LTE-Unlicensed
JOSH FORGIE
CTS
Flavors
• LTE-U / LAA
– New deployments
• LWA
– Link Aggregation - Expands operator deployments into existing WiFi
• WiFi
– New deployments - 802: .11ac/.11ad/.11ax/.11ay
• MultiFireTM
– ‘Stand-Alone’ without anchor carrier – neutral host suitable
– Association to develop global technical standards and certifications
– Expansion of LTE into new deployments
• LTE-U Forum
– Created by Verizon, Alcatel-Lucent, Ericsson, LG, Qualcomm and Samsung
LTE-U
• Continually Changing
• Industry defined coexistence with 3GPP Release 12 – primarily USA
– Already incorporates 3GPP 10 and 11
– Built on carrier aggregation of LTE-Advanced
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No license required to use spectrum
Radios must comply with existing FCC Part 15 regulations
Non-exclusive spectrum use
Spectrum subject to interference
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Consistency, Accessibility and Reliability
Disrupts existing WiFi
Quality of Service
Discontinuous Transmission
• Capacity over Coverage
– No new deployments in locations without existing licensed coverage
• Significant performance gains over WiFi
LTE-U Frequencies
 Power
 Frequency and use specific
 Typical:
200 mW indoor
1 W outdoor
LTE-U Deployments
• AT&T
– Trials in 2016
– 5 GHz in 20MHz channels
• Verizon
– Trials beginning in 2015-2016
– 5 GHz and 3.5 GHz
• T-Mobile
– 5 GHz in 2016
– Uses LTE-U enabled small cells from Alcatel-Lucent NOKIA
LAA
• License-Assisted Access
– Intended to allow WiFi and LTE-U to coexist
 Clear Channel Assessment / Listen before Talk – eNodeB Fairness
– Instantaneous access not guaranteed
 Opportunistic use of spectrum
– Increases capacity
– Part of 3GPP Release 13
– Deployed in Europe and Japan/Asia
– Supports Gigabit Class LTE - 5 Gbps near future
• Combines LTE in unlicensed 5GHz downlink with licensed LTE
– Carrier Aggregation
– Targeted for new small cell deployments
– Issue: Hotspot 2.0 / Passpoint
LAA
• AT&T reported as saying LAA is a better option
than LTE-U
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Cost of spectrum
Listen before Talk is seen as a good technique to reduce interference
Certified by 3GPP
LAA ‘restricts’ usage to LAA
• Intended rollouts
– AT&T – LTE-U in test; Upgradable to LAA
– Verizon – some this year
– T-Mobile - some this year
• Handsets
– Available in 2016
Coexistence and Fairness
• Control and scheduling controlled by carrier
• Coexistence can be divided into two regimes:
1. No regulations specifying what is “fair”
2. Listen Before Talk is required by regulation
Architectures
Enabling unlicensed
secondary carriers and
be seamlessly
controlled by the
network
Markets without LBT
Requirements
• Mainly US, China and South Korea (2014)
• Proprietary coexistence mechanisms
– Comply with 3GPP LTE Releases 10-13
– Generally software based
Fast prototyping
Support for new frequencies and changing
features
Three No LBT
Coexistence Mechanisms
1. Channel Section
– Simplicity
 Small cell chooses ‘cleanest’ channel based on WiFi and LTE measurements
 Falls through to CSAT (#2)
– Channel interference is determined by energy detection
 Independent of interference type
 Independent of interference source
 Sensitivity improvement by:
– Technology specific measurements
WiFi preambles estimate and detect neighbor Access Points
Detect neighboring LTE-U’s PSS, SSS, and PBCH channel
Device assistance
802.11k and UE measurements – hidden node effect
Three No LBT Coexistence
Mechanisms
Channel Section and Flow Chart
Three No LBT Coexistence
Mechanisms
2. Carrier-Sensing Adaptive Transmission – CSAT
CSAT amounts to channel sharing using Time Division Multiplexing
Three No LBT Coexistence
Mechanisms
Carrier-Sensing Adaptive Transmission
 Useful is dense environments where a ‘clean’ channel is difficult to
find
 Containing many WiFi and Small Cells
 CSAT
 LTE MAC control elements control the activation of LTE-U and determine
timing as per 3GPP Release 10-12
 When the channel is off, the channel is available to other WiFi users
 The eNodeB measures WiFi utilization during the off period to determine
LTE-U duty cycle requirements
 100’s of millisecond time scale
Three No LBT Coexistence
Mechanisms
3. Opportunistic SDL - Supplemental Downlink
 Anchor carrier in licensed band is always available
 SDL is available as needed
 SDL is used when traffic crosses a threshold and users in an area are present
 SDL provides above threshold offload
 SDL can also reduce or eliminate interference caused by continuous Reference Signal
transmissions from LTE-U in and around a given channel
Three No LBT Coexistence
Mechanisms
Aggregate Qualcomm Simulation Results
LTE-U Median User Downlink
Data Rate Gain: 3.1 over WiFi
alone
Carrier WiFi improves too:
10%.
