Utilizing Un-Licensed Spectrum with

Power of Technologies – LTE-U & Wi-Fi

1. Introduction Access to unlicensed spectrum has been the key to the development and

adoption of innovative wireless technologies like Wi-Fi, Bluetooth, and

ZigBee for providing network connectivity in a small area with limited data

rates.

Now days, data requirement of per user is exponentially and thus technology

has upgrade it’s to a new level where one can see the throughput in order of

1000s of Mbps. Two global wireless technologies named LTE and Wi-Fi are

looking to play a great role to meet up these requirements.

Wi-Fi technology using unlicensed spectrum and very mature due to its

ecosystem. On the other hand LTE technology is the leading mobile wireless

technology and broadly deployed in licensed bands and it is evolving to

operate in unlicensed band and emerging as a stronger competitor to Wi-Fi in

unlicensed band.

LTE-U is one of version of this technology developed by a group of

Organizations under name of LTE-U Forum, while License Assisted Access

(LAA) is 3GPP’s ongoing effort to standardize simultaneous operation across

licensed and unlicensed bands as part of LTE Release 13. People use the term

“LTE in unlicensed” to refer to both LTE-U and LAA collectively.

Mehndi Sadeghian, Mohit Luthra, Rahul Atri, Rahul Sharma, Preet Rekhi, Sukhvinder Malik May 8th, 2016

Contents

1. Introduction 2. Un-Licensed Spectrum

3. Wi-Fi Technology

Overview

4. LTE-Unlicensed

5. LTE-U Deployment

Use case

6. LTE-U Eco System

and Standardization

7. Summary and Last

words

8. References

LTE-U & Wi-Fi

LTE operating in unlicensed band is anchored by a license carrier and it operates on licensed and unlicensed

bands simultaneously: licensed spectrum is used for its guaranteed availability and for transmission of control

and QoS traffic, while unlicensed spectrum is used for best-effort data and capacity requirements. This

approach provides a higher spectral efficiency, increased control, and streamlines management compared to

Wi-Fi offloading to mobile operators in order to overcome the challenge meeting the capacity requirements.

In these respects, LTE in unlicensed provides another example of the innovation unlocked by unlicensed

spectrum and big mobile operators are showing great interest as they do not need to pay for the spectrum the

most costly thing.

As a result of dominance of these two technologies, the unlicensed spectrum is becoming a battle ground. Wi-

Fi proponents want to preserve as much unlicensed spectrum as they can for Wi-Fi service, and on the other,

mobile operator want the ability to innovate to improve their customers’ experience through fast emerging

LTE-U. Now the question comes, can these two technologies co-exist? We will get to know the facts and

figures about this in the coming sections of this paper.

2. Un-Licensed Spectrum

The FCC makes spectrum available either on a licensed or unlicensed basis. Any innovator or consumer can

use unlicensed spectrum just by following technical rules - most notably, a limit on total transmission

power. Unlicensed spectrum is decentralized: there are no license payments or central control for users. This

low-regulation system lets innovators deliver millions of unlicensed offerings such as Wi-Fi hotspots; medical

equipment; industrial/logistics/inventory systems; wireless headsets etc.

2.4GHz, 3.5GHz and 5GHz are the Un-Licensed Bands. The 2.4GHz band is currently the most utilized band

shared by different wireless users such as cordless phone, ZigBee, Bluetooth and Wi-Fi. Along with 2.4 GHz

band, 5GHz band is less congested.

The unlicensed 60GHz band has more abundant bandwidth, making it feasible for bandwidth-intensive

multimedia services. However, the severe oxygen absorption and atmospheric attenuation at 60 GHz band

imposes great challenges in the design of physical layer specifications and air interfaces. The frequency band

of most interest for 3GPP is the 3.5GHz and 5GHz band, which has a lot of unlicensed spectrum available

globally, much more than the 2.4GHz frequency band.

2.1 Motivation behind moving to Un-Licensed Spectrum

Demands for mobile traffic have been increasing exponentially, and will continue to increase

dramatically for years to come.

The supply of licensed frequency spectrum allocated to cellular operators is very limited; operators

have been feeling the crunch and heat of cost.

An abundance of unlicensed spectrum, about 800 MHz bandwidth is free below 6 GHz.

2.2 5 GHz Un-Licensed Bands:

The 5GHz unlicensed spectrum is divided into mainly three different bands with different RF requirements.

These are the three Unlicensed National Information Infrastructure (U-NII) bands.

May 8th, 2016 Page 2

LTE-U & Wi-Fi

These three bands are U-NII-1 (5150-5250MHz), U-NII-2 (5250-5725MHz) and U-NII-3 (5725-5850MHz).

5350-5470MHz segment in UNII-2 is restricted from usage by FCC. In addition, the 60MHz in 5590-5650MHz

are currently blocked by FCC for TDWR interference issues. U-NII-2 band has the additional requirement of

DFS (Dynamic Frequency Selection), it is recommended that U-NII-2 band can be considered for LTE-U in the

future. The following band numbering will be used for the U-NII bands.

U-NII-1: Band number 252 for U-NII-1 spectrum (5150-5250MHZ).

U-NII-2: Band numbers 253 and 254 are reserved for U-NII-2 spectrum (5250-5725MHZ) for future usage.

U-NII-3: Band number 255 for U-NII-3 spectrum (5725-5850MHZ)

Most Regulatory Areas offer a large amount of spectrum in the 5 GHz band .In Europe there is 455 MHz of

spectrum available, and 580MHz in the US. The bandwidth for each region is depicted in figure 1 and table 1.

The use of this unlicensed spectrum usually carries some regulatory requirements, such as being able to detect

if a radar system is using the band or being able to co-exist with other users of the band.

