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Proceedings the 10th students scientific research conference analyzing Monte Carlo for evaluating research stages, they have concluded that one can achieve long-term strategy by combining moving average crossover strategy with CANSLIM method of William Oneil (Iavnov & Beyoglu, 2008)” (Mehdi Majafi, Farshid Asgari,Using CANSLIM Analysis for Evaluating Stocks of the Companies Admitted in Tehran Stock Exchange, Journal of American Science 2013) Modeling and simulation of wireless communication networks of VNU-IS Group sciences: Trần Hoàng Anh Nguyễn Văn Sơn Nguyễn Văn Dũng Lê Tự Quốc Thắng Class: MIS2015A Sciences Advisors: Associate Prof Lê Trung Thành MSc Lê Duy Tiến 222 Proceedings the 10th students scientific research conference CHAPTER 1: INTRODUCTION TO WIRELESS LAN 1.1 Introduction[1] Communication systems that rely on cabling are inherently faster, more reliable, and more secure than wireless systems Installing a cabling infrastructure can be expensive Furthermore, if the network traverses public highways, it is subject to regulation and requires the services of a licensed operator Wireless communication has the advantage of mobility and obviates the need for cabling, but the radio frequency spectrum is also heavily regulated Nevertheless, the allocation of unlicensed parts of the spectrum has facilitated the growth in wireless local area networks (WLANs) The European Telecommunications Standards Institute(ETSI) published the first WLAN standard, HiperLAN/1, finalised in 1995, and followed by HiperLAN/2 in 2000 However, it is the IEEE 802.11 WLAN standard that has become the most widely accepted Portable devices such as laptops, personal digital assistants (PDAs) and even mobile phones have 802.11 chipsets built in as standard Furthermore, wireless infrastructure equipment (access-points) is relatively inexpensive WLAN technology has progressed at a rapid pace The original IEEE 802.11 standard supported data rates up to Mb/s In 2010, devices capable of 54Mb/s are commonplace Furthermore, devices that utilize MIMO (multiple inputs, multiple outputs) technology, which can support up to 300 Mb/s, are growing in popularity The 802.11 standard has been very successful in incorporating advances in modulation techniques while maintaining interoperability with legacy schemes New modulation schemes, however, not replace subsequent schemes 802.11 can select any scheme 223 Proceedings the 10th students scientific research conference from the current set of modulation schemes in order to optimise frame transmission In this way, wireless devices can link rate adapt according to the channel conditions 802.11 has not been without its problems, especially with regard to security WLANs are particularly vulnerable to eavesdropping, unauthorised access and denial of service due to their broadcast nature The original 802.11 standard had no security provisions at all, neither authentication, encryption or data integrity Some access-point vendors offered authentication of the client’s physical address The standard was amended in 1999 to support a basic protection mechanism Wired equivalent privacy (WEP) used cryptographic methods for authentication and encryption The security flaws in WEP, however, have given rise to a complete research field In 2001, Fluhrer, Mantin, and Shamir showed that the WEP key could be obtained within a couple hours with just a consumer computer[2] The authors highlighted a weakness in RC4’s key scheduling algorithm and showed that it was possible to derive the key merely by collecting encrypted frames and analysing them Sincethen, more sophisticated WEP attacks have been developed Along with advances in computing power, the WEP key can be recovered in seconds A further vulnerability with WEP is that the pre-shared key is common to all users on the same SSID Any user associated with an SSID, therefore, can decrypt packets of other users on the same SSID These problems have largely been resolved with the deprecation of WEP and the introduction of enhanced security methods As with the introduction of new modulation techniques, interoperability is an issue The current security methods rely on modern cryptography techniques which are only available on new devices On legacy devices, interim solutions have been adopted 1.2 I EEE 802 Standard [2] The Institute of Electrical and Electronic Engineers (IEEE) is a large non-profit, professional society concerned with technological research and development Its standards board oversees the development of IEEE standards and is accredited by the American National Standards Institute (ANSI) Project802 was initiated in1980 with the aim of defining asset of