This document discusses LTE-U and its operation in unlicensed spectrum. It covers key topics such as: 1) LTE-U uses carrier aggregation to combine licensed LTE spectrum with unlicensed bands like 5GHz to boost data rates. 2) It employs listen-before-talk and dynamic frequency selection to share spectrum fairly with WiFi and avoid interference. 3) Qualcomm developed LTE-U to bring LTE's benefits like speed and capacity to unlicensed spectrum for use cases like offloading cellular traffic.

1. LTE-U
Mustafa Khaleel
APWC Course
(Advanced Wireless Telecommunications- Master Program)
Politehnica University of Bucharest

2. Contents
 Unlicensed Spectrum
 Design Principles
 Dynamic frequency selection (DFS) And Listen-before-talk (LBT)
 Licensed-Assisted Access
 Carrier aggregation
 LTE-U Scheduled Transmission
 Mechanisms for scheduling LTE-U and Wi-Fi
 Ecosystem and LTE-U
 Wi-Fi and LTE-U Comparison
 Benefits of LTE-U

3. Unlicensed Spectrum
• The unlicensed spectrum has enabled many low-cost wireless services from medical monitors to
walkie-talkie and Wi-Fi.
• The 2.4 GHz band is currently the most utilized band shared by different wireless users such as
cordless phone, ZigBee, Bluetooth and Wi-Fi .
• with 2.4 GHz band, 5 GHz band is less congested and mainly used by Wi-Fi
(11a) devices.
• 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

4. The 5GHz frequency band
 This band is frequently referred as 5GHz UNII (Unlicensed National Information
Infrastructure) band, having 3 sub-bands (1,2 & 3)
 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 use of 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
 In some regulatory areas, like Europe and Japan, there is a specific requirement for
supporting LBT (Listen-Before-Talk) or Clear Channel Assessment (CCA) at milliseconds
scale is required
 In other regulatory areas, like US, Korea and China, there are no such requirements
 Other techniques are also needed like DFS (Dynamic Frequency Selection) in UNII-2
sub-band for optimizing the co-existence between different systems or technologies

5. Band A
Indoor only
30-200mW
5150 (200MHz) 5350
Band C
Outdoor
1W
(125MHz) 5850
Band B
Outdoor
1W
5470 (255MHz) 5725
The 5GHz frequency band

6. LTE-U
 Originally developed by Qualcomm, using the 4G
LTE radio communications technology in unlicensed
spectrum, such as the 5 GHz band used by dual-
band Wi-Fi equipment.
 LTE-U was first introduced in Rel13 of the 3GPP
standards, LTE-U is built upon the carrier aggregation
capability of LTE-Advanced.

7. Design Principles
Some fundamental principles and regulations are imposed to guarantee the
harmonious coexistence between LTE-U and other incumbent systems
 The transmission power
 Dynamic frequency selection and Listen Before Talk
 Licensed Assisted Access
 Carrier aggregation

8. The transmission power
 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 23 dBm in Europe or 24 dBm in US.
 outdoor, e.g. hotspot Picocell, 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 (TPC) 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.

9. Dynamic frequency selection (DFS)
 Meteorological 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.
Dynamic frequency selection (DFS) And Listen-before-talk (LBT)

10. Dynamic frequency selection (DFS) And Listen-before-talk (LBT)
 listen-before-talk (LBT) mechanism
Any device wishing to use the band must listen to see if it is occupied. 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.
 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.

11. Licensed-Assisted Access
 Licensed-Assisted Access operation
- Aggregation of a primary cell, operating in licensed
spectrum to deliver critical information and guaranteed
Quality of Service, with a secondary cell, operating in
unlicensed spectrum to opportunistically boost data rate
- The secondary cell operating in unlicensed spectrum
can be configured either as downlink-only cell or contain
both uplink and downlink

12. Licensed-Assisted Access
 The UE can only gain access to the SCells (on unlicensed bands) through the PCell(on licensed
band).
 LAA as supplemental downlink will be evaluated. This is usually the more interesting case as
typically the downlink data traffic is significantly larger than

13. Carrier aggregation
 Carrier aggregation (CA)increase the overall bandwidth available to a user equipment
by enabling it to use more than one channel, either in the same band, or within another
band.
 Carrier Aggregation 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.