Figure 1: Spectrum Available in Different Regions

The transmission power allowed also varies depending on the part of the band, the lower portion is restricted to

indoor use, with a transmit power of 200 mW or less, while the upper part of the spectrum allows higher

transmission power, about 1 W. In some cases, like US 5.725 GHz to 5.85 GHz, there are no specific

requirements expect the transmission power. In some regulatory areas, like Europe and Japan, there is a specific

requirement for supporting Listen-Before-Talk or Clear Channel Assessment (CCA) at milliseconds scale is

required while in other regulatory areas, like US, Korea and China, there are no such requirements.

Unlicensed Bands U-NII-1 (Band 252) 5150-5250MHz

U-NII-2 (Band 253) 5250-5350MHz

U-NII-2 (Band 254) 5470-5725MHz

U-NII-3 (255) 5725-5825MHz

EIRP Limits 17dBm/23dBm 23dBm/30dBm 23dBm/30dBm 23dBm/30dBm/ 36dBm

India Indoor Indoor Not Available Indoor/Outdoor

United State /Canada Indoor Indoor/Outdoor Indoor/Outdoor (Only Canada not in US)

Indoor/Outdoor

European Union Indoor Indoor Indoor/Outdoor Not Available

Korea Indoor Indoor/Outdoor Indoor/Outdoor Indoor/Outdoor

Japan Indoor Indoor Indoor/Outdoor Not Available

China Indoor Indoor Not Available Indoor/Outdoor

Australia Indoor Indoor/Outdoor Indoor/Outdoor Indoor/Outdoor

Inter-Modulation Interference with Licensed Bands

800MHz,1.7GHz,2.6GHz

800MHz,1.7GHz,2.6GHz

1.8GHz,900MHz 1.9GHz,1.4GHz

Table 1:Un-Licensed bands and Their Specification

May 8h, 2016 Page 3

LTE-U & Wi-Fi

3. Wi-Fi Technology Overview Wi-Fi is a local area wireless computer networking technology that allows electronic devices to connect to the

network, mainly using the unlicensed 2.4 GHz UHF band (Ultra High Frequency) and 5 GHz SHF band (Super

High Frequency) from ISM frequencies. It is also known as WLAN. Wi-Fi Transmission at 5 GHz offers

higher throughput at shorter distances. At the 2.4 GHz there's an extended coverage area that can be

provided, because the signal propagates through solid objects better than the 5 GHz signals do.

Wi-Fi is supported by many applications and devices including video game consoles, home networks, PDAs,

mobile phones, major operating systems, and other types of consumer electronics. Any products that are tested

and approved as "Wi-Fi Certified" (a registered trademark) by the Wi-Fi Alliance are certified as

interoperable with each other, even if they are from different manufacturers. They use 802.11 networking

standards, which come in several flavors and characteristics. The date rates depicted in table are Physical layer

throughputs.

Standards Release Year Frequency of Operation Bandwidth Data Rate

802.11 1997 2.4 GHz 22 MHz 2 Mbps

802.11a 1999 3.7 GHz & 5 GHz 20 MHz 54 Mbps

802.11b 1999 2.4 GHz 22 MHz 11 Mbps

802.11g 2003 2.4 GHz 20 MHz 54 Mbps

802.11n 2009 2.4 GHz & 5GHz 20 MHz

40 MHz

72.2 Mbps

150 Mbps

802.11ac 2013 5 GHz 20 MHz

40 MHz

80 MHz

160 MHz

96.3 Mbps

200 Mbps

433 Mbps

867 Mbps

802.11 ad 2016 60 GHz 2.16 GHz Up to 7 Gbps

Table 2: Wi-Fi Standards

3.1 Wi-Fi Standards:

These standards works at frequencies of 2.4GHz or 5GHz and uses orthogonal frequency-division

multiplexing (OFDM), a more efficient coding technique that splits that radio signals into several sub-signals

before they reach a receiver.

IEEE 802.11 Wi-Fi standards are shown in table 2. In the 802.11 protocol standards, one that came out was the

802.11, it came out in June of 1997. The frequency range was focused at 2.4 GHz, and the bandwidth was

22MHz. The stream data rate was 1 or 2 Mbps. 802.11a and b and these were released in 1999. 802.11a and

are capable of 5GHz and 3.7GHz with bandwidth of 20MHz and the data rate incensements are really high up

to 54 Mbps.

The 802.11b works on the 2.4 GHz, which is the same frequency band as the 802.11-1997 version and

bandwidth is the same, the 22 MHz, and the data rates in the original 1997 version it could only go up to 1 or 2

Mbps, but in 11b standards throughput can go up to 11 Mbps. The 802.11g was released in 2003 and it operates

at the 2.4 GHz range, uses the same 20 MHz bandwidth and the data rates would enable speed up to 54 Mbps.

More recently in 2009, the 802.11n version came out which uses the 2.4 and the 5 GHz range it could achieve

higher data rates reach up to 72.2 Mbps or you could go up to 150 Mbps based upon channel bandwidth

May 8h, 2016 Page 4

LTE-U & Wi-Fi

May 8th, 2016 Page 5

802.11ac is one of the newest standards as of early 2013. It is yet to be widely adopted, and is still in draft form

at the Institute of Electrical and Electronics Engineers (IEEE), but devices that support it are already on the

market. Other 802.11 standards focus on specific applications of wireless networks, like wide area networks

(WANs) inside vehicles or technology that lets you move from one wireless network to another seamlessly.

Today each mobile, laptop, a tablet etc. device has inbuilt Wi-Fi facility which makes it widely used

technology in the world.

802.11 ac operates on 5GHz ISM band and having flexible bandwidth from 20MHz to 160MHz. As demand

for data is increasing day by day, so people are searching new technology standards that could meet the

consumer’s data demands in the unlicensed bands. IEEE is also introducing a new standard named as 802.11ad

to meet these expectations and support data rates up to 7 Gbps. The standard 802.11ad is expected to be

released in 2016. It will be using the 60GHz ISM band where there is a large bandwidth available.

