Slide title In CAPITALS 50 pt Slide subtitle 32 pt Active Queue Management for LTE uplink in eNodeB Yifeng Tan Supervisor: Professor Riku Jäntti Instructor: D.Sc. Riikka Susitaival

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Long-Term Evolution (LTE)  Evolved 3G Radio Access Network  Provides high data rate –Downlink: up to 300 Mbps –Uplink: 50 Mbps  ”Mobile Internet” –TCP/IP over wireless R99Rel4Rel5Rel6 4 Rel7Rel8 WCDMAHSDPAHSPAHSPA evolution LTE

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential TCP basics  One of the core protocols of the Internet  Provides reliable transmission –Automatic Repeat reQuest (ARQ): Receiver sends ACKs to indicate the reception of segments.  TCP sender’s window: How many packets are ”in flight” –Ideally: Sender’s window = Pipe Capacity (Bandwidth ∙ RTT) –Smaller: under-utilization of the link –Bigger: queuing of packets. When queue exceeds buffer limit, some packets have to be discard → congestion

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential TCP Congestion Control  TCP sender tries to ”probe” optimal send-window –ACK received →Increase send-window ”More bandwidth available” –Packet loss → Decrease send-window ”Light congestion” –Time-outs → Start probing from scratch ”Serious congestion”

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential TCP Congestion Control example

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Queue Management  Passive Queue Management –Drop packets when the buffer is full –We can only decide ”which” but not ”when” –Drop-tail, drop-front, random-drop –PQM may cause some problems  Significant end-to-end delay  Unfair sharing  Viscous web browsing  Active Queue Management –Drop packets even there is space –We can decide both ”which” and ”when”

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Advantages of AQM  Maintains lower average queue size as well as end-to- end delay than PQM –Important when e.g. Web browsing  Prevents lock-out –Avoid the situation where one or a few TCP flows dominate the link  Reduce the number of packet drops –There is enough space to accommodate the packets in burst

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Data transmission in LTE uplink  Buffer Status Report (BSR): created by UE and sent to eNodeB to indicate the queue size in UE’s buffer UE BSR Data

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Example: PDCP discard  Specified in 3GPP TS V8.2.1 for each outgoing packet (PDCP SDU) if (delay > delayThreshold ) discard packet else transmit packet  Suffer throughput degradation UE BSR Data PDCP discard

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Transmitter-AQM Algorithm for each outgoing packet if(size <= lowerDropThreshold) transmit packet else if (delay > minAgeThreshold AND (now-previousDropTime > minInterDropTime)) OR (delay >maxAgeThreshold)) discard packet previousDropTime=now else transmit packet UE channel RLC eNodeB Drop triggered? No Yes PDCP PDUs RLC SDU RLC PDU  Improve the throughput of PDCP discard  Maintains congestion window bigger than PC –> minAgeThreshold  Prevent from consecutive packet drops -> minInterDropTime  Prevent from drop when queue size is small -> lowerDropThreshold  Drain buffer fast -> maxAgeThreshold

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Implement in eNodeB?  Why? –Transmitter-AQM was suggested to be standardized but not accepted –UE with or without AQM may have quite different performance –We may control the UE buffer from eNodeB by Receiver-AQM so that all the UEs can have improved throughputs  We need to know – queue size (BSR) – packet delay -> How? UE BSR Data R-AQM

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential A method to estimate queuing delay  The method estimate the delay of headmost data in a queue  some assumptions 1.We can monitor the queue length (Q i ) discontinuously with small time intervals 2.The amount of data left the queue in each time interval is known (L i ) 3.The length of time interval is known (∆t i )  The amount of new incoming data (R i ) in each time interval can be calculated by R i = Q i + L i – Q i-1

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Waiting time Queue size ∆t 1 /2 0Q1 Time t0 0 Time t1 Time t2 Q1 + R2R2 ∆t 1 /4+∆t 2 ∆t2∆t2 Q2 ∆t 1 /2+∆t 2 At the beginning...

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Waiting time Queue size 0 0 RnRn ∆tn∆tn ∙∙∙∙∙∙ At Time tn Q n-1 + R s QnQn

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential How to implement in eNodeB  Queue length (Q i ) -> BSR  ∆t i -> time interval of receiving BSRs  Leaving data (L i ) -> the data delivered to higher layer in eNodeB during each ∆t i

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Estimated delay vs. Real delay

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Receiver-AQM Algorithm for each outgoing packet if(BsrSize <= lowerDropThreshold) transmit packet else if (estimatedDelay > minAgeThreshold AND (now - previousDropTime> minInterDropTime)) discard packet previousDropTime=now else transmit packet Drop triggered? RLC UE eNodeB PDCP PDUs RLC SDU No Yes channel UE BSR Data R-AQM  Drop packets in eNodeB  The algorithm is similar to T-AQM –Queue size reported by BSR -> real queue size –Estimated delay -> real delay

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Performance comparison with one TCP flow

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Performance comparison with multiple TCP flows

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Performance if both AQM implemented (Bandwidth = 3 Mbps)

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential Some conclusions  Using AQM can efficiently reduce the end-to-end delay in LTE uplink.  PDCP discard may cause considerable throughput reduction in some situations.  R-AQM and T-AQM can maintain small delay as well as high throughput in most situations.  R-AQM is a good option to enhance the performance of UE from network side, no matter if the UE has implemented any AQM itself.

Top right corner for field-mark, customer or partner logotypes. See Best practice for example. Slide title 40 pt Slide subtitle 24 pt Text 24 pt Bullets level pt Ericsson Confidential