LTE Basic Principle

LTE Basic Principle
9/13/2020 1
Prepared by:
Eng:AbdulEllah Qasim

Course Contents
1) Introduction.
2) LTE/SAE Key feature.
3) LTE/SAE Air Interface.
4) LTE/SAE Network Elements(Architecture).
5) LTE/SAE Network Interfaces.
6) SAE/LTE Interworking with 2G/3G Networks.
7) SAE/LTE Interworking with cdma2000 Networks.
8) LTE-Channel.
10) Basic Signaling inter eNB handover.
9/13/2020 2

LTE Introduction
9/13/2020 3
LTE evolution
Although there are major step changes between LTE and its 3G predecessors, it is nevertheless looked upon
as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different form of radio interface, using
OFDMA / SC-FDMA instead of CDMA, there are many similarities with the earlier forms of 3G architecture
and there is scope for much re-use.LTE can be seen for provide a further evolution of functionality, increased
speeds and general improved performance.
WCDMA
(UMTS)
HSPA
HSDPA / HSUPA
HSPA+ LTE
Max downlink speed
bps
384 k 14 M 28 M 100M
Max uplink speed
bps
128 k 5.7 M 11 M 50 M
Latency
round trip time
approx
150 ms 100 ms 50ms (max) ~10 ms
3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8
Approx years of initial
roll out
2003 / 4 2005 / 6 HSDPA
2007 / 8 HSUPA
2008 / 9 2009 / 10
Access methodology CDMA CDMA CDMA OFDMA / SC-FDMA
In addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6.
There is also no basic provision for voice, although this can be carried as VoIP.

Introduction
9/13/2020 4
LTE has introduced a number of new technologies when compared to the previous cellular systems.
They enable LTE to be able to operate more efficiently with respect to the use of spectrum, and also
to provide the much higher data rates that are being required.
OFDM (Orthogonal Frequency Division Multiplex): OFDM technology has been incorporated into
LTE because it enables high data bandwidths to be transmitted efficiently while still providing a high
degree of resilience to reflections and interference. The access schemes differ between the uplink
and downlink: OFDMA (Orthogonal Frequency Division Multiple Access is used in the downlink;
while SC-FDMA(Single Carrier - Frequency Division Multiple Access) is used in the uplink. SC-FDMA
is used in view of the fact that its peak to average power ratio is small and the more constant power
enables high RF power amplifier efficiency in the mobile handsets - an important factor for battery
power equipment.
MIMO (Multiple Input Multiple Output): One of the main problems that previous
telecommunications systems has encountered is that of multiple signals arising from the many
reflections that are encountered. By using MIMO, these additional signal paths can be used to
advantage and are able to be used to increase the throughput. When using MIMO, it is necessary
to use multiple antennas to enable the different paths to be distinguished. Accordingly
schemes using 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used. While it is relatively easy to
add further antennas to a base station, the same is not true of mobile handsets, where the
dimensions of the user equipment limit the number of antennas which should be place at
least a half wavelength apart.

LTE specification overview
9/13/2020 5
PARAMETER DETAILS
Peak downlink speed
64QAM
(Mbps)
100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO)
Peak uplink speeds
(Mbps)
50 (QPSK), 57 (16QAM), 86 (64QAM)
Data type All packet switched data (voice and data). No circuit
switched.
Channel bandwidths
(MHz)
1.4, 3, 5, 10, 15, 20
Duplex schemes FDD and TDD
Mobility 0 - 15 km/h (optimised),
15 - 120 km/h (high performance)
Latency Idle to active less than 100ms
Small packets ~10 ms
Spectral efficiency Downlink: 3 - 4 times Rel 6 HSDPA
Uplink: 2 -3 x Rel 6 HSUPA
Access schemes OFDMA (Downlink)
SC-FDMA (Uplink)
Modulation types supported QPSK, 16QAM, 64QAM (Uplink and downlink)

LTE/SAE Key Features – EUTRAN 1/2
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SAE (System Architecture Evolution): With the very high data rate and low latency
requirements for 3G LTE, it is necessary to evolve the system architecture to enable
the improved performance to be achieved. One change is that a number of the
functions previously handled by the core network have been transferred out to the
periphery. Essentially this provides a much "flatter" form of network architecture.
In this way latency times can be reduced and data can be routed more directly to
its destination.
SAE Features:
Evolved NodeB(eNB)
•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

LTE/SAE Key Features – EUTRAN 2/2
9/13/2020 7
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 them
dynamically to users and channels
•This provides greater flexibility than the older system
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 services
Self configuration
•Currently under investigation
•Possibility to let Evolved Node Bs configure themselves
•It will not completely substitute the manual configuration and optimization.

