DEPARTMENT OF TECHNOLOGY AND BUILT ENVIRONMENT
ENVIRONMENT
DEVELOPMENT OF AN
EMI MEASUREMENT SYSTEM
Performance Analysis of Bluetooth communication
under noise environment
Javier Ferrer Coll, Félix Pérez Castelló
Sept 2008
Master’s Thesis in Electronics/Telecommunications
Master’s Programme in Electronics/Telecommunications
Examiner: Claes Beckman
Supervisors: Jose Chilo, Peter Stenumgaard
1
AKNOWLEDGEMENTS
First of all we want to thank the people, who have contributed to this work and
supported us during the thesis, specially our supervisors Jose Chilo and Peter
Stenumgaard. But we can’t forget to be grateful to Claes Beckman and Per Ängskog for
all the help offered when we needed it. We have to admit the collaboration of the
“Centre for RF Measurements Technology of Gävle”, where we were working full-time.
We would also like to thank our mates from Sätra, who offered us a good year
and very good moments, and with their support the work for the thesis went smoother
and softer, specially Milena Manceva. And finally we are very grateful for the aid of our
family and their trust in us.
2
ABSTRACT
This thesis is a project carried out at the “Centre for RF Measurements
Technology of Gävle”. The first aim of this work was basically to develop an EMI
measurement system, to that purpose, it has been used an EMI Tester receiver,
Spectrum Analyzer and a broadband antenna. Tables and graphics are shown to provide
the values of the different detectors utilized.
Using this measurement system, an interference file was recorded and then
inserted in a Bluetooth communication model. The interference file was simulated with
Matlab Simulink, to check how the interference affected the communication; the effects
of the signal degradation are presented in a graphic.
Finally a real Bluetooth communication was established using two Bluetooth
modules from Free2Move Company, to prove that the effect of microwave oven
interferences produces the increase of transmission time and therefore decrease the
Throughput.
3
TABLE OF CONTENTS
1
Introduction ............................................................................................... 8
2
Goals ......................................................................................................... 9
3
Theory ..................................................................................................... 10
3.1
EMI Measurement ................................................................................ 10
3.1.1 Introduction ..................................................................................... 10
3.1.2 Antennas.......................................................................................... 11
3.1.3 The Antenna Factor ......................................................................... 12
3.1.4 Polarization, Polar Pattern, and Distance ........................................ 12
3.1.5 Detectors used in EMI measurements ............................................. 13
3.1.6 Receiver Specifications per CISPR 16-1-1: .................................... 15
3.2
Bluetooth ............................................................................................... 17
3.2.1 Introduction ..................................................................................... 17
3.2.2 Bluetooth Transmission Technology .............................................. 18
3.2.3 Frequency Hopping Spread Spectrum ............................................ 18
3.2.4 Radio Characteristics ...................................................................... 19
3.2.5 Modulation Characteristics ............................................................. 19
3.2.6 Time Slots ....................................................................................... 19
3.2.7 Packets ............................................................................................ 20
3.2.8 Error Correction .............................................................................. 20
3.2.9 Bluetooth Version 2.1. .................................................................... 21
4
Results ..................................................................................................... 22
4.1
EMI Test receiver Vs Spectrum Analyzer ............................................ 22
4.2 Simulink, Bluetooth communication under noise environment
simulations .............................................................................................................. 30
4.2.1 Bluetooth 1.0 with different interferences ...................................... 30
4.2.2 Bluetooth Model version 2.1 ........................................................... 32
4.3
5
Real Bluetooth communication under noise environment simulations 33
Conclusions ............................................................................................. 37
4
6
References ............................................................................................... 38
7
APPENDIX ............................................................................................. 41
APPENDIX A: EMI TESTER MEASUREMENTS ....................................... 41
APPENDIX B: M-FILES USED ..................................................................... 42
APPENDIX C: BiLog® ANTENNA 30MHz - 2GHz CBL 6112B ................ 43
APPENDIX D: SIMULINK MODELS ........................................................... 45
APPENDIX E: F2M03GLA BLUETOOTH MODULES ............................... 48
APPENDIX F:
EVALUATION KIT FOR GENERAL PURPOSE
BLUETOOTH™ MODULES DATASHEET.................................................... 50
APPENDIX G: MODULES AND MICROWAVE OVEN EXPERIMENT .. 51
5
LIST OF ABBREVIATIONS
8DPSK (8-Differential Phase Shift Keying)
AC (Alternating Current)
ACL (Asynchronous Connection-less Link)
AF (Antenna Factor)
ARQ (Automatic Repeat Request)
BER (Bit Error Rate)
C/I (Carrier to Interference ratio)
CISPR (Comité Internationale Spécial des Perturbations Radioelectrotechnique International Special Committee on Radio Interference-)
CRC (Cyclic Redundancy Code)
CW (Continuous Wave)
DC (Direct Current)
DQPSK (Differential Quadrature Phase Shift Keying)
EDR (Enhanced Data Rate)
EMC (Electromagnetic Compatibility)
EMI (Electromagnetic Interference)
EN (European Norm)
EUT (Equipment under Test)
FCC (Federal Communications Commission-USA-)
FEC (Forward Error Correction code)
FHSS (Frequency Hopping Spread Spectrum)
FM (Frequency Modulation)
FSK (Frequency Shift Keying)
FTDI (Future Technology Devices International Ltd)
GFSK (Gaussian Frequency Shift Keying)
GPIB (General Purpose Interface Bus)
GSM (Global System for Mobile Communications)
HEC (Header Extension Code)
6
IEV (International Electrotechnical Vocabulary)
IF (Intermediate Frequency)
IMT-2000 (International Mobile Telecommunications-2000)
ISM (Industrial, Scientific and Medical)
MIL-STD (Military Standard)
NFC (Near Field Communication)
PSK (Phase Shift Keying)
RBW (Resolution Bandwidth)
RF (Radio Frequency)
RFI (Radio Frequency Interference)
RMS (Root Mean Square)
SCO (Synchronous Connection-Oriented Link)
SIG (Special Interest Group)
TDD (Time Division Duplex)
TTL (Transistor-Transistor Logic)
UART (Universal Asynchronous Receiver-Transmitter)
UMTS (Universal Mobile Telephone System)
USB (Universal Serial Bus)
WiFi (Wireless Fidelity)
WLAN (Wireless Local Area Network)
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1 INTRODUCTION
Nowadays the EMC (electromagnetic compatibility) has a really big importance
in the market. EMC studies the unintentional, generation, propagation and reception of
electromagnetic energy with reference to the unwanted effects such as energy may
induce, this energy is known as EMI (Electromagnetic Interference). All devices need to
carry out the standard corresponding for the product which is controlled by international
standards. The regulator commission for EMC is CISPR (Comité International Spécial
des Perturbations Radioélectriques), wich imposes the rules to be reliable for the
market.
The thesis is going to show the steps and results of the process to measure the
impulses in a laboratory environment. The measures were taken in ‘‘Centre for RF
Measurements Technology of Gävle’’. EMI measurement system could be used to
check the problems that wireless communications can have in an industrial environment
and also, to give an idea to stall a new wireless systems in companies and hospitals
where sometimes the wireless communications suffers a hard degradation.
The system used to measure the Impulses was composed by EMI Tester,
Spectrum Analyzer and BiLog Antenna. The first step was to connect, configure and
install the software necessary for the measure. Secondly, was to measure the
interference included from 30MHz to 2GHz (range of the BiLog Antenna). The EMI
Tester software provides a graph of the spectrum in different detectors and a list of the
highest peaks.
The second part in the thesis was to simulate a Bluetooth communication under
noisy environment. The tools Simulink from MatLab were used to simulate a
communications with different modulations or systems. These systems were simulated
with the points that the EMI Tester measures. A Bluetooth model from Carl Karlsson
[1] was utilized and improved. The original model from Carl consists of transmitter,
receiver and channel interference; in the new model several noises were inserted in the
channel to study the behavior with different interferences as Microwave Oven, GSM,
WiFi and EMI measurements. On the other hand, the version of the Bluetooth model
provided by Carl Karlsson [1] was 1.0, however the last version of Bluetooth is 2.1 and
it was developed in Simulink.
The third part of our work is in relation with interferences which are produced in
a real Bluetooth communication. By using two Bluetooth models from Free2Move and
Microwave Oven a system was carried out, which shows how the Microwave Oven
affects the communication of theses Bluetooth modules. These two devices work in
ISM-band. This band covers the frequencies around 2.45GHz and it’s free access causes
many applications to use it. The two modules were configured to transfer a file. The
time of the transmission was compared with the measured time by using a Microwave
Oven as interference. There are some conclusion about the throughput and how this
interference affects the Bluetooth communication.
The report is presented in three sections: the theory to understand the basic
concepts, the work made where the results are shown, the conclusion and finally some
future applications to follow the research started in this thesis.
