LTE Evolution and Technologies Explained

Copyright©2011 Huawei Technologies Co., Ltd. All Rights Reserved.
LTE
Long Term Evolution

Copyright©2011 Huawei Technologies Co., Ltd. All Rights Reserved. 2
Mobile communication system evolution
1G (First
Generation)
2G (Second
Generation)
3G (Third
Generation)
4G (Fourth
Generation)
AMPS
TACS
ETACS
Advanced Mobile
Telephone System
Total Access
Communications System
Extended Total Access
Communication System
GSM
CDMA One (IS-95)
DAMPS（IS-136)
Global System for Mobile
communications
Code Division Multiple Access
Based on IS-95
Digital - Advanced Mobile Phone
System Based on
IS-136
Other
UMTS
WCDMA
TD-SCDMA
CDMA2000
WiMAX
LTE Advanced
UMB
EV-DO Rev C
WiMAX
802.16m

2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
R99 R4 R5 R6 R7 R8 R9 R10
UMTS
HSPA
DL
HSPA
UL
LTE
LTE
Adv
HSPA
+
EPC
Common
IMS
IMS
MMTel
3GPP Time Line and Evolution

IMT Advanced Requirements
Specific requirements of the IMT-Advanced report included:
 All-IP packet switched network and Interoperability with existing wireless standards.
 Share and use the network resources to support more simultaneous users per cell
 Scalable channel bandwidth 5–20 MHz, optionally up to 40 MHz
 Seamless connectivity and global roaming across multiple networks (smooth handovers).
 1 Gbit/s in the downlink should be possible over less than 67 MHz bandwidth
 Data rate :
100 Mbit/s (high speeds)
1 Gbit/s (fixed positions).
 Peak link spectral efficiency :
15 bit/s/Hz (downlink)
 6.75 bit/s/Hz (uplink)
 In the downlink spectral efficiency up to :
3 bit/s/Hz/cell (outdoor)
2.25 bit/s/Hz/cell (indoor)
14

LTE Background Introduction
• What is LTE？
 LTE (Long Term Evolution) is known as the evolution of radio access technology conducted by 3GPP.
 The radio access network will evolve to E-UTRAN (Evolved UMTS Terrestrial Radio Access Network), and the
correlated core network will evolved to SAE (System Architecture Evolution).
What can LTE do？
 Flexible bandwidth configuration: supporting 1.4MHz,
3MHz, 5MHz, 10Mhz, 15Mhz and 20MHz
 Peak date rate (within 20MHz bandwidth): 100Mbps for
downlink and 50Mbps for uplink
 Time delay: <100ms (control plane), <5ms (user plane)
 Provide 100kbps data rate for mobile user (up to 350kmph)
 Support eMBMS
 Circuit services is implemented in PS domain: VoIP
 Lower cost due to simple system structure

LTE Network Architecture
• Main Network Element of LTE
 The E-UTRAN consists of e-NodeBs, providing the user plane and control plane.
 The EPC consists of MME, S-GW and P-GW.
Compare with traditional 3G network,
LTE architecture becomes much more
simple and flat, which can lead to
lower networking cost, higher
networking flexibility and shorter time
delay of user data and control
signaling.
Network Interface of LTE
 The e-NodeBs are interconnected with each other by means of the X2 interface, which enabling direct transmission of
data and signaling.
 S1 is the interface between e-NodeBs and the EPC, more specifically to the MME via the S1-MME and to the S-GW via
the S1-U
eNB
MME / S-GW MME / S-GW
eNB
eNB
S1
S1
S
1
S
1
X2
X
2
X
2
E-UTRAN
UMTS LTE

• SAE Brief Introduction
 SAE（System Architecture Evolution）considers evolution for the whole system architecture, including：
 Flat Functionality. Take out the RNC entity and part of the functions are arranged on e-NodeB in order to reduce the latency and enhance
the schedule ability, such as interference coordination, internal load balance, etc.
 Part of the functions are arranged on core network. To enhance the mobility management, all IP technology is applied, user-plane and
control-plane are separated. The compatibility of other RAT is considered.
SGi
S4
S3
S1-MME
PCRF
S7
S6a
HSS
Operator’s IP Services
(e.g. IMS, PSS etc.)
Rx+
S10
UE
GERAN
UTRAN
SGSN
“LTE-Uu”
EUTRAN
MME
S11
S5
Serving
SAE
Gateway
PDN
SAE
Gateway
S1-U
SAE