LTE/SAE Key Features – EPC
(Evolved Packet Core)
9/13/2020 8
Packet Switched Domain only
No circuit switched domain is provided
If CS applications are required, they must be implemented via IP
Only one mobility management for the UE in LTE.
3GPP (GTP) or IETF (MIPv6) option
The EPC can be based either on 3GPP GTP protocols (similar to PS domain in
UMTS/GPRS) or on IETF Mobile IPv6 (MIPv6)
Non-3GPP access
The EPC will be prepared also to be used by non-3GPP access networks (e.g. LAN,
WLAN, WiMAX, etc.)
This will provide true convergence of different packet radio access system

LTE/SAE Air Interface 1/3
9/13/2020 9
OFDMA
•Downlink multiplexing
•Orthogonal Frequency Division Multiple Access
•Receiver complexity is at a reasonable level
•it supports various modulation schemes from BPSK,
QPSK, 16QAM to 64 QAM.
SC-FDMA
•Uplink multiplexing
•Single Carrier Frequency Division Multiple Access, a
variant of OFDMA
•The advantage against OFDMA to have a lower PAPR
(Peak-to-Average Power Ratio) meaning less power
consumption and less expensive RF amplifiers in the
terminal.
64QAM
Modulation

9/13/2020 10
MIMO
•Multiple Input Multiple Output
•LTE will support MIMO as an option,
•It describes the possibility to have multiple
transmitter and receiver antennas in a system.
•Up to four antennas can be used by a single LTE cell
(gain: spatial multiplexing)
•MIMO is considered to be the core technology to
increase spectral efficiency.
HARQ
•Hybrid Automatic Retransmission on request
•HARQ has already been used for HSDPA and HSUPA.
•HARQ especially increases the performance (delay and
throughput) for cell edge users.
• HARQ simply implements a retransmission protocol
on layer 1/layer 2 that allows to send retransmitted
blocks with different coding than the first one.
HARQ Hybrid
Automatic
Repeat Request

9/13/2020 11
Scalable bandwidth
• LTE air interface allows to drive cells with
1.4 MHz, 3 MHz, 5 MHz, 10MHz & 20 MHz
•This gives the required flexibility for
operators to use spectrum allocations not
available to a non-scalable wide-band or
ultra-wide-band system.
DL: OFDMA
UL: SC-FDMA
scalable

Requirements for LTE Air Interface
9/13/2020 12
DOWNLINK
UPLINK
HSUPA (Rel6) Target SAE/LTE
Peak Bit Rate
(Mbps)
5.67 > 50 57
Spectral
Efficiency
(bps/Hz/cell)
0.26 2..3 times
HSUPA
0.67
SC-FDMA (Single Carrier Frequency Division Multiple Access)
SC-FDMA is technically close to OFDMA, but is more power
efficient
OFDMA (Orthogonal Frequency Division Multiple Access)
HSDPA (Rel6) Target SAE/LTE
Peak Bit Rate
(Mbps)
14.4 > 100 144
Spectral
Efficiency
(bps/Hz/cell)
0.75 3..4 times
HSDPA
1.84

LTE/SAE Network Elements
9/13/2020 13
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
Evolved
Node B
(eNB)
cell
LTE-Uu
LTE-UE

Evolved Node B (eNB)
9/13/2020 14
•It is the only network element defined as
part of EUTRAN.
•It replaces the old Node B / RNC
combination from 3G.
•It terminates the complete radio interface
including physical layer.
•It provides all radio management
functions
•An eNB can handle several cells.
•To enable efficient inter-cell radio
management for cells not attached to the
same eNB, there is a inter-eNB interface X2
specified. It will allow to coordinate inter-
eNB handovers without direct involvement
of EPC during this process.
Inter-cell RRM: HO, load balancing between cells
Radio Bearer Control: setup, modifications and
release of Radio Resources
Connection Mgt. Control: UE State Mgmt. MME-UE
Connection
Radio Admission Control
eNode B Measurements
Collection and evaluation
Dynamic Resource
Allocation (Scheduler)
eNB Functions
IP Header Compression/ de-compression
Access Layer Security: ciphering and integrity
protection on the radio interface
MME Selection at Attach of the UE
User Data Routing to the SAE GW.
Transmission of Paging Message coming from MME
Transmission of Broadcast Info (System info, MBMS)
Evolved
Node B
(eNB)cell
LTE-Uu
LTE-UE

Mobility Management Entity (MME)
9/13/2020 15
Evolved
Node B
(eNB)
MME
Serving
Gateway
S1-U
S1-MME
S11
HSS
S6a
• It is a pure signaling entity inside the EPC.
• SAE uses tracking areas to track the position of idle UEs.
The basic principle is identical to location or routing areas
from 2G/3G.
• MME handles attaches and detaches to the SAE system, as
well as tracking area updates
• Therefore it possesses an interface towards the HSS (home
subscriber server) which stores the subscription relevant
information and the currently assigned MME in its
permanent data base.
• A second functionality of the MME is the signaling
coordination to setup transport bearers (SAE bearers)
through the EPC for a UE.
• MMEs can be interconnected via the S10 interface
• It generates and allocates temporary ids for UEs
Non-Access-Stratum (NAS)
Signalling
Idle State Mobility Handling
Tracking Area updates
Security (Authentication,
Ciphering, Integrity protection)
Trigger and distribution of
Paging Messages to eNB
Roaming Control (S6a interface
to HSS)
Inter-CN Node Signaling
(S10 interface), allows efficient
inter-MME tracking area updates
and attaches
Signalling coordination for
SAE Bearer Setup/Release & HO
Subscriber attach/detach
Control plane NE in EPC
MME Functions

