Overview of LTE, its an old one @ 2009.

1. Presenting the Future:
LTE
3GPP Release 8
By
Chaitanya T K
Email:tkchaitanya@tataelxsi.Co.In

2. Discontent is the first step in the
progress of a man or a nation.
-Oscar Wilde

3. Why LTE ?
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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

4. 
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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

5. Requirements
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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

6. Requirements

7. Frequency Bands

8. BW Comparison:

9. Block Diagram

10. Functionality of All the
Components in LTE
eNobeB:
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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.

11. MME: Mobility management
Entity
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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)

12. S-GW:
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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 (SGWSGSN)
Lawful interception and accounting
Provides local mobility

13. PDN GW:
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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

14. HSS:Home Subscriber Service
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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

15. PCRF
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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

16. Redundancy
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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)

17. Layer 3
Layer 2
Layer 1
Control / Measurements
Protocol Stack
Radio Resource Control (RRC)
Logical channels
Medium
(MAC)
Access
Physical layer
Control
Transport channels

18. Layers Functionality:
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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;

19. MAC (Contd…):
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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.

20. RLC sub layer:
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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;

21. RLC (Contd…..)
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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;

22. RLC (Contd…..)
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In-sequence delivery of upper layer
PDUs except at HO;
Duplicate Detection;
Protocol error detection and
recovery;
SDU discard;
Reset.

23. RRC and NAS:
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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.

24. RRC in detail:
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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.

25. RRC in detail(Contd…):
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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 intercell and inter-RAT mobility;
 Handover;
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UE cell selection and reselection
and control of cell selection and
reselection;
 Context transfer at handover.

26. RRC in detail(Contd…):
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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.

27. LTE Access Network Architecture

28. Functional Split between EUTRAN and EPC

29. RLC Layer

30. PDCP Functional Overview

31. PDCP Sub layer

32. ARQ and HARQ
ARQ:
 ACK/NACK based scheme
 RLC mechanism
HARQ:
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ACK/NACK based scheme
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MAC layer mechanism
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Buffers the corrupted packets and
waits for the next packet, based on
that 2 packets it decodes the original
packet.
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Implicit Link adaptation technique
(Coarse Data rate selection)

33. ARQ and HARQ (Contd...)
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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.

34. L2 Structure for Down Link
The PDCP, RLC and MAC layers together constitute
L2.

36. L2 Structure for UP Link

37. ROHC (RFC 3095 and 5225)
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Modes:
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Unidirectional Mode
Bi-directional optimistic mode
Bi-directional reliable mode
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States:
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Initialization & Refresh,
First-Order
Second-Order States
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38. QOS:
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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.

39. QOS Bearers

40. Mobility States of a UE in LTE

41. A Typical Uninterrupted Hand
Off

42. Idle Mobility Management
using Traffic Areas

43. Comparison b/w Release7and8:

44. PHY Layer Concepts: OFDMA Vs.
SCFDMA

45. Time Domain Comparison:

46. Comparison Contd……

47. Channel Dependent Scheduling:

48. General Block Diagram:

49. Comparison b/w different
schemes:

50. Framing:

51. Type 1 Frame Structure:

52. Type 2 Frame Structure:

53. Resource Grid:

54. BW/Resource Configuration:

55. Logical Channels in LTE

56. Transport Channels in LTE

57. Mapping of Logical to Transport
Channels
Note: The mappings shown in dotted lines
are still being studied by 3GPP.

58. LTE Vs WiMax: 2 Sibling
Rivalries
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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

59. Contd….
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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.

60. 3 Current Hot Technologies:

61. Comparing all the Contemporary
Technologies

62. Future
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Release-9 (LTE advanced) is on the way,
draft initialization will start in Dec2008 and Dec-2009 1st draft release is
expected.
LTE-advanced supports data rates of 1
gig/s
It also aims on improvising the predefined global roaming.

63. Its not that I am so smart , its just that
I stay with problems longer
- Albert Einstein

64. Thank You 