FDMA TDMA CDMA and OFDMA

Introduction
 OFDM （Orthogonal Frequency Division Multiplexing） is a modulation
multiplexing scheme. The system bandwidth is divided into a plurality of
orthogonal.
 Orthogonality of different subcarriers is achieved by the baseband IFFT.
OFDM
 OFDM has many advantages that can meet the needs of E-
UTRAN, which is one of B3G and 4G key technology.
 OFDM is a modulation multiplexing scheme, and the
corresponding multi-access techniques is OFDMA. OFDMA are
used in LTE downlink.
 For LTE uplink the multiple access scheme is SC-FDMA .
OFDM
…
Sub-carriers
FFT
Time
Symbols
System Bandwidth
Guard
Intervals
…
Frequency
…
Sub-carriers
FFT
Time
Symbols
System Bandwidth
Guard
Intervals
…
Frequency
OFDM与OFDMA的比较

OFDMA and SC-FDMA Block Diagram
29

Cyclic Prefix
CP
Normal
5,2 µs first symbol
4,7 µs other symbol
Extended 16,7 µs
ISI (Inter Symbol Interference)
COPY and insert
24

OFDM & OFDMA
 OFDM (Orthogonal Frequency Division Multiplexing) is a
modulation multiplexing technology, divides the system
bandwidth into orthogonal subcarriers. CP is inserted between
the OFDM symbols to avoid the ISI.
 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.
 Disadvantage: Strict requirement of time-frequency domain
synchronization. High PAPR.
DFT-S-OFDM & SC-FDMA
 DFT-S-OFDM (Discrete Fourier Transform Spread OFDM)
is the modulation multiplexing technology used in the LTE
uplink, which is similar with OFDM but can release the UE
PA limitation caused by high PAPR. 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.
Low PAPR.
 The subcarrier assignment scheme includes Localized
mode and Distributed mode.
OFDMA & SC-FDMA
User 1
User 2
User 3
Sub-carriers
TTI: 1ms
Frequency
System Bandwidth
Sub-band：12Sub-carriers
Time
User 1
User 2
User 3
User 1
User 2
User 3
Sub-carriers
TTI: 1ms
Frequency
System Bandwidth
Time
Sub-carriers
TTI: 1ms
Frequency
Time
System Bandwidth
User 1
User 2
User 3
Sub-carriers
TTI: 1ms
Frequency
Time
System Bandwidth
User 1
User 2
User 3
User 1
User 2
User 3

Frequency Band of LTE
E-UTRA
Band
Uplink (UL) Downlink (DL) Duplex
Mode
FUL_low – FUL_high FDL_low – FDL_high
1 1920 MHz – 1980 MHz 2110 MHz – 2170 MHz FDD
5 824 MHz – 849 MHz 869 MHz – 894MHz FDD
9 1749.9 MHz
–
1784.9 MHz 1844.9 MHz
–
1879.9 MHz
FDD
11
1427.9 MHz – 1452.9 MHz 1475.9 MHz – 1500.9 MHz FDD
… … … …
... … … …
E-UTRA
Band
Uplink (UL) Downlink (DL) Duplex
Mode
FUL_low – FUL_high FDL_low – FDL_high
33 1900 MHz – 1920 MHz 1900 MHz – 1920 MHz TDD
TDD Frequency Band
FDD Frequency Band
From LTE Protocol:
 Duplex mode: FDD and TDD
 Support frequency band form 700MHz to 2.6GHz
 Support various bandwidth: 1.4MHz, 3MHz, 5MHz,
10MHz, 15MHz, 20MHz
Protocol is being updated, frequency information could be
changed.

