Architectures and Algorithms for Future Wireless Local Area Networks 110987654321Chapter

Architectures and Algorithms for Architectures and Algorithms for Future Wireless Local Area Future Wireless Local Area

NetworksNetworks

PhD Defense2012-12-14Peter Dely

Architectures and Algorithms for Future Wireless Local Area Networks 210987654321Chapter

High speeds require small distances

1

10

100

1000

10000

100000

1995 1998 2001 2004 2006 2009 2012 2014 2017

Year

PHY

Rate

(Mbi

t/s)

802.11n 802.11ac

802.11ac802.11ad

802.11g802.11a

802.11b802.11

60 GHz5 GHz2.4 GHz

2 Mbit/s

7000 Mbit/s

2

Carrier: 2.4 GHzModulation: BPSKChannel: 20 MHz

Carrier: 2.4 GHzModulation: BPSKChannel: 20 MHz

Carrier: 60 GHzModulation: QAM256Channel: 1800 MHz

Carrier: 60 GHzModulation: QAM256Channel: 1800 MHz

Architectures and Algorithms for Future Wireless Local Area Networks 310987654321Chapter

AP selection with small WLAN “cells”

Case 1: AP selection for mobility management

2

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AP selection with small WLAN “cells”

Case 2: AP selection for load balancing

2

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Research questions

1. Which AP should a station select at a given time?2. How to design and implement an architecture

that enables fair resource distribution and mobility management?

3. How to estimate the quality of an AP?

Architectures and Algorithms for Future Wireless Local Area Networks 610987654321Chapter

Greedy is not always best

Handover Handover

6 Mbit/s

54 Mbit/s

Given a certain “cost” for a handover, when is it beneficial

to perform that handover?

Given a certain “cost” for a handover, when is it beneficial

to perform that handover?

4

Architectures and Algorithms for Future Wireless Local Area Networks 710987654321Chapter

Dynamic model finds best AP for the known future

Mixed Integer Linear Program

Solver

1. Which station uses which AP at what point in time2. Which rate it can use for downloading

Compute

Describe system state

Describe system characteristics

Important constraints1. Capacity of the wireless channel2. Data transfer only after a station has been connected to an AP for a certain time

Important parameters1. Cost of a handover2. Link rates between APs and stations3. Interference

Maximize minimum average throughput

Objective

4

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Evaluation scenario Comparison of

– Greedy – Hysteresis– k-Handover

Mobile stations “walk” on the corridors

Random waypoint with fixed waypoints

Comparison metric:– Normalized throughput– Relative to optimal solution with

dynamic model– 1 = Optimum

4

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Mobility and handover costs reduce performance

Impact of mobility Impact of handover cost

More mobility =Less performance

Higher handover costs ~Less performance

4

Architectures and Algorithms for Future Wireless Local Area Networks 1010987654321Chapter

Internet

AP selection in wireless mesh networks

5

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Max-min fair rate allocations and single path routing cannot be found through a simple MILP

Solution algorithm

1. Which traffic is sent via which route2. Rates between the stations and the Internet3. Which station uses which AP

Compute

Describe system state

Describe system characteristics

Important constraints1. As in the pure AP scenario2. Flow conservation constraints3. Single-path routing constraints

Important parameters1. Network graph2. Interference set3. Association opportunities

Max-min fair rate allocation

ObjectiveMixed Integer Linear Program

Solver

Solve partial problem

ReformulateModel

5

Max-min fair optimization is multi-objective optimizationMax-min fair optimization is multi-objective optimization

Standard algorithms are very slow Design of

heuristic MESHMAX-FAST(*)

Standard algorithms are very slow Design of

heuristic MESHMAX-FAST(*)

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MESHMAX-FAST* is better than a straight forward linear relaxation

In 50% of cases, the performance is greater

than 95% of the optimum

In 50% of cases, the performance is greater

than 95% of the optimum

5

Better

Architectures and Algorithms for Future Wireless Local Area Networks 1310987654321Chapter

MESHMAX-FAST is suitable for online optimization

5

Optimal solution:> 1000 seconds

Optimal solution:> 1000 seconds

MESHMAX-FAST*:< 10 seconds with

comparable results

MESHMAX-FAST*:< 10 seconds with

comparable results

Architectures and Algorithms for Future Wireless Local Area Networks 1410987654321Chapter

Research questions

1. Which AP should a station select at a given time?2. How to design and implement an architecture

that enables fair resource distribution and mobility management?

