LTE Long Term Evolution for future mobile services

LTE INDEX
• INTRODUCTION
• LTE-Basic Specification
• Duplex Schemes
• LTE Frames and Subframes
• LTE Channel Types
• LTE UE Catagories
• Main LTE Technologies
• OFDM
• MIMO
• SAE
• LTE Self Organising Networks
• Voice over LTE
• SRVCC
• LTE Security
• 4G Aim, Features and Requirements
• LTE Advance
• LTE Advance Technologies

INTRODUCTION
• Developed by the 3GPP(3rd Generation Partnership Project).
• Specified in Release 8 and Release 9 document series.
• For wireless communication of high-speed data for mobile phones and
data terminals.
• Based on the GSM/EDGE and UMTS/HSPA network technologies.
• Increased capacity and speed using different radio interfaces together
with core network improvements.
• LTE is natural upgrade path for carriers with both GSM/UMTS networks
and CDMA2000 networks.
• Different LTE frequencies and bands used in different countries.--
• Only multi-band phones will be able to use LTE in all countries where it is
supported.
• 4G LTE does not satisfy the technical requirements of 3GPP LTE
advance.
• Originally set forth by ITU-R in IMT advance specification.
• Due to marketing pressures and the significant advancements, LTE with
WiMax etc. called 4G.

3G LTE evolution
• Also LTE is an all IP based network, supporting both IPv4 and IPv6.
• Originally there was no provision for voice.
• Voice over LTE(VoLTE) was chosen by GSMA as standard.
3GPP: 3rd Generation Partnership Project
WCDMA: Wideband CDMA
HSPA: High Speed Packet Access
HSDPA/HSUPA: High Speed Downlink/Uplink Packet Access
UMTS: Universal Mobile Telecommunication System
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

3G LTE-Basic Specification
LTE BASIC SPECIFICATIONS
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 times Rel 6 HSUPA
Access schemes OFDMA (Downlink)
SC-FDMA (Uplink)
Modulation types supported QPSK, 16QAM, 64QAM (Uplink and downlink)

Duplex Schemes
• Cellular communications system must be able to transmit in both
directions simultaneously.
• It is necessary to specify direction of transmission.
• Two links are differentiated based on amount of data carried,
transmission format and channels implemented. The two links are
defined:
• Uplink: transmission from UE or user equipment to eNodeB or base
station.
• Downlink: transmission from eNodeB or base station to UE or user
equipment.
• To be able to transmit in both directions, UE or base station must
have a duplex scheme FDD/TDD.

LTE VARIANTS (Duplex Schemes)
• Long-Term Evolution Time-Division Duplex (LTE-TDD),or
Time-division Long-Term Evolution (TD-LTE) co-developed by
an international coalition of companies.
• Developed with idea of migration to 4G from 3G TD-SCDMA.
• Frequency-Division Long-Term Evolution (LTE-FDD).
• Differences between LTE-TDD and LTE-FDD:
• How data is uploaded and downloaded.
• What frequency spectra the networks are deployed in.

LTE VARIANTS (Duplex Schemes)
• LTE-FDD
• Uses paired frequencies to upload and download data.
• Works better at lower frequencies.
• LTE-TDD
• Uses a single frequency to upload and download data alternatively.
• The ratio between uploads and downloads changes dynamically based on
load.
• Works better at higher frequencies. (1850 MHz to 3800 MHz)
• Spectrum is cheaper to access and has less traffic.
• With bands overlapping WiMAX, later can be easily upgraded to
support LTE-TDD.
• Handshaking-
• Despite the differences, TE-TDD and LTE-FDD share 90 percent of their
core technology.
• Makes it possible for the same chipsets and networks to use both
versions of LTE.

Advantages / disadvantages of LTE TDD and LTE FDD
PARAMETER LTE-TDD LTE-FDD
Paired spectrum Does not require as both transmit and receive occur on
the same channel.
Requires with sufficient frequency
separation to allow simultaneous
transmission and reception.
Hardware cost Lower. No diplexer needed to isolate Tr. and Recr.
Lower cost of UEs.
Diplexer is needed and cost is higher.
Channel reciprocity Channel propagation same in both directions using one
set of parameters.
Channel characteristics different in both
directions as use different frequencies.
UL / DL asymmetry Possible to dynamically change UL and DL capacity
ratio to match demand.
UL / DL capacity determined by frequency
allocation. Not possible to change
dynamically to match capacity. Regulatory
changes would be required and capacity is
same in either direction.
Guard period / guard band Required to avoid uplink and downlink transmissions
clash. Large guard period will limit capacity. Larger
guard period required if distances increased to
accommodate larger propagation times.
Guard band required to provide sufficient
isolation between uplink and downlink.
Large guard band does not impact capacity.
Discontinuous transmission Required to allow both uplink and downlink
transmissions. Can degrade performance of RF power
amplifier in the transmitter.
Continuous transmission is required.
Cross slot interference Base stations need to be synchronized with uplink and
downlink transmission times. If neighboring base
stations use different uplink and downlink assignments
and share same channel, interference may occur
between cells.
Not applicable

LTE TDD / TD-LTE and TD-SCDMA
• With advantages of using LTE TDD / TD-LTE with TD-SCDMA,
there needs to be a 3.9G and later a 4G successor to the
technology.
• With unpaired spectrum allocated for TD-SCDMA and UMTS
TDD, upgrade path will benefit from vastly increased speeds and
improved facilities of LTE.
• Subframe structure adopted within LTE TDD / TD-LTE is upgrade
path for TD-SCDMA.
• Although LTE TDD has significant advantage of higher spectrum
efficiency, it is anticipated that LTE FDD will be more widespread.
• It is also anticipated that phones will be able to operate using either
LTE FDD or LTE-TDD (TD-LTE) modes.
• LTE UEs will be dual standard phones and able to operate in any
country.
• The main problem will then be the frequency bands that the phone
can cover.

