LTE Long Term Evolution Tutorial

8/16/2019 LTE Long Term Evolution Tutorial

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LTE Introduction &

TutorialLTE, Long Term Evolution is the successor to 3G UMTS and

HSPA providing much higher data download speeds and

setting the foundations for 4G LTE Advanced. Discover more

about LTE basics in this tutorial.


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Table of Contents

LTE Long Term Evolution Tutorial & Basics ............................................................................................................ 3

3G LTE evolution ........................................................................................................................................................... 3

LTE basics:- specification overview ............................................................................................................................... 4

Main LTE technologies .................................................................................................................................................. 5

LTE OFDM, OFDMA SC-FDMA & Modulation ......................................................................................................... 6

LTE modulation & OFDM basics .................................................................................................................................... 6

LTE channel bandwidths and characteristics ................................................................................................................ 6

LTE OFDM cyclic prefix, CP ............................................................................................................................................ 7

LTE OFDMA in the downlink ......................................................................................................................................... 7

Downlink carriers and resource blocks ......................................................................................................................... 8

LTE SC-FDMA in the uplink ............................................................................................................................................ 8

LTE MIMO: Multiple Input Multiple Output Tutorial.............................................................................................. 9

LTE MIMO basics ........................................................................................................................................................... 9

LTE MIMO ...................................................................................................................................................................... 9

LTE MIMO modes ........................................................................................................................................................ 10

LTE FDD, TDD, TD-LTE Duplex Schemes ............................................................................................................... 11

Duplex schemes .......................................................................................................................................................... 11

Advantages / disadvantages of LTE TDD and LTE FDD for cellular communications .................................................. 12

LTE TDD / TD-LTE and TD-SCDMA ............................................................................................................................... 13

LTE Frame and Subframe Structure ..................................................................................................................... 14

Type 1 LTE Frame Structure ........................................................................................................................................ 14

Type 2 LTE Frame Structure ........................................................................................................................................ 14

LTE TDD / TD-LTE Subframe allocations ...................................................................................................................... 15

LTE Physical, Logical and Transport Channels ...................................................................................................... 16

3G LTE channel types .................................................................................................................................................. 16

3G LTE physical channels ............................................................................................................................................ 16

LTE transport channels ................................................................................................................................................ 18

LTE logical channels .................................................................................................................................................... 18

LTE Frequency Bands & Spectrum Allocations ..................................................................................................... 19

FDD LTE frequency band allocations ........................................................................................................................... 19

TDD LTE frequency band allocations .......................................................................................................................... 20

LTE UE Category & Class Definitions .................................................................................................................... 22

LTE UE category rationale ........................................................................................................................................... 22

LTE UE category definitions ........................................................................................................................................ 22

LTE Category 0 ............................................................................................................................................................. 23

LTE UE category summary .......................................................................................................................................... 24


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LTE SAE System Architecture Evolution ............................................................................................................... 25

Reason for SAE System Architecture Evolution .......................................................................................................... 25

SAE System Architecture Evolution basics .................................................................................................................. 26

LTE SAE Distributed intelligence ................................................................................................................................. 28

LTE SON Self Organizing Networks ...................................................................................................................... 29

LTE SON development................................................................................................................................................. 29

Major elements of LTE SON ........................................................................................................................................ 29

LTE SON and 3GPP standards ...................................................................................................................................... 30

Voice over LTE - VoLTE Tutorial ........................................................................................................................... 31

Options for LTE Voice .................................................................................................................................................. 31

Voice over LTE, VoLTE formation ................................................................................................................................ 32

Voice over LTE, VoLTE basics ...................................................................................................................................... 32

VoLTE codecs............................................................................................................................................................... 33

VoLTE IP versions ........................................................................................................................................................ 34

4G LTE Advanced Tutorial ................................................................................................................................... 35

Key milestones for ITU-R IMT Advanced evaluation ................................................................................................... 35

LTE Advanced development history ........................................................................................................................... 35

LTE Advanced key features ......................................................................................................................................... 36

LTE Advanced technologies......................................................................................................................................... 37

LTE CA: Carrier Aggregation Tutorial ................................................................................................................... 39

LTE carrier aggregation basics ..................................................................................................................................... 39

RF aspects of carrier aggregation................................................................................................................................ 40

Carrier aggregation bandwidths ................................................................................................................................. 41

LTE aggregated carriers ............................................................................................................................................... 42

Carrier aggregation cross carrier scheduling .............................................................................................................. 42

4G LTE CoMP, Coordinated Multipoint Tutorial ................................................................................................... 44

LTE CoMP and 3GPP .................................................................................................................................................... 44

LTE CoMP - the advantages......................................................................................................................................... 44

What is LTE CoMP? - the basics .................................................................................................................................. 45

Downlink LTE CoMP .................................................................................................................................................... 46

Uplink LTE CoMP ......................................................................................................................................................... 47

Overall requirements for LTE CoMP ........................................................................................................................... 47

LTE Advanced Heterogeneous Networks, HetNet ................................................................................................ 48

LTE heterogeneous network basics ............................................................................................................................ 48

LTE HetNet features .................................................................................................................................................... 48


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LTE Long Term Evolution Tutorial & Basics

- developed by 3GPP, LTE, Long Term Evolution is the successor to 3G UMTS and HSPA providing much higher data

download speeds and setting the foundations for 4G LTE Advanced. Discover more about LTE basics in this tutorial.

LTE, Long Term Evolution, the successor to UMTS and HSPA is now being deployed and is the way forwards

for high speed cellular services.

In its first forms it was a 3G or as some would call it a 3.99G technology, but with further additions the

technology fulfilled the requirements for a 4G standard. In this form it was referred to as LTE Advanced.

There has been a rapid increase in the use of data carried by cellular services, and this increase will only

become larger in what has been termed the "data explosion". To cater for this and the increased demands

for increased data transmission speeds and lower latency, further development of cellular technology have

been required.

The UMTS cellular technology upgrade has been dubbed LTE - Long Term Evolution. The idea is that 3G LTE

will enable much higher speeds to be achieved along with much lower packet latency (a growing

requirement for many services these days), and that 3GPP LTE will enable cellular communications services

to move forward to meet the needs for cellular technology to 2017 and well beyond.

Many operators have not yet upgraded their basic 3G networks, and 3GPP LTE is seen as the next logical

step for many operators, who will leapfrog straight from basic 3G straight to LTE as this will avoid providing

several stages of upgrade. The use of LTE will also provide the data capabilities that will be required for

many years and until the full launch of the full 4G standards known as LTE Advanced.

3G LTE evolution

Although there are major step changes between LTE and its 3G predecessors, it is nevertheless looked

upon as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different form of radio

interface, using OFDMA / SC-FDMA instead of CDMA, there are many similarities with the earlier forms of

3G architecture and there is scope for much re-use.

In determining what is LTE and how does it differ from other cellular systems, a quick look at the

specifications for the system can provide many answers. LTE can be seen for provide a further evolution offunctionality, increased speeds and general improved performance.


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WCDMA

(UMTS)

HSPA

HSDPA / HSUPAHSPA+ LTE

Max downlink speed

bps384 k 14 M 28 M 100M

Max uplink speed

bps128 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 / 42005 / 6 HSDPA

2007 / 8 HSUPA2008 / 9 2009 / 10

Access methodology CDMA CDMA CDMA OFDMA / SC-FDMA

In addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. Originally there was also

no basic provision for voice, although Voice over LTE, VoLTE was added was chosen by GSMA as the

standard for this. In the interim, techniques including circuit switched fallback, CSFB are expected to be

used

LTE basics:- specification overview

It is worth summarizing the key parameters of the 3G LTE specification. In view of the fact that there are a

number of differences between the operation of the uplink and downlink, these naturally differ in the

performance they can offer.

