Wireless Link for Controlling and
Monitoring Electronic Billboards
Presented by : 05gr797
Bayu Anggoro Jati
Nurul Huda Mahmood
Puri Novelti Anggraeni
Satya Ardhy Wardana
INTRODUCTION
CHANNEL
MODULATION TECHNIQUE
ACCESS TECHNIQUE
SIMULATION
RESULT AND DISCUSSION
MOVING FORWARD
WORKING PROCESS
INTRODUCTION
Electronic Billboard
"These animated, electronic billboards incorporated into network sign
systems enable advertisers to bring a specific message at a specific
time to a specific audience …”[1]
[1] Benoit Strauven, marketing manager at Barco
Current trends
Today the network of electronic billboards
are connected through:
– Internet: Last mile provided through DSL or wifi
• DSL lease is expensive and high setup cost for remote
location
• Existing wifi structure is not so wide.
– Satellite
• In large metropolitan areas, having a satellite setup is costly.
– Using existing GSM cellular connection
• Practical upload rates of 56 Kbps
Too slow to be uploading a 1 GB file (5 hours)
Current trends
source: Trask, Richard F. How InfoChannel works. www.scala.com
Problem Definition
• If the billboards could be connected via a
wireless network that is cost effective and easily
scalable, it would be possible to deploy
electronic billboards virtually anywhere.
• In this project we are going to design the
wireless link for such a network.
– Listen to HEARTBEAT of the billboard
– Upload advertisements/information
Design Consideration
The main design objectives are:
• Operating in unlicensed band (we have to
deal with interference)
• Reliability (sufficiently fast and with
minimum error)
• Security (avoid any sort of interception on
the link and upload unwanted message)
• Low cost
Key Assumptions
Assumptions from P0[1]
• The data size is 1 Gb
• The data rate is 2 Mbps
• Low cost system
• The distance is 10 kilometers
• Static Station
• Works in Unlicensed Band
• Wireless link implements spread spectrum
technique
[1] 05gr797 P0 Project Report
Key Assumptions
Assumptions made for P1
• Unlicensed band used is 2400-2483.5 MHz[1]
• Don’t consider antenna type, assuming
– The central use 8 -15 dBi omnidirectional antenna[2]
– Billboards use 14 - 30 dBi directional antenna[3]
• Noise Figure is around 3 dB[4]
• Revised Data Rate is 512 kbps, thus bandwidth is 1 MHz
• The distance is 4 kilometers at maximum
[1] 05gr797 P0 Project Report
[2] 2.4 GHz Outdoor Omnidirectional Antenna. Hyperlink Technologies. http://www.hyperlinktech.com/web/ antennas
2400 out omni.php#. 28 November2005.
[3] 2.4 GHz Outdoor Directional Antenna. Hyperlink Technologies. http://www.hyperlinktech.com/web/ antennas 2400
out directional.php#. 28 November 2005.
[4] 2.4GHz Wireless High-Gain Antennas.SMC.
http://www.multitaskcomputing.co.uk/wireless/80211b/SMC%20HIGH%20GAIN.pdf. 27 November2005.
P1 Scope and Outline
The designed link is between central and billboard. The link
is semi duplex.
• Theoretical background of several modulation
techniques and access techniques are studied. Channel
properties in deployment environment are investigated.
• Decisions on system parameters are made based on
properties of deployment environment.
• Decision about modeling and simulation techniques are
made considering our system design.
• Simulation is performed and result are taken and
evaluated to our initial requirements.
CHANNEL
Channel Properties
•
•
•
•
•
•
Fading
Path Loss Model
Link Budget Calculation
Coherence Bandwidth
Coherence Time
Channel Propagation Model
Fading
• Envelope Fading
Due to propagation loss, results in path
loss
Path Loss Model
• Proposed model with correction factor based on
empirical derived model[1]
d
PL  A  10 log
s
d0
A  20log (
4 d 0

d  d0
)
• The model is calculated for 100m distance but
upscaled to meet our distance requirement.
besides that, some terrain correction factor is
also added in γ.
