Wireless Link for Controlling and Monitoring Electronic Billboards

Wireless Link for Controlling and Monitoring Electronic Billboards

Presented by : 05gr797Bayu Anggoro Jati

Nurul Huda MahmoodPuri Novelti AnggraeniSatya 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 AssumptionsAssumptions 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]

• 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.

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dP A log s d d

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[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]

mod f hPL PL PL PL

[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

Path Loss

Noise Margin

148.6 dB

20.4 dB

EIRP = 20 dBW

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


Coherence Time

Measured doppler spectra for fixed wireless channel at 2.5GHz[1]


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

Yes No Yes No Yes NoASK v v vFSK v v * vPSK v v DPSK v

* : non-coherent FSK

Linear Coherent Constant Envelope

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

Generation of DBPSK signalb(k) 1 0 0 1 0 0 1 1d(k-1) 1 1 0 1 1 0 1 1d(k) = b(k) XOR d(k-1) 1 1 0 1 1 0 1 1 1transmitted phase (rad) 0 0 0 0 0 0 0

Detection of DBPSK signalreceived phase (rad) 0 0 0 0 0 0 0d(k) 1 1 0 1 1 0 1 1 1d(k-1) 1 1 0 1 1 0 1 1b(k) = d(k) XOR d(k-1) 1 0 0 1 0 0 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 and demodulation of the received signal.

FHSS block diagram (transmitter)


FHSS block diagram (receiver)


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

Fast and Slow FHSS


Example: Fast FHSS with M =4 and m = 2

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


DSSS Example


DSSS Spectrum


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


FHSS vs. DSSS:COMPARISON

System Collocation

DSSS FHSS

Symbol rate = 11 Mcps

Each band 22 MHz, with separation of 30 MHz

Available BW = 83.5 MHz

3 systems can be collocated

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 FHSS

Wideband Interference

May completely block system.

Only part of the hops will be blocked

Narrowband Interference

Interference is multiplied with the spread code, thus spreading it. Immune to narrow band interference up to a great extent

Interference signal present on a specific frequency will block hops on that specific frequencies. Hops on other frequencies will not be affected.

Illustration on how DSSS handles narrow band interference

Source: http://www.odessaoffice.com/wireless/fh_vs_ds.pdf

Noise and Interference Immunity

Signals from nearby active transmitters may be received at the receiver at higher power than the intended user.

Near Far Problem

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 is more sensitive to multipath than FHSS, especially when operating at higher bit rate.

DSSS FHSS

Multipath components generated due to signal reflection between transmitter and receiver,

The pulse is spread. So, narrow pulses of DSSS are more sensitive. Inter Symbol Interference

FHSS systems have better chances to be undisturbed by the 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

Throughput

DSSS FHSS

Single system:

IEEE 802.11 defines rates of up to 11Mbps, though practically up to 7 Mbps is achievable

In IEEE 802.11 standard FSSS system has throughput of up to 3 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.

• 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

Comparison: 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.

Spread Spectrum: Conclusion

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)

• 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) + 48fx(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.

Frequency Hop code

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.



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 – THE WHOLE SYSTEM

• Access technique : FHSS • Digital modulation : DBPSK• The channel model : SUI5 3 tap delay model• Hop sequence : IEEE 802.11• Hopping distance : 6 MHz• Carrier frequency : 2.4 GHz• Number of channel : 32 • Hopping rate : 32 hops/second • Dwell time : 31 ms dwell time• Bitrate : 512 kbps• Bit size in one hop : 31 ms x 512 kbps ≈ 16 kbits


• The simulation is frame by frame • Hopping distance 6 MHz -> uncorrelated

• Monte Carlo simulation to get accurate resultThe 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 controlSome 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


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

• 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.

FER (Frame Error Rate) Requirement

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 : 2.5 10−2

- at 12,8 dB for directional antenna : 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

• Good relationship among the members.

• We divided our job based on the strength of each member.

• Flexible way of working.

• Good supervisor.

• Lack of project management.

• Punctuality.

• Our flexible way of working has its own weakness.

Wireless Link for Controlling and Monitoring Electronic Billboards

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