Improving loss resilience with multi radio diversity in wireless networks
This presentation is the property of its rightful owner.
Sponsored Links
1 / 22

Improving Loss Resilience with Multi-Radio Diversity in Wireless Networks PowerPoint PPT Presentation


  • 47 Views
  • Uploaded on
  • Presentation posted in: General

Improving Loss Resilience with Multi-Radio Diversity in Wireless Networks. Allen Miu, Hari Balakrishnan, C. Emre Koksal Presented by Yu-En Tsai (Slides partially from Allen Miu’s Mobicom presentation). The problem. New wireless applications demand high performance

Download Presentation

Improving Loss Resilience with Multi-Radio Diversity in Wireless Networks

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Improving loss resilience with multi radio diversity in wireless networks

Improving Loss Resilience with Multi-Radio Diversity in Wireless Networks

Allen Miu, Hari Balakrishnan, C. Emre Koksal

Presented by Yu-En Tsai

(Slides partially from Allen Miu’s Mobicom presentation)


The problem

The problem

  • New wireless applications demand high performance

  • But: wireless channels are loss-prone

    • Interference

    • Noise

    • Attenuation

    • Multi-path

    • Mobility, etc…

       Inconsistent and poor performance


Current solutions are inefficient for recovering losses

Current solutions are inefficient for recovering losses

  • Coding (e.g., FEC)

    • Hard on highly variable channels

  • Retransmission

    • Wasteful: outage durations can be long (tens to hundreds of milliseconds)

  • Bit-rate adaptation

    • Hard on variable channels

    • Slows down other clients


Improving loss resilience with multi radio diversity in wireless networks

Internet

Today’s wireless LAN (e.g., 802.11)

  • Uses only one communication path

  • Clients choose the “best” AP

May use only one path

AP1


Multi radio diversity mrd uplink

MRDC

Internet

AP2

Multi-Radio Diversity (MRD) – Uplink

Today’s wireless LAN (e.g., 802.11)

May use only one path

  • Allow multiple APs to simultaneously receive transmissions from a single transmitter

10%

AP1

20%

Loss independence 

simultaneous loss = 2%


Are losses independent among receivers

Are losses independent among receivers?

  • Broadcast 802.11 experiment at fixed bit-rate: 6 simultaneous receivers and 1 transmitter

  • Compute loss rates for the 15 receiver-pair (R1, R2) combinations

    • Frame loss rate FLR(R1), FLR(R2) vs. simultaneous frame loss rate FLR(R1 ∩ R2)


Improving loss resilience with multi radio diversity in wireless networks

Individual FLR > Simultaneous FLR

y = x

FLR

R1

R2

R1*R2

FLR(R1 ∩ R2)


Challenges in developing mrd

Challenges in developing MRD

  • How to correct simultaneous frame errors?

    • Frame combining

  • How to handle retransmissions in MRD?

    • Request-for-acknowledgment protocol

  • How to adapt bit rates in MRD?

    • MRD-aware rate adaptation


Bit by bit frame combining

Patterns

CRC Ok

1100 0000

1

R1

1100 0000

--

1100 0010

X

1101 1010

R2

1

1100 1000

X

0001 1010

1100 1010

0

1. Locate bits with

unmatched value

2. Select bit combination at unmatched bit locations, check

CRC

O

Corrected frame

Bit-by-bit frame combining

TX: 1100 1010

Combine failure

Problem: Exponential # of CRC checks in # of unmatched bits.


Block based frame combining

Block-based frame combining

  • Observation: bit errors occur in bursts

    • Errors may be restricted to few blocks

  • Divide frame into NB blocks (e.g., NB = 6)

  • Attempt recombination with all possible block patterns until CRC passes

    • # of checks upper bounded by 2NB

    • Failure rate increases with smaller NB


Failure decreases with n b and burst size

Failure decreases with NB and burst size

1.0

Frame size = 1500B

Probability of failure

0.8

0.6

NB = 2

0.4

NB = 4

0.2

NB = 6

NB = 16

0

10

20

30

40

50

0

Burst error length parameter


Flawed retransmission schemes

Flawed retransmission schemes

  • Conventional link-layer ACKs do not work

    • Final status known only to MRDC

  • Two levels of ACKs are redundant

    • Cannot disable link-layer ACKs


Request for acknowledgment rfa for efficient feedback

DATA

RFA

DATA

DATA

MRD-ACK

ACK

Request-for-acknowledgment (RFA) for efficient feedback

IP

IP

MRD

MRD

link

link

link

MRDC


Mrd aware rate adaptation

MRD-aware rate adaptation

  • Standard rate adaptation does not work

    • Reacts only to link-layer losses from 1 receiver

    • Uses sub-optimal bit-rates

  • MRD-aware rate adaptation

    • Reacts to losses at the MRD-layer

Implication: First use multiple paths,

then adapt bit rates.


Experimental setup

Experimental setup

~20 m

R2

R1

L

  • 802.11a/b/g implementation in Linux (MADWiFi)

  • L transmits 100,000 1,500B UDP packets w/ 7 retries

  • 802.11a @ auto bit rate (6, 9, 12, 18, 24, 36, 48, 54)

  • L is in motion at walking speed, > 1 minute per trial

  • Variants: R1, R2, MRD (5 trials each)


Mrd improves throughput

18.7 Mbps

2.3x Improvement

8.25 Mbps

MRD improves throughput

Throughput (Mbps)

R1

R2

MRD

Each color shows a different trial


Mrd maintains high bit rate

MRD maintains high bit-rate

Fraction of transmitted frames

Frame recovery data

(% of total losses at R1)

via R2 42.3%

frame combining 7.3%

Total 49.6%

(Raw FLR was 35%)

0

6

9

12

18

24

36

48

56

Selected bit rate (Mbps)

LOWER VARIANCE MEANS BETTER FOR TCP


Delay analysis

Delay Analysis

Fraction of delivered packets

User space implementation caused high delay

0

10-3

10-2

10-1

1

10-4

One way delay (10x s)


Discussions

Discussions

  • This paper takes advantage of path diversity

    • Frame losses are often path-dependent (multi-path fading), location-dependent (noise)

    • Statistically independent between different receiving radios

  • 2 radios (APs) are available within the sender’s coverage.

    • How to place the radios? Not too close and not too far

    • Cost reduced? Then why not use 3 or more APs?

  • MRD complements both ARQ and rate adaptation

    • ARQ-based retransmissions work well for losses in short time scales

    • Rate adaptation works well for losses in large time scales


Discussions cont

Discussions (cont.)

  • It’s not clear in the paper that whether physical antenna diversity would be helpful.

  • Will the computation cost be a problem when we implement MRDC in a low-end platform (e.g. router)?

    • All experiments are done on desktop/laptop.

  • Convention: first adapt bit rates, then use alternative paths.

  • MRD: first use multiple paths, then adapt bit rates.


Summary

Summary

  • Design of Multi-Radio Diversity WLAN

    • Block-based frame combining

    • Request-for-acknowledgment protocol

    • MRD-aware rate adaptation

  • Analysis of block-based frame combining

  • Experimental evaluation

    • MRD reduces losses by 50% and improves throughput by up to 2.3x


Related work

Related work

  • Physical layer spatial diversity techniques

    • Antenna diversity

    • 802.16 MIMO/802.11n

  • Retransmission with memory [Sindhu ’77]

  • Opportunistic forwarding [Biswas ‘05][Jain ’05]

  • Bit rate selection (AARF, RBAR, MiSer, OAR, Sample Rate)


  • Login