Carrier Frequency EARFCN Calculation
eNB
UE
FDL = FDL_low + 0.1(NDL - NOffs-DL)
FUL = FUL_low + 0.1(NUL - NOffs-UL)
The values of FDL_low，NDL，NOffs-DL can be found from 3GPP 36.101,
as below：

Radio Frame Structures Supported by LTE:
 Type 1, applicable to FDD
 Type 2, applicable to TDD
FDD Radio Frame Structure:
 LTE applies OFDM technology, with subcarrier spacing f=15kHz and 2048-order IFFT. The time unit in
frame structure is Ts=1/(2048* 15000) second
 FDD radio frame is 10ms shown as below, divided into 20 slots which are 0.5ms. One slot consists of 7
consecutive OFDM Symbols under Normal CP configuration
#0 #1 #2 #3 #19
#18
One radio frame, Tf = 307200Ts = 10 ms
One slot, Tslot = 15360Ts = 0.5 ms
One subframe
FDD Radio Frame Structure
Concept of Resource Block:
 LTE consists of time domain and frequency domain resources. The minimum unit for schedule is RB
(Resource Block), which compose of RE (Resource Element)
 RE has 2-dimension structure: symbol of time domain and subcarrier of frequency domain
 One RB consists of 1 slot and 12 consecutive subcarriers under Normal CP configuration
Radio Frame Structure (1)

Resource Block

• TDD Radio Frame Structure:
 Applies OFDM, same subcarriers spacing and time
unit with FDD.
 Similar frame structure with FDD. radio frame is
10ms shown as below, divided into 20 slots which
are 0.5ms.
 The uplink-downlink configuration of 10ms frame are
shown in the right table.
One slot,
Tslot=15360Ts
GP UpPTS
DwPTS
One radio frame, Tf = 307200Ts = 10 ms
One half-frame, 153600Ts = 5 ms
30720Ts
One subframe,
30720Ts
GP UpPTS
DwPTS
Subframe #2 Subframe #3 Subframe #4
Subframe #0 Subframe #5 Subframe #7 Subframe #8 Subframe #9
Uplink-downlink Configurations
Uplink-downlink
configuration
Downlink-to-Uplink
Switch-point periodicity
Subframe number
0 1 2 3 4 5 6 7 8 9
0 5 ms D S U U U D S U U U
1 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
DwPTS: Downlink Pilot Time Slot
GP: Guard Period
UpPTS: Uplink Pilot Time Slot
TDD Radio Frame Structure
D: Downlink subframe
U: Uplink subframe
S: Special subframe

• 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.
Configuration of special subframe
Special Subframe Structure
Special subframe
configuration
Normal cyclic prefix
DwPTS GP UpPTS
0 3 10
1
1 9 4
2 10 3
3 11 2
4 12 1
5 3 9
2
6 9 3
7 10 2
8 11 1

• CP Length Configuration:
 Cyclic Prefix is applied to eliminate ISI 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.
Configuration DL OFDM CP Length
UL SC-FDMA CP
Length
Sub-carrier of
each RB
Symbol of
each slot
Normal CP f=15kHz
160 for slot #0
144 for slot #1~#6
160 for slot #0
144 for slot #1~#6 12
7
Extended
CP
f=15kHz 512 for slot #0~#5 512 for slot #0~#5 6
f=7.5kHz 1024 for slot #0~#2 NULL 24 (DL only) 3 (DL only)
CP Configuration
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)

Brief Introduction of Physical Channels
Downlink Channels：
 Physical Broadcast Channel (PBCH): Carries system information for cell search,
such as cell ID.
 Physical Downlink Control Channel (PDCCH) : Carries the resource allocation
of PCH and DL-SCH, and Hybrid ARQ information.
 Physical Downlink Shared Channel (PDSCH) : Carries the downlink user data.
 Physical Control Format Indicator Channel (PCFICH) : Carriers information of
the OFDM symbols number used for the PDCCH.
 Physical Hybrid ARQ Indicator Channel (PHICH) : Carries Hybrid ARQ
ACK/NACK in response to uplink transmissions.
 Physical Multicast Channel (PMCH) : Carries the multicast information.
Uplink Channels：
 Physical Random Access Channel (PRACH) : Carries the random access
preamble.
 Physical Uplink Shared Channel (PUSCH) : Carries the uplink user data.
 Physical Uplink Control Channel (PUCCH) : Carries the HARQ ACK/NACK,
Scheduling Request (SR) and Channel Quality Indicator (CQI), etc.
BCH PCH DL-SCH
MCH
Downlink
Physical channels
Downlink
Transport channels
PBCH PDSCH
PMCH PDCCH
Uplink
Physical channels
Uplink
Transport channels
UL-SCH
PUSCH
RACH
PUCCH
PRACH
Mapping between downlink transport channels
and downlink physical channels
Mapping between uplink transport channels
and downlink physical channels
Physical Layer
MAC Layer
Physical Layer
MAC Layer

