4. Evolution of Mobile Communication Networks
1st
2nd
3rd
4th
Generation or 1G
Generation or 2G , 2nd Generation Transitional or 2.5G,2.75G
Generation or 3G , 3rd Generation Transitional or 3.5G,3.75G,3.9G
Generation or 4G
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5. LTE Parallel Evolution Path to HSPA+
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6. 3GPP RELEASES & LTE TERMINOLOGY
Long Term Evolution (LTE) and System Architecture
Evolution (SAE) are specified by the Third Generation
Partnership Project (3GPP) in Release 8 specifications.
A detailed description of SAE/LTE Specifications are available at
the 3GPP website: http://www.3gpp.org/ftp/Specs/archive/
The standard development in 3GPP is grouped into two
work items, where LTE targets the radio network evolution
and System Architecture Evolution (SAE) targets the
evolution of the packet core network.
Long Term Evolution (LTE) : Evolution of 3GPP UMTS
Terrestrail Radion Access (E-UTRA) Technology.
Evolved Packet System (EPS) : Evolution of the complete
3GPP UMTS Radio Access, Packet Core and its integration
into legacy 3GPP/non-3GPP network.
EPS includes:
Evolved UTRAN (eUTRAN) ” Radio Access Network
Evolved Packet Core (EPC) ” System Architecture.
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7. E-UTRA Design Performance Targets
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 Txantenna 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)
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.
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8. E-UTRA Air Interface Capabilities
UE e-NB Communication Link
E-UTRA Air Interface Capabilities
Bandwidth support
Flexible from 1.4 MHz to 20 MHz
Waveform
OFDM in Downlink
SC-FDM in Uplink
Duplexingmode
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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Single & same link of communication for DL & UL
DL serving cell = UL serving cell
No UL or DL macro-diversity
”UE’s Active Set size = 1
Hard-HO based mobility
”UE assisted (based on measurement reports) and
network controlled (handover decision at specific
time) by default.
”During a handover, UE uses a RACH based mobility
procedure to access the target cell
”Handover is UE initiated if it detects a RL failure
condition.
Load indicator for inter-cell load control
(interference management)
”Transmitted over X2 interface
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9. LTE DRIVERS
Branding
For branding image
For competition
Marketing
For better data service
For SME & Industry user
Technical
For frequency issue
For network quality
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12. LTE DRIVERS
LTE operation benefits
Enhanced
experience for
E2E quality
Spectrum
flexibility
Lower cost
LTE/SAE introduces the mechanism to fullfill the
requirement of a next generation of mobile network.
Higher speed (x10)
Lower latency (1/4 )
Lager capacity (x3)
New or re-farmed spectrum
Varity channel bandwidth
IP based flat network
architecture
Low OPEX: SON
High re-use of asset
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Flat Overall Architecture
2-nodes architechture
IP routable transport architechture
Lower cost.
Improved Radio Aspects
Peak data rates [Mbps] DL=300,UL=75
Scalable Bandwidth:1.4,3,5,10,15,20 MHz
Short latency: <100ms (control plane), <5ms
(user plane)
New Core Architechture
Simplified Protocol Stack
Simple , more efficient QoS
UMTS backward compatibility security
Circuit Switch service is implemented in PS
domain :VoIP.
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13. Achievable & Supported Peak Data Rates
Achievable LTE Peak Data Rate
Peak Data rate scale with the bandwidth
2x2 MIMO supported for the initial LTE
deployment.
UE Supported Peak Data Rate (Mbps)
Similar peak data rates defined for FDD & TDD.
All categories support 20 MHz, 64QAM
downlink and receive antenna diversity.
Category 2,3 ,4 expected in the first phase with
bit rates up to 150 Mbps.
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18. LTE EVOLUTION (LTE-Advanced)
LTE-Advanced (LTE-A) is introduced in 3GPP release10 and it’s the Global 4G solution.
Improves spectrum efficiency, delivers increases in capacity and coverage, and the ability to support more
customers /devices more efficiently, to maintain and improve the user experience of mobile broadband.
[Key features]
Multicarrier Enables Flexible Spectrum Deployments
Carrier Aggregation
Higher order MIMO
SON/Hetnets
Interference management
Relays
Increased data rates and lower latencies for all users in the cell.
Data rates scale with bandwidth„Up to 1 Gbps peak data rate.
