Tài liệu Bluetooth P2 pdf

Let’s examine the traditional headset and mobile phone and decide if Bluetooth technology makes this more convenient for the user.With current free technology, you have to decide in adva

notwithstanding, the added value from simply being wireless convinced

con-sumers to try it and use it! However, for products that are inherently static, the

added value may just be initial “desire” and not really a viable investment in both resources and dollars

Consider the static devices in our wired PAN (Figure 1.1)—for example, the ubiquitous mouse and keyboard Both are dependant for their power supply requirements upon their host PC, so if made wireless, the subject of batteries becomes crucial.This added value of wireless connectivity can only be enjoyed if the user does not have to change or re-charge the batteries every week! Our static devices—desktop PCs with the obligatory mains power cable—would be perhaps better served by a wired Ethernet link rather than a Bluetooth LAN point (both cables embedded under the floor in your office as standard) Electric lights are another facet to consider—just think of the reduced installation costs in

an office building of no wiring loom Here, however, we do require power So is wireless really adding value? It could be valuable if added as a control extra.The user could then connect via a handheld device or static panel to whichever light they wished to control At the other end of the scale, the end user value of a Bluetooth PCMCIA card is easily visible, and will provide complete wireless connectivity

Ensure that your product will really give the user added value by being wire-less, not just offer a gimmick If the consumer has to connect a power cable, then consider what other functionality can be offered.The desktop PC, although best served by a wired Ethernet connection, will still need to connect to our laptop and PDA, and thus requires both wired and wireless connectivity

An intriguing application would be a wireless pen—consider its use for signa-ture authentication provided by the credit company, bank, or reception desk, a super method to try and eliminate fraud If a wireless implementation could be designed for the stringent size constraint, how would we stop users from walking off with it? Why are the ordinary pens always attached to the counters? Would being wireless really add value to this application?

Investigating Convenience

Added user value is a “big plus” for the consumer but wireless communications may not necessarily make the product more convenient to use.We assume that consumers are all comfortable with gadgets and electronic devices, but can your friends all program their VCRs yet?

Let’s examine the traditional headset and mobile phone and decide if Bluetooth technology makes this more convenient for the user.With current free technology, you have to decide in advance if you require the hands-free option.This involves fitting your car with a hands-hands-free kit—a microphone or headset plugged in, with the wire trailing from it to your phone which is either

in your pocket, clipped to your jacket/belt, in a cradle on your dashboard, or like most of us, fallen down between the seat and the handbrake!

When you receive a call, you answer by pressing a button on the cable;

volume control is available via a button on the cable.The limitation is that you always have to have your telephone with you; it can only be as far away as the cable is long.Thus, it is always a conscious decision to use the headset, and to decide to plug it in! With a Bluetooth headset and phone, the phone can be inside your briefcase, in the boot of the car, in your jacket on the hook in the office, in fact, absolutely anywhere—as long as it’s within the range of the headset In much the same way as the conventional technology, you press a button on the headset to receive a call or to adjust the volume.The connection between the two devices is extremely different, however, and although virtually invisible to the user, it will incur a connection time overhead First, the headset must “pair” with the Audio Gateway (AG), the Bluetooth part of the phone.This allows Bluetooth addresses to be swapped, and link keys to be established.The headset will then be able to make a connection to the AG or the AG will be able

to connect to the headset—the exact operation is a software application issue If the headset connects to the phone, then the phone needs to know why, either to set up voice dialing, action voice dialing, or some other function If the phone connects to the headset, it patches a SCO link across and the headset can be used

to take the incoming call

The connection time could be a problem if you must connect every time a call comes in After ten seconds of trying to make a connection, the caller has probably decided you are not going to answer and given up! A low power park mode allows headset and phone to stay constantly connected without draining their batteries; this overcomes the slow connection problem So you must beware—if connection time is an issue for your product, make absolutely sure your system supports park mode—although it’s becoming increasingly common, it’s still possible to buy devices that do not support it