standards for local area network (LAN) technology The standards cover the data link and physical layers of the International Organization for Standardization (ISO) open system interconnection (OSI) seven layer reference model The data link layer is concerned with the reliable transfer of data frames over the 224 Proceedings the 10th students scientific research conference physical channel It implements various forms of error control, flow control and synchronisation In the 802 reference model, the data link layer comprises two sublayers, the logical link control (LLC) sub-layer and the medium access control (MAC) sub-layer Figure 1.1: shows the 802 reference model [3] Data link layer Logical link control (LLC) Media access control(MAC) Physical layer Physical medium 225 Proceedings the 10th students scientific research conference Figure 1.2: Wireless LANs Number Standard Bridging Logical link control 802.1 802.2 Comment ( LLC ) 802.3 CSMA/CD Enthernet-like 802.4 Token bus Dishanded 802.5 Token Ring Inactive 802.11 Wireless LANs Wi – FI 802.15 Wireless PANs Bluetooth and Zigbee 802.16 Wireless MANs WiMAX LLC is defined in the IEEE 802.2 standard Its primary function is to provide an interface between the MAC layer and the higher layers (network layer) It performs multiplexing functions in order to support multiple upper layer protocols Furthermore, it is responsible for flow control and error control Both connectionless and connection-orientated frame delivery schemes are supported LLC is unconcerned with the specific details of the LAN medium itself That is the responsibility of the MAC sub-layer which is primarily concerned with managing access to the physical channel The physical layer of 802 is responsible for the transmission and reception of bits, encoding and decoding of signals and synchronisation (preamble processing) The physical layer hides the specifics of the medium from the MAC sub-layer The first 802 standards were wired LANs Carrier sense multiple access with collision detect (CSMA/CD) based LANs (802.3) are the most widely used Token bus (802.4), token ring (802.5) and fibre distributed data interface (FDDI) were also defined Wireless network standards emerged in the 1990s IEEE 802.11 defined a wireless LAN technology that operates in license free bands 802.11 is commonly referred to as WiFi 802.11 employs a CSMA protocol similar to 802.3 (and Ethernet) However, instead of using collision detection, it uses collision avoidance Wireless personal area networks (PANs) are covered specifiestheBluetoothstandardand802.15.4 by defines 802.15, where 802.15.1 Zigbee.IEEE802.16isawireless metropolitan area network (MAN) also known as WiMAX Table 1.1 shows a summary of some of the 802 standards 1.2.1 The 802.11 Working Group [4] 226 Proceedings the 10th students scientific research conference The IEEE 802.11 was formed in July 1990 to develop CSMA/CA, a variation of CSMA/CD (Ethernet)−based wireless LANs The working group produced the first 802.11 standard in 1997, which specifies wireless LAN devices capable of operating up to Mbps using the unlicensed 2.4−GHz band Currently, the working group has nine basic task groups and each is identified by a letter from a to i Following are the current 802.11 task groups and their primary responsibilities:  802.11a Provides a 5−GHz band standard for 54−Mbps transmission rate  802.11b Specifies a 2.4−GHz band standard for up to 11−Mbps transmission rate  802.11c Gives the required 802.11−specific information to the ISO/IEC 10038 (IEEE 802.1D) standard • 802.11d Adds the requirements and definitions necessary to allow 802.11 wireless LAN equipment to operate in markets not served by the current 802.11 standard  802.11e Expands support for LAN applications with Quality of Service requirements.• 802.11f Specifies the necessary information that needs to be exchanged between access points to support the P802.11 DS functions  802.11g Develops a new PHY extension to enhance the performance and the possible applications of the 802.11b compatible networks by increasing the data rate achievable by such devices  802.11h Enhances the current 802.11 MAC and 802.11a PHY with network management and control extensions for spectrum and transmit power management in 5−GHz license exempt bands  802.11i Enhances the current 802.11 MAC to provide improvements in security 1.2.2 The 802.11 Standard Details [4] The 802.11 standard specifies wireless LANs that provide up to Mbps of transmission speed and operate in the 2.4−GHz Industrial, Scientific, and Medical (ISM) band using either frequency−hopping spread spectrum (FHSS) or direct−sequence spread spectrum (DSSS)[5] The IEEE approved this standard in 1997 The standard defines a