LTE Frame And Sub-Frame
• 3G LTE system has a defined LTE frame and subframe structure
for the E-UTRA, the air interface for 3G LTE (Evolved UMTS Terrestrial
Radio Access) so that:
• 3G LTE system can maintain synchronization.
• System is able to manage different types of information carried
between the base-station or eNodeB and UE.
• The frame structures differ for TDD and FDD modes as there are
different requirements on segregating the transmitted data.
• There are two types of LTE frame structure:
• Type 1: used for the LTE FDD mode systems.
• Type 2: used for the LTE TDD systems.

Type 1 LTE Frame Structure
• The basic type 1 LTE frame has an overall length of 10ms.
• Length divided into 20 individual slots.
• LTE Subframes consist of two slots.
• Hence there are ten LTE subframes within a frame.

• The 10ms frame comprises just two half frames, each 5ms long.
• The LTE half-frames are further split into five subframes, each
1ms long.

• The subframes divided into standard subframes of special
subframes consisting of three fields;
• DwPTS - Downlink Pilot Time Slot. – (End of downlink)
• GP - Guard Period
• UpPTS - Uplink Pilot Time Slot. – (Beginning of uplink)
• The total length of all three together must be 1ms. (E.g. Frame 2, 6).
• Allows dynamic change of up and downlink balance.
• These are also used within TD-SCDMA.
• They have been carried over into LTE TDD (TD-LTE) and thereby
help the upgrade path.
• The fields are individually configurable in terms of length.

Sub-Frame Allocation
• LTE TDD allows dynamic change of up and downlink balance and
characteristics to meet the load conditions.
• To achieve it in an ordered fashion, a total of seven up / downlink
configurations have been set within the LTE standards.
• These use either 5ms or 10ms switch periodicities.
• 5ms switch periodicity:- Special subframe exists in both half
frames.
• 10ms switch periodicity:- Special subframe exists in first half
frame only.
• Subframes 0, 5 and DwPTS are always reserved for the downlink.
• UpPTS and subframe immediately following special subframe are
always reserved for uplink transmission.

Sub-Frame Allocation
• D is a subframe for downlink transmission
• S is a "special" subframe used for a guard time
• U is a subframe for uplink transmission
UPLINK-
DOWNLINK
CONFIGURATION
DOWNLINK TO
UPLINK SWITCH
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

• Example

3G LTE Frequency Bands Allocations
• FDD and TDD LTE frequency bands
• FDD spectrum requires pair bands, one of the uplink and one for
the downlink.
• TDD requires a single band for Uplink and downlink but time
separated.
• Band allocations for TDD and FDD may overlap.
• UE will need to detect whether a TDD or FDD transmission is
being made on that particular LTE band in its current location.
• LTE frequency bands are allocated numbers.
• Currently the LTE bands between 1 & 22 are for paired spectrum,
i.e. FDD.
• LTE bands between 33 & 41 are for unpaired spectrum, i.e. TDD.

LTE Channel Types
• To transport data across LTE radio interface, various "channels" are used.
• Segregates different types of data to be transported across radio access
network in an orderly fashion.
• Provides interfaces to higher layers within the LTE protocol structure.
• Various data channels are grouped in Three categories :-
• Physical channels: 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.
• LTE physical channels vary between the uplink and the downlink as each
has different requirements and operates in a different manner.

3G LTE Physical channels-Downlink
• Physical Broadcast Channel (PBCH):
• Carries system information for UEs to access the network.
• Only carries Master Information Block (MIB) messages.
• The modulation scheme is always QPSK.
• Information bits are coded and rate matched.
• Bits are then scrambled using a scrambling sequence specific to
the cell to prevent confusion with data from other cells.
• The MIB message on the PBCH is mapped onto the central 72
subcarriers or six central resource blocks regardless of the
overall system bandwidth.
• A PBCH message is repeated every 40ms, i.e. one TTI of PBCH
includes four radio frames.
• The PBCH transmissions has 14 information bits, 10 spare bits,
and 16 CRC bits.

• PBCH
• 3 bits for system bandwidth
• 3 bits for PHICH information,
• 1 bit to indicate normal or extended PHICH
• 2 bit to indicate the PHICH Ng value
• 8 bits for system frame number for initial sychronization and periodic sync.
• 10 bits are reserved for future use
• CRC also conveys number of transmit antennas used by eNodeB.
• MIB CRC is scrambled or XORed with antenna specific mask.
• Generation periodicity –duration 40 ms between two consecutive MIB
information generated by the higher layers for physical layer.
• System frame number within each MIB,- a rolling number between 0-255.
• Changesg every MIB but other contents may or may not change.
• Transmission periodicity – duration between two consecutive PBCH
transmission by the physical layer.
• Contents within 4 consecutive PBCH remains same as PBCH carries MIB.
• MIB can change only after 40 milliseconds since first PBCH transmission.

• Physical Broadcast Channel (PBCH):

PBCH Transmission
• CRC Generation – 16 bit CRC by CRC module, scrambled with
antenna specific mask.
• CRC attachment to MIB – CRC is attached to MIB payload total 40
bits (24 bit of MIB + 16 bit of CRC)
• Convolution encoding – Tail bit convolution encoding performed over
40 bits.
• Output is 3 streams of 40 bits each(120 bits)
• Rate matching – Repetition coding, 120 bits repeated 16 times to get
1920 bits.
• MIB is a very vital information, UE cannot afford to lose.
• Scrambling – These 1920 bits are scrambled with a scrambling sequence
as long as 1920 bits
• Modulation (QPSK) – A QPSK performed over 1920 bits to obtain 960
complex QPSK symbols

PBCH Transmission
• PBCH has to be transmitted every 10 milliseconds on subframe 0 of all
radio frames.
• PBCH modulation buffer is divided into 4 sub-buffers each 240 complex
symbols.
• By the time last sub buffer is transmitted on PBCH, a new MIB is arrived
from higher layer.
• 4 consecutive radio frames transmit same MIB information.
• UE has to find 4 consecutive system frame numbers that are same to
understand 40 millisecond boundary.
• UE can decode MIB & 40 millisecond boundary in 40 milliseconds for
the best case and 70 milliseconds for the worst case.

