Bluetooth Evaluation Project - UVic Department of Electrical and

Bluetooth Evaluation Project

Written for:

Dr. Peter Driessen ELEC/CENG 499A

Written by:

BlueSuit Research (Group 19) Andus Chan

Gabriel Wiebe Robert Schoffner

William Chow

Date Submitted:

August 3, 2001

Bluetooth Technology Evaluation Project ii

Table of Content 1 Introduction ................................................................................................................. 1 2 Comparison Between Bluetooth, Wi-Fi and HomeRF................................................ 3

2.1 An Overview of Wireless Technologies In Our World....................................... 3 2.1.1 Wireless Local Area Networks ................................................................... 3 2.1.2 Wireless Personal Area Networks............................................................... 4

2.2 General Descriptions of Available Wireless Technologies................................. 4 2.2.1 Bluetooth ..................................................................................................... 5 2.2.2 Wi-Fi ........................................................................................................... 5 2.2.3 HomeRF ...................................................................................................... 6

2.3 Market Trends for Bluetooth, HomeRF, and Wi-Fi............................................ 6 2.3.1 Market Space............................................................................................... 6 2.3.2 Manufacturer’s Support............................................................................... 7 2.3.3 Projected Growth Rates............................................................................... 8

2.4 Consumer Confidence ....................................................................................... 10 2.5 Physical Layer Comparison Bluetooth, WI-FI and HomeRF ........................... 11

2.5.1 Overview ................................................................................................... 11 2.5.2 Modulation Techniques............................................................................. 11 2.5.3 Frequency Bands and Channel Arrangement............................................ 14 2.5.4 Bluetooth and Wi-Fi Coexistence ............................................................. 15 2.5.5 Summary of Physical Layer Specifications .............................................. 16

2.6 Data Link Layer ................................................................................................ 16 2.6.1 Packet Format............................................................................................ 16 2.6.2 Channel Access ......................................................................................... 17 2.6.3 Error Correction ........................................................................................ 20 2.6.4 Security...................................................................................................... 21

2.6.4.1 Data Compromises ................................................................................ 21 2.6.4.2 Unauthorized Access............................................................................. 23 2.6.4.3 Denial of Service................................................................................... 23

2.6.5 Discovering Services On Other Nodes...................................................... 24 3 Implementing a Video Stream Over Bluetooth......................................................... 25

3.1 Introduction ....................................................................................................... 25 3.2 Process............................................................................................................... 25

3.2.1 Getting to Know the Chat Application from Ericsson .............................. 25 3.2.2 Demo Tools to AVT.................................................................................. 26 3.2.3 Developing the Server ............................................................................... 27 3.2.4 Developing the Client................................................................................ 28 3.2.5 Optimizing the System .............................................................................. 29

3.3 Recommendations and Conclusions.................................................................. 30 4 System Level Tests.................................................................................................... 31

4.1 Introduction ....................................................................................................... 31 4.2 Issues Effecting Range ...................................................................................... 31

4.2.1 Output Power............................................................................................. 31 4.2.2 Receiver Sensitivity................................................................................... 31

Bluetooth Technology Evaluation Project iii

4.2.3 Antenna Gain............................................................................................. 32 4.3 Test Setup and Configuration............................................................................ 32 4.4 Results ............................................................................................................... 33 4.5 Conclusion......................................................................................................... 33 4.6 Recommendations ............................................................................................. 33

Bluetooth Technology Evaluation Project iv

Table of Figures

Figure 1. Wireless Market Interdependencies........................................................................ 7 Figure 2. Bluetooth Enabled Devices Expected Growth........................................................ 9 Figure 3. Home Networking Expected Growth ..................................................................... 9 Figure 4. Enterprise WLAN Expected Revenue .................................................................. 10 Figure 5. WLAN Sales in 2000............................................................................................ 10 Figure 6. Narrowband vs. Spread Spectrum in the presence of interference ....................... 11 Figure 7. Forms of Spread Spectrum ................................................................................... 12 Figure 8. Typical Wi-Fi (IEEE 802.11b) Base Band Signal Power..................................... 13 Figure 9. Typical Bluetooth Signal Power Spectrum........................................................... 13 Figure 10. Bluetooth Frequency Occupancy Example......................................................... 14 Figure 11. Frequency Occupancy of Three Wi-Fi Networks............................................... 15 Figure 12. Packet Structure for Bluetooth, Wi-Fi, HomeRF and Ethernet .......................... 17 Figure 13. The hidden node problem and the exposed node problem ................................. 18 Figure 14. Bluetooth example of authentictiy sceurity ....................................................... 22 Figure 15. Original Video Sever / Client Model.................................................................. 26 Figure 16. Intermediary Video Sever / Client Model........................................................... 27 Figure 17. Final Video Sever / Client Model ....................................................................... 28 Table of Tables

Table 1. General Comparison Between Bluetooth, Wi-Fi and HomeRF ...................................... 5 Table 2. Summary of Physical Layer Specifications .......................................................... 16 Table 3. Available Power Classes for Bluetooth................................................................. 31 Table 4. Scenario Range Results......................................................................................... 33

Bluetooth Technology Evaluation Project v

Summary This report is the result of the work performed on the Bluetooth Technology Evaluation Project by BlueSuit Research, a university group. The main objectives of the Bluetooth Technology Project were to evaluate the Bluetooth wireless communications standard and to provide a comparison between Bluetooth with similar technologies, such as IEEE802.11b (Wi-Fi), and HomeRF. To meet these objectives, the project was divided into the following well-defined tasks: Comparison Between Bluetooth, Wi-Fi, and HomeRF � Research specifications for each technology entailing methods used to handle

physical layer (radio) and data link layer (baseband) issues. � Research market trends for each technology covering issues such as

manufacturer’s support, projected growth rates, and consumer confidence. Bluetooth Evaluation � Develop a sample application to support the use of Bluetooth as a viable solution

for providing short-range wireless communication � Evaluate the performance of Bluetooth in terms of distance of operations and its

immunity to noise interference Evaluation of Bluetooth’s, Wi-Fi’s, and HomeRF’s methods to handle radio and data link layer issues were performed, along with market trends for each technology. Our results show that Bluetooth is a new and emerging technology that currently has no main competitors in its technology space. Bluetooth is a wireless communications standard with its market space geared more towards wireless personal area networks and mobile communications. Wi-Fi and HomeRF are similar wireless technologies, however the focus on Wi-Fi is towards wireless LANs (Local Area Networks) applications, while HomeRF deals more with wireless LANs and wireless PANs (Personal Area Networks) for the home network. Research shows that although there are few Bluetooth-enabled products at present, the number of Bluetooth-enabled devices that will be introduced in the market are projected to skyrocket in the next few years. We successfully developed a sample application that transfers streaming video over a short-range Bluetooth wireless link. The application consists of transferring a compressed H.263 video file (video encoder/decoder provided by AVT1) from one computer (server) to another (client). The performance of the Bluetooth link in terms of distance of operations and its immunity to microwave (noise) interference was determined. Our sample results of 40 m line-of-sight, and correct operation within 30 cm of microwave interference indicate that Bluetooth is a viable solution for short-range wireless communication