physical layer (PHY), a medium access control (MAC) layer, the security primitives, and the basic operation modes The Physical Layer 227 Proceedings the 10th students scientific research conference The 802.11 standard supports both radio frequency− and infrared−based physical network interfaces However, most implementations of 802.11 use radio frequency, and we only discuss the radio frequency−based physical interface here 802.11 Frequency Bandwidth 802.11 standard−compliant devices operate in the unlicensed 2.4−GHz ISM band Due to the limited bandwidth available when the electromagnetic spectrum is used for data transmission, many factors have to be considered for reliable, safe, and high−performance operation These factors include the technologies used to propagate signals within the RF band, the time that a single device is allowed to have an exclusive transmission right, and the modulation scheme For these reasons, FCC regulations require that radio frequency systems must use spread spectrum technology when operating in the unlicensed bands Spread Spectrum Technology The 802.11 standard mandates using either DSSS or FHSS In FHSS, the radio signal hops within the transmission band Because the signal does not stay in one place on the band, FHSS can elude and resist radio interference DSSS avoids interference by configuring the spreading function in the receiver to concentrate the desired signal, and to spread out and dilute any interfering signal Direct−Sequence Spread Spectrum (DSSS) In DSSS the transmission signal is spread over an allowed band The data is transmitted by first modulating a binary string called spreading code A random binary string is used to modulate the transmitted signal This random string is called the spreading code The data bits are mapped to a pattern of "chips" and mapped back into a bit at the destination The number of chips that represent a bit is the spreading ratio The higher the spreading ratio, the more the signal is resistant to interference The lower the spreading ratio, the more bandwidth is available to the user The FCC mandates that the spreading ratio must be more than 10 Most products have a spreading ratio of less than 20 The transmitter and the receiver must be synchronized with the same spreading code Recovery is faster in DSSS systems because of the ability to spread the signal over a wider band Frequency−Hopping Spread Spectrum (FHSS) 228 Proceedings the 10th students scientific research conference This spread spectrum technique divides the band into smaller subchannels of usually MHz The transmitter then hops between the subchannels sending out short bursts of data for a given time The maximum amount of time that a transmitter spends in a subchannel is called the dwell time In order for FHSS to work correctly, both communicating ends must be synchronized (that is, both sides must use the same hopping pattern), otherwise they lose the data FHSS is more resistant to interference because of its hopping nature The FCC mandates that the band must be split into at least 75 subchannels and that no subchannel is occupied for more than 400 milliseconds Debate is always ongoing about the security that this hopping feature provides Since there are only 75 subchannels available, the hopping pattern has to be repeated once all the 75 subchannels have been hopped HomeRF FHSS implementations select the initial hopping sequence in a pseudorandom fashion from among a list of 75 channels without replacement After the initial 75 hops, the entire sequence is repeated without any replacement or change in the hopping order An intruder could possibly compromise the system by monitoring and recording the hopping sequence and then waiting till the whole sequence is repeated Once the hacker confirms the hopping pattern, he or she can predict the next subchannel that hopping pattern will be using thereby defeating the hopping advantage altogether HomeRF radios, for example, hop through each of the 75 hopping channels at a rate of 50 hops per second in a total of 1.5 seconds, repeating the same pattern each time, enabling a hacker to guess the hopping sequence in seconds Nevertheless, this technique still provides a high level of security in that expensive equipment is needed to break it Many FHSS LANs can be colocated if an orthogonal hopping sequence is used Since the subchannels in FHSS are smaller than DSSS, the number of colocated LANs can be greater with FHSS systems The most commonly used standard based on FHSS is HomeRF The MAC Layer The MAC layer controls how data is to be distributed over the physical medium The main job of the MAC protocol is to regulate the usage of the medium, and this is done through a channel access