June 23, 2004, P. R. Kumar Towards proliferation of ad hoc wireless networks P. R. Kumar (with V....

June 23, 2004, P. R. Kumar

Towards proliferation of ad hoc wireless networks

P. R. Kumar

(with V. Borkar, G. Baliga, S. Graham, P. Gupta, K. Huang, V. Kawadia, S. Narayanaswamy, V. Raghunathan, R. Rozovsky, L-L. Xie)

Dept. of Electrical and Computer Engineering, andCoordinated Science LabUniversity of Illinois, Urbana-Champaign

Email [email protected] http://black.csl.uiuc.edu/~prkumar

Microsoft Mesh Networking Summit, Snoqualmie, June 23, 2004


One modest effort-in-the-making towards proliferation

How to proliferate ad hoc networks? We don’t know what the “killer” applications are

– Much genius in society» Applications will emerge

– Great hunger for communication» Instant Messenger

Our attempt in the making: Idea– Develop a product– Give it away free– See what happens

Have developed software which will self-install– Addresses, routing, anonymity– Linux and Windows– Have not yet developed a distributed chat application

How to spark adoption?– A “business model” for giving it away free


Another vision: Interaction with world

What are the right abstractions?

What should be the architecture of the system?– Application independent, Context

independent architecture

– Same architecture for

» Building-wide temperaturecontrol system?

??

Date Fusion Layer

Coordination/Coherence Layer

Local layer

What are the right abstractions?What is the

architecture?

The next phase of IT revolution may involve the active interaction and alteration with the environment– Achieved through the convergence of control (sensing and actuation) with

communication and computation

Question: How do we organize them?– Distributed Real-time Physics-based systems


Session Layer Session Layer

Presentation Layer Presentation Layer

Application Layer Application Layer

Transport Layer Transport Layer

Network Layer Network Layer

Data Link Layer Data Link Layer

Physical Layer Physical Layer

The importance of architecture

Success of Internet is due to its architecture– Notion of peer-to-peer protocols

– Hierarchy of layers

– Allows plug-and-play

– Proliferation of technology

Hardware Software

Success of serial computing– von Neumann bridge (Valiant)

– Hardware designers and softwaredesigners need only to conform toabstractions of each other

Plant

Controller

Control system paradigm– Plant and controller separation


Middleware: EtherArch Software Time translation

– Knowledge of per-packet delay important for control Location independence

– Car can request for a camera covering coordinates(50,50) - Infrastructure finds the corresponding camera

– Car need not know the IP address or port System startup and evolution during execution

– Installing application code components at start-up/run-time Automatic migration of components to reduce communication or

computation burden

Computer 1

Kalman filter

Computer 2

Carcontroller

Excessive communication overhead

Computer 2

Kalman filter

Carcontroller

Communication overhead is reduced

Migrate Kalman filter toComputer 2


Information TechnologyConvergence Lab:The Systems

Vision Sensors

Automatic Control

Ad Hoc Network

Planning and Scheduling


IT Convergence Lab

Movie

QuickTime™ and aCinepak decompressorare needed to see this picture.


Ad Hoc Wireless Networks Ad Hoc Networks

– Current proposal for operation: Multi-hop transport» Nodes relay packets until they reach their destinations

» Fully decode packets at each stage treating allinterference as noise

Interference+

Noise

Interference+

Noise

Interference+

Noise

Interfering packets destructively collide witheach other


However wireless networks are not wired networks …

“There are more things in heaven and earth, Horatio,Than are dreamt of in your philosophy.”— Hamlet

Wireless networks are formed by nodes with radios– There is no a priori notion of “links”– Nodes simply radiate energy

Amplify and forward

D

E

FA

BC X

Signal

Interference + Noise

Reduce by cancellation

Subtractloud

signal

Interference is not interferenceInterference is information

Need an information theory for networks

Nodes can cooperate in many complex ways


Nevertheless the good news is …

Multi-hop is nearly optimal

– Transport packets over many

hops of distance

Nearly optimal multi-hop architecture

c

n

1n

0 Range

Bit-MetersPer SecondPer Node

c

n

BroadcastNo

connectivityMulti-hopNetworks

To execute this we need– Power control– MAC– Routing– Transport

What are some second generation protocols for these?