• Physical Control Format Indicator Channel (PCFICH) :
• PCFICH informs UE about the format of the signal being received.
• It indicates number of OFDM symbols used for PDCCHs (1, 2, or 3).
• Information within PCFICH is essential because the UE does not have
prior information about the size of the control region.
• A PCFICH is transmitted on the first symbol of every sub-frame and
carries a Control Format Indicator, CFI field.
• The CFI contains a 32 bit code word that represents 1, 2, or 3.
• CFI 4 is reserved for possible future use.
• The PCFICH uses 32,2 block coding which results in a 1/16 coding
rate and 16 symbols.
• QPSK modulation to ensure robust reception.
• PCFICH carried by 4 REGs evenly distributed across whole band
regardless of B/W. (Resource Element Group)
• Exact position of PCFICH determined by cell ID and bandwidth.

• PDCCH: Physical downlink control channel
• PDSCH: Physical downlink shared channel

• Physical Downlink Control Channel (PDCCH) :
• Main purpose of this channel is to carry scheduling information
of different types:
• Downlink resource scheduling
• Uplink power control instructions
• Uplink resource grant
• Indication for paging or system information
• PDCCH contains message Downlink Control Information,.
• DCI carries control information for a particular UE or group of
UEs.
• The DCI format has different types defined with different sizes.
• The different format types include: Type 0, 1, 1A, 1B, 1C, 1D,
2, 2A, 2B, 2C, 3, 3A, and 4.

• Physical Downlink Shared Channel (PDSCH) : Main data bearing
channel allocated to users on a dynamic basis.
• Also used to transmit broadcast information not transmitted on the
PBCH e.g. System Information Blocks (SIB) and paging & RRC
signalling messages.
• PDSCH is also used to transfer application data.
• QPSK, 16QAM, 64QAM modulation types.
• QPSK is most robust, used for transmission of SIB and Paging.
• RBs are shared among all active connections.
• Paging messages-Broadcast using PDSCH channel.
• LTE UE in RRC IDLE mode monitor PDCCH for paging indications.
• It decodes paging message carried in PDSCH RBs.
• Downlink RRC Signalling messages-Carried by PDSCH.
• Signalling Radio Bearers(SRB) will use PDSCH.
• Every connection usually will have its own set of SRB.

CP- Cyclic Prefix

• Physical Hybrid ARQ Indicator Channel (PHICH) :
• Channel is used to report the Hybrid ARQ status.
• It carries the HARQ ACK/NACK signal indicating whether a
transport block has been correctly received.
• The HARQ indicator is 1 bit long –
• "0" indicates ACK, "1" indicates NACK.
• The PHICH is transmitted within the control region of the
subframe.
• It is typically only transmitted within the first symbol.
• If the radio link is poor, then the PHICH is extended to a
number symbols for robustness.

3G LTE Physical channels-Uplink
• Physical Uplink Control Channel (PUCCH) :
• Provides various control signalling requirements.
• Number of different PUCCH formats defined to enable channel to
carry required information in most efficient format for particular
scenario encountered.
• Includes ability to carry SRs, Scheduling Requests.
PUCCH FORMAT UPLINK CONTROL
INFORMATION
MODULATION
SCHEME
BITS PER SUB-
FRAME
NOTES
Format 1 SR N/A N/A
Format 1a 1 bit HARQ ACK/NACK
with or without SR
BPSK 1
Format 1b 2 bit HARQ ACK/NACK
with or without SR
QPSK 2
Format 2 CQI/PMI or RI QPSK 20
Format 2a CQI/PMI or RI and 1 bit
HARQ ACK/NACK
QPSK + BPSK 21
Format 2b CQI/PMI or RI and 2 bit
HARQ ACK/NACK
QPSK + BPSK 22
Format 3 Provides support for carrier
aggregation.

• Physical Uplink Shared Channel (PUSCH) :
• Uplink counterpart of PDSCH
• Physical Random Access Channel (PRACH) :
• Used for random access functions.
• The only non-synchronised transmission that the UE can make
within LTE.
• The downlink and uplink propagation delays are unknown when
PRACH is used.
• Therefore it cannot be synchronised.
• PRACH instance is made up from two sequences:
• a cyclic prefix
• a guard period.
• The preamble sequence may be repeated to enable the eNodeB
to decode the preamble when link conditions are poor.

3G LTE Transport channels-Downlink
• Downlink:
• Broadcast Channel (BCH) : Maps to Broadcast Control Channel
(BCCH)
• Downlink Shared Channel (DL-SCH) : Main channel for downlink
data transfer.
• Used by many logical channels.
• Paging Channel (PCH) : To convey the PCCH
• Multicast Channel (MCH) : Used to transmit MCCH information to
set up multicast transmissions.
•
• Uplink:
• Uplink Shared Channel (UL-SCH) : Main channel for uplink data
transfer.
• Used by many logical channels.
• Random Access Channel (RACH) : Used for random access
requirements.