8
2 GOALS
The main goal of this thesis was to design a system which is able to measure an
Electromagnetic Interferences in industrial and other environments. To develop the EMI
measurement system, EMI Tester receiver, Spectrum Analyzer and a broadband antenna
were used. The EMI Tester was made to measure especially EMI emissions; on the
other hand the Spectrum Analyzer has a general purpose.
The results of these measurements are shown with tables and graphs obtaining
the interferences found in the margin with regard to the CISPR they have with
maximum power levels.
Using our system a file with noise has been created within the frequency band
and then used in the simulation model. The spectrum obtained by the EMI Tester and
Spectrum Analyzer is compared and added to simulated system in Simulink. The model
from Simulink consists of a Bluetooth 1.0 communication. The measurements from the
EMI Tester and other interferences are added in the channel checking what happens in
the reception. The Bluetooth model is improved to version 2.1 by changing the
modulator and completing the components necessary for the channel.
With regard to interferences and Bluetooth, to check the communication
between two real Bluetooth modules, interference was created using a Microwave
Oven. The goal of this section is, to prove if the Oven affects the Bluetooth
communication.
9
3 THEORY
This section presents the knowledge which is necessary to understand the
obtained results. The first point consists of the explanation of EMI theory, the principal
concepts about EMI, definitions and classification of EMI. After that there is an
exposition of the antenna used, features, polarization and antenna factor. The detectors
utilized to measure are explained and differentiated by how they work and what limits
for the different frequencies they have.
The second point of the theory exposes the basic concepts of Bluetooth as:
modulation, radio characteristics, Frequency Hopping Spread Spectrum and error
correction. All of the above mentioned is going to help to understand the behaviour of
the results obtained.
3.1 EMI Measurement
3.1.1 Introduction
EMC (Electromagnetic Compatibility) studies the unintentional, generation,
propagation and reception of electromagnetic energy with reference to the unwanted
effects such as energy may induce. This energy is known as EMI (Electromagnetic
Interference, also called radio frequency interference or RFI). There are some kinds of
interferences that can affect the RF, natural interferences, like solar radiation, electrical
storm or atmospheric fields, and the artificial interferences made from human. The
artificial interferences can be divided in conducted and radiated.
The conducted interferences are generated by conductors and the radiated by
electromagnetic fields. There are two different radiated emissions, inductive fields,
nearby sources, and radiation fields, distant sources.
Opposed to conducted interferences the radiated interferences could be found in
all space, therefore is difficult to know the direction of radiated fields, so to obtain the
interference strength an antenna is needed that could measure the field in all the
directions. In our case we are interested in these kind of interference.
Another classification for interferences deals about the features of the signal.
There are two important categories: narrowband signals and broadband signals.
The International Electro technical Vocabulary (IEV) defines a narrowband
disturbance as “an electromagnetic disturbance, or component thereof, which has a
bandwidth less than or equal to that of a particular measuring apparatus, receiver or
susceptible device”. Consequently, a broadband disturbance is defined as “an
electromagnetic disturbance which has a bandwidth greater than that of a particular
measuring apparatus, receiver or susceptible device”.
This means that the classification of a signal as narrowband or broadband is
determined by the occupied frequency spectrum of the signal under investigation,
related to the resolution bandwidth (RBW) of the instrument used for measurement. If
the signal spectrum is completely contained in the pass band of the IF filter, it is defined
as a narrowband signal. See figure 3.1.
10
Figure 3.1. Generic definition of narrowband and broadband signals
EMI is a temporary unstable signal, an impulsive noise which features, so like
narrowband or unpredictable amplitude power are difficult to be measured, but possible
when different detectors have been used to obtain the desired results. These detectors
will be commented after.
3.1.2 Antennas
The standard that defines the requirements for antennas to be used in EMC
measurement is publication 16-1: 1993, “Specification for Radio Disturbance and
Immunity Measuring Apparatus and Methods, Part 1”. [2]
CISPR measurements officially require tuned dipoles, but a note in most
standards allows the use of broadband antennas where they can be shown to give
equivalent results. Then in the reception with broadband antennas must be considerate
the Antenna Factor (AF), which will be explained in the next section. In addition, the
antenna polarization and the conditions to obtain the maximum gain will be described.
Historically, two types of antenna have been used for emissions measurement,
biconical and log-periodic. These are electric-field linear polarized and typically cover
frequency ranges from 30 to 300 MHz and 300 to 1000 MHz, respectively. Early
biconical designs could reach only 200 MHz, but a modification to the structure has
removed a resonance between 200 and 300 MHz, allowing that specification to be
stretched.
The two types can also be combined into one device that will exhibit the
characteristics of each, increasing the relevant frequency range. This device is called
BiLog antenna. These different types of antenna are shown in the following figure:
11
Figure 3.2. Common antenna types are a) BiLog, b) log-periodic, and c) biconical
3.1.3 The Antenna Factor
Antenna Factor (AF) is perhaps the most widely used device descriptor in the
EMC area. However, it is one that is definitely not part of standard antenna
terminology. Antenna Factor reflects the use of an antenna as a field measuring device
or probe. Succinctly stated, the antenna factor is the factor by which one would multiply
the output voltage of a receiving antenna to obtain or recover the incident electric field.
Thus, the electric field Antenna Factor is given by:
(1)
The antenna factor includes losses and mismatch in the antenna and its
associated equipment (such as a balun or matching transformer). However, it does not
account for the use of an intervening transmission line (such as coaxial cable) to connect
the antenna to the receiver. So the losses in the transmission line can be easily
accounted for with a multiplicative factor, see the equation.
(2)
Where CA=eαl is the loss factor of the transmission, α is the attenuation of the
cable in nepers/meter and l is the length of the cable in meters.
3.1.4 Polarization, Polar Pattern, and Distance
When a single antenna factor is specified, an assumption has been made that the
antenna will be used under conditions of maximum gain. For the log-periodic antenna,
this is in the direction toward which the antenna is pointing, while for the biconical, it is
perpendicular to the antennas axis. In all other directions, the response of the antenna
falls off and the antenna factor becomes invalid. The polar-pattern response for a dipole
is within 1 dB of the on-axis value over an azimuth variation of 45°; for a log-periodic
array, the beam is narrower. This is particularly significant when the antenna is used at
high frequencies with a height scan from 1 to 4 m and a close-in distance of 3 m. Under
such conditions, the antenna will no longer be properly aligned with the EUT
(Equipment Under Test), and an error may result.
12
Polarization of the antenna refers to the plane of polarization of the electric-field
component. CISPR 16 requires that the cross-polarization be better than 20 dB, which
implies that the design of the antenna must ensure linear polarization.
EMC testing requires a fixed and known distance between the antenna and the
EUT. In log-periodic or combination antennas, the active element (known as the phase
center) shifts with frequency, and so the measuring distance must change. It is therefore
a practical necessity to choose a specific point on the antenna boom against which the
AF should be calibrated and to mark this permanently on the antenna itself.
The inclination of the antenna could be vertical or horizontal. The fields with
vertical polarity are greater than the fields with horizontal polarity. Then choice of the
inclination must be vertical. The reason why the horizontal component is lower than the
vertical component is caused by the effect of the ground plane, so the floor absorbs a
part of horizontal component. This is the reason to put the antenna in vertical
orientation.
3.1.5 Detectors used in EMI measurements
There are many different types of detectors in use in signal analysis systems.
Each has a unique definition as well as differing advantages and disadvantages. And
choosing the right one is critical to obtaining valid data. The following points explain
different detectors used in EMI measurements, these are Peak, Quasi-Peak, Average and
RMS (Root Mean Square).
• Peak Detector:
Initial EMI measurements are made using the peak detector. This mode is much
faster than quasi-peak or average modes of detection. Signals are normally displayed on
spectrum analyzers or EMC analyzers in peak mode. Since signals measured in peak
detection mode always have amplitude values equal to or higher than quasi-peak or
average detection modes, it is a very easy process to take a sweep and compare the
results to a limit line.
The EMC analyzer has an envelope or peak detector in the IF (Intermediate
Frequency) chain which has a time constant such that the voltage at the detector output
follows the peak value of the IF signal at all times. In other words, the detector can
follow the fastest possible changes in the envelope of the IF signal, but not the
instantaneous value of the IF sine wave.
The peak detector mode calculates the maximum magnitude at each discrete
spectral value, thus:
(3)
• Quasi-Peak Detector:
Most radiated and conducted limits are based on quasi-peak detection mode.
Quasi-peak detectors weigh signals according to their repetition rate.
13
As the repetition rate increases, the quasi-peak detector does not have time to
discharge as much resulting in a higher voltage output. For CW (Continuous Wave)
signals the peak and the quasi-peak are the same. Quasi-peak measurements are much
slower by 2 or 3 orders of magnitude compared to using the peak detector.
The quasi-peak detector has a charge rate much faster than the discharge rate;
therefore the higher the repetition rates of the signal the higher the output of the quasipeak detector. The quasi-peak detector also responds to different amplitude signals in a
linear fashion. High amplitude low repetition rate signals could produce the same output
as low amplitude high repetition rate signals. See Figure 3.3.
