flipped diversity aloha in wireless networks with long and …zhengl/materials/gc11zl_slides.pdf ·...

Motivation The Flipped Diversity Aloha Summary

Flipped Diversity Aloha in Wireless Networkswith Long and Varying Delay

Lei Zheng Lin Cai

Department of Electrical & Computer EngineeringUniversity of Victoria, British Columbia, Canada

{zhengl, cai}@ece.uvic.ca

IEEE GLOBECOM, Dec. 2011

Flipped Diversity Aloha L. Zheng, L. Cai ECE@UVIC December 2, 2011 1 / 23


Outline

1 MotivationThe Propagation Delay Problem & ChallengesExisting SolutionsMain Contributions Of The Paper

2 The Flipped Diversity AlohaOur SolutionPerformance AnalysisSimulation Results

3 Summary



The Basic Problem That We Studied

Medium Access Protocols In Wireless Networks.

With coordinator=⇒ such as PCF in IEEE 802.11, TDMA/CDMA basedscheduling for Cellular Networks, etc.;Random access (without coordinator)=⇒ such as Aloha, p-persistent CSMA, DCF in IEEE802.11, etc.;Most of these protocols are designed without consideringthe propagation delay.

Propagation Delay In Wireless Networks.Terrestrial Satellites Underwater

Propagation Distance Small Large SmallPropagation Speed Fast Fast SlowPropagation Delay Short Long Varying



The Challenges Of The Problem

SynchronizationScheduling or coordination becomes difficult;Slotted based random access would also fail.

Communications Efficiency

Throughputestimal =PacketTransmissionDelay

RoundTripTime+PacketTransmissionDelay

Communications EffectivenessCSMA based: Carrier Sensing may not be effective anymore;Slotted Aloha degrades to pure Aloha: About 50%throughput loss.



Existing Solutions

Diversity Slotted Aloha (DSA) [1]Slotted Aloha based;Each Packet is transmitted multiple times.

dist-control

Collision Resolution Diversity Slotted Aloha (CRDSA) [2]Extending DSA with Interference Cancellation (IC).

RemarksRelying on TimeSynchronization;Vulnerable to DelayUncertainty;Still Not Efficient. Figure: Packet decoding in CRDSA.



Our Design Goals & Contributions

Our Goals of DesigningA random access MAC protocol;

Be an asynchronous MAC protocol;

Be immune to long & varying propagation delay.

Our ContributionsA new random access MAC protocol=⇒ The Flipped Diversity Aloha (FDA);

Analysis of performance bound;

Comprehensive simulations.



Assumptions

AssumptionsA scenario with one central destination node and multipleuniformly distributed source nodes;Single channel & Single half-duplex radio;Channel information is known at receiver;Protocol channel model.

Zigzag Decoding [3]Designed to solve the "Hidden Terminal Problem" in IEEE802.11.

Figure: Two packetscollided.Zigzag decoding.

Figure: Networks scenario example.Flipped Diversity Aloha L. Zheng, L. Cai ECE@UVIC December 2, 2011 11 / 23


Assumptions

AssumptionsA scenario with one central destination node and multipleuniformly distributed source nodes;Single channel & Single half-duplex radio;Channel information is known at receiver;Protocol channel model.

Zigzag Decoding [3]Designed to solve the "Hidden Terminal Problem" in IEEE802.11.

Figure: Two packetscollided.Zigzag decoding.

RemarksDiversity Slotted Aloha (DSA)anti-long delayZigzag decodinganti-varying delay



What does "Flipped" mean?

Diversity Slotted Aloha with Zigzag decoding ?Packet identifying problem when collision happens;Channel estimation error.

Flipped Diversity Aloha (FDA)√

To combine Diversity Aloha & Zigzag decodingin a Flipping way.

Figure: The DSA with Zigzagdecoding The flipping operationThe back-to-back transmission Thesuper-packet & FDA

DecodingFailure

=⇒withoutFlipping



Cases Study

Identified Six Resolvable Collision Cases.According to the overlapping of packet collision.

Figure: Six resolvable collision cases.

An example, case (a): no collision or two-packet collision

P1 = Pc2 + 2Pc · (e−λT − e−2λT ), where Pc = e−2λT



Performance Bound

Upper Bound For Packet Loss Ratio, PLRu

PLRU = 1− Ps

Lower Bound For Throughput, SL

PLRU = λ · Ps

where:

Ps = P1 + P2 + Pu ·(

1 + Pr/Pc

)2,

Pr = Pc ·∞∑

k=1

(P4/Pc + e−λT − e−2λT )k,

Pu =[C1

2P3 + C13P5 + C1

3P6.].



Settings & Result-1

Simulation Settings

Uniformly distributed nodes;Uniformly distributedpropagation delay;Poisson traffic with theaggregated load λ.

Benefits Of "Flipping"

Case-I: throughputcontribution from flipping;Case-II: throughputcontribution from Zigzagdecoding.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Traffic load

Theo

reti

cal

Thro

ughput

Pure Aloha

DSA

FDA

Case−I (FDT only)

Case−II (Zigzag decoded)

Case−II

Case−I

Figure: Analysis throughput.



Results-2

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.20

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Traffic load

Sim

ula

tion T

hro

ughput

Pure Aloha

Slotted Aloha

DSA

CRDSA

FDA

FDA SL

Figure: Simulation throughput.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

10−2

10−1

100

Traffic loadP

acket

Loss

Rat

io

0.7 0.8 0.9 1 1.1 1.2

100

Pure Aloha

DSA

CRDSA

FDA

FDA PLRU

Figure: Simulation PLR with finite nodes.



Results-3

0 0.2 0.4 0.6 0.8 1 1.20

2

4

6

8

10

12

14

16

18

Traffic load

Num

ber

of S

ourc

e N

odes

Pure Aloha, PLR<0.1DSA, PLR<0.1FDA, PLR<0.1Pure Aloha, PLR<0.2DSA, PLR<0.2FDA, PLR<0.2

Figure: Maximum admission region.

Definition of Admission Region:The maximum admissible numberof source nodes with given λ.

Given PLR threshold as 0.1,λ = 0.3;FDA: more than 10 sourcenodes;Pure Aloha or DSA: only onesource node.



Conclusion & Outlook

In this paper, we proposed a Flipped Diversity Aloha(FDA), which is

combining Diversity Aloha & Zigzag decoding in a flippedway;suitable for asynchronous wireless networks;immune to impact of duration & variation of propagationdelay.

OutlookThe performance of FDA with signal capture effect;An opportunistic channel estimation based on FDA;Application of FDA for channel access with limited delay.



For Further Reading

G. Choudhury and S. Rappaport, "Diversity Aloha - arandom access scheme for satellite communications," IEEETransactions on Communications, vol. 31, no. 3, pp.450–457, Mar. 1983.

E. Casini, R. De Gaudenzi, and O. Herrero, "ContentionResolution Diversity Slotted Aloha (CRDSA): An enhancedrandom access scheme for satellite access packetnetworks," IEEE Transactions on WirelessCommunications, vol. 6, no. 4, pp. 1408–1419, April 2007.

S. Gollakota and D. Katabi, “Zigzag decoding: combatinghidden terminals in wireless networks,” in ACMSIGCOMM’2008, New York, NY, USA, 2008, pp.159–170.



Thanks!

Question/Comment?


flipped diversity aloha in wireless networks with long and …zhengl/materials/gc11zl_slides.pdf ·...

Documents