Now, there's another technology called dual band, unlike ordinary Wi-Fi equipment that only supports to use

one single band at a time, dual band has the capability to transmit both on the 5 GHz and on the 2.4 GHz band

simultaneously. In other words at the 5 GHz band you could using 802.11a, 11n, 11ac, and also at the 2.4 GHz

band it could be using 11b, 11g, and 11n.

For an example, if the access point is capable of dual band services, then 2.4GHz band for email, or to surf the

web, and for the wider bandwidth. The more throughput can be provided through the 5GHz ISM band, which

can be used for streaming high definition, video and play online video games.

3.2 Wi-Fi and LTE-U Comparison:

Wi-Fi and LTE-U both operates on the un-licensed frequency and have following difference based on the

technology at physical layer listed in Table 3.

Wi-Fi LTE-U

PHY is half-duplex PHY is typically full-duplex

PHY is packet oriented – sync on each packet

PHY operates continuously always on – sync is interspersed

PHY provides a single channel with a single modulation for each packet

PHY provides multiple channels simultaneously with varying modulation

Access is by CSMA/CA , Probabilistic - based on random back off e.g. Networks function without frequency planning

All client access is scheduled based on algorithms. They can do not coordinate each other together and they have backhaul property btw the cells

Stochastic interference Deterministic Interference.

The access points coordinate together They can do not coordinate each other together and they have backhaul property btw the cells.

Table 3: Wi-Fi and LTE-U Comparison

LTE-U & Wi-Fi

May 8th, 2016 Page 6

4. LTE-Unlicensed

LTE-U is a system of wireless communication designed to use unlicensed spectrum – which is open to

everyone, within certain limits – to ease the burden on big mobile carriers’ networks. LTE-U was first

introduced in Rel13 of the 3GPP standards; LTE-U is built upon the carrier aggregation capability of LTE-

Advanced.

Regular LTE is the system they use to transmit and receive information across their licensed spectrum – to

which only they have access. LTE-U uses the same technology to operate on the unlicensed spectrum, which

the carriers don’t have to spend billions of dollars to acquire with anchoring done by the licensed carrier

LTE-U is not intended to replace existing LTE connectivity, but supplement its speed and services in high-

congestion areas. A device would connect simultaneously on a typical LTE connection while acquiring

additional bandwidth through nearby LTE-U signal. Due to the regulations set by the FCC, LTE-U devices

must meet the same power limitations as the Wi-Fi devices that exist today, limiting their range to about 300

feet. 4.1 Motivation behind using LTE in Unlicensed spectrum:

The need to use LTE with unlicensed spectrum is the increase in traffic volumes and the number of mobile

broadband users globally. As mentioned previously, the 5 GHz spectrum offers a large amount of bandwidth.

With LTE technology, a number of the following could be achieved:

Better spectrum efficiency than the current technologies in use with the 5 GHz band. Since LTE radio

technology is based on state of the art technology, it can achieve both high data rates and at the same

time high spectral efficiency, also in the unlicensed band. As well as higher capacity, LTE technology

offers better coverage, especially when combined with the use of licensed band operation.

From the network management point of view, using the unlicensed band with LTE instead of an

alternative radio technology provides a solution that is well integrated to the operator’s existing radio

network setup, avoiding multiple solutions for network management, security or authentication. Having

only a single technology simplifies the overall network maintenance. The use of LAA is fully

transparent to the LTE core network, avoiding the need to upgrade any of the Evolved Packet Core

(EPC) elements.

4.2 Design Principle of LTE-U

Some fundamental principles and regulations are imposed to guarantee the harmonious coexistence between

LTE-U and other incumbent systems.

The Transmission Power for LTE-U Cell

Dynamic Frequency Selection (DFS) and Listen Before Talk (LBT) for fair sharing of Spectrum

LTE-U in Carrier aggregation Mode

Licensed-Assisted Access Operation/Anchored with Licensed carrier

Enchantments in LTE air-interface

Ensuring co-existence with existing Technologies

Transmission power for LTE-U Cell: The first issue in the use of unlicensed spectrum is the regulation of

transmission power. Such regulation is specified to manage the interference among unlicensed users. Indoor

wireless access points (APs) in business buildings, which often falls within the 5.15 − 5.35 GHz spectrum

band, the maximum transmission power is 23dBm in Europe or 24dBm in US.

LTE-U & Wi-Fi

May 8th, 2016 Page 7

Outdoor, e.g. hotspot small cell, allows a maximum of 30 dBm which usually happens within the 5.47 − 5.85

GHz spectrum band. Besides the maximum transmission power, the 5.25 − 5.35 GHz and 5.47 − 5.725 GHz

spectrum has mandated (TPC) mechanisms. Transmit power control Mechanism (TPM) reduces the power of a

radio transmitter to the minimum necessary, in order to avoid interference to other users and/or extend the

battery life while maintaining the link transmission quality.

Dynamic Frequency Selection (DFS) and Listen before Talk (LBT) for fair sharing of Spectrum

Radar systems also operate on the 5 GHz unlicensed spectrum, thus the unlicensed devices may drop non-

negligible interference upon the normal radar. LTE-U devices periodically detect whether there are radar

signals and will switch the operating channel to one that is not interfering with the radar systems upon

detection. Mechanism named dynamic frequency selection (DFS) is adopted in 5.25−5.35 GHz and 5.47−5.725

GHz spectrum to avoid interference to the radar system.

Other mechanism which can be used “Listen before Talk” for fair sharing of spectrum avoiding interference to

other existing technologies, where any device wishing to use the band must listen to see if it is occupied or

not. If the band isn’t busy, the device can seize it and start transmitting. The band can only be held for a

maximum of 10 milliseconds after which it must be released and the LBT process repeated.

Clear channel assessment (CCA) mechanism is used to detect the energy level during sensing. If the energy

level is below a threshold, the channel is deemed to be clear and can be used for LTE-U transmission.