[1] Erceg, V. et. al. An empirically based path loss model for wireless channels in suburban
environments. IEEE JSAC, vol. 17, no. 7, July 1999, pp. 1205-1211.
Path Loss Model
• This model is proposed for a receiver antenna
height of 2 m and operating frequency of 2 GHz.
• ΔPLf is correction factor for freq as Δ PLh is for
height[1]
PLmod  PL  PL f  PLh
[1] Erceg, V. et al. Channel models for fixed wireless applications, IEEE 802.16 Broadband Wireless
Access Working Group. 2001-07.
Link Budget
• Overall Link Budget Calculation
LINK BUDGET CALCULATION
Transmitted Output Power
5 dBm
Transmit Antenna Gain
15 dB
Effective Radiated Power
20 dBm
Path Loss
-148.6 dB
Receiver Antenna Gain
35 dB
Receiver Noise Figure
3 dB
Receiver Equivalent Noise Bandwidth
10 MHz
Receiver Sensitivity
-114 dBm
Noise Fade Margin
20.4dB
Link Budget
EIRP = 20 dBW
148.6 dB
Path Loss
Noise Margin
20.4 dB
Received Power =
78.2 dBW
Fading
• Flat and Frequency Selective Fading
– Because of multipath effect
– From maximum delay spread can be
investigated the coherence bandwidth
• Slow and Fast Fading
– Because of the movement of the environment
– From doppler spread can be investigated the
coherence time
Coherence Bandwidth
• RMS delay spread = 0.13 μs[1]
• Coherence BW = 1.3 MHz
• Thus, the uncorrelated frequency separation
(with autocorrelation < 0.05) = 5.83 MHz
• freq selective channel => wideband channel
• From coherence bandwidth, required separation
between frequency to ensure uncorrelated
frequency is 6 MHz
[1] Porter, J.W. and J.A. Thweatt. Microwave propagation characteristics in the MMDS frequency
band. ICC2000 Conference Proceedings, pp. 1578-1582.
Coherence Time
• Doppler frequency in similar environment
= 2 Hz[1]
• Coherence Time = 50 ms
• We choose to have a time invariant
channel thus, dwell time have to be below
50 ms
• dwell time 31 ms => hop rate = 32 hop/s
[1] Erceg, V. et al. Channel models for fixed wireless applications, IEEE 802.16 Broadband Wireless
Access Working Group. 2001-07.
Coherence Time
Measured doppler spectra for fixed wireless channel at 2.5GHz[1]
[1] Erceg, V. et al. Channel models for fixed wireless applications, IEEE 802.16 Broadband Wireless
Access Working Group. 2001-07.
Channel Propagation Model
• Rayleigh Channel
• Rician Channel
Channel Propagation Model
• We choose rician because our application
has one strong LOS component
• K factor = 0.5[1]
• The measurement was done in 1.9 GHz
but can safely adopted in 2.4 GHz[2]
[1] Greenstein, L.J., S. Ghassemzadeh, V.Erceg, and D.G. Michelson. Ricean K-factors in narrowband
fixed wireless channels: Theory, experiments, and statistical models. WPMC99 Conference
Proceedings, Amsterdam, Sep 1999.
[2] Erceg, V. et al. Channel models for fixed wireless applications, IEEE 802.16 Broadband
Wireless Access Working Group. 2001-07.
Channel Summary
• System Bandwidth is 1 MHz which is
below coherence bandwidth of 1.3 MHz.
Uncorrelated frequency spacing is 6 MHz
• Channel dwell time is 31 ms.
• The channel is wideband channel and will
be modeled as Rician fading channel.
• We have ensure that the channel has
properties of Time invariant channel and
frequency of each channel is uncorrelated.
MODULATION
TECHNIQUE
Modulation
• Definition: Modulation is the process of
using the carrier signal to carry the
message signal.
