Converged Wireless Access: The New Normal Karthik Sundaresan WNPE, Univ of Washington, June 2016 www.nec-labs.com
5G Services • Services drive network requirements for 5G Source: Ericcson 2
5G Services • Services drive network requirements for 5G • Wireless technology and access plays a critical role in this vision Source: Ericcson 3
Wireless Technology Evolution SISO MIMO MU-MIMO 802.11g 802.11b 802.11a 802.11n 802.11ac WiFi 2014 2009 2003 1999 3GPP 4
Wireless Technology Evolution MU-MIMO MIMO OFDM 802.11a/b 802.11ac 802.11g 802.11n Massive MIMO, mmWave WiFi 2009 2014 2003 1999 5G 3GPP 5
Access: Two Isolated Worlds • Cellular (LTE) • WiFi - Synchronous, coordinated - Asynchronous, distributed access access - Synchronous transmit/ - Asynchronous transmit/ receive receive - Coupled downlink and - De-coupled downlink and uplink (BS schedules) uplink 6
Convergence in Access? • Licensed spectrum crunch - Supplement licensed with unlicensed channels • Co-existence challenges Source: Qualcomm - Co-existence with WiFi and other LTE operators - Asynchronous access in traditional synchronous network LTE (1) Wi-Fi • Boundaries of access getting blurred • Is this a one-off problem? LTE (2) 7
A Paradigm Shift in Access Wi-Fi (1) Wi-Fi (2) LTE (1) Wi-Fi (3) LTE (2) • New paradigm: Asynchronous Access with Opportunistic Synchronous Transmissions - Norm rather than exception in 5G Wi-Fi - Unlicensed LTE: one simple manifestation LTE • WiFi: synchronous transmissions (network MIMO) for capacity “NEMOx: Scalable Network MIMO for Wireless Networks”, ACM MobiCom 2013. • LTE: asynchronous access for co-existence, scalability, IoT “MIDAS: Empowering 802.11ac Networks with Multiple-Input Distributed Antenna Systems”, ACM CoNEXT 2014. 8
LTE-WiFi Co-existence • 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 9
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 1 0.8 0.6 CDF 0.4 50 On 50 Off 10 On 10 Off 0.2 2 On 2 Off 0 0 20 40 60 LTE Inter-Packet Delay (ms) Wi-Fi 10
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 Source: Cable labs 11
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 1 20 2-on-2-off WiFi Bitrate (Mbps) 0.8 4-on-4-off 15 10-on-10-off 0.6 50-on-50-off CDF 10 0.4 50 On 50 Off 5 10 On 10 Off 0.2 2 On 2 Off 0 0 0 20 40 60 8 16 27 Inter-Packet Delay (ms) 12 SIR (dB)
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) 10 2 -62 dBm 13dB WiFi Bitrate (Mbps) 19dB LTE Wi-Fi 27dB 10 0 LTE 10 -2 -84 dBm -52 -63 -80 Wi-Fi LTE Power at STA (dBm) 13
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) -62 dBm • Can we homogenize channel access policies to LTE deliver better latencies, Wi-Fi throughput efficiency? LTE -84 dBm Wi-Fi 14
Ideal Solution eNodeB CC 1 CC 2 CC 5 MAC MAC MAC … PHY PHY PHY WiFi WiFi WiFi sensing / sensing / sensing / notification notification notification • WiFi sensing and preamble notification on every component carrier - Changes to the PHY; technology (WiFi) specific • Scalable realization without PHY modifications? 15
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 1 Subframe LAA-LTE Subframes - Single WiFi sensing module spans multiple CCs; LTE CTS LTE LTE LTE scheduler balances traffic … Energy or Total ON duration Carrier Sensing 16 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) 20 20 LTE Throughput (Mbps) Ultron Ultron WiFi Throughput (Mbps) No Ultron LAA-LTE 15 15 3x 2x 10 10 5 5 0 0 15 8 3 8 16 23 SINR at UE (dB) SINR at STA (dB) 17
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 operators and business models • LTE-WiFi co-existence barely scratches the surface - Both technical and policy challenges • Right time to get involved! 18
Thanks! Questions/Comments? 19
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