14. Carrier aggregation
In (a), is 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.
In (b) shows 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
In (c) show inter-band non-contiguous
carrier aggregation ,In this case the carriers
fall in different parts of the radio spectrum,
such as 900MHz and 1800MHz.

15. LTE-U Scheduled Transmission
In some country like US, Korea, China, the answer is Yes, you (a cell) can use the allowed spectrum at anytime as
long as it would not create serious Co-Existance problem. But in some countries like EU and Japan, the answer is NO.
The cell should perform a specific process called LBT (Listen Before Talk) .

16. LTE-U Scheduled Transmission
 LTE-U the cell use another mechanism called CSAT (Carrier-Sensing Adaptive
Transmission). Technically, CSAT is very similar to CSMA, the main difference is
that CSAT monitors(senses) the medium for much longer duration (around 10 s of
msec to 200 msec) comparing to normal Wi-Fi CSMA, so that it would not infer not
only with Wi-Fi data transmission (QoS traffic) but also with more sporadic
transmission like discovery signals.
 Why LTE-U is such a friendly neighbor to Wi-Fi. LTE-U does not use all of the
available 5 GHz band, over 200 MHz is exclusively available for Wi-Fi. LTE-U is a
downlink-only technology, meaning LTE-U end devices will not generate any
interference to Wi-Fi or any other technologies in the 5GHz band. An LTE-U small
cell scans portions of 5 GHz looking for a vacant channel, and if there is no vacant
channel, it finds the least occupied channel. It then takes turns using that channel
with Wi-Fi users, ensuring that it never uses the channel more.

18. Mechanisms for scheduling LTE-U and Wi-Fi
 Within different access classes for Wi-Fi, each Wi-Fi station gets equal
opportunity to access airtime. We right said the pre-standard proposals for
LTE-U operate much differently. Those scenarios use a duty cycle
approach, which means the LTE-U operator determines if there’s Wi-Fi
operating in the channel LTE-U intends to use, makes an assessment
of the environment, and then decides what percentage of the airtime
should be allocated for Wi-Fi and for LTE operations is, then all are
scheduled but in Wi-Fi are probabilistic based on contention .

19. Ecosystem and LTE-U
 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, LTE-U will ensure that resources are shared
fairly. This way, Wi-Fi access points in the area will 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 .

20. Unlicensed spectrum in TDD and FDD
 FDD deployments provide greater coverage than TDD Mobile devices in a Frequency Division
Duplexing (FDD) system transmit on a continuous basis, which enables devices to achieve cell
edge rates farther from the base station. Mobile devices in a Time Division Duplexing (TDD)
system transmit periodically (e.g., 1/2 or 1/3 of the time compared to FDD); hence, required
rates cannot be achieved at similar distances when compared to FDD. The FDD advantage is
consistent regardless of the radio technology being used.

21. Wi-Fi and LTE-U Comparison
Wi-Fi LTE-U
PHY is half-duplex PHY is typically full-duplex
PHY is packet oriented – sync on each
packet
PHY operates continuously – 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:Networks function without frequency
planning
All client access is scheduled 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 .

22.  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.
 The use of both licensed and unlicensed spectrum offers end users higher data rates and
overall better performance when the unlicensed band operation is available. The use of
carrier aggregation means the licensed spectrum can quickly take over to ensure service
quality should the unlicensed spectrum become unusable for any reason, such as reduced
coverage, interference from another system or avoidance of, for example, a radar operating in
the band.
 Based on the studies conducted, the LTE technology can meet the regulatory requirements
for the unlicensed band and allow coexistence with the other LTE systems as well as other
technologies, such as Wi-Fi, operating on the same frequency band.
Benefits of LTE-U

23. Reference
1.https://www.youtube.com/watch?v=q-jkSqJLV1s
2.http://hightechforum.org/why-lte-unlicensed-outperforms-wi-fi/
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5.Coexistence of Wi-Fi and Heterogeneous Small Cell Networks Sharing Unlicensed Spectrum
Haijun Zhang, Xiaoli Chu, Weisi Guo and Siyi Wang.
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14.https://en.wikipedia.org/wiki/IEEE_802.11#802.11a_.28OFDM_waveform.29
15.“Half duplex “The 802.11 family consists of a series of half-duplex over-the-air modulation techniques that use the same basic
protocol.”
16.LTE-Unlicensed: The Future of Spectrum Aggregation for Cellular Networks Ran Zhang, Miao Wang, Lin X. Caiy, Zhongming
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