• Three parameters of sinusoid signal:
amplitude, frequency, and phase
– This will results in different modulation
techniques
Consideration to choice a
suitable modulation scheme
•
•
•
•
High spectral efficiency (bps/Hz)
High power efficiency
Low cost and easy to implement
Robust
➔Trade off between simplicity and
performance
Digital Modulation Classification
• Linear and non-linear modulation
– Relation between modulated and modulating
signal
• Coherent and non-coherent modulation
– Synchronization in the receiver
• Constant and non-constant envelope
– Amplitude of the modulated signal
Digital Modulation Techniques
Some digital modulation techniques are:
• Amplitude Shift Keying (ASK)
• Frequency Shift Keying (FSK)
• Phase Shift Keying (PSK)
• Differential Phase Shift Keying (DPSK)
• Other advance modulation techniques:
– GMSK, M-QAM, and so on
Modulation Techniques
Classification
ASK
FSK
PSK
Linear
Yes No
v
v
v
Coherent Const ant Envelope
Yes No
Yes
No
v
v
v
*
v
v DPSK
v
* : non-coherent FSK
Theoretical BER vs SNR
Comparison
Modulation Technique of Our
System
• We consider the modulation technique
which has less complexity (which means
without synchronization) and good BER
performance
• We choose DBPSK modulation technique
which is non-coherent and has better BER
performance than non-coherent FSK
DBPSK Modem Block
• Block diagram of DBPSK transmitter [1]
• Block diagram of DBPSK receiver [2]
[1] Haykin, Simon. Communication Systems 4 th ed.. John Wiley and Sons, 2001
[2] Feher, Kamilo. Wireless Digital Communication Modulation and Spread Spectrum Applications.
Prentice Hall PTR, New Jersey : 1995
Generat ion of DBPSK signal
b(k)
1
d(k-1)
1
d(k) = b(k) XOR d(k-1) 1 1
t ransm it t ed phase (rad) 0 0
0
1
0

0
0
1
0
1
1
1
0
0
1
0

0
0
1
0
1
1
1
0
1
1
1
0
Det ect ion of DBPSK signal
received phase (rad)
0
d(k)
1
d(k-1)
b(k) = d(k) XOR d(k-1)

0
1
0
0
1
0
0
0
1
1
1

0
1
0
0
1
0
0
0
1
1
1
0
1
1
1
0
1
1
1
Simulation of DBPSK
Modulator and Demodulator
• We built our own DBPSK modulator and
demodulator function for simulation in
MATLAB based on the DBPSK block
• Compare them with MATLAB built in
DBPSK function and theoretical DBPSK
BER to verify our DBPSK modem function
Performance of DBPSK (BER
over SNR) in AWGN Channel
Performance of DBPSK (BER over
SNR) in AWGN Channel: Discussion
• The simulation result shows that our DBPSK
modem seems to has a better performance
than the theoretical formula and DBPSK built
in MATLAB function.
• We found that the problem is in our DBPSK
demodulation function.
• Our function does not consider the imaginer
part but only the real part of the signal.
• We were not using our DBPSK function in
overall system simulation
Summary of Modulation Technique
• Our design criteria are low cost and good
performance. Thus we chosen DBPSK as
modulation technique since it has a good
trade off between the performance and
simplicity
• We were not using our DBPSK modem
function in the overall system simulation
since we could not fix the problem in our
DBPSK demodulation function
ACCESS
TECHNIQUE
What is Access Technique
• Digital Modulation maps the message
signal to a constellation point.
• To transmit, the constellation point has to
be mapped to a real frequency.
• Access Technique is a method to do that.