LTE basic specifications

Parameter Details

Peak downlink speed64QAM

(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

Mobility0 - 15 km/h (optimised),

15 - 120 km/h (high performance)

LatencyIdle to active less than 100ms

Small packets ~10 ms

Spectral efficiencyDownlink: 3 - 4 times Rel 6 HSDPA

Uplink: 2 -3 x Rel 6 HSUPA

Access schemesOFDMA (Downlink)

SC-FDMA (Uplink)

Modulation types supported QPSK, 16QAM, 64QAM (Uplink and downlink)

These highlight specifications give an overall view of the performance that LTE will offer. It meets the

requirements of industry for high data download speeds as well as reduced latency - a factor important for

many applications from VoIP to gaming and interactive use of data. It also provides significant

improvements in the use of the available spectrum.


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Main LTE technologies

LTE has introduced a number of new technologies when compared to the previous cellular systems. They

enable LTE to be able to operate more efficiently with respect to the use of spectrum, and also to provide

the much higher data rates that are being required.

OFDM (Orthogonal Frequency Division Multiplex): OFDM technology has been incorporated into

LTE because it enables high data bandwidths to be transmitted efficiently while still providing a highdegree of resilience to reflections and interference. The access schemes differ between the uplink

and downlink: OFDMA (Orthogonal Frequency Division Multiple Access is used in the downlink;

while SC-FDMA(Single Carrier - Frequency Division Multiple Access) is used in the uplink. SC-FDMA

is used in view of the fact that its peak to average power ratio is small and the more constant

power enables high RF power amplifier efficiency in the mobile handsets - an important factor for

battery power equipment.

MIMO (Multiple Input Multiple Output): One of the main problems that previous

telecommunications systems have encountered is that of multiple signals arising from the many

reflections that are encountered. By using MIMO, these additional signal paths can be used to

advantage and are able to be used to increase the throughput.

When using MIMO, it is necessary to use multiple antennas to enable the different paths to be

distinguished. Accordingly schemes using 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used. While

it is relatively easy to add further antennas to a base station, the same is not true of mobile

handsets, where the dimensions of the user equipment limit the number of antennas which should

be place at least a half wavelength apart.

SAE (System Architecture Evolution): With the very high data rate and low latency requirements

for 3G LTE, it is necessary to evolve the system architecture to enable the improved performance to

be achieved. One change is that a number of the functions previously handled by the core networkhave been transferred out to the periphery. Essentially this provides a much "flatter" form of

network architecture. In this way latency times can be reduced and data can be routed more

directly to its destination.

A fuller description of what LTE is and the how the associated technologies work is all addressed in much

greater detail in the following pages of this tutorial.


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LTE OFDM, OFDMA SC-FDMA & Modulation

- LTE, Long term Evolution uses the modulation format, OFDM - orthogonal frequency division multiplex, adapted

to provide a multiple access scheme using OFDMA and SC-FDMA.

One of the key elements of LTE is the use of OFDM, Orthogonal Frequency Division Multiplex, as the signal

bearer and the associated access schemes, OFDMA (Orthogonal Frequency Division Multiplex) and SC-

FDMA (Single Frequency Division Multiple Access).

OFDM is used in a number of other of systems from WLAN, WiMAX to broadcast technologies including

DVB and DAB. OFDM has many advantages including its robustness to multipath fading and interference. In

addition to this, even though, it may appear to be a particularly complicated form of modulation, it lends

itself to digital signal processing techniques.

In view of its advantages, the use of ODFM and the associated access technologies, OFDMA and SC-FDMA

are natural choices for the new LTE cellular standard.

LTE modulation & OFDM basics

The use of OFDM is a natural choice for LTE. While the basic concepts of OFDM are used, it has naturally

been tailored to meet the exact requirements for LTE. However its use of multiple carrier each carrying a

low data rate remains the same.

The actual implementation of the technology will be different between the downlink (i.e. from base station

to mobile) and the uplink (i.e. mobile to the base station) as a result of the different requirements between

the two directions and the equipment at either end. However OFDM was chosen as the signal bearer

format because it is very resilient to interference. Also in recent years a considerable level of experience

has been gained in its use from the various forms of broadcasting that use it along with Wi-Fi and WiMAX.

OFDM is also a modulation format that is very suitable for carrying high data rates - one of the key

requirements for LTE.

In addition to this, OFDM can be used in both FDD and TDD formats. This becomes an additionaladvantage.

LTE channel bandwidths and characteristics

One of the key parameters associated with the use of OFDM within LTE is the choice of bandwidth. The

available bandwidth influences a variety of decisions including the number of carriers that can be

accommodated in the OFDM signal and in turn this influences elements including the symbol length and so

forth.

LTE defines a number of channel bandwidths. Obviously the greater the bandwidth, the greater the

channel capacity.

Note on OFDM:

Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced

carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each

other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted

is split across all the carriers to give resilience against selective fading from multi-path effects..


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The channel bandwidths that have been chosen for LTE are:

1. 1.4 MHz

2. 3 MHz

3. 5 MHz

4. 10 MHz

5. 15 MHz

6.

20 MHz

In addition to this the subcarriers spacing is 15 kHz, i.e. the LTE subcarriers are spaced 15 kHz apart from

each other. To maintain orthogonality, this gives a symbol rate of 1 / 15 kHz = of 66.7 µs.

Each subcarrier is able to carry data at a maximum rate of 15 ksps (kilosymbols per second). This gives a 20

MHz bandwidth system a raw symbol rate of 18 Msps. In turn this is able to provide a raw data rate of 108

Mbps as each symbol using 64QAM is able to represent six bits.

It may appear that these rates do not align with the headline figures given in the LTE specifications. The

reason for this is that actual peak data rates are derived by first subtracting the coding and control

overheads. Then there are gains arising from elements such as the spatial multiplexing, etc.

LTE OFDM cyclic prefix, CP

One of the primary reasons for using OFDM as a modulation format within LTE (and many other wireless

systems for that matter) is its resilience to multipath delays and spread. However it is still necessary to

implement methods of adding resilience to the system. This helps overcome the inter-symbol interference

(ISI) that results from this.

In areas where inter-symbol interference is expected, it can be avoided by inserting a guard period into thetiming at the beginning of each data symbol. It is then possible to copy a section from the end of the

symbol to the beginning. This is known as the cyclic prefix, CP. The receiver can then sample the waveform

at the optimum time and avoid any inter-symbol interference caused by reflections that are delayed by

times up to the length of the cyclic prefix, CP.

The length of the cyclic prefix, CP is important. If it is not long enough then it will not counteract the

multipath reflection delay spread. If it is too long, then it will reduce the data throughput capacity. For LTE,

the standard length of the cyclic prefix has been chosen to be 4.69 µs. This enables the system to

accommodate path variations of up to 1.4 km. With the symbol length in LTE set to 66.7 µs.

The symbol length is defined by the fact that for OFDM systems the symbol length is equal to the

reciprocal of the carrier spacing so that orthogonality is achieved. With a carrier spacing of 15 kHz, this

gives the symbol length of 66.7 µs.

LTE OFDMA in the downlink

The OFDM signal used in LTE comprises a maximum of 2048 different sub-carriers having a spacing of 15

kHz. Although it is mandatory for the mobiles to have capability to be able to receive all 2048 sub-carriers,not all need to be transmitted by the base station which only needs to be able to support the transmission

of 72 sub-carriers. In this way all mobiles will be able to talk to any base station.

