Investigating BluetoothTM Modules:The First Step in Enabling YourDevice with a Wireless Link

Application Note 1333-2

Introduction

Note: This Application Note is designed for

vendors or manufacturers who plan to add

a wireless link to their products by installing

commercially-available, pre-built Bluetooth

modules into them. It is addressed to a

wide audience working in electronics

whose knowledge and skills may vary, but

assumes no specific knowledge of RF

(radio frequency) techniques.

Bluetooth is an innovative new tech-nology that provides wireless connec-tivity to a growing variety of electron-ic devices—computers, laptops,Personal Digital Assistants (PDAs),peripherals, cameras, cellularphones, pagers, and wireless head-sets. Even use with home appliancessuch as refrigerators has beenexplored. With Bluetooth technology,small transceiver modules can bebuilt into a wide range of products,allowing fast and secure transmissionof data and/or voice within a givenradius (usually 10 meters). Cablesmay soon be a thing of the past-forthe first time ever, personal area net-works can be created on an ad hoc orsemi-permanent basis without cablesor connectors and network adminis-tration problems.

Bluetooth operates in the 2.4 GHzISM (Industrial, Scientific, andMedical) band, an unlicensed portionof the spectrum that is already well-used. Not only do microwave ovensoperate within this range, but otherRF communications technologies aswell, most notable of which areHomeRF and IEEE 802.11b. Becausethis spectrum is unlicensed, evenmore uses for it are expected to bedevised in the future. As the bandbecomes more widely used, radiointerference will increase. To counterthis interference, Bluetooth technolo-gy incorporates several techniques toprovide robust linkages. Among theseare cyclical redundancy encoding,packet re-transmission, and frequen-cy hopping which can occur up to1600 times per second.

Originally conceived as a cablereplacement, Bluetooth will obviouslybecome much more as users continueto increase their reliance on informa-tion transfer and connectivity.Bluetooth is estimated to be installedin more than a billion devices by theyear 2005! And it seems it is here tostay. It is currently the fastest-grow-ing standard in the electronics indus-try. In short, Bluetooth technology isa key component of the wirelessfuture (Figure 1).

Installing pre-built Bluetooth mod-ules, as opposed to creating wireless

capability from scratch, has theadvantage of requiring fewerresources, allowing shorter develop-ment times and enabling faster time-to-market. This option allows compa-nies to gradually develop competencein installing Bluetooth modules whilealso gaining experience in marketingwireless products-or, alternatively, to leverage the expertise of theirBluetooth suppliers in enabling their products with a wireless link.

The purpose of this publication is toguide you on how to analyze Bluetoothmodules, to discern which one will be

most suited to your type of device,and to anticipate the kinds of issuesyou could encounter in integration.By anticipating, investigating, andunderstanding these issues, you’ll bein a much better position to integrateBluetooth modules into your deviceswith a minimum of time, engineeringeffort, and cost. However, with a fast-changing technology such asBluetooth, no publication can coverevery contingency, so guidance at thispoint must be very general.

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Figure 1. Bluetooth will connect together a growing universe of wireless devices.

Introduction 1

1. The Bluetooth Module 4

2. Type of Device 5Category 1: Adapters 5Category 2: Appliances 5Category 3: Embedded Systems 5Category 4: Mobile Phones 5

3. Module Specification Issues 63. 1 Module Capabilities 6

Size 6Operating Temperature Range 6Operating Range 6Profile/Maximum Data Throughput/

Packet Type 6Sensitivity 6Radio Performance 7

3.2 Physical and Electrical Characteristics of Module 7

Physical Characteristics 7Electrical Characteristics 7

3.3 Module Test Tools 8Test Access Points 8Test Mode 8

3.4 Regulatory Approval 9

4. Pre-integration Factors 104.1 Power Supply and Battery 10

Battery Life 10Power Consumption 10Power Supply Noise 10

4.2 Radiated and Conducted Interference 10

Step 1. Analysis with a BluetoothTest Set 11Analysis in Normal Mode 11Analysis in Test Mode

(Transmit Mode) 12Analysis in Test Mode

(Loopback Mode) 13Important Note:

Link Establishment Problem 13Step 2. Analysis with a Bluetooth

Test Set and Spectrum Analyzer 154.3 Bluetooth Interference with “Host” 154.4 Antenna Radiation Pattern 16

Appendix A : Agilent Test Equipment for BluetoothTechnology 17

Appendix B : References 19

For More Information 20

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Table of Contents

A Bluetooth module consists primari-ly of three functional blocks—a RFtransceiver unit, a baseband link controller unit, and a support unit forlink management and host controllerinterface (HCI) functions (Figure 2).Another functional component is ofcourse the antenna, which may beintegrated on the PCB or come as astandalone item. A fully implementedBluetooth module also incorporateshigher-level software protocols(which can be resident in flash

memory) which govern functionalityand interoperability with other mod-ules. All Bluetooth modules havethese same functional blocks, but dif-ferent vendors’ implementations willhave different attributes such as sizeand degree of integration in silicon(e.g., single-chip solution vs. two ormore chips).