mechanism A channel access mechanism is a way to divide the available bandwidth resource between subchannels—the radio channel—by regulating the use of it It tells each subchannel when it can transmit and 229 Proceedings the 10th students scientific research conference when it is expected to receive data The channel access mechanism is the core of the MAC protocol With most wired LAN using the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) it was a logical choice for the 802.11 Working Group to apply the CSMA/CD technology when developing the MAC layer for the 802.11 standard The working group chose the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), a derivative of CSMA/CD, as the MAC protocol for the 802.11 standard CSMA/CA works as follows: The station listens before it sends If someone is already transmitting, it waits for a random period and tries again If no one is transmitting, then it sends a short message This message is called the ready−to−send message (RTS) This message contains the destination address and the duration of the transmission Other stations now know that they must wait that long before they can transmit The destination then sends a short message, which is the clear−to−send message (CTS) This message tells the source that it can send without fear of collisions Upon successful reception of a packet, the receiving end transmits an acknowledgment packet (ACK) Each packet is acknowledged If an acknowledgment is not received, the MAC layer retransmits the data This entire sequence is called the four−way handshake 1.2.3 802.11 Security [4] IEEE 802.11 provides two types of data security authentication and privacy Authentication is the means by which one station verifies the identity of another station in a given coverage area In the infrastructure mode, authentication is established between an AP and each station When providing privacy, a wireless LAN system guarantees that data is encrypted when traveling over the media There are two types of authentication mechanisms in 802.11: open system or shared key In an open system, any station may request authentication The station receiving the request may grant authentication to any request, or to only those from stations on a preconfigured user−defined list In a shared−key system, only stations that possess a secret encrypted key can be authenticated Shared−key authentication is available only to systems having the optional encryption capability The 802.11 standard mandates the use of Wired Equivalent Privacy (WEP) for providing confidentiality of the data transmitted over the air at a level of security 230 Proceedings the 10th students scientific research conference comparable to that of a wired LAN WEP is a security protocol, specified in the IEEE wireless fidelity (Wi−Fi) standard that is designed to provide a wireless LAN with a level of security and privacy comparable to what is usually expected of a wired LAN WEP uses the RC4 Pseudo Random Number Generator (PRNG) algorithm from RSA Security, Inc to perform all encryption functions A wired LAN is generally protected by physical security mechanisms (for example, controlled access to a building) that are effective for a controlled physical environment, but they may be ineffective for wireless LANs because radio waves are not necessarily bounced by the walls containing the network WEP seeks to establish protection similar to that offered by the wired network's physical security measures by encrypting data transmitted over the wireless LAN This way even if someone listens in to the wireless packets, that eavesdropper will not be successful in understanding the content of the data being transmitted over the wireless LAN 1.2.4 Operating Modes [4] The 802.11 standard defines two operating modes: the ad hoc and the infrastructure mode To understand how an 802.11 wireless LAN operates, let's understand the basic terminologies used to describe the two modes Terminologies The terminologies describing the two operating modes include a station, an independent basic service set (IBSS), a basic service set (BSS), an extended service set (ESS), an access point (AP), and a distribution system (DS) Each of these is discussed in the paragraphs that follow An 802.11 Station An 802.11 station is defined as an 802.11−compliant device This could be a computer equipped with an 802.11−compliant network card Basic Service Set (BSS) A BSS consists of two or more stations that communicate with each other An Access Point (AP) An AP is a station in an 802.11 wireless LAN that routes the traffic between the stations or among stations within a BSS The AP can simply be a routing device with 802.11 capabilities An AP must have a network address, it must act