Within the OFDM signal it is possible to choose between three types of modulation for the LTE signal:


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1. QPSK (= 4QAM) 2 bits per symbol

2. 16QAM 4 bits per symbol

3. 64QAM 6 bits per symbol

The exact LTE modulation format is chosen depending upon the prevailing conditions. The lower forms of

modulation, (QPSK) do not require such a large signal to noise ratio but are not able to send the data as

fast. Only when there is a sufficient signal to noise ratio can the higher order modulation format be used.

Downlink carriers and resource blocks

In the downlink, the subcarriers are split into resource blocks. This enables the system to be able to

compartmentalise the data across standard numbers of subcarriers.

Resource blocks comprise 12 subcarriers, regardless of the overall LTE signal bandwidth. They also cover

one slot in the time frame. This means that different LTE signal bandwidths will have different numbers of

resource blocks.

Channel bandwidth

(MHz)1.4 3 5 10 15 20

Number of resource blocks 6 15 25 50 75 100

LTE SC-FDMA in the uplink

For the LTE uplink, a different concept is used for the access technique. Although still using a form of

OFDMA technology, the implementation is called Single Carrier Frequency Division Multiple Access (SC-

FDMA).

One of the key parameters that affects all mobiles is that of battery life. Even though battery performance

is improving all the time, it is still necessary to ensure that the mobiles use as little battery power aspossible. With the RF power amplifier that transmits the radio frequency signal via the antenna to the base

station being the highest power item within the mobile, it is necessary that it operates in as efficient mode

as possible. This can be significantly affected by the form of radio frequency modulation and signal format.

Signals that have a high peak to average ratio and require linear amplification do not lend themselves to

the use of efficient RF power amplifiers. As a result it is necessary to employ a mode of transmission that

has as near a constant power level when operating. Unfortunately OFDM has a high peak to average ratio.

While this is not a problem for the base station where power is not a particular problem, it is unacceptable

for the mobile. As a result, LTE uses a modulation scheme known as SC-FDMA - Single Carrier Frequency

Division Multiplex which is a hybrid format. This combines the low peak to average ratio offered by single-

carrier systems with the multipath interference resilience and flexible subcarrier frequency allocation thatOFDM provides.

Note on QAM, Quadrature Amplitude Modualtion:

Quadrature amplitude modulation, QAM is widely sued for data transmission as it enables better elvels of spectral

efficiency than other forms of modulation. QAM uses two carriers onth e same frequency shifted by 90° which are

modulated by two data streams - I or Inphase and Q - Quadrature elements.


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LTE MIMO: Multiple Input Multiple Output Tutorial

- MIMO is used within LTE to provide better signal performance and / or higher data rates by the use of the radio

path reflections that exist.

MIMO, Multiple Input Multiple Output is another of the LTE major technology innovations used to improve

the performance of the system. This technology provides LTE with the ability to further improve its data

throughput and spectral efficiency above that obtained by the use of OFDM.

Although MIMO adds complexity to the system in terms of processing and the number of antennas

required, it enables far high data rates to be achieved along with much improved spectral efficiency. As a

result, MIMO has been included as an integral part of LTE.

LTE MIMO basics

The basic concept of MIMO utilises the multipath signal propagation that is present in all terrestrial

communications. Rather than providing interference, these paths can be used to advantage.

General Outline of MIMO system

The transmitter and receiver have more than one antenna and using the processing power available at

either end of the link, they are able to utilise the different paths that exist between the two entities to

provide improvements in data rate of signal to noise.

MIMO is being used increasingly in many high data rate technologies including Wi-Fi and other wireless

and cellular technologies to provide improved levels of efficiency. Essentially MIMO employs multiple

antennas on the receiver and transmitter to utilise the multi-path effects that always exist to transmit

additional data, rather than causing interference.

LTE MIMO

The use of MIMO technology has been introduced successively over the different releases of the LTE

standards.

Note on MIMO:

Two major limitations in communications channels can be multipath interference, and the data throughput

limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist

between a transmitter and receiver to significantly improve the data throughput available on a given channel with its

defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital

signal processing, MIMO technology enables the system to set up multiple data streams on the same channel,

thereby increasing the data capacity of a channel.


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MIMO has been a cornerstone of the LTE standard, but initially, in releases 8 and 9 multiple transmit

antennas on the UE was not supported because in the interested of power reduction, only a single RF

power amplifier was assumed to be available.

It was in Rel. 10 that a number of new schemes were introduced. Closed loop spatial multiplexing for SU-

MIMO as well as multiple antennas on the UE.

LTE MIMO modes

There are several ways in which MIMO is implemented in LTE. These vary according to the equipment

used, the channel function and the equipment involved in the link.

Single antenna: This is the form of wireless transmission used on most basic wireless links. A

single data stream is transmitted on one antenna and received by one or more antennas. It may

also be referred to as SISO: Single In Single Out or SIMO Single In Multiple Out dependent upon the

antennas used. SIMO is also called receive diversity.

Transmit diversity: This form of LTE MIMO scheme utilises the transmission of the same

information stream from multiple antennas. LTE supports two or four for this technique.. Theinformation is coded differently using Space Frequency Block Codes. This mode provides an

improvement in signal quality at reception and does not improve the data rate. Accordingly this

form of LTE MIMO is used on the Common Channels as well as the Control and Broadcast channels.

Open loop spatial multiplexing: This form of MIMO used within the LTE system involves sending

two information streams which can be transmitted over two or more antennas. However there is

no feedback from the UE although a 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 : This form of LTE MIMO is similar to the open loop version, but as

the name indicates it has feedback incorporated to close the loop. A PMI, Pre-coding Matrix

Indicator is fed back from the UE to the base station. This enables the transmitter to pre-code thedata to optimise the transmission and enable the receiver to more easily separate the different

data streams.

Closed loop with pre-coding: This is another form of LTE MIMO, but where a single code word is

transmitted over a single spatial layer. This can be sued as a fall-back mode for closed loop spatial

multiplexing and it may also be associated with beamforming as well.

Multi-User MIMO, MU-MIMO: This form of LTE MIMO enables the system to target different

spatial streams to different users.

Beam-forming: This is the most complex of the MIMO modes and it is 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. In this asingle 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.


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LTE FDD, TDD, TD-LTE Duplex Schemes

- information, overview, or tutorial about the LTE TDD and LTE FDD duplex schemes used with LTE and including

TD-LTE.

LTE has been defined to accommodate both paired spectrum for Frequency Division Duplex, FDD and

unpaired spectrum for Time Division Duplex, TDD operation. It is anticipated that both LTE TDD and LTE

FDD will be widely deployed as each form of the LTE standard has its own advantages and disadvantages

and decisions can be made about which format to adopt dependent upon the particular application.

LTE FDD using the paired spectrum is anticipated to form the migration path for the current 3G services

being used around the globe, most of which use FDD paired spectrum. However there has been an

additional emphasis on including TDD LTE using unpaired spectrum. TDD LTE which is also known as TD-LTE

is seen as providing the evolution or upgrade path for TD-SCDMA.

In view of the increased level of importance being placed upon LTE TDD or TD-LTE, it is planned that user

equipments will be designed to accommodate both FDD and TDD modes. With TDD having an increased

level of importance placed upon it, it means that TDD operations will be able to benefit from the

economies of scale that were previously only open to FDD operations.

