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
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 …”  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 • 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  05gr797 P0 Project Report
Key Assumptions Assumptions made for P1 • Unlicensed band used is 2400-2483.5 MHz • Don’t consider antenna type, assuming • The central use 8 -15 dBi omnidirectional antenna • Billboards use 14 - 30 dBi directional antenna • Noise Figure is around 3 dB • Revised Data Rate is 512 kbps, thus bandwidth is 1 MHz • The distance is 4 kilometers at maximum  05gr797 P0 Project Report 2.4 GHz Outdoor Omnidirectional Antenna. Hyperlink Technologies. http://www.hyperlinktech.com/web/ antennas 2400 out omni.php#. 28 November2005. 2.4 GHz Outdoor Directional Antenna. Hyperlink Technologies. http://www.hyperlinktech.com/web/ antennas 2400 out directional.php#. 28 November 2005. 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 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 • 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.  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  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
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 • 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  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 • 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  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  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 • The measurement was done in 1.9 GHz but can safely adopted in 2.4 GHz  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. 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 • 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 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  • Block diagram of DBPSK receiver   Haykin, Simon. Communication Systems 4 th ed.. John Wiley and Sons, 2001  Feher, Kamilo. Wireless Digital Communication Modulation and Spread Spectrum Applications. Prentice Hall PTR, New Jersey : 1995
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: 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
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) 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)