The RF Transceiver specificationdefines the frequency bands, channelarrangement, and transceiver charac-teristics of a Bluetooth system. The

Baseband Processor specificationdefines packet formats, physical andlogical channels, plus the differentmodes of operation which supportthe transfer of voice and databetween devices. The Host ControllerInterface (HCI) provides a commoninterface between the Bluetoothmodule and the host.

Bear in mind that all Bluetooth mod-ules will need to pass the SIG qualifi-cation test, but this does not meanthat they will all have the same characteristics.

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1. The Bluetooth Module

Figure 2. Block diagram of a Bluetooth module, with two models shown.

The target application for yourBluetooth module will be your firstconsideration. Quite simply, in whatkind of device will you install yourBluetooth module? The usage modelof the device will largely determinenot only the electrical and physicalenvironment in which the module isplaced, but the primary factors toconsider for integration as well.Among the growing classes ofBluetooth enabled devices are these:

Category 1: Adapters

PCMCIA card, compact FlashBluetooth card, USB Bluetoothadapter, RS-232 Bluetooth dongle,Bluetooth printer port converter, etc. Such devices will allow you toadd a wireless link to your existingdesktop PC, laptops, personal digitalassistants (PDAs), printers, etc. withBluetooth technology.

Category 2: Appliances

Wireless headsets which send andreceive audio signals to and fromphones, cell phones, computer audio,MPEG players, home entertainmentcenters, etc., and computer peripher-als such as keyboards, mice, joysticks,speakers and the like.

Category 3: Embedded Systems

The device will normally be a comput-er or peripheral, but in this case theBluetooth module will be built direct-ly into the device without using theinterfaces of Category 1.

This category can include desktops,laptops, PDAs, or even printers, scan-ners and fax machines. Obviously, itcan overlap with Category 2 or 4. PCseventually will have Bluetooth cir-cuitry directly on the motherboard.

Category 4: Mobile Phones

Bluetooth capability can be added tomobile phones in several ways—forexample, via battery packs, adapters,or direct integration into the host.Hence this category can be a specialinstance of Category 1 or Category 3but because of the expected marketpenetration, is treated as its ownclass.

Having a full understanding of thedevice you plan to convert to wirelesswill make it easier to define the speci-fications of the Bluetooth module youneed, what performance factors youshould consider, and what kind oftests you may need to perform.

The following table (Table 1) providesan overview of some module specifi-cation and pre-integration issues youshould consider and analyze inpreparing for proper integration of amodule into your device. The list isnot meant to be exhaustive. Pleasenote that specifications can be pro-vided by the manufacturer, whileanalysis of pre-integration factorsmay require specific measurements to be performed.

We will now look at these topics inmore detail.

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Table 1. Module Specification Issues and Pre-integration FactorsBy Bluetooth Device Category

Category 1 Category 2 Category 3 Category 4

Module Specification Issues-Information can be provided by your supplier.

Size

Operating Temperature Range

Operating Range

Sensitivity

Profile /Maximum Data Throughput / Packet Type

Radio Performance

Physical & Electrical Characteristics

Test Mode

Test Access Points

Regulatory Approval

Pre-integration Factors-Analysis may require you to do specific measurements.

Battery life

Power consumption

Power supply noise

Radiated interference

Conducted interference

BT interference with “host”

Radiation pattern

indicates that you should analyze this specification or pre-integration factor. indicates that you should think about it. indicates that you need not be concerned with it.

2. Type of Device

Technical performance specificationsof a Bluetooth module will usually beprovided by a vendor’s data or specsheets. The specifications mentionedin this section should be consideredin detail to ensure proper operationof the module in your final device.

3.1 Module Capabilities

Size

Obviously, a Bluetooth module mustfit physically into its host device,preferably with as little modificationto device design and manufacture aspossible.