1 AVT is a Victoria based company specializes on wireless video products. http://www.avt.net/

Bluetooth Technology Evaluation Project 1

1 Introduction BlueSuit Research is a university group whose focus is to evaluate Bluetooth, a new and current short-range wireless communications technology. The project members consist of four university electrical and computer engineering undergraduate students supervised by Dr. Peter Driessen. The time duration for this work is four months as per University of Victoria ELEC/CENG 499A course guidelines2. Wireless is revolutionizing telecommunications; new devices and personal connectivity together will drive the wireless future - no cables allowed. We are living in an information world where people require flexible access to a network in any conceivable situation. The global demand for wireless technologies is booming and is impacting our lives and business environments. People no longer work in the traditional office, they also work while sitting in traffic, riding a cab, or relaxing in a hotel room. New innovative technologies allow access to the Internet, a corporate intranet or your own home-based network from wherever you can obtain cellular service. One of these new exciting technologies is Bluetooth. The Bluetooth Technology Evaluation Project presents an overview of the Bluetooth wireless technology standard, a comparison between Bluetooth with similar wireless technology standards, and showcases a Bluetooth sample application of transferring streaming video over a Bluetooth wireless link.

Bluetooth is a relatively new wireless standard in the communications industry. Initially developed in 1998 by Ericsson, Bluetooth began with the sole purpose of being a cable replacement technology. It has, however, evolved into a global de facto standard, with the goal of having added capabilities such as facilitating the connection of multiple mobile devices, with auto-detection and synchronization.

The work conducted by BlueSuit Research shall provide a framework and reference for future projects that wish to use a new and developing short-range wireless technology, such as Bluetooth. Future projects may include developing a wireless headset or auto-detection and transferring of files between a Personal Digital Assistant (PDA) and computer.

2University of Victoria Engineering Department, http://www.ece.uvic.ca/499/499guidelines.html


This document outlines the work conducted for the Bluetooth Technology Evaluation Project and may be broken down into five major sections: � Overview of wireless LANS and PANS � Market trends involving Bluetooth, Wi-Fi, and HomeRF � Comparison between Bluetooth, Wi-Fi, and HomeRF � Software development for sample Bluetooth applications � System-level testing covering range limitations, and interference

The first section of this report shall provide background knowledge of wireless Local Area Networks and wireless Personal Area Networks discussing the benefits of each wireless system over its wired counterparts. The discussion will then introduce three of the more popular wireless technologies competing in this market space, Bluetooth, Wi-Fi, and HomeRF. (IEEE802.11b is commonly referred to as Wi-Fi and for the remainder of this document, Wi-Fi shall be the term used to signify IEEE802.11b.) The second section presents a comparison between Bluetooth, Wi-Fi, and HomeRF, which acknowledges the similar technologies that are available in the market. As shall be shown, however, Wi-Fi and HomeRF may be thought of more as a complement to Bluetooth, and less as a competing technology. Additional evidence will be provided in the third section, market trends, involving the three technologies to further demonstrate this view. A sample application of transferring streaming video over a Bluetooth wireless link was successfully developed and serves to prove Bluetooth technology’s capabilities as an adequate mobile short-range wireless technology. The results for the developed Bluetooth application are documented in the final two sections of this report covering software development, and system level tests for operating distances and performance under noise interference.


2 Comparison Between Bluetooth, Wi-Fi and HomeRF

2.1 An Overview of Wireless Technologies In Our World This section will provide an overview on two main wireless categories, Local Area Networks and Personal Area Networks. Moreover, this section will also discuss their benefits, standards, future trends and limitations.

2.1.1 Wireless Local Area Networks A wireless local area network (WLAN) is a flexible data communications system. It transmits and receives data over the air, minimizing the need for wired connections. Thus, WLANs can combine data connectivity with user mobility. Through a wireless network, workers can access information from anywhere in the company - a conference room, cafeteria or remote branch office. WLANs have gained strong popularity in a number of markets, including health-care, retail, manufacturing, warehousing, and academia. These industries have profited from the productivity gains of using hand-held terminals and notebook computers to transmit real-time information to centralized hosts for processing. In addition with WLANs, users can access shared information without looking for a place to plug in, and network managers can set up or augment networks without installing or moving wires. WLANs offer the following productivity, convenience, and cost advantages over traditional wired networks: � Mobility: WLAN systems can provide LAN users with access to real-time

information anywhere in their organization. This mobility supports productivity and service opportunities not possible with wired networks.

� Installation Speed and Simplicity: Installing a WLAN system can be fast and easy,

and can eliminate the need to pull cable through walls and ceilings. � Installation Flexibility: Wireless technology allows the network to go where wire

cannot go. � Reduced Cost-of-Ownership: While the initial investment required for WLAN

hardware can be higher than the cost for wired LAN hardware, overall installation expenses and life-cycle costs can be significantly lower. Long-term cost benefits are greatest in dynamic environments requiring frequent moves and changes.

Flexibility and mobility make WLANs both effective extensions and attractive alternatives to wired networks. WLANs provide all the functionality of wired LANs,


without the physical constraints of the wire itself. In addition to offering user mobility within a networked environment, WLANs enable portable networks, allowing LANs to move.

2.1.2 Wireless Personal Area Networks Traditionally people have been limited to using cables, connectors and adapters to set up a Personal Area Network (PAN). A PAN is used to connect devices such as a printer, mouse, speaker cables, and scanner cables to a notebook computer. With a Wireless Personal Area Network (WPAN) all of the connections can be done without the use of a single cable. WPANs are an innovative and new technology in our world with only two WPAN special interest groups founded thus far: IEEE802.15 and Bluetooth Special Interest Group. Research into PANs began in March 1998 when the Institute of Electrical and Electronic Engineers (IEEE) formed the WPAN Study Group. The WPAN Study Group was formed with the goal of investigating the need for a wireless network standard for devices within a personal operating area. Ten months later, the WPAN study group became IEEE 802.15. The Bluetooth SIG, composed of a consortium of wireless technology companies, was formed in May 1998. Nine promoter companies currently lead the Bluetooth SIG: Ericsson, Nokia, Toshiba, IBM, Lucent, 3Com, Microsoft, Motorola, and Intel. These companies continue to define the Bluetooth standard and promote the technology3. WPAN standards generally focus on three key issues in regards to product development: � Low power consumption in order to lengthen the battery life of portable products. � Portability requirements to make them easy to carry about or even wear. � Decreased cost so that they can become as universal as possible.

If these issues can be overcome, WPANs will not only apply around the office or home, but conceivably in any location in the future.