Design requirement
• Our design preferences:
– Susceptibility
– Communication over long distance
– Relative immunity to interference
– Low cost and therefore simplicity
– High data rate is not a major design
requirement
What is Spread Spectrum
• Modulated waveform spread to a broader
portion of the radio frequency
• Bandwidth of the transmitted signal is
much greater than that of the original
message
• Two types, Frequency Hopping (FHSS)
and Direct Sequence (DSSS)
FHSS
• The wide bandwidth is divided into narrow
sub-bands or channels
• The message signal is hopped from one
channel to another.
• At the transmitter, the modulated message
signal is transmitter at a transmit
frequency determined by certain hopping
algorithm.
FHSS Example
Source: William Stallings, Data and Computer Communications, 7th Edition
PN sequence generator
• A PN sequence generator generates a periodic
PN sequence based on a hopping algorithm.
• The generated PN sequence is fed to a
frequency synthesizer, which then determines
the frequency channel at which to transmit the
message frame.
• m bit PN generator identifies 2m -1 possible
frequencies.
FHSS Receiver
• At the receiver there is an identical PN
generator synchronized with the received
signal.
• Receiver therefore knows which at frequency
current frame will be transmitted.
• Thus
enabling
correct
detection
demodulation of the received signal.
and
FHSS block diagram (transmitter)
Source: William Stallings, Data and Computer Communications, 7th Edition
FHSS block diagram (receiver)
Source: William Stallings, Data and Computer Communications, 7th Edition
Fast and Slow FHSS
• Two types of FHSS, Fast and Slow
• If the hopping rate > message symbol rate,
it is fast FHSS
• If message symbol rate  hopping rate, it
is slow FHSS
• fast FHSS gives improved performance in
noise (or jamming)
Fast and Slow FHSS
Example: Slow FHSS with M =4 and m = 2
Source: William Stallings, Data and Computer Communications, 7th Edition
Fast and Slow FHSS
Example: Fast FHSS with M =4 and m = 2
Source: William Stallings, Data and Computer Communications, 7th Edition
Direct Sequence SS (DSSS)
• Spreads the signal by expanding it over a wide
radio band.
• Frequency of the carrier is constant for each
system.
• At transmitter, message signal is multiplied by
PN sequence to spread the message signal.
• The spreading is proportional to number of bits
used, a 10 bit spreading code spreads signal
across 10 times bandwidth of 1 bit code.
DSSS Transmitter
Source: William Stallings, Data and Computer Communications, 7th Edition
DSSS Example
Source: William Stallings, Data and Computer Communications, 7th Edition
DSSS Spectrum
Source: William
Stallings, Data and
Computer
Communications,
7th Edition
DSSS
• At receiver end, received signal is
multiplied by the same PN sequence as in
transmitter before demodulation to get
back the original message signal.
• This de-spreads the received signal to the
bandwidth of original message signal.
• Transmitter and receiver has to
synchronized to have the same PN code.
DSSS Receiver
Source: William Stallings, Data and Computer Communications, 7th Edition
FHSS vs. DSSS:
COMPARISON
System Collocation
DSSS
Symbol rate = 11 Mcps
Each band 22 MHz, with
separation of 30 MHz
Available BW = 83.5 MHz
3 systems can be
collocated
FHSS
79 different channels and 78
hopping sequences.
Grouped in three sets of 26
sequences.
Theoretically, 26
collocated FHSS systems.
Practically the number is
around 10 to 15.
Noise and Interference Immunity
DSSS
Wideband Interference
May completely block
system.
Narrowband Interference
Interference is multiplied
with the spread code, thus
spreading it. Immune to
narrow band interference up
to a great extent
FHSS
Only part of the hops will be
blocked
Interference signal present
on a specific frequency will
block hops on that specific
frequencies. Hops on other
frequencies will not be
affected.
Noise and Interference Immunity
Illustration on how DSSS handles narrow band interference
Source: http://www.odessaoffice.com/wireless/fh_vs_ds.pdf
Near Far Problem
Signals from nearby active transmitters may be received
at the receiver at higher power than the intended user.
DSSS
FHSS
Could make the receiver
unable to extract information
from intended user.