Aggregating 40 MHz to 100 MHz provide peak data rates of 300 Mbps to 750
Mbps1(2x2 MIMO) and over 1 Gbps(4x4 MIMO)
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19. LTE EVOLUTION (LTE-A)
LTE-A introduces higher order MIMO 8x8 DL MIMO, 4x4 UL MIMO and UL Beamforming
More Antennas to
Leverage Diversity
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20. [2] EVOLVED PACKET SYSTEM (EPS)
ARCHITECTURE & PROTOCOLS
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21. System Architecture Evolution (SAE)
EPS is all PS (IP based ” no CS domain )
[Main drivers]
All-IP based
Reduce network cost
Reduce data latency &
signalling load
Better network topology
scalability & reliability
Inter-working & seamless
mobility among heterogeneous
access networks(3GPP & non3GPP).
Better always-on user
experience
Simpler and more flexible Qos
Suppport
Higher level of security
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22. PS Domain Architecture Evolution
EPS flat architecture, with User Plane direct tunneling between SAE-GW and eNode B is similar to the ‚super‛ flat architecture
option for HSPA+, where GGSN connects directly to a collapsed RNC+Node B entity or to an evolved Node B. As the color legend
shows, the location of the migrated network functions in EPS are as follows:
RNC functions are in eNB & MME
SGSN functions are in the MME
GGSN functions are in SGW &
PGW
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23. Overall EPS Architecture
Main Network Element of EPS (Evolved Packet System)
E-UTRAN (Evolved UTRAN ) consists of e-NodeBs, providing the user plane and control plane.
EPC (Evolved Packet Core ) consists of MME, S-GW and P-GW.
Network Interface of EPC (Evolved Packet System)
e-NodeBs are interconnected with each other by means of the X2 interface, enabling direct transmission of data and signaling.
S1 is the interface between e-NodeBs and the EPC, to the MME via the S1-MME and to S-GW via the S1-U.
EPC includes;
MME (Mobility Management
Entity) handling Control Plane.
S-GW (Serving Gateway) & P-GW
(PDN Gateway) handling User Plane
Note:
HSS (Home Subscriber Server) is
‚formally‛ out of the EPC, and will
need to be updated with new EPS
subscription data and functions.
PCRF and Gx/Rx provide QoS Policy
and Charging control (PCC),
similarly to the UMTS PS domain.
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24. E-UTRAN Entities/Interfaces
Evolved Node B (eNB) provides the E-UTRA User Plane (PDCP/RLC/MAC/PHY) and Control Plane (RRC) protocol terminations toward
the UE. An eNB can support FDD mode, TDD mode, or dual mode operation. eNBs can optionally be interconnected with each
other by means of the X2 interface or connected by means of the S1 interface to the Evolved Packet Core (EPC).
e-Node hosts the following functions:
Radio Resource Management: Radio Bearer Control,
Radio Admission Control, Connection Mobility Control,
Dynamic allocation of resources to UEs in both uplink and
downlink (scheduling)
IP header compression
Encryption /Integrity protection of user data
MME selection (among MME pool)
Routing of User Plane data towards S-GW
Scheduling and transmission of paging and broadcast
messages (originated from the MME)
Measurement and measurement reporting configuration
for mobility and scheduling
S1 interface
Can be split S1-U (S-GW) & S1-C(MME).
X2 interface
Used for inter-eNB handover, load balacing and
interference cancellation.
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25. EPC Entities/Interfaces
MME (Mobility Management Entity) main functions:
NAS signaling and security
AS Security control
Idle state mobility handling
P-GW and S-GW selection
EPS (Evolved Packet System) bearer control;
Support paging, handover, roaming and authentication
S-GW (Serving Gateway) main functions:
Packet routing and forwarding
E-UTRAN and inter-3GPP mobility anchoring
E-UTRAN Idle mode DL packet buffering
UL and DL charging per UE, PDN, and QCI
Transport level QoS mapping
P-GW (PDN Gateway) main functions:
Per-user based packet filtering
UE IP address allocation
UL and DL service level charging
User Plane anchoring for 3GPP and non-3GPP mobility
S5 interface
Between S-GW and P-GW
Called S8 for Inter-PLMN connection (roaming)
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S10 interface
Support mobility between MMEs
S11 interface
Support EPS Bearer management between MME & S-GW
S6a interface
Used for subscription & security control between MME&HSS
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26. LTE Radio Protocol Stack
Two Planes in LTE Radio Protocol: (1) User-plane: For user data transfer (2) Control-plane: For system signaling transfer
Over LTE-Uu radio interface, protocols are split in:
(AS) Access Stratum: RRC/PDCP/RLC/MAC/PHY.
(NAS) Non Access Stratum: EMM (Mobility Management) and ESM (Session Management)
Control plane
Main Functions of Control-plane:
RLC and MAC layers perform the same functions as for the user plane
PDCP layer performs ciphering and integrity protection
RRC layer performs broadcast, paging, connection management, RB
control, mobility functions, UE measurement reporting and control
NAS layer performs EPS bearer management, authentication, security
control
Over S1 and X2 interfaces, two RNL application protocols (S1-AP and X2AP), using a new transport protocol called SCTP (Stream Control
Transmission Protocol).
