0. Patrick Murphy, Erik Welsh & Patrick Frantz May 7, 2002
Using Bluetooth for Short-Term Connections Between Moving Vehicles: A Feasibility Study
Patrick Murphy, Erik Welsh & Patrick Frantz May 7, 2002

1. Some Bluetooth Background
Frequency Hopping Spread Spectrum
1600 Hops/second
79 1MHz Bands in 2.4GHz ISM Spectrum
GFSK Modulation
1Mbs Raw Data Rate ( 768kbs User Data)
Objectives
Low Power, Low Cost

2. Some Bluetooth Background
3 Radio Classes
Class 1, 20dBm, 100m ( 300ft)
Class 2, 4dBm, 10m ( 30ft)
Class 3, 0dBm, 1m ( 3ft)

3. The Problem How Suitable is Bluetooth for Use in Mobile Environments?
Speeds >= 10mph?
Doppler Shift?
Fading & Multipath?
How Long Does it Take to Make Connections to Other Devices?

4. Speed Calculations (Class 1 Radio)
Vehicle Speed
Max Time
“In Range” (s)
km/hr
m/s 20
5.56
36.00 40
11.11
18.00 60
16.67
12.00 80
22.22
9.00
100
22.78
7.20

5. How Are Connections Made
Devices Must “Discover” Other Devices through an Inquiry Process
Inquiry State (potential master)
Inquiry Scan State (potential slave)
Once Devices are Discovered, Connections Can be Made Quickly

6. Inquiry Timing Parameters

7. Our Analysis Characterize the Device Discovery Process
Empirical Analysis
Simulation (RIBBIT)
Rice Bluetooth Baseband Inquiry Tester
Test Range of Bluetooth Devices
Suggest Improvements to Baseband to Decrease Device Discovery Times
Without Increasing “Collisions” Between Devices

8. Experimental Setup 5 Class 2 Bluetooth Devices
All Devices in Range of Other Devices
Variety of Manufacturers and Host OS’s
Control of Two Inquiry Process Parameters
Maximum Search Time
Maximum Number of Responses

9. Number of Devices Discovered

10. Length of First Connection Establishment (1 Master, 4 Slaves)
Number of Trials
Mean Time (sec)
Median Time (sec)
1142
0.79
0.53

11. Time to 1st Device Discovery
Time to First Discovery (sec)

12. Connection Time to 1 Bluetooth Device
Number of Trials
Mean Time (s)
Median Time (s)
Device 1
600
2.26
1.72
Device 2
505
2.63
1.95
Device 3
610
2.11
1.35
Device 4
499
2.10
1.36

13. Simulations Simulate the Inquiry Process and Record Collisions
Modify the Baseband and Report Results of
Eliminating Random Backoff
Using a Single 32-hop Page Train
Combination

14. Number of Devices Found in a 1 Second Search (Normalized)

15. Outdoor Range Tests
Range of Our Bluetooth Devices Far Exceeded the Specification
Maximum Range (m)
Spec Range (m)
Class 1 (20 dBm)
250
100
Class 2 (4 dBm)
122 10

16. Range vs. Throughput

17. Speed Recalculations (Class 1 Radio)
Vehicle Speed
Max Time
“In Range” (s)
km/hr
m/s 20
5.56
90.00 40
11.11
45.00 60
16.67
30.00 80
22.22
22.50
100
22.78
18.00

18. Conclusions Bluetooth is a Viable Option for Mobile Environments
Baseband can be Modified to Improve Connection Setup Times up to 75%

19. Future Work Perform Empirical Analysis With Channel Emulator
Doppler Shift, Fading, Multipath
Put Hardware on Rice Shuttle System
Implement Large Ad Hoc Network Testbed
Start with Bluetooth
Integrate Other Wireless Interfaces in Future