3G LTE Logical channels
• Cover the data carried over the radio interface.
• Service Access Point, SAP between MAC sublayer and the RLC
sublayer provides the logical channel.
• Control channels: Carry the control plane information:
• Broadcast Control Channel (BCCH) : Provides system information
to all mobile terminals connected to the eNodeB.
• Paging Control Channel (PCCH) : Used for paging information
when searching a unit on a network.
• Common Control Channel (CCCH) : Used for random access
information, e.g. for actions including setting up a connection.
• Multicast Control Channel (MCCH) : Used for Information needed
for multicast reception.
• Dedicated Control Channel (DCCH) : Used for carrying user-
specific control information, e.g. for controlling actions
including power control, handover, etc..

3G LTE Logical channels
• Traffic channels: Carry the user-plane data:
• Dedicated Traffic Channel (DTCH) : Used for the transmission of
user data.
• Multicast Traffic Channel (MTCH) : Used for transmission of
multicast data.

3G LTE UE Category
• LTE categories define standards to which a particular handset,
dongle or other equipment will operate.
• Needed to ensure that base station can communicate correctly with
user equipment.
• LTE category defines overall performance and capabilities of UE.
• The eNB communicates using UE capabilities and not beyond.
• 9 different LTE UE categories are defined with wide range in the
supported parameters and performance.
• Example:
• LTE category 1 does not support MIMO, but LTE UE category 5
supports 4x4 MIMO.
• UE class 1 does not offer performance offered by that of HSPA.
• LTE UE categories are capable of receiving transmissions from up
to four antenna ports.

3G LTE UE Category
• Headline data rates for category 8 exceed the requirements for
IMT-Advanced by a considerable margin.
• Headline rates show the maximum data rates achievable.
HEADLINE DATA RATES FOR LTE CATEGORIES
LTE UE CATEGORY
LINK 1 2 3 4 5 6 7 8
Downlink 10 50 100 150 300 300 300 1200
Uplink 5 25 50 50 75 50 150 600

3G LTE UE Category
ULAND DL PARAMETERS FOR LTE UE CATEGORIES
LTE CATEGORY
PARAMETER LTE CAT
1
LTE CAT
2
LTE CAT
3
LTE CAT
4
LTE CAT
5
LTE CAT
6
LTE CAT
7
LTE CAT
8
Max number of DL-SCH
transport block bits received
in a TTI
10 296 51 024 102 048 150 752 302 752 299 552 299 552 1 200 000
Max number of bits of a DL-
SCH block received in a TTI
10 296 51 024 75 376 75 376 151 376 TBD TBD TBD
Total number of soft channel
bits
250 368 1 237 248 1 237 248 1 827 072 3 667 200 3 667 200 TBD TBD
Maximum number of
supported layers for spatial
multiplexing in DL
1 2 2 2 4
Max number of bits of an UL-
SCH transport block received
in a TTI
5 160 25 456 51 024 51 024 75 376 TBD TBD TBD
Support for 64-QAM in UL No No No No Yes No Yes, up to
RAN 4
Yes
• DL-SCH = Downlink shared channel
• UL-SCH = Uplink shared channel
• TTI = Transmission Time Interval

3G LTE UE Category 0
• LTE category needed focusing on developing technologies:
• Internet of Things(IoT)
• General machine to machine(M2M) communications.
• Requirements are
• much lower data rates,
• short bursts,
• remote device to be able to draw low current levels.
• LTE Category 0 has a reduced performance requirement.
• Meets the needs of many machines while significantly reducing
complexity and current consumption.
• In spite of reduced specification, it complies with LTE system
requirements.
• New LTE Cat 0 was introduced in Rel 12 of the 3GPP standards.

3G LTE UE Category 0
• One major advantage of LTE Category 0:
• Modem complexity is considerably reduced when compared to other LTE
Categories.
• 50% that of a Category 1 modem.
LTE CATEGORY 0 PERFORMANCE SUMMARY
PARAMETER LTE CAT 0 PERFORMANCE
Peak downlink rate 1 Mbps
Peak uplink rate 1 Mbps
Max number of downlink spatial layers 1
Number of UE RF chains 1
Duplex mode Half duplex
UE receive bandwidth 20 MHz
Maximum UE transmit power 23 dBm

Main LTE Technologies - 1
1. OFDM (Orthogonal Frequency Division Multiplex):
• Enables high data bandwidths to be transmitted efficiently.
• High degree of resilience to reflections and interference.
• Differ between the uplink and downlink:
• OFDMA (Orthogonal Frequency Division Multiple Access )–
downlink.
• SC-FDMA(Single Carrier - Frequency Division Multiple
Access) - uplink.
• Specialized FDM with all carrier signals orthogonal to one another.
• Crosstalk between sub-channels eliminated and inter-carrier guard
bands not required.
• Unlike conventional FDM, a separate filter for each sub-channel is
not required.

Main LTE Technologies- -OFDM
• OFDM (Orthogonal Frequency Division Multiplex):
• But multiple signals arising from the many reflections.
• Limits use of OFDM in high-speed vehicles.
• FDM requires very accurate frequency synchronization between
receiver and transmitter.
• OFDMA is a multi-user version of OFDM.
• Multiple access achieved by assigning subsets of subcarriers to
individual users.
• Allows simultaneous low data rate transmission from several users.
• SC-FDMA interpreted as linearly precoded OFDMA scheme.
• Assigns multiple users to a shared communication resource.
• SC-FDMA has small peak to average power ratio.
• Desirable for uplink wireless transmission where transmitter power
efficiency is of paramount importance.
• More constant power enables high RF power amplifier efficiency in
mobile handsets.

2. MIMO (Multiple Input Multiple Output):
• Additional signal paths due to reflections are used to advantage.
• Increase the throughput.
• Multiple antennas to enable different paths to be distinguished.
• 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used at base station.
• Dimensions of user equipment limit number of antennas to be
place at least half wavelength apart.
• Improves performance of system.
• Provides LTE with ability to improve its data throughput and
spectral efficiency above OFDM.
• Enables far high data rates and much improved spectral efficiency.
• MIMO an integral part of LTE.

LTE MIMO Basics
• Transmitter and Receiver have more than one antenna.
• Provide improvements in data rate and efficiency.
• MIMO has been a cornerstone of the LTE standard.
• Initially, in releases 8 and 9 multiple transmit antennas on the UE
was not supported as only interested in power reduction.
• Rel. 10 has number of new schemes introduced.
• Closed loop spatial multiplexing for SU-MIMO as well as multiple
antennas on the UE.

LTE MIMO Modes
• MIMO modes depend on equipment used and channel functions.
• Single antenna:
• Used on most basic wireless links.
• Single data stream transmitted by one antenna and received by one
or more antennas.
• SISO or SIMO dependent upon the antennas used.
• SIMO is also called Receive Diversity.
• Transmit diversity:
• Utilizes transmission of same information stream from multiple
antennas.
• Information is coded differently using Space Frequency Block
Codes.
• Provides an improvement in signal quality at reception but does
not improve the data rate.
• Used on Common Channels as well as Control and Broadcast
channels.

LTE MIMO Modes
• Open loop spatial multiplexing:
• Sends two information streams transmitted over two or more
antennas.
• No feedback from the UE.
• TRI, Transmit Rank Indicator transmitted from the UE can be used
by the base station to determine the number of spatial layers.
• Close loop spatial multiplexing :
• Similar to open loop version, but has feedback incorporated to
close the loop.
• PMI, Pre-coding Matrix Indicator is fed back from the UE to the
base station.
• Enables transmitter to pre-code data to optimize transmission.
• Enable receiver to more easily separate different data streams.

LTE MIMO Modes
• Closed loop with pre-coding:
• Single code word is transmitted over a single spatial layer.
• Used as a fall-back mode for closed loop spatial multiplexing.
• May also be associated with beamforming as well.
• Precoding matrix selection at receiver and precoding operation at
transmitter.
• Achieves good tradeoff between system complexity and
performance gain given by closed-loop transmission.
• Multi-User MIMO, MU-MIMO: space-division multiple access
• Enables the system to target different spatial streams to different
users.
• Set of users each with one or more antennas communicate with
each other.
• Multiple access (multi-user) capabilities to MIMO

LTE MIMO Modes
• Beam-forming:
• Most complex of the MIMO modes.
• Likely to use linear arrays that will enable the antenna to focus on
a particular area.
• This will reduce interference, and increase capacity as the
particular UE will have a beam formed in their particular direction.
• A single code word is transmitted over a single spatial layer.
• A dedicated reference signal is used for an additional port.
• The terminal estimates the channel quality from the common
reference signals on the antennas.

3. SAE (System Architecture Evolution):
• For very high data rate and low latency, system architecture is
evolved for improved performance.
• Number of functions handled by core network transferred to
periphery.
• Provides a much "flatter" form of network architecture.
• Latency times can be reduced and data can be routed more directly
to its destination.
• Fully compatible with LTE Advanced.
• Based on GSM / WCDMA core networks to enable simplified
operations and easy deployment.

SAE-Advantages
• Improved data capacity: With 3G LTE data rates 100 Mbps and
focus on mobile broadband, network should handle greater levels
of data.
• Hence necessary system architecture must be adopted.
• All IP architecture: With 3G evolution, voice evolved from
circuit switched to IP data.
• New SAE schemes have adopted an all IP network configuration.
• Reduced latency: SAE concepts evolved to ensure levels of
latency reduced to 10ms for increased interaction and much faster
responses.
• Ensure applications using 3G LTE will be sufficiently responsive.
• Reduced OPEX and CAPEX: Any new design reduces capital
expenditure and the operational expenditure.
• Flat architecture of SAE means only two node types are used.
• A high level of automatic configuration is introduced to reduce
set-up and commissioning time.

SAE-Basics
• Based on GSM / WCDMA core networks to enable simplified
operations and easy deployment.
• SAE network brings major changes to allow more efficient
effective transfer of data.
• Several common principles used in the development of LTE SAE
network:
• Common gateway node and anchor point for all technologies.
• Optimized architecture for user plane with only two node types.
• All IP based system with IP based protocols used on all interfaces.
• Split in control plane / user plane between mobility management
entity (MME) and gateway.
• Radio access network / core network functional split similar to that
used on WCDMA / HSPA.
• Integration of non-3GPP access technologies (e.g. cdma2000,
WiMAX, etc) using client as well as network based mobile-IP.

LTE SAE-Evolved Packet Core
• Evolved Packet Core or EPC is main element of the LTE SAE
network.
• This connects to eNodeBs.
• LTE SAE EPC consists of four main elements as :

LTE SAE-EPC Elements
• Mobility Management Entity, MME: Main control node for LTE
SAE access network.
• Handles features:
• Idle mode UE tracking
• Bearer activation / de-activation
• Choice of SGW for a UE
• Intra-LTE handover involving core network node location
• Interacting with HSS to authenticate user on attachment
• Implements roaming restrictions
• Acts as a termination for Non-Access Stratum (NAS)
• Provides temporary identities for UEs
• Acts as termination point for ciphering protection for NAS signaling.
• Also handles security key management.
• It is the point at which lawful interception of signaling may be made.
• Paging procedure
• The S3 interface terminates in the MME thereby providing the control
plane function for mobility between LTE and 2G/3G access networks.
• Also terminates the S6a interface for the home HSS for roaming UEs.
• Overall provides a considerable level of overall control functionality.