Figure 3.3. Quasi-Peak detector response diagram
The Quasi-Peak detector mode evaluates the emission according to a
physiological disturbance against amplitude-modulation radio.
• Average detector:
The average detector is required for some conducted emissions tests in
conjunction with using the quasi-peak detector. Also, radiated emissions measurements
above 1 GHz are performed using average detection. The average detector output is
always less than or equal to peak detection.
Average detection is similar in many aspects to peak detection. The output of the
envelope detector is the modulation envelope. Peak detection occurs when the post
detection bandwidth is wider than the resolution bandwidth. For average detection to
take place, the peak detected signal must pass through a filter whose bandwidth is much
less than the resolution bandwidth. The filter averages the higher frequency
components, such as noise, at the output of the envelope detector.
The average detector mode calculates the mean spectrum from the spectrogram.
The formulation for this detector is:
(4)
• RMS Detector:
RMS amplitude measurement is the best way to relate AC quantities to DC
quantities, or other AC quantities of differing waveform shapes, when dealing with
14
measurements of electric power. The RMS detector output is always less than or equal
to peak detection, and the value is always the same as or just a little bit larger than the
average.
The RMS detector mode calculates the RMS value of the magnitude of the
spectrogram as follows:
(5)
As it is described in the equation, to determine RMS value, three mathematical
operations are carried out on the function representing the AC waveform; The square of
the waveform function (usually a sine wave) is determined, the function resulting from
this step is averaged over time and finally the square root of the averaged function.
The figure 3.44 below is a comparison between Peak, RMS and Average
detectors; it is possible to see the difference of amplitude in each detector depending on
the waveform of the signal to detect.
RMS = 0.707
AVG = 0.637
PK = 2
RMS = Peak
AVG = Peak
PK = 2
RMS = 0.577
AVG = 0.5
PK = 2
Figure 3.4. Amplitude difference in each detector used
3.1.6 Receiver Specifications per CISPR 16-1-1:
Most commercial EMI standards reference CISPR 16-1-1 as the standard
defining the specifications of EMI receivers where the input, impedance, detector
characteristics and IF bandwidth shapes are specified. The current version of CISPR 161-1 calls out receiver specifications for the frequency range from 9 kHz to 18 GHz
15
where the realization of the bandwidths, the provision of the required dynamic range for
the quasi-peak detector or overload protection is not defined. CISPR 16-1-1 is a system
specification which defines the response of a receiver to defined input signals.
• Resolution Bandwidths:
Frequency resolution is the ability of an EMI receiver to separate two input
signals into distinct responses on the display. Specific resolution bandwidths are called
out for measurements in different frequency ranges. In general, receiver IF filters are
usually specified by a bandwidth and additional information about its frequency
response. CISPR 16-1-1 references the 6 dB bandwidth values of three IF filters to be
used in the frequency range to 2 GHz, these filters, in each range of frequency use, are:
−
200 Hz (for 9 kHz to 150 kHz)
−
9 kHz (for 150 kHz to 30 MHz)
−
120 kHz (for 30 MHz to 2 GHz)
• Devices classification and limits:
The CISPR 16-1-1 classified the devices under testing in two groups depending
on their use, class A and class B:
−
Class A:
A device which is marketed for use in an industrial application and is not
intended for use in the home or residential area. Since the product is being sold to a
commercial market, the emissions limits are significantly less stringent than Class B
(residential) devices.
Products that fall under the category of Class A do not require an official
submittal, but simply need a Verification test performed and the data must be keep on
hand by the manufacturer.
−
Class B:
That one is a device which is marketed for use at home or in a residential area
by the customer. Class B devices can require Verification, Certification, or Self
Declaration depending on the type of product.
Depending on the range of frequency analyzed and the distance from the EUT,
the standard CISPR 16-1-1 limits the strength of the field. The measured value can’t be
higher than the limits established and showed in the following table:
Frequency
Limit @ 3 Meters Limit @ 10 Meters
30 MHz to 230 MHz
40 dBµV/m
30 dBµV/m
230 MHz to 1000 MHz
47 dBµV/m
37 dBµV/m
Table 3.1. CISPR 16-1-1 limits, Quasi Peak detector, class B
16
3.2 Bluetooth
3.2.1 Introduction
The Bluetooth technology has mead a very important step in the world of the
communications, allowing the wireless interconnection of different devices.
Some years ago the connection among the different peripherals of the computer
was carried out by means of cabling, which caused diverse problems, as the complexity
of the connection or the excess of cabling that it rebounded in the devices mobility.
All these problems have been solved by this technology, allowing more
comfortable and quick connections, and also allowing the inclusion of this technology
in eventual smaller devices, giving access to mobile devices.
From the beginning, Bluetooth technology was intended to hasten the
convergence of voice and data to handheld devices, such as cellular telephones and
portable computers.
Figure 3.5. Capability of Bluetooth connections
As the idea grew, the SIG (Special Interest Group) was formed to create a
standard for this technology. The original SIG, formed in 1998, consisted of five
companies:Ericsson, IBM, Intel, Nokia, and Toshiba. And other companies join later:
Microsoft, 3Com, Lucent and Motorola.
Through the efforts of its developers and the members of the Bluetooth SIG, it is
now emerging with features and applications that not only remain true to its original
intent, but also provide for broader uses of its technology. Nowadays the Bluetooth SIG
has over 10,000 member companies developing, manufacturing, and selling thousands
of Bluetooth enabled products worldwide.
Now Bluetooth is a norm that defines a wireless global standard of
communication, which facilitates the voice and data transmission among different teams
by means of a connection for radio frequency.
17
3.2.2 Bluetooth Transmission Technology
One of the primary advantages of the Bluetooth system is ease of computer
vendor product integration. Other key benefits of this technology are low power, long
battery life, low cost, low complexity, and wireless connectivity for personal space, peer
to peer, cable replacement, and connectivity.
The Bluetooth transceiver operates in the globally available 2.4 GHz ISM band
(Industrial Scientific Medicine). In most countries around the world the range of this
frequency band is 2400 – 2483.5 MHz.
However, several countries have national limitations in this frequency range, and
in order to comply, special frequency hopping algorithms have been specified for these
countries.
Bluetooth uses 79 channels for the communication. The 79 RF channels are
spaced 1 MHz apart. The channel is divided into time slots of 625 µs in length. A guard
band is used at the lower and upper band edge to comply with out-of-band regulations.
3.2.3 Frequency Hopping Spread Spectrum
The ISM band is occupied by other RF emitters, ranging from WLANs, baby
monitors, and cordless phones. Bluetooth is based on a critical technology known as
FHSS (Frequency-Hopping Spread Spectrum), applied to combat interference, fading,
and to facilitate optional operation at power levels up to 100 mW.
FHSS spreads the signal by transmitting a short burst on one frequency and then
hops to another frequency for another short burst and so on, figure 3.6. In the FHSS
system the carrier frequency of the transmitter hops in accordance with a pseudorandom hopping sequence, unique to each piconet.
The frequency-hopping rate is 1600 hops/s for a single slot packet and slightly
decreases for multi-slot packets. The transmitter and receiver synchronize to the hop
sequence to ensure communication. The average signal strength on any given frequency
is relatively low.
Hopping also provides enhanced data reception in the presence of interfering
signals, like fixed frequency radio networks or microwave ovens. If interference at a
specific frequency is experienced, only a portion of the frequency hops will be blocked
instead of the whole signal. The unblocked hops make it possible to recover the original
data by re-transmitting the-message. Constant interference on a given frequency affects
the radio network for only a short time on that specific frequency.
18
Figure 3.6. Working mode of FHSS and collision
3.2.4 Radio Characteristics
Bluetooth devices are divided into three power classes, Class 1, Class 2 and
Class 3. The Bluetooth core specification classifies the transmitter equipment as having
three classes of radio transmission power, namely 100mW (20dBm), 2.5mW (4dBm)
and 1mW (0dBm). With 0dBm power, the communication range may be up to 10
meters while 20dBm transmit power increases the range to100 meters. Above 4dBm,
there is power control to transmit appropriate radio power corresponding to the
communication distance.
The receiver actual sensitivity level is defined as the input level for which a raw
BER (Bit Error Rate) of 0.1% is met for 723kbps. The Bluetooth receiver requires an
actual sensitivity level of –70 dBm or better. The carrier to interference ratio (C/I)
requirement is 11 dB for Co-Channel interference. Adjacent interference on 1 MHz
channels is 0dB and -30dB on 2MHz channels. Adjacent channels greater than 3 MHz
require a signal to interference ratio of -40dB.