Operating Temperature Range

The behavior of a module, and conse-quently of your device, can be affect-ed by high temperature (coming froma power supply, as in Category 1 and3) or by low temperature (mobilephone used in a really cold environ-ment, Category 4). Temperature canhave a different effect depending onthe electrical characteristics of themodule (analog or digital design).Digital circuits will make occasionalerrors at high and low temperatures,and eventually cease to functionwhen temperature stress is sufficient.With analog circuits, such as RFamplifiers and voltage controlledoscillators (VCOs) etc., degradation is likely to be more gradual and con-tinuous. If, for example, a referenceoscillator in the transmitter or receiverdrifts, it may not seem to affect theworking of the module at all. However,the bit error rate (BER) of the linkmaybe greatly affected, since thetransmitted frequency has drifted.That is why it is important to check to see if the Bluetooth module has the right temperature specificationsto support the temperature of theenvironment of your device.

Operating Range

Bluetooth modules transmit between10cm and up to 100m according totheir Transmit Power Class: PowerClass 1 (+20dBm max power, 100mmax range), Power Class 2 (+4dBmmax power), Power Class 3 (0dBmmax power, 10m max range). Be sureto check that the module you’re con-sidering will operate over the rangeyou need. You should not use a PowerClass 1 module if you want to maxi-mize the battery life of your device(Category 2 and 4). On the otherhand, it may be exactly the powerclass you want if a maximum range is required.

Profile/Maximum Data Throughput/Packet Type

The usage model of your device willdetermine the appropriate profile(Reference 2) you should pursue. Theprofile will determine the type of datatransfers likely—for example, a printerwill not use voice data transmissionand will likely run in asymmetricalmode.

With profiles, the issues of syn-chronous vs. asynchronous as well as symmetrical vs. asymmetrical linkswill be raised. The asynchronouschannel can support an asymmetriclink of 721kB/s maximum in eitherdirection, while permitting 57.6kB/sin the return direction, or 433.9kB/ssymmetric. The synchronous channelcan support 64kB/s in each direction.

For synchronous links, reserved forsynchronous voice connections, somesubjective listening tests (Reference4) indicate that the HV3 packet typeis the most robust.

Similarly, for asynchronous links,reserved for data connections, someanalyses (Reference 4) show the following:

• DH5 packet type is best for low levels of interference

• DH3 packet type is best for themajority of interference

• DH1 packet should be used only inlow bandwidth (<200kB/s) applica-tions

Thus, depending on the type of deviceyou intend to enable, it is importantto know if your Bluetooth module will provide you with the right datathroughput and support the rightpacket type.

For details about the definition of the different packet types, refer toSpecification of the Bluetooth System(Reference 1).

Sensitivity

Sensitivity of the product enabledwith Bluetooth technology may be amajor issue confronting a productdesigner. Sensitivity specifications of a Bluetooth module are likely to be under optimum conditions—anyimplementation will probably resultin a degradation in the sensitivity fig-ure as specified for the module itself.Real-world operating conditions bothinside and outside the device—such as high RF noise, metallic shielding,or high temperatures-can badlyreduce sensitivity.

Some Bluetooth modules may actual-ly exceed the Bluetooth specificationfor sensitivity, but check to see thatthis is not compromised as you pro-gressively integrate the module intoits host device. Sensitivity should beverified not only at the outset, butthroughout the integration and testcycle of the device. Various tests canbe performed to analyze and antici-pate the degradation of the sensitivityof the module during implementationand determine if the module still meetsthe sensitivity specifications goal forthe target device (see “Pre-integrationFactors,” Part 4.2, “Radiated andConducted Interference”).

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3. Module Specification Issues

Radio Performance

If the information is available, youshould check the radio interferencerejection of your module. This specifi-cation can vary depending on howthe radio receiver was designed. Theperformance specified by theBluetooth Special Interest Group(SIG) (Reference 1) is:

• Co-channel interference: 11dB Interferer is in the same channel at 11dB below the wanted signal.

• Adjacent channel interferencerejection: 0dB Interferer is in the adjacent channelat the same power level as thewanted signal.

Some Bluetooth modules will havemore robust radio performance thanothers. A high-performance radiomight have the following specifica-tions:

• Co-channel interference: 8dB Interferer is in the same channel at 8dB below the wanted signal.

• Adjacent channel interferencerejection: -10dB Interferer is in the adjacent channelat +10dB above the wanted signal.

Example: Using these two levels ofperformance as an example, anexperiment (Reference 4) was done inwhich the following measurementswere taken:

• Degradation of link performance in the presence of interference

• Throughput in the presence of aspecific amount of interference

• Throughput as a function of range

The results were as follows:

• The number of piconets that couldbe established before the aggregatethroughput started to decrease wasimproved from 20 (with a standardradio) to 40 with the high-perfor-mance radio.