Duplex schemes

It is essential that any cellular communications system must be able to transmit in both directions

simultaneously. This enables conversations to be made, with either end being able to talk and listen as

required. Additionally when exchanging data it is necessary to be able to undertake virtually simultaneous

or completely simultaneous communications in both directions.

It is necessary to be able to specify the different direction of transmission so that it is possible to easily

identify in which direction the transmission is being made. There are a variety of differences between the

two links ranging from the amount of data carried to the transmission format, and the channels

implemented. The two links are defined:

Uplink: the transmission from the UE or user equipment to the eNodeB or base station.

Downlink the transmission from the eNodeB or base station to the UE or user equipment.

Uplink and downlink transmission directions

In order to be able to be able to transmit in both directions, a user equipment or base station must have a

duplex scheme. There are two forms of duplex that are commonly used, namely FDD, frequency division

duplex and TDD time division duplex.


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Both FDD and TDD have their own advantages and disadvantages. Accordingly they may be used for

different applications, or where the bias of the communications is different.

Advantages / disadvantages of LTE TDD and LTE FDD for cellular

communications

There are a number of the advantages and disadvantages of TDD and FDD that are of particular interest to

mobile or cellular telecommunications operators. These are naturally reflected into LTE.

Comparison of TDD LTE and FDD LTE Duplex Formats

Parameter LTE-TDD LTE-FDD

Paired spectrum Does not require paired spectrum as both transmit

and receive occur on the same channel

Requires paired spectrum with sufficient frequency

separation to allow simultaneous transmission and

reception

Hardware cost

Lower cost as no diplexer is needed to isolate the

transmitter and receiver. As cost of the UEs is of

major importance because of the vast numbers

that are produced, this is a key aspect.

Diplexer is needed and cost is higher.

Channel reciprocity

Channel propagation is the same in both

directions which enables transmit and receive to

use on set of parameters

Channel characteristics different in both directions

as a result of the use of different frequencies

UL / DL asymmetry It is possible to dynamically change the UL and DL

capacity ratio to match demand

UL / DL capacity determined by frequency

allocation set out by the regulatory authorities. It is

therefore not possible to make dynamic changes

to match capacity. Regulatory changes would

normally be required and capacity is normally

allocated so that it is the same in either direction.

Guard period /

guard band

Guard period required to ensure uplink and

downlink transmissions do not clash. Large guardperiod will limit capacity. Larger guard period

normally required if distances are increased to

accommodate larger propagation times.

Guard band required to provide sufficient isolationbetween uplink and downlink. Large guard band

does not impact capacity.

Discontinuous

transmission

Discontinuous transmission is required to allow

both uplink and downlink transmissions. This can

degrade the performance of the RF power

amplifier in the transmitter.

Continuous transmission is required.

Cross slot

interference

Base stations need to be synchronised with

respect to the uplink and downlink transmission

times. If neighbouring base stations use different

uplink and downlink assignments and share the

same channel, then interference may occur

between cells.

Not applicable

Note on TDD and FDD duplex schemes:

In order for radio communications systems to be able to communicate in both directions it is necessary to have what

is termed a duplex scheme. A duplex scheme provides a way of organizing the transmitter and receiver so that they

can transmit and receive. There are several methods that can be adopted. For applications including wireless and

cellular telecommunications, where it is required that the transmitter and receiver are able to operate

simultaneously, two schemes are in use. One known as FDD or frequency division duplex uses two channels, one for

transmit and the other for receiver. Another scheme known as TDD, time division duplex uses one frequency, but

allocates different time slots for transmission and reception.


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LTE TDD / TD-LTE and TD-SCDMA

Apart from the technical reasons and advantages for using LTE TDD / TD-LTE, there are market drivers as

well. With TD-SCDMA now well established in China, there needs to be a 3.9G and later a 4G successor to

the technology. With unpaired spectrum allocated for TD-SCDMA as well as UMTS TDD, it is natural to see

many operators wanting an upgrade path for their technologies to benefit from the vastly increased

speeds and improved facilities of LTE. Accordingly there is a considerable interest in the development of

LTE TDD, which is also known in China as TD-LTE.

With the considerable interest from the supporters of TD-SCDMA, a number of features to make the mode

of operation of TD-LTE more of an upgrade path for TD-SCDMA have been incorporated. One example of

this is the subframe structure that has been adopted within LTE TDD / TD-LTE.

While both LTE TDD (TD-LTE) and LTE FDD will be widely used, it is anticipated that LTE FDD will be the

more widespread, although LTE TDD has a number of significant advantages, especially in terms of higher

spectrum efficiency that can be used by many operators. It is also anticipated that phones will be able to

operate using either the LTE FDD or LTE-TDD (TD-LTE) modes. In this way the LTE UEs or user equipments

will be dual standard phones, and able to operate in countries regardless of the flavour of LTE that is used -the main problem will then be the frequency bands that the phone can cover.


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LTE Frame and Subframe Structure

- information, overview, or tutorial about the LTE frame and subframe structure including LTE Type 1 and LTE Type

2 frames.

In order that the 3G LTE system can maintain synchronisation and the system is able to manage the

different types of information that need to be carried between the base-station or eNodeB and the User

Equipment, UE, 3G LTE system has a defined LTE frame and subframe structure for the E-UTRA or Evolved

UMTS Terrestrial Radio Access, i.e. the air interface for 3G LTE.

The frame structures for LTE differ between the Time Division Duplex, TDD and the Frequency Division

Duplex, FDD modes as there are different requirements on segregating the transmitted data.

There are two types of LTE frame structure:

1. Type 1: used for the LTE FDD mode systems.

2. Type 2: used for the LTE TDD systems.

Type 1 LTE Frame Structure

The basic type 1 LTE frame has an overall length of 10 ms. This is then divided into a total of 20 individual

slots. LTE Subframes then consist of two slots - in other words there are ten LTE subframes within a frame.



The frame structure for the type 2 frames used on LTE TDD is somewhat different. The 10 ms frame

comprises two half frames, each 5 ms long. The LTE half-frames are further split into five subframes, each

1ms long.


(shown for 5ms switch point periodicity).


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The subframes may be divided into standard subframes of special subframes. The special subframes

consist of three fields;

DwPTS - Downlink Pilot Time Slot

GP - Guard Period

UpPTS - Uplink Pilot Time Stot.

These three fields are also used within TD-SCDMA and 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, although the

total length of all three together must be 1ms.

LTE TDD / TD-LTE Subframe allocations

One of the advantages of using LTE TDD is that it is possible to dynamically change the up and downlink

balance and characteristics to meet the load conditions. In order that this can be achieved in an ordered

fashion, a number of standard configurations have been set within the LTE standards.

A total of seven up / downlink configurations have been set, and these use either 5 ms or 10 ms switch

periodicities. In the case of the 5ms switch point periodicity, a special subframe exists in both half frames.

In the case of the 10 ms periodicity, the special subframe exists in the first half frame only. It can be seen

from the table below that the subframes 0 and 5 as well as DwPTS are always reserved for the downlink. It

can also be seen that UpPTS and the subframe immediately following the special subframe are always

reserved for the 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

Where:

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 subframe configurations for LTE TDD (TD-LTE)


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LTE Physical, Logical and Transport Channels

- overview, information, tutorial about the physical, logical, control and transport channels used within 3GPP, 3G

LTE and the LTE channel mapping.

In order that data can be transported across the LTE radio interface, various "channels" are used. These are

used to segregate the different types of data and allow them to be transported across the radio access

network in an orderly fashion.

Effectively the different channels provide interfaces to the higher layers within the LTE protocol structure

and enable an orderly and defined segregation of the data.