Automatic power control
required, thus increasing
complexity.
Worst case will be that the
other transmitter will block
some hops, forcing the
FHSS system to work in less
than optimum conditions
Multipath
DSSS
FHSS
Multipath components generated due to signal reflection between
transmitter and receiver,
The pulse is spread. So, narrow
FHSS systems have better
pulses of DSSS are more sensitive. chances to be undisturbed by the
Inter Symbol Interference
presence of multipath effects.
Multipath components result in
frequency selective fading.
As long as the average level is high
enough, the DSSS receiver will be
able to detect the radio signal.
FHSS systems have narrow
bandwidth with signals located at
different carrier frequencies.
Transmitted signal at significantly
faded frequencies cannot be
received accurately
DSSS is more sensitive to multipath than FHSS, especially when operating
at higher bit rate.
Throughput
DSSS
FHSS
Single system:
IEEE 802.11 defines rates of up to In IEEE 802.11 standard FSSS
11Mbps, though practically up to 7 system has throughput of up to 3
Mbps is achievable
Mbps (2 Mbps practically)
Collocated system:
With three systems collocated:
net throughput of 3 X 7 = 21
Mbps.
Net throughput of 10~15 X 2 =
~25 Mbps.
Comparison: Conclusion
• DSSS provides higher capacity links, but it
is very sensitive.
• FHSS system has lower capacity links, but
is a more robust technology, with better
performance in harsh environment
Spread Spectrum: Conclusion
• Our design preferences:
–
–
–
–
–
Susceptibility
Communication over long distance
Relative immunity to interference
Low cost and therefore simplicity.
High data rate is not a major design requirement.
• Considering the performance of FHSS and
DSSS, a frequency hopped system would better
suit our requirement.
• Thus our Access technique is FHSS.
Frequency Hop code
• Hopping pattern in FHSS, driven by different
hopping codes, is used to control the carrier
frequency.
• Number of different hop codes
• Example:
Linear Congruence Code (LCC),
Quadratic Congruence Code (QCC),
Cubic Congruence Code (CCC),
Hyperbolic Congruence Code (HCC),
Welch-Costas Array (WC),
Lempel-Costas Array (LC)
Frequency Hop code
• Hop Sequence from IEEE 802.11 Standard
– North America and most of Europe:
[b(i) + x]mod(79) + 2
– Japan: [(i − 1)x]mod(23) + 73
– Spain: [b(i) + x]mod(27) + 47
– France: [b(i) + x]mod(35) + 48
fx(i) is the channel number for ith frequency in xth hopping pattern.
• Designed to ensure some minimum distance in
frequency between contiguous hops. In our application it
is 6 MHz.
SIMULATION
OVERALL MODELING BLOCK
SIMULATION STEPS
• The first step :
Verification of DBPSK modem block
• The second step :
Verification of channel block
• The third step :
Simulation for the whole system
SIMULATION – CHANNEL BLOCK
• We used SUI5 3-tap delay model [1].
• SUI5 channel model defines a three tap delay model for
a channel in urban terrain type with a τrms of 2.842 μs.
• For different antenna types (omnidirectional and
directional antenna) and different K factors, different
power levels at each of the inputs are defined.
[1] Erceg, V. et al. Channel models for fixed wireless applications, IEEE 802.16
Broadband Wireless Access Working Group. 2001-07.
SIMULATION – CHANNEL BLOCK
Our parameter :
– K factor = 0.5
– RMS delay spread (τrms) is 0.13 μs.
– We re-scaled the delay tapes into 0, 0.2 μs, and 0.4
μs respectively to fit our case (τrms of 0.122 μs).