• Throughput performance in thepresence of interference was sub-stantially increased

• The maximum range doubled

These differences show that it isessential to consider radio interfer-ence rejection specifications in char-acterizing a Bluetooth module.

If, for any reason, these specificationsare not provided by a supplier, youcan determine them by performing aC/I (Carrier-to-Interference) perfor-mance test. C/I performance is mea-sured by sending co-channel or adja-cent channel Bluetooth modulatedsignals in parallel with the desiredsignal and then measuring the receiv-er’s BER. This test can be accom-plished by using two signal genera-tors, both supporting Bluetooth capa-bilities and one supporting BER mea-surement (for example, an AgilentESG-D series signal generator withoptional Bluetooth personality andinternal BER analyzer). For moreinformation, refer to AgilentApplication Note # AN 1333,Performing Bluetooth RFMeasurements Today (Reference 5).This test could also be performed byusing a Bluetooth test set (for exam-ple, Agilent E1852A) for the desiredsignal and a signal generator for theinterfering signal.

3.2 Physical and ElectricalCharacteristics of ModuleEven if physical and electrical charac-teristics are not primary issues indeveloping your device, you should be aware of them in consideringBluetooth modules.

Physical Characteristics

Some Bluetooth suppliers have chosento adopt a multi-chip design, employ-ing CMOS devices for the basebandDSP and microcontroller and bipolardevices for the RF functions. Othervendors have taken a radically differ-ent approach with a complete, single-chip Bluetooth solution fabricatedentirely in CMOS. You should beaware of the physical characteristicsof your module in case you experi-ence problems during or after manu-facturing test—how easy will it be torepair or replace the module, assuminga cheap replacement is not available?

More significantly, you will noticethat physical characteristics will havean influence on electrical characteris-tics of your module. For example, tobe able to increase the level of circuitintegration, several designers havechosen a quadrature mixing design(IQ modulator/digital demodulatordesign), moving signal processing intoDSP and away from analog circuits.

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Electrical Characteristics

Bluetooth radios cover a wide rangeof electrical design, from direct fre-quency modulated VCO/analog dis-criminator (Figure 3) to IQ modula-tor/digital demodulator designs(Figure 4). Each design can have dis-tinct advantages, such as better inter-ference rejection or longer battery lifeor simply early delivery. While eachsupplier will certify its Bluetoothanalog and digital modules, the testresults you obtain may be different.

That is why it is so important tounderstand what normal stand-alonemodule behavior looks like—beforeintegrating it into your device. Forexample, if you check the modulationcharacteristics (Initial CarrierFrequency Tolerance and FrequencyDrift) of an IQ modulator/digitaldemodulator design, you may noticethat the signal looks bumpy due to IQimbalance (Figure 6, page 9). This isnot likely to happen with a frequencymodulated VCO/analog discriminatordesign (Figure 5, page 9).

3.3 Module Test ToolsTo be able to test the module (if need-ed) and your device after integration,you should check which access pointsare available on the Bluetooth moduleand if the module supports “TestMode”.

Test Access Points

Access points are typically the HostController Interface (HCI), the RFInterface, and the RF-to-BasebandController Interface. Access pointscan be provided by either hardwareor software.

If you want to perform certain testson the module (for instance, analyz-ing pre-integration factors, as in Part4), you should make sure that you atleast have access to the RF interface(via an RF connector if possible). Ifyou don’t have a module fixture, youcan check with the module manufac-turer to see if an evaluation board isavailable to test the module in yourdevice’s environment. Some compa-nies are providing these for earlystages of integration.

Test Mode

Test Mode gives you the choice ofhaving a Bluetooth module transmit a defined packet (Transmit Mode) orretransmit received data (LoopbackMode), with control of differentparameters such as bit pattern, fre-quency selection, Tx frequency, andpoll period. Having this capabilitywill make the detection of problemseasier and will expedite testing ofboth the Bluetooth module and fin-ished device. Test Mode should besupported by any Bluetooth module,since it is mandated in the Bluetoothspecifications. It could be, however,that some modules do not yet supportthis feature.

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Figure 3. Direct frequency modulated VCO/analog discriminator block diagram.

Figure 4. IQ modulator/digital demodulator block diagram.

3.4 Regulatory ApprovalThe type of regulatory approval usedto certify the module is not exactly amodule specification issue, but it is a factor that you should take intoaccount for future tests and certifica-tion of your device. You must knowwhich regulatory agencies and certifi-cation bodies a supplier has consult-ed to certify his Bluetooth modules.For example, modules destined forthe European Union (EU) must com-ply with the RTTE Directive (RadioTelecommunications TerminalEquipment), while the FCC (FederalCommunications Commission) and a Telecommunications CertificationBody (TCB) must be consulted for thecertification of modules destined forthe USA. Each certification agencywill have its own regulatory require-ments. Hence, when you choose yourBluetooth module, it is your responsi-bility to know the various global regu-latory requirements and adhere tothem in marketing your Bluetoothdevices.

