Electrical and Computer Engineering

Matt Brennan

Nick Nunns

Brian Roberts

Jeremy Vight

Mid-term Design Review

Buddy Bug

2Electrical and Computer Engineering

Background Wide spread use of personal

electronics devices (PEDs) • MP3 players, cell phones, personal

gaming systems Popularity of online friend/dating

services• eHarmoney: 10,000 to 15,000 new

users every day• Friendster: 19 million members

Buddy Bug• Filling the gap

3Electrical and Computer Engineering

Usage Interests are uploaded from a PC to

the Buddy Bug Buddy Bug is carried by the user Devices communicate and exchange

interests Mating

• Physical connection between bugs• Exchange selective contact information

4Electrical and Computer Engineering

Example

REDSOX

SINGLE ROCKHIKING REDSOX

FASHION ROCKBOOKS

REDSOX

SINGLEBOOKS JAZZ

5Electrical and Computer Engineering

Why is this hard/interesting? Small form factor

• Beeper sized

Power efficiency• Limit the number/size of transmissions• Power down unused components when idle

Ad-Hoc network• Multiple Access Protocol• Transmission collisions

Dynamic Patterns

6Electrical and Computer Engineering

Dynamic Patterns - Convergence Shared interest found

• Must have same pattern

Simple! Just average!

Uh-oh. Better be more creative.

Color

Fre

q

7Electrical and Computer Engineering

Dynamic Patterns - Divergence Several different interests Must be distinguishable

• Red Sox don’t want to find Yankees by accident

Model nature• Brownian Motion

• Stability• Atomic Structure

• Ideal• Implementation?

Color

Fre

q

8Electrical and Computer Engineering

Convergence Algorithm: Structure Separate pattern into 4 channels

• 1 for red, green and blue• 1 for frequency

Channels have 3 distinct settings• Each color channel can be bright, dim or off• Frequency can be fast, medium or slow

Benefits• Easily pack pattern into a byte: RR GG BB FF• Allows for 34 – 3 = 78 unique patterns• Use only one algorithm to match all 4 channels

Enumerate interests with unique IDs• Master list of 28 = 256 interests stored on PC

9Electrical and Computer Engineering

Convergence Algorithm: Methods Matching similar interests

• Compare received interest IDs with your list of IDs

Merging with different received patterns• Transition your channels toward received channels

Avoiding domination of ‘dim’ and ‘medium’• Randomly restrict receivers to only transition up or down

Bright

Off Dim

Bright

Dim Dim

Bright

Bright Bright

10Electrical and Computer Engineering

Convergence Algorithm: Simulation

11Electrical and Computer Engineering

Basic Communication Process

LISTEN

RECEIVE_COMPLETE

HANDLE_PACKET()UPDATE_NET_STATUS()RECALC(B_RATE)

TIMER_EXPIRE(B_RATE)BROADCAST_DETECTED

TRANSMITRECEIVE

TIMER_EXPIRE(B_RATE)

TIMER_RESTART(B_RATE)

TRANSMIT_COMPLETE

TIMER_RESTART(B_RATE)

Carrier Sense Multiple Access (CSMA)START

12Electrical and Computer Engineering

Broadcast Protocol: Issues Propagation delay

• Depends on transmission distance and speed of light

• Transmitting nodes cannot detect collisions

Hidden Node Problem• Due to transmission range

limitation• Receiving nodes can detect

collisions

1

2

3

Hidden NodeProblem

PropagationDelay

13Electrical and Computer Engineering

Example: Bandwidth ≈ 100

• 50 nodes 1.0 broadcast/sec

• 100 nodes 0.5 broadcast/sec

Broadcast Collisions: Solutions Exponential Backoff - Adapt

transmission rate to estimated channel usage

Adapt transmission rate based on:• Number of active nodes • Received collisions• Time spent receiving

Chen Xiaoming and Hong Geok-Soon, “A Simulation Study of the Predictive p-persistent CSMA Protocol” 2002

broadcasts second

14Electrical and Computer Engineering

Hardware Design – Block Diagram

15Electrical and Computer Engineering

Antenna Microstrip patch

• Very directional• Relatively large (λ/2=16 cm)• Expensive to produce (additional fees for impedance control)

Microstrip wire• Directional• Post fabrication inflexibility

Monopole wire whip• Somewhat directional• Simple• easy to replace and modify• inexpensive

16Electrical and Computer Engineering

Hardware Design – PCBTOP BOTTOM

POWER GROUND

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Hardware Design - PCB

CC1010

Power Regulation LEDs

LED Controller

TOP BOTTOM

6.0cm

3.8cm

4.0 cm

18Electrical and Computer Engineering

Hardware Design - Cost

Item Cost to us Cost in bulk

PCB $22 $7

CC1010 $07 $5

Other ICs $13 $7

LEDs / LCD $08 $5

Passives $10 $6

Total: $60 $30

19Electrical and Computer Engineering

BudgetItem Total Cost

Initial Funding$500

ComCol Grant970

Software0

Bugsx15 -900

Programmer-20

Remaining:$550

20Electrical and Computer Engineering

MDR deliverables Development of two prototype Buddy Bugs Implementation of Buddy Bug simulator Demonstration of wireless communication

between two Buddy Bugs Demonstration of LED patterns and LCD display

21Electrical and Computer Engineering

Comments / Questions?

12

3

Bright

Off Dim

Color

Fre

q