Simulation results and
simulation conditions are
specific.
Read the whitepaper for
details.
Take Away:
Performance Improvement
http://assets.fiercemarkets.net/public/newsletter/fiercewireless/qualcommlteuwhitepaper.pdf
Markets with LBT
Requirements
• Mainly Europe, Japan and India (2014)
• Regulations require periodically checking for the presence of signals
before initiating a transmission
• Frame based
• Checks occur on a millisecond time scale
• Check window duration is called Clear Channel Assessment – CCA
(yellow)
• Channel Occupancy is defined as being between 1 and 10 ms (green)
• If the channel is empty during CCA, one Channel Occupancy period may
be used
• Longer transmissions require additional CCA checks
LBT Required Coexistence
Mechanism
Listen Before Talk Framing
LBT Required Coexistence
Mechanism
• Requires design modifications to LTE PHY and MAC layers to
implement LBT
Actively being discussed by 3GPP (Release 13+)
Regulated LTE-U Qualcomm Simulation
Results
LTE-U Median User Downlink
Data Rate Gain: 2.8 over WiFi
alone
Simulation results and
simulation conditions are
specific.
Read the whitepaper for
details.
Take Away:
Performance Improvement
http://assets.fiercemarkets.net/public/newsletter/fiercewireless/qualcommlteuwhitepaper.pdf
LTE-U Verification
• Prototype and Test LTE-U
– Physical Layer
– Performance Assessment
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Throughput
Fairness
Assess Interference
Discontinuous Transmission
– Standards Compliance
http://www.ni.com/white-paper/53044/en/
• Workshops
– Wi-Fi Alliance Wi-Fi and LTE-U Coexistence Test
Workshop – April 2016
http://www.wi-fi.org/wi-fi-alliance-wi-fi-and-lte-u-coexistence-test-workshop-0
References
• Qualcomm
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https://www.qualcomm.com/documents/progress-laa-and-its-relationship-lte-u-and-multefire
https://www.qualcomm.com/invention/technologies/lte/laa
https://www.qualcomm.com/news/onq/2015/06/11/introducing-multefire-lte-performance-wi-fi-simplicity
https://www.qualcomm.com/media/documents/files/lte-unlicensed-coexistence-whitepaper.pdf
• RCR Wireless News
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http://www.rcrwireless.com/20160301/carriers/making-sense-of-lte-u-laa-multifire-and-more-tag17
• Android Headlines
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http://www.androidheadlines.com/2016/02/ah-tech-talk-topics-avoided-by-the-wireless-industry-at-mwc.html
http://www.androidheadlines.com/2016/03/att-is-considering-laa-as-an-alternative-to-lte-u.html
• Radio Electronics
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http://www.radio-electronics.com/info/cellulartelecomms/lte-long-term-evolution/lte-u-unlicensed-laa-license-assistedaccess.php
• National Instruments
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http://www.ni.com/white-paper/53044/en/
http://www.ni.com/product-documentation/52533/en/
References
• Huawei
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http://www.huawei.com/ilink/en/download/HW_327803
• Wi-Fi Alliance
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http://www.wi-fi.org/wi-fi-alliance-wi-fi-and-lte-u-coexistence-test-workshop-0
• Fierce Wireless
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http://www.fiercewireless.com/tech/story/att-verizon-t-mobile-throw-support-behind-new-lte-u-laa-coalition/2015-09-28
http://www.fiercewireless.com/tech/story/att-trial-lte-u-early-2016/2015-09-09