S1-AP: Supports all necessary EMM-eNB signaling and procedures,
including RAB management, mobility, paging, NAS transport, and many
other S1 related functions.
X2-AP: Supports Intra LTE-Access-System Mobility, Uplink Load
Management, and X2 error handling functions.
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27. LTE Radio Protocol Stack
User-plane
User plane on the S1-U uses GTP-U for
tunneling. The same protocol stack
would apply to the X2 interface, for
data packet forwarding during handover
between eNBs.
The concatenation of LTE RB + S1 Bearer
+ S5 Bearer makes the EPS Bearer,
which can be shared by multiple Service
Flows with the same level of QoS.
EPS Bearer (similar to a PDP context of
previous 3GPP releases) is defined between
the User Equipment (UE) and the P-GW
node in the EPC (which provide the end
users IP point of presence towards
external networks).
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28. LTE Radio Interface structure
The radio interface is structured in a layered
model, similar to WCDMA, with a layer 2
bearer (here called EPS Bearer Service),
which corresponds to a PDP-context in Rel. 6,
carrying layer 3 data and the end-to-end
service.
The EPS bearer is carried by the E-UTRA
Radio Bearer Service in the radio interface. The
E-UTRA radio bearer is carried by the radio
channels.
The radio channel structure is divided into
logical, transport and physical channels.
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29. LTE UE STATES AND AREA CONCEPTS
LTE is developed to have a simpler
architecture (fewer nodes) and
less signaling (fewer messages) than
the UTRAN. The number of states
which the UE can be in (corresponding
to RRC states) are reduced from five in
the UTRAN (DETACHED, IDLE,
URA_PCH, CELL_FACH, CELL_DCH)
to only three in the eUTRAN
(DETACHED, IDLE and CONNECTED)
In LTE only one area for idle mode
mobility is defined; the Tracking Area
(TA). In UTRAN, Routing Area (RA) and
UTRAN Registration Area (URA) is
defined for PS traffic and
Location Area (LA) for CS traffic.
In ECM-IDLE (EPS Connection
Management IDLE) the UE position is
only known by the network on TA level,
whereas in ECM-CONNECTED, the UE
location is known on cell level by the
eNodeB.
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30. [3] LTE AIR INTERFACE
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31. Duplex Techology
Frequency Division Duplex (FDD):
Distinguish uplink and downlink according to frequencies.
Time division duplex (TDD):
Distinguish uplink and downlink according to timeslots.
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33. OFDM Basics
LTE radio interface is based on OFDM (Orthogonal Frequency Division Multiplex) and OFDMA (Orthogonal Frequency Division
Multiple Access) in DL and SC-FDMA (Single Carrier Frequency Division Multiple Access) in UL.
OFDM uses a large number of closely spaced narrowband carriers.In a conventional FDM system, the frequency spacing between
carriers is chosen with a sufficient guard band to ensure that interference is minimized and can be cost effectively filtered. In OFDM,
however, the carriers are packed much closer together.
OFDM Orthogonality
Each of the 15 kHz LTE air interface subcarriers are ‘Orthogonal’ to each
other , there is zero inter-carrier interference at the center frequency of each
subcarrier. Orthogonality allows simultaneous transmission on many
subcarriers in a tight frequency space without interference from each other.
The spectrums of the subcarriers are not separated, but overlap.
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34. OFDM Basics
The transmitter combines all the subcarriers using an Inverse Fast Furrier Transform (IFFT) function where the outcome is single
signal which is basically a sum of sinusoids having an amplitude that varies depending on the number of subcarriers. The receiver
uses a Fast Fourier Transform (FFT) function to recover each subcarrier.
System Bandwidth
FFT
Sub-carriers
Guard
…
Intervals
Symbols
Frequency
…
Time
OFDM also shows very good performance in highly
time dispersive radio environments (i.e. many
delayed and strong multipath reflections).
FFT = Fast Fourier Transform, IFFT = Inverse FFT
FFT/IFFT allows to move between time and frequency domain representation
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That is because the data stream is distributed over
many subcarriers. Each subcarrier will thus have a
slow symbol rate and correspondingly, a long
symbol time. This means that the Inter Symbol
Interference (ISI) is reduced.
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35. OFDM & SC-FDMA
OFDM & OFDMA
DFT-S-OFDM & SC-FDMA
OFDM (Orthogonal Frequency Division Multiplexing) is a
modulation multiplexing technology, divides the system
bandwidth into orthogonal subcarriers.