By evaluating all of the specifications,you will know, or at least have a bettergrasp of, which Bluetooth module(s)is best adapted for your device.Knowing the module has been certi-fied by the supplier and works asspecified, you should be ready to inte-grate the module into your device.

However, to make an even moreinformed choice, or to anticipate thekinds of problems that can occur dur-ing integration, some pre-integrationfactors should also be analyzed.These factors are primarily powersupply noise, power consumption,battery life, radiated and conductedinterference, Bluetooth interferencewith “host,” and antenna radiationpattern. You should investigate thesefactors prior to integrating aBluetooth module into your device.Part 4 will provide you with moreinformation about these factors andthe type of measurements you mayperform.

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Figure 5. Agilent E1852A display showing a modulation measurement of a Bluetoothmodule designed with a direct frequency modulated VCO/analog discriminator.

Figure 6. Agilent E1852A display showing a modulation measurement of a Bluetoothmodule designed with IQ modulator/digital demodulator.

Pre-integration factors cannot be analyzed just by reading the moduledatasheet or information which thesupplier provides. If you want to opti-mize their analysis and anticipate theproblems that could be generatedduring your integration, you will needto perform certain measurements. Asmentioned before, the list of pre-inte-gration factors is not intended to be acomplete list of all the issues that youshould investigate to ensure that theBluetooth module you’re consideringwill work after integration into yourdevice. But it is an excellent place tostart.

4.1 Power Supply and Battery

Battery Life

If you are adding Bluetooth capabilityto a battery-powered device (Category2 and 4), it is important to know howvarious Bluetooth modules will beaffected by battery conditions. Byusing a DC source that can duplicatethe performance of your device’s bat-tery, you can analyze the behaviorchanges of a Bluetooth module usinga signal analyzer (see Figure 7 for anexample of measurement setup andFigure 8 for a list of parameters thatcould be analyzed).

Power Consumption

The data sheets of Bluetooth modulesshould provide you some standardpower consumption characteristics.However, it could be that they willnot provide some specific characteris-tics, such as peak power consumption.

Some DC sources will have the capa-bility of doing current measurements.With this feature, you can analyzehow much current the Bluetoothmodule consumes, what its peakpower consumption is, and, based onthe result, determine if the battery orpower supply of your device will han-dle that peak consumption. If possi-ble, you should ensure that the powerconsumption of the Bluetooth moduleis only a small fraction of that of yourhost device.

Power Supply Noise

A power supply can generate consid-erable RF noise. Hence, it is impor-tant to analyze how the power supplyof your device (Category 1 and 3) willinfluence a Bluetooth module-forexample, how well your power supplyis decoupled. Measurements of powerversus time during DH5 bursts andcareful monitoring of the frequencyerror measurements (Figure 11) canuncover DC bias power-related prob-lems. Noise may be seen as a ripple in the Frequency Drift measurement(Figure 10).

Agilent Technologies offers a com-plete line of DC power supplies suit-able for testing these kinds of powersupply/battery issues. The Agilent66319/21 Mobile Communications DC Sources, for example, provide features designed specifically forwireless testing. These include fasttransient response and low-currentmeasurement capability (useful forevaluating current consumption), aswell as programmable output resis-tance that allows you to do accurateemulation of particular battery characteristics.

4.2 Radiated and ConductedInterference Keep in mind that the Bluetooth mod-ule you’re going to buy has been certi-fied and works in stand-alone mode.Your goal should be to determine ifthe module still works properly in theenvironment of your device. Hence,you must try to determine the type ofinterference the device and its largerenvironment can create. Radiatedinterference can come from virtuallyanywhere—a system working in theISM band IEEE 802.11b, HomeRF,microwave ovens, etc.); a systemworking in another band (GSM,UMTS, etc.); a power supply; LocalOscillators (LOs) of a cell phone; ordigital noise of a PC, PDA, or otherelectronic device.

Conducted interference can comefrom a power supply, clock circuit, orother application components. If yourdevice is a PCMCIA card, data busescan interfere, and more generally,digital control lines. Long cablesbetween modules can also be path-ways for conducted interference.

