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LTE Fundamentals
TELCOMA
The Complete Course

Content:
Brief history about wireless ecosystem.
What is LTE (Long Term Evolution) ?
How is it different from older technologies ?

Network architecture in LTE
Radio Access network (RAN)
Evolved Packet Core (EPC)
Bearers in LTE

Interfaces in LTE
Life Cycle of a UE


Walk through Agenda

Content contd:
LTE RAN overview
Architecture and requirements
Channel bandwidths and operating bands
OFDMA and SC-FDMA
Frequency (LTE-FDD) and time division duplexing (LTE-TDD)
Multiple Antenna techniques in LTE
Channels in LTE and protocol Stack

LTE EPC overview
Architecture
Functions of various elements in EPC



Introduction to Radio Access Network (RAN)

Brief history about wireless ecosystem

1980s
1G
Analog
AMPS
Voice
1990s
2G
Digital
GSM, IS-95, IS-136
Voice capacity
2000s
3G
WCDMA, CDMA2000
Voice & data
2010s
4G
LTE/LTE-A, 802.16m
Broadband data & video
2020s
5G
Time
Speed/ Throughput Mbps

Comparison of Wireless technologies
Generation
1G
2G
3G
4G
5G
Deployment
1970-84
1980-89
1990-2002
2000-18
2020+
Throughput
2Kbps
14-64 Kbps
2 Mbps
200 Mbps
1Gbps+
Services
Analog Voice
Digital Voice SMS,MMS
Integrated HD Video and data
High Speed Data, Voice over LTE (VoLTE)
Ultra-low Latency, massive IoT,V2V
Underlying Technology std.
AMPS,TACS
D-AMPS,CDMA (IS-95)
CDMA2000,EVDO,W-CDMA,HSPA+
LTE, VoLTE, LTE Advanced, LTE Advanced Pro

5G-NR

How is LTE different from the previous technologies ?

How is LTE different ?
LTE benefits (Compared to 3G) include :

High Data rates
Reduced Latency
Improved end-user throughputs for applications such as a Voice and Video
Flexibility of radio frequency deployment since LTE can be deployed in various bandwidth configurations (1.4, 3, 5, 10, 15, 20 MHz)
Multiple Input Multiple Output (MIMO)
Flat all-IP network with fewer network elements which leads to lower latency.
Offers a TDD solution (LTE-TDD) in addition to FDD (LTE-FDD)

- Caters to variety of Operators – Spectrum rich and not so Spectrum rich

Network Architecture in LTE

Network Architecture in LTE:
LTE architecture is composed of 2 parts –
Radio Access Network: Evolved UTRA Network (E-UTRAN)
Core Network Architecture : Evolved Packet Core (EPC)
Evolved Packet Core (EPC)
Radio Access Network (RAN a.k.a E-UTRAN)
UTRA stands for Universal Terrestrial Radio Access
Has 2 parts

Network Architecture in LTE contd:
Eutran is also known as RAN
UE is User equipment
Is the closest to the UE
EPC is centrally located or can be distributed according to Geography
User Plane and control Plane.
Difference explain


Network Architecture in LTE contd.
EUTRAN:
Evolved NodeB (eNodeB)
Radio Resource management
Synchronization and Interference control
MME Selection among MME Pool
Routing of User Plane data from/to S-GW
Encryption/Integrity protection of user data
IP Header Compression

Next we will break it out
What is radio resource ? Chunks of Spectrum
Synchronization – Multiple users are transmitted at the same time. Need to keep them in sync. Resources are finite.High Speed data so timing is critical


Network Architecture in LTE contd.
EPC:
Mobility Management Entity (MME)
NAS (non-access stratum) signaling and its security
Tracking Areas List management
PDN GW and SGW selection.
Roaming and Authentication
EPS bearer management
Signaling for mobility management between 3GPP RANs


Network Architecture in LTE contd.
EPC Contd.:
Home Subscription Server (HSS)
User Authentication
Subscription/Profile management –
Roaming
Speed/throughput limits


Network Architecture in LTE contd.
EPC Contd.:
Serving Gateway (S-GW)
Packet routing and forwarding
EUTRAN Idle mode DL packet buffering
EUTRAN and inter-3GPP mobility anchoring
UL and DL charging per UE, PDN and QCI


Network Architecture in LTE contd.
EPC Contd:
Packet Data Network Gateway (P-GW)
IP Address allocation
Packet filtering and Policy enforcement
Transport Level QoS mapping and marking.
User Info anchoring for 3GPP and non-3GPP handovers.