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Packet Data Network (PDN) SAE Gateway
MME
Serving
Gateway
S5/S8
PDN SAE
Gateway
PDN
SGi
PCRF
S7 Rx+
S11
S6a
Policy Enforcement (PCEF)
Per User based Packet Filtering (i.e.
deep packet inspection)
Charging Support
PDN Gateway Functions
IP Address Allocation for UE
Packet Routing/Forwarding between
Serving 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)
Lawful Interception support
• The PDN gateway provides the connection
between EPC and a number of external data
networks.
• Thus it is comparable to GGSN in 2G/3G
networks.
• A major functionality provided by a PDN gateway
is the QoS coordination between the external PDN
and EPC.
• Therefore the PDN gateway can be connected via
S7 to a PCRF (Policy and Charging Rule Function).
• If a UE is connected simultaneously to several
PDNs this may involved connections to more than
one PDN-GW

Policy and Charging Rule Function (PCRF)
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MME
Serving
Gateway
S5/S8
PDN SAE
Gateway
PDN
SGi
PCRF
S7 Rx+
S11
S6a
Charging Policy: determines how
packets should be accounted
PCRF: Policy & Charging Rule
Function
QoS policy negotiation with PDN
• 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 the external Data network (PDN)
• This function can be used to check and modify the QoS associated with a SAE bearer setup
from SAE or to request the setup of a SAE bearer from the PDN.
•This QoS management resembles the policy and charging control framework introduced for
IMS with UMTS release 6.

Home Subscriber Server (HSS)
9/13/2020 18
MME
HSS
S6a
Permanent and central subscriber
database
HSS Functions
Stores mobility and service data for
every subscriber
Contains the Authentication Center
(AuC) functionality.
• The HSS is already introduced by UMTS
release 5.
• With LTE/SAE the HSS will get additionally
data per subscriber for SAE mobility and
service handling.
•Some changes in the database as well as in
the HSS protocol (DIAMETER) will be
necessary to enable HSS for LTE/SAE.
•The HSS can be accessed by the MME via
S6a interface.

LTE/SAE Network Interfaces
9/13/2020 19
LTE-UE
MME S10
S6a
Serving
Gateway
S1-U
S11
S1-MME
PDN
Gateway
PDN
PCRF
S7
Rx+
SGiS5/S8
Evolved
Node B
(eNB)
cell
X2
LTE-Uu
HSS
MME: Mobility Management Entity
SAE
Gateway
User plane
Control Plane
Control Plane + User plane

LTE Radio Interface and the X2 Interface
9/13/2020 20
(E)-RRC 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
IP
L1/L2
TS 36.424
X2-UP
(User Plane)
X2-CP
(Control Plane)
X2-AP
SCTP
IP
L1/L2TS 36.421
TS 36.422
TS 36.423
TS 36.421
TS 36.420
[currently also in TS 36.300 §20]
NAS Protocols
Control Plane User Plane
TS 36.223
TS 36.331
LTE-Uu
Air interface of EUTRAN
Based on OFDMA in downlink and SC-FDMA in uplink
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 signaling protocol
During HO, Source eNB can use the X2 interface to
forward downlink packets still buffered or arriving
from the serving gateway to the target eNB.
This will avoid loss of a huge amount of packets during
inter-eNB handover.

S1-MME & S1-U Interfaces
9/13/2020 21
MME
Serving
Gateway
S1-MME
(Control Plane)
S1-U
(User Plane)
NAS Protocols
S1-AP
SCTP
IP
L1/L2
User PDUs
GTP-U
UDP
IP
L1/L2
TS 36.411
TS 36.411
TS 36.412
TS 36.413
TS 36.414
TS 36.410
[currently in TS 36.300 §19]
eNB
S1-MME
Control interface between eNB and MME
S1flex allows 1 eNB to connect to several MME
MME and UE will exchange non-access stratum
signaling via eNB through this interface.
E.g.: if a UE performs a tracking area
update the TRACKING AREA UPDATE
REQUEST message will be sent from UE to eNB
and the eNB will forward the message via S1-
MME to the MME.
S1AP:S1 Application Protocol
S1-U
User plane interface between eNB and serving
gateway.
It is a pure user data interface (U=User plane).
S1flex-U also supported: a single eNB can connect to
several Serving GWs.
Which Serving GW a user’s SAE bearer will have to
use is signaled from the MME of this user.