The ideal situation would be to simu-late your device’s total working envi-ronment, which is very complex.More realistically, you should try toplace the Bluetooth module in yourhost device (via a fixture) and get thedevice to do some “work.” For exam-ple, if your device is a mobile phone,make a telephone call. If your deviceis a PCMCIA card, calculate somelarge numbers in Excel, start a videosignal, or download a file over theLAN. The idea is to get the host toproduce as much electrical noise aspossible consistent with its normaloperation.

Then, to optimize the analysis of themodule’s behavior in your device, youcould perform the following steps:

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4. Pre-integration Factors

Step 1. Analysis with a Bluetooth Test Set

Analysis in Normal Mode

• With a Bluetooth test set, establisha normal link with the Bluetoothmodule via a wire (or antenna ifthe wire connection is not possible)(Figure 7).

• Analyze the results. For instance, if you use the Agilent E1852ABluetooth Test Set, check to see ifthere are any red bars shown onthe Measurement Summary win-dow (Average Power, Peak Power,Frequency Offset, FrequencyDeviation, Frequency Drift, PacketError Rate; see Figure 8).

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Figure 7. Setup of normal link between an Agilent E1852A Bluetooth Test Set and a Bluetooth moduleplaced in its device environment.

Figure 8. The Agilent E1852A Bluetooth Test Set features a Measurement Summary window which offers instantaneous readouts of each measurement parameter, pluseasy-to-read pass/fail indicators.

Pass/fail:Green/red indicator

• Then drop the power and see if thePER (Packet Error Rate) gets affect-ed at the expected level. This testwill allow you to check how muchthe sensitivity of the module hasbeen degraded by implementing itinto your device environment.

• Analyze the “Power versusChannel” measurement and checkto see if all the channels have beenused. They should be equally usedif you have a wire connection(Figure 9).

If you notice any errors or anomalies,investigate them by analyzing theBluetooth module in Test Mode(Transmit and Loopback Modes).

Analysis in Test Mode (Transmit Mode)

Go to Test Mode and get the moduleto transmit 11111111 on a DH5 pack-et if possible. Using the longest pack-et with a bit pattern of Constant Onewill make the analysis of results easi-er. You should look for evidence of a ripple on the modulation graph(Figure 10). Similarly, bad numericresults for Frequency Drift orFrequency Deviation could indicateproblems (for this measurement youwill need to use a bit pattern suchas11110000 or 101010101; see Figure11). The main VCO is usually sharedbetween the transmitter and receiverpaths. If you don’t get errors inTransmit Mode, it will probably meanthat you will not get errors in thereceiver tests (Loopback mode).However, there may be other ways inwhich conducted interference couldget into the demodulated signal.

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Figure 9. Agilent E1852A display showing a repartition of the power on the 79 Bluetoothchannels.

Payload—No ripple

DH5 Packet—2870µs

Figure 10. Agilent E1852A display showing a modulation analysis (frequency versustime). Setup uses a DH5 packet with a bit pattern of Constant One and a maximumlength payload (339).

Figure 11. Agilent E1852A display showing the parameters ICFT (Frequency Offset),Frequency Deviation, and Frequency Drift which you should analyze.

Analysis in Test Mode (Loopback Mode)

Go to Loopback Mode and perform aBER measurement. Drop the powerlevel down and see if the sensitivity isas good as it was when you measuredthe module by itself (Figures 12 and13). If it is not, it indicates that aradiated or conducted signal isdesensitizing the receiver.

Important Note: Link EstablishmentProblem

In performing someof the tests above,you may experienceproblems in theestablishment of a link between theBluetooth moduleand the Bluetoothtest set. This could be due to either ahardware problem or firmware prob-lem with the module (for example,the Bluetooth module version maynot be consistent with the version ofthe tester).

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Figure 13. Graphics (in linear and logarithmic scale) of a Bluetooth module’s BER measurement as a function of received power level

Figure 12. Picture of three Agilent E1852A displays showing a BER measurement done at three different power levels (-35dBm, -69dBm, -75dBm)

Power level = -35dbm

Power level = -69dbm

Power level = -75dbm

BER=0.1%

Sensitivity=-82dBm

To detect where the problem comesfrom, you can use the “Test facilities”utility of the Bluetooth module (if it is implemented). This utility has theability to make the Bluetooth moduleact like a transmitter or like a receiver.By putting the module in the transmitmode, you can check to see if aBluetooth signal is being generated by the module. The measurement canbe performed using a spectrum ana-lyzer supporting a Bluetooth person-ality (for instance, Agilent ESA series

with Option 303 or 304) or an AgilentE1852A Bluetooth Test Set by usingits “RF-Analyzer” capability. Usingthis capability will provide you thesame measurement parameters youget when you establish a real link(Figure 14).