3.2.5 Modulation Characteristics
The Bluetooth modulation scheme is GFSK (Gaussian Frequency Shift Keying)
with a symbol rate of 1Msym/s and modulation index between 0.28 - 0.35. The
Gaussian-shaped binary FSK modulation minimizes transceiver complexity. Using
positive frequency deviation a binary one is represented while a binary zero is
represented by a negative frequency deviation, that is the Bluetooth carrier is in 150
kHz to transmit ‘1’ and -150 kHz to transmit ‘0’. Maximum frequency deviation is
between 140 kHz and 175 kHz. If the frequency change is allowed to occur
instantaneously, this can lead to ISI (inter-symbol interference) at the receiver. ISI
makes it difficult to interpret what state the bit is trying to represent, this produces the
transmission data errors. To reduce the spectral spreading that causes ISI, Bluetooth
uses a Gaussian Filter (B·Tb = 0.5) to slow the transitions between the two frequencies.
3.2.6 Time Slots
A Time Division Duplex (TDD) scheme is used where master and slave
alternatively transmit. The baseband burst rate is 1Mbps. A TDD user frequency
channel is shared with other users who have time slots allocated at different times.
19
Bluetooth allocates one slot at the transmit frequency and one slot on the receive
frequency. The master only starts its transmission in even numbered time slots while the
slave starts its transmission in odd-numbered time slots. A single packet obtains the RF
hop frequency to be used from the current Bluetooth clock value. Multi-slot packet
obtains the RF hop frequency to be used for the entire packet from the clock value in the
first slot of the packet.
3.2.7 Packets
The packets are broken down into their constituent parts such as access code,
packet header, payload header, and payload, figure 3.7.
LSB
MSB
ACCESS CODE
72 bits
HEADER
PAYLOAD
54 bits
0-2745 bits
Figure 3.7. Bluetooth Packet
There are currently 14 packet types defined, split into 4 segments; Common
Packets, both ACL (Asynchronous Connection-Less) and SCO (Synchronous
Connection-Oriented), Single slot, ACL 3 and ACL 4 slot packets. Each packet type has
a different level of error correction and protection and different size payloads.
The Access code is used to detect the presence of a packet and to address the
packet to a specific device. The header packet contains control information associated
with the packet such as the address of the Slave for which the packet is intended.
Finally, the payload contains the message information.
The payload field of all ACL packets is split into the payload header, the
payload data and the Cyclic Redundancy Check (CRC) field.
Before the payload is sent over the air interface, several bit manipulations are
performed in the transmitter to increase reliability and security. An HEC (Header
Extension Code) is added to the packet header, the header bits are scrambled with a
whitening word, and FEC (Forward Error Correction code) coding is applied. In the
receiver, the inverse processes are carried out.
3.2.8 Error Correction
Three data error-correction schemes defined for the baseband controllers are:
1/3, 2/3 rate Forward Error Correction code (FEC), and Automatic Repeat Request
(ARQ) scheme. FEC is implemented on the data payload to reduce the number of
retransmissions. In a reasonable error-free environment, FEC adds unnecessary
overhead, which reduces the throughput. 1/3 FEC uses a simple repetition code that
repeats the bit three times. The 2/3 FEC scheme encodes data using a shortened
hamming code. In the ARQ scheme packets are transmitted and retransmitted until the
transmitting device receives an acknowledgement of a successful reception.
Depending on the characteristics of the data that will be transmitted, Bluetooth
uses several types of data packets. These packets differ by their payload length and FEC
options. The application chooses the packet type to use, depending on the requirements
of data rate and degree of error protection. Among various packet types, the ones that
are used in broadcasting are asynchronous connectionless packets (ACL).
The ACL packets are further classified as DM1, DM3, DM5, DH1, DH3 and
DH5, figure 3.8. The difference between the packets DM and DH is that DM has error
protection 2/3 FEC and DH doesn’t have protection, and the number (1, 3, 5) refers the
20
size of the packet. There are two factors that affect packet type selection: one is current
bit error rate (BER) of the radio channel (which is also related to the interference level)
and the other is effectiveness of the FEC scheme applied in the selected packet type.
Figure 3.8. Different kind of packets
3.2.9 Bluetooth Version 2.1.
The main advantage of Bluetooth version 2.1 is the increase of the Basic Rate,
due to the use of EDR (Enhanced Data Rate) with different modulation for the payload.
For the EDR, PSK (Phase Shift Keying) is used as the modulation scheme. Two
variants are specified, π/4-DQPSK (Differential Quadrature Phase Shift Keying) and
8DPSK (Differential Phase Shift Keying). By keeping the symbol rate at a constant 1
Msym/s for all modulation strategies the Basic Rate achieves a maximum of 1 Mbps,
the Enhanced Data Rate achieves 2 Mbps maximum for π/4-DQPSK and 3Mbps for
8DPSK.
The format of the packet is different, figure 3.9:
LSB
ACCESS
CODE
72 bits
MSB
HEADER
54 bits
GUARD
5µs
SYNC
11µs
EDR PAYLOAD
TRAILER
16-8200 bits
Figure 3.9. Bluetooth v.2.1. EDR Packet format
The Access Code and Header packet are modulated in FSK, but Synchronism,
EDR Payload and Trailer packets are modulated in PSK. The Trailer payload is used for
DC compensation. Guard is not a payload is only a security time and Synchronism is a
time used to synchronize the communication.
21
4 RESULTS
4.1 EMI Test receiver Vs Spectrum Analyzer
EMI measurements require a different approach than other types of RF
measurements because EMI are unpredictable signals in frequency and power. The test
equipment needed to perform measurements is composed by antennas, amplifiers,
filters, and the testing device. Two instruments are usually used for EMI testing: EMI
Test receivers and Spectrum Analyzers. We needed to compare these two instruments to
understand which is better for each measurement. These instruments are often working
together as the same thing. The differences between the two devices can start to be
explored by the parameters necessary to configure each instrument, there is an article
comparing these parameters according to [3]:
−
−
EMI Tester (R&S EMI Test Receiver 9 kHz to 2500 MHz ESPC):
•
Start/Stop Frequency
•
Resolution Bandwidth filter (3 or 6 dB)
•
Detectors (Peak, Quasi-Peak, Average)
•
Measurement Time
•
Step size
Spectrum Analyzer (R&S FSQ Signal Analyzer):
•
Start/Stop Frequency
•
Resolution Bandwidth filter (3 or 6 dB)
•
Detectors (Peak, Quasi-Peak, Average, RMS)
•
Sweep Time
•
Video Bandwidth
The EMI Tester from R&S that we use is made for EMI measurements, and it
can obtain the EMI measurement directly, then why to use another instrument for these
measurements? One of the principal advantages to use the Spectrum Analyzer is the
versatility and familiarity of this instrument, since in most laboratories there is one of
these devices, and everyone knows its behavior and possibilities. But Spectrum
Analyzers measure everything that falls in the pass band of the RF front end. In the case
of high amplitude and wide frequency signal could cause overload, and is needed a
preselection filter.
On the other hand the EMI Tester Receiver doesn’t need the preselector filter,
because is included in the device. This instrument is recommended to use for EMI
applications by standards bodies like CISPR, EN, FCC, MIL-STD and others. Some of
the advantages of this instrument are the automatic control of the measurements, like
automatic control of RF attenuation, RBW filtering, preselection filtering,
preamplification settings, and the step size. The possibility to insert the antenna factor
22
and cable loss into the instrument to obtain the correct EMI measurements is another
important advantage. The main disadvantage of EMI Testers is that they are slower than
analyzers, and have limited use outside of the area of specialization.
The measurements have been taken in the Laboratory of the “Centre for RF
Measurements Technology of Gävle”. The devices used in this experiment are: EMI
Tester, Spectrum Analyzer, antenna, cable, and computer. The system components are
explained below:
−
The EMI Tester utilized is EMI Test Receiver R&S ESPC, with a large
frequency range from 150 kHz to 1000 MHz, but can be extended from 9
kHz to 2500 MHz. The device has Peak, Quasi-Peak and Average
detectors and a fast synthesizer with a frequency resolution of 10 and 100
Hz. Is possible add up to 22 transducer factors for the cable effect and
antenna factor. The results are showed in a graph directly in the computer
by the software of the Tester (ESxS-K1), and the data could be extracted
and used in Matlab after some correction with an M-File (APPENDIX
B). This device has the option of output a comprehensive test report on a
printer or plotter.
−
By means of the Signal Analyzer R&S FSQ is realized the function of the
Spectrum Analyzer. The device is a combination of two instruments,
with a demodulation and analysis bandwidth that has been enhanced to
120 MHz. It has EMI filters of 6 dB bandwidth (200 Hz, 9 kHz, and 120
kHz). The different detectors that the Analyzer has are Max Peak, Min
Peak, Auto Peak (Normal), Sample, RMS, Average, Quasi-Peak. The
results of the measurements are obtained, connecting the analyzer with
the computer by GPIB, using Matlab and an M-File for store the values
of the measurement (APPENDIX B).
−
The antenna used for this measurement is a hybrid Bilog periodic (CBL
6112A), which is a broadband antenna (30 MHz-2GHz), linearly
polarized and exhibits an excellent balance and cross polarization
performance (APPENDIX C). The antenna has a combination of
frequency coverage and high power, handling capability and is the
antenna recommended for EMC testing, the following Figure 4.1, shows
the Antenna Factor of our antenna.