S10 & S6a Interfaces
9/13/2020 22
S10
Interface between different MMEs
Used during inter-MME tracking area updates
The new MME can contact the old MME the user
had been registered before to retrieve data
about identity (IMSI), security information
(security context, authentication vectors) and
active SAE bearers (PDN gateways to contact,
QoS, etc.)
Obviously S10 is a pure signaling interface, no
user data runs on it.
S6a
Interface between the MME and the HSS
The MME uses it to retrieve subscription
information from HSS (handover/tracking
area restrictions, external PDN allowed,
QoS, etc.) during attaches and updates
The HSS can during these procedures also
store the user’s current MME address in its
database.
MME
HSS
S6a
(Control Plane)
S6a Appl.
SCTP
IP
L1/L2
DIAMETER
TR 29.801
MME
S10
(Control Plane)
UDP
IP
L1/L2
GTP-C
TR 29.801

S11 & S5/S8 Interfaces
9/13/2020 23
Serving
Gateway
PDN
Gateway
PDN
Sgi
S5/S8 GTP Candidates
(Control and User Plane)
User PDUs
GTP-U
UDP
IP
L1/L2
GTP-C
TS 23.401 / TR 29.801
MME
UDP
IP
L1/L2
GTP-C
S5/S8 IETF Candidates
(Control and User Plane)
User PDUs
MIPv6
Tunneling
Layer
IPv4/IPv6
L1/L2
PMIPv6
TS 23.402 / TR 29.801
IPv4
IPv6
S11
Interface between MME and a Serving
GW
A single MME can handle multiple
Serving GW each one with its own S11
interface
Used to coordinate the establishment
of SAE bearers within the EPC
SAE bearer setup can be started by the
MME (default SAE bearer) or by the
PDN Gateway.
S11
(Control Plane)
S5/S8
Interface between Serving GW and PDN GW
S5: If Serving GW and PDN GW belong to the
same network (non-roaming case)
S8:If this is not the case (roaming case)
S8 = S5 + inter-operator security functions
Mainly used to transfer user packet data
between PDN GW and Serving GW
Signaling on S5/S8 is used to setup the
associated bearer resources
S5/S8 can be implemented either by reuse of
the GTP protocol from 2G/3G or by using
Mobile IPv6 with some IETF enhancements.

S7 & SGi Interfaces
9/13/2020 24
PDN
Gateway
IMS/PDN
PCRF
S7 (Control Plane)
SGi
(User Plane)
Application
UDP or TCP
IPv4/IPv6
L1/L2
S7 Application
SCTP
IP
L1/L2
TR 23.401
DIAMETER
SGi
Interface used by the PDN GW to send and receive data to and from the
external data network
It is typically either IPv4 or IPv6 based
Downlink data coming from the external PDN must be assigned to the right
SAE bearer of the right user by analysis of the incoming packet’s IP addresses,
port numbers, etc.
This interface corresponds to the Gi interface in 2G/3G networks
S7 (Also referred as Gx)
Interface between PDN
GW and PCRF (Policy and
Charging Rule Function)
It allows:
-the PCRF to request the
setup of a SAE bearer
with appropriate QoS
-allows the PDN GW to
ask for the QoS of an SAE
bearer to setup
-to indicate EPC status
changes to the PCRF to
apply a new policy rule.

Rx+ Interface
9/13/2020 25
Rx+
Interface between PCRF(Policy & Charging Rules
Function) and the external PDN network/operators
IMS
Standardized in 3GPP TS 23.203.
Rx+
(Control Plane)
PDN
Gateway
PDN
PCRF
S7
SGi
RX+ Application
SCTP
IP
L1/L2
TR 23.203
DIAMETER

SAE/LTE Interworking with 2G/3G Networks
9/13/2020 26
LTE-UE
MME
S6a
Serving
Gateway
S1-U
S11
S1-MME
PDN
Gateway
PDN
PCRF
S7
Rx+
SGiS5/S8
HSS
SGSN
S3
UTRAN
Iu-PS
S4
Evolved
Node B
(eNB)
cell
LTE-Uu
GERAN
Gb
Gr
GGSN
Gn
PDN
Gi

S3 & S4 Interfaces
9/13/2020 27
S4
(User Plane)
SGSN
MME
Serving
Gateway
S3
(Control Plane)
UDP
IP
L1/L2
GTP-C
TR 29.801 / TS 23.401
UDP
IP
L1/L2
GTP-U
TR 29.801 / TS 23.401
User PDUs
S3/S4
Interfaces between EPC and 2G/3G packet switched core network domain
They would allow inter-system changes between SAE and 2G/3G
The S3 is a pure signalling interface used to coordinate the inter-system change between MME and
SGSN
The S4 is the user plane interface and it is located between SGSN and Serving SAE GW.
These 2 interfaces are based on the Gn interface between the SGSN and the GGSN.
This would allow to either forward packet data from EUTRAN via Serving SAE GW to SGSN (and then
to GGSN) or from 2G/3G RAN to SGSN to Serving SAE GW to PDN GW.