Figure 2: Listen Before Talk Mechanism for LTE-U

LTE-U in Carrier Aggregation Mode:

Carrier aggregation (CA) increases the overall bandwidth available to user equipment by enabling it to use

more than one channel, either in the same band, or within another band. Carrier Aggression is done based on

Carrier Components (CCs) and at max 5 CC can be combined and each CC can be of maximum bandwidth as

20MHz. In Carrier Aggression out of 5 CCs one CC is known as Primary Carrier while other 4 CCs are known

Secondary Carriers. It can be applied to both Frequency Division Duplex (FDD) and Time Division Duplex

(TDD) variants of LTE and it allows the combination of different carrier bandwidths in number of ways as

listed below.

Intra band Contiguous CA

Intra band Non Contiguous CA

Intra band Non Contiguous CA

LTE-U & Wi-Fi

May 8th, 2016 Page 8

Intra band CA, where the carriers are contiguous and lie within the same frequency band. In this case it is

feasible for a mobile device to handle the signals using a single transceiver, providing it is able to operate

efficiently over the aggregate bandwidth. For example CC1- 2305-2310MHz, CC2- 2330-2350MHz. In this

case the duplex mode shall be same either FDD or TDD for both carrier components as both belong same band.

It can be seen in figure 3

Figure 3: Intraband Contiguous CA Figure 4: Intraband Non Contiguous CA Figures 5:Interband Non Contiguous CA

Intra-band non-contiguous carrier aggregation, in which the carriers lie within the same frequency band, but

they are not adjacent. In this case it is necessary for the mobile device to use a separate transceiver for each

carrier. For example CC1-2305-2310MHz, CC2- 2375-2395MHz.In this case also duplex mode shall be same

either FDD or TDD for both carrier components as both belong same band. Figure 4 depict the same.

Inter-band non-contiguous carrier aggregation, In this case the carriers components (CC) fall in different parts

of the radio spectrum, like CC1 700MHz and CC2 2300MHz. In this case also it is necessary for the mobile

device to use a separate transceiver for each carrier. Here it also possible that one CC1 may be FDD while

other may be TDD in this particular case mobile device need to support both duplex modes. Figure 5 shows

Inter-band non-contiguous CA.

LTE- U also operates in Carrier aggression mode, where primary carrier is always from the licensed band and

secondary carrier component can be from unlicensed band. LTE-U form has provided some band combination

where LTE-U can be used as carrier aggression mode. Band 2 (1900 PCS) Band 4 (2100 AWS-1) and Band 13

(700 c) has been chosen from the licensed band as primary carrier. These band are chosen such that the inter

modulation interface should not impact the licensed carrier.

There secondary carrier components are chosen from U-NII 1 and U-NII 3 Band. LTE-U form has defined

some band combination as shown in Table 3. This table specifies two flavors of carrier aggression.

Inter-band Carrier Aggression

Inter-band + Unlicensed intra-band contiguous Carrier Aggression

Inter-band Carrier Aggression where primary carrier component and secondary components are from different

band e.g. B2+ B252, B2 + B255.

Inter-band + Unlicensed intra-band contiguous carrier aggression where secondary carrier components are from

the same band e.g. B2+B252+B252 and B13+B255+ B255. From this combination we can see that two

secondary carrier components are from same un-licensed band.

Band 2 and Band 4 have flexibility to choose primary carrier bandwidth 5,10,15,20 MHz while Band 13 has

only 10 MHz option available. The unlicensed band is always utilized to maximum bandwidth in LTE which is

20 MHz. From the table if use max bandwidth from licensed (20) and unlicensed band (20+20) we can achieve

60 MHz bandwidth which can provide a downlink throughput 150x3= 450 Mbps in 2x2 and 300x3 =900 Mbps

roughly.

LTE-U & Wi-Fi

May 8th, 2016 Page 9

Band

Combination

Licensed

Band

Un-Licensed

Band

BW (MHz) CA configuration

B13+B252+B252 B13 U-NII-1 10+20+20 Inter-band + Unlicensed intra-band

contiguous DL CA w/o UL CA B13+B255+B255 B13 U-NII-3 10+20+20

B13+B252 B13 U-NII-1 10+20 Inter-band DL CA without UL CA

B13+B255 B13 U-NII-3 10+20

B2+B252+B252 B2 U-NII-1 [5,10,15,20]+20+20 Inter-band + unlicensed intra-band

contiguous DL CA without UL CA B2+B255+B255 B2 U-NII-3 [5,10,15,20]+20+20

B2+B252 B2 U-NII-1 [5,10,15,20]+20 Inter-band DL CA without UL CA

B2+B255 B2 U-NII-3 [5,10,15,20]+20

B4+B252+B252 B4 U-NII-1 [5,10,15,20]+20+20 Inter-band + unlicensed intra-band

contiguous DL CA without UL CA B4+B255+B255 B4 U-NII-3 [5,10,15,20]+20+20

B4+B252 B4 U-NII-1 [5,10,15,20]+20 Inter-band DL CA without UL CA

B4+B255 B4 U-NII-3 [5,10,15,20]+20

Table 4: LTE-U Carrier Aggression Band Combinations

Licensed-Assisted Access Operation/Anchored with Licensed carrier

LTE-U is designed to work in carrier aggregation mode as said and operates as secondary cell to fulfill the

capacity requirements; secondary cell is anchored by primary licensed carrier owned by operator. The UE can

only gain access to the SCells (on unlicensed bands) through the PCell(on licensed band) ,and all UE in the cell

may not get access to SCell, PCells shall select those UE based on algorithms considering radio condition, QoS

, Cell Load etc and reconfigure the UE to get access SCell. Aggregation of a primary cell, operating in licensed

spectrum to deliver control information and guaranteed Quality of Service, with a secondary cell, operating in

unlicensed spectrum to opportunistically boost data rate.