Downlink Physical Channel
Scrambling
Modulation
mapper
Layer
mapper
Precoding
Resource element
mapper
OFDM signal
generation
Resource element
mapper
OFDM signal
generation
Scrambling
Modulation
mapper
layers antenna ports
code words
Downlink Physical Channel Processing
 scrambling of coded bits in each of the code words to be transmitted on a physical channel
 modulation of scrambled bits to generate complex-valued modulation symbols
 mapping of the complex-valued modulation symbols onto one or several transmission layers
 precoding of the complex-valued modulation symbols on each layer for transmission on the antenna ports
 mapping of complex-valued modulation symbols for each antenna port to resource elements
 generation of complex-valued time-domain OFDM signal for each antenna port
Modulation Scheme of Downlink
Channel
 Shown at the right table
Phy Ch Modulation Scheme Phy Ch Modulation Scheme
PBCH QPSK PCFICH QPSK
PDCCH QPSK PHICH BPSK
PDSCH QPSK, 16QAM, 64QAM PMCH QPSK, 16QAM, 64QAM

Uplink Physical Channel
Uplink Physical Channel Processing
 scrambling
 modulation of scrambled bits to generate complex-valued symbols
 transform precoding to generate complex-valued symbols
 mapping of complex-valued symbols to resource elements
 generation of complex-valued time-domain SC-FDMA signal for each antenna port
Modulation Scheme of Downlink Channel
 Shown at the right table
Phy Ch Modulation Scheme
PUCCH BPSK, QPSK
PUSCH QPSK, 16QAM, 64QAM
PRACH Zadoff-Chu
Scrambling
Modulation
mapper
Transform
precoder
Resource
element mapper
SC-FDMA
signal gen.

0

l
0
R
0
R
0
R
0
R
6

l 0

l
0
R
0
R
0
R
0
R
6

l
One
antenna
port
Two
antenna
ports
Resource element (k,l)
Not used for transmission on this antenna port
Reference symbols on this antenna port
0

l
0
R
0
R
0
R
0
R
6

l 0

l
0
R
0
R
0
R
0
R
6

l 0

l
1
R
1
R
1
R
1
R
6

l 0

l
1
R
1
R
1
R
1
R
6

l
0

l
0
R
0
R
0
R
0
R
6

l 0

l
0
R
0
R
0
R
0
R
6

l 0

l
1
R
1
R
1
R
1
R
6

l 0

l
1
R
1
R
1
R
1
R
6

l
Four
antenna
ports
0

l 6

l 0

l
2
R
6

l 0

l 6

l 0

l 6

l
2
R
2
R
2
R
3
R
3
R
3
R
3
R
even-numbered slots odd-numbered slots
Antenna port 0
Antenna port 1
Antenna port 2
Antenna port 3
Downlink Physical Signals (1)
Downlink RS (Reference Signal):
 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.
Cell-Specific RS
Mapping in Time-
Frequency Domain
One
Antenna
Port
Two
Antenna
Ports
Four
Antenna
Ports
Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3
Characteristics:
 Cell-Specific Reference Signals are generated from cell-specific RS
sequence and frequency shift mapping. RS is the pseudo-random
sequence transmits in the time-frequency domain.
 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.
 Serried RS distribution leads to accurate channel estimation, also high
overhead that impacting the system capacity.
MBSFN: Multicast/Broadcast over a
Single Frequency Network
RE
Not used for RS
transmission on this
antenna port
RS symbols on this
antenna 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