OFDMA is the multi-access technology related with
OFDM, is used in the LTE downlink. OFDMA is the
combination of TDMA and FDMA essentially.
Advantage: High spectrum utilization efficiency due to
orthogonal subcarriers need no protect bandwidth.
Support frequency link auto adaptation and scheduling.
Easy to combine with MIMO.
DFT-S-OFDM (Discrete Fourier Transform Spread
OFDM) is the modulation multiplexing technology
used in the LTE uplink, Each user is assigned part of
the system bandwidth.
SC-FDMA（Single Carrier Frequency Division
Multiple Accessing）is the multi-access technology
related with DFT-S-OFDM.
Advantage: High spectrum utilization efficiency due
to orthogonal user bandwidth need no protect
bandwidth.
Disadvantage: Strict requirement of time-frequency
domain synchronization. High Peak-to-Average Power
Ratio (PAPR).
Low Peak-to-Average Power Ratio (PAPR)
System Bandwidth
System Bandwidth
Sub-carriers
Sub-carriers
TTI: 1ms
Frequency
TTI: 1ms
Frequency
User 1
User 2
User 3
Time
User 1
User 2
Time
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Sub-band：12Sub-carriers
Sub-band：12Sub-carriers
SC-FDMA : PRB’s are grouped to bring down PAPR , better power efficiency at the UE
User 3
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36. Time & Frequency Domain Organization
LTE Time Domain is organized as
Frame (10 ms)
Sub-frame (1ms)
Slot (0.5ms)
Symbol (duration depends on configuration)
Radio Frame Structures Supported by LTE:
Type 1, applicable to FDD
Type 2, applicable to TDD
LTE Frequency Domain
LTE DL/UL air interface waveforms use a number of
Orthogonal subcarriers to send users & control data.
Pre-defined spacing between these subcarriers (15 KHz
for regular operation and 7.5 KHZ for MBSFN operation)
.
DC subcarrier which has no energy and is located at the
center of the frequency band.
Two guard bands at the edges of the OFDM/OFDMAsignal (no RF transmission in this subcarriers). This is a
guard band to avoid interference with adjacent bands.
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37. Frequency Domain Configurations
Various channel bandwidths that may be considered for LTE deployment are shown in the table.
One of the typical LTE deployment options (10 MHz) is highlighted.
Assuming 15 KHz Carrier Spacing
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38. UL/DL Resource Grid Definitions
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
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39. UL/DL Resource Grid Definitions
Resource Element Group (REG)
Groups of Resource Elements to carry control information.
4 or 6 REs per REG depending on number of reference signals per
symbol, cyclic prefix configuration.
REs used for DL Reference Signals (RS) are not considered for the
REG.
” Only 4 usable REs per REG.
Control Channel Element (CCE)
Group of 9 REGs form a single CCE.
” 1 CCE = 36 REs usable for control information.
Both REG and CCE are used to specify resources for LTE
DL control channels.
Antenna Port
One designated reference signal per antenna port.
Set of antenna ports supported depends on reference signal
configuration within cell.
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40. TDD Radio Frame Structure
Applies OFDM, same subcarriers spacing and time unit with FDD.
Uplink-downlink Configurations
Similar frame structure with FDD. radio frame is 10ms shown as
below, divided into 20 slots which are 0.5ms.
Uplinkdownlink
configuration
Downlink-to-Uplink
Switch-point
periodicity
The uplink-downlink configuration of 10ms frame are shown in
the right table.
0
Subframe number
1
2
3
4
5
6
7
8
9
5 ms
D
S
U
U
U
D
S
U
U
U
1
Special Subrame Structure
Special Subframe consists of DwPTS, GP and UpPTS .
9 types of Special subframe configuration.
Guard Period size determines the maximal cell radius. (100km)
DwPTS consists of at least 3 OFDM symbols, carrying RS, control
message and data.
UpPTS consists of at least 1 OFDM symbol, carrying sounding RS or
short RACH.
0
5 ms
D
S
U
U
D
D
S
U
U
D
2
5 ms
D
S
U
D
D
D
S
U
D
D
3
10 ms
D
S
U
U
U
D
D
D
D
D
4
10 ms
D
S
U
U
D
D
D
D
D
D
5
10 ms
D
S
U
D
D
D
D
D
D
D
6
5 ms
D
S
U
U
U
D
S
U
U
D
DL to UL switch point in special subframe #1 and #6 only
Other subframes allocated to UL or DL
Sum of DwPTS, GP and UpPTS always 1 ms
Subframe #0 and #5 always DL
- Used for cell search signals (S-SCH)
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41. Cyclic Prefix (CP) Transmission
CP Length Configuration:
Cyclic Prefix is applied to eliminate ISI (Inter-symbol Interference) of OFDM.