SAE/LTE Interworking with 3G - Alternative
9/13/2020 28
MME
S6a
Serving
Gateway
S1-U
S11
S1-MME
PDN
Gateway
PDN
PCRF
S7
Rx+
SGiS5/S8
HSS
SGSN
S3S4
UTRAN
Iu-PS
Evolved
Node B
(eNB)
cell
LTE-Uu
GERAN
Gb
Gr
GGSN
Gn
PDN
Gi
S12
Direct Tunnels from
Serving GW to RNC
(User Plane)

S12 Interface
9/13/2020 29
Serving
Gateway
UDP
IP
L1/L2
GTP-U
TR 29.801 / TS 23.401
User PDUs
UTRAN
S12
(User Plane)
S12
Interfaces between EPC and 3G Radio access network
It would allow inter-system changes between SAE and 3G
The S12 is the user plane interface used for tunneling user data directly between the
Serving SAE GW and the UTRAN.
This would allow to forward packet data from 3G RAN to Serving SAE GW to PDN GW.
It is based on the Gn interface between the SGSN and the GGSN and so uses the GTP-U
protocol.

SAE/LTE Interworking with cdma2000 Networks
9/13/2020 30
LTE-UE
MME
S6a
Serving
Gateway
S1-U
S11
S1-MME
PDN
Gateway
PDN
PCRF
S7
Rx+
SGiS5/S8
HSS
S103
S101
Evolved
Node B
(eNB)
cell
LTE-Uu
A11
HSGW
PDN
eHRPD
Access
Network
Cdma2000 Network (eHRPD) S2a

S101 & S103 Interfaces
9/13/2020 31
SGSN
S101(Control
Plane)
UDP
IP
L1/L2
S101-APeHRPD
Access
Network
S103
(User Plane)
Serving
Gateway
(LTE)
UDP
IP
L1/L2
User PDUs
HSGW
(cdma2000)
GRE
S101/S103
Interfaces between EPC and cdma2000
They would allow inter-system changes between LTE and cdma2000
The S101 is a pure signaling interface used to coordinate the inter-system change
between MME and SGSN
The S103 is the user plane interface and it is located between the Serving GW and the
HSGW.

MIMO
9/13/2020 32
MIMO stands for Multiple Input Multiple Output.
It is a key technology to increase a channel’s capacity by using multiple transmitter and
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.

Downlink Peak Bit Rate
9/13/2020 33
2x2 MIMO (2 antennas for TX, 2 Antennas for RX)
64QAM
Control overhead 7.1%
Reference symbol overhead 7.7%
172 Mbps in 20 MHz and 86 Mbps in 10 MHz
Resource blocks 6 15 25 50 100
Subcarriers 72 180 300 600 1200
Modulation coding 1.4 MHz 3.0 MHz 5.0 MHz 10 MHz 20 MHz
QPSK 1/2 Single stream 0.9 2.2 3.6 7.2 14.4
16QAM 1/2 Single stream 1.7 4.3 7.2 14.4 28.8
64QAM 3/4 2x2 MIMO 7.8 19.4 32.4 64.8 129.6
64QAM 1/1 2x2 MIMO 10.4 25.9 43.2 86.4 172.8
64QAM 1/1 4x4 MIMO 20.7 51.8 86.4 172.8 345.6

Uplink Peak Bit Rate
9/13/2020 34
Single stream transmission with 64QAM assumed
Reference symbol overhead 14.3%
One resource block for Physical Uplink Control Channel (PUCCH)
85 Mbps in 20 MHz and 42 Mbps in 10 MHz
Resource blocks 5 14 24 49 99
Subcarriers 60 168 288 588 1188
Modulation coding 1.4 MHz 3.0 MHz 5.0 MHz 10 MHz 20 MHz
QPSK 1/2 Single stream 0.7 2.0 3.5 7.1 14.3
64QAM 1/1 V-MIMO (cell) 8.6 24.2 41.5 84.7 171.1

LTE UE Categories
9/13/2020 35
• All categories support 20 MHz
• 64QAM mandatory in downlink, but not in uplink (except Class 5)
• 2x2 MIMO mandatory in other classes except Class 1

LTE-Channel
9/13/2020 36
Physical channels: These are transmission channels that carry user data and control
messages.
Transport channels: The physical layer transport channels offer information transfer
to Medium Access Control (MAC) and higher layers.
Logical channels: Provide services for the Medium Access Control (MAC) layer within
the LTE protocol structure.

