# Presentation: 731533

## Empirical Study of 802.11bWireless Networks in the Presenceof Bluetooth Interference

Cameron McKay and Fukumasa MasudaInstitute for Telecommunication Sciences
National Telecommunicationsand Information Administration
Boulder, CO
cmckay@its.bldrdoc.gov

- Cameron McKay and Fukumasa MasudaInstitute for Telecommunication Sciences
- National Telecommunicationsand Information Administration
- Boulder, CO
- cmckay@its.bldrdoc.gov

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Outline

- Current Wireless Technologies
- The Interference Problem
- Throughput Testing
- Setup/Methodology
- Results

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Current Wireless Technologies

**2.4 GHz**
**Band**

**5 GHz**
**Band**

- Two bands commonly used
- for wireless networking

- International Symposium on Advanced Radio Technologies

- September 10, 1999

**Notes:**
An analogy can be made between at circuit switched, or analog phone technology, and railroads versus packet switched digital technologies that are more like a highway system.

## Current Wireless Technologies

**5 GHz Band**

- 5.15 – 5.35 GHz and 5.725 – 5.825 GHz
- 300 MHz total
- Home to...
- 802.11a (54 Mbps)

- International Symposium on Advanced Radio Technologies

- September 10, 1999

**Notes:**
An analogy can be made between at circuit switched, or analog phone technology, and railroads versus packet switched digital technologies that are more like a highway system.

## Current Wireless Technologies

**2.4 GHz Band**

- 2.4 – 2.483 GHz
- 83 MHz total
- Home to...
- Bluetooth (1 Mbps)
- 802.11b (11 Mbps)
- 802.11g (54 Mbps)

- International Symposium on Advanced Radio Technologies

- September 10, 1999

**Notes:**
An analogy can be made between at circuit switched, or analog phone technology, and railroads versus packet switched digital technologies that are more like a highway system.

## Current Wireless Technologies

- Two big players
- 802.11b (aka Wi-Fi)
- 11 Mbps
- Used for medium-range wireless networks
- 100 m nominally
- 15 – 20 dBm power output

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Current Wireless Technologies

- Two big players
- Bluetooth
- 1 Mbps
- Frequency-hopping
- Included with many cell phones and PDAs
- Used for short-range cable replacement
- Syncing PDAs with computers, wireless headsets, connecting cell phones with PDAs/laptops
- Three power classes
- 0 dBm: 10 cm range
- 4 dBm: 10 m range (most common)
- 20 dBm: 100 m range

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## The Interference Problem

- Bluetooth and 802.11b are **complementary** (not competing) technologies that need to coexist...
**BUT**
- Since they use the same 2.4 GHzfrequency band, there will be somelevel of interference

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## The Interference Problem

- Frequency

- 2.4 GHz

- 2.483 GHz

- Time

**802.11b Data Transmission**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## The Interference Problem

- Frequency

- 2.4 GHz

- 2.483 GHz

- Time

**Bluetooth Data Transmission**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## The Interference Problem

**The Interference Problem**

- Frequency

- 2.4 GHz

- 2.483 GHz

- Time

**Combined Data Transmission**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## The Interference Problem

**The Interference Problem**

- Frequency

- 2.4 GHz

- 2.483 GHz

- Time

**Combined Data Transmission**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## The Interference Problem

- How do Bluetooth devices affect the
- speed of nearby 802.11b links?

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

- Previous work
- Simulations
- Laboratory Experiments
- idealized conditions
- Few real-world empirical studies

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

- Our work
- Speed measurements under real-world conditions
- Multiple Bluetooth interferers

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

- Our Testing – Basic Idea
- Set up an 802.11b link
- Vary its SNR
- Measure the link speed without interference
- Activate some Bluetooth devices and measure the speed again

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

|  | 50 | 45 | 40 | 35 | 30 | 25 | 20 | 15 | 10 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 0 |  |  |  |  |  |  |  |  |  |
| 1 |  |  |  |  |  |  |  |  |  |
| 2 |  |  |  |  |  |  |  |  |  |
| 3 |  |  |  |  |  |  |  |  |  |

- 802.11b SNR (dB) **measured** **before interference**

- Number of Interferers

- In other words, we want to fill in this matrix with speed numbers

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

- How to measure the SNR?

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

- How to measure the link speed?
- Network testing application (Chariot) would have been easiest
- FTP works just fine (and is free)
- Send a file over the wireless network
- Speed = (File Size)/(Time)

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

**Test Setup – Hardware**

- 802.11b Access Point

- FTP Server
- (connected via100 Mbps Ethernet
- to the Access Point)

- 802.11b-equipped Laptop

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

**Test Setup – Hardware**

- Throughput bottleneck isthe wireless link – speed isnot limited by the FTP server
- or the Ethernet segment

- 100 Mbps

- 11 Mbps

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

- Pair of Bluetooth-equippedcomputers **(Interferers)**

- 1 m

**Test Setup – Hardware**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Throughput Testing

**Test Setup – Hardware**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Results

**Data Rate – No Interference**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Results

**Data Rate – One Interferer**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Results

**Data Rate – One Interferer**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Results

**Percentage Network Speed Lost**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Results

**Data Rate – Multiple Interferers**

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Results

- Single Interferers
- 50% network speed lost at SNR of 25 dB
- Multiple Interferers
- Effects are highly dependent on SNR

- International Symposium on Advanced Radio Technologies

- September 10, 1999

## Questions

- International Symposium on Advanced Radio Technologies

- September 10, 1999