2.2 General Descriptions of Available Wireless Technologies Bluetooth, Wi-Fi, and HomeRF are three of the more popular wireless technologies for WLANs and WPANs available today. They are all similar in that they use radio frequencies to replace cables, however they differ in terms of their target applications, range of communications, and data rates. Bluetooth’s main advantages over the other two standards are less power and cost requirements. Bluetooth requires between 100 and 1000 times less power than established systems like Wi-Fi, while HomeRF is more expensive than Bluetooth to implement.

3 City University of Hong Kong, http://www.ee.cityu.edu.hk/~knyung/aoe14.htm


Table 1. General Comparison Between Bluetooth, Wi-Fi and HomeRF

Technology Application(s) Frequency Range Speed Bluetooth WAN/LAN/PAN 2.45GHz 10 m 1 Mbps Wi-Fi WAN 2.45Ghz 200 m-300 m 10 Mbps HomeRF LAN 2.45Ghz 50 m 10 Mbps

2.2.1 Bluetooth In 1998, a group of industry heavyweights - Ericsson, IBM, Intel, Nokia and Toshiba - formed a special interest group to develop a standard for WPANs. Bluetooth (named after a Viking king) is a low-power radio link operating in the unlicensed 2.4GHz industrial-scientific-medical (ISM) band. The link has a range of about 10 meters, and a data transfer rate of up to 721Kbps. Bluetooth supports non-line-of-sight transmission through walls and briefcases, and allows several devices to be connected at once. It also allows many users to be in close proximity with each other without either interfering with each other. Another feature of Bluetooth is its ability to eliminate the need for cables between electronic devices such as PCs, mobile phones, headsets, handheld computers, printers, and LANs. Compared to current wired solutions requiring cables, Bluetooth technology will provide an easier way for a variety of mobile computing, communications and other devices to communicate with one another.

2.2.2 Wi-Fi In 1997, the Institute of Electrical and Electronics Engineers (IEEE) created standards for WLANs. The IEEE ratified the original 802.11 specifications, which provided 1 Mbps and 2 Mbps data rates along with a set of fundamental signaling methods and other services. However, these data rates were too slow to support most general business applications, so the IEEE evolved 802.11 to the 802.11b standard (also known as 802.11 High Rate and referred to as Wi-Fi) to add transmission speeds of 5.5 Mbps and 11 Mbps. Using radio waves to communicate, Wi-Fi WLANs allowed mobile users to achieve Ethernet levels of performance, throughput and availability. Wi-Fi was originally designed for the office or campus LAN and it offers high-speed access to data up to 300 feet from the base station. Multiple base stations can be linked to increase that distance as needed, with support for multiple clients per access point.


2.2.3 HomeRF HomeRF currently offers throughput rates comparable to Wi-Fi, and supports the same types of terminal devices in both point-to-point and multi-point configurations as targeted by Wi-Fi. HomeRF transmits over a range of about 50m from the base station, period. This limits its utility in places like auto parts stores, manufacturing facilities and many other small business settings, but is fine for the average home and yard. The key advantage that HomeRF has over Wi-Fi in the home environment is its ability to adapt to interference from devices like portable phones and microwave ovens. As a frequency hopper, it coexists well with other frequency hopping devices, and adapts readily in the face of competing signals that proliferate in the home. HomeRF and Bluetooth are directed at a similar segment of the home networking market. HomeRF replaces cables as Bluetooth, but HomeRF is working in home or consumer markets only. HomeRF is a wireless network protocol providing blanket coverage within the home and its close environs. Moreover, HomeRF is not concerned with low cost and small form factor because the environment in which HomeRF will exist contains devices that are neither highly mobile nor ubiquitous. 2.3 Market Trends for Bluetooth, HomeRF, and Wi-Fi In this section we will discuss the current market trends relating to each technology’s market space, manufacturer’s support, projected growth rates, and consumer confidence.

2.3.1 Market Space In general, Bluetooth can be thought of as targeting different applications then that of Wi-Fi and HomeRF. Bluetooth is marketed towards mobile and fixed wireless PANs, and Wi-Fi with fixed wireless LANs. The third major technology, HomeRF, market’s itself as the solution for both fixed PANs and LANs. This is shown in Figure 1.


Figure 1. Wireless Market Interdependencies

The competition between Wi-Fi and HomeRF has been firmly established as they battle for market supremacy in wireless LANs. The consensus among industry observers, from both HomeRF and Wi-Fi supporters is that Bluetooth can be thought of as a standard that can co-exist with them. Recently the governing bodies have expanded the spectrum available to frequency hopping technologies (Home RF and Bluetooth), which would seem to give them the upper hand by boosting the maximum bandwidth of those systems from 1.6 Mbps to about 10 Mbps. But analysts said the market momentum is firmly behind Wi-Fi, which has an especially strong hold in the enterprise. "It will be hard for [the HomeRF vendors] to keep going against the big companies that are backing Wi-Fi," 4. It should be noted though that the Wi-Fi standard has also evolved their standards, IEEE802.11b High Bit Rate, to include capabilities for data rates of 5.5Mbps and 11Mbps.

2.3.2 Manufacturer’s Support Bluetooth and Wi-Fi both share wide appeal from manufacturers and developers because they are both open standards. In an open standard, the company or group makes available to the public all of the details of the technology in order to stimulate interest and development in their idea. On the other end of the spectrum, HomeRF has been developed as a closed standard and therefore restricts access to its members only. The Bluetooth Special Interest Group (SIG) supports Bluetooth and provides free membership to join. The Wireless Ethernet Compatibility Alliance (WECA) supports Wi-Fi and HomeRF Working Group supports HomeRF. The latter two both require a nominal

4 Todd Spangler, “Wireless LANs – Where are the Standards?”, ZDNet India Tech Zone, September 18, 2000.


membership fee to join. Companies that are interested in one of the above technologies would have to join the respective standard’s special interest group to access additional information and to provide guidance on the developments of the standard. Each standard has its fair share of support by industry heavyweights. Such companies as Compaq Computer Corporation, Motorola Inc., Proxim, Inc., Intel Corp. and Germany’s Siemens AG support the HomeRF standard, while companies supporting the Wi-Fi standard include Apple Computer, 3Com Corporation, Cisco Systems and Lucent Technologies. Bluetooth’s major supporters consist of Erickson, Nokia, as well as a mixture of the major companies listed above.