Synchronization Signal:
 synchronization signals are used for time-frequency synchronization between UE and E-UTRAN during cell search.
 synchronization signal comprise two parts:
 Primary Synchronization Signal, used for symbol timing, frequency synchronization and part of the cell ID detection.
 Secondary Synchronization Signal, used for detection of radio frame timing, CP length and cell group ID.
Synchronization Signals Structure
Characteristics:
 The bandwidth of the synchronization signal is
62 subcarrier, locating in the central part of
system bandwidth, regardless of system
bandwidth size.
 Synchronization signals are transmitted only in
the 1st and 11rd slots of every 10ms frame.
 The primary synchronization signal is located in
the last symbol of the transmit slot. The
secondary synchronization signal is located in
the 2nd last symbol of the transmit slot.
Downlink Physical Signals (2)

Uplink RS (Reference Signal):
 The uplink pilot signal, used for synchronization between
E-UTRAN and UE, as well as uplink channel estimation.
 Two types of UL reference signals:
 DM RS (Demodulation Reference Signal), associated with
PUSCH and PUCCH transmission.
 SRS (Sounding Reference Signal), without associated with
PUSCH and PUCCH transmission.
Characteristics:
 Each UE occupies parts of the system bandwidth since SC-FDMA
is applied in uplink. DM RS only transmits in the bandwidth
allocated to PUSCH and PUCCH.
 The slot location of DM RS differs with associated PUSCH and
PUCCH format.
 Sounding RS’s bandwidth is larger than that allocated to UE, in
order to provide the reference to e-NodeB for channel estimation in
the whole bandwidth.
 Sounding RS is mapped to the last symbol of sub-frame. The
transmitted bandwidth and period can be configured. SRS
transmission scheduling of multi UE can achieve
time/frequency/code diversity.
DM RS associated with PUSCH is mapped to
the 4th symbol each slot
Time
Freq
Time
Freq
Time
Freq
DM RS associated with PUCCH (transmits
UL ACK signaling) is mapped to the central 3
symbols each slot
DM RS associated with PUCCH (transmits
UL CQI signaling) is mapped to the 2
symbols each slot
PUCCH is mapped to up & down
ends of the system bandwidth,
hopping between two slots.
Allocated UL bandwidth of one UE
System bandwidth
Uplink Physical Signals

Downlink Resource Structure
• Downlink Resource Structure
 Type I frame, single antenna, ΔF = 15 kHz
 Standard RB:
 One of center 6 RBs:
 Legend:
Downlink Reference Signals

Downlink Resource Structure
OFDM
Symbol 0
CP
OFDM
Symbol 1
CP
OFDM
Symbol 3
CP
OFDM
Symbol 4
CP
OFDM
Symbol 5
CP
OFDM
Symbol 6
CP
OFDM
Symbol 2
CP
Legend:
Downlink Reference signals
PBCH
PSS
SSS
PDCCH / PHICH / PCFICH
PDSCH
1 subframe = 2 slot (1 ms)
1 frame =
10 subframe (10 ms)
SF 0 SF 1 SF 2 SF 3 SF 4 SF 5 SF 6 SF 7 SF 8 SF 9
7 OFDM symbols at normal CP per slot (0.5 ms)
0 1 2 3 4 5 6 0 1 2 3 4 5 6
Centre
6
RBs

Uplink Resource Structure
OFDM
Symbol 0
CP
OFDM
Symbol 1
CP
OFDM
Symbol 3
CP
OFDM
Symbol 4
CP
OFDM
Symbol 5
CP
OFDM
Symbol 6
CP
OFDM
Symbol 2
CP
Legend:
UL DMRS (Uplink Demodulation Reference Signal)
UL SRS (Uplink Sounding Reference Signal)
PUCCH (Physical Uplink Control Channel)
(incl.HARQ feedback and CQI reporting)
Demodulation Reference Signal for PUCC
PUSCH (Physical Uplink Shared Data Channel)
SF 0 SF 1 SF 2 SF 3 SF 4 SF 5 SF 6 SF 7 SF 8 SF 9
7 OFDM symbols at normal CP per slot (0.5 ms)
0 1 2 3 4 5 6 0 1 2 3 4 5 6
1 subframe = 2 slot (1 ms)
1 frame =
10 subframe (10 ms)

Basic Principle of Cell Search:
 Cell search is the procedure of UE synchronizes with E-UTRAN in
time-freq domain, and acquires the serving cell ID.
 Two steps in cell search:
 Step 1: Symbol synchronization and acquirement of ID within
Cell Group by demodulating the Primary Synchronization Signal;
 Step 2: Frame synchronization, acquirement of CP length and
Cell Group ID by demodulating the Secondary Synchronization
Signal.
About Cell ID：
 In LTE protocol, the physical layer Cell ID comprises two parts:
Cell Group ID and ID within Cell Group. The latest version defines
that there are 168 Cell Group IDs, 3 IDs within each group. So
totally 168*3=504 Cell IDs exist.
 represents Cell Group ID, value from 0 to 167;
represents ID within Cell Group, value from 0 to 2.
(2)
ID
(1)
ID
cell
ID 3 N
N
N 

(1)
ID
N
(2)
ID
N
Initial Cell Search:
 The initial cell search is carried on after the UE power on. Usually, UE doesn’t
know the network bandwidth and carrier frequency at the first time switch on.
 UE repeats the basic cell search, tries all the carrier frequency in the spectrum to
demodulate the synchronization signals. This procedure takes time, but the time
requirement are typically relatively relaxed. Some methods can reduce time, such
as recording the former available network information as the prior search target.
 Once finish the cell search, which achieve synchronization of time-freq domain
and acquirement of Cell ID, UE demodulates the PBCH and acquires for system
information, such as bandwidth and Tx antenna number.
 After the procedure above, UE demodulates the PDCCH for its paging period that
allocated by system. UE wakes up from the IDLE state in the specified paging
period, demodulates PDCCH for monitoring paging. If paging is detected, PDSCH
resources will be demodulated to receive paging message.
Physical Layer Procedure — Cell Search

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.
 Two steps in physical layer random access:
 UE transmission of random access preamble
 Random access response from E-UTRAN
Detail Procedure of Random Access:
 Physical Layer procedure is triggered upon request of a preamble
transmission by higher layers.
 The higher layers request indicates a preamble index, a target preamble
received power, a corresponding RA-RNTI and a PRACH resource .
 UE determines the preamble transmission power is preamble target
received power + Path Loss. The transmission shall not higher than the
maximum transmission power of UE. Path Loss is the downlink path loss
estimate calculated in the UE.
 A preamble sequence is selected from the preamble sequence set using
the preamble index.
 A single preamble is transmitted using the selected preamble sequence
with calculated transmission power on the indicated PRACH resource.
 UE Detection of a PDCCH with the indicated RA-RNTI is attempted
during a window controlled by higher layers. If detected, the
corresponding PDSCH transport block is passed to higher layers. The
higher layers parse the transport block and indicate the 20-bit grant.
RA-RNTI: Random Access Radio Network Temporary Identifier
Physical Layer Procedure — Radom Access

Basic Principle of Power Control:
 Downlink power control determines the EPRE (Energy per
Resource Element);
 Uplink power control determines the energy per DFT-SOFDM
(also called SC-FDMA) symbol.
Uplink Power Control:
 Uplink power control consists of opened loop power and closed loop power control.
 A cell wide overload indicator (OI) is exchanged over X2 interface for integrated inter-
cell power control, possible to enhance the system performance through power
control.
 PUSCH, PUCCH, PRACH and Sounding RS can be controlled respectively by uplink
power control. Take PUSCH power control for example:
 PUSCH power control is the slow power control, to compensate the path loss and
shadow fading and control inter-cell interference. The control principle is shown in
above equation. The following factors impact PUSCH transmission power PPUSCH: UE
maximum transmission power PMAX, UE allocated resource MPUSCH, initial
transmission power PO_PUSCH, estimated path loss PL, modulation coding factor △TF
and system adjustment factor f (not working during opened loop PC)
UE report CQI
DL Tx Power
EPRE: Energy per Resource Element
DFT-SOFDM: Discrete Fourier Transform Spread OFDM
f(i)}
(i)
Δ
PL
α(j)
(j)
P
(i))
(M
,
{P
(i)
P TF
O_PUSCH
PUSCH
MAX
PUSCH 




