Week 7-8 CSCD609 Mobile and Wireless Networks (Radio Propagation) PDF

CSCD609: Mobile and Wireless Networks Radio Propagation Week 7 I have no picture of this electromagnetic field that is in any sense accurate...I see some kind of vague, shadowy, wiggling, lines...so if you have some difficulty in making such a picture, you...

CSCD609: Mobile and Wireless Networks Radio Propagation Week 7 I have no picture of this electromagnetic field that is in any sense accurate...I see some kind of vague, shadowy, wiggling, lines...so if you have some difficulty in making such a picture, you should not be worried that your difficulty is unusual. -Richard Feyman Nobel Prize laureate in Physics F Apietu 1 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Lecture Outline Introduction to radio wave propagation Types of Radio waves Propagation mechanisms Free space propagation Model Land propagation F Apietu 2 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Types of Radio Waves Type Frequency Range Key Uses Submarine VLF 10 – 100 km 3–30 kHz communication LF 1 – 10km 30–300 kHz Maritime navigation MF 100 – 1000m 300 kHz–3 MHz AM radio broadcasting Shortwave radio, global HF 10 – 100m 3–30 MHz communication FM radio, TV VHF 1 – 10m 30–300 MHz broadcasting UHF 10cm – 10m 300 MHz–3 GHz Mobile phones, Wi-Fi Satellite SHF 1 – 10cm 3–30 GHz communication, radar Space communication, EHF 30–300 GHz scientific research F Apietu 3 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Propagation of Waves The basic modes by which radio waves are transmitted to a receiving antenna are: Free Space Propagation Ground (Surface) Waves Space Waves Sky Waves Satellite Communication F Apietu 4 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Free Space Propagation Key Characteristics: 1.Straight-Line Path: 1. Radio waves travel in a straight line from the transmitter to the receiver (line-of-sight propagation). 2.No Obstacles: 1. There are no physical barriers such as buildings, mountains, or trees to obstruct or alter the wave. 3.Ideal Conditions: 1. No atmospheric effects like refraction, scattering, or absorption that would degrade the signal. Inverse Square Law: The strength of the signal decreases with the square of the distance from the source. F Apietu 5 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Free Space Propagation Applications: 1.Satellite Communication: 1.Signals travel through space between ground stations and satellites. 2.Space Exploration: 1.Used for communication with spacecraft and interplanetary missions. 3.Point-to-Point Wireless Communication: 1.Microwave links or laser-based communication systems in ideal conditions. F Apietu 6 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Free Space Propagation Advantages: Predictable and consistent signal behavior. No multipath fading or distortion caused by obstacles. Maximum efficiency in transmitting high-frequency signals. Limitations: 1.Attenuation with Distance: 1. Signal strength decreases rapidly over long distances due to the inverse square law. 2.Limited to Line-of-Sight: 1. Requires a clear, unobstructed path between transmitter and receiver. 3.Environmental Sensitivity: 1. Not practical in environments with obstacles or atmospheric7 F Apietu Katsriku/CSCD609/Sem1/2014_15 interference.  CSCD609: Ground (Surface) Waves Ground Wave Propagation: 1.Radio waves travel along the Earth's surface. 2.Best for low-frequency waves (e.g., AM radio). 3.Limited by terrain and obstacles. F Apietu 8 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Ground Waves Important on the LF and MF portion of the radio spectrum. Used to provide relatively local radio communications coverage, especially by radio broadcast stations that require to cover a particular locality. Ground wave radio signal propagation is ideal for relatively short distance propagation on these frequencies during the daytime. F Apietu 9 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Ground (Surface) Waves These travel along the surface of the earth (more or less following the contour of the earth) and must be vertically polarized to prevent short-circuiting. F Apietu 10 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Ground Waves They can travel considerable distances, well over the visual horizon. As the wave propagates over the earth, it tilts over more and more. (A current is induced in the earth’s surface by the electromagnetic wave, the result is the wavefront near the surface slows down). This causes the wave to short circuit completely at some distance (in wavelengths) from its source. F Apietu 11 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Ground Waves Follows contour of the earth Can Propagate considerable distances Frequencies up to 2 MHz Example – AM radio F Apietu 12 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Surface Waves Disadvantages – Requires relatively high transmission power – They are limited to very low, low and medium frequencies