Physical Channels
9/13/2020 37
Uplink:
Physical Uplink Control Channel (PUCCH) : A physical uplink control channel is a
transmission channel that is used to transport user signaling data from one or more
mobiles that can transmit on the control channel. The PUCCH transports the
acknowledgment responses and retransmission requests (ARQ, ACK, NAK), sends
service scheduling requests, and transfers channel quality information measured by the
mobile to the system.
Physical Uplink Shared Channel (PUSCH) : This physical channel found on the LTE uplink is
the Uplink counterpart of PDSCH(Transmit user data)
Physical Random Access Channel (PRACH) : This uplink physical channel is used for random
access functions. (Transmit random access preamble)

Physical Channels
9/13/2020 38
Downlink:
Physical Broadcast Channel (PBCH): This physical channel carries system information for UEs requiring to
access the network.
Physical Control Format Indicator Channel (PCFICH) : Informs the UE about the number of OFDM symbols
used for the PDCCHs.
Physical Downlink Control Channel (PDCCH) : The main purpose of this physical channel is to carry
mainly scheduling information.
Physical Hybrid ARQ Indicator Channel (PHICH) : As the name implies, this channel is used to report the
Hybrid ARQ status.
Physical Downlink Shared Channel (PDSCH) : This channel is used for uncast and paging functions.
Physical Multicast Channel (PMCH) : This physical channel carries system information for multicast
purposes.
Physical Control Format Indicator Channel (PCFICH) : This provides information to enable the UEs to
decode the PDSCH.

Transport Channels
9/13/2020 39
Downlink:
Broadcast Channel (BCH) : The LTE transport channel maps to Broadcast
Control Channel (BCCH)
Downlink Shared Channel (DL-SCH) : This transport channel is the main
channel for downlink data transfer. It is used by many logical channels.
Paging Channel (PCH) : To convey the PCCH
Multicast Channel (MCH) : This transport channel is used to transmit
MCCH information to set up multicast transmissions.
Uplink:
Uplink Shared Channel (UL-SCH) : This transport channel is the main channel
for uplink data transfer. It is used by many logical channels.
Random Access Channel (RACH) : This is used for random access requirements.

Logical Channels
9/13/2020 40
Control channels:
Broadcast Control Channel (BCCH) : This control channel provides system information to all mobile
terminals connected to the eNodeB.
Paging Control Channel (PCCH) : This control channel is used for paging information when searching a
unit on a network.
Common Control Channel (CCCH) : This channel is used for random access information, e.g. for actions
including setting up a connection.
Multicast Control Channel (MCCH) : This control channel is used for Information needed for multicast
reception.
Dedicated Control Channel (DCCH) : This control channel is used for carrying user-specific control
information, e.g. for controlling actions including power control, handover, etc..
Traffic channels:
Dedicated Traffic Channel (DTCH) : This traffic channel is used for the transmission of user data.
Multicast Traffic Channel (MTCH) : This channel is used for the transmission of multicast data.

LTE Radio Frames, Slots and Sub frames
FDD mode bit rate calculation
9/13/2020 41
The basic EUTRAN Radio Frame is 10 ms long.
The EUTRAN Radio Frame is divided into 20 slots, each one 0.5 ms long.
Always two slots together form a sub frame. The sub frame (1 ms) is the smallest
time unit the scheduler assigns to physical channels.
In case of FDD there is a time offset between uplink and downlink transmission.
Slot
#0
Slot
#1
Slot
#2
Slot
#3
Slot
#16
Slot
#17
Slot
#18
Slot
#19
. . .
Slot
#0
Slot
#1
Slot
#2
Slot
#3
Slot
#16
Slot
#17
Slot
#18
Slot
#19
. . .
f
DL carrier
UL carrier
radio frame 10 ms
radio frame 10 ms
subframe 0 subframe 1 subframe 8 subframe 9
DL/ULTimeoffset
time

LTE Radio Frames, Slots and Sub frames
FDD mode bit rate calculation
9/13/2020 42
If TDD mode is used, sub frame 0 and sub frame 5 must be downlink, all other sub
frames can dynamically be used as uplink or downlink period.
Slot
#0
Slot
#1
Slot
#2
Slot
#3
Slot
#16
Slot
#17
Slot
#18
Slot
#19
. . .
f
time
UL/DL
carrier
radio frame 10 ms
. . .
Downlink Sub frame Uplink Sub frame

LTE Frame Structure
9/13/2020 43
The number of
Symbols per Slot
(0.5 ms) could be
6 or 7 depending
on the Cyclic
Prefix length
(Refer to next
slide for details)

LTE Slot
9/13/2020 44
The LTE Slot carries:
• 7 symbols with short cyclic prefix
• 6 symbols with long prefix

OFDM Resource Block for LTE/EUTRAN
9/13/2020
• EUTRAN combines OFDM symbols in so
called resource blocks RB.
• A single resource block is always 12
consecutive subcarriers during one
subframe (2 slots, 1 ms):
• 12 subcarriers * 15 kHz=
180 kHz
•It is the task of the scheduler to assign
resource blocks to physical channels
belonging to different users or for general
system tasks.
•A single cell must have at least 6 resource
blocks (72 subcarriers) and up to 110 are
possible (1320 subcarriers).
frequency
time
Subcarriers
Sub frame 1ms
Subcarrier
Bandwidth
15kHz
Bandwidth
180kHz
Slot Slot