23
ANTENNA FACTOR CBL6112A
30
25
dBµV/m
20
15
10
5
0
1
10
2
3
10
10
MHz
Figure 4.1 Antenna Factor CBL6112A
−
The cable is TS7878-48, a Tensolite coaxial cable of 48 inches (1.21 cm).
The insertion losses, in the range of the measurements taken, are around
0.7 – 1 dB, such as is possible to see in [4]. The insertion losses of the
connectors must be included in this factor, in the system are used two
connectors, this means that are 0.2 dB (0.1 dB each connector).
−
The computer needs the software for scan automatically the interferences
through the EMI Test Receiver; this program is ESxS-K1 and uses GPIB
(General-Purpose Instrumentation Bus) connection for the
communication between computer and receiver. To control the Spectrum
Analyzer by GPIB, is needed Matlab with GPIB toolbox. The full system
is a connection of the EMI Test Receiver, the Signal Analyzer and the
computer via GPIB.
The Figure 4.2 shows the measurement system, Antenna, EMI Tester and
Spectrum Analyzer:
24
Figure 4.2. EMI Measurement System, EMI Tester, Spectrum Analyzer and Antenna
25
The developed system was tested to measure the noisy environment of the RF
laboratory in the “Centre for RF Measurements Technology of Gävle”. The
measurements were taken with the EMI Tester and the Spectrum Analyzer. The scan
using the EMI Tester gave us the following graph of the signal spectrum interference.
The figure 4.3 represents the power in dBµV/m in each frequency of the range covered
by the antenna (30 MHz-2GHz). This scanner uses Peak and Average detectors, the
graph of Quasi-Peak and Average detectors could be look up in (APPENDIX A).
Figure 4.3. ESPC- Graphic of EMI Tester of different detectors: Peak/Average
From the graph values it has designed a table (Table 4.1) showing the principal
peaks of the interferences measured with the EMI Tester. The interferences are
classified according to the frequency; in each frequency the range where the
interference is worst is specified.
In the table 4.3 the results of the EMI Tester measurements are obtained with
each kind of detector, Peak, Quasi-Peak and Average. It is possible to see the difference
of strength field between each detector. The explanation of the columns is the
following:
−
Frequency and range: represents the frequency where is located the
interference.
−
Peak, Quasi-Peak and Average: show the reading value in the EMI Tester
for the different kind of detector.
−
Limit: limit established by the standard CISPR for correct reception of
the signal.
26
−
Margin: difference between the measured value, Quasi-Peak
measurement, and the limit. If the signal doesn’t exceed this value, the
interference will not be dangerous for the transmission of the signal.
−
Utilization: is the real utilization, considerate in the Swedish frequency
allocation table [5], of the frequency range where is found the
interference.
Frequenc
y (MHz)
Range (MHz)
Peak
(dBµV/m)
QuasiPeak
(dBµV/m)
Average
(dBµV/m)
Limit
(dBµV/m)
Margin
(dB)
Utilization
88-108
87.5-108
52.5
51
50
40
11
FM Sound
Analogue,
Broadcasting
660
470-790
39
38
32
47
-9
Broadcasting
Television
956
890-915 (UPL)
935-960
(DWL)
42
39
36
47
-8
GSM
82
83
59
80
3
GSM
79
77
73
80
-3
GSM
51
48
39
80
-32
UMTS (3G),
IMT-2000
1818
1834
1973.6
17101785(UPL)
18051880(DWL)
1710-1880
1885-2025
(UPL)
2110-2200
(DWL)
Table 4.1. EMI Tester measurements results
With regard to Spectrum Analyzer the steps done are the same, measure the
noisy environment of the laboratory. In this case it has to notate that the device has a
RMS detector, contrary to EMI Tester. One of the principal disadvantages is the
impossibility to add the AF to the instrument, and configure the Spectrum Analyzer like
the EMI Tester; this inconvenient is solved adding the reading value to the correction
factor, as is showed in the table 4.2.
The scan obtained with the Spectrum Analyzer using Peak, Average and RMS
detectors is showed in the following figure 4.4:
27
Electric field strength [dBµV/m]
60
Peak
RMS
Average
50
40
30
20
10
0
-10
500
1000
1500
Frequency [MHz]
2000
Figure 4.4. Graphic of Signal Analyzer of different detectors: Peak, RMS, Average
Viewing the power values of the measure with the Spectrum Analyzer it has
constructed a table similar to (Table 4.1).
Frequency
(MHz)
Peak
(dBµV/m)
RMS
(dBµV/m)
Average
(dBµV/m)
Quasi-Peak
(dBµV/m)
Correction
Factor
(dBµV/m)
Limit
(dBµV/m)
Margin
(dB)
88-108
38
36
32
27
9.9~11.9
40
7.9~5.9
660
22
20
17
15
20.1
47
-4.7
956
1818
1834
25
47
45
22
43
42
20
39
39
17
35
33
22
28.5
28.5
47
80
80
0
-4.5
-6.5
1973.6
21
18
16
14
29.5
80
-29.5
Utilization
FM Sound
Analogue,
Broadcasting
Broadcasting
Television
GSM
GSM
GSM
UMTS (3G),
IMT-2000
Table 4.2. Spectrum Analyzer results
If the reading value is added to the correction factor the results in each device
are approximately the same. But the EMI Tester reads more power than the Spectrum
Analyzer due to the Tester takes more time to evaluate the interference, and the
Analyzer show the signal in real time.
The results with the EMI Tester are obtained directly to the computer after
configure the options of scan; against this, the Spectrum Analyzer measures everything
that falls in the range. With the Spectrum Analyzer the signal represented is changeable
because the measured signal is from impulsive noise. By means of the EMI Tester the
signal is stable but is impossible to see variations immediately, the Tester needs more
time to scan the interferences. In this way, the Spectrum Analyzer is better because is
28
possible to see the changes of the signal in real time. On contrary, since as the EMI
Tester is designed especially for EMI measurements, the Tester set up automatically
some important features like the reception filter, and the Spectrum Analyzer must be
configured manually.
29
4.2 Simulink, Bluetooth communication under noise environment
simulations
4.2.1 Bluetooth 1.0 with different interferences
The interference model is developed in Matlab Simulink and uses the following
Simulink libraries: Simulink standard block set, Communications block set, Signal
processing block set and Stateflow. The model is composed as separate objects that can
be turned off, depending if they are used or not. This gives the user many simulation
options and opportunities for how the model is used.
The model is based on the model [1]. The changes realized are located in the
channel. Firstly it has been added a real interference measurement of a noisy
environment instead of microwave oven interference used in [1]. The other change is
about the Bluetooth version, since as actually is used the version 2.1.
The following figure 4.5. it is possible to see the improvements of the model [1].
The figure shows the new model with the changed blocks. In this model, the noise block
has one Sum box to add the new interferences to the microwave oven interferences of
[1]. These interferences are: EMI Tester measurements, WiFi and GSM.
CHANNEL
RECEPTION
UU(R,C)
FFT
Spectrum Scope Rx
Before Demodulation
FDATool
[Tx]
-50
z
From7
In1
Out1
IF Filter
Select 1MHz band
u
[Rx]
M-FSK
Move to a
symbol
boundary
M-FSK
Demodulator
Baseband
UU(R,C)
Power Meter [dBm]
TOTAL
INTERFERENCE
To
Frame
M-FSK
-K- Gain
FFT
[Hops]
Spectrum Scope Rx
After Modulation
Generate
79 possible carriers
-39MHz to 39MHz
[GSM]
MEASUREMENT SYSTEM
[MicroWave_Oven]
0
[EMI_Tester]
[WiFi]
Display
0
[T x]
From2
0
Total Power Interference (dBm)
[Rx]
From3
Tx
Error Rate
Calculation
Rx
Error Rate
Calculation
T hroughput (Mbps)1
Data rate1
BER
Data rate2
Data rate3
Calculate
T hroughput
0
T h Effective (%)
0
Effective Velocity (Mbps)
Figure 4.5. Bluetooth transmission with, Microwave Oven and EMI measurements,
WiFi, GSM
With regard to the interferences, it was decided to add interferences which affect
to Bluetooth communication. WiFi transmission is working in the same band frequency
than Bluetooth, then it could be important to count with this interferer signal.
30
GSM (Global System for Mobile communications) is working in 900 and 1800
MHz, theoretically this signal doesn’t affect the Bluetooth communication, but it is
added to the model because is interesting to prove that any signal could be summed as
noise. So that the interferences affect the Bluetooth system, every signal is inserted in
baseband.
As is described in the last section the EMI measurement covers the range from
30 MHz to 2 GHz. In this range, the signal doesn’t affect the Bluetooth communication,
but it can be simulated in baseband also.