CP length is related with coverage radius. Normal CP can fulfill the requirement of common
scenarios. Extended CP is for wide coverage scenario.
Longer CP, higher overheading.
Slot structure under Normal
CP configuration
(△f=15kHz)
Slot structure under Extended
CP configuration
(△f=15kHz)
Slot structure under Extended
CP configuration
(△f=7.5kHz)
Configuration
DL OFDM CP Length
UL SC-FDMA CP
Length
Extended CP
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160 for slot #0
160 for slot #0
144 for slot #1~#6
144 for slot #1~#6
f=15kHz
512 for slot #0~#5
512 for slot #0~#5
f=7.5kHz
Normal CP
1024 for slot #0~#2
NULL
Sub-carrier of
each RB
f=15kHz
Symbol of
each slot
7
12
6
24 (DL only)
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42. Cyclic Prefix (CP) Transmission
In OFDM, multipath causes loss of orthogonality
Delayed paths cause overlap between symbols
Cyclic Prefix (CP) insertion helps maintain
orthogonality Reduces efficiency (or Usable
Symbol time, Tu) .
Mitigates Inter-Symbol Interference (ISI)
Reduces efficiency
” Useable time per symbol is Tu/(Tu+TCP)
Selection of Cyclic Prefix governed by delay
spread
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44. LTE Channel Structure
Transport Channel
Logical Channel
Control Channel
DL Channel
Broadcast Control Channel (BCCH)
” DL broadcast of system control information.
Paging Control Channel (PCCH)
” DL paging information. UE position not known on cell level
Common Control Channel (CCCH)
” UL/DL. When no RRC connection exists.
Multicast Control Channel (MCCH)
” DL point-to-multipoint for MBMS scheduling and control, for
one or several MTCHs.
Dedicated Control Channel (DCCH)
” UL/DL dedicated control information. Used by UEs having
an RRC connection.
Broadcast Channel (BCH)
– System Information broadcasted in the entire coverage area of the
cell.Beamforming is not applied.
Downlink Shared Channel (DL-SCH)
– User data, control signaling and System Info. HARQ and link
adaptation.Broadcast in the entire cell or beamforming. DRX and
MBMS supported.
Paging Channel (PCH)
– Paging Info broadcasted in the entire cell. DRX
Multicast Channel (MCH)
– MBMS traffic broadcasted in entire cell. MBSFN is supported.
Traffic Channel
Dedicated Traffic Channel (DTCH)
– UL/DL Dedicated Traffic to one UE, user information.
Multicast Traffic Channel (MTCH)
– DL point-to-multipoint. MBMS user data.
Uplink Shared channel (UL-SCH)
– User data and control signaling. HARQ and link adaptation.
Beamforming may be applied.
Random Access Channel (RACH)
– Random Access transmissions (asynchronous and synchronous). The
transmission is typically contention based. For UEs having an RRC
connection there is some limited support for contention free access.
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UL Channel
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45. LTE Channel Structure
Physical channels
Physical Downlink Shared Channel (PDSCH)
” transmission of the DL-SCH transport channel
Physical Uplink Shared Channel (PUSCH)
” transmission of the UL-SCH transport channel
Physical Control Format Indicator Channel (PCFICH)
” indicates the PDCCH format in DL
Physical Downlink Control Channel (PDCCH)
” DL L1/L2 control signaling
Physical Uplink Control Channel (PUCCH)
” UL L1/L2 control signaling
Physical Hybrid ARQ Indicator Channel (PHICH)
Physical signals
Reference Signals (RS)
– support measurements and coherent demodulation in
uplink and downlink.
Primary and Secondary Synchronization signals (P-SCH
and S-SCH)
– DL only and used in the cell search procedure.
Sounding Reference Signal (SRS)
– supports UL scheduling measurements
” DL HARQ info
Physical Broadcast Channel (PBCH)
” DL transmission of the BCH transport channel.
Physical Multicast Channel (PMCH)
” DL transmission of the MCH transport channel.
Physical Random Access Channel (PRACH)
” UL transmission of the random access preamble as given by
the RACH transport channel.