like a regular station on the network, and it must be addressable by the other stations on the network 231 Proceedings the 10th students scientific research conference M = 0.5; % heavy fog afogloss = fogpl(R,fc77,T,M); agasloss = gaspl(R,fc77,T,P,ROU); % Multiply by for two-way loss semilogy(R,2*[apathloss arainloss afogloss agasloss]); grid on; xlabel('Propagation Distance (m)'); ylabel('Path Loss (dB)'); legend('Free space','Rain','Fog','Gas','Location','Best') title('Path Loss for 77 GHz Radar'); Figure 3.5: Path loss for 77 GHz Radar The plot suggests that for a 77 GHz automotive radar, the free space path loss is the dominant loss Losses from fog and atmospheric gasses are negligible, accounting for less than 0.5 dB The loss from rain can get close to dB at 180 m Propagation Delay and Doppler Shift on Top of Propagation Loss 263 Proceedings the 10th students scientific research conference Functions mentioned above for computing propagation losses, are useful to establish budget links To simulate the propagation of arbitrary signals, we also need to apply range-dependent time delays, gains and phase shifts The code below simulates an air surveillance radar operated at 24 GHz fc = 24e9; First, define the transmitted signal A rectangular waveform will be used in this case waveform = phased.RectangularWaveform; wav = waveform(); Assume the radar is at the origin and the target is at a km range, of the direction of 45 degrees azimuth and 10 degrees elevation In addition, assume the propagation is along line of sight (LOS), a heavy rain rate of mm/h with no fog Rt = 5e3; az = 45; el = 10; pos_tx = [0;0;0]; pos_rx = [Rt*cosd(el)*cosd(az);Rt*cosd(el)*sind(az);Rt*sind(el)]; vel_tx = [0;0;0]; vel_rx = [0;0;0]; loschannel = phased.LOSChannel( 'PropagationSpeed',c, 'OperatingFrequency',fc, 'SpecifyAtmosphere',true, 'Temperature',T, 'DryAirPressure',P, 'WaterVapourDensity',ROU, 'LiquidWaterDensity',0, % No fog 'RainRate',rr, 'TwoWayPropagation', true) loschannel = phased.LOSChannel with properties: 264 Proceedings the 10th students scientific research conference PropagationSpeed: 299792458 OperatingFrequency: 2.4000e+10 SpecifyAtmosphere: true Temperature: 15 DryAirPressure: 101300 WaterVapourDensity: 7.5000 LiquidWaterDensity: RainRate: 16 TwoWayPropagation: true SampleRate: 1000000 MaximumDistanceSource: 'Auto' The received signal can then be simulated as y = loschannel(wav,pos_tx,pos_rx,vel_tx,vel_rx); The total loss can be computed as L_total = pow2db(bandpower(wav))-pow2db(bandpower(y)) L_total = 289.6873 To verify the power loss obtained from the simulation, compare it with the result from the analysis below and make sure they match Lfs = 2*fspl(Rt,c/fc); Lr = 2*rainpl(Rt,fc,rr,el,tau); Lg = 2*gaspl(Rt,fc,T,P,ROU); L_analysis = Lfs+Lr+Lg L_analysis = 289.6472 Multipath Propagation Signals may not always propagate along the line of sight Instead, some signals can arrive at the destination via different paths through reflections and may add up either constructively or destructively This multipath effect can cause significant fluctuations in the received signal Ground reflection is a common phenomenon for many radar or wireless communication systems For example, when a base station sends a signal to a mobile 265 Proceedings the 10th students scientific research conference unit, the signal not only propagates directly to the mobile unit but is also reflected from the ground Assume an operating frequency of 1900 MHz, as used in LTE, such a channel can be modeled as fc = 1900e6; tworaychannel = phased.TwoRayChannel('PropagationSpeed',c, 'OperatingFrequency',fc); Assume the mobile unit is 1.6 meters above the ground, the base station is 100 meters above the ground at a 500 meters distance Simulate the signal received by the mobile unit pos_base = [0;0;100]; pos_mobile = [500;0;1.6]; vel_base = [0;0;0]; vel_mobile = [0;0;0]; y2ray = tworaychannel(wav,pos_base,pos_mobile,vel_base,vel_mobile); The signal loss suffered in this channel can be computed as L_2ray = pow2db(bandpower(wav))-pow2db(bandpower(y2ray)) L_2ray = 109.1524 The free space path loss is given by L_ref = fspl(norm(pos_mobile-pos_base),c/fc) L_ref = 92.1673 The result suggests that in this configuration, the channel introduces an extra 17 dB loss to the received signal compared to the free space case Now assume the mobile user is a bit taller and holds the mobile unit at 1.8 meters above the ground Repeating the simulation above suggests that this time the ground reflection actually provides a dB gain! Although free space path loss is essentially the same in the two scenarios, a 20 cm move caused a 23 dB fluctuation in signal power pos_mobile = [500;0;1.8]; y2ray = tworaychannel(wav,pos_base,pos_mobile,vel_base,vel_mobile); L_2ray = pow2db(bandpower(wav))-pow2db(bandpower(y2ray)) L_ref = fspl(norm(pos_mobile-pos_base),c/fc) L_2ray = 86.2165 266 Proceedings the 10th students scientific research conference L_ref = 92.1666 Wideband Propagation in a Multipath Environment Increasing a system's bandwidth increases the capacity of its channel This enables higher data rates in communication systems and finer range resolutions for radar systems The increased bandwidth can also improve robustness to multipath fading for both systems Typically, wideband systems operate with a bandwidth of greater than 5% of their center frequency In contrast, narrowband systems operate with a bandwidth of 1% or less of the system's center frequency The narrowband channel in the preceding section was shown to be very sensitive to multipath fading Slight changes in the mobile unit's height resulted in considerable signal losses The channel's fading characteristics can be plotted by varying the mobile unit's height across a span of operational heights for this wireless communication system A span of heights from 10cm to 3m is chosen to cover a likely range for mobile unit usage % Simulate the signal fading at mobile unit for heights from 10cm to 3m hMobile = linspace(0.1,3); pos_mobile = repmat([500;0;1.6],[1 numel(hMobile)]); pos_mobile(3,:) = hMobile; vel_mobile = repmat([0;0;0],[1 numel(hMobile)]); release(tworaychannel); y2ray = tworaychannel(repmat(wav,[1 numel(hMobile)]), pos_base,pos_mobile,vel_base,vel_mobile); The signal loss observed at the mobile unit for the narrowband system can now be plotted L2ray = pow2db(bandpower(wav))-pow2db(bandpower(y2ray)); plot(hMobile,L2ray); xlabel('Mobile Unit''s Height (m)'); ylabel('Channel Loss (dB)'); title('Multipath Fading Observed at Mobile Unit'); 267 Proceedings the 10th students scientific research conference grid on; Figure 3.6: Multipath Fading Observed at Mobile Unit(1) The sensitivity of the channel loss to the mobile unit's height for this narrowband system is clear Deep signal fades occur at heights that are likely to be occupied by the system's users Increasing the channel's bandwidth can improve the communication link's robustness to these multipath fades To this, a wideband waveform is defined with a bandwidth of 10% of the link's center frequency bw = 0.10*fc; pulse_width = 1/bw; fs = 2*bw; waveform = phased.RectangularWaveform('SampleRate',fs, 'PulseWidth',pulse_width); wav = waveform(); A wideband two-ray channel model is also required to simulate the multipath reflections of this wideband signal off of the ground between the base station and the mobile unit and to compute the corresponding channel loss widebandTwoRayChannel = 268 Proceedings the 10th students scientific research conference phased.WidebandTwoRayChannel('PropagationSpeed',c, 'OperatingFrequency',fc,'SampleRate',fs); The received signal at the mobile unit for various operational heights can now be simulated for this wideband system y2ray_wb = widebandTwoRayChannel(repmat(wav,[1 numel(hMobile)]), pos_base,pos_mobile,vel_base,vel_mobile); L2ray_wb = pow2db(bandpower(wav))-pow2db(bandpower(y2ray_wb)); hold on; plot(hMobile,L2ray_wb); hold off; legend('Narrowband','Wideband'); Figure 3.7: Multipath Fading Observed at Mobile Unit (2) As expected, the wideband channel provides much better performance across a wide range of heights for the mobile unit In fact, as the height of the mobile unit increases, the impact of multipath fading almost completely disappears This is because the difference in propagation delay between the direct and bounce path signals 269 Proceedings the 10th students scientific research conference is increasing, reducing the amount of coherence between the two signals when received at the mobile unit Conclusion This example provides a brief overview of RF propagation losses due to atmospheric and weather effects It also introduces multipath signal fluctuations due to bounces on the ground It highlighted functions and objects to calculate attenuation losses and simulate range-dependent time delays and Doppler shifts 3.2 Simulation of signal propagation in an area with multi-walls 3.2.1 Indoor Propagation Models Ideally, for getting the optimal propagation model we should solve the Maxwell equations (FDTD models) based on the information provided by the shape of the objects present in the room/building As this method would be highly complex computationally, the deterministic models (based on Geometrical Optics) can be use as an alternative These models use the optical geometry and try to simulate the environment, based on provided information of objects, focus direction and illumination… Although the results obtained by these deterministic