• Serving Gateway, SGW: It is a data plane element within LTE
SAE.
• Main purpose:
• Manage user plane mobility.
• Acts as main border between the Radio Access Network, RAN
and core network.
• Maintains data paths between eNodeBs and PDN Gateways.
• Forms interface for data packet network at E-UTRAN.
• Serves as mobility anchor ensuring data path when UEs move
across areas served by different eNodeBs.
• PDN Gateway, PGW: Provides connectivity for the UE to external
packet data networks
• Fulfills function of entry and exit point for UE data.
• UE may have connectivity with more than one PGW for accessing
multiple PDNs. (Packet Data Network)

• Policy and Charging Rules Function, PCRF: Generic name for
entity within the LTE SAE EPC.
• Detects the service flow.
• Enforces charging policy.
• For applications requiring dynamic policy or charging control, a
network element Applications Function, AF is used.

LTE Self Organising Networks
• LTE requires smaller cell sizes for greater data traffic to be
handled.
• Need to reduce costs by reducing manual input.
• Results in more complicated networks.
• Difficult to plan and manage the network centrally.
• Need self organising networks.
• LTE major driver behind self-organising network, SON
philosophy.
• 3GPP developed requirements for LTE SON alongside basic
functionality of LTE.
• Standards for LTE SON are embedded within the 3GPP standards.

LTE SON-Major Elements
• Self configuration:
• To enable new base stations to become "Plug and Play" items.
• Should need as little manual intervention in the configuration
process as possible.
• Be able to organise RF aspects.
• Configure backhaul.
• Self optimisation:
• After set up, enables base station to optimise operational
characteristics to best meet the needs of the overall network.
• Self-healing:
• Enables network to self-heal.
• By changing characteristics of the network to mask the problem
until it is fixed.
• For example, the boundaries of adjacent cells can be increased by
changing antenna directions and increasing power levels, etc..

Voice Over LTE –Why?
• Originally-
• LTE - IP cellular system for data,
• 2G / 3G systems or VoIP for voice
• Leads to:
• Fragmentation and incompatibility, not allowing all phones to
communicate with each other.
• Reduced voice traffic.
• SMS services still widely used, reducing revenue from voice
calls and SMS.
• Viable and standardised scheme needed to provide voice and SMS
services to protect this revenue.

LTE – Options for Voice
• CSFB, Circuit Switched Fall Back: Standardised under 3GPP
specification 23.272.
• Uses variety of processes and network elements for fall back to the 2G or
3G connection (GSM, UMTS, CDMA2000 1x) before a circuit switched
call is initiated.
• Allows SMS using an interface SGs allowing messages to be sent over
an LTE channel.
• SV-LTE - Simultaneous Voice LTE: Allows packet switched LTE
services to run simultaneously with a circuit switched voice service.
• Has disadvantage, two radios to run at the same time within the handset
with serious impact on battery life.
• VoLGA, Voice over LTE via GAN: 3GPP Generic Access Network
aims for consistent set of voice, SMS and other circuit-switched services
as they transit between GSM, UMTS and LTE access networks.
• For mobile operators, aims to provide low-cost and low-risk approach
for bringing primary revenue generating services (voice and SMS) onto
the new LTE network deployments.
• Voice over LTE, VoLTE: Chosen by GSMA for use on LTE.
• Standardised method for providing SMS and voice over LTE.

V0LTE – Basics
• IP Multimedia Subsystem, IMS-based specification.
• Enables system integration with suite of applications available on
LTE.
• Cut down version reduced number of entities required in IMS
network, but simplified interconnectivity focusing on VoLTE
elements.
• Entities within the reduced IMS network used for VoLTE:
• HSS: Home subscriber server
• P-CSCF: Proxy-Call Session Control Function
• I-CSCF: Interrogating-Call Session Control Function
• S-CSCF: Serving-Call Session Control Function
• IP-CAN : IP connectivity access network
• AS: Application server

V0LTE – Basics
• IP-CAN, IP Connectivity Access Network: Consists of EUTRAN
and MME.
• P-CSCF, Proxy Call State Control Function: User to network proxy.
• All SIP signalling to/ from user runs via P-CSCF whether in home /
visited network.
• I-CSCF, Interrogating Call State Control Function: Used for
forwarding an initial SIP request to the S-CSCF when initiator does not
know which S-CSCF should receive the request.
• S-CSCF, Serving Call State Control Function: Undertakes variety of
actions within overall system.
• Has number of interfaces to communicate with other entities within the
overall system.
• AS, Application Server: Handles voice as an application.
• HSS, Home Subscriber Server: Main subscriber database used within
IMS.
• Provides details of subscribers to other entities within IMS network, to
be granted access or not dependent upon their status.

V0LTE – Basic operation
• The IMS calls for VoLTE are processed by subscriber's S-CSCF in
the home network.
• The connection to the S-CSCF is via P-CSCF.
• Dependent upon network in use and overall location within a
network, the P-CSCF will vary.
• Hands back to circuit switched legacy networks in a seamless
manner, while only having one transmitting radio in the handset to
preserve battery life.
• A system known as SRVCC - Single Radio Voice Call Continuity
is required for this.

SRVCC- Single Radio Voice Call Continuity
• It is level of functionality, required within VoLTE systems for
packet domain calls on LTE to be handed over to legacy circuit
switched voice systems like GSM, UMTS and CDMA 1x in a
seamless manner.
• SRVCC enables:
• Inter Radio Access Technology, Inter RAT handover,
• handover from packet data to circuit switched data voice calls.
• Handovers made while-
• maintaining existing quality of service,
• ensuring that call continuity meets critical requirements for
emergency calls.
• Requires single active radio in the handset and some upgrades to
the supporting network infrastructure.

SRVCC- Network Architecture
• SRVCC originally included in 3GPP Rel 8.
• 3GPP Rel 10 implemented later as this ensures a considerably
lower level of voice interruption and dropped calls.
• SRVCC demands software upgrades to MSS, Mobile SoftSwitch
subsystem in MSC, IMS subsystem and LTE/EPC subsystem.
• No upgrades required for radio access network of the legacy
system.
• Majority of legacy system remains unaffected.
• Upgrades to MSC are relatively easy to manage.
• MSC centrally located and not dispersed around the network.
• Makes upgrades easier to manage.
• Dedicated MSC may be used that has been upgraded to handles the
SRVCC requirements.

