1© 2018 NYU WIRELESS 1

Low Latency NetworksSHIVENDRA PANWAROCTOBER 23, 2018

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Quality of Service (QoS) requirements in 5G

AR/VR requirements

(otherwise can cause nausea or sickness)

Data Rates 100Mbps-1Gbps

Interruptions

0.1/min

Video stall (pause)

<10 ms

Source: Nokia, VR/AR in the 5G Era NEM Summit November 23, 2016 Image source: https://videohive.net

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The good news:

• Latencies will drop from about 50 ms (current 4G LTE networks) to about 10ms in 5G

• This will allow control loops to be off-boarded to edge computing platforms• Savings in computing, battery power needs and weight in the vehicles• Congestion/traffic control and planning will be easier

What can 5G provide to automated vehicles?

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The not so good news:

• Sub-millisecond control loops will need to stay on the vehicle• There will be signal dead spots and signal blockages due to mobile

blockers• Less dead spots for sub-6Ghz signals, but less bandwidth as well

(~100Mbps)• More dead spots and blockages at mmWave, but much higher bandwidth

(~1Gbps)• Communication needs to be optimally split between the two• Careful design of computation split between computation on the vehicle

and edge computing

What can 5G provide to automated vehicles

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Can 5G mmWave networks meet QoS requirements?

•In an urban mmWave cellular network:

For blockage probability 1e-3, a high BS density (350 BS/) is required.

NLOS paths may reduce the BS density to 270 BS/, but, still the requirement is very high.

Blocker Density= 0.01 bl/Blocking rate= 1 blockage/10sec

Blocker Density= 0.01 bl/Blocking rate= 1 blockage/10sec

Blocker Density= 0.1 bl/Blocking rate= 1 blockage/secBlocker Density= 0.1 bl/Blocking rate= 1 blockage/sec

Jain I. K., Kumar R., Panwar S., “Can Millimeter Wave Cellular Systems provide High Reliability and Low Latency? An analysis of the impact of Mobile Blockers,” arXiv preprint arXiv:1807.04388, Jul. 2018.Jain I. K., Kumar R., Panwar S., “Driven by capacity or blockage? A millimeter wave blockage analysis,” Proc. of IEEE ITC30, Sep. 2018.

R

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Recent Advances in Transport Layer Protocols

N. Cardwell et al., “BBR: congestion-based congestion control,” ACM Queue, vol. 14, no. 5, pp. 50:20–50:53, 2016.

TCP BBR promises high throughput with low latency

o Operate around Bandwidth delay product (BDP)

o Four phases to constantly estimate BW and RTT

• Startup phases: Estimates BW using binary search

• Drain Phase: Estimates RTT using exponential decay of sending rate

• After these two phases, initial BDP estimate is obtained and enters to the steady state

• Probe BW: Constant Update of BW and minimum RTT to keep operating at BDP

Different pacing gain to update BW and RTT

• Probe RTT: Enters if minimum RTT is not updated in 10 Seconds

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TCP BBR inefficiency in varying RTT wireless links

Performance evaluation of TCP Cubic, BBR with and without patch: measured throughput, latency, and BBR RTTs over gigabit Ethernet and WiGig links. The vertical bar represents the BDP of links, which is kept same for both types of links.

• BBR performance degrades significantly in Wireless link due to variations in RTT • Google’s patch: Aims to mitigate throughput loss in wireless links

Measures impairment in wireless link as the silent periods o Silent period: TCP client is prohibited to transmit due to exhaustion of congestion windowo Improves throughput at the cost of higher latency

• Targets a higher congestion window than BDP (No longer operates at BDP)

N. Cardwell et. al., “BBR congestion control work at Google IETF 101 update,” Tech. Rep., Mar. 2018. [Online]. Available: https://bit.ly/2NNB1xW

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Latency-bandwidth tradeoffs

• Alleviate the effect RTT variation Reduce the effect of RTT variation in numerator: decrease RTT

update windowo Select RTT update window based upon BW estimate

o Reduce the effect of RTT variation in denominator: increase BW probe window

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(m

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BBR without and with patch

Proposed Algorithm

BBR without and with patch

Proposed Algorithm

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Buffer Insertion Ring based handoff

Buffer insertion ring: reduces handover time in cellular network

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Industrial Affiliates

Acknowledgement to our NYU WIRELESS Industrial Affiliates and NSF