models are used to be satisfactory, the amount of data required which means a high time cost does not compensate us That is the reason why the empirical models (COST, ITU…) are possible alternatives These models are based in measures previously done and try to generate a pattern that can be useful to fully define the event However, these models are not complex enough to predict instantaneous changes or specific signal variations, for this reason we would need the deterministic models The positive part is that the complexity required is much more reduced, and number of input parameters is small compared with the previous model; that is why the computational cost is in consequence also reduced In this study, focusing on indoor propagation models, we have analysed several different Empirical models: The Free Space-Path Loss [18], the ITU-R P.1238-7 [19] and the different models provided by the COST Project, which are the Linear Attenuation Model (LAM), One-Slope Model (1SM) and the Multi-Wall Model (MWM) Others more complex models such as the Multi-Wall Multi-Floor model or 270 Proceedings the 10th students scientific research conference the Motley-Keenan model were out of our purpose for their complexity and trade-off precision-computational cost could not be as good as with the models provided here Even though there are more empirical models that could be useful apart of these as in [18], we have focused on the “classical ones” The more interesting ones are the ITU-R P.1238-7 and the MWM, the rest are too simple: the Free-Space Path Loss is the basic structure for modelling the wireless system and the LAM or the 1SM just simply add one additional parameter for modelling the others losses, which is not enough complex for obtaining accurate results The others, as mentioned, are outside our study Some studies show a similar performance between the ITU-R P.1238-7 and the COST231 MWC for different scenarios, that is why for simplicity and computational time we have chosen a modified version of the ITU model, due to we are interested in flat layout models representing only one floor (considering only the losses due to walls and not to floors) That is why we will focus on these two models in this Project The ITU-R P.1238 [12] models the Loss using as a parameters the frequency (), the distance ( ), the distance power loss coefficient ( ) and the penetration Loss factor () which depends on the frequency and the number of floors between the transmitter and receiver ( ) There is important to mention that these parameters have been empirically found and also say that must be greater than meter for the validity of this model as we can see again in[12]: L(dB) 20log( f ) Nlog(d) Lf (n) 28 737\* MERGEFORMAT (.) Values used for this model are: For our work bands (2.4 GHz and GHz) we have this parameters based on various measurement results found in[12]: Power Loss Coefficient N: Frequency (GHz) 2.4 Residential 28 28-30* Office 30 31 *: depending on the materials used in the walls (concrete or wooden) Floor penetration loss factors, L f ( n) (dB) with n being the number of floors penetrated, for indoor transmission loss calculation (n ≥ 1): 271 Proceedings the 10th students scientific research conference Frequency (GHz) Residential Office 2.4 5-10* 14 713* 16 Table: Floor Penetration Loss Factor for different environments and frequencies *: depending on the materials used in the walls (5 or for each wooden Wall, 10 or 13 for each concrete wall) The COST-231 Multi-Wall Model (MWM)[12], as it is showed in Equation and Equation gives the path loss as the free space loss ( L fs ( n, d ) ) added with losses introduced by the walls and floors penetrated by the direct path between the transmitter and the receiver This model considers different types of walls ( K wi ) depending on their losses ( Lwi , penetration losses) but always the same type of floors ( Kf ( K f 2 K f 1 b ) Lf ) It has been observed that the total floor loss is a non-linear function of the number of penetrated floors This is compensated by adding an empirical parameter b (usually around 0.5) Also we have n as a power decay index and as a Loss constant The multiwall model (MWM) can then be expressed in form: N L(dB)  L fs(n,d)  Lc   Lwi K wi  K f i1 ( K f 2 K f 1 b) Lf a 838\* MERGEFORMAT (.) L fs(n,d)  10 * n* log10 ( 4 )  939\* MERGEFORMAT (.) 