My conclusion would be that Bluetooth technology would make answering

my phone far more convenient, although extremely expensive at the moment! I

do not have to worry where my phone is, per-equip my car, or have to endure a

cable running from my ear If the complex connection issues are invisible to me and I look as cool as Lara Croft (she wore the original Ericsson Bluetooth

headset in the Tomb Raider movie), who really cares! However if it turns into a software setup nightmare and I have to read through vast user guides, I would not

be so sure

The medical sector offers many opportunities for Bluetooth technology to add convenience In hospitals, patient medical data could be stored on PDA type devices that would update a central database when brought within range

of an access point (small scale trials for this application in the neurology depart-ment at the University Hospital in Mainz, Germany, have already begun) Wireless foot controls for medical equipment, respiratory monitors that transmit data to a PDA rather than a body-worn data collection system, ambulatory monitoring equipment for easier patient access in emergency situations… the list goes on The questions of interference and security will need to be

addressed in some of these applications, but if they are not “life-dependant” these issues could be overcome

Regarding the LAN access points, we need to consider the issue of range If the consumer has to get up and walk to be within range, there is no added

con-venience—in fact, it would become very inconvenient A Class 1 Bluetooth

device has a range of approximately 100 meters In reality, this could be much further, which would be viable in an office, home, or a hotel/airport lounge sce-nario, thus making possible the unconscious convenience of the airport check-in and car rental confirmation detailed at the beginning of this chapter

With our own personal “toys” the added convenience is unequivocal Our laptops will be able to play multiuser Quake with our colleagues in the airport or the office! Our PDAs and phones will synchronise with our laptops—gone are the days of database management Our presentations can be shown at meetings directly on the laptops of the attendees without the need for a projector or any worries about forgetting your laptop’s I/O expander

Against this optimistic picture there are a few inconveniences envisaged that will affect the consumer I wouldn’t be happy if my new wireless product spends longer attached to a battery charger than it can be used without one, if the poor placement of an antenna within a handheld product means I had be a contor-tionist to be able to hold it and have it function, or if calls get dropped while waiting for my headset to connect to my phone But the BIG one is inevitably the man-machine interface (MMI)—it must be simple to use, it must be simple to set

up, it simply must be simple: “connect to Adam’s PDA, Petra’s phone, or the

fridge?” Using the word “convenience” in the product marketing blurb is a hollow promise if the consumers requires a software degree to get their new PDA to con-nect to their laptop! If people still can’t program their home AV equipment, how will they know what a windows “system tray” is, where to put a dll file, or where

to find the setup section in their mutlilayered phone menu system?

It is your challenge as an applications writer to make sure that the MMI is usable Succeed and your products could be extremely popular—fail, and your products will likewise fail in the marketplace

Enhancing Functionality

Convenience is one attribute that Bluetooth technology can bring to our prod-ucts, but how else can it benefit us? It can also add enhanced functionality—

features that would not be an implementation consideration in a wired product

Central heating control? A programmable thermostat and a Bluetooth radio inte-grated into the common light switch, this integration would allow the mains wiring to the light switch to power the controller.When the room is at the tem-perature programmed by the user, it connects wirelessly to the boiler in the utility room and can turn the entire system off Alternatively, if each individual radiator is equipped with Bluetooth technology, the controller can connect to each individual radiator and shut the solenoid valve, turning only that specific radiator off! In this application, we can see the enhanced functionality; no addi-tional wiring is required to achieve single room climate control and the humble light switch becomes multifunctional.The Set Top Box that sits anonymously in our TV stand and has been delivering cable channels and e-mail to the TV screen could be made capable of connecting to our laptops, offering us another option

to the modem in our homes

As mentioned earlier, the people who make Nokian tires are adding Bluetooth links to pressure monitors built into car wheel rims.This is a good application since the data could not easily be transferred by other methods: wire and optical wouldn’t work, other radio technologies are too expensive, and being able to remotely read tire pressure is a real gain in functionality

Bluetooth technology in our digital cameras and mobile phones will provide

us with the ability to send the “instant postcard” shown in Figure 1.5.This could become almost as popular as Short Message Service (SMS) text messages.We take

a picture with our camera, which instantly transmits the photo to our mobile phone that has a connection to the Internet via the Global System for Mobile

Communication (GSM) network From there, the picture is sent over the

Internet to our friend’s PC It’s a simple process which adds a new dimension to both products

What if our gas and electricity meters could be read by the utility’s serviceman simply by walking into the foyer of an apartment block and connecting to each apartment’s meters individually to determine utility consumption? Not having to knock on each door would improve the efficiency of the job function but would inevitably mean that fewer personnel were required.With an application of this type, the cost implication and durability of Bluetooth technology comes to the fore.The ubiquitous gas and electricity meters have to last a long time, far longer than our favourite mobile phone or PDA which we change according to personal taste or consumer trends.The cost of replacing the meter infrastructure in our homes far exceeds the overhead of including Bluetooth technology, something which makes utility companies adverse to new technologies Experiments have been conducted, but so far there has been no serious uptake

Figure 1.5 The “Instant Postcard”

GSM Internet

With our children’s toys, the possibilities become endless Big soft toys are able to communicate with PC games allowing for communication and interac-tion external to the PC Multiplayer handsets for our Playstainterac-tions become pos-sible without a mass huddle around the console and the constraint of the cable length Action figures and robotic toys could be remotely controlled from a PC,

or could transmit pictures from a camera accessory to the PC

Far more serious is the added functionality that can be provided for the dis-abled consumer, a headset could provide a life enhancing benefit to the physi-cally compromised user—voice control for their heating, lights, AV, and security systems—allowing control from anywhere in their home Wireless Internet access can also be of benefit For instance, the National Star College in Cheltenham, UK has just installed a Red-M Bluetooth network to allow their disabled students to wirelessly access online resources and submit their course-work directly from their laptops Discrete intelligent proximity sensors commu-nicating with a headset could help the visually compromised, or a vibrating dongle could indicate to a deaf consumer that the doorbell is ringing or could

be programmed to vibrate on other sound recognitions All of these applica-tions simply extend the functionality of conventional products by being Bluetooth-enabled

Do You Have Time?

Okay, so we’ve decided we want to be wireless.We “must have” Bluetooth tech-nology in our next product.The consumer market is not quite sure why they want it yet, but they do, so the first and most difficult hurdle is over with But what do we need to do? And how long will it take? Both of these are serious questions After all, implementing any new technology often incurs risks that may outweigh the advantages of the technology itself

First of all, the Bluetooth Specification by the Special Interest Group (SIG) is

an extremely comprehensive document, which needs to be digested before any form of implementation can begin Both the hardware and software implementa-tion are required in order to adhere to this specificaimplementa-tion and be able to utilize the intellectual property (IP) contained within it It is essential to stick with the spec-ification to be able to interoperate with any other Bluetooth device irrespective

of manufacturer or solution provider; interoperability is the “key” to consumer uptake of Bluetooth technology and the realization of the Bluetooth Dream

Going up the Bluetooth learning curve can take significant time Courses are

available which make it easier, but you must still allow significant learning time in your development cycle

If you are late in the product implementation cycle, you may not have time

to build in Bluetooth technology Or you may not have enough market infor-mation to reassure yourself that it will add sufficient value to justify the cost of shipping Bluetooth components in every product Many early adopters initially added Bluetooth technology to existing products as “add-ons,” either as dongles

or accessories to battery packs—mobile telephones being the principal

example

Using an “add-on” strategy allows you to decouple the Bluetooth develop-ment from your main product developdevelop-ment.This means that you do not risk the Bluetooth development holding up your product launches Since consumers can buy mobile phones, laptop computers and access points with Bluetooth tech-nology fully integrated, this shows that the risks can be conquered successfully Devices which implement Bluetooth technology as an “add-on” are likely to be less attractive to consumers when competing with built-in devices So, when considering whether to build in or add on, you must survey the competition and decide whether your launch date means an “add-on” will not be as lucrative There is more to consider than the time to develop and manufacture your product For any Bluetooth design to be able to display the Bluetooth logo, the design has to undergo a stringent qualification procedure and pass a vast array of tests on every aspect of the system from the radio, baseband, and software stack through to the supported profiles.This is achieved at a Bluetooth Qualification Test Facility (BQTF) Such test facilities can now be found globally, though they are becoming exceptionally busy and require booking many weeks in advance In addi-tion to the Bluetooth Qualificaaddi-tion Program, product developers and manufacturers are required to meet all relevant national regulatory and radio emissions standards and requirements.This involves going through national type approval processes which vary from country to country Qualification and type approval can signifi-cantly delay product launches, so they MUST be allowed for in your schedule