which require large antennas – Losses on the ground vary considerably with surface material Advantages – Given enough power they can be used to communicate between any two points in the world – They are relatively unaffected by changing atmospheric conditions F Apietu 13 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Space wave propagation This includes radiated energy that travels in the lower few miles of the earth’s atmosphere. They include both direct and ground reflected waves. Direct waves travel in essentially a straight line between the transmitting and receiving antennas. The most common name is line of sight propagation. The field intensity at the receiving antenna depends on the distance between the two antennas and whether the direct and ground reflected waves are in phase. F Apietu 14 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Line-of-Sight Propagation F Apietu 15 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Line-of-Sight Propagation Optical line of sight d  3.57 h Effective, or radio, line of sight d  3.57 h d = distance between antenna and horizon (km) h = antenna height (m) K = adjustment factor to account for refraction, rule of thumb K = 4/3 F Apietu 16 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Line-of-Sight Propagation Maximum distance between two antennas for LOS propagation:  3.57 h1  h2  h1 = height of antenna one h2 = height of antenna two F Apietu 17 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Sky Wave Propagation F Apietu 18 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Sky Wave Propagation Signal reflected from ionized layer of atmosphere back down to earth Signal can travel a number of hops, back and forth between ionosphere and earth’s surface Reflection effect caused by refraction Examples – Amateur radio – CB radio F Apietu 19 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Sky Wave Propagation D region: – This region attenuates the signals as they pass through. The level of attenuation depends on the frequency. Low frequencies are attenuated more than higher ones. E region: – little attenuation of the signals, this region reflects, or more correctly refracts signals – The level of refraction reduces with frequency, higher frequency signals may pass through this region and on to the next region. – The E region is of great importance for HF propagation at the lower end of the HF spectrum and even the MF spectrum. F Apietu 20 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Sky Wave Propagation F region: Enables HF for worldwide communications. During the day this region often splits into F1 and F2 regions. F Apietu 21 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Effects of the Ionosphere on the Sky wave If we consider a wave of frequency , f incident on an ionospheric layer whose maximum density is N then the refractive index of the layer is given by 81N n  1 2 f F Apietu 22 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Critical Frequency If the frequency of a wave transmitted vertically is increased, a point will be reached where the wave will not be refracted sufficiently to curve back to earth and if this frequency is high enough then the wave will penetrate the ionosphere and continue on to outer space. The highest frequency that will be returned to earth when transmitted vertically under given atmospheric conditions is called the critical frequency. fc  9 N F Apietu 23 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Maximum Usable Frequency There is a best frequency for communication between any two points under specific ionospheric conditions. The highest frequency that is returned to earth at a given distance is called the Maximum Usable Frequency (MUF). f muf  9 N sec F Apietu 24 Katsriku/CSCD609/Sem1/2014_15  CSCD609: Optimum Working Frequency This is the frequency which provides the most consistent communication and is therefore the best to use. For transmission using the F2 layer it is defined as f owf  0.85  9 N sec F Apietu 25 Katsriku/CSCD609/Sem1/2014_15 CSCD609: Lowest Usable Frequency This is set by the attenuation in the ionosphere. A practical value of this is usually taken as 3 MHz. F Apietu 26 Katsriku/CSCD609/Sem1/2014_15 Propagation characteristics of wireless channels  Contents Introduction Radio propagation mechanisms Path loss modeling Effects of multi-path  Introduction Nature of radio channels makes them complicated – Wired medium provides reliable guided link – Wireless medium is unreliable – Has low bandwidth – Inherently a broadcast type – Different signals on a wired medium are physically conducted through different wires – All wireless transmission share the same medium Cellular 1GHz PCS and WLAN 2GHz WLAN 5GHz Local multipoint distribution service 28-60 GHz Optical communication IR  Introduction It is heavily site dependent accurate characterization is thus important in predicting signal coverage. – Terrain – Frequency of operation – Speed of mobile