Figures 6: LTE Licensed Assisted Access Figures 7: LTE-U Carrier Aggression

The secondary cell operating in unlicensed spectrum can be configured either as downlink-only cell or contain

both uplink and downlink based on the capacity requirements. Unlicensed carriers can be integrated and

therefore take advantage of the existing LTE system deployed in licensed carriers for efficient usage as well as

system co-existence purposes. The anchor carrier can be from any bandwidth supported by LTE i.e.

1.4,3,5,10,15 or 20 MHz and un-licensed carrier shall be always 20 MHz of bandwidth.

LTE-U & Wi-Fi

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Enchantments in LTE air-interface The fundamental and design of LTE should remain with only necessary changes while the advanced

numerology features of LTE, e.g., eNodeB-based resource allocation and scheduling, link adaptation, control

channel robustness to interference, uplink power control, are used to ensure point-to-point and system

performance, in terms of both end-to-end QoS and physical layer transmission quality.

To avoid co-existence issues and to meet requirements by regulations, it makes necessity for some

modifications to the existing LTE air interface, for the compliance to listen-before-talk (LBT) requirements and

for fair and efficient co-existence. Following potential medications shall be expected in the LTE air interface to

support the above mentioned requirements.

1. Enhancing CA mechanism to facilitate opportunistic use

As required by LBT, the transmission of both traffic data and the common channels of LTE-U should

be based on the knowledge of channel availability by instantaneous channel sensing. As it is known in

integrated LTE network, unlicensed carriers should be operated as secondary carriers (SCell-U)

associated to a licensed LTE primary carrier through carrier aggregation (CA). The activation and

deactivation of SCells defined in CA can already enable the opportunistic use of unlicensed spectrum,

which is still based on the always-on common channel transmission, continuous channel measurement

and corresponding reports in LTE Rel-11 and earlier releases. Such a restriction will be solved to some

extent by the standardization of small cell on/off in LTE Rel-12 where quick on-off switching of a cell

will be supported and during cell off period UE would quit legacy channel measurement. Of course,

further enhancements to ensure more flexibility in terms of opportunistic synchronization /measurement

scheduling of SCell shall be needed.

2. Adaptive LTE frame structure for LBT support

Two types of LBT schemes are defined by regulation known as Frame Based Equipment (FBE) and

Load Based Equipment (LBE).The differences between FBE and LBE include whether a strict frame

structure should be followed, interference avoidance mechanism, and channel occupancy time. For both

schemes, some modifications are needed to ensure the consistency between the strict frame structure

defined in existing licensed LTE layer and the opportunistic occupancy of unlicensed band, and at the

same time allow for flexible channel sensing and occupancy to offer a potentially good channel

contention capability.

3. UL transmission Support

LBT basically represents a mechanism of transmitter sensing by which each device decides its

transmission opportunities based on self-detection of channel availability. However, in LTE the UL

transmission grant and channel availability sensing are decided by the eNodeB and UE respectively.

Thus it could be even more difficult to support UL transmission with respect to the case that an eNodeB

may schedule a UE UL grant but this UE fails to get access the channel in scheduled time due to

contention. These problems should be addressed to ensure UL transmission can be supported without

change of basic scheduling mechanism in LTE.

4. Interference coordination for complex interference scenarios in unlicensed spectrum

Sensing-based channel occupancy provides a preliminary mechanism to achieve interference

coordination between co-existing operator LTE-U cells can allow efficient use of unlicensed spectrum

even in high load scenarios, in which the simple channel sensing and avoidance may not work well, so

it requires more complex algorithms to handle these scenarios.

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To ensure co-existence within LTE-U and Other Access Networks Due to the non-exclusive use of unlicensed spectrum, co-existence issues shall be addressed from the beginning

of the LTE-U design in order for co-existence between LTE-U deployments. To ensure this LTE -U protocol

stack shall consider different operators LTE-U as well as different Access Networks e.g. LTE-U and Wi-Fi

systems co-existence. Some insight on the co-existence issues by LTE-U in dense deployments are listed

below.

Coexistence between Inter-operator LTE-U Deployment

Coexistence between Different Access Networks

Coexistence between Inter-operator LTE-U Deployment

As Un-Licensed spectrum is non-exclusive and no one is the owner of it, so any operator can use. If multiple

operators deploy LTE-U in the same unlicensed band, the lack of joint network planning may result in

geographical overlapping or even closely-located LTE-U cells and hence result in severe cross-site/operator

interference and performance degradation. It is obvious that compared with well-planned licensed LTE

deployment, user experience degrades due to the closely-located inter-operator interference.

Two scheme shall be adopted to mitigate such interference and achieve good sharing of unlicensed spectrum by

multiple operators:

Scheme #1: An agreement can be reached between multiple operators for orthogonal/exclusive use of the

unlicensed spectrum within a given region. The agreement can totally avoid inter-operator interference, with

the cost of potentially inefficient use of spectrum due to the lack of dynamic spectrum sharing. In some

countries, it could be difficult to reach such an agreement, due to the competition between operators as usually.

Even considering possibility of good cooperation between operators, such an agreement exclusive use of

unlicensed spectrum by a group of operator may still be problematic e.g. if there are six operator servicing

country and only four blocks of un-licensed are available then any of the two operator spectrum will collide.

This scheme is depicted in figure 9

Figure 8: Multi-Operator Figure 9:Co-Operative Spectrum Figure 10: Dynamic Spectrum

LTE-U Deployment Sharing among Operator Sharing among Operator

Scheme #2: Relatively dynamic schemes for shared use of unlicensed radio resources. The use of unlicensed

spectrum depends on the instantaneous/semi-static traffic load of LTE-U. Such a flexible and efficient

occupancy/release of the unlicensed carriers requires some dynamic coordination and information exchange

between operators. Despite the lack of standard backhaul between operators, monitoring of LTE transmission

over the air interface could provide potentially enough cooperation information between LTE Nodes from

different operators. This technique requires intelligence algorithms to decodes radio information and apply for

the spectrum selection. This scheme is shown in figure 10.