3G LTE channel types

There are three categories into which the various data channels may be grouped.

Physical channels: These are transmission channels that carry user data and control messages. Transport channels: The physical layer transport channels offer information transfer to Medium

Access Control (MAC) and higher layers.

Logical channels: Provide services for the Medium Access Control (MAC) layer within the LTE

protocol structure.

3G LTE physical channels

The LTE physical channels vary between the uplink and the downlink as each has different requirements

and operates in a different manner.

Downlink:

o Physical Broadcast Channel (PBCH): This physical channel carries system information for

UEs requiring to access the network. It only carries what is termed Master Information

Block, MIB, messages. The modulation scheme is always QPSK and the information bits are

coded and rate matched - the 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 40 ms, i.e. one TTI of PBCH includes four radio frames.

The PBCH transmissions has 14 information bits, 10 spare bits, and 16 CRC bits.

o Physical Control Format Indicator Channel (PCFICH) : As the name implies the PCFICH

informs the UE about the format of the signal being received. It indicates the number of

OFDM symbols used for the PDCCHs, whether 1, 2, or 3. The information within the 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 FormatIndicator, CFI, field. The CFI contains a 32 bit code word that represents 1, 2, or 3. CFI 4 is

reserved for possible future use.


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The PCFICH uses 32,2 block coding which results in a 1/16 coding rate, and it always uses

QPSK modulation to ensure robust reception.

o Physical Downlink Control Channel (PDCCH) : The main purpose of this physical channel is

to carry mainly scheduling information of different types:

Downlink resource scheduling

Uplink power control instructions Uplink resource grant

Indication for paging or system information

The PDCCH contains a message known as the Downlink Control Information, DCI which carries the control

information for a particular UE or group of UEs. The DCI format has several different types which are

defined with different sizes. The different format types include: Type 0, 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3,

3A, and 4.

o Physical Hybrid ARQ Indicator Channel (PHICH) : As the name implies, this 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, and "1" indicates NACK.

The PHICH is transmitted within the control region of the subframe and 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.

Uplink:

o Physical Uplink Control Channel (PUCCH) : The Physical Uplink Control Channel, PUCCH

provides the various control signalling requirements. There are a number of different

PUCCH formats defined to enable the channel to carry the required information in the most

efficient format for the particular scenario encountered. It includes the ability to carry SRs,

Scheduling Requests.

The basic formats are summarised below:

PUCCH Format Uplink Control InformationModulation

Scheme

Bits per Sub-

frameNotes

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.

o Physical Uplink Shared Channel (PUSCH) : This physical channel found on the LTE uplink is

the Uplink counterpart of PDSCH

o Physical Random Access Channel (PRACH) : This uplink physical channel is used for random

access functions. This is the only non-synchronised transmission that the UE can make

within LTE. The downlink and uplink propagation delays are unknown when PRACH is usedand therefore it cannot be synchronised.


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The PRACH instance is made up from two sequences: a cyclic prefix and a guard period. The

preamble sequence may be repeated to enable the eNodeB to decode the preamble when

link conditions are poor.

LTE transport channels

The LTE transport channels vary between the uplink and the downlink as each has different requirements

and operates in a different manner. Physical layer transport channels offer information transfer to mediumaccess control (MAC) and higher layers.

Downlink:

o Broadcast Channel (BCH) : The LTE transport channel maps to Broadcast Control Channel

(BCCH)

o Downlink Shared Channel (DL-SCH) : This transport channel is the main channel for

downlink data transfer. It is used by many logical channels.

o Paging Channel (PCH) : To convey the PCCH

o Multicast Channel (MCH) : This transport channel is used to transmit MCCH information to

set up multicast transmissions. Uplink:

o Uplink Shared Channel (UL-SCH) : This transport channel is the main channel for uplink

data transfer. It is used by many logical channels.

o Random Access Channel (RACH) : This is used for random access requirements.

LTE logical channels

The logical channels cover the data carried over the radio interface. The Service Access Point, SAP between

MAC sublayer and the RLC sublayer provides the logical channel.

Control channels: these LTE control channels carry the control plane information:

o Broadcast Control Channel (BCCH) : This control channel provides system information to

all mobile terminals connected to the eNodeB.

o Paging Control Channel (PCCH) : This control channel is used for paging information when

searching a unit on a network.

o Common Control Channel (CCCH) : This channel is used for random access information, e.g.

for actions including setting up a connection.

o

Multicast Control Channel (MCCH) : This control channel is used for Information neededfor multicast reception.

o Dedicated Control Channel (DCCH) : This control channel is used for carrying user-specific

control information, e.g. for controlling actions including power control, handover, etc.

Traffic channels:These LTE traffic channels carry the user-plane data:

o Dedicated Traffic Channel (DTCH) : This traffic channel is used for the transmission of user

data.

o Multicast Traffic Channel (MTCH) : This channel is used for the transmission of multicast

data.

It will be seen that many of the LTE channels bear similarities to those sued in previous generations ofmobile telecommunications.


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LTE Frequency Bands & Spectrum Allocations

- a summary and tables of the LTE frequency band spectrum allocations for 3G & 4G LTE - TDD and FDD.

There is a growing number of LTE frequency bands that are being designated as possibilities for use with

LTE. Many of the LTE frequency bands are already in use for other cellular systems, whereas other LTE

bands are new and being introduced as other users are re-allocated spectrum elsewhere.

FDD and TDD LTE frequency bands

FDD spectrum requires pair bands, one of the uplink and one for the downlink, and TDD requires a single

band as uplink and downlink are on the same frequency but time separated. As a result, there are different

LTE band allocations for TDD and FDD. In some cases these bands may overlap, and it is therefore feasible,

although unlikely that both TDD and FDD transmissions could be present on a particular LTE frequency

band.

The greater likelihood is that a single UE or mobile will need to detect whether a TDD or FDD transmission

should be made on a given band. UEs that roam may encounter both types on the same band. They will

therefore need to detect what type of transmission is being made on that particular LTE band in its current

location.

The different LTE frequency allocations or LTE frequency bands are allocated numbers. Currently the LTE

bands between 1 & 22 are for paired spectrum, i.e. FDD, and LTE bands between 33 & 41 are for unpaired

spectrum, i.e. TDD.

LTE frequency band definitions

FDD LTE frequency band allocations

There are a large number of allocations or radio spectrum that has been reserved for FDD, frequency

division duplex, LTE use.

The FDD LTE frequency bands are paired to allow simultaneous transmission on two frequencies. The

bands also have a sufficient separation to enable the transmitted signals not to unduly impair the receiver

performance. If the signals are too close then the receiver may be "blocked" and the sensitivity impaired.

The separation must be sufficient to enable the roll-off of the antenna filtering to give sufficientattenuation of the transmitted signal within the receive band.


