if a retransmitted PDU does not fit entirely into the new TB used for retransmission then the RLC PDU is re-segmented;
The number of re-segmentations is not limited;
Concatenation of SDUs for the same radio bearer;
In-sequence delivery of upper layer PDUs except at HO;
Duplicate Detection; Protocol error detection and recovery;
SDU discard; Reset.
RLC (Contd…..)
RRC (terminated in eNB on the network side) performs the functions listed below:- Broadcast;- Paging;- RRC connection management;- RB control;- Mobility functions;- UE measurement reporting & control.
NAS control protocol (terminated at MME)
- EPS bearer management;- Authentication;- ECM-IDLE mobility handling;- Paging origination in ECM-IDLE;- Security control.
RRC and NAS:
RRC in detail:
Broadcast of System Information related to the non-access stratum (NAS);
Broadcast of System Information related to the access stratum (AS);
Paging; Establishment, maintenance and release of an RRC connection between the UE and E-UTRAN including:
Allocation of temporary identifiers between UE and E-UTRAN;
Configuration of signalling radio bearer(s) for RRC connection: Low priority SRB and high priority SRB.
Security functions including key management; Establishment, configuration, maintenance and release of point to point Radio Bearers;
Mobility functions including: UE measurement reporting and control of the reporting for inter-cell and inter-RAT mobility;
Handover; UE cell selection and reselection and control of cell selection and reselection;
Context transfer at handover.
RRC in detail(Contd…):
Notification for MBMS services; Establishment, configuration, maintenance and release of Radio Bearers for MBMS services;
QoS management functions; UE measurement reporting and control of the reporting;
NAS direct message transfer to/from NAS from/to UE.
RRC in detail(Contd…):
eNB
MME / S-GW MME / S-GW
eNB
eNB
S1
S1
X2 E-UTRAN
LTE Access Network Architecture
Functional Split between E-UTRAN and EPC
internet
eNB
RB Control
Connection Mobility Cont.
eNB MeasurementConfiguration & Provision
Dynamic Resource Allocation (Scheduler)
PDCP
PHY
MME
S-GW
S1MAC
Inter Cell RRM
Radio Admission Control
RLC
E-UTRAN EPC
RRC
Mobility Anchoring
EPS Bearer Control
Idle State Mobility Handling
NAS Security
P-GW
UE IP address allocation
Packet Filtering
RLC Layer
radio interface
lower layers(i.e. MAC sub layer and physical layer)
transmittingTM RLC entity
transmittingUM RLC entity
AM RLC entityreceiving
TM RLC entityreceiving
UM RLC entity
receivingTM RLC entity
receivingUM RLC entity
AM RLC entitytransmitting
TM RLC entitytransmitting
UM RLC entity
lower layers(i.e. MAC sub layer and physical layer)
upper layer (i.e. RRC layer or PDCP sub layer)
upper layer (i.e. RRC layer or PDCP sub layer)
eNB
UE
SAP betweenupper layers
logical channel
logical channel
SAP betweenupper layers
PDCP Functional Overview
Radio Interface (Uu)
UE/E-UTRAN E-UTRAN/UE
Transmitting PDCP entity
Ciphering
Header Compression (u-plane only)
Receiving PDCP entity
Sequence numbering
Integrity Protection (c-plane only)
Add PDCP header
Header Decompression (u-plane only)
Deciphering
Remove PDCP Header
Re-ordering (u-plane only)
Integrity Verification (c-plane only)
Packets associated to a PDCP SDU
Packets associated to a PDCP SDU
Packets not associated to a
PDCP SDU
Packets not associated to a
PDCP SDU
PDCP Sub layer
Radio BearersUE/E-UTRAN
PDCP sublayer
...
RLC sublayer
PDCP entiy
PDCP - PDU
RLC - SDU
C-SAP
PDCP-SAP PDCP-SAP
RLC UM-SAP RLC AM-SAP
...
PDCP entity PDCP entity
ARQ and HARQ
ARQ: ACK/NACK based scheme RLC mechanismHARQ: ACK/NACK based scheme MAC layer mechanism Buffers the corrupted packets and waits for the next packet, based on that 2 packets it decodes the original packet.
Implicit Link adaptation technique (Coarse Data rate selection)
Tx an encoded packet incrementally which saves BW
It reduces the amount of redundancy Synchronous in UL but Asynchronous in DL
Parallel Processes of HARQ are allowed in MAC layer
These 2 techniques along with the TCP retransmissions provide robust and reliable medium.
ARQ and HARQ (Contd...)
L2 Structure for Down Link
The PDCP, RLC and MAC layers together constitute L2.
L2 Structure for UP Link
ROHC (RFC 3095 and 5225)
Modes: Unidirectional Mode Bi-directional optimistic mode Bi-directional reliable mode States: Initialization & Refresh, First-Order Second-Order States
QOS:
There are 9 QOS classes categorized into BR and GBR with different priorities.
DSCP is also used here. Each class is represented by a Qos Class Identifier (QCI)
Classes are configured based on the latency, packet loss and data rate.
Applications requiring similar QOS are clubbed together as an SDF aggregate allocating a single EPS bearer for those 2 flows.
QOS Bearers
P-GWS-GW PeerEntity
UE eNB
EPS Bearer
Radio Bearer S1 Bearer
End-to-end Service
External Bearer
Radio S5/S8
Internet
S1
E-UTRAN EPC
Gi
S5/S8 Bearer
Mobility States of a UE in LTE
A Typical Uninterrupted Hand
Off
Idle Mobility Management using Traffic Areas
Comparison b/w Release7and8:
PHY Layer Concepts: OFDMA Vs. SCFDMA
Time Domain Comparison:
Comparison Contd……
Channel Dependent Scheduling:
General Block Diagram:
Comparison b/w different schemes:
Framing:
Type 1 Frame Structure:
Type 2 Frame Structure:
Resource Grid:
BW/Resource Configuration:
Logical Channels in LTE
Transport Channels in LTE
Mapping of Logical to Transport Channels
Note: The mappings shown in dotted lines are still being studied by 3GPP.
LTE Vs WiMax: 2 Sibling Rivalries
2 different technologies so cannot compare.They do not compete in same market
Wimax is ready for deployment whereas LTE will be deployed mass in 2013.
LTE is superior to 802.16e when compared to speed, but 802.16m will achieve almost the same speeds as LTE.
For fixed and low roaming Wimax but for High Roaming-LTE.Alternatively LTE can be used for macro cellular coverage and Wimax for Micro cell coverage
Contd….
LTE release 8 supports interop between LTE and Wimax.
Also HSPA+ is highly used and also for most of the users it provides sufficient BW and data rate @ 14 Mbps
So the three technologies may co exist For Wimax we require new equipment but for LTE service providers can upgrade.
3 Current Hot Technologies:
Comparing all the Contemporary Technologies
Future
Release-9 (LTE advanced) is on the way, draft initialization will start in Dec-2008 and Dec-2009 1st draft release is expected.
LTE-advanced supports data rates of 1 gig/s
It also aims on improvising the pre-defined global roaming.
Its not that I am so smart , its just that I stay with problems longer
- Albert Einstein
Thank You