You can also use the utility to makethe module act as a receiver. In thiscase, you could generate a Bluetoothsignal using a signal generator, injectthe signal into the Bluetooth module,and read the BER measurement with

the utility. By performing this test,you’ll have a good idea whether theproblem comes from the module’shardware or its firmware. If you don’tget a problem in using this utility butthe measurement results are wrong, it means that you probably have afirmware problem. Conversely, if youcan’t generate or receive a signalusing this utility, you probably have a hardware problem.

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Figure 14. Agilent E1852A display showing “RF-Analyzer” menu and a list of measurement parameters you get by using this menu.

Channel 17:2402+17=2419Mhz<freq<2042+18=2420MhzFrequencyBand including 2418.6Mhz (product of the 17.4Mhz main systemreference frequency)

Frequency HoppingOFF

Figure 15. Agilent E1852A display showing configuration of the Test Modemenu for a single frequency in Channel 17.

Step 2. Analysis with a BluetoothTest Set and Spectrum Analyzer

If you have a spectrum analyzer, usea close field probe to check your hostdevice for main system reference frequencies, using the device’s blockdiagram as a guide. Once havingdetermined a frequency (for example,17.4MHz), multiply it by a number nso that it falls within the 2.4GHz(2402-2483.5MHz) band. (For exam-ple, 17.4MHz x 139 = 2418.6MHz).Repeating this procedure, find all ofthe odd harmonics of each referencefrequency within the band (they havea larger influence than even harmon-ics). For each calculated frequency,configure the Bluetooth test set toestablish a link in Test Mode (fre-quency hopping OFF, see Figure 15,page 14) with the desired channeland see if there is any change in thebehavior of the Bluetooth module.For any given system reference fre-quency, you may need to test severalfrequencies in the 2.4GHz band. Forexample, there are two odd harmonicsof 17.4MHz within the 2.4GHz band:2418.6MHz and 2453.4MHz, n being139 and 141.

This test provides another way foryou to see if radiated and conductedinterference coming from your devicewill affect the Bluetooth module.

4.3 Bluetooth Interference with “Host”Bluetooth module behavior can beaffected by the environment of itsdevice, and conversely, RFI (radiofrequency interference) from theBluetooth module can affect the per-formance of the host, especially if itgenerates its own RF emissions orhas its own receiver (e.g., cellularphones).

By having been certified, a Bluetoothmodule should have passed “out-of-band spurious emissions” tests. Thesetests involve measuring conductedemissions (antenna or output connec-tor) and radiated emissions generatedby the Bluetooth module. The exactspecifications the module must meetwill depend on where it is used, e.g.,USA or Europe (see Part 3.4,“Regulatory Approval”).

Ordinarily, a certified Bluetooth mod-ule should not affect your host device.However, if your device has a receiverand you have a spectrum analyzer, itis beneficial to look for possible spu-rious emissions from the Bluetoothmodule. To do so, establish a normallink between the Bluetooth test set

and the Bluetooth module over theair. And by using a spectrum analyzerwith an antenna (Figure 16), you cananalyze the spurious emission of themodule (Figure 17). An Agilent ESA-E Series will allow you to do somemeasurements up to 26GHz if needed.

The Bluetooth signal shown in Figure17 did not fail the certification test,but obviously multiple signals havebeen generated. You should makesure that these signals will not haveany influence on your device or itsenvironment.

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Figure 17. Agilent ESA-E spectrum analyzer display, showing a spurious analysis in the12.5 GHz band.

Figure 16. Picture of Agilent ESA-E spectrum analyzer receiving a Bluetoothsignal over the air using a RangeStarBluetooth antenna

4.4 Antenna Radiation Pattern As mentioned in Part 1, certain sup-pliers may provide modules with anintegrated antenna. If you choosesuch a module, you should determineif the antenna provided will be appro-priate for your device. Similarly, ifyou choose a module without anantenna, you must decide which typeof antenna you will integrate intoyour device.

A high-quality radio link requires thesufficient link gain and desired pat-tern of radiation. Loss of gain reducestransmitter-coverage area. Alterna-tively, if the loss is compensated byincreasing transmit power, it willreduce the Bluetooth device’s operat-ing time and/or power efficiency.Gain is affected by losses in the cir-cuit, including mismatch loss (forexample, the antenna does not looksimilar to 50 Ω). If the antenna is notplaced close to the power amplifier(PA), losses can occur in the printed

circuit board (PCB) or transmissionline and connector mismatch lossesleading to the antenna.