SRVCC- Working
• Controls transfer of calls in both directions.
• LTE to legacy network handover
Required when user moves out of LTE coverage area.
• Handover undertaken in two stages:
• Radio Access Technology transfer: Handover for the radio access
network.
• Well-established protocol e.g. transfers from 3G to 2G.
• Session transfer: New element required for SRVCC.
• To shift access control and voice media anchoring from Evolved
Packet Core, EPC of packet switched LTE network to legacy
circuit switched network.
• During handover, CSCF in IMS architecture maintains control of
whole operation.

SRVCC- Working
• Voice handover using SRVCC on LTE

SRVCC- Working
• The SRVCC handover process takes place in a number of steps:
• Process initiated by a request for session transfer from IMS CSCF.
• The IMS CSCF responds simultaneously with two commands,
• one to the LTE network,
• other to the legacy network.
• LTE network receives radio Access Network handover execution
command through MME and LTE RAN.
• This instructs user device to prepare to move to a circuit switched
network for the voice call.
• The destination legacy circuit switched network receives a session
transfer response preparing it to accept the call from the LTE
network.
• After all the commands have been executed and acknowledged, the
call is switched to the legacy network with the IMS CSCF still in
control of the call.

SRVCC- Working
• Legacy network to LTE
When returning a call to the LTE network much of same
functionality is again used.
• To ensure VoLTE device return to LTE RAN from legacy RAN,
there are two options the legacy RAN can implement to provide a
swift and effective return:
• Allow LTE information to be broadcast on the legacy RAN so the
LTE device is able to perform the cell reselection more easily.
• Simultaneously release the connection to the user device and
redirect it to the LTE RAN.

SRVCC- Interruption performance
• One of key issues with VoLTE and SRVCC is interruption time of
handover from LTE RAN to legacy RAN.
• Time reduces if simultaneously performs redirections of RAN and
session.
• User experience is maintained.
• Actual interruption time is not unduly noticeable.
• Session redirection is the faster of the two handovers,
• therefore necessary for overall handover methodology to
accommodate the fact that there are difference between the two.
• USIM: For LTE, SIM upgraded to USIM- UMTS Subscriber
Identity Module may be used.
• Gives more functionality, has a larger memory.
• Older SIM cards are not compatible and may not be used.

LTE Security
• LTE security requirements:
• Must provide at least same level of security that was provided by 3G
services.
• Should not affect user convenience.
• Should provide defense from attacks from the Internet.
• Should not affect the transition from existing 3G services to LTE.
• The USIM currently used for 3G services should still be used.
• Changes required to implement level of LTE security are :
• Hierarchical key system introduced, keys changed for different purposes.
• Security functions for Non-Access Stratum, NAS, and Access Stratum,
AS have been separated.
• The NAS functions - functions for which processing is accomplished
between core network and mobile terminal UE.
• The AS functions - communications between - network edge, i.e. eNB
and UE.
• Concept of forward security introduced for LTE security.
• Security functions introduced between existing 3G and LTE network.

4G - AIM
• Upgrading of 3G UMTS to 4G mobile communications
technology.
• Simplifying the architecture of the system.
• Transitions from existing UMTS circuit/packet switching
combined network to all-IP flat architecture system.

4G - FEATURE
• Peak download rates - 299.6 Mbit/s and upload rates - 75.4 Mbit/s
depending on the user equipment.
• Five different terminal classes defined from audio to peak data rates.
• All terminals will be able to process 20 MHz bandwidth.
• Lower latencies for data transfer, handover and connection setup
time than before.
• Improved support for mobility up to 350 km/h or 500 km/h
depending on the frequency band.
• OFDM access for the downlink, single carrier FDMA for the
uplink to conserve power.
• Support for both FDD and TDD, also half-duplex FDD
communication systems with the same radio access technology.

4G - FEATURE
• Increased spectrum flexibility: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz,
15 MHz and 20 MHz wide cells are standardized.
• Support for cell sizes from tens of meters radius (femto and Pico
cells) up to 100 km radius macrocells.
• Lower frequency bands to be used in rural areas for,
• 5 km is the optimal cell size,
• 30 km having reasonable performance,
• and up to 100 km cell sizes supported with acceptable performance.
• In city and urban areas, higher frequency bands are used to support
high speed mobile broadband for cell sizes 1 km.

4G - FEATURE
• Supports at least 200 active data clients in every 5 MHz cell.
• Simplified architecture with network side of E-UTRAN composed
only of eNODE-Bs.
• Support for inter-operation and co-existence with legacy standards
like GSM/EDGE, UMTS and CDMA2000.
• Packet switched audio interface.
• Support for MBSFN(Multicast Broadcast Single Frequency Network)
• Can deliver services such as Mobile TV using the LTE
infrastructure,
• Is a competitor for DVB-H-based TV broadcast (Digital Video
Broadcasting – Handheld)
• Does not provide backward compatibility to previous standard
such as 2G and 3G.

4G - Requirements
 Support for all frequency bands currently used by IMT systems by
ITU-R.
 It must be an all IP-based packet switching network.
 Must provide data peak rates of up to approximately:
 100 Mbit/s for highly mobile access.
 1 Gbit/s for low mobility
 User-friendly applications, services, and equipment
 Dynamically use and share resources network to support more
simultaneous users per cell.
 Must be able to provide a scalable channel BW of 5–20 MHz .
 High QOS that supports next generation multimedia services .