The figure 4.6 shows the interference measured by the EMI Tester, which is
added to the Bluetooth model:
Figure 4.6. EMI measurement interference
The channel of the last model sums all of interferences created, GSM, WiFi,
Microwave Oven and EMI interferences, this sum produce a total interference that is
added to the transmitted signal of Bluetooth, this total interferences has a power which
is calculated by a Power Meter showed in the model. The Total Power Interference can
be increased by the Gain situated after the sum; this will allow the degradation of the
Bluetooth signal, detecting in the receiver a worse Bit Error Rate.
The effect of the Total Power Interference on the Bluetooth communication is
showed on the figure 4.7. The BER is decreasing at the same time that the Total Power
interference increases. How is showed in the features of the Bluetooth modules
(APPENDIX E) has a sensibility of 0.1 with regard to the BER, then is easy to see the
maximum of Total Power Interference, 60 dBm. When the noise exceed this threshold
the communication using this system is not feasible.
31
10
10
BER
10
10
10
10
10
0
-1
-2
-3
-4
-5
-6
0
20
40
60
80
Total Power Interference [dBm]
100
Figure 4.7 Graphical of BER against Total Power Interferences (Microwave Oven,
EMI measurements, WiFi and GSM signals) of Bluetooth
4.2.2 Bluetooth Model version 2.1
The actual Bluetooth version 2.1 is composed by different modulations. As is
described in theory, two modulations are used, GFSK and PSK (π/4-DQPSK or
8DPSK). The upper branch, header cost of 126 bits modulated in GFSK, this branch is
concatenated with the down branch, total payload bits modulated in PSK. In this case
the PSK modulation used for the payload bits is π/4-DQPSK, this provides basic rates to
2Mbs, it could modulate with 8DPSK. After the concatenation the signal is transmitted
to the channel like in the other model. The figure of the signal transmitted is in the
APPENDIX D, and is possible to see the combination of two modulations, viewing the
difference with the transmitted signal in version 1.0 from the model of [1].
In the figure 4.8 is possible see the transmission of this new version 2.1.
TRANSMISSION
Random
Integer
Random Integer
Generator3
CPM
Buffer
GFSK
Modulation
Vert Cat
-KMatrix
Concatenation
Random
Integer
Random Integer
Generator1
DQPSK
Buffer1
DQPSK
Modulator
Baseband
Zero-Order
Hold
Quantizer
Gain
[T x_Signal]
Goto1
TX SIGNAL
To
Frame
From2
[Hops]
M-FSK
U(R,C) U
Generate
79 possible carriers
-39MHz to 39MHz
FFT
Figure 4.8. Bluetooth transmission version 2.1
32
4.3 Real Bluetooth communication under noise environment
simulations
This section of the thesis deals about the experiment with real Bluetooth
modules in noisy environment. The modules used are from Swedish company
Free2move AB. Specifically are the modules F2M03GLA [6] with the evaluation board
kit F2M03G-KIT. The Bluetooth module uses Bluetooth v 2.0+EDR, and has a range up
to 350 meters (line of sight), but can be improved with another omnidirectional antenna
on the circuit board and reach a range up to 1000 meters. Nowadays there are studies
with Bluetooth modules that could reach 30 km. With this kind of ranges we can think a
lot of possibilities for new applications.
F2M03G-KIT has the possibility of easily evaluating the wireless UART
(Universal Asynchronous Receiver-Transmitter) firmware as well as customizing it and
access to an extensive range of I/O ports. It is possible to connect the evaluation kit to
the computer by serial cable (RS232), USB (Universal Serial Bus) or TTL (TransistorTransistor Logic). USB has the advantage that is self–powered and, using serial
converter software in the computer (FTDI), is the best way to connect the device.
When the module is connected to the computer and detected, the device can be
properly set up using the Bluetooth configuration software that come with the product to
set connection modes, connect accept settings, security modes, PIN-code, baud rate, etc.
For this thesis, only the basic options have been used. Once the modules have been
configured, one of the modules will be the master and the other the slave to establish the
communication, see the assembly in APPENDIX G.
To check the good behavior of the modules, it has been sent information from
one module to other by a terminal program, Br@y++ Terminal [7], see main window in
figure 4.9. The election of this program was the different configurations and options that
it has. The possibilities of Br@y++ Terminal are huge, it can send files or separated
characters, and measure the time of transmission, view the graph of received data,
change the baud rate, the parity, the handshaking and other useful options.
Figure 4.9. Main window of Br@y++ Terminal
33
Once the modules are configured and the terminal is working, the next step is
send files and measure the time of transmission. Using different Baud Rate for the
transmission, it is possible to measure the velocity of the communication, and finally
compare the measures with a noisy environment. This case the noisy environment is the
presence of microwave interferences.
The next graphics (4.10 and 4.11) provide the result of the experiment. The
figure 4.10 is for baud rate of 57600 bps, and the figure 4.11 is for 115200 bps. The
baud rate is the number of symbols per second transferred. The graph has three
columns, the first column is the theoretical throughput, this means the maximum
expected for the modules in ideal conditions (APPENDIX E). The other columns are for
the communication with and without interference. The interference used is the
microwave oven (APPENDIX G).
This experiment checks if there is some effect in the transmission. The effective
throughput is obtained dividing the size of the file (bits) by the transmission time
(seconds). In this experiment the size of the file is 51020 bytes.
Figure 4.10. Throughput in Bluetooth communication with 57600 bps
34
Figure 4.11. Throughput in Bluetooth communication with 115200 bps
The following table compares the Throughput without and with microwave
oven, is possible to observe the reduction of the throughput, in other words, the
increment of the transmission.
Theoretical
Throughput
(kbps)
Throughput (kbps)
without
interferences
Throughput (kbps)
with microwave
oven
Reduced
Throughput (%)
57.6
45.35
40.82
9.98
115.2
102.04
81.63
20
Table 4.3. Comparative of Throughputs without and with microwave oven interference
The resolution of calculation is not too much useful, because the transmission
time measured is done with the terminal [7] for communicate the modules and has only
1 second of resolution, with another resolution the measurement could be more reliable.
But bearing in mind this is possible to take some conclusions about the measurement of
the time transmission in the communication with the two modules sending a file of
fixed size. It is possible calculate the Throughput and see the difference with the theory.
The measurements were taken first with the two modules without any
interference and after this was added the effect of a microwave oven. To increase the
effect of the microwave oven interference the door was half-opened, because the
microwave oven doors are prepared to isolate the radiation. The transmission time of the
file with the microwave oven interfering is greater than without interference; this is due
to the retransmission of packets when there is some transmission error.
35
The BER of a radio channel is the dominant parameter that affects the effective
throughput and reliability of a transmission. To obtain the BER is needed a specific
analyzer, a Bluetooth BER Tester. In the other hand is possible relate throughput with
BER, but the BER must be a fixed value of the channel behavior; this relation is
exposed in reference [8].
One important result is that the throughput stays reasonable up to a threshold
BER value, but after that it falls down quite fast, see figure 4.12. The threshold BER
value depends on the packet type. A packet type that has error protection has a higher
value for this threshold, which is what was expected. It is showed in the figure the
relation with the use of different Bluetooth packets, BER and effective Throughput.
Figure 4.12. Relationship BER, Throughput and packets used
36
5 CONCLUSIONS
In industrial environment there are a lot of interferences caused by the industrial
machinery that emit impulsive interferences. This is an important problem where
innovative systems can be added like, wireless communication for the communication
between machines and computers. If the industry wants to renew the communication
and use wireless technology it must be checked if it is possible to use this technology,
because the machines, as a motor, could interfere with the system.
In the thesis these interferences are measured in a laboratory of ‘‘Centre for RF
Measurements Technology of Gävle’’, but these measures can be also taken in an
industrial environment. With this information it is possible to simulate the real effect of
these interferences in a Bluetooth communication, and assure that a Bluetooth
communication is possible in a specific noisy environment.
Depending on the environment and the necessrey frequencies to be scanned
change of the antenna is needed and maybe the EMI Tester. The measurements in this
thesis were limited by the range of the antenna available (30MHz to 2 GHz). Then, the
study realized, can be extended using another antenna with a bigger range and scanning
different environment as an in industry or hospitals.
Other way to continue this thesis could be in the field of simulation. The realized
work was focused in Bluetooth communications with interferences, but this can be
extended to other technologies. Also, the noise inserted in Simulink was from
laboratory environment and could be from anyplace, industry, hospitals, markets, cities,
etc.
Finally a real case of interferences in a Bluetooth communication has been tested
using a terminal to connect and check the difference between, with as well as without
interferences. To extend the research with the modules, the measurements could be
taken using a BER Tester for Bluetooth which measures the BER and extends the
conclusions about the interferences created by the Microwave Oven. In addition, the
modules were separated around a half meter where future investigation could measure
the throughput and BER between the modules by inserting different obstacles like
walls and also increasing the distance or testing the behavior in an environment
industry.
