The document discusses LTE in unlicensed spectrum and its relationship with Wi-Fi. It notes the massive shift to wireless traffic driven mostly by Wi-Fi. It also discusses why mobile operators are interested in unlicensed spectrum to overcome limitations of licensed spectrum. The document summarizes several simulations that have been done on the performance of LTE unlicensed versus Wi-Fi. It finds that LTE unlicensed generally has better spectral efficiency while Wi-Fi performance may be better under lighter traffic loads. Combining LTE unlicensed and Wi-Fi can provide higher overall capacity than Wi-Fi alone.

1. LTE unlicensed and Wi-Fi:
moving beyond coexistence
Monica Paolini, Senza Fili
May 12, 2015

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Why LTE unlicensed?
June 15, 2015
• Massive shift to wireless traffic
– Mostly driven by Wi-Fi
– Cellular only a small part of it
• Much of wireless access over 2.4 GHz band
• High value of unlicensed spectrum
– High resource utilization
– High spectral reuse
– Increasing importance to carry IP traffic
– Increasing demand for unlicensed spectrum
• Mobile operators have become interested in
unlicensed spectrum
– Overcome diffidence of Wi-Fi, when Wi-Fi offload
became necessary
– LTE unlicensed widens the opportunities to used
the unlicensed band
Densification and multi-faceted networks make coexistence and integration of
multiple technologies and co-located networks crucial to efficient resource utilization

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Some terminology to start
June 15, 2015

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Wi-Fi or LTE unlicensed? A comparison
June 15, 2015

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Factors affecting relative performance
of Wi-Fi and LTE unlicensed
• LTE unlicensed specifications (3GPP LAA-LTE specifications
are not yet finalized, so current simulations and trials
have to make assumptions on what the specifications will
be)
• Physical environment and deployment topology (including
indoor versus indoor locations)
• Technologies features and versions
• Hardware vendor, equipment specifications
• Channel size; TDD or FDD inclusion of uplink; frequency
reuse
• Spatial distribution of UEs and infrastructure nodes
(macro and small cells, Wi-Fi AP); collocated/non
collocated equipment
• Synchronization
• Traffic model, including assumptions on traffic mix (e.g.,
voice and video as a percentage of traffic)
• Other simulation parameters
June 15, 2015
• Multiple
simulations and
trials
done/ongoing
• Difficult to
compare and
generalize results
• Differences
among results
reflect
differences
among
assumptions
• Useful to look at
directionality of
performance
drivers

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Directional trends in LTE unlicensed
and Wi-Fi performance
June 15, 2015
Wi-Fi vs LTE
(stand alone)
Wi-Fi and LTE
(coexistence)
LTE has better spectral efficiency:
- Transmission
- Interference management
- Coverage
LTE performance is more robust with:
- Increased traffic load
- Number of users
Combined Wi-Fi and LTE capacity can be
higher than Wi-Fi only
Wi-Fi performance may increase with LTE
as neighbor (instead of Wi-Fi)
Unclear impact of LBT and fair
coexistence mechanisms
- Standardization still in progress, so
difficult to assess impact
- Could LBT erase most of the
performance advantages of LTE over
Wi-Fi?
Spread of performance measurements vary among simulations and tests,
but the trends are clear

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LWA, LAA, and LWA with LAA
June 15, 2015
Source: Alcatel-Lucent
• LTE and Wi-Fi integration is also getting traction
– Confirmation of importance of 5 GHz spectrum (traditionally not considered for
cellular)
• 3GPP standardization for Release 13
• Integration with Wi-Fi at the edge
– Complementary to other mechanisms for integration
• Can complement or substitute LAA

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Concluding remarks
• LTE unlicensed attracts attention of mobile operators because of increased
spectral efficiency
• Wi-Fi users may feel threatened by LTE unlicensed
– Some consider 5 GHz as “Wi-Fi spectrum”, but it is not only for Wi-Fi
– Fair coexistence is possible, but industry collaboration is needed
(beyond regulation)
• Success of LTE unlicensed is contingent on
– Availability and cost to add LTE unlicensed to mobile devices
– Acceptance of LTE unlicensed by the Wi-Fi ecosystem
– Performance advantage of LTE unlicensed over Wi-Fi (with LBT)
– Per-bit cost spread for LTE unlicensed over Wi-Fi
– Advancement in the Wi-Fi and cellular integration, as possible
alternative to LTE unlicensed
June 15, 2015

9. June 15, 2015
Monica Paolini
Senza Fili
www.senzafiliconsulting.com
monica.paolini@senzafiliconsulting.com
Cover photo by Lukas Rebec/Shutterstock.com; icons from Stoker-13/Shutterstock
Download the report from http://content.rcrwireless.com/Analyst_Angle_LTE_Report
New Senza Fili Report on LTE unlicensed and
Wi-Fi in collaboration with RCR Wireless News

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The 3GPP approach to LAA standardization
June 15, 2015
Agreement to focus
on the 5 GHz band
Commitment to find
a global solution
LBT, with maximum
transmission
duration
Dynamic frequency
selection for radar
avoidance
Carrier selection
Transmit power
control
Covered areas:
• Regulatory requirements
• Deployment scenarios
• Design targets and functionalities
• Coexistence evaluation and methodology

11. Backup slides

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Why do operators care about LTE unlicensed?
June 15, 2015
• Efficient resource utilization
is crucial
– Increase in traffic
– Stationary ARPU
– IoT
• Spectrum is a finite resource,
but spectral efficiency/area
can increase
• Density
• Technology
• Topology
• 5 GHz band is a good target for
spectrum utilization improvement
– But use of unlicensed spectrum
requires a new approach from
mobile operators (this is not
Wi-Fi offload)

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Beyond LTE unlicensed in the 5 GHz band:
alternatives and complementary approaches
Stand-alone
LTE unlicensed
Carrier Wi-Fi
LTE and Wi-Fi
aggregation
3.5 GHz LTE
LTE unlicensed
in other bands
June 15, 2015

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The LAA in LTE unlicensed:
links between licensed and unlicensed transmission
June 15, 2015

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Mechanisms for LTE unlicensed and Wi-Fi coexistence
June 15, 2015

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3GPP standardization crucial to establish LTE
unlicensed worldwide
From 3GPP R-141817, on coexistence with Wi-Fi:
It is not enough to minimize interference simply for
regulatory aspects. It is also essential to insure that a
deployed system will operate as a “good neighbour”,
and not significantly impact legacy systems.
[The purpose is to] identify and define design targets
for coexistence with other unlicensed spectrum
deployments, including fairness with respect to Wi-Fi
and other LAA services. This should be captured in
terms of relevant fair sharing metrics, e.g., that LAA
should not impact Wi-Fi services (data, video and
voice services) more than an additional Wi-Fi
network on the same carrier; these metrics could
include throughput, latency, jitter etc. This should
also capture in-device coexistence for devices
supporting LAA with multiple other-technology radio
modems, where it should, e.g., be possible to detect
Wi-Fi networks during LAA operation
June 15, 2015

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3GPP LAA deployment scenarios
June 15, 2015
Scenario 1: CA between licensed macro cell (F1) and unlicensed small cell (F3)
Scenario 2: CA between licensed small cell (F2) and unlicensed small cell (F3), no macro coverage (e.g.,
indoor deployment)
Scenario 3: CA between licensed small cell (F1) and unlicensed small cell (F3), with macro coverage
Scenario 4: CA between licensed small cell (F2) and unlicensed small cell (F3), with macro coverage
(F1). With ideal backhaul between macro and small cell, CA among F1, F2 and F3 is possible. Dual
connectivity between macro cell and small cell can be enabled.

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NTT DOCOMMO deployment scenarios
and architecture
June 15, 2015
NTT DOCOMO deployment scenarios
Source: NTT DOCOMO
NTT DOCOMO has considered
indoor and outdoor scenarios, with
and without co-location of licensed
and unlicensed small cells.
Integration between licensed and
unlicensed LTE is highest when CA is
used.
NTT DOCOMO LTE unlicensed architecture
Source: NTT DOCOMO
LTE unlicensed can be integrated
closely at the RAN. The offloading
region is more restricted, but
HetNet functionality can be more
effectively implemented.

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Sources of interference in the 5 GHz band
with LTE unlicensed and Wi-Fi
June 15, 2015
Source: NTT DOCOMO
Intra-RAT interference among LTE unlicensed network can be managed with
intra-operator or inter-operator synchronization. Inter-RAT transmission can
be managed with LBT.

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Wi-Fi and LTE performance comparison: single
operator
June 15, 2015
Source: NTT DOCOMO
In NTT DOCOMO’s simulation, as the traffic load increases, LTE unlicensed
spectral efficiency decreases more slowly than for Wi-Fi, making LTE
unlicensed better in high-traffic environments.

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In NTT DOCOMO’s simulation, under medium traffic load assumptions, LTE is
more spectrally efficient than Wi-Fi and, when combined with Wi-Fi, lead to an
overall increase in spectral efficiency.
Source: NTT DOCOMO
Wi-Fi and LTE performance comparison:
coexistence scenario, two operators