Network Architecture in LTE contd:

Network Architecture in LTE contd:
Each Bearer can have specific QoS requirements.
What is a bearer ? Logical connection between entities. Can be composed of multiple Bearers

Network Architecture in LTE contd:

Network Architecture in LTE contd:
Imagine you have LTE router/Mifi device. This picture shows the end-to-end connection

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Interfaces in LTE Network

Interfaces in LTE
What is an interface ?
Interface represents a channel on which 2 network entities exchange information.

Why do we need interfaces ?
Interfaces are needed in LTE to deliver information (signaling or user data) for a subscriber or network element.

Who defines these interfaces ?
The various network interfaces are defined by 3GPP. All network vendors or manufacturers are required to comply to these standards.

Do these interfaces remain static ?
No. Depending on new capabilities and requirements 3GPP continues to make changes to the interface standards. However in most cases they are backward compatible.




Interfaces in LTE contd:
3GPP References:
EUTRAN
TS 36.401,36.300,23.002
S1 Interface
TS 36.41x series, TS 29.274, 24.301
X2 Interface
TS 36.42x series
MME functions and interfaces
TS 23.401, 23.402, 23.002
S10/S11
TS 29.274
S6a
TS 29.272
SGW and PGW functions
TS 23.401, 23.402, 23.002
S5/S8 interface
TS 29.274, 29.275
SGi Interface
TS 29.061

specifications


Evolution in LTE
*Source – 3GPP
Evolution in LTE. Rel 8 for the first LTE

Life Cycle of a UE

Life Cycle of a UE
1. Network Acquisition
2. Signaling connection
3. Attach
4. Authentication
5. IP Connectivity
6. Service Request
7. Radio Access bearer
8. Scheduling requests and grants
9. Handover
10. Release
Imagine you are riding a Taxi and you pick up your phone to send a whatsapp Text. Trace the steps of the process. In the subsequent sections we will take a look at each aspect

LTE-RAN Overview



Radio Access Network:

Interfaces – Uu, S1 and X2

Scalable BW – 1.4, 3, 5, 10, 15, 20 MHz

Latency - < 100 msec (C-Plane) and < 5 msec (U-Plane)

Mobility support for low (< 15 Km/h) and high speeds ( upt 500 Km/h)

Downlink uses OFDM (orthogonal Frequency division multiplexing)

Uplink uses SC-FDMA (single carrier frequency divison multiple Access)

E-UTRA
Downlink: 300 Mbps
Uplink: 75 Mbps
OFDM and MIMO
Using 20 MHz

LTE Frequency Bands.
OFDM converts a single carrier system to n-carrier one. The advantage is that data rate of each subcarrier is 1/n of total data rate, which expands symbol time by a factor of n. We love large symbol time as it makes the system robust against intersymbol interference (ISI)

Radio Access network contd.
LTE Downlink
OFDMA
High Spectral Efficiency
Robust against Multipath
Support for MIMO
Time and frequency allocation
OFDM converts a single carrier system to n-carrier one. The advantage is that data rate of each subcarrier is 1/n of total data rate, which expands symbol time by a factor of n. We love large symbol time as it makes the system robust against intersymbol interference (ISI)

Radio Access network contd.
SC-FDMA
Reduced Peak-to-average Power Ratio
Better Cell-edge performance due to low PAPR
LTE Uplink
A major challenge associated with OFDM is high PAPR of the transmitted signal. This is a consequence of the IFFT summing of multiple independent symbols, which are all integer number of cycle over the symbol time; whenever they add constructively the result is a high peak power.

SC-FDMA also has High PAPR but it is overcome by transmitted symbols sequentially rather in parallel.

OFDMA
Several multiple access techniques exist – TDMA, FDMA, CDMA, OFDMA
OFDMA is not new and has existed for quite some time.
The idea is to divide entire bandwidth into chunks called subcarriers. These subcarriers can then be allocate in time and frequency domain.
Subcarriers are orthogonal in nature.

OFDMA Contd.

OFDMA Contd.
In LTE transmission happens every 1 msec a.k.a TTI (transmit time interval)
Concepts –
Slot
Symbol
Sub frame
Radio Frame

OFDMA Contd.