37
6 REFERENCES
[1] Carl Karlsson, “Coexistence of IEEE 802.11 and Bluetooth in industrial
applications”, Master’s Thesis in Electronics/Telecommunications at University of
Gävle, Januari 2008.
[2] The Comite International Special des Perturbations Radioelectriques,
http://www.cclab.com/cispr.htm, [2008/06/05].
[3] Rhode & Schwarz, System Support Center, “EMI measurements, Test Receiver vs.
Spectrum Analyzer”.
[4] Cable loss, http://www.tensolite.com/v2/productFiles/TS.pdf, [2008/05/02]
[5] Eva Liljefors, “General guidelines of the Swedish National Post and Telecom
Agency on the Swedish frequency allocation table”, PTSFS 2005:4, Swedish National
Post and Telecom Agency, 16 August 2005.
[6] Free2move AB main page, http://www.free2move.se [2008/03/08]
[7] Br@y++ Terminal download, http://www.smileymicros.com/download/,
[2008/03/20].
[8] Kaan Dogan, Guray Gurel A., Kerim Kamci, Ibrahim Korpeoglu, “A Performance
Analysis of Bluetooth Broadcasting Scheme”,
[9] Schaefer, W., “Measurement of Impulsive Signals with a Spectrum Analyzer or
EMI Receiver”, Electromagnetic Compatibility, 2005. EMC 2005. 2005 International
Symposium on Volume 1, Issue, 8-12 August 2005 Page(s): 267 - 271 Vol. 1.
[10] Jussi Savolainen, “Automatic Bluetooth Radio Frequency Measurement System”,
Elcoteq Design Center Oy, Salo, May 2006.
[11] Lynch, Jamel Pleasant, “Co-Channel Interference In Bluetooth Piconets”, Master
Thesis in Electrical and Computer Engineering, October 2002.
[12] Tihany L., “Electromagnetic Compatibility in Power Electronics”, IEEE Press
1995.
[13] Clayton R. Paul, “Introduction to Electromagnetic Compatibility”, Wiley
Interscience, January 2006.
[14] Mark T. Ma, Motohisa Kanda and Myron L. Crawford, “A review of
electromagnetic compatibility/interference measurement methodologies”, Proceedings
of the IEEE, Volume 73, No 3, March 1985.
38
[15] Zeng, Z.; Alien, B.; Aghvami, A.H., “Performance evaluation of a Bluetooth
interference canceller in IEEE 802.11b wireless networks”, Consumer Electronics,
IEEE Transactions on, Volume 51, Issue 4, Nov. 2005 Page(s): 1188-1196.
[16] Ferro, E.; Potorti, F., “Bluetooth and Wi-Fi wireless protocols: a survey and a
comparision”, Wireless Communications, IEEE Personal Communications, Volume 12,
Issue 1, Feb. 2005 Page(s): 12-26.
[17] Shah, A.; Jalil, A., “Investigation and Performance Evaluation of different
Bluetooth voice packets against ambient error conditions”, Multitopic Conference,
2006. INMIC’06. IEEE, 23-24 Dec. 2006 Page(s): 11-16.
[18] James McLean, Robert Sutton, Rob Hoffman, “Interpreting Antenna Performance
Parameters for EMC Applications”, Part 3, TDK RF Solutions Inc., 2002,2003.
[19] Ling-Jyh Chen, Rohit Kapoor, M. Y. Sanadidi, Mario Gerla, “Enhancing Bluetooth
TCP Throughput via Packet Type Adaptation”, Dept. of Computer Science, UCLA,
2004 IEEE International Conference on Communications, 20-24 June, 2004, Paris.
[20] Eung-in Kim, Jung-Ryun Lee, and Dong-Ho Cho, “Throughput Analysis of Data
Link Protocol with Adaptive Frame Length in Wireless Networks”, AEÜ Int. J.
Electron. Commun., 51 (2003) No. 1, 1.8, Ministry of Science and Technology, Korea.
[21] Schaefer, W., “Narrowband and broadband discrimination with a spectrum
analyzer or EMI receiver”, Electromagnetic Compatibility, 2006. EMC 2006. 2006
IEEE International Symposium on, Volume 2, 14-18 August 2006 Page(s): 249-255.
[22] Markus Tengvall, “Smart Sensors.Detection of infrasonic waves”, Master Thesis
project at The Royal Institute of Technology of Stockholm, June 2007.
[23] EMC Testing, http://www.conformity.com/artman/publish/printer_167.shtml,
[2008/05/13].
[24] Southwick, R.; Runger, G., “A theory to optimize the detection and measurement
of EMI signals”, Electromagnetic Compatibility, 1989. IEEE 1989 National Symposium
on 23-25 May 1989 Page(s):12-15.
[25] Special Interest Group of Bluetooth, https://www.bluetooth.org/apps/content/,
[2008/04/07].
[26] How it Works Bluetooth, http://www.bluetooth.com/bluetooth/ [2008/06/04].
[27] Tim Williams, “What to Look for in an EMC Antenna”, http://www.cemag.com/99ARG/Williams97.html, [2008/04/20].
[28] Electronic Theses and Dissertations, http://scholar.lib.vt.edu/theses/, [2008/03/18].
39
[29] Peter F. Stenumgaard, Lars-Erik Juhlin, Erling Pettersson, Jenny Skansen, “A
Novel Method to Identify Pulsed Interference Sources in Radiated Emission
Measurements”, The Swedish Defense Research Agency, ABB Power Systems,
February 2008.
[30] Joel Galmor, “Smart Sensors Evaluation and implementation of wireless standard
for remote infrasonic detection”, Master of Science Thesis at KTH of Stockholm, 2007.
[31] Matlab main page, http://www.mathworks.com/ [2008/04/04]
[32] Rhode & Schwarz main page, http://www2.rohde-schwarz.com/ [2008/04/19]
[33] Schaefer, W., “Signal detection with EMI receivers”, Electromagnetic
Compatibility, 1998. 1998 IEEE Syposium on, Volume 2, 24-28 August 1998 Page(s):
761-765 vol.2.
40
7 APPENDIX
APPENDIX A:
EMI TESTER MEASUREMENTS
Figure A.2. ESPC- Graphic of EMI Tester with different detectors: Quasi-Peak/Average
Figure A.3. ESPC- List of peaks with different detectors: QuasiPeak/Average
41
APPENDIX B:
M-FILES USED
The results of the measurements with the EMI Tester can be stored in the computer in format .DAT. This
format must be transformed to a vector to be represented in Matlab. The m-File used in this case is the
next:
%Change the file with data results from EMI Tester to the correct
vectors
>>[s, msg] = replaceinfile(',', '.', 'MEASLAB.DAT'); %M_file to change
the characters ASCII for another
%ASCII character, in our case change the (,) for (.).
%MEASLAB.DAT is the EMI Tester file
>>fid = fopen('MEASLAB.DAT');
%text in ASCII and numbers. Each format column must be specificate in
the order
% %s its for cell(ASCII) %d8 for (int) %f32(numbers with 32 bits) %u
for (natural number)
%Now the same order but adding a functionality to eliminates a lines,
because its needed to delete the beginners lines
>>C = textscan(fid, '%s %d8 %u %f32 %d8 %d8', 'headerlines', 130);
>>fclose(fid);
>>semilogx(C{3},C{4})
>>AXIS([0 2*10^9 -40 80]) %AXIS([XMIN XMAX YMIN YMAX]) sets scaling
for the x- and y-axes on the current plot.
>>grid
In the measurements with the Signal Analyzer the data results are obtained by means of GPIB
communication. It is possible to plot the graph through Matlab, now the data mustn’t be transformed, all
that is needed is a GPIB communication. The instructions to draw the graph of the Signal Analyzer are
the followings:
%To construct a GPIB object connected to an Nation Instrument
% board at index 0 with an instrument at primary address 1:
>>g = gpib('ni', 0, 1);
% To connect the GPIB object to the instrument:
XMA? 200,500
>>fopen(g)
>>fprintf(g,'XMA? 210,600')
>>points=[fscanf(g)];
>>y = str2num(points);%To change the format of the dates recived, Char
to double.
>>n=length(y); % Ask the length of the vector y
>>x=[1:n];%Create a vector x with the same length than y
>>plot(x,y)
%To disconnect the GPIB object from the instrument.
>>fclose(g);
42
APPENDIX C:
6112B
BiLog® ANTENNA 30MHz - 2GHz CBL
The CBL 6112B is a high gain ultra
wideband BiLog® antenna for emission
and immunity EMC testing.
Three Antennas In One
The CBL 6112B operates over the
unprecedented, wide range 30MHz to
2GHz. It effectively combines the
performance of three standard EMC
antennas, the Biconical, the Log
Periodic and the Waveguide Horn.