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Coexistence between Different Access Networks Bluetooth, ZigBee and Wi-Fi technology uses un-licensed band, Bluetooth and ZigBee are mostly used in

indoor and less power applications while Wi-Fi is used for indoor& Outdoor applications. Wi-Fi is widely

deployed and popular access technology in unlicensed spectrum and it can co-exist with LTE-U. Due to the

fundamental differences in the PHY/MAC design between LTE and Wi-Fi, a direct implementation of LTE

may impact the opportunistic channel occupancy of co-channel Wi-Fi especially in some high-load cases where

the complete channel bandwidth is occupied.

Figure 11: LTE-U and Wi-Fi Coexistence

One shall consider following cases to validate the Co-existence and interference matrix:

Case 1: A Wi-Fi AP is interfered by a paired Wi-Fi AP.

Case 2: A Wi-Fi AP is interfered by a paired LTE-U small cell operating in DL only mode.

Case 3: A Wi-Fi AP is interfered by a paired LTE-U small cell operating in TDD mode, where LTE UL

sub-frames are fake transmission to provide the access of paired Wi-Fi AP.

Case 4: A LTE-U small cell is interfered by a LTE-U paired cell both cell of them are operating DL

only mode.

From the target Access Point perspective (case 1), when there is increase of traffic load, the competition for

resources from paired interfering AP would significantly deteriorate the performance of Wi-Fi. LTE small cell

performs much more robust even with high-load interfering Access Point nearby (case 2). This robustness

contribution result of link adaptation and HARQ retransmission in LTE, and other strong MAC and PHY

features of LTE. On the other hand, as the paired interfering AP, LTE-U small cell in TDD mode with fake UL

sub frames in (case 3) is seen as a similar or more friendly neighbor to Wi-Fi (compared to case 1) even

without assistance of additional transmission restriction (e.g. LBT), which means less performance degradation

of Wi-Fi is observed if the interfering AP is LTE-U rather Wi-Fi Access Point, especially in low-load cases.

In short, for operators to exploit unlicensed spectrum where is already crowded with unlicensed deployment,

LTE is a better choice to offer good performance in terms of robust self-protection, as well as less impact on

the existing competing systems. Even for less-used spectrum, LTE deployment can provide future-assured

performance with respect to the possibly subsequent deployment in the vicinity. Of course, despite the

potentially less impact of LTE to neighboring Wi-Fi, it is still preferred to adopt the co-existence mechanisms,

including TPC/DFS/LBT for LTE-U to meet the requirements imposed by regional regulations, and to achieve

more efficient co-existence between different systems.

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May 8th, 2016 Page 13

5. LTE-U Deployment use case

Due to low power transmission restriction imposed by regulations in the unlicensed spectrum, the coverage will

be relatively small. Moreover, as unlicensed spectrum is usually in higher-frequency bands compared to

licensed ones, coverage holes in the unlicensed band shall be expected in licensed and unlicensed when

deploying co-located cell. In addition, the use of unlicensed spectrum should follow regulatory restriction(s) to

reduce negative impact on nearby co-existing systems. This may result in noncontiguous/opportunistic use of

unlicensed spectrum and render the transmission of important control and common channels of LTE system in

unlicensed carriers as un-reliable. Therefore, the existing LTE system in the licensed spectrum with good

coverage jointly operating with an unlicensed carrier is the key enabler for efficient use of unlicensed spectrum.

LTE –U cell can be deployed in two ways:

LTE & LTE-U Co-Located Deployment

LTE & LTE-U Non-Co-Located Deployment

Operator-deployed small cells with co-located unlicensed and licensed carriers are the preferred due to low

extra cost for new sites or backhaul is shown in figure 12. In addition, inter-site aggregation between licensed

carriers and unlicensed carriers is also possible in case of non-co-located cell deployment, which requires high

speed backhaul between Macro cell and small cell, e.g. in case of optical fiber between Macro eNodeB and

remote radio head (RRH) shown in Figure 13.

Figure 12: LTE & LTE-U Co-Located Deployment Figure 13: LTE & LTE-U Non-Co-Located Deployment

As mentioned the design principle of LTE-U is the integration between unlicensed and licensed carriers both

operating LTE is the key operating mechanism. The unlicensed carriers are operated as Secondary Carriers

associated to and controlled by the existing licensed LTE Primary Carriers, thus the joint operation and flexible

offload between licensed and unlicensed carriers can be easily achieved.

Through carrier aggregation, unlicensed carriers can be well integrated within the operator’s network while

preserving the key benefits of LTE technology. For example, UE mobility is still under the control of the

licensed LTE network, while the joint scheduling between LTE and LTE-U carriers is done in the centralized

nodes for smooth load shifting and channel adaptation. Security and service QoS can also be ensured due to the

assistance of the licensed LTE network. Most important advantage of the economy of scale can be achieved

due to the reuse of basic LTE physical-layer design and numerology so that additional development and

implementation cost may be insignificant.

Figure 14: LTE & LTE-U Deployment Benefits

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May 8th, 2016 Page 14

5.1 Advantage of LTE deployments in Un-Licensed Spectrum

Compared to the currently used technologies in the unlicensed spectrum, LTE-U can potentially provide many

benefits in terms of operator OPEX/CAPEX reduction as well as better end user experience.

Reuse of existing infra reduce additional CAPEX/OPEX cost.

Good end user experience and more operator revenue.

LTE Technology, ensures highly efficient use of unlicensed spectrum compare to Wi-Fi

Reuse of existing infra reduce additional CAPEX/OPEX cost for operator

The CAPEX of LTE-U deployment shall be reduced for operators because free unlicensed spectrum and all the

existing backhaul, core network and even sites deployed for licensed LTE carriers can be reused for the

operation of unlicensed spectrum with software updates only in eNodeBs as shown in Figure 15. In addition,

LTE-U would provide more efficient use of unlicensed spectrum compared to other unlicensed technologies

which may in turn lower the efforts of operators in deploying cells to offer a given amount of traffic offload by

unlicensed spectrum.

From an operational view a common RAN across the whole network allows unified operation and management

between licensed and unlicensed spectrum, including OAM configuration, authorization, charging and RRM

management can be used as illustrated as in Figure 16. Also joint scheduling and flexible traffic offload

between both layers can be easily achieved, since the secondary component cells (LTE-U cell) could be

activated/deactivated by Primary cell (LTE cell) the network can select licensed or unlicensed layers for traffic

offload in a dynamic and OPEX-efficient way.

Figure 15: LTE, LTE-U and Wi-Fi Network Architecture Figure 16: LTE RAN Sharing for LTE-U

Good end user experience and more operator revenue

In LTE-U system, enable or disable of the unlicensed secondary carriers can be seamlessly controlled by the

network without need of manual configuration by the user. In this sense, LTE-U can enable traffic volume to

be carried on an unlicensed or licensed carrier in a transparent way from the user perspective as shown in

Figure 17. On the other hand, the existence of licensed Primary cell ensures the basic service continuity and

QoS guarantee, especially for low-latency traffic e.g. continuity of voice traffic can be guaranteed even in case

of the existence of neighboring interference in unlicensed layer.

LTE-U & Wi-Fi

May 8th, 2016 Page 15

Figure 17: Operator and user experience

From an end user point of view, efficient and convenient use of unlicensed spectrum shall eventually lead to

better service experience. With both LTE-U and Wi-Fi capabilities on the same unlicensed carrier, network can

provide more flexibility for UEs to be served by appropriate RAT based on the available access point, charging

mode, service quality, etc. As a result, the user experience improvement and transparent use of unlicensed

spectrum could provide operators more flexibility on charging strategy to get larger revenue from exploiting

unlicensed spectrum. It would in turn encourage operators to exploit unlicensed spectrum.

LTE Technology, ensures highly efficient use of unlicensed spectrum compare to Wi-Fi

The first phase LTE networks (Release 8) provide up to 150 Mbps data rate, while the latest LTE-Advanced

supports up to 300 Mbps downlink peak data rate. Although LTE capabilities are evolving continuously and

will ultimately enable higher data rates of up to 1 Gbps or even more, the next steps after 300 Mbps are support

of 450 Mbps and 600 Mbps downlink peak rates. These rates will be achieved when devices supporting more

than two aggregated LTE downlink carriers become available.

The LTE performance study found to be roughly twice the data rate of a comparable Wi-Fi network

(802.11ac).The results indicate the extra performance achievable with a single 20 MHz carrier on unlicensed

spectrum The relative capacity of the LTE network would be even higher when the offered load and number of

users is further increased, as Wi-Fi capacity will not increase further or will even go down, while the LTE

network can still reach a higher throughput.

If we consider a single access node with a large amount of traffic (a hot spot), the LTE design allows the

system to stay robust while serving a very large number of users, while the Wi-Fi access capacity would start to

drop sharply with increased traffic. The advanced features for handling the load in LTE can also be applied

when operating in the unlicensed band, ensuring high capacity when faced with a large number of users.

Specifically, better link budget, coverage and higher system throughput can be achieved by the LTE air

interface compared to Wi-Fi because better Physical and MAC layer features even in isolated deployment

scenarios, as illustrated by Figure 18, while in dense deployment LTE is expected to achieve even larger

performance advantages over Wi-Fi by its inherent interference mitigation mechanisms.

This allows fewer nodes for a given area to reach the same capacity as a Wi-Fi network. This enables a trade-

off in deployment between the total network capacity and the number of LTE nodes being deployed for the

unlicensed band. So using LTE technology in unlicensed help better utilization with higher spectral efficiency

in both co-existed and standalone deployments, a sample test result published by an OEM is shown in figure 19

when Wi-Fi node are replaced with LTE-U cells.

Figure 18: LTE-U and Wi-Fi Isolated Deployment Figure 19: Improvement in Average Throughput With LTE-U Node Network

6. LTE-U Eco System and Standardization The ecosystem for unlicensed wireless is vast. It involves regulatory authority operators, equipment vendors,

consumer products and millions of users. Equipment technology in unlicensed bands is varied: Wi-Fi,

Bluetooth, ZigBee .These technologies and devices have sources .Their basic principle is" Live and let Live.

“If they see interference, they Back off, if they see someone else using the resources, they wait for their turn.

With CSAT 9Carrier-Sensing Adaptive Transmission) scheduling features, LTE-U shall ensure that resources

are shared fairly. This way, Wi-Fi access points in the area shall not be starved just because LTE-U is also

operating in the same area. LTE-U has the ability to intelligently switch off transmission so that resources are

released for Wi-Fi. We can say the ecosystem of LTE technology is mature enough.

3GPP Release 13 is to include standardization for LTE operation in unlicensed band once LAA is completed.

3GPP started the work with a workshop on LTE unlicensed in June 2014, with the formal study starting in

September 2014. The ongoing study is scheduled to be completed in June 2015, as shown in Figure 19 and

shall cover the necessary mechanisms for co-existence. Once complete, the work item phase will finalize the

detailed specification, including the necessary band combinations to enable LTE operation with 5 GHz band

aggregated with another licensed frequency band.

The assumption with 3GPP work is that LTE is not operated as a standalone system on the unlicensed band but

will be used in conjunction with a Primary Cell in the licensed band. The specification work for Release 13

LTE operation in unlicensed spectrum is expected to be ready by mid-2016. Once the basis is specified, 3GPP

will define the necessary bands and band combinations to be used with the 5 GHz band, which can be done as

Release independent on top of Release 13.