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FDD LTE Bands & Frequencies

LTE Band

Number

Uplink

(MHz)

Downlink

(MHz)

Width of Band

(MHz)

Duplex Spacing

(MHz)Band Gap (MHz)

1 1920 - 1980 2110 - 2170 60 190 130

2 1850 - 1910 1930 - 1990 60 80 20

3 1710 - 1785 1805 -1880 75 95 20

4 1710 - 1755 2110 - 2155 45 400 355

5 824 - 849 869 - 894 25 45 20

6 830 - 840 875 - 885 10 35 25

7 2500 - 2570 2620 - 2690 70 120 50

8 880 - 915 925 - 960 35 45 10

9 1749.9 - 1784.9 1844.9 - 1879.9 35 95 60

10 1710 - 1770 2110 - 2170 60 400 340

11 1427.9 - 1452.9 1475.9 - 1500.9 20 48 28

12 698 - 716 728 - 746 18 30 12

13 777 - 787 746 - 756 10 -31 41

14 788 - 798 758 - 768 10 -30 40

15 1900 - 1920 2600 - 2620 20 700 680

16 2010 - 2025 2585 - 2600 15 575 560

17 704 - 716 734 - 746 12 30 18

18 815 - 830 860 - 875 15 45 30

19 830 - 845 875 - 890 15 45 30

20 832 - 862 791 - 821 30 -41 71

21 1447.9 - 1462.9 1495.5 - 1510.9 15 48 33

22 3410 - 3500 3510 - 3600 90 100 10

23 2000 - 2020 2180 - 2200 20 180 160

24 1625.5 - 1660.5 1525 - 1559 34 -101.5 135.5

25 1850 - 1915 1930 - 1995 65 80 15

26 814 - 849 859 - 894 30 / 40 10

27 807 - 824 852 - 869 17 45 28

28 703 - 748 758 - 803 45 55 10

29 n/a 717 - 728 11

30 2305 - 2315 2350 - 2360 10 45 35

31 452.5 - 457.5 462.5 - 467.5 5 10 5

TDD LTE frequency band allocations

With the interest in TDD LTE, there are several unpaired frequency allocations that are being prepared for

LTR TDD use. The TDD LTE bands are unpaired because the uplink and downlink share the same frequency,

being time multiplexed.

TDD LTE Bands & Frequencies

LTE BandNumber

Allocation (MHz) Width of Band (MHz)

33 1900 - 1920 20

34 2010 - 2025 15


22/5021 | P a g e

TDD LTE Bands & Frequencies

LTE Band

NumberAllocation (MHz) Width of Band (MHz)

35 1850 - 1910 60

36 1930 - 1990 60

37 1910 - 1930 20

38 2570 - 2620 5039 1880 - 1920 40

40 2300 - 2400 100

41 2496 - 2690 194

42 3400 - 3600 200

43 3600 - 3800 200

44 703 - 803 100

There are regular additions to the LTE frequency bands / LTE spectrum allocations as a result ofnegotiations at the ITU regulatory meetings. These LTE allocations are resulting in part from the digital

dividend, and also from the pressure caused by the ever growing need for mobile communications. Many

of the new LTE spectrum allocations are relatively small, often 10 - 20MHz in bandwidth, and this is a cause

for concern. With LTE-Advanced needing bandwidths of 100 MHz, channel aggregation over a wide set of

frequencies many be needed, and this has been recognized as a significant technological problem. . . . . . . .

.


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LTE UE Category & Class Definitions

- LTE utilizes UE or User Equipment categories or classes to define the performance specifications an enable base

stations to be able to communicate effectively with them knowing their performance levels. Some like LTE Cat 3,

LTE Cat 4 and LTE Cat 0 are widely quoted and used. Other like LTE Cat 7 and LTE Cat 8 are much newer.

In the same way that a variety of other systems adopted different categories for the handsets or user

equipments, so too there are 3G LTE UE categories. These LTE categories define the standards to which a

particular handset, dongle or other equipment will operate.

LTE UE category rationale

The LTE categories or UE classes are needed to ensure that the base station, or eNodeB, eNB can

communicate correctly with the user equipment. By relaying the LTE UE category information to the base

station, it is able to determine the performance of the UE and communicate with it accordingly.

As the LTE category defines the overall performance and the capabilities of the UE, it is possible for the

eNB to communicate using capabilities that it knows the UE possesses. Accordingly the eNB will not

communicate beyond the performance of the UE.

LTE UE category definitions

There are 9 different LTE UE categories that are defined. As can be seen in the table below, the different

LTE categories have a wide range in the supported parameters and performance. LTE category 1, for

example does not support MIMO, but LTE UE category five supports 4x4 MIMO.

It is also worth noting that UE class 1 does not offer the performance offered by that of the highest

performance HSPA category. Additionally all LTE UE categories are capable of receiving transmissions from

up to four antenna ports.

A summary of the different LTE UE category parameters is given in the tables below.

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

It can be seen that the headline data rates for category 8 exceed the requiremetns for IMT-Advanced by a

considerable margin.

While the headline rates for the different LTE UE categories or UE classes show the maximum data rates

achievable, it is worth looking in further detail at the underlying performance characteristics.

UL and DL parameters for LTE UE Categories 1 - 5

LTE Category


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Parameter LTE Cat 1 LTE Cat 2 LTE Cat 3 LTE Cat 4 LTE Cat 5

Max number of DL-SCH transport block

bits received in a TTI10 296 51 024 102 048 150 752 302 752

Max number of bits of a DL-SCH block

received in a TTI10 296 51 024 75 376 75 376 151 376

Total number of soft channel bits 250 368 1 237 248 1 237 248 1 827 072 3 667 200

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 TTI5 160 25 456 51 024 51 024 75 376

Support for 64-QAM in UL No No No No Yes

UL and DL parameters for LTE UE Categories 6, 7, 8

LTE Category

Parameter LTE Cat 6 LTE Cat 7 LTE Cat 8

Max number of DL-SCH transport block bits

received in a TTI299 552 299 552 1 200 000

Max number of bits of a DL-SCH block received

in a TTITBD TBD TBD

Total number of soft channel bits 3 667 200 TBD TBD

Maximum number of supported layers for

spatial multiplexing in DL

Max number of bits of an UL-SCH transport

block received in a TTITBD TBD TBD

Support for 64-QAM in UL No Yes, up to RAN 4 Yes

From this it can be seen that the peak downlink data rate for a Category 5 UE using 4x4 MIMO is

approximately 300 Mbps, and 150 Mbps for a Category 4 UE using 2x2 MIMO. Also in the Uplink, LTE UE

category 5 provides a peak data rate of 75 Mbps using 64-QAM.

Note:

DL-SCH = Downlink shared channel

UL-SCH = Uplink shared channel

TTI = Transmission Time Interval

LTE Category 0

With the considerable level of development being undertaken into the Internet of Things, IoT and general

machine to machine, M2M communications, there has been a growing need to develop an LTE category

focussed on these applications. Here, much lower data rates are needed, often only in short bursts and an

accompanying requirement is for the remote device or machine to be able to draw only low levels of

current.

To enable the requirements of these devices to be met using LTE, and new LTE category was developed.Referred to as LTE Category 0, or simply LTE Cat 0, this new category has a reduced performance

requirement that meets the needs of many machines while significantly reducing complexity and current


25/5024 | P a g e

consumption. Whilst Category 0 offered a reduced specification, it still complied with the LTE system

requirements.

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

The new LTE Cat 0 was introduced in Rel 12 of the 3GPP standards. And it is being advanced in further

releases.

One major advantage of LTE Category 0 is that the modem complexity is considerably reduced when

compared to other LTE Categories. It is expected that the modem complexity for a Cat 0 modem will be

around 50% that of a Category 1 modem.

LTE UE category summary

In the same way that category information is used for virtually all cellular systems from GPRS onwards, so

the LTE UE category information is of great importance. While users may not be particularly aware of the

category of their UE, it will match the performance an allow the eNB to communicate effectively with all

the UEs that are connected to it.


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LTE SAE System Architecture Evolution

- information, overview, or tutorial about the basics of the 3G LTE SAE, system architecture evolution and the LTE

Network

Along with 3G LTE - Long Term Evolution that applies more to the radio access technology of the cellular

telecommunications system, there is also an evolution of the core network. Known as SAE - SystemArchitecture Evolution. This new architecture has been developed to provide a considerably higher level of

performance that is in line with the requirements of LTE.