terminal – Interference sources – Other dynamic factors  Introduction Attenuation is a major limitation on performance of mobile systems If path is line of sight then signal loss may not be severe In urban surroundings the path may be indirect and signal would reach final destination after reflection, diffraction, refraction and scattering – Signal strength depends on distance travelled Obstacles they have reflected from or passed through Architecture of the environment Location of objects from receiver and transmitter  Introduction Frequency of operation affects propagation characteristics – GHz, Low power transmitters can be use (1 W), antenna sizes are much smaller order of a couple of cm, diversity schemes can be employed Signal strength loss at first metre is high, greater loss when passing through obstacles eg walls – >10 GHz, Signals confined within walls of a room – >60 GHz Atmospheric gases such as oxygen absorb the signals.  Introduction Three most important radio propagation characteristics – Achievable signal coverage This determines the size of the cell in a cellular topology as well as range of operation of the BS – path loss models – Maximum data rate that can be supported by the channel This is influenced by multipath structure and fading characteristics – The rate of fluctuation in the channel Caused by movement of transmitter, receiver or objects in between Characterized by the doppler spread of the channel  Wireless Transmission Impairments Attenuation and attenuation distortion Free space loss Noise Atmospheric absorption water vapor and oxygen contribute to attenuation  Wireless Transmission Impairments Multipath obstacles reflect signals so that multiple copies with varying delays are received Refraction bending of radio waves as they propagate through the atmosphere Line of sight propagation  Radio propagation mechanisms Most mobile communication systems are characterized by these N-LOS conditions: Reflection Diffraction Scattering A direct (line of sight) between two antennae. Reflection of the electromagnetic wave at a boundary. Reflection - occurs when signal encounters a surface that is large relative to the wavelength of the signal Diffraction of the electromagnetic wave at the edge of a building. Diffraction - occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave  Scattering of the electromagnetic wave. Scattering – occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less The signal reaches the receiver through reflection and diffraction. The signal reaches the receiver through reflection and scattering, as well as via a direct path. The most general case of signal reception, consisting of a direct path, a reflected path, a scattered path, and a diffracted path.  Path loss Path loss is the average propagation loss in signal strength over an area. It is the ratio of the transmitted power to the received power and includes all possible loss factors associated with the propagation wave between the transmit and receive antennas. Path loss Path loss  Free Space Propagation What is the received power in dBm in free space of a signal whose transmit power is 1 W and carrier frequency 2.4GHz if the receiver is at a distance of 1 mile from the transmitter? Assume the gains of both the receiver and transmitter are 1.6. What is the path loss in dB What is the transmission delay in ns Free Space Propagation Free Space Propagation  Free Space Propagation Develop an interactive implementation of the solution in Matlab. Your program must allow the user to specify all variables Show a plot of the received signal over distance Two Ray Model  Distance Power Relation The received signal power is proportional to the distance between transmitter and receiver raised to some exponent alpha, the distance power gradient; Po Pr   Po d  d 10 logPr   10 logP0   10 logd  If path loss in dB at a distance of 1m is: Lo  10 logPt   10 logPo  Total path loss is then: L p  Lo  10 logd  For direct path r  d 2 so that power received at a distance d Pt Gr Gt 2 r d   4 2 d 2 L Free space loss is given as    L free  20 log10  dB  4d  This can be rewritten as L free  32.44  20 log10  f   20 log10 d  This is an ideal case. The attenuation is much faster than predicted by inverse square law. r  d  v Given the power at a reference point then the received power 2   r d   r d ref  ref  d  d  If we combine this with the previous equation we obtain d  r d dBm  10 log10 r d ref   v log10  ref   d  d ref this is the reference distance (100m) Received power for different values of loss parameter v(v=2 corresponds to free space). Increased loss is seen as v goes up.  Path loss modeling Attenuation Strength of signal falls off with distance over transmission medium Attenuation factors for unguided media: Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal Signal must maintain a level sufficiently higher than noise to be received without error Attenuation is greater at higher frequencies, causing distortion  Fading This is a process that describes the fluctuation of the received signal as it travels to the receiving antenna. It can be described in terms of – primary cause multi-path or doppler – statistical distribution of the received envelop Rican, lognormal or Rayleigh – duration of fading long-term/short term, fast/slow  multipath/shadow  Multi-path this results from the existence of multiple paths between the transmitter and receiver. – The signals arriving will have different phases. The phase of the arriving signals will change rapidly and hence the received signal amplitude will fluctuate. The Rayleigh distribution is used to characterize this type of fading. r  r2  f r   2 exp   r0   2  2 – Random signal amplitude, r  Rician Distribution If with the signals arriving there is a strong LOS component then the Rician distribution is used to described it. r  (r 2  K 2   Kr  f rician r   2 exp  Io  2  r  0 K  0   2 2    K is a factor that determines how strong the LOS component is.  Lognormal Distribution This is the random shadowing effects that occur over a large number of measurement locations. It is also known as shadow fading or slow fading. Shadow because the fluctuation is caused by blockage of signal by buildings. Slow because the fluctuations are much slower with distance than that caused by another phenomenon also multi-path. r  (ln x   2  f LN r   exp   2 x  2 2   Power loss showing the three major effects: attenuation, long-term fading, and short-term fading.  It is important to know for how long a signal will be below a specified value (duration of fade) how often it crosses a threshold value (fading rate). These factors are important for the design of efficient coding schemes.  Doppler shift For a mobile user, motion will result in frequency shift of signal being received. This is called Doppler shift, fd v f d  f o cos  c  Pulse duration The duration of the pulse is an important factor. – If the duration of the pulse is very short, then changes introduced by motion will be slow and have no impact on the received signal – for large duration pulse, fast changes will be introduced as a result of motion and will thus affect transmission. Slow versus fast fading can be expressed in terms of the coherence time 9 Tc  16f d  (a) A transmitted pulse. (b) The multiple pulses produced due to the multipath arriving at different times and with different powers, leading to a broadened envelope of the pulse.  The Effects of Multipath Propagation Multiple copies of a signal may arrive at different phases If phases add destructively, the signal level relative to noise declines, making detection more difficult Intersymbol interference (ISI) One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit. The most common methods in reducing it are use of guard time, pulse shaping, signal coding and equalisation  Example: BS has a 900 MHz transmitter and a receiver is moving at the speed of 30 mph. Calculate the frequency of the received carrier and the coherence time if the vehicle is moving – i) directly toward the BS. – Ii) directly away from the BS  Loss Prediction Models A number of models have been proposed to predict the median loss. These models take into account the different ways in which the signal can reach the receiver. Two widely used models are: Okumura-Hata Model COST 231 Model  Loss Prediction Models Okumura-Hata Model : It is possible to calculate the free space loss between any two points based on empirical formula derived from experimental data for an urban area with correction factors then added for Antenna height suburban, quasi-open or open space or hilly terrain Diffraction loss due to mountains Sea or lake areas Road slope  The effective height of the BS antenna. The loss is given in terms of effective heights The median path loss in urban areas for the Okumura-Hata Model is Lp (dB)  69.55  26.16 log10  f o   44.9  6.55 log10 hb log10 d  13.82 log10 hb  ahmu  Correction Factors are as follows Large cities a hmu   3.2log10 11.75hmu   4.97 f  400MHz  2 o Small and Medium Cities ahmu   1.1log10  f o   0.7hmu  1.56 log10  f o   0.8  Median Loss in Suburban areas Lsub dB   Lp  2log10  f o / 28  5.4 2 where Lp is the loss in small to medium cities Median loss in Rural areas Lsub dB   Lp  4.78log10  f o   18.33  5.4 log10  f o  - 40.94 2  Where fo – carrier frequency – d distance between base station and mobile (km) – hb base station antenna height – hmu mobile unit antenna height is valid the model150 f  1500 oforMHz the ff parameter range 30  hb  200m 1  hmu  10m 1  d  20km Loss calculations based on the Hata model for four different environments. Carrier frequency = 900 MHz, base station antenna height = 150 m, MU antenna height = 1.5m.  COST 231 Model It is a combination of empirical and deterministic models for estimating path loss in urban area over frequency range of 800-2000MHz. The model is used in Europe for the GSM1800 system Lp  L f  Lrts  Lms or Lp  L f when Lrts  Lms  0 where L f free space loss Lrts rooftop - street diffraction and scatter loss Lms multiscreen loss  COST 231 Model The rooftop-to-street loss is given as Lrts  -16.9-10 logW  10 log f o  20logΔhm  Lo where W is the street width (m) hm  hr - hm (m) Lo  9.646dB 0    35o Lo  2.5  0.075  35dB 35    55o Lo  4  0.114  55dB 55    90o  is the incident angle relative to the street  COST 231 Model The multiscreen (multiscatter) loss is given as Lms  Lbsh  ka  kd log d  k f log f o  9 log b where b is the distance between buildings along radio path (m) Lbsh  18 log11  hb hb  hr Lbsh  0 hb  hr ka  54 hb  hr ka  54  0.8hb d  500m; hb  hr ka  54  1.6hb d d  500m; hb  hr  COST 231 Model kd  18 hb  hr 15hb ka  18  hb  hr hm  f  k f  4  0.7 c  1 for midsize cities and suburban  925   fc  k f  4  1.5  1 for metropolitan areas  925   Indoor Models Extra Large Zone There is a single base station outside the building which handles all traffic. Ideal for a region with a number of small offices and shops Large Zone Ideal for large building with low population density. A single base station housed with the building is used. Middle Zone The building is large and heavily populated eg shopping mall. A number of base stations housed within the building are used. Small Zone and Microzone Building with many partitions material properties of wall will determine signal penetration. Each room should have its own base station  The Finite Element Method       0 2 2       0 2 2  The Finite Element Method Find the variational integral whose first variation is zero for the given boundary conditions. Choose an appropriate trial function and expand the field components as a sum of the trial functions. Substitute the trial fields in the variational integral and find the first variation and equate it to zero The resulting simultaneous equations from the weak formulation of the boundary value problem x  x  0 are equivalent to a standard eigenvalue matrix equation of the form  The Finite Element Method Basic Concepts in the finite element method In the finite element method, the key ideas are the discretization of the region of interest into elements and using interpolating polynomials to describe the variation of the field within each of the elements  The Finite Element Method Example of an arbitrary shape domain with several regions of different material types  The Finite Element Method Steps involved in the finite element analysis discretize the domain under investigation into sub- domains or elements. The functionals for which the variational principle should be applied for the elements are then derived assemble all the element contributions to form a global matrix. solve the system of equations that is obtained, in this case a matrix equation The Finite Element Method  The Finite Element Method  The Finite Element Method x  x  0  11  12  13      21  22   23  Be   N   N  d    31  32  33  Ae   Q  ˆ  Q  d  1  FEM in Wireless Propagation        2 2 j 2k o no  2  2  k o n  no  2 2 2 z x y   j2 z        2    0       2 2 ko n N N   N x N x  T T dxdy e     ko2n 2 N N T dxdy e  FEM in Wireless Propagation Solution Methods Forward Difference Scheme     k 1 k  z z         2 k 2 k j 2k o no k 1   k   k o n  no  2 2 2 k z x 2 y 2  k 1   k  FEM in Wireless Propagation The Crank-Nicolson Method    k 1 k 1  z 2z  FEM in Wireless Propagation The Crank-Nicolson Method      k      2 k 2 k j 2k o no k 1      2  k  k o n  no   2 2 2 z  x y 2  z k  0.5 z  k  0.5   k 1  k   2  FEM in Tropospheric Propagation Antenna height 150m Beamwidth kf=11 Vertically polarized wave Simple boundary condition at upper level  FEM in Tropospheric Propagation Without Boundary Condition With Boundary Condition  Frequency of 200MHz FEM in Tropospheric Propagation FEM in Tropospheric Propagation Different Intensity Profiles  100MHz Paraxial form of Helmholtz Equation  1GHz Paraxial form of Helmholtz Equation Path Loss at different frequencies Propagation Modelling in Forest 30MHz Propagation Loss in Forest 100MHz  Path Loss with receiver height  Tunnel Propagation Signal Intensity at Tunnel end 40MHz Signal Intensity at Tunnel end 100MHz Signal Intensity at Tunnel end 700MHz Signal Intensity at Tunnel end 5GHz  Urban Streets All material presented in this course is based on the book by D. Dalcher and L. Brodie  Urban Streets All material presented in this course is based on the book by D. Dalcher and L. Brodie  Urban Streets All material presented in this course is based on the book by D. Dalcher and L. Brodie  Urban Streets All material presented in this course is based on the book by D. Dalcher and L. Brodie  Received Power at 100MHz All material presented in this course is based on the book by D. Dalcher and L. Brodie  Next Steps Characterisation of EM wave propagation in soil? – Determine accurately the permittivity of soil – Solve propagation equation using improved value of epsilon All material presented in this course is based on the book by D. Dalcher and L. Brodie