Low Latency Networks SHIVENDRA PANWAR OCTOBER 23, NYU WIRELESS

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1 Low Latency Networks SHIVENDRA PANWAR OCTOBER 23, NYU WIRELESS 1 1

2 Quality of Service (QoS) requirements in 5G AR/VR requirements Source: Nokia, VR/AR in the 5G Era NEM Summit November 23, 2016 Data Rates 100Mbps1Gbps Interruptio ns 0.1/min Video stall (pause) <10 ms (otherwise can cause nausea or sickness) Image source: 2

3 What can 5G provide to automated vehicles? 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 3

4 What can 5G provide to automated vehicles 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 4

5 Can 5G mmwave networks meet QoS requirements? R In an urban mmwave cellular network: Blocker Density= 0.1 bl/ Blocking rate= 1 blockage/sec Blocker Density= 0.01 bl/ Blocking rate= 1 blockage/10sec 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. 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: , Jul Jain I. K., Kumar R., Panwar S., Driven by capacity or blockage? A millimeter wave blockage analysis, Proc. of IEEE ITC30, Sep

6 Recent Advances in Transport Layer Protocols 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 N. Cardwell et al., BBR: congestion-based congestion control, ACM Queue, vol. 14, no. 5, pp. 50:20 50:53,

7 TCP BBR inefficiency in varying RTT wireless 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 window o Improves throughput at the cost of higher latency Targets a higher congestion window than BDP (No longer operates at BDP) 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. N. Cardwell et. al., BBR congestion control work at Google IETF 101 update, Tech. Rep., Mar [Online]. Available: 7

8 Latency-bandwidth tradeoffs PING Latency (ms) Alleviate the effect RTT variation Reduce the effect of RTT variation in numerator: decrease RTT update window o Select RTT update window based upon BW estimate o Reduce the effect of RTT variation in denominator: increase BW probe window Throughput (Mbps) BBR without and with patch Proposed Algorithm BBR without and with patch Proposed Algorithm 8

9 Buffer Insertion Ring based handoff Buffer insertion ring: reduces handover time in cellular network 9

10 Industrial Affiliates Acknowledgement to our NYU WIRELESS Industrial Affiliates and NSF 10