9/13/2020 46
frequency
time
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
…
Slot = 0.5 ms
12subcarriers
6 or 7 Symbols/slot
OFDM Symbol
Resource Block
(RB)
• OFDM symbols are arranged in a 2 dimensional matrix called the resource grid:
– One axis of the grid is the subcarrier index
– The other axis is the time.
• Each OFDM symbol has its place in the resource grid.
Subframe = 1 ms
OFDM resource Grid for LTE/EUTRAN

OFDM resource Grid for LTE/EUTRAN. Channel
Estimation
9/13/2020 47
•Channel estimation based
on reference symbols.
•Interpolation in time and
frequency domain
•In WCDMA common pilot
channel (CPICH) was used for
this (together with reference
symbols on DCH)

Modulation Schemes for LTE/EUTRAN
9/13/2020 48
•Each OFDM symbol even within a resource block can have a different
modulation 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 on
carrier 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 bit rate calculation
9/13/2020 49
• From the 3gpp specification:
-1 Radio Frame = 10 Sub-frame
LTE bit rate calculation
-1 Sub-frame = 2 Time-slots
-1 Time-slot = 0.5 ms (i.e 1 Sub-frame = 1 ms)
-1 Time-slot = 7 Modulation Symbols (when normal CP length is used)
-1 Modulation Symbols = 6 bits; if 64 QAM is used as modulation scheme
Radio resource is manage in LTE as resource grid....
-1 Resource Block (RB) = 12 Sub-carriers
Assume 20 MHz channel bandwidth (100 RBs), normal CP
Therefore, number of bits in a sub-frame
= 100RBs x 12 sub-carriers x 2 slots x 7 modulation symbols x 6 bits
= 100800 bits
Hence, data rate = 100800 bits / 1 ms = 100.8 Mbps
* If 4x4 MIMO is used, then the peak data rate would be 4 x 100.8 Mbps = 403
Mbps.
* If 3/4 coding is used to protect the data, we still get 0.75 x 403 Mbps = 302
Mbps as data rate.

Basic Signaling
A.Attached Request
B. Handover (Inter & Intra Ho)
9/13/2020 50

9/13/2020 51
Signalling example, Attach Request
UE eNB MME
S1AP: INITIAL CONTEXT SETUP REQUEST +
EMM ATT_ACC + ESM ACT_DEF_BEAR_REQ
S1AP: INITIAL CONTEXT SETUP RESPONSE
RRC: RRCConnectionReconfiguration + EMM
ATT_ACC + ESM ACT_DEF_BEAR_REQDRB and SRB2
Configuration RRC: RRCConnectionReconfigurationComplete
NAS Security Establishment (Authentication + NAS security start)
RRC: UECapabilityEnquiry
RRC: UECapabilityInformation
UE radio capabilities available
à DRB can be established
S1AP: UE CAPABILITY INFO INDICATION
PRACH RANDOM ACCESS
PRACH RANDOM ACCESS RESPONSE
PUSCH (Msg3) RRC: Connection Request
random access procedure
RRC: Connection Setup
RRC: Connection Setup Complete + EMM
ATT_REQ + ESM PDN CONN_REQ
S1AP: INITIAL UE MESSAGE + EMM ATT_REQ +
ESM PDN CONN_REQ
Create Session (S11)
RRC: Security Mode Command
RRC: Security Command Complete
RRC: UL NAS INFO TRANSFER (EMM
ATT_COMPLETE + ESM ACT_DEF_BEAR_SUCC
S1AP: UL NAS TRANSPORT (EMM ATT_COMPLETE
+ ESM ACT_DEF_BEAR_SUCC)
Step 1: RACH
procedure
Step 2: SRB1
establishment +
initial NAS msg
Step 3: NAS
security + S1
setup Step 4: RRC
security + UE
capability
Step 5: SRB2 +
DRB setup for
default bearer

Type of Handover & Handover Signaling
9/13/2020 52

Handovers Event A3 used for Better Cell HO
9/13/2020 53
time
RSRP
RSRP Neighbour Cell
Serving Cell RSRP
a3TimeToTrigger
Measurement
Report
a3offset
eNB
a3Report Interval
Measurement
Report
RSRP at serving cell + a3Offset < RSRP at neighbor cell
A3 condition met
reporting condition met
after Time To Trigger

Handovers Event A5
9/13/2020 54
time
threshold3a
RSRP
Neighbour Cell RSRP
Serving Cell RSRP
a5TimeToTrigger
Measurement
Report
eNB
a5Report Interval
Measurement
Report
RSRP at serving cell < threshold3
AND (&&)
RSRP at target > threshold3a
threshold3
-140 dBm
threshold3a
threshold3

Inter eNB Handover Simplified
9/13/2020 55
UE eNB9 MMEeNB4
1.
2.
3.
4.
5.
6.
7.
9.
8.
10.
11.
12.