SIMULATION – CHANNEL BLOCK
SIMULATION – CHANNEL BLOCK
SIMULATION – THE WHOLE SYSTEM
•
•
•
•
•
•
•
•
•
•
•
Access technique
Digital modulation
The channel model
Hop sequence
Hopping distance
Carrier frequency
Number of channel
Hopping rate
Dwell time
Bitrate
Bit size in one hop
: FHSS
: DBPSK
: SUI5 3 tap delay model
: IEEE 802.11
: 6 MHz
: 2.4 GHz
: 32
: 32 hops/second
: 31 ms dwell time
: 512 kbps
: 31 ms x 512 kbps ≈ 16 kbits
SIMULATION – THE WHOLE SYSTEM
•
•
The simulation is frame by frame
Hopping distance 6 MHz -> uncorrelated
•
Monte Carlo simulation to get accurate result
The simulation is repeated 10 times.
(considering the server capability and processing time)
For BER up to 10−4 we generated 105 bit data ≈ (10 times 16kbit)
•
Simulation without power control
Some hops can have higher fade that the others.
This hops would result in higher bit error.
Power control can overcome this problem (use higher power).
We assume that power control has been implemented in place.
We assume that every channel has the same condition
SIMULATION – THE WHOLE SYSTEM
We simulated the performance of the system in :
– AWGN channel
– wideband channel using SUI5 3-tap delay model
for directional antenna (billboard)
– wideband channel using SUI5 3-tap delay model
for omnidirectional antenna (base station)
RESULT
&
DISCUSSION
BER (Bit Error Rate) Requirement
• number of bits received in error relative to number of
transmitted bits
• Our requirement : 10-4
– Bluetooth : 10-3 [1]
– Video transmission : 10-9 - 10-12
[2]
• Video quality is not so important because the distance
between viewer and billboard is far
• Not a video streaming (error can be fixed by retransmission)
[1] Cavigioli, Chris. Bluetooth demands system tools.
http://www.mwee.com/features/showArticle.html?articleID=12801538. 16 November 2005.
[2] http://www.fiber-optics.info/articles/dtv-hdtv.htm
FER (Frame Error Rate) Requirement
• number of bits that would result in the frame to be in error.
• For typical billboard, 14 bit used to represent one pixel.
[1]
• We define if 1 pixel is error, i.e. 14 bits are received with
error in one frame, then frame error has occurred.
[1] Electromedia. Techical Data of Large Outdoor Display. http://www.electromediaintl. com/services.html.
11 December 2005.
BER PERFORMANCE RESULT
BER 10-4 can be achieved at SNR of :
• 11,5 dB for omnidirectional antenna
• 14 dB for directional antenna
FER PERFORMANCE RESULT
FER :
- at 10,4 dB for omnidirectional antenna
- at 12,8 dB for directional antenna
: 2.5 10−2
: 4.5 10−2
CONCLUSION
• On a bit level, we were able to achieve our
target BER of 10−4.
• We can use SNR up to 20 dB to get better BER
performance.
• On frame level, FER :
– at 10,4 dB for omnidirectional antenna is 2.5 10−2
– at 12,8 dB for directional antenna is 4.5 10−2
MOVING FORWARD
MOVING FORWARD
The following issues that can be considered :
– Addressing scheme for the billboards
– Protocol for communication
• setup and disconnect
• Transferring data
• Routing
– Time and frequency synchronization
– Designing a multihop network for wider area network
WORKING
PROCESS
WORKING PROCESS
P0 Period
• All group member arrived two and half weeks late.
• We got a lot of new experiences in Aalborg
University – project oriented learning
• We had a good relationship among members, clear
job division, and cooperation from supervisor
WORKING PROCESS
P1 Period
• Arrangement of our P1 timeline based on the
problem definition and the scope of project.
• Meeting with supervisor once a week.
• Internal group meeting.
WORKING PROCESS– P1 TIME LINE
WORKING PROCESS
STRENGTH >< WEAKNESS
• Lack of project
• Good relationship
management.
among the members.
• We divided our job
based on the
strength of each
member.
• Flexible way of
working.
• Good supervisor.
• Punctuality.
• Our flexible way of
working has its own
weakness.