The Power Control problem

How do we choose power levels of transmissions in wireless networks?

– Power level influences range– Power levels determine interference– Power levels affect routes

Conceptualization problem for Power Control Which Layer?

– Physical layer» Quality of reception

– Network layer» Impact on routing

– Transport layer» Higher power impacts congestion

How to fit Power Control in the hierarchical OSI framework?

Session Layer Session Layer

Presentation Layer Presentation Layer

Application Layer Application Layer

Transport Layer Transport Layer

Network Layer Network Layer

Data Link Layer Data Link Layer

Physical Layer Physical Layer


Our own suggestion: Network Layer solution for Power Control

Power Control has global impact

– Connectivity is a global property

– Clustering is regional– Routing is over network

Interdependence of Power Control and Routing

So joint solution for Power Control and Routing situated at the Network Layer

Connectivity Routes

Power levels

Kernel Routing Table = RDP(t)

Driver Set data_power

RDP(t)

IP

User space

Transport Layer: Sets skb-power_field

RDPmaxRDP(t)+1RDP(t)-1RDPmin …. ….

Power Control Agent

Sys V Message Queue

Kernel space ioctl() to set default powerfor DATA packets

change_power()

Card

Scheduler

Our own attempts– COMPOW, CLUSTERPOW, etc


Can we develop a better second generation higher performance MAC?

IEEE 802.11 MAC– Silences two neighborhoods

– Real as well as virtual carrier sensing

– Backoff counters

– PLCP header at low rate

Our own attempt: SEEDEX– Based on exchanging pseudo-random

number seeds to coordinate schedules

– Reservations without making reservations

– Silences only one neighborhood

– No backoff counters

– But is a slotted protocol

– Slot synchronization needed

T R

Will listen May transmit Will listen


Additional functionalities of routing Forwarding

– Delivering packets to the right destination Load adaptation

– Can we design an adaptive distributed asynchronousrouting algorithm that adapts routes

» To the topology of the network» To the prevailing traffic conditions, e.g., is

delay adaptive?

Load balancing– How to distribute the loading on different

areas of the network

Our own attempt: Wardrop algorithm– All used paths have same delay

– All unused paths have larger delay

s

d

s

d


Last but not least

Hardware– That we can develop on

– That gives enough interfaces that we can write software

– That we can experiment with

That will spark proliferation– A la IEEE 802.11


To obtain papers

Papers can be downloaded from

http://black.csl.uiuc.edu/~prkumar

For hard copies send email to

[email protected]


Some thoughts on Mesh Networks


Some preliminaries on accessing a base-station

Multiple-access channel

Capacity region is completely characterized

All rate vectors satisfying

for some distribution are feasible


Optimal strategy vs. TDMA

Optimal strategy– Successive subtraction and decoding strategy

» Decode one user» Subtract that user’s signal if channel known» Decode next user» …

– Requires multi-user decoding

Optimal capacity per user is

On the other hand simple TDMA can yield

– Every user simply transmits directly to base-station


So what are the issues in multi-hopping to a base-station?

Protocol issues– Power control can be used to

» Save energy at mobile nodes» Trade-off between energy and delay

– Medium access issues may get complicates» If power control gets sophisticated

– Routing may be simplified if there is only one sink

– Transport level may need design due to need for interfacing multi-hop wireless with wired Internet

– Interesting cross-layer design issues» Power control, medium access, routing, transport

– Further interesting issues when allowing operation in ad hoc as well as just reaching base-station

June 23, 2004, P. R. Kumar Towards proliferation of ad hoc wireless networks P. R. Kumar (with V....

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