LTE FDD vs TDD

Multiple Antenna Techniques in LTE
Transmit and Receive diversity
SU-MIMO and MU-MIMO
Beamforming

Multiple Antenna Techniques
Diversity
MIMO
Beamforming
Receive Div.
Transmit Div
SU-MIMO
MU-MIMO

Multiple Antenna Technologies contd.
Downlink
Uplink
Intelligent use of space, time and frequency to send multiple copies of signal at receiver (UE)
Multiple antennas at receiver to leverage the signal variation in space by suitable combing copies of signal sent by UE
Each color represents an antenna
2x2 Antenna System

Multiple Antenna Technologies contd. SU-MIMO
Downlink
Bit Stream for UE is divided among Antenna elements. Each element sends a different Bit stream effectively doubling the throughput
UE receives bit streams from both antennas and combines them to receive data at twice the speed compared to TxD
2x2 Antenna System
Each color represents an antenna

Multiple Antenna Technologies contd. MU-MIMO
Downlink
Bit Streams for UEs is divided among Antenna elements. Each element sends a different Bit stream effectively doubling the throughput
UEs receives bit streams from both antennas and combines them to receive data at twice the speed compared to TxD
2x2 Antenna System
Each color represents an antenna

Physical Channels in LTE:
Physical broadcast Channel – Transmits broadcast and system overhead information.
Physical Downlink Control Channel. Transmits control messages for UE (power control, scheduling assignments)
Physical Downlink Shared Channel. Transmits user data.
Physical Control Format Indicator Channel. Indicates number of OFDM symbols used for control information.
Physical Hybrid Indicator. Transmits ACK/NACk for uplink data.
Uplink
Downlink
Physical Random Access Channel. Carries RA request from UE.
Physical Uplink Shared Channel. Carries Uplink data.
Physical Uplink Control Channel. Carrier information re channel quality, acknowledgements, scheduling requests
What is a channel ? It is like a path that has a specific function.
Channel – think of it as a transport mechanism that leads to a specific destination and has a specific purpose. Airports for planes, railway station for trains

Protocol Stack in LTE:
MME

LTE-EPC Overview

Life Cycle of a UE
1. Network Acquisition
2. Signaling connection
3. Attach
4. Authentication
5. IP Connectivity
6. Service Request
7. Radio Access bearer
8. Scheduling requests and grants
9. Handover
10. Release
Tasks in Red boxes are mainly controlled by EUTRAN. Rest are controlled BY EPC

LTE-EPC:

Mobility Management Entity (MME):
MME is responsible for the following functions in EPC –
Managing and storing UE contexts
Generating temporary UE Identifiers
Managing Idle state mobility
Distributing Paging messages
Controlling Security functions such as authentication
Controlling EPS bearers
Selection of S-GW and P-GW


Mobility Management Entity (MME):
SCTP (Stream control transmission protocol) is a tunneling protocol used between eNodeB and MME. S1-AP uses SCTP.

Home Subscriber Server (HSS):
HSS is responsible for the following functions in EPC –
Master database that stores subscription related information to support call control and session management entities
Storehouse for subscription profiles and user Identities
Involved in User authentication
Works with MME to authenticate user

Serving Gateway (S-GW):
SGW is responsible for the following functions in EPC –
Anchor for inter-enodeb handover in LTE
Buffers data in downlink for Idle mode Users until they are
In connected state
Generated Usage records which can be used
for billing
The S1 user-plane interface (S1-U) is a standard reference point between the eNB
and the S-GW. The S1-U interface provides non-guaranteed delivery of userplane
PDUs between the eNB and the S-GW. The user-plane protocol stack on
the S1 interface is shown in Fig. The transport network layer is built on IP
transport and GTP-U is used on top of UDP/IP to carry the user-plane PDUs
between the eNB and the S-GW.

Packet Gateway (P-GW):
PGW is responsible for the following functions in EPC –
Acts as router for the UE traffic
Allocated IP address to the UE/bearer
Performs DSCP/QoS marking for UE packets
The S1 user-plane interface (S1-U) is a standard reference point between the eNB
and the S-GW. The S1-U interface provides non-guaranteed delivery of userplane
PDUs between the eNB and the S-GW. The user-plane protocol stack on
the S1 interface is shown in Fig. The transport network layer is built on IP
transport and GTP-U is used on top of UDP/IP to carry the user-plane PDUs
between the eNB and the S-GW.

LTE-EPC:
Wrap up.

LTE-EPC:
Wrap up.

Thanks
Wrap up.