4G- WiMAX
• Wimax-Worldwide interoperability for Microwave access
• IP based wireless broadband telecommunication technology.
• Aimed at providing high speed data, voice, video, also digital wireless
communication to mobile.
• Initially designed to provide up to 30 - 40 Mbit/s data rate upgraded to 1 Gbit/s.
• Developed as an alternative to DSL (digital subscriber line)
• Sometimes referred as Wifi on steroids , provides VoIP, IPTV and other
internet based services.
• Two standards to Wimax: Fixed Wimax and Mobile Wimax.
• Fixed Wimax: IEEE 802.16-2004 or IEEE 802.16d;
• Fixed wireless access technology.
• Aimed at servicing fixed and mobile applications.
• Purpose is to replace the Subscriber digital line (DSL)standard and to serve as
backhaul for wifi access points or for mobile networks, and subsequently
provide basic voice and broadband access.
• Mobile Wimax-
• Mobile wireless access standard
• Only capable to work on NLOS environments.
• For fixed and mobile applications with a greater indoor penetration.

4G- LTE
• Though originally sold as 4G, LTE didn't satisfy the ITU-R
technical requirements.
• Due to marketing pressures and advancements of LTE, ITU later
decided LTE as 4G technology.
• LTE is a first-generation 4G technology to reach speeds of around
100Mbit/s.
• Originally lacked in download speed, uplink spectral efficiency
and speed.
• Uplink spectral efficiency is efficiency of upload and transmit data
rate from smartphone.
• Falls short of true 4G capacity because –
• lack of carrier aggregation
• phones not having many antennae.
• Better carrier aggregation and MIMO leads to 'true' 4G: LTE
Advanced.

4G LTE - LTE Advance
• 4G technology, IMT Advanced developed under 3GPP termed LTE
Advanced.
• ITU-R started development for terrestrial components of IMT
Advanced radio interface in competition with LTE Advanced
solution.
• Key milestones for ITU-R IMT Advanced evaluation
KEY MILESTONES ON THE DEVELOPMENT OF 4G LTE-ADVANCED
MILESTONE DATE
Issue invitation to propose Radio Interface
Technologies.
March 2008
ITU date for cut-off for submission of proposed Radio
Interface Technologies.
October 2009
Cutoff date for evaluation report to ITU. June 2010
Decision on framework of key characteristics of IMT
Advanced Radio Interface Technologies.
October 2010
Completion of development of radio interface
specification recommendations.
February 2011

4G LTE - LTE Advance
COMPARISON OF LTE-A WITH OTHER CELLULAR TECHNOLOGIES
WCDMA
(UMTS)
HSPA
HSDPA / HSUPA
HSPA+ LTE LTE ADVANCED
(IMT ADVANCED)
Max downlink speed
bps
384 k 14 M 28 M 100M 1G
Max uplink speed
bps
128 k 5.7 M 11 M 50 M 500 M
Latency
round trip time
approx
150 ms 100 ms 50ms (max) ~10 ms less than 5 ms
3GPP releases Rel 99/4 Rel 5 / 6 Rel 7 Rel 8 Rel 10
Approx years of
initial roll out
2003 / 4 2005 / 6 HSDPA
2007 / 8 HSUPA
2008 / 9 2009 / 10 2014 / 15
Access methodology CDMA CDMA CDMA OFDMA / SC-
FDMA
OFDMA / SC-FDMA

LTE Advance - Key Features
• LTE Advanced aims for :
• Peak data rates: downlink - 1 Gbps; uplink - 500 Mbps.
• Spectrum efficiency: 3 times greater than LTE.
• Peak spectrum efficiency: downlink - 30 bps/Hz; uplink - 15
bps/Hz.
• Spectrum : ability to support scalable bandwidth use and spectrum
aggregation where non-contiguous spectrum needs to be used.
• Latency: from Idle to Connected in less than 50 ms and then
shorter than 5 ms one way for individual packet transmission.
• Cell edge user throughput to be twice that of LTE.
• Average user throughput to be 3 times that of LTE.
• Mobility: Same as that in LTE
• Compatibility: LTE Advanced shall be capable of interworking
with LTE and 3GPP legacy systems.

LTE Advance - Technologies
• Orthogonal Frequency Division Multiplex, OFDM : Forms
basis of radio bearer.
• OFDMA with SC-FDMA used in hybrid format.
• Multiple Input Multiple Output, MIMO: Other key enabler for
LTE Advanced.
• Enables data rates to be increased beyond what basic radio bearer
would normally allow.
• Additional antennas to enable additional paths at cost of overheads
and return per additional path
• Beamforming may be used to enable antenna coverage to be
focused where it is needed.

LTE Advance - Technologies
• Carrier Aggregation, CA: Operators are able to utilise multiple
channels either in the same bands or different areas of the spectrum
to provide the required bandwidth.
• Coordinated Multipoint : Interference from adjacent cells along
with poor signal quality lead to a reduction in data rates and poor
performance at the cell edges.
• Coordinated multipoint has been introduced.
• LTE Relaying: Enables signals to be forwarded by remote
stations from a main base station to improve coverage.
• Device to Device, D2D: Enables fast swift access via direct
communication.
• Facility essential for emergency services on the scene of an
incident.

Reference
• https://en.wikipedia.org/wiki/LTE_(telecommunication)
• http://www.pcadvisor.co.uk/feature/mobile-phone/whats-difference-
between-4g-lte-3605656/
• http://www.in.techradar.com/news/phone-and-communications/mobile-
phones/4G-and-LTE-everything-you-need-to-
know/articleshow/38880546.cms
• http://www.ijarcsse.com/docs/papers/Volume_4/11_November2014/V4I1
1-0300.pdf
• http://www.academia.edu/4861088/4G_and_the_future_of_mobile_telec
ommunication
• http://www.radio-electronics.com/info/cellulartelecomms/lte-long-
term-evolution

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