2.3.3 Projected Growth Rates Growth rates for WLANs and WLAN-related products are projected to remain strong for the next five years in both the Enterprise and Home Networking market. This is due to the laptop penetration in the market, increased user mobility, universal access to the Internet and intranets and newly introduced voice over IP (VoIP) capabilities. A study was done in the U.S. that suggests that laptops will number in excess of 100 million by 2004, and network interface cards (NICs) that support wireless LANs will reach in excess of 18 million5. These facts not only promote both Wi-Fi and HomeRF's standards, but also Bluetooth's projected growth rates, since Bluetooth can be seen as complement to a WLAN. As stated by Larry Swasey, senior vice president of communications research for Allied Business Intelligence: “Bluetooth”, Swasey says, “complements everything. It’s the final element between laptops and cell phones” with which you can create your own LAN (local-area network) or PAN (personal area network)6. In addition to growth in WLANs, Bluetooth can expect to benefit from growth in the use of Personal Digital Assistants, and other such portable devices (e.g. digital cameras). This will spur the demands for applications such as transferring data between devices using a Bluetooth link. Even though Bluetooth is still in development, manufacturers are predicting that the potential market is enormous. To further support the argument for strong growth in the WLAN and PAN sectors, studies that project growth rates pertaining to Bluetooth products, as well as Wi-Fi and HomeRF’s market space, are presented in the following graphs. (See Figure 2, Figure 3, and Figure 4.)

5 The Phillips Group-Infotech, “Wireless LANs: U.S. Market Demand and Opportunity Assessment”, March 2000. 6 Michael Sweet, “The Future’s so Bright, Market Trends”, Vol.4, Issue 4, Pages 182-185, December 2000.


0

0.25

0.5

0.75

1

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ts in

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2000 2001 2002 2003 2004 2005

Bluetooth-Enabled Equipment

Figure 2. Bluetooth Enabled Devices Expected Growth7

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ts in

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1999 2000 2001 2002 2003

Projected Growth In Home Networking

Figure 3. Home Networking Expected Growth8

7 Cahners In-Stat Group, “Access Anytime, Anywhere: Bluetooth will make it so!”, Report#MM0106BW, April 2001. 8 HomeRF Working Group, Inc. “Home Networking Technologies”, May 2001.


0500

100015002000250030003500

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ts in

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1999 2000 2001 2002 2003 2004 2005

Enterprise WLAN Market Projected Revenue

Figure 4. Enterprise WLAN Expected Revenue9

2.4 Consumer Confidence At present, both HomeRF and Wi-Fi have an advantage over Bluetooth in terms of consumer confidence. Currently, the wireless LAN is reaching its growth stage, and both HomeRF and Wi-Fi are evolving into a mature technology with well-defined standards and certified products in the market place. A recent study of Retail Wireless LAN sales in the retail market seems to indicate, however, that Wi-Fi is winning in the battle between over HomeRF.

Figure 5. WLAN Sales in 200010

9 Mobile Info., “Wireless LAN Market Approaches 3.2 Billion, Study Says”, Issue#2001-17, April 2001. 10 ISP Planet Staff, “Wi-Fi Rules Retail Sales In 2000”, ISP Fixed Wireless, March 2001.


Although there are some Bluetooth enabled products in the market place too, Bluetooth is still considered in its development stage and has yet to reach the market11. This claim is further supported by the fact that people can still expect to see lots of Bluetooth prototypes at computer shows, such as COMDEX, which are not yet ready to be placed on the market12.

2.5 Physical Layer Comparison Bluetooth, WI-FI and HomeRF

2.5.1 Overview This section discusses the RF/Radio section of each of the technologies. The lowest layer of the OSI model defines the electrical and mechanical rules governing how data is transmitted and received from one point to another. The topics include digital modulation techniques, frequency band of operation, range/power requirements, and maximum data rates. At the conclusion of this section some methods of coexistence between the technologies will be discussed.

2.5.2 Modulation Techniques All three technologies use a digital modulation technique called spread spectrum. Spread spectrum reduces the vulnerability of a radio system to both interference from jammers and multipath fading by distributing the transmitted signal over a larger region of the frequency band than would otherwise be necessary to send the information (see Figure 6). This allows the signal to be reconstructed even though part of it may be lost or corrupted in transit.

Figure 6. Narrowband vs. Spread Spectrum in the presence of interference

11 Geof Wheelwright, “Wireless Court Battle Brewing”, Canada Computer Paper Inc., April 2001. 12 Bob Brewin, “Bluetooth Still in Teething Stage at Comdex” ComputerWorld, an IDG.net Site, November 2001.


The two primary approaches to spread spectrum are direct sequence (DSSS) and frequency hopping (FHSS), either of which can generally be adapted to a given application. The direct sequence spread spectrum is produced by multiplying the transmitted data stream by a much faster, noise-like repeating pattern. The frequency hopping spectrum system, however, spreads the spectrum by transmitting the data signal as usual, but varying the carrier frequency rapidly according to a pseudo-random pattern over a broad range of channels. The two approaches are illustrated in Figure 7.

Figure 7. Forms of Spread Spectrum

The Wi-Fi system is based on the direct sequence standard where the data is transmitted using binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) constellations. A square root raised cosine pulse shaping filter with a relatively large excess bandwidth may also be use to conform to the Wi-Fi standard. A typical spectral mask is shown in Figure 8.


Figure 8. Typical Wi-Fi (IEEE 802.11b) Base Band Signal Power

The Bluetooth standard is based on the frequency hopping spread spectrum standard The Bluetooth radio module uses GFSK (Gaussian Frequency Shift Keying) where a binary one is represented by a positive frequency deviation and a binary zero by a negative frequency deviation. The spectral mask of the Bluetooth signal is shown in Figure 9. Bluetooth devices hop over 79 frequencies that are 1MHz wide. Thus, over time, Bluetooth devices occupy 79MHz, but at any specific instance only 1MHz is occupied. The 1MHz center frequency changes (or hops) deterministically at a rate of 1600 times per second.

Figure 9. Typical Bluetooth Signal Power Spectrum


Home RF also uses the frequency hopping spread spectrum standard and a constant envelope frequency shift keying (FSK) modulation scheme. In comparison Home RF hops between 50 and 100 hops/s over 75 center frequencies, however the signal bandwidth is the same at 1MHz.

2.5.3 Frequency Bands and Channel Arrangement Wi-Fi, Bluetooth and HomeRF products all operate in the unlicensed 2.4GHz ISM band and therefore must follow the many regulations that apply to this band. Section 15.247 of the FCC regulations contains the key requirements for high-power direct sequence and frequency hopping spread spectrum transmissions allowed in the band. The 2.4GHz ISM band is 83.5MHz wide with a lower limit of 2.400GHz and an upper limit of 2.4835GHz. The FCC regulations limits operation of high-power transmitters (up to 1 Watt) in the band for direct sequence spread spectrum (DSSS) and frequency hop spread spectrum (FHSS) technologies. Figure 10 shows how Bluetooth hops in the 2.4GHz ISM band. Each rectangle represents a Bluetooth transmission. Bluetooth is a slotted protocol. Each slot is 625µs long.

Figure 10. Bluetooth Frequency Occupancy Example

Each Wi-Fi network maintains the same frequency usage over time and only uses a subset of the 83.5MHz available. The Wi-Fi standard defines 11 possible channels that may be used. Each channel is defined by its center frequency. The center frequencies are at intervals of 5MHz from one another. The associated channels are numbered from 1 to 11. Since the 20dB bandwidth of a Wi-Fi signal could easily be as great at 16MHz, using adjacent channels in the same location would result in interference. For this reason Wi-Fi networks are typically operated on channels 1, 6 and 11 to prevent interference. In such a scenario, three collocated networks would occupy approximately 3 x 16MHz = 48MHz of the available 83.5MHz in the ISM band.