3. How to estimate the quality of an AP?

6 7

Architectures and Algorithms for Future Wireless Local Area Networks 1510987654321Chapter

Internet

A software defined mesh network

OpenFlow Control Server

Monitoring and Control Server

Build network graph Run MESHMAX-FAST Trigger actions at the OpenFlow control server

Build network graph Run MESHMAX-FAST Trigger actions at the OpenFlow control server

Configure routes Configure rate shapers Trigger handovers

Configure routes Configure rate shapers Trigger handovers

Programmable forwarding unit (OpenFlow) Legacy routing protocol in a virtual network

Programmable forwarding unit (OpenFlow) Legacy routing protocol in a virtual network

6

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MESHMAX performance in real networksTestbed setup

IEEE 802.11a links, fixed PHY Download from “Internet” Gateways are connected via “DSL”

Results with 6 Mbit/s GW links

SNR = Use AP with best signal Hop-count = Use AP closest to GW MESHMAX = Use optimal AP

6

1

2

3

4

5

6

8

9

7

10

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Internet

CloudMAC distributes MAC processing

OpenFlow Controller

Policy

Application

Application

Virtual AP

Virtual WLAN NIC

Virtual AP

Virtual WLAN NIC

Virtual AP

Virtual WLAN NIC

Programswitch

7

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Internet

CloudMAC enables simple handovers

OpenFlow Controller

Policy

Application

Application

Virtual AP

Virtual WLAN NIC

Virtual AP

Virtual WLAN NIC

Virtual AP

Virtual WLAN NIC

ProgramswitchChange flow table

7

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CloudMAC reduces data loss during handovers

Median reduction in packet lossfrom approx. 10000 to 3.5

Standard IEEE 802.11: scan and re-association CloudMAC: Association state in Virtual AP no reassociation

7

Architectures and Algorithms for Future Wireless Local Area Networks 2010987654321Chapter

Research questions

1. Which AP should a station select at a given time?2. How to design and implement an architecture

that enables fair resource distribution and mobility management?

3. How to estimate the quality of an AP?

98

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Finding the AP with the best link is hard

8

Interference Cross traffic

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RSSI is not a good indicator for throughput

100% loss

0% loss

8

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BEST-AP uses regular traffic for performance estimation

BEST-AP Server

Internet

BW Estimation

Handover

BW Estimation

8

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Dynamic AP selection with stationary users

8

Testbed setup

Two APs Interference according to real traces

Interference Interference

Results

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Time

BufferLevel

Quality forcurrent AP starts

to decrease

Connection completely

breaks

Video playout freezes

Scan for new APs

Connect to new AP

Video playout resumes

Evaluation with mobile users

9

Video freeze duration

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BEST-AP reduces video freezesTestbed setup

9

Results

BEST-AP has fewer and shorter freezes than Linux

A dedicated scan card is not necessary

0%

5%

10%

15%

20%

25%

30%

% o

f tim

e in

free

ze m

ode

BEST-AP/BW-Estimation/No scan cardBEST-AP/RSSI/No scan card BEST-AP/RSSI/Scan card Linux/Optimized scanning Linux/Standard scanning

Architectures and Algorithms for Future Wireless Local Area Networks 2710987654321Chapter

Summary of contributions

1. Theoretical study of AP selection problem– Considering handover costs– Wireless mesh backhauls

2. Architecture proposals and their implementation– For the centralized management of wireless mesh

networks– For distributing MAC layer processing

3. Quality estimation of APs– Bandwidth estimation method– Improved video streaming

10

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Future directions Use other modeling frameworks

– Convex optimization – Robust optimization

Unify architectures– Use CloudMAC in mesh networks– Integrate bandwidth estimation in system

Comprehensive tests in large networks– More realistic traffic loads– Scalability tests

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Architectures and Algorithms for Future Wireless Local Area Networks 2910987654321Chapter

Thank you!

Watch this talk on youtube.com/kaumesh

Architectures and Algorithms for Future Wireless Local Area Networks 3010987654321Chapter

Backup slides

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… but this comes at a cost From 2.4 GHz to 60 GHz

Higher path loss Higher attenuation by walls etc.

From BSPK to QAM256 More constellations More susceptible to noise

From 20 MHz to 160 MHz channels Less spatial reuse Higher energy use

2.4 GHz60 GHz

BSPK QAM256

36 40 44 48 52 56 60 64

To achieve high speeds short distances between the AP and

the stations are necessary.

To achieve high speeds short distances between the AP and

the stations are necessary.

2

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Main idea: use predictions of the future for optimization

Optimize each time slot using the estimate of the future

Using predictions to improve performance

More estimationerrors

4

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MESHMAX-FAST improves performance

5

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Key ideas of MESHMAX-FAST Observation: APs are traffic aggregation points for many

stations Algorithm sketch:

1. Compute a multi-path solution between the APs and the stations

2. Assign stations to APs according to the capacity of the APs3. Re-compute the multi-path solution and give priority to APs

with many stations4. Move stations to other APs if it increases the minimum rate5. Repeat steps 3-4 until the minimum rate cannot be increased

anymore6. Finally, find a single-path for each station

5