Investigating Product Performance

In some of the applications previously mentioned, we can see that the many ben-efits of Bluetooth technology may outweigh the limitations, nevertheless we have only examined the subjective questions of added value and enhanced function-ality Now it’s time to consider in depth some of the technical limitations that

may actually influence our choice of adding Bluetooth technology to our prod-ucts, despite the much desired benefits

In this section, we shall look at connection times, quality of service in con-nections, voice communications, and the various sources of interference

Evaluating Connection Times

As we have mentioned, Bluetooth devices can’t connect instantly It can take up

to ten seconds to establish a Bluetooth link (although this is not a typical figure;

tests with BlueCore chips show that 2.5 seconds is far more common).The con-nection time overhead is a limitation that could have serious consequences if you require an instant connection—a “panic button” would not be a viable applica-tion for Bluetooth technology.We will examine why and how this overhead can

be reduced with a “known device” connection

Wired networks are for the most part static Components of the network are connected together with cables, and once connected, normally remain in the same position A printer that was available on the network yesterday is expected

to still be available tomorrow However, you do have the initial overhead of con-figuring your PC to use it, the procedure being:

■ Physically connect cables to new device

■ Type in address name on system that needs to use the new device

■ Install drivers and configure software on system which needs to use new device

Bluetooth piconets are highly dynamic—they change rapidly, with devices appearing and disappearing.The members of a piconet may change, or the whole piconet may be dissolved in a moment In such a dynamic network, it is not viable to spend significant time acquiring information about devices and config-uring software to use them: this process must be automatic.The Bluetooth core specification provides this automatic discovery and configuration For a Bluetooth device, the steps to using a new device are:

■ Perform device discovery to find devices in the area

■ Perform service discovery to get information on how to connect to ser-vices on each device discovered

■ Choose a service to use, and use information obtained during service discovery to connect to it

Potentially, the user could simply select the option to print, and the processes

of device discovery, service discovery, and connection could happen automatically without further intervention from the user.The application software should pre-sent this to us transparently, but it is still a worthwhile exercise to understand the complete procedures; they are covered in the following sections

Discovering Devices

Before any two devices can go through device discovery, they must be in inquiry and inquiry scan modes.The inquiring device must be trying to discover

neigh-bouring devices, and the inquiry scanning device must be willing to be discov-ered (see Figure 1.6)

The inquiring device transmits a series of inquiry packets.These short packets are sent out rapidly in a sequence of different frequencies.The inquiring device changes frequencies 3200 times a second (twice the rate for a device in a normal connection).This fast frequency hopping allows the inquirer to cover a range of frequencies as rapidly as possible.These packets do not identify the inquiring device in any way; they are ID packets containing an inquiry access code which inquiry scanning devices will recognize

Figure 1.6 Bluetooth Device Discovery

I am in inquiry scan mode

I am in inquiry scan mode

I am in inquiry mode

Inquiry Inquiry response

Inquiry Inquiry response

I see a phone and a PDA

The inquiry scanning device changes frequencies very slowly: just once every 1.28 seconds Because the scanner changes very slowly while the inquirer changes rapidly, they will ultimately meet on the same frequency

Scanning devices cannot stay on a fixed frequency, because any frequency chosen might be subject to interference, but hopping very slowly is the next best strategy for seeking the inquiring device It responds to inquiries by sending a Frequency Hop Synchronisation (FHS) packet, which tells the inquiring device all the relevant information needed to be able to establish a connection

NOTE

To guarantee that the inquiring device can locate all the devices in inquiry scan mode that are within range, the Bluetooth Specification defines an inquiry time of 10.24 seconds.

When a device that is scanning for inquiries receives an inquiry, it waits for a short random period, then if it receives a second inquiry, it transmits a response back It does not transmit this response immediately, because this may lead to all devices in a single area responding to the first inquiry sent out, causing an unde-sirable high-power coordinated pulse of radiation in the ISM band.The random delay prevents this coordinated effect

Connecting Devices

Before two devices can establish a connection, they must be in page and page scan

mode; the paging device initiates the connection, while the page scanning device responds In order to be able to page, the paging device must know the ID of the page scanning device; it can calculate the ID from the page scanning device’s 48-bit Bluetooth device address.The page scanning device’s Bluetooth device address can be obtained in several ways:

■ From an inquiry response via FHS

■ From user input

■ By preprogramming at manufacture