Figure 11 shows a typical frequency occupancy for three Wi-Fi networks. Each Wi-Fi network operates exclusively on one channel. The figure shows networks operating on channels 1, 6 and 11. The transmissions of each channel are distinguished by the color of each packet. The duration of each Wi-Fi packet varies based on the amount of data in the packet. There is typically a short acknowledgement packet after each data packet on the network.

Figure 11. Frequency Occupancy of Three Wi-Fi Networks

2.5.4 Bluetooth and Wi-Fi Coexistence Bluetooth and Wi-Fi share the same unlicensed 2.4 GHz ISM band that extends from 2.4 to 2.4835. However, systems in this band must operate under certain constraints that are supposed to enable multiple systems to coexist in time and place. This is due to the fact that these technologies are complementary rather than competing technologies. Based on research13 done by Mobilian Corporation, which received wide acceptance by the industry as the definitive treatment of this issue, It was determined that the performance of Wi-Fi generally suffers more from Bluetooth activity than vice versa. As a result of the potentially negative impacts of collocated Wi-Fi and Bluetooth devices, many companies have begun researching and developing solutions for coexistence. Potential approaches include: � Simple device collocation with no coexistence mechanisms; � Restricted or adaptive band hopping for Bluetooth devices; � Switching between the two protocols;

13 Mobilian Corporation, White Paper - Wi-Fi™ (802.11b) and Bluetooth Simultaneous Operation: Characterizing the Problem


� System-level approaches covering the entire wireless sub-system and many of the above techniques.

2.5.5 Summary of Physical Layer Specifications The following table summarizes the physical layer specifications for Bluetooth, Wi-Fi and HomeRF.

Table 2. Summary of Physical Layer Specifications

Bluetooth Wi-Fi (802.11) Home RF

Spreading Technique FHSS DSSS FHSS

Frequency 2.4GHz ISM 2.4GHz ISM 2.4GHz ISM

Modulation GFSK FSK BPSK

Hops/sec 1600 N/A 50-100

Range 10m 200-300m 50m

2.6 Data Link Layer This section provides an overview of the approach taken by Bluetooth, Wi-Fi, and HomeRF in implementing the data link layer protocol and outlines features provided by each standard. The data link layer, placed directly above the physical layer of the OSI model, is responsible for managing the direct delivery between two devices on a specific physical layer. Features that the data link layer implements include the packetisation of data, channel access and set-up, error control and security. In a radio device, the section that implements the data link layer functions is commonly referred to as the Medium Access Control (MAC).

2.6.1 Packet Format The packetisation scheme employed by Bluetooth, Wi-Fi, and HomeRF are very similar as they all use variable frame length formats, known as packets. The frame structure for Wi-Fi and HomeRF packets is borrowed heavily from the IEEE802.3 (Ethernet) standard, as opposed to Bluetooth packets, which only use Ethernet addressing formats. Ethernet is a popular standard used for wired LANs.


Each of the three standards’ packet formats includes fields that address issues essential in media access control: � Data synchronization � Packet type field to determine service required � Device addressing fields � Flow control � Header error checks or CRCs to check packet integrity

A breakdown of a typical frame structure for each standard is shown below for comparison. Figure 12 also contains a typical Ethernet frame to exemplify the borrowing of the Ethernet standard by Wi-Fi and HomeRF packets.

Access Code Packet Header Payload

PREAMBLE Sync Word

Active MemberAddress TYPE FLOW ARQN SEQN HEC

Access Code

Packet Header

Bluetooth Packet Format

Ethenet Packet Format

HomeRF Packet Format

Start of Frame DestinationAddress

SourceAddress

PacketLength/Type

of framePayload Padding CRC

SyncronizationField Start of Frame Flags Packet Length Network ID Payload

ControlDestination

AddressSource

Address Payload CRC

Wi-Fi Packet Format

Frame Control Field Duration ID DestinationAddress

SourceAddress

Base StationID

SequenceControl

WirelessDistribution

SystemAddress

Payload CRC

IP Protocol VersionType, Sub-TypePower Management Features

IP Protocol VersionType, Sub-Type"TDMA" ack

Figure 12. Packet Structure for Bluetooth, Wi-Fi, HomeRF and Ethernet

2.6.2 Channel Access How does each system handle channel access and set-up? This section shall attempt to convey each standard’s solution. In general, there are three main classes of channel access mechanisms for radio: CSMA/CA, TDMA, and polling. CSMA/CA is a connectionless message passing mechanism that is appropriate for asynchronous data links, which could contain bursty traffic, such as TCP/IP. TDMA is a connection-oriented channel access mechanism that is well suited for non-bursty traffic such as required in


synchronous voice links. Polling can be thought of as a mixture between CSMA/CA and TDMA. This section will begin with a study of the Wi-Fi’s channel access protocol that uses a CSMA/CA only, followed by HomeRF’s solution using both CSMA/CA and TDMA. In the last part of this section, Bluetooth’s use of polling will be discussed. Wi-Fi Channel Access Wi-Fi standard specifies the use of a carrier sense multiple access with collision avoidance system (CSMA/CA) protocol. In this protocol, when a device is ready to transmit a packet, it first listens to ensure that no other node is transmitting (carrier sense). If the channel is clear, it then transmits the packet. If the channel is not clear however, the device will then chose a random “back off factor” which determines the amount of time the device must wait until it can transmit the data (multiple access). With the assignment of a back off factor, the device will decrement its back off counter until it reaches zero during periods in which the channel is clear. Otherwise if the channel is busy, it does not decrement its back off counter. When the back off counter has reached zero, the device then transmits the packet (collision avoidance). Since the probability that two devices will choose the same back off factor is small, collision between packets are minimized. The CSMA/CA protocol gives rise to the hidden node problem and the exposed node problem for wireless devices. These problems are best explained with the help of the illustration below (see Figure 13).