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46. Synchronization Signals (PSS & SSS)
PSS and SSS Functions
”Frequency and Time synchronization
Carrier frequency determination
OFDM symbol/subframe/frame timing determination
”Physical Layer Cell ID (PCI) determination
Determine 1 out of 504 possibilities
PSS and SSS resource allocation
”Time: subframe0 and 5 of everyFrame
”Frequency: middle of bandwidth (6 RBs = 1.08 MHz)
Primary Synchronization Signals (PSS)
”Assists subframe timing determination
”Provides a unique Cell ID index (0, 1, or 2) withina Cell ID group
Secondary Synchronization Signals (SSS)
”Assists frame timing determination
”Provides a unique Cell ID group number among 168 possible Cell ID groups
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47. Cell Identity Determination from PSS and SSS
Physical Cell Identity (PCI) is uniquely defined by:
A number in the range of 0 to 167, representing the Physical
Cell Identity (PCI) group
A number in the range of 0 to 2, representing the physical
identity within the Physical Cell Identity (PCI) group
S-SCH
Provides 168 sequences, each associated to a cell ID group
information
These sequences are interleaved concatenations of two length31 binary sequences
P-SCH
Three (NID=0,1,2) frequency domain Zadoff-Chu sequences of
length 62
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48. Physical Broadcast Channel (PBCH)
PBCH Function
”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)
TTI = 40 ms
” 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
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49. System Information in PBCH & PDSCH
The System Information (SI) that is broadcasted in the whole cell area, is carried by the logical channel BCCH, which in turn is
carried by either of the transport channels BCH or DL-SCH. A static part of SI is called MIB (Master Information Block) is
transmitted on the BCH, which in turn is carried by the PBCH. A dynamic part of SI, called SIBs (System Information Blocks) is
mapped onto RRC System Information messages (SI-1,2,3…) on DL-SCH, which in turn is carried by PDSCH.
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50. System Information (MIB & SIB)
MIB (Master Information Block) Repeats every 4 frames (40 ms) and includes DL Tx bandwidth, PHICH configuration, and SFN. This
information is necessary to acquire (read) other channels in the cell. ***( LTERelease 8 has 11 different SIB types)
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51. Physical Control Format Indicator Channel (PCFICH)
Carries the Control Format Indicator (CFI)
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 band
4 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
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52. Physical Downlink Control Channel (PDCCH)
Used for:
” 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
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53. Physical Downlink Shared Channel (PDSCH)
Transmits DL packet data
One Transport Block transmission per UE’s 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.
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54. Physical Downlink Shared Channel (PDSCH)
PDSCH Generalized Transmission Scheme
Code Words (maximum of 2)
A code word represents an output from the channel coder
1 code word for rank 1 Transmission
2 code words for rank 2/3/4 Transmissions
Layer Mapping
Number of layers depends on the number of Tx antennas and Wireless Channel Rank
Fixed mapping schemes of code words to layers
Tx Antennas (maximum of 4)
Maximum of 4 antennas (potentially upto 4 layers)
Pre-coding
used to support spatial multiplexing
Code book based precoding
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55. Physical HARQ Indicator Channel (PHICH)
Used for ACK/NAK of UL-SCH transmissions
Transmitted in:
Time
”Normal duration: 1st OFDM 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
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56. DL Reference Signals (RS)
The downlink reference signals consist of so-called reference symbols which are known symbols inserted within in the OFDM
time/frequency grid.
Similar with Pilot signal of CDMA. Used for downlink physical channel demodulation and channel quality measurement (CQI)
Three types of RS in protocol. Cell-Specific Reference Signal is essential and the other two types RS (MBSFN Specific RS & UE-Specific RS)
are optional.
Characteristics:
Cell-Specific Reference Signals are generated from cell-specific RS sequence and frequency shift mapping. RS sequence also carriers one
of the 504 different Physical Cell ID.
The two-dimensional reference signal sequences are generated as the symbol-by-symbol product of a two-dimensional orthogonal
sequence and a two-dimensional pseudo-random sequence:
There are 3 different two-dimensional orthogonal sequences
There are 168 different two-dimensional pseudo-random sequences
The frequency interval of RS is 6 subcarriers.
RS distributes discretely in the time-frequency domain, sampling the channel situation which is the reference of DL demodulation.
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57. R0
One antenna port
One Antenna
Port
DL Reference Signals (RS)
Downlink RS consist of know reference symbol locations
Antenna ports 0 and 1
R0
R0
Inserted in two OFDM symbols (1st and 3rd last OFDM symbol) of each slot.
6 subcarriers spacing and 2x staggering (45kHz frequency sampling)
R0
R0
R0
R0
Antenna ports 2 and 3
Inserted in one OFDM symbol (2nd OFDM symbol) of each slot.
6 subcarriers spacing and 2x staggering across slots.