Considerable savings in the order of
40 - 50% can be made in expensive test time, plus the
added benefit of improved repeatability and reliability
by not having to laboriously disconnect and reconnect
antennas during testing:
Ideal for FCC15, EN/CISPR
Compliance emission testing
VHF radio approval applications
Immunity testing to 300W CW
Excellent balance < 1dB
No rotational offsets
Easily transportable
Individual calibration
The CBL 6112B is primarily an emission measuring
antenna but can handle CW powers up to 300 watts,
making it suitable for most immunity measurements
requiring fields up to 10V/m, or even greater. The
CBL 6112B is linearly polarised and exhibits
excellent balance.
Technical
6112B:
specifications
− Frequency range:
− Impedance (Nominal):
− Gain 6dB Typical:
− 8dB Typical:
− Connector:
− VSWR Average:
− Size L x W x H cm:
− Weight:
− Max. Power:
CBL
30MHz - 2GHz
50 Ω
200MHz - 700MHz
700MHz - 2GHz
N Female
2:1
153 x 139 x 63
4.2kg
300W CW
CBL 6112B BiLog mounted on optional tripod CTP6097A
43
ANTENNA FACTOR CBL6112A
30
25
dBµV/m
20
15
10
5
0
1
10
2
3
10
10
MHz
44
SIMULINK MODELS
APPENDIX D:
Buffer
TRANSMISSION
Random
Integer
Random Integer
Generator
[Hops]
Goto4
[GSM]
Goto7
[WiFi]
Goto3
[Tx]
Goto1
CPM
GFSK
Modulation
To
Frame
[EMI_Tester]
Goto5
[MicroWave_Oven]
INTERFERENCES
Out1
Microwave Oven
Out1
EMI Tester
Tx Signal
Transmitter WiFi
Out1
GSM
System
Mix to appropriate
hop frequency
U(R,C)U
Spectrum Modulated
with carrier
FFT
M-FSK
Generate
79 possible carriers
-39MHz to 39MHz
CHANNEL
[GSM]
[MicroWave_Oven]
[EMI_Tester]
[WiFi]
-K-
In1
Out1
To
Frame
IF Filter
Select 1MHz band
FDATool
RECEPTION
u
M-FSK
[Tx]
From2
[Rx]
From3
-50
z
Move to a
symbol
boundary
[Hops]
FFT
Spectrum Scope Rx
Before Demodulation
[Rx]
FFT
Spectrum Scope Rx
After Modulation
759
0.02429
3.125e+004
1.022
Display
0.9757
Throughput (Mbps)1
0.9972
Th Effective (%)
Effective Velocity (Mbps)
UU(R,C)
Data rate1
Data rate2
Data rate3
Calculate
Throughput
BER
M-FSK
Demodulator
Baseband
M-FSK
UU(R,C)
Error Rate
Calculation
Tx
Error Rate
Calculation
Rx
MEASUREMENT SYSTEM
Generate
79 possible carriers
-39MHz to 39MHz
41.96
Total Power Interference (dBm)
Power Meter [dBm]
Gain
TOTAL
INTERFERENCE
[Hops]
HOPS GENERATOR
Random
Integer
Random Integer
Generator1
Figure D.1. Bluetooth communication with, Microwave Oven and EMI measurements, WiFi,
GSM
45
Hops
Random
Integer
-11
Display1
Goto
[Hops]
Buffer1
Buffer
TRANSMISSION
Random
Integer
Random Integer
Generator3
Random
Integer
Random Integer
Generator1
Random Integer
Generator
u-39
CPM
GFSK
Modulation
DQPSK
DQPSK
Modulator
Baseband
[T x_Signal]
u
Vert Cat
Matrix
Concatenation
RECEPTION
-50
z
Move to a
symbol
boundary
To
Frame
Generate
[Hops]
79 possible carriers
-39MHz to 39MHz
1
M-FSK
Zero-Order
Hold
To
Frame
From2
[Hops]
Quantizer
M-FSK
Generate
79 possible carriers
-39MHz to 39MHz
M-FSK
M-FSK
Demodulator
Baseband
Buffer2
Gain
-K-
-5
z
Delay
UU(R,C)
Goto1
FFT
T X SIGNAL
FFT
RX SIGNAL
FFT
CARRIERS GENERATED
[Tx_Signal]
UU(R,C)
UU(R,C)
[Rx]
Goto2
Figure D.2. Model Bluetooth v.2.1. (GFSK and DQPSK modulations)
46
Figure D.3. Bluetooth v.2.1. modulated signal (GFSK and DQPSK)
47
APPENDIX E:
F2M03GLA BLUETOOTH MODULES
Features:
• Fully qualified end product with Bluetooth™ v2.0+EDR, CE and FCC
• Low power consumption
• Integrated high output antenna
• Transmit power up to +8dBm
• Class1/ 2/ 3 Configurable
• Range up to 350m (line of sight)
• Piconet and Scatternet capability, support for up to 7 slaves
• Require only few external components
• Industrial temperature range -40°C to +85°C
• USB v2.0 compliant
• Extensive digital and analog I/O interface
• PCM interface for up to 3 simultaneous voice channels
• Large external memory for custom applications
• Support for 802.11b/g Co-Existence
• RoHS compliant
Applications:
• Industrial and domestic appliances
• Cable replacement
• Medical systems
• Automotive applications
• Stand-alone sensors
• Embedded systems
• Cordless headsets
• Computer peripherals
(Mice, Keyboard, USB dongles, etc.)
• Handheld, laptop and desktop computers
• Mobile phones
48
General Description:
F2M03GLA is a Low power embedded Bluetooth™ v2.0+EDR module with built-in high output antenna.
The module is a fully Bluetooth™ compliant device for data and voice communication. With a transmit
power of up to +8dBm and receiver sensibility of down to
–83dBm combined with low power consumption the F2M03GLA is suitable for the most demanding
applications. Developers can easily implement a wireless solution into their product even with limited
knowledge in Bluetooth™ and RF. The module is fully Bluetooth™ v2.0+EDR qualified and it is
certified according to CE and FCC, which give fast and easy Plug-and-Go implementation and short time
to market.
The F2M03GLA comes with an on board highly efficient omnidirectional antenna that simplifies the
integration for a developers Bluetooth™ solution. The high output power combined with the low power
consumption makes this module ideal for handheld applications and other battery powered devices.
F2M03GLA can be delivered with the exceedingly reliable and powerful easy-to-use Wireless UART
firmware implementing the Bluetooth™ Serial Port Profile (SPP).
The following table shows the maximum achieved throughput when streaming data between two
connected modules with different configuration and baud rate:
Direction
Baud Rate
Maximum
Maximum
Throughput (kbit/s
Throughput (kbit/s)
(throughput mode))
(latency mode)
Master to Slave
57600
~57.6
~57.6
Slave to Master
57600
~57.6
~57.6
Full duplex
57600
~57.6
~50.5
Master to Slave
115200
~115.1
~93.9
Slave to Master
115200
~115.1
~79.6
Full duplex
115200
~114.5
~42.0
Master to Slave
230400
~223.1
~158.0
Slave to Master
230400
~221.4
~117.7
Full duplex
230400
~172.7
~86.2
Master to Slave
460800
~228.6
~206.7
Slave to Master
460800
~222.7
~154.1
Full duplex
460800
~173.3
~109.8
Master to Slave
921600
~240.1
~235.7
Slave to Master
921600
~235.4
~186.0
Full duplex
921600
~174.7
~150.5
49
APPENDIX F:
EVALUATION KIT FOR GENERAL
PURPOSE BLUETOOTH™ MODULES DATASHEET
Key Features:
10 GPIO:s with push buttons and led indication
Analog audio interface (mono) (speaker and microphone, 3.5mm socket)
Power supply through USB-connector or external adaptor
USB-interface (virtual com port or direct HCI access)
Programming interface for Free2move’s flash utility (parallel port)
RS232-interface
Pin headers for all digital and analog I/O:s
F2M03G-KIT-1 Contains:
F2M02BG1 (Evaluation board)
USB-cable
Serial cable
Parallel cable
CD (Manuals and software)
General Description:
F2M03G-KIT is a new evaluation kit for Free2move’s general-purpose Bluetooth modules. The
evaluation board has extensive I/O functionality for both data and audio streams. The evaluation board is
primary made to evaluate the Wireless UART firmware but is also intended to be used for other
firmwares and custom made applications. The evaluation board gives the possibility to upgrade the
Bluetooth module with new firmware using Free2move’s Flash utility.
The F2M03G-KIT has both RS232 and USB-interface for data communication. The USB-interface can
either act as a direct connection to the module through HCI or it can be used as a virtual com port for
computers without a physical com port. All digital and analog I/O can be accessed from pin headers on
the evaluation board for external communication.
The evaluation board is equipped with an audio codec and amplifier for direct microphone and speaker
drive. External audio streams can be connected using the PCM interface.
The F2M03G-KIT is delivered with all necessary cables and a CD with manuals and software. The
evaluation kit can both be delivered as a single or a double kit. The kit does NOT include any Bluetooth
OEM-board. They are ordered separately!
50
APPENDIX G:
MODULES AND MICROWAVE OVEN
EXPERIMENT
51
52