AA CCBB AA DDBB CC

HIDDEN NODE PROBLEM EXPOSED NODE PROBLEM

Figure 13. The hidden node problem and the exposed node problem

The hidden node problem arises from the fact that all devices may not hear each other because the attenuation is strong between them. As shown above, a collision between device A and device C occurs because device A believes it is safe to transmit for two


reasons: 1) because it believes device B is silent and 2) it is out of listening range with respect to device C’s transmission. The exposed node problem arises from the fact that devices may be within listening range with another device that may be transmitting data to a fourth device. Referring back to Figure 13, the scenario occurs when device B is within listening range of device C and will not transmit data to its intended target device A even though device C is not communicating with device A. A solution to these problems that Wi-Fi standard uses is to implement RTS/CTS (Request to send/Clear to Send) handshaking. Before sending the packet, the transmitter sends a RTS and waits for a CTS from the receiver. The transmitter will only send data upon reception of the CTS (which would indicate that the channel is clear). In addition, devices within the channel’s operating range will overhear the CTS signal and know that a transmission is about to occur and will inhibit their own communications to avoid collision for the estimated transaction period (the transaction period is indicated in the CTS). HomeRF Channel Access Access to HomeRF specifications and relevant technology features is made available to members only. Due to the lack of material provided by HomeRF, the amount of material available in the description for HomeRF’s section of channel access and set-up is limited. HomeRF, like Wi-Fi, implements CSMA/CA service as well for data communication, but in addition, it has incorporated data link layer features from the existing Digital Enhanced Cordless Telephony (DECT) standard to handle synchronous data links in order to provide adequate quality of service for interactive voice and other time-critical communications. Wi-Fi has specified a point-coordinate function as an option in its standard, which allows you to assign priority in traffic flow for time-critical communications, but it is not adequate for providing telephony quality of service. The channel mechanism used by HomeRF for telephony applications, based on DECT standards, is to use a Time Division Multiple Access (TDMA) scheme. In TDMA, a master device (the base station) is in charge of coordinating the other devices (slaves) on the network. The time on the channel is divided into time slots, which are generally of fixed size. Each device on the network is allocated a fixed amount of time slots that it may use for transmitting purposes. Slots are organized in a frame, which is repeated on a regular basis. The frame organization is specified in a management frame (a beacon) as determined by the base station. Each slave needs only follow the instructions as specified in the beacon. HomeRF differentiates itself from Bluetooth in terms of voice communications in many ways. First, HomeRF provides up to eight simultaneous prioritized streaming media sessions or eight simultaneous toll-quality two-way cordless voice connections. This is made possible through the use of the reserved TDMA scheme it uses for channel access


of synchronous data. Bluetooth is limited only to two active calls. Second, with the incorporation of the DECT standard in its channel access and set-up scheme, HomeRF may provide a rich suite of digital features such as Call Line ID, call waiting, etc… along with features such as 911 breakthrough, which Bluetooth does not support. Lastly, although Bluetooth is capable of providing two active calls, when two active calls are present, the remaining data bandwidth is only similar to that of an analog modem (whereas in HomeRF, two active calls leaves plenty of data bandwidth that exceeds almost any DSL or cable modem connection) [Wireless Networking Choices for the Broadband Internet Home]. However, it should be noted that the IEEE has formed a 802.15 Personal Area Networking group with plans to adopt the Bluetooth specifications for its 1Mbits/s recommendations and the group is hoping to develop a high-rate version at 20+Mbits/s in the future. Bluetooth Channel Access Bluetooth uses polling as its channel access mechanism. In polling, like TDMA, a master device retains control of the channel. However, the frame content is no longer fixed, as variable size packets may be sent. Transmission by a slave may occur only if the slave has received a poll packet by the master. The poll packet is essentially the master checking to see if the slave needs to transmit data. The master may either poll permanently all slaves (if the number of slaves on the network is small) or reservation slots may be allocated whereby each node may request either a connection or a packet transmission.

2.6.3 Error Correction There are generally three responses when handling error detection14: � Forward Error Correction (FEC) – When the receiver detects an error, it will try to

correct the error before passing on the data any further. � ARQ scheme – Request a retransmission of the data sent. � Muting – Tag the data as being incorrect and passing it along to the data sink.

Wi-Fi Error Correction Schemes To handle interference problems, Wi-Fi simply retransmits (i.e. ARQ scheme), or waits for the higher-level TCP/IP protocol to sort out signal from noise. This works well for data but can make voice transmissions sound choppy and thus leading to poor voice quality of service. However, 802.11b treats voice and data the same way, converting voice into data packets. 802.11b is not designed to provide adequate interference adaptation and voice quality for the home.

14 Stephen B. Wicker, Error Control Systems For Digital Communications and Storage, Prentice-Hall, 1995.


Bluetooth Error Correction Schemes There are three error-correction schemes defined for Bluetooth: 1/3 FEC, 2/3 FEC, and ARQ scheme for data. The purpose of the FEC scheme on data payload is to reduce the number of retransmissions when an error is encountered, while the ARQ scheme may be used for error-free environments. The user has the option of choosing which error-correction scheme with which they wish to implement. However, because packet headers contain valuable link information, it is always protected by a 1/3 rate FEC. HomeRF Error Correction Schemes HomeRF error-correction schemes are not available as details pertaining to this subject were limited. This is due to the restricted access of HomeRF specifications for members only at the HomeRF website.

2.6.4 Security When discussing the security of a wireless network, there are three main categories to look at: � Data Compromises � Unauthorized Accesses � Denial of Services

The following section will look at how BT, HomeRF, and Wi-Fi deal with these situations.

2.6.4.1 Data Compromises A data compromise is anytime an unintended party is disclosed information. HomeRF: HomeRF uses a 128-bit encryption key that is seeded by a 32-bit initialization vector (IV). This IV is selected by a defined procedure and therefore minimizes the chance that the same IV is repeated before all other IVs are used. At 32-bits, the average repeat interval is half a year Wi-Fi: Wi-Fi uses a 40-bit encryption key that is seeded by a 24-bit initialization vector, which is not provisioned for by the standard. According to a paper publish at Berkeley University, this means that even if the encryption key is increased to a larger size at the Wired Equivalent Privacy, WEP still could remain vulnerable to brute force attacks. At 24-bits, the average repeat interval is half a day. There is currently a group working on a WEP2 that will deal with most of the issues raised by the Berkeley report. The goal is to create a firmware upgrade so that existing devices could be updated. The release of this is expected for late 2002.


Bluetooth: At the highest security level (3), Bluetooth uses a 128-bit encryption key and a 128-bit link key that are shared between the participants. Though the keys are 128-bits, they are calculated purely on the user’s 4 digit PIN and publicly transmitted information such as node address and unit key. The following example15 outlines how a device could gain access to information that it did not have permission for. � Some time in the past device B and C create and terminate a link � Devices A and B create a link using A’s unit key as the link key (1) � Devices A and C create a link and also use A’s unit key as the link key(2) � Device B can decrypt communications between A & C since it has knowledge of

A’s key and B’s address (3)

Figure 14. Bluetooth example of authentictiy sceurity

As shown in Figure 14, the above example, device B knows all the information that is required in order for it to ease drop on the communications between devices A and C: it knows the link key and both A and B’s addresses. (All device address’ are unique and therefore if device B and C had ever communicated before, B would have a record of C’s address). Though not easy, but shown possible by Lucent Technologies16, device B could emulate device A and communicate with C or visa versa.