3.2.2 Simulation Here are some cases where the placement of APs is changed and Matlab is used for simulation: 272 Proceedings the 10th students scientific research conference Figure 3.8: One AP in an area with multiwall As seen on the picture, the signal level of wifi coverage Placed in the corner between the two walls with high wave breaking help the wifi can pass the next room The corner of the rest is made of materials with less break wave so the wifi is less attenuated and can still be covered Although, could not pass the next wall Figure 3.9: Three AP set in different places 273 Proceedings the 10th students scientific research conference Figure 3.10: Three AP set in different places Figure 3.11: Three AP set in different places 274 Proceedings the 10th students scientific research conference Figure 3.12: Four AP set in different places By changing AP pointers on Matlab simulation software, from there we have to figure out how to optimize the wifi system … Conclusion and Recommendation Experience and benefits learned from the study of topic:  Proficiency in C programming language, Matlab  Understand the latest wireless networking technologies and how to operate a wifi system  Proficient in simulation methods, modeling a signal system Conclusion: This project proposes a common approach to facilitate the evaluation and measurement of Wi-Fi signals in order to find the best installation solution for the wifi system It suggests that a comprehensive approach needs to be used for the design, implementation, monitoring, evaluation, and review of such interventions This method is not intended to be prescriptive and can be applied flexibly to each place context It is hoped that it will promote the use of a common understanding/logic on 275 Proceedings the 10th students scientific research conference how attraction and retention interventions work, using a systems perspective It starts with a common set of indicators, which enable comparison between various cases, and facilitates reviews of real situations References [1] a A I M Scott R Fluhrer, "" Weaknesses in the key scheduling algorithm of rc4 In SAC ’01: Revised Papers from the 8th Annual International Workshop on Selected Areas in Cryptography,"" 2001 [2] S Sotillo, "Handbook of Computer Communications Standards, 2nd edition, volume 2," 1990 [3] C.-Y H Alan Holt, "802.11 Wireless Networks: Security and Analysis Computer Communications and Networks," (in English), p 212, 2010 [4] A K Jahanzeb Khan, "Building Secure Wireless Networks with 802.11," (in English), 2003 [5] S Fluhrer, I Mantin, and A Shamir, "Weaknesses in the Key Scheduling Algorithm of RC4, Eighth Annual Workshop on Selected Areas in Cryptography," 2001 [6] Ron_Olexa, ""Implementing_802.11,_802.16_and_802."." [7] J Berg, The IEEE 802.11 Standardization – Its History, Specifications, Implementations, and Future (Technical Report GMU-TCOM-TR-8, George Mason University) [8] "Globalstar Value Proposition," Globalstar Spectrum Holdings - Investor Relations Solutions," 2014 [9] Wikipedia, "Shannon–Hartley theorem, Available at: https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem," 2015 [10] J Berg, "The IEEE 802.11 Standardization – Its History, Specifications, Implementations, and Future (Technical Report GMU-TCOM-TR-8, George Mason University)." [11] C Gabriel, ""Towards 2020: Emerging Opportunities for Wi-Fi Services," Maravedis-Rethink," 2015 [12] S J Park, C H Lee, K T Jeong, H J Park, J G Ahn, and K H Song, "Fiberto-the-home services based on wavelength-division-multiplexing passive optical network," IEEE Journal of Lightwave Technology, vol 22, pp 25822591, 2004 [13] T S Rappaport, ""Wireless Communications Principles and Practice," IEEE Press/Prentice Hall PTR, Upper Saddle River, New Jersey," 1996 [14] "Recommendation ITU-R P.525-2," 1994 [15] Z Li, Z Chen, and B Li, "Optical pulse controlled all-optical logic gates in SiGe/Si multimode interference," Optics Express, vol 13, no 3, pp 1033-1038, 2005 276 Proceedings the 10th students scientific research conference [16] [17] [18] [19] "Recommendation ITU-R P.840-3," 2013 "Recommendation ITU-R P.676-10," 2013 R E e al, ""A new generic model for signal propagation in Wi-Fi and Wimax environments", in Wireless Days," 2008 R I.-R P.1238-7, ""Propagation data and prediction methods for the planning of indoor radiocommunication systems and radio local area networks in the frequency range 900 MHz to 100 GHz P Series Radiowave propagation,"" 02/2012 277 ... new frequency bands? The answer is easy, despite of the different channels of the ISM band; the truth is that is a “free band” for different uses and not only for the 802.11b/g/n standards It causes... products It is also the basis for wired ADSL technology and some HDTV transmissions standards 2.2.3 Frequency Bands By law, the relation between the standard 802.11 and the frequency bands is direct,... main job of the MAC protocol is to regulate the usage of the medium, and this is done through a channel access mechanism A channel access mechanism is a way to divide the available bandwidth