Converged Wireless Access: The New Normal Karthik Sundaresan WNPE, - - PowerPoint PPT Presentation

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Converged Wireless Access: The New Normal

Karthik Sundaresan WNPE, Univ of Washington, June 2016

5G Services

• Services drive network requirements for 5G

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Source: Ericcson

5G Services

• Services drive network requirements for 5G
• Wireless technology and access plays a critical role in

this vision

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Source: Ericcson

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Wireless Technology Evolution

802.11b 1999 2003 2014 802.11g 2009 802.11a 802.11n 802.11ac SISO MIMO MU-MIMO

WiFi 3GPP

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Wireless Technology Evolution

802.11a/b 1999 2003 2014 802.11g 2009 OFDM 802.11n MIMO 802.11ac MU-MIMO

Massive MIMO, mmWave

5G

WiFi 3GPP

Access: Two Isolated Worlds

• WiFi
• Asynchronous, distributed

access

• Asynchronous transmit/

receive

• De-coupled downlink and

uplink

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• Cellular (LTE)
• Synchronous, coordinated

access

• Synchronous transmit/

receive

• Coupled downlink and

uplink (BS schedules)

Convergence in Access?

• Licensed spectrum crunch
• Supplement licensed with

unlicensed channels

• Co-existence challenges
• Co-existence with WiFi and
• ther LTE operators
• Asynchronous access in

traditional synchronous network

• Boundaries of access getting

blurred

• Is this a one-off problem?

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Source: Qualcomm

Wi-Fi LTE (1) LTE (2)

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Wi-Fi (3) LTE (1) LTE (2) LTE Wi-Fi Wi-Fi (1) Wi-Fi (2)

A Paradigm Shift in Access

• WiFi: synchronous transmissions (network MIMO) for capacity
• LTE: asynchronous access for co-existence, scalability, IoT
• New paradigm: Asynchronous Access with Opportunistic

Synchronous Transmissions

• Norm rather than exception in 5G
• Unlicensed LTE: one simple manifestation

“NEMOx: Scalable Network MIMO for Wireless Networks”, ACM MobiCom 2013. “MIDAS: Empowering 802.11ac Networks with Multiple-Input Distributed Antenna Systems”, ACM CoNEXT 2014.

LTE-WiFi Co-existence

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• Two modes of operation
• LTE-U
• Duty cycling at time scales of 100 ms
• Can be realized today: switch on/off unlicensed carriers

Source: Cable labs

LTE-WiFi Co-existence

• LTE-U
• Duty cycling at time scales of 100 ms
• Can be realized today: switch on/off unlicensed carriers
• Short-term unfairness to WiFi, higher latency

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20 40 60

Inter-Packet Delay (ms)

0.2 0.4 0.6 0.8 1

CDF

50 On 50 Off 10 On 10 Off 2 On 2 Off

Wi-Fi LTE

LTE-WiFi Co-existence

• LTE-U
• Duty cycling at time scales of 100 ms
• Short-term unfairness to WiFi, higher latency
• LAA-LTE: License assisted access
• Energy sensing CCA; Operation at 1-10 ms granularity
• Modification to LTE specification for Listen-before-Talk

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Source: Cable labs

LTE-WiFi Co-existence

• LTE-U
• Duty cycling at time scales of 100 ms
• Short-term unfairness to WiFi, higher latency
• LAA-LTE: License assisted access
• Energy sensing CCA; Operation at 1-10 ms granularity
• Reduced throughput efficiency of smaller TxOP

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20 40 60

Inter-Packet Delay (ms)

0.2 0.4 0.6 0.8 1

CDF

50 On 50 Off 10 On 10 Off 2 On 2 Off

8 16 27

SIR (dB)

5 10 15 20

WiFi Bitrate (Mbps)

2-on-2-off 4-on-4-off 10-on-10-off 50-on-50-off

Challenge

• Im-balanced channel access
• WiFi detects/notifies other WiFi through “WiFi carrier”

sensing/notification (-84 dBm sensitivity)

• WiFi-LTE detect each other through “energy” sensing

alone (-62 dBm sensitivity)

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Wi-Fi LTE Wi-Fi LTE

• 62 dBm
• 84 dBm
• 52
• 63
• 80

LTE Power at STA (dBm)

10 -2 10 0 10 2

WiFi Bitrate (Mbps)

13dB 19dB 27dB

Challenge

• Im-balanced channel access
• WiFi detects/notifies other WiFi through “WiFi carrier”

sensing/notification (-84 dBm sensitivity)

• WiFi-LTE detect each other through “energy” sensing

alone (-62 dBm sensitivity)

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Wi-Fi LTE Wi-Fi LTE

• 62 dBm
• 84 dBm
• Can we homogenize

channel access policies to deliver better latencies, throughput efficiency?

Ideal Solution

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MAC PHY

CC 1

WiFi sensing / notification

MAC PHY

CC 2

WiFi sensing / notification

MAC PHY

CC 5

WiFi sensing / notification

…

eNodeB

• WiFi sensing and preamble notification on every

component carrier

• Changes to the PHY; technology (WiFi) specific
• Scalable realization without PHY modifications?

ULTRON: Unlicensed LTE Radio Node

• Homogenized channel access
• WiFi Embedding
• Embeds Tx notification (CTS-

to-Self) in LTE transmissions

• WiFi Sensing
• Detects WiFi signals to realize
• 84 dBm sensitivity
• Single WiFi sensing module

spans multiple CCs; LTE scheduler balances traffic

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CTS LTE LTE LTE

…

1 Subframe LAA-LTE Subframes Total ON duration Energy or Carrier Sensing

Time

ULTRON: Unlicensed LTE Radio Node

• Homogenized channel access
• Detects WiFi signals to realize -84 dBm sensitivity
• Embeds Tx notification to WiFi in LTE transmissions
• Efficient and fair LTE-WiFi co-existence (2x-3x gain)

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15 8 3

SINR at UE (dB)

5 10 15 20

LTE Throughput (Mbps)

Ultron LAA-LTE

8 16 23

SINR at STA (dB)

5 10 15 20

WiFi Throughput (Mbps)

Ultron No Ultron

2x 3x

Summary

• Boundaries between synchronous and asynchronous

access models will get blurred in 5G

• Need a deeper understanding of how to realize

converged access

• Several interesting and important problems
• Critical for innovation in unlicensed spectrum: new
• perators and business models
• LTE-WiFi co-existence barely scratches the surface
• Both technical and policy challenges
• Right time to get involved!

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Thanks!

Questions/Comments?

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