As a result it is anticipated that operators will commence introducing hardware conforming to the new

System Architecture Evolution standards so that the anticipated data levels can be handled when 3G LTE is

introduced.

The new SAE, System Architecture Evolution has also been developed so that it is fully compatible with LTE

Advanced, the new 4G technology. Therefore when LTE Advanced is introduced, the network will be able

to handle the further data increases with little change.

Reason for SAE System Architecture Evolution

The SAE System Architecture Evolution offers many advantages over previous topologies and systems used

for cellular core networks. As a result it is anticipated that it will be wide adopted by the cellular operators.

SAE System Architecture Evolution will offer a number of key advantages:

1. Improved data capacity: With 3G LTE offering data download rates of 100 Mbps, and the focus of

the system being on mobile broadband, it will be necessary for the network to be able to handle

much greater levels of data. To achieve this it is necessary to adopt a system architecture that lends

itself to much grater levels of data transfer.

2. All IP architecture: When 3G was first developed, voice was still carried as circuit switched data.

Since then there has been a relentless move to IP data. Accordingly the new SAE, System

Architecture Evolution schemes have adopted an all IP network configuration.

3. Reduced latency: With increased levels of interaction being required and much faster responses,

the new SAE concepts have been evolved to ensure that the levels of latency have been reduced to

around 10 ms. This will ensure that applications using 3G LTE will be sufficiently responsive.

4. Reduced OPEX and CAPEX: A key element for any operator is to reduce costs. It is therefore

essential that any new design reduces both the capital expenditure (CAPEX)and the operational

expenditure (OPEX). The new flat architecture used for SAE System Architecture Evolution means

that only two node types are used. In addition to this a high level of automatic configuration is

introduced and this reduces the set-up and commissioning time.


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SAE System Architecture Evolution basics

The new SAE network is based upon the GSM / WCDMA core networks to enable simplified operations and

easy deployment. Despite this, the SAE network brings in some major changes, and allows far more

efficient and effect transfer of data.

There are several common principles used in the development of the LTE SAE network:

a common gateway node and anchor point for all technologies.

an optimised architecture for the user plane with only two node types.

an all IP based system with IP based protocols used on all interfaces.

a split in the control / user plane between the MME, mobility management entity and the gateway.

a 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.

The main element of the LTE SAE network is what is termed the Evolved Packet Core or EPC. This connects

to the eNodeBs as shown in the diagram below.

LTE SAE Evolved Packet Core

As seen within the diagram, the LTE SAE Evolved Packet Core, EPC consists of four main elements as listed

below:

Mobility Management Entity, MME: The MME is the main control node for the LTE SAE access

network, handling a number of features:

o Idle mode UE tracking

o Bearer activation / de-activation

o Choice of SGW for a UE

o Intra-LTE handover involving core network node location

o Interacting with HSS to authenticate user on attachment and implements roaming

restrictions

o It acts as a termination for the Non-Access Stratum (NAS)


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o Provides temporary identities for UEs

o The SAE MME acts the termination point for ciphering protection for NAS signaling. As part

of this it also handles the security key management. Accordingly the MME is the point at

which lawful interception of signalling may be made.

o Paging procedure

o The S3 interface terminates in the MME thereby providing the control plane function for

mobility between LTE and 2G/3G access networks.

o The SAE MME also terminates the S6a interface for the home HSS for roaming UEs.

It can therefore be seen that the SAE MME provides a considerable level of overall control functionality.

Serving Gateway, SGW: The Serving Gateway, SGW, is a data plane element within the LTE SAE.

Its main purpose is to manage the user plane mobility and it also acts as the main border between

the Radio Access Network, RAN and the core network. The SGW also maintains the data paths

between the eNodeBs and the PDN Gateways. In this way the SGW forms a interface for the data

packet network at the E-UTRAN.

Also when UEs move across areas served by different eNodeBs, the SGW serves as a mobility

anchor ensuring that the data path is maintained.

PDN Gateway, PGW: The LTE SAE PDN gateway provides connectivity for the UE to external

packet data networks, fulfilling the function of entry and exit point for UE data. The UE may have

connectivity with more than one PGW for accessing multiple PDNs.

Policy and Charging Rules Function, PCRF: This is the generic name for the entity within the LTE

SAE EPC which detects the service flow, enforces charging policy. For applications that require

dynamic policy or charging control, a network element entitled the Applications Function, AF is

used.

LTE SAE PCRF Interfaces


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LTE SAE Distributed intelligence

In order that requirements for increased data capacity and reduced latency can be met, along with the

move to an all-IP network, it is necessary to adopt a new approach to the network structure.

For 3G UMTS / WCDMA the UTRAN (UMTS Terrestrial Radio Access Network, comprising the Node B's or

basestations and Radio Network Controllers) employed low levels of autonomy. The Node Bs were

connected in a star formation to the Radio Network Controllers (RNCs) which carried out the majority of

the management of the radio resource. In turn the RNCs connected to the core network and connect in

turn to the Core Network.

To provide the required functionality within LTE SAE, the basic system architecture sees the removal of a

layer of management. The RNC is removed and the radio resource management is devolved to the base-

stations. The new style base-stations are called eNodeBs or eNBs.

The eNBs are connected directly to the core network gateway via a newly defined "S1 interface". In

addition to this the new eNBs also connect to adjacent eNBs in a mesh via an "X2 interface". This providesa much greater level of direct interconnectivity. It also enables many calls to be routed very directly as a

large number of calls and connections are to other mobiles in the same or adjacent cells. The new

structure allows many calls to be routed far more directly and with only minimum interaction with the core

network.

In addition to the new Layer 1 and Layer 2 functionality, eNBs handle several other functions. This includes

the radio resource control including admission control, load balancing and radio mobility control including

handover decisions for the mobile or user equipment (UE).

The additional levels of flexibility and functionality given to the new eNBs mean that they are more

complex than the UMTS and previous generations of base-station. However the new 3G LTE SAE network

structure enables far higher levels of performance. In addition to this their flexibility enables them to be

updated to handle new upgrades to the system including the transition from 3G LTE to 4G LTE Advanced.

The new System Architecture Evolution, SAE for LTE provides a new approach for the core network,

enabling far higher levels of data to be transported to enable it to support the much higher data rates that

will be possible with LTE. In addition to this, other features that enable the CAPEX and OPEX to be reduced

when compared to existing systems, thereby enabling higher levels of efficiency to be achieved.


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LTE SON Self Organizing Networks

- LTE, Long Term Evolution and the requirements for LTE SON, Self Organising Networks

With LTE requiring smaller cell sizes to enable the much greater levels of data traffic to be handled, there

networks have become considerably more complicated and trying to plan and manage the network

centrally is not as viable. Coupled with the need to reduce costs by reducing manual input, there has beena growing impetus to implement self-organizing networks.

Accordingly LTE can be seen as one of the major drivers behind the self-organizing network, SON

philosophy.

Accordingly 3GPP developed many of the requirements for LTE SON to sit alongside the basic functionality

of LTE. As a result the standards for LTE SON are embedded within the 3GPP standards.

LTE SON development

The term SON came into frequent use after the term was adopted by the Next Generation Mobile

Networks, NGMN alliance. The idea came about as result of the need within LTE to be able to deploy many

more cells. Femtocells and other microcells are an integral part of the LTE deployment strategy. With

revenue per bit falling, costs for deployment must be kept to a minimum as well as ensuring the network is

operating to its greatest efficiency.