Gain also varies with the radiationpattern. Radiation patterns oftenhave nulls, or areas where gain is low(Figure 18). For example, a Bluetoothdesktop device should ideally have ahemispherical circularly polarizedpattern, but not all the antennas pro-vide this. This ensures that compati-ble devices will work at any angle andpolarization above the desktop. Theantenna-radiation pattern (and there-fore, gain) is affected by the proximi-ty of other objects. If the antenna isnot placed appropriately, nulls canform so that communication is pooror impossible in certain orientations.

Whether the antenna is integratedinto the module or not, the aboveissues should be checked.

A basic test can be performed todetect radiation pattern problems.

Similarly to the description of Part4.2 tests, put the module into itsdevice fixture and establish a normallink with a Bluetooth test set over theair. Move the Bluetooth device around(if you can!), or the Bluetooth test set,and analyze the power measurement(Figure 19). Check to see if the powerdrops.

16

Figure 18. Example of a radiation patterndiagram: A polar diagram of a dipoleantenna showing area with low gain ornulls.

Figure 19. Graphs showing how a received power signal changes theoretically with distance. Left graph shows the result of twoBluetooth modules placed in a hard-partitioned office. Right graph shows the result of two Bluetooth modules placed in free space.

Test Equipment with Bluetooth Capability

E1852A Bluetooth Test Set

Has the ability to establish a linkusing standard Bluetooth protocoland verify the performance ofBluetooth transceivers.

Signal Generators, ESG-D Series (3-4GHz), Option UND, UN7, UN8

Bluetooth signal for transmitter tests,custom Bluetooth modulated interfer-ence signals for receiver testing,Bluetooth receiver BER analysis.

Spectrum Analyzer, ESA-A Series (3-26GHz), Bluetooth Bundles (Option 303, 304)

Automated “one button” test execu-tion for Bluetooth transmitter mea-surements. Performs a broad range of spectrum measurements.

EPM Power Meter and E9320 Power Sensors

Make quick, easy, and accurateBluetooth transmitter power measurements.

Simulation Software, ADS withBluetooth DesignGuide

Useful software tool for the designand simulation of custom Bluetoothsystems. Pre-defined Bluetooth com-ponent models to speed the simula-tion process. Can be linked with theESG-D Series and 89600 Series.

17

Appendix A. Agilent Test Equipment for Bluetooth Technology

Other Test Equipment

Vector Signal Analyzers, 89400/89600 Series

Versatile and precise signal analysis,with complete Bluetooth transmittermeasurements. Provides modulationquality analysis for Bluetooth signals,including constellation and eye diagrams.

DC Sources, 66319B/D

Fast programmable dynamic DC powersources with battery emulation.

Logic Analyzers, 16700 Series

Provides comprehensive system-leveldebugging for multiple processor/busdesigns.

Mixed Signal Oscilloscopes, 54620Series

Useful for verification and debuggingof Bluetooth baseband signals.

Network Analyzers, 8753E Series

Provides measurement of AntennaVSWR.

Accessories

Oscilloscope Probe–54006A

Passive probes with very low capacitance (0.25pF).

Close Field Probe–11940A

Measures magnetic field radiation up to 1GHz.

Splitter–11667A

Useful for ratio measurements andequal power splitting.

Directional coupler–773D

Useful for monitoring one RF wave-form while two Bluetooth devices areconnected by cables.

Dual directional coupler–772D

Useful for monitoring both RF wave-forms while two Bluetooth devicesare connected by cables.

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The Official Bluetooth Website,www.bluetooth.com. includes informa-tion on Bluetooth history, technology,news, specifications, applications,products, events, and BluetoothSpecial Interest Group (SIG).

1. Specification of the BluetoothSystem - version 1.1, Volume 1“Core”, February 22, 2001-Bluetooth SIG

2. Specification of the BluetoothSystem - version 1.1, Volume 2“Profiles”, February 22, 2001 -Bluetooth SIG

3. Bluetooth Test Specification - RF A:2, 20.B.153/0.9, March 24,2000 - Bluetooth SIG

4. Bluetooth Performance in DenselyPacked Environments, BluetoothDevelopers Conference, 5-7December 2000, San Jose, CA.

5. Bluetooth RF MeasurementFundamentals, Agilent ApplicationNote # AN 1333-1 (lit. no. 5988-3760EN).

6. Bluetooth RF Testing—The RightTest for the Radio Design, Agilentarticle, May 2000

7. Agilent Solutions for BluetoothWireless Technology, brochure(lit. no. 5980-3032EN)

References 4, 5, 6, and 7 are accessible via the Agilent website: www.agilent.com/find/bluetooth

19

Appendix B. References

www.agilent.com

www.agilent.com/find/bluetooth

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