Figure 19: LTE-U Standardization, 3GPP Timelines

LTE-U & Wi-Fi

May 8th, 2016 Page 16

7. Summary and Last Words

LTE “long term evolution” is proving its name and evolving continuously in Release 13 and one of the

evolution is the deployment of LTE in the 5 GHz unlicensed band. The License Assisted Access (LAA) with

LTE will allow co-existence with Wi-Fi without any specific coordination and will meet all the regulatory

requirements for 5 GHz unlicensed band operation. This is an important feature of LAA which allows its

deployment in shopping malls and corporate offices, same as Wi-Fi networks.

The interference effect on a Wi-Fi network from a LTE-U network can be an issue for LTE-U and Wi-Fi co-

existence. Now the question may come that, should we worried as a customer, No, not at all. This problem

between Wi-Fi and LTE-U is a nice problem to have. The conflict reflects the fundamental dynamism of the

wireless technologies. Technologies rise and fall based on their usefulness and subsequent adoption. We have

witnessed many wireless technologies: AMPS, 2G, GSM, HSPA+, LTE, WiMAX, Bluetooth, ZigBee, Active

RFID (433MHz, 900MHz, etc.). Each with their set of advantages and success rate. The whole point of

competition is that the organizations are trying to find out the best, sometimes it is a win and sometimes a loss.

Bring it on and we as consumers can decide what works best for us.

Successful co-existence in unlicensed bands will take work and determination. A couple of decades ago,

skeptics said CDMA was too complex to work on a wide scale. But CDMA persevered, becoming the

backbone of global 3G systems. Similarly, over time, technologists will solve spectrum sharing challenges,

including threading the needle for harmonious LTE and Wi-Fi co-existence.

However, LTE-U network can reach higher capacity than a Wi-Fi network. Especially in an environment where

the traffic density is high, LTE-U (LAA) can be option to utilize the unused band of the 5 GHz spectrum. With

the ability of LTE-U to control the type of deployment, such as in a corporate office, it is very easy to find fully

empty channels from the 5 GHz band will be relatively easy, allowing LTE to reach its full performance.

LTE for unlicensed band rely on the existing LTE core network and uses the existing LTE security and

authentication architecture, means no change in the core network elements is required. The use of LTE

unlicensed together with the licensed band operation brings a major capacity boost from the unlicensed band

while still ensuring end user quality of service, regardless of the interference situation in the unlicensed band

and cost effective solution.

The major player of Wireless industry have quoted following for LTE-U used in un-licensed spectrum. There is

broad consensus that licensed spectrum is superior; LTE-U does not reduce or dilute the need for licensed

spectrum.

FCC Chairman: “Folks, you’ve got to come together and resolve this in a broad-based standard”

Nokia Networks: “Simple methods enable fair band sharing between Wi-Fi & LTE-U. Still, better to use

separate channels”.

Israeli Association of Electronics & Software Industries (IAESI): “channel sharing based on energy

detection is bad for both 802.11 and LTE-U”.

NTT Docomo: “Coexistence with Wi-Fi needs to be carefully studied”.

Samsung Electronics: “UE will have to implement two technologies for the same spectrum; decrease the value

of current licensed spectrum? QoS? “

Broadcom: “Regional LTE-U technology bad for everybody; LTE-U must address the global market; 5 GHz

band is not green field spectrum regulatory aspects to be studied”

AT&T: “LTE-U should not negatively impact existing services; peaceful coexistence with Wi-Fi is required;

comprehensive protection assessment a must; globally inclusive; LTE-U should not have adverse impact on

future licensed spectrum allocation.”

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May 8th, 2016 Page 17

l

May 8th, 2016 Page 18

May 8h, 2016 Page 17

8. References

3GPP TSG RAN Workshop on LTE in Unlicensed Spectrum RWS‐140020 Sophia Antipolis, France,

June 13, 2013.

Comments of Google Inc. on LTE and Wi-Fi in Unlicensed Spectrum.

LTE in Unlicensed Spectrum “Department of Electrical Engineering and Computer Science

Northwestern University.

LTE in Unlicensed Spectrum: European Regulation and Co-existence Considerations.

LTE in Unlicensed Spectrum Wikipedia.

NTT DOCOMO’s view on LTE unlicensed Presentation.

Wi-Fi LTE Co-existence in Unlicensed band Presentation by FLORIDA International University.

Prepared By:

LTE-U & Wi-Fi

Mehdi Sadeghian

He holds M.Sc.

Degree from the dept.

of Comp. Network in

Islamic Azad

University, 2014.

His research areas

include Wireless

Network, telecomm &

etc.

Mohit Luthra He holds Bachelor

Degree in engineering

from MDU

University, 2010.

His area of interest

includes RF Hardware

design & dev, testing

etc.

Rahul Atri He holds Bachelor

Degree in Engg. from

PTU University,

2010.

His area of interest

including testing and

designing the next

generations’ network

including 4G, 5G,

Wi-Fi etc.

Rahul Sharma He holds Bachelor

Degree in Engg. from

IP University Delhi,

2011 & Pursuing

Master from USA.

His area of interest

including design the

NGN including 4G,

5G Physical Layer.

Preet Rekhi He holds Bachelor

Degree in Engg. from

IP University Delhi,

2010.

His area of interest

including design the

NGN including 4G,

5G, IOT & etc.

Sukhvinder Malik He holds Bachelor

Degree in engineering

from MDU

University, 2010.

His area of interest

including testing of

LTE and LTE-A

Access Nodes in Lab

and Field etc.

Disclaimer:

Authors state that this whitepaper has been compiled meticulously and to the best of their knowledge as of the date of publication. The

information contained herein the white paper is for information purposes only and is intended only to transfer knowledge about the respective

topic and not to earn any kind of profit.

Every effort has been made to ensure the information in this paper is accurate. Authors does not accept any responsibility or liability whatsoever

for any error of fact, omission,