R0
l0
l6 l0
l6
Resource element (k,l)
Two antenna ports
Two Antenna
Ports
R0
R0
R0
R0
R1
R0
R0
R0
Four antenna ports
Four Antenna
Ports
R0
l6
R0
l0
R0
R0
even-numbered slots
odd-numbered slots
Antenna port 0
Antenna Port 0
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l6
l0
R2
R1
R1
even-numbered slots
R3
R3
R2
l6 l0
R3
R2
l6
odd-numbered slots
Antenna
Antennaport 1 1
Port
R1: RS transmitted in 1st ant port
R2: RS transmitted in 2nd ant port
R3: RS transmitted in 3rd ant port
R4: RS transmitted in 4th ant port
R2
R1
R1
l6 l0
l6
R1
R1
R0
l0
R1
R1
R0
Reference symbols on this antenna port
l6 l0
R1
R0
Not used for transmission on this antenna port
R1
R1
l6 l0
R0
R1
R1
R0
l0
R1
R1
l0
R3
l6 l0
even-numbered slots
l6
odd-numbered slots
Antenna
Antenna port 2 2
Port
l0
l6 l0
even-numbered slots
l6
odd-numbered slots
Antenna port 3
Antenna Port 3
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58. DL Reference Signals (RS) ” Measurement Reference
3GPP is defining following measurements:
” RSRP (Reference Signal Received Power)
” RSRQ (Reference Signal Received Quality)
RSRP, 3GPP definition
RSRP is the average received power of a single RS resource element.
UE measures the power of multiple resource elements used to transfer the reference signal but then takes
an average of them rather than summing them.
Reporting range -44…-140 dBm
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59. DL Reference Signals (RS) ” Measurement Reference
RSSI (Received Signal Strength Indicator)
RSSI not reported to eNodeB by UE
” Can be computed from RSRQ and RSRP that are reported by UE
RSSI measures all power within the measurement bandwidth
” Measured over those OFDM symbols that contain RS
” Measurement bandwidth RRC-signalled to UE
RSSI = wideband power= noise + serving cell power + interference power
Without noise and interference, 100% DL PRB activity: RSSI=12*N*RSRP
” RSRP is the received power of 1 RE (3GPP definition) average of power levels received across all Reference Signal
symbols within the considered measurement frequency bandwidth
” RSSI is measured over the entire bandwidth
” N: number of RBs across the RSSI is measured and depends on the BW
Based on the above, under full load and high SNR:
RSRP (dBm)= RSSI (dBm) -10*log (12*N)
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60. DL Reference Signals (RS) ” Measurement Reference
RSRQ ,3GPP definition
RSRQ = N x RSRP / RSSI
” N is the number of resource blocks over which the RSSI is
measured, typically equal to system bandwidth
” RSSI is pure wide band power measurement, including intracell
power, interference and noise
RSRQ reporting range -3…-19.5dB
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61. Uplink RS (Reference Signal)
Uplink RS (Reference Signal):
The uplink pilot signal, used for synchronization between EUTRAN and UE, as well as uplink channel estimation.
Two types of UL reference signals:
[1] DM RS (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
[2] SRS (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 and PUCCH)
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62. Physical Random Access Channel (PRACH)
Basic Principle of Random Access :
Random access is the procedure of uplink synchronization between UE and E-UTRAN.
Prior to random access, physical layer shall receive the following information from the higher layers:
Random access channel parameters: PRACH configuration, frequency position and preamble format, etc.
Parameters for determining the preamble root sequences and their cyclic shifts in the sequence set for the cell, in
order to demodulate the random access preamble.
1.Either network indicates specific PRACH resource or UE selects from
common PRACH resources.
2.UE sends random access preambles at increasing power.
3.UE receives random access response on the PDCCH which includes
assigned resources for PUSCH transmission.
“Physical Resource Blocks (PRB) and Modulation and Coding
Scheme (MCS)
4.UE sends signaling and user data on PUSCH.
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63. Physical Uplink Shared & Control Channel (PUSCH & PUCCH)
Physical Uplink Control Channel (PUCCH)
Carries Hybrid ACK/NACK reponse DL transmission
” Always transmitted using QPSK
” Is punctured into UL-SCH to avoid errors due
to missed DL assignments and thus different
interpretations of ACK/NACK symbols
Carries Sceduling Request (SR)
Carries CQI (Channel Quality Indicator)
Physical Uplink Shared Channel (PUSCH)
Carries data from the Uplink Shared Channel (ULSCH) transport Channel.
If data and control are transmitted simultaneously -> PUSCH
” control located in the same region as data (time multiplexed)
” required to preserve single-carrier properties
If only control is transmitted -> PUCCH
” control located at reserved region at band edges
” one RB is shared by multiple UEs through orthogonal spreading
sequences
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64. Initial Acquisition Procedure ( Cell Search)
Cell search is the process of identifying and obtaining downlink synchronization to cells, so that the broadcast information from
the cell can be detected. This procedure is used both at initial access and at handover.