15 Cathal Mc Daid, March 2001, http://www.palowireless.com/bluearticles/cc2_security3.asp 16 Jakobsson M., Wetzel S. Security Weakness in Bluetooth, 2001, http://www.bell-labs.com/user/sgwetzel/bt.html


2.6.4.2 Unauthorized Access An unauthorized access is when someone who should not have access network resource, accesses a network facility. HomeRF HomeRF uses a 24-bit networkID (NWID) that must be known to synchronize with the frequency hopping done in the physical layer. For this reason it is almost impossible to listen in on the network traffic and therefore gain access. Getting the NWID can be done in one of two fashions: be coded into the device by an information technology manager or learned from an existing node in the network. This learning process can only be triggered by human intervention (ie. pushing a button) to tell one of the devices to teach and the other to learn the NWID. Wi-Fi Wi-Fi’s default method for nodes to gain access to the network is to listen for a beacon from a control point and then request access to the network. The control point will then either grant access to all requests or only to devices that are on a user entered list. This approach is often referred to as Open System Authorization. Bluetooth Bluetooth encourages nodes to connect with each other, therefore at level 1 and 2 security, the question of whether the device is welcomed is not asked. At level 3 security, each device must supply a 4 digit PIN, which must be agreed upon by all devices before the connection is allowed. One advantage that Bluetooth has is that it has a short transmission length; usually 10 m. This means that an unauthorized user would have to be very close to the network in question in order for them to gain access.

2.6.4.3 Denial of Service A denial of service occurs when a network cannot handle its normal activities because something is blocking it. An example of such a problem is what happened to Yahoo and Ebay in February of 2000 when they were saturated by a large number of bogus requests. The result of this form of disruption was that each website could not handle their normal operations which effectively brought the websites down. HomeRF As stated in section 2.6.4.2, in order for a new device to gain access to the network, it must know the current NWID to synchronize with the frequency hopping physical layer. As a result, it is very difficult for an unwelcome node to send erroneous message on the network to saturate it.


Wi-Fi As stated in section 2.6.4.2, Wi-Fi uses a Open System Authorization scheme where anyone has the ability to listen to the control frames and request things like “can I join the network?” or “is it clear to send?” As a result it is very possible for someone to be malicious and send numerous request thereby bogging down the network without ever being authorized on it. Bluetooth As stated in section 2.6.4.2, Bluetooth encourages connections and therefore Bluetooth devices are very susceptible to having the network brought down by repeated request for what services are available.

2.6.5 Discovering Services On Other Nodes The following section will look at how HomeRF, Wi-Fi and Bluetooth deal with searching for services that may be offered by other nodes. These services may include: a portal onto a LAN, a printer or access to a database. HomeRF HomeRF does not provide any method to query other nodes to find out what services they can provide. It is assumed that whatever platform is using the network will provide this feature. Wi-Fi Wi-Fi does not provide any method to query other nodes to find out what services they can provide. It is assumed that whatever platform is using the network will provide this feature. Bluetooth Bluetooth provides a well-defined procedure known as the Service Discovery Protocol (SDP) for dealing with searching for services offered by other nodes. Instead of relaying on the platforms using the networking technology, Bluetooth outline the use of a SDP server and SDP client. The purpose of the SDP server is to answer question posed by SDP clients on other nodes. The queries may consist of specific question such as: “do you have a colour laser printer?” or may simply be, “what services can you offer me?” By asking the question before a formal connection is made, fewer devices may need to operate on the same network. This also allows all devices to query each other independent of what platform each node is running.


3 Implementing a Video Stream Over Bluetooth 3.1 Introduction The goal of this part of the project was to modify an existing program that was included with the Bluetooth demo boards from Ericsson to stream video instead of text messages. The demo program was created to showcase the abilities of Bluetooth to find other Bluetooth enabled devices, discover what services they can offer and then create a simple instant messenger client.

3.2 Process The following section will outline the processes that we went through to develop the Bluetooth video stream application.

3.2.1 Getting to Know the Chat Application from Ericsson Our first step was to become familiar with the Chat application that Ericsson created and packed with the demo boards. To do this we tried to use the USB connection to connect the evaluation boards to the PCs. Though the documentation stated that this method would work fine, we found that this was not true. Problem – USB connection not reliable When we tried to establish a wireless link using the chat software, it would seldom find the Bluetooth unit (BU) attached to the local machine let alone detect the other BU running next to it. Every time the BUs would fail we would have to reset the boards (via a push button) and kill the communications thread running on the PC (bt_comserver). This was a large inconvenience since it was a very common occurrence (9 out of 10 times) and it did not make sense since we were using Ericsson stock code and boards. Solution Due to the unreliable USB connection and the poor customer support provided by Ericsson, we decided to try connecting to the evaluation board via a serial RS232 connection. To our surprise, this worked very well and the application ceased to fail nearly as often (1 out of 10 times), and when it did, the whole setup did not need to be reset.


3.2.2 Demo Tools to AVT Once we had the tools from Ericsson working, we set out to demo our findings to AVT and get a better feel for how to get the video from the web cam, compress it, decompress it and display it to the client. Problem – How do we get a video stream from the Window OS to a small enough bandwidth to transmit it, then rebuilt it on the other side? Our initial model looked like this (see Figure 15):

BT Reference Stack

Web Cam Drivers

USBDriver

USBDriver

Win 2000

Our CodeBTModule

Server

BT Reference Stack

USBDriver

Win 2000

Our Code

Net Meting

BTModule

Client

Figure 15. Original Video Sever / Client Model

Solution After talking with members of AVT, we decided that for the first release of our product, it would be too complicated to: � redirect a video stream from window � encode it on the fly � work out all the Bluetooth stuff (packeting, buffering etc) � decode the packets � recreate a video stream recognized by Windows

Instead, AVT gave us a copy of H.263 encoder / decoder and a sample YUV420 video file that could be encoded, and decoded in real-time. Since none of the members of our group were comfortable with Windows event based programming, this first step would demonstrate the Bluetooth technology without having to get too involved with the OS. The resulting model was (see Figure 16):


BT Reference Stack

USBDriver

SecurityBT Module

ServerEncoder

carp

hone

.qci

f

Server

BT Reference Stack

USBDriver

BT ModuleSecurity

ClientDecoderViewer

Client

Figure 16. Intermediary Video Sever / Client Model

3.2.3 Developing the Server When we setout to create the server, we did so with the intention to start with the Ericsson chat application as our foundation but modify it to suit our needs. This strategy made the most sense since the chat program took care of discovering other Bluetooth enabled devices, discovering what services they had to offer, and establishing a link. All that was required was to send packets of video in a timely manner, as opposed to sending strings of text sporadically. Problem – How do we synchronize the Server with the Video Encoder? Since our group had little to no Windows programming experience going into this project, this problem seemed fairly big. We were not sure how to send inter-application messages to manage something like a bounded buffer and therefore we had no known means of telling the encoder to slow down or speed up. Solution As a first step, we decided that since we were encoding a pre-recoded file anyways that we might as well just compress the video off-line and then just transmit the results. Though this did not reflect what we wanted in the end, it was a good simplification of the system so that we could concentrate on the Bluetooth link. As a result, our system model became (see Figure 17):


BT Reference Stack

SerialDriver

SecurityBT Module

Server

carp

hone

.263

Server

BT Reference Stack

SerialDriver

BT ModuleSecurity

ClientDecoderViewer

Client

Figure 17. Final Video Sever / Client Model

The rest of the Server creation went well. A timer was utilized to periodically read data from the file and pass that data to the Bluetooth protocol stack via a COM_DataSend method used in the chat application. The rate of the timer and the size of payload sent pre method call will be discussed later in section 3.2.5).