3GPP, the Third Generation Partnership Programme has created the standards for SON and as they aregenerally first to be deployed with LTE, they are often referred to as LTE SON.

While 3GPP has generated the standards, they have been based upon long term objectives for a 'SON-

enabled broadband mobile network' set out by the NGMN.

NGMN has defined the necessary use cases, measurements, procedures and open interfaces to ensure that

multivendor offerings are available. 3GPP has incorporated these aspirations into useable standards.

Major elements of LTE SON

Although LTE SON self-optimising networks is one of the major drivers for the generic SON technology, the

basic requirements remain the same whatever the technology to which it will be applied.

The main elements of SON include:

Self configuration: The aim for the self configuration aspects of LTE SON is to enable new base

stations to become essentially "Plug and Play" items. They should need as little manual intervention

in the configuration process as possible. Not only will they be able to organise the RF aspects, butalso configure the backhaul as well.


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Self optimisation: Once the system has been set up, LTE SON capabilities will enable the base

station to optimise the operational characteristics to best meet the needs of the overall network.

Self-healing: Another major feature of LTE SON is to enable the network to self-heal. It will do this

by changing the 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..

Typically an LTE SON system is a software package with relevant options that is incorporated into an

operator's network.

.

LTE SON and 3GPP standards

LTE Son has been standardised in the various 3GPP standards. It was first incorporated into 3GPP release 8,

and further functionality has been progressively added in the further releases of the standards.

One of the major aims of the 3GPP standardization is the support of SON features is to ensure that multi-

vendor network environments operate correctly with LTE SON. As a result, 3GPP has defined a set of LTE

SON use cases and the associated SON functions.

As the functionality of LTE advances, the LTE SON standardisation effectively tracks the LTE networkevolution stages. In this way SON will be applicable to the LTE networks.

Note on SON, Self Organizing Networks:

SON mainly came out of the requirements of LTE and the more complicated networks that will arise. However the

concepts behind SON can be applied at any network enabling its efficiency to be increased while keeping costs low.

Accordingly, it is being used increasingly to reduce operational and capital expenditure by adding software to the

network to enable it to organise and run itself


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Voice over LTE - VoLTE Tutorial

- operation of Voice over LTE VoLTE system for providing a unified format of voice traffic on LTE, and other systems

including CSFB, and SV-LTE.

The Voice over LTE, VoLTE scheme was devised as a result of operators seeking a standardised system for

transferring traffic for voice over LTE.

Originally LTE was seen as a completely IP cellular system just for carrying data, and operators would be

able to carry voice either by reverting to 2G / 3G systems or by using VoIP in one form or another.

From around 2014 Phones like this iPhone6 incorporated VoLTE as standard

However it was seen that this would lead to fragmentation and incompatibility not allowing all phones to

communicate with each other and this would reduce voice traffic. Additionally SMS services are still widely

used, often proving a means of set-up for other applications.

Even though revenue from voice calls and SMS is falling, a format for voice over LTE and messaging, it was

as necessary to have a viable and standardized scheme to provide the voice and SMS services to protect

this revenue.

Options for LTE Voice

When looking at the options for ways of carrying voice over the LTE system, a number of possible solutions

were investigated. A number of alliances were set up to promote different ways of providing the service. Anumber of systems were prosed as outlined below:

CSFB, Circuit Switched Fall Back: The circuit switched fall-back, CSFB option for providing voice

over LTE has been standardised under 3GPP specification 23.272. Essentially LTE CSFB uses a variety

of processes and network elements to enable the circuit to fall back to the 2G or 3G connection

(GSM, UMTS, CDMA2000 1x) before a circuit switched call is initiated.

The specification also allows for SMS to be carried as this is essential for very many set-up

procedures for cellular telecommunications. To achieve this the handset uses an interface known as

SGs which allows messages to be sent over an LTE channel.

SV-LTE - Simultaneous Voice LTE: SV-LTE allows packet switched LTE services to run

simultaneously with a circuit switched voice service. SV-LTE facility provides the facilities of CSFB at


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the same time as running a packet switched data service. It has the disadvantage that it requires

two radios to run at the same time within the handset which has a serious impact on battery life

which is already a major issue.

VoLGA, Voice over LTE via GAN: The VoLGA standard was based on the existing 3GPP Generic

Access Network (GAN) standard, and the aim was to enable LTE users to receive a consistent set of

voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE

access networks. For mobile operators, the aim of VoLGA was to provide a low-cost and low-risk

approach for bringing their primary revenue generating services (voice and SMS) onto the new LTE

network deployments.

One Voice / later called Voice over LTE, VoLTE: The Voice over LTE, VoLTE scheme for providing

voice over an LTE system utilises IMS enabling it to become part of a rich media solution. It was the

option chosen by the GSMA for use on LTE and is the standardised method for providing SMS and

voice over LTE.

Voice over LTE, VoLTE formation

Originally the concept for an SMS and voice system over LTE using IMS had been opposed by many

operators because of the complexity of IMS. They had seen it as far too expensive and burdensome to

introduce and maintain.

However, the One Voice profile for Voice over LTE was developed by a collaboration between over forty

operators including: AT&T, Verizon Wireless, Nokia and Alcatel-Lucent.

At the 2010 GSMA Mobile World Congress, GSMA announced that they were supporting the One Voice

solution to provide Voice over LTE.

To achieve a workable system, a cut down variant of IMS was used. It was felt that his would be acceptable

to operators while still providing the functionality required.

The VoLTE system is based on the IMS MMTel concepts that were previously in existence. It has been

specified in the GSMA profile IR 92.

Voice over LTE, VoLTE basics

VoLTE, Voice over LTE is an IMS-based specification. Adopting this approach, it enables the system to be

integrated with the suite of applications that will become available on LTE.

In order that IMS was implemented in fashion that would be acceptable to operators, a cut down version

was defined. This not only reduced the number of entities required in the IMS network, but it also

simplified the interconnectivity - focussing on the elements required for VoLTE.

Note on IMS:

The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem, IMS is an architectural framework for

delivering Internet Protocol, IP multimedia services. It enables a variety of services to be run seemlessly rather than

having several disparate applications operating concurrently.


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Reduced IMS network for VoLTE

As can be seen there are several entities within the reduced IMS network used for VoLTE:

IP-CAN IP, Connectivity Access Network: This consists of the EUTRAN and the MME.

P-CSCF, Proxy Call State Control Function: The P-CSCF is the user to network proxy. In this respect

all SIP signalling to and from the user runs via the P-CSCF whether in the home or a visited network.

I-CSCF, Interrogating Call State Control Function: The I-CSCF is used for forwarding an initial SIP

request to the S-CSCF. When the initiator does not know which S-CSCF should receive the request.

S-CSCF, Serving Call State Control Function: The S-CSCF undertakes a variety of actions within the

overall system, and it has a number of interfaces to enable it to communicate with other entities

within the overall system.

AS, Application Server: It is the application server that handles the voice as an application.

HSS, Home Subscriber Server: The IMS HSS or home subscriber server is the main subscriber

database used within IMS. The IMS HSS provides details of the subscribers to the other entities

within the IMS network, enabling users to be granted access or not dependent upon their status.

The IMS calls for VoLTE are processed by the subscriber's S-CSCF in the home network. The connection to

the S-CSCF is via the P-CSCF. Dependent upon the network in use and overall location within a network, the

P-CSCF will vary, and a key element in the enablement of voice calling capability is the discovery of the P-

C

Documents

LTE Long Term Evolution Tutorial