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66. LTE MIMO (Multiple Input Multiple Output)
LTE specifications support the use of multiple antennas at both transmitter (tx) and receiver (rx). MIMO (Multiple Input Multiple
Output) uses this antenna configuration.
LTE specifications support up to 4 antennas at the tx side and up to 4 antennas at the rx side (here referred to as 4x4 MIMO
configuration).
In the first release of LTE it is likely that the UE only has 1 tx antenna, even if it uses 2 rx antennas. This leads to that so called
Single User MIMO (SU-MIMO) will be supported only in DL (and maximum 2x2 configuration).
OFDM works particularly well with MIMO
” MIMO becomes difficult when there is time dispersion
” OFDM sub-carriers are flat fading (no time dispersion)
3GPP supports one, two, or four transmit Antenna Ports
Multiple antenna ports
Multiple time-frequency grids
Each antenna port defined by an associated Reference Signal
LTE DL transmission modes
Multiple layers means that the time- and frequency resources (Resource Blocks) can be reused in the different layers up to a number of times
corresponding to the channel rank. This means that the same resource allocation is made on all transmitted layers.
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67. LTE MIMO (Multiple Input Multiple Output)
DL Single User MIMO ”with 2 antennas
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68. LTE MIMO (Multiple Input Multiple Output)
DL Multi User MIMO (MU-MIMO)
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69. LTE MIMO (Multiple Input Multiple Output)
UL Multi user MIMO (virtual MIMO)
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75. CSFB (CIRCUIT SWITCHED FALLBACK )
Flash CSFB (R9 Redirection with SIB)
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76. SON (SELF ORGANIZING NETWORKS)
SON (Self Organization Network) is introduced in 3GPP release 8. This function of LTE is required by
the NGMN (Next Generation Mobile Network) operators.
From the point of view of the operator’s benefit and experiences, the early communication systems
had bad O&M compatibility and high cost.
New requirements of LTE are brought forward, mainly focus on FCAPSI (Fault, Configuration, Alarm,
Performance, Security, Inventory) management:
Self-planning and Self-configuration, support plug and play
Self-Optimization and Self-healing
Self-Maintenance
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77. SON (SELF ORGANIZING NETWORKS)
Three SON RRM functionalities have been standardized in Rel 8.
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78. SON_ANR (Automatic Neighbor Relation)
The ANR function relies on cells broadcasting their identity on a global level
”E-UTRAN Cell Global Identifier (ECGI)
“The eNB instructs UE to perform measurements on neighbor cells
“The eNB can decide to add this neighbor relation and can use the Physical Cell ID and ECGI to:
”Look up transport layer address to the new eNB
”Update Neighbor Relation List
”If needed, set up a new X2 interface toward the new eNB
Main ANR management functions:
Automatic detection of missing neighboring cells
Automatic evaluation of neighbor relations
Automatic detection of Physical Cell Identifier (PCI) collisions
Automatic detection of abnormal neighboring cell coverage
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Automatic Neighbor Relation (ANR) can automatically add and
maintain neighbor relations. The initial network construction,
however, should not fully depend on ANR for the following
considerations:
ANR is closely related to traffic in the entire network
ANR is based on UE measurements but the delay is
introduced in the measurements.
After initial neighbor relations configured and the number of UEs
increasing, some neighboring relations may be missing. In this case,
ANR can be used to detect missing neighboring cells and add
neighbor relations.
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![Contents
[1] LTE/SAE INTRODUCTION
EVOLUTION OF MOBILE COMMUNICATION NETWORKS
3GPP RELEASES & LTE TERMINOLOGY
LTE DRIVERS
FREQUENCY BANDS
LTE-ADVANCED (LTE-A)
[2] EVOLVED PACKET SYSTEM (EPS) ARCHITECTURE & PROTOCOLS
OVERVIEW EPS ARCHITECTURE
EPS FUNCTIONALITY
LTE PROTOCOL STACK
LTE UE STATES AND AREA CONCEPTS
[3] LTE AIR INTERFACE
OFDMA/SC-FDMA BASICS
LTE FRAME & CHANNEL STRUCTURE
LTE DOWNLINK & UPLINK PHYSICAL CHANNEL
[4] LTE KEY TECHNOLOGY INTRODUCTION
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MULTIPLE INPUT MULTIPLE OUTPUT (MIMO)
CSFB (CIRCUIT SWITCHED FALLBACK )
SON (SELF ORGANIZING NETWORKS)
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