3.2.4 Developing the Client The development of the client followed the same path as the server in that we started with the chat application as a foundation. To prove that the server was transmitting data, the first version of the client did not try to decode the stream but rather store it to a file. This step was not hard to create and we were soon able to stream the video file from the server to the client, store that data to a file and then decode and view that file off-line. Problem – How do we link the H.263 decoder to the Bluetooth client? Solution The first step in solving this problem was to modify the code so that the decoder was no longer reading data from a file, but was instead reading the data from standard IO. The only issue during this step was the need to set the IO properties to treat the data as binary instead of the default of ASCII. Step 2 was creating a pipe (similar to what is used in UNIX to direct output and input from the command line) to allow the client to direct the data to the decoder. To do this we use the CreatePipe()system call, and linked the client to the decoder that was spawned once the connection was made. By doing this, the OS took care of the buffering that was needed between the two processes.


3.2.5 Optimizing the System With the video transfer portion of the program working correctly, the next step was to try increasing the data rate so that the video was always smooth. As described in section 3.2.3, we were using a timer to periodically transmit the next packet of video directly from the encoded file. To determine what rate at which the timer should run at, we looked at the encoder’s status message to get the ideal data rate for this video stream. The optimal data rate for this file was 102.7 kbits/sec. Problem – How do we reach a data throughput of 102.7 kbits/sec? Solution Since we were using the same method used by the chat application to transmit a packet of data (COM_DataSend), we were governed by some its limitations. Step 1: Increasing the packet size. Our first plan was to increase amount read from the file each time the transmit method was called. Though not documented by Ericsson, we found that they put an upper limit of 127 bytes and if we exceeded this size, the application would crash. We could not find a way to change this amount since we were not give access to the code executing this method, just the method call. Step 2: Increase the rate of packets sent. Knowing that we can only transmit 127 bytes at a time, we set out to increase our packet rate. In order to achieve the desired 102.7 kbits/sec data rate, the following calculations were done:

sec101

sec*8*127

sec7.102

packets

packetsbytebits

packetbyteskbits

=∴

=

α

α

or 1 packet every 9.9 milliseconds By decreasing the rate of the timer to increase our packet rate, we found that a buffer overflow error would error in our application if we tried a period of less then 40 milliseconds. This was due to the how the Bluetooth protocol stack was initially used by the chat application. (Each packet is buffered until it could be sent). If we increased the packet rate, this buffer filled too fast, and therefore saturated occurred causing error.


3.3 Recommendations and Conclusions This part of the project contained successes and failures. We were able to modify the Ericsson chat application to stream and decode a prerecorded video file in real-time. Though not streaming at the full data rate needed for the video, this process showed that is was possible to create a Bluetooth application and utilize some of features of Bluetooth including the search discover protocol. If future work is done on this application, areas of interest should include: � Increasing data rate � Encoding on the fly � Connection loss recovery


4 System Level Tests 4.1 Introduction The system level tests provide a means of verifying the actual Bluetooth range for noisy, unobstructed and obstructed scenarios. This section will begin by providing information on the issues effecting range such as transmitter power, receiver sensitivity and antenna gain. The remainder of this section will discuss the tests, which were conducted and finish with a conclusion and some recommendations for further testing.

4.2 Issues Effecting Range Three very important parameters define the coverage of a wireless device: � Output power � Receiver sensitivity � Antenna gain

4.2.1 Output Power Three power classes are available for Bluetooth, Class 1, 2 & 3. Each class has the following characteristics:

Table 3. Available Power Classes for Bluetooth

Device Power Class

Max Output Power (mW)

Max Output Power (dBm)

Expected Range

Class 1 100mW 20dBm 100m

Class 2 2.5mW 4dBm ~10m

Class 3 1mW 0dBm 10cm to 10m

4.2.2 Receiver Sensitivity Bit Error Rate (BER) is the criterion used to determine the receiver performance. The sensitivity level is defined as the input level for which a raw BER of 0.1% is met. The requirement for a Bluetooth receiver is an actual sensitivity of –70dBm or better.


4.2.3 Antenna Gain Antenna gain appears twice in the picture as the receiving and the transmitting antenna gain. Therefore antennas play an important role in how far away, for example, a printer can be placed from a mobile computer in a Bluetooth equipped office. Friis transmission equation17:

Where: P = Power λ =Wavelength R = Distance between transmitting and receiving devices n = Environment parameter (free space = 2.0, hard partition office = 3.0) G = Antenna gain (0 dBi = 1)

From this fundamental formula it becomes obvious that antenna performance plays a key role in the operating range of Bluetooth devices.

4.3 Test Setup and Configuration The test configuration consisted of two computers one of which was a fixed desktop unit and the other a mobile laptop. Each computer had a Bluetooth unit connected to both the serial and USB port. The serial port is used for the data and the USB connection is used to supply the operating voltage. The Bluetooth module operates as a class 3 device and uses a Planar Inverted “F” Antenna (PIFA), which is directly etched into the ungrounded PCB. The video streaming software as detailed in Section 3 is used as an indicator for determining the range. As the mobile laptop, which was receiving the video stream via the Bluetooth link, would move out of range, the video would begin to drop frames. At this point the range was measured. Three scenarios were tested

1. Unobstructed (line of site) 2. Obstructed (through four walls) 3. Noisy Environment (microwave in direct path of line of sight)

17 Haykin, Simon – Communication Systems 4th Edition


4.4 Results The follow table outlines our results.

Table 4. Scenario Range Results

Scenario Range [meters]Unobstructed 40

Obstructed (through four walls) 10Noisy Environment (microwave)* 30

*The link worked until the Bluetooth unit came within 30cm of the microwave.

4.5 Conclusion As can be seen from the results in Table 3, the range matched or exceeded the expected range in all scenarios. Of particular note is the range of 40 meters for the unobstructed (line of site) scenario. There are two possibilities for this extended range. The first possibility may be due to the signal reflecting down the hallway thereby extending the range. The second possibility comes from the software decoder, which may have had an error concealing mechanism preventing the video from dropping frames by extrapolating the image bits and therefore extended the range.

4.6 Recommendations Further testing of the RF section should include the coexistence between Bluetooth and Wi-Fi devices.

Documents

Bluetooth Evaluation Project - UVic Department of Electrical and