 10
log
10
min
Downlink Power Control:
 The transmission power of downlink RS is usually constant. The
transmission power of PDSCH is proportional with RS transmission power.
 Downlink transmission power will be adjusted by the comparison of UE
report CQI and target CQI during the power control.
X2
UL Tx Power
System adjust
parameters
Physical Layer Procedure — Power Control

Page 34
Adaptive Modulation and Coding
2 bits per symbol in
each carrier.
each carrier.
each carrier.
The most appropriate modulation and coding scheme can be adaptively selected according to the channel propagation
conduction, then the maximum throughput can be obtained for different channel situation.

LTE Feature
• MIMO
• ICIC
• SON
 ANR
 Automatic Detection and Collision PCI
 Mobility Load Balancing
• CSFB

Downlink MIMO
 MIMO is supported in LTE downlink to achieve spatial
multiplexing, including single user mode SU-MIMO and multi user
mode MU-MIMO.
 In order to improve MIMO performance, pre-coding is used in
both SU-MIMO and MU-MIMO to control/reduce the interference
among spatial multiplexing data flows.
 The spatial multiplexing data flows are scheduled to one single
user In SU-MIMO, to enhance the transmission rate and
spectrum efficiency. In MU-MIMO, the data flows are scheduled
to multi users and the resources are shared within users. Multi
user gain can be achieved by user scheduling in the spatial
domain.
Uplink MIMO
 Due to UE cost and power consumption, it is difficult to implement
the UL multi transmission and relative power supply. Virtual-MIMO,
in which multi single antenna UEs are associated to transmit in the
MIMO mode. Virtual-MIMO is still under study.
 Scheduler assigns the same resource to multi users. Each user
transmits data by single antenna. System separates the data by
the specific MIMO demodulation scheme.
 MIMO gain and power gain (higher Tx power in the same time-freq
resource) can be achieved by Virtual-MIMO. Interference of the
multi user data can be controlled by the scheduler, which also bring
multi user gain.
Pre-coding vectors
User k data
User 2 data
User 1 data
Channel Information
User1
User2
User k
Scheduler Pre-coder
S1
S2
Pre-coding vectors
User k data
User 2 data
User 1 data
Channel Information
User1
User2
User k
Scheduler Pre-coder
S1
S2
User 1 data
Channel Information
User1
User2
User k
Scheduler
MIMO
Decoder
User k data
User 1 data
User 1 data
Channel Information
User1
User2
User k
Scheduler
MIMO
Decoder
User k data
User 1 data
DL-MIMO Virtual-MIMO
MIMO

Page 37
DL MIMO
codeword
UE1
User1
S
F
B
C
Mod
SFBC (Transmit Diversity)
Same stream transmitted simultaneously in certain
form of MIMO coding at the same time-frequency
resource from both antenna ports (Rank = 1)
Depending on the environment & number of antennas,
SFBC can reduce fading margin by 2~8 dB, to
extend coverage, and enhance system capacity
UE1
Layer 1, CW1, AMC1
UE2
Layer 2, CW2, AMC2
MIMO
encoder
and layer
mapping
MCW (Spatial Multiplexing)
Multiple data streams transmitted at the same time-
frequency resource from different antenna ports
The terminal must have at least 2 Rx antennas for spatial
multiplexing (SM)

Frequency
Cell 3,5,7
Power
Frequency
Cell 3,5,7
Power
Frequency
Cell 2,4,6
Power
Frequency
Cell 2,4,6
Power
 ICIC is one solution for the cell interference control, is essentially a schedule strategy. In LTE, some coordination schemes( ICIC )
can control the interference in cell edges to enhance the frequency reuse factor and performance in the cell edges.
1
2
3
6
5
7
4
1
2
3
6
5
7
4
The edge band is assigned to the users in
cell edge. The eNB transmit power of the
edge band can be high.
Center Band
Cell 2,4,6 Primary Band
Frequency
Cell 1
Power
Frequency
Cell 1
Power
Cell 1 Edge Band
Center Band
Cell 3,5,7P Edge Band
The center band is assigned to the users in cell
center. The eNB transmit power of the center band
should be reduced in order to avoid the
interference to the edge band of neighbor cells.
Center Band
Center Band
ICIC（Inter-Cell Interference Coordination）