LTE-UE Categories

UE Categories:
UE category of a UE represents a set of functions/capablities the UE is capable of performing.
Categories are defined by 3GPP in the document 3GPP TS 36.306
A single UE category defines both the uplink and downlink capabilities. This is different from UMTS which uses separate categories for HSDPA and HSUPA
UE capabilities are transferred to the EUTRAN during the “UE Capability information exchange” procedure.

UE Categories:

LTE-Advanced Overview

LTE Advanced:
LTE-Advanced (LTE Rel 10/11) extended the capabilities of LTE Rel-8/9 by introducing new features -
Carrier Aggregation
Enhanced Multi-Antenna techniques (SU-MIMO and MU-MIMO) – Discussed in section on multiple antenna techniques before.
Coordinated Multi-point operation (COMP)
Enhancements to UE Categories

Wrap up.

Carrier Aggregation:
LTE Rel-8/9 specified system bandwidths of 1.4, 3, 5, 10, 15, and 20 MHz to meet different spectrum deployment requirements. Support of wider bandwidths up to 100 MHz was one of the distinctive features of IMT-Advanced systems. The IMT-Advanced systems targeted peak data rates in excess of 1 Gbps for low mobility and 100 Mbps for high mobility scenarios. In order to support wider transmission bandwidths, LTE Rel-10 introduced the carrier aggregation concept where two or more component carriers with arbitrary bandwidths belonging to the same or different frequency bands could be aggregated.

Enables operators to use different chunks of spectrum in combination to deliver greater throughputs to UEs.

Enables network operator to use fragmented pieces of spectrum. Not all operators are spectrum rich.

Operators can use up to 100 MHz of combine bandwidth

Wrap up.

Carrier Aggregation:
Deployment Scenarios:

Intra-band contiguous carrier aggregation
Intra-band non-contiguous carrier aggregation
Inter-band non-contiguous carrier aggregation

Each of the CC (Component Carrier) can be 1.4,3,5,10,15 or 20 MHz.
CC is a component carrier
In FDD systems, a serving cell comprises a pair of
different carrier frequencies for downlink and uplink transmissions, whereas for
TDD, a serving cell is defined as a single-carrier frequency where downlink and
uplink transmissions occur in different transmission time intervals. Given that
component carriers do not have to be contiguous in frequency which enables
utilization of fragmented spectrum, operators with a fragmented spectrum can
provide high data-rate services based on the availability of a virtually wide
bandwidth even though they do not own a single wideband spectrum allocation.

Carrier Aggregation:
Fc1 and fc2 are 2 frequencies with similar coverage
Fc1 and fc2 are 2 frequencies with different coverage
CC is a component carrier
In FDD systems, a serving cell comprises a pair of
different carrier frequencies for downlink and uplink transmissions, whereas for
TDD, a serving cell is defined as a single-carrier frequency where downlink and
uplink transmissions occur in different transmission time intervals. Given that
component carriers do not have to be contiguous in frequency which enables
utilization of fragmented spectrum, operators with a fragmented spectrum can
provide high data-rate services based on the availability of a virtually wide
bandwidth even though they do not own a single wideband spectrum allocation.

Coordinated Multipoint (COMP):
We need comp to combat effects of interference
An UE can experience Interference even when MIMO is being used.
- SU-MIMO (Inter Stream interference)
- MU-MIMO (inter User interference)
Interference can be from neighboring cells/sites as well.
Quality of a channel is depicted by SINR (Signal to interference plus
noise ratio (SINR)
SINR = (Signal )/(Interference + Noise)
High SINR means better quality
Low SINR means low quality
As SINR decreases so does throughput therefore interference can
impact throughput => implies we need interference control

Take a look at the different interference scenarios. Interference decrease SINR which leads to decrease in throughput. Coz of increase in BER

Coordinated Multipoint (COMP):
COMP can be implemented in DL or UL
Each of the these implementations is meant to reduce interference.

DL COMP
Join Processing
Coordinated Scheduling/Beamforming
Take a look at the different interference scenarios. Interference decrease SINR which leads to decrease in throughput. Coz of increase in BER

Coordinated Multipoint (COMP):
Each of the these implementations is meant to reduce interference.

UL COMP
Joint Reception
Coordinated Scheduling/Beamforming
Take a look at the different interference scenarios. Interference decrease SINR which leads to decrease in throughput. Coz of increase in BER

UE Categories – Updated!
Take a look at the different interference scenarios. Interference decrease SINR which leads to decrease in throughput. Coz of increase in BER

Thanks

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