Handover Preparation, step 1/3
9/13/2020 56
UE Source Target MME GW
1. RRC Reconfiguration
2. Measurement report
3. HO
decision
4. HO request
5. Admission
control
6. HO request ack.
1. The source eNB configures
the UE measurement
procedures with an RRC
RECONFIGURATION
2. UE is triggered to send
MEASUREMENT REPORT
to the source eNB. It can
be event triggered or
periodic
3. Source eNB makes
handover decision based
on UE report + load and
service information
4. The source eNB issues a
HANDOVER REQUEST to
the target eNB
5. Target eNB performs
admission control
6. Target eNB sends the
HANDOVER REQUEST
ACKNOWLEDGE to the
source eNB
RRC Reconfiguration Complete

Handover Execution, step 2/3
9/13/2020 57
Presentation / Author / Date
7. RRC Reconfiguration
8. Status transfer
Forward
packets to
target
Buffer
packets
from
source
9. Synchronization
10. UL allocation and timing advance
11. RRC Reconf. Complete
7. Source eNB generates the RRC
RECONFIGURATION towards
UE informing it to move to the
target cell
Source eNB starts forwarding
packets to target eNB
8. Source eNB sends status
information to target eNB
9. UE performs the final
synchronisation to target eNB
and accesses the cell via RACH
procedure
DL pre-synchronisation is
obtained during cell
identification and
measurements
10. Target eNB gives the uplink
allocation and timing advance
information
11. UE sends RRC
RECONFIGURATION
COMPLETE to target eNB
Target eNB can begin to send data
to UE

Handover Completion, step 3/3
9/13/2020 58
12. Path switch request
13. User plane update
request
14. Switch
downlink
path
15. User plane
update response
16. Path switch request ack.
17. Release resources
18. Release
resources
12.Target eNB sends a PATH SWITCH
message to MME to inform that the
UE has changed cell
13.MME sends a USER PLANE UPDATE
REQUEST message to Serving
Gateway
14.Serving Gateway switches the
downlink data path to the target
side
15.Serving Gateway sends a USER
PLANE UPDATE RESPONSE
message to MME
16.MME confirms the PATH SWITCH
message with the PATH SWITCH
ACK message
17.By sending RELEASE RESOURCE the
target eNB informs success of
handover to source eNB and
triggers the release of resources
18.Upon reception of the RELEASE
RESOURCE message, the source
eNB can release radio and C-plane
related resources associated to the
UE context

Intra-eNB handover
9/13/2020 59
UE
eNB CellID 8706 MMEeNB CellID
8706

Tracking Area Update (TAU)
9/13/2020 60
•Tracking area (TA) is similar to Location/Routing area in 2G/3G .
•Tracking Area Identity = MCC (Mobile Country Code), MNC (Mobile Network Code)
and TAC (Tracking Area Code).
•When UE is in ECM-Idle, MME knows UE location with Tracking Area accuracy.

HARQ in EUTRAN
9/13/2020 61
Packet
L1 NACK ReTX
The L1 retransmission procedure (Hybrid ARQ,
HARQ) achieves following:
• L1 signaling to indicate need for
retransmission -> fast round trip time
facilitated between UE and BTS
• Decoder does not get rid off the received
symbols when decoding fails but combines the
new transmission with the old one in the
buffer.

HARQ
9/13/2020 62
•The lower part of the MAC entity is the HARQ (Hybrid Automatic Retransmission on
reQuest) entity.
• Note that only certain transport channel types (UL-SCH) can have this unit.
•The assembled transport block from the multiplexer will be stored in one of the HARQ’s
buffers and simultaneously sent to the physical layer:
- If the eNB/UE receives the transport block correctly, it will send an ACK indication via a
special physical channel. This would delete the transport channel from the buffer.
- If no indication or a NACK indication is received, the HARQ entity will retransmit the
transport block.
MAC will tell the
physical layer, whether a
transport block is new
or it is a retransmission
FDD | TDD - Layer 1
DL:OFDMA,UL:SC-TDMA
Multiplexing
HARQ
Scheduling/Priority
…
TrCH
Transport Block
(1 per TTI) TB ACK|NACK
MAC LogCH LogCH LogCHLogCH
…

Radio Resource Management (RRM)
9/13/2020 63
RRM is responsible for the administration of the available radio resources to
enable provisioning of high quality services to users without compromising
overall radio network capacity and performance.
RRM provides the following L3
and above (L3+) functions to the
system:
•Radio Bearer Control (RBC)
•Radio Admission Control (RAC)
•Connection Mobility Control
(CMC)
•Dynamic Resource Allocation
(DRA)
•Inter-cell interference RRM &
load management (ICR)
•Radio Configuration (RC)
•Inter-RAT RRM (IRR)
•RRM L3 functions use the following
lower layer functions defined in
L1/L2 to modify behavior of the
system:
•UL/DL Power Control
•Congestion Control
•DTX/DRX Control
•Link Adaptation (Adaptive
Modulation and Coding)
•Link Quality Control
•HARQ Control
•MIMO and Aerial Control

64
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LTE Basic Principle

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