SON（ Self-Organising Networks ）
• SON Brief Introduction
 SON (Self Organization Network) is the functions of LTE that 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

Add new Sites
New site configured site
Description:
• Auto configure and optimize Neighbor
relations, intra-LTE and inter-RAT
• X2 automatic setup
• Operator defined rules and monitoring
supported
Benefits:
• Fast definition of Neighbor Relations
• up to 95% lower cost of neighbor relation
planning and optimization
• Improve customer experience by reducing
HO failure caused by missing neighbor
relations
SON_ANR (Automatic Neighbor Relation)

ANR functionality
 ANR management is implemented through the following 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
 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.

ANR functionality
 Two main type of ANR:
 Event triggered
 Periodical reporting – fast ANR
• Both Event triggered and Fast ANR are applicable for same system or different systems

SON_Automatic Detection of PCI Collisions
• A PCI collision means the serving cell and a neighboring cell have the same PCI but different
ECGIs. PCI collisions may be caused by improper network planning or abnormal neighboring cell
coverage (also known as cross-cell coverage). If two neighboring cells have the same PCI,
interference will be generated.
• When a PCI collision occurs, the eNodeB cannot determine the target cell for a handover. In this
situation, the handover performance deteriorates and the handover success rate is reduced.
• After a PCI collision is removed, the following conditions are met:
 The PCI is unique in the coverage area of a cell.
 The PCI is unique in the neighbor relations of a cell.

SON_Automatic Detection of PCI Collisions Cont.
Automatic Detection of PCI Collisions
• After a neighbor relation is added to the NRT, the eNodeB compares the PCI of the new neighboring cell with the
PCIs of existing neighboring cells in the case of IntraRatEventAnrSwitch is set to ON. If the new neighboring cell and
an existing neighboring cell have the same ECGI but different PCIs, the eNodeB reports a PCI collision to the M2000.
The M2000 collects statistics about PCI collisions and generates a list of PCI collisions.
Reallocating PCIs
• PCI reallocation is a process of reallocating a new PCI to a cell whose PCI collides with the PCI of another cell. The
purpose is to remove PCI collisions.
• The M2000 triggers the PCI reallocation algorithm to provide suggestions on PCI reallocation.
Note:
• After the PCI of a cell is changed, the cell needs to be reestablished and the services carried on the cell are
disrupted. Therefore, the PCI reallocation algorithm only provides reallocation suggestions. A PCI can be reallocated
manually or automatically through a scheduled task configured on the M2000.

Cell A Cell B Cell C
Cell C
Cell B
Cell A
Description:
• Exchange cell load information over X2
• Offload congested cells
• Optimize cell reselection / handover
parameters
Benefits:
• Increase 10% system capacity and 10%-20%
access success rate in unbalance scenario
call drop rate, handover failure rate, and
unnecessary redirection caused by
unbalanced load
SON_MLB( Mobility Load Balancing)

How to solve
Mobility Problems?
PING PONG
unnecessary HO Rate
HO successful rate
Value
Before adopt MRO After adopt MRO
Description:
• HO parameters are optimized based
upon long term UE mobility behavior
• Avoid Ping-Pong handover, handover too
early, handover too late, etc
Benefits:
• Reduce cost of mobility optimization
call drop rate and handover failure rate
SON_MRO( Mobility Robust Optimization )

PAPR
Cyclic Prefix

LTE Evolution and Technologies Explained

Recommended

Recommended

More Related Content

Similar to LTE Evolution and Technologies Explained

Similar to LTE Evolution and Technologies Explained (20)

Recently uploaded

Recently uploaded (20)

LTE Evolution and Technologies Explained