EE 552/452 Wireless Communications (and Networks) 2007 PDF

EE 552/452, Spring, 2007 Wireless Communications (and Networks) Zhu Han Department of Electrical and Computer Engineering Class 8 Feb. 8th, 2007  Outline  Class rescheduling –...

EE 552/452, Spring, 2007 Wireless Communications (and Networks) Zhu Han Department of Electrical and Computer Engineering Class 8 Feb. 8th, 2007  Outline  Class rescheduling – Feb. 15th and Feb 22th , two more classes – Mar 8th, Mar. 15th. no class, Mar. 13th: first mid-term – Mar. 22nd, Mar. 29th two more classes – Apr. 12th, Apr. 19th, no class, Apr. 17th: second mid-term – Food preference? Pizza, Subs, Baja Fresh … Taboo?  Review – Propagation mechanism: too theoretical for practice use. concept  Reflection  Diffraction  Scattering – Log-distance path loss model and log-normal shadowing: too simple  Tradeoff between simplicity and accuracy – Outdoor propagation models – Indoor propagation models EE 552/452 Spring 2007  Longley-Rice Model  Point-to-point from 40MHZ to 100GHz. irregular terrain model (ITS).  Predicts median transmission loss, Takes terrain into account, Uses path geometry, Calculates diffraction losses  Inputs: – Frequency – Path length – Polarization and antenna heights – Surface refractivity – Effective radius of earth – Ground conductivity – Ground dielectric constant – Climate  Disadvantages – Does not take into account details of terrain near the receiver – Does not consider Buildings, Foliage, Multipath  Original model modified by Okamura for urban terrain EE 552/452 Spring 2007 Longley-Rice Model, OPNET implementation EE 552/452 Spring 2007  Durkin’s Model  It is a computer simulator for predicting field strength contours over irregular terrain. Adopted in UK  Line of sight or non-LOS  Edge diffractions using Fresnel zone  The disadvantage are that it can not adequately predict propagation effects due to foliage, building, and it cannot account for multipath propagation. EE 552/452 Spring 2007  2-D Propagation Raster data  Digital elevation models (DEM) United States Geological Survey (USGS) EE 552/452 Spring 2007  Algorithm for line of sight (LOS)  Line of sight (LOS) or not EE 552/452 Spring 2007  Multiple diffraction computation EE 552/452 Spring 2007  Okumura Model  It is one of the most widely used models for signal prediction in urban areas, and it is applicable for frequencies in the range 150 MHz to 1920 MHz  Based totally on measurements (not analytical calculations)  Applicable in the range: 150MHz to ~ 2000MHz, 1km to 100km T-R separation, Antenna heights of 30m to 100m EE 552/452 Spring 2007  Okumura Model  The major disadvantage with the model is its low response to rapid changes in terrain, therefore the model is fairly good in urban areas, but not as good in rural areas.  Common standard deviations between predicted and measured path loss values are around 10 to 14 dB.  G(hre) ：  h  G (hte ) 20 log  te  1000m  hte  30 m  200   hre  G (hre ) 10 log   hre 3 m  3   hre  G (hre ) 20 log  10m  hre  3 m  3  EE 552/452 Spring 2007  Okumura and Hata’s model  Example 4.10 EE 552/452 Spring 2007  Hata Model  Empirical formulation of the graphical data in the Okamura model. Valid 150MHz to 1500MHz, Used for cellular systems  The following classification was used by Hata: Urban area LdB  A  B log d  E Suburban area LdB  A  B log d  C Open area LdB  A  B log d  D A 69.55  26.16 log f  13.82hb B 44.9  6.55 log hb C 2(log( f / 28)) 2  5.4 D 4.78 log( f / 28) 2  18.33 log f  40.94 E 3.2(log(11.75hm )) 2  4.97 for large cities, f 300MHz E 8.29(log(1.54hm )) 2  1.1 for large cities, f  300MHz E (1.11log f  0.7)hm  (1.56 log f  0.8) for medium to small cities EE 552/452 Spring 2007  PCS Extension of Hata Model  COST-231 Hata Model, European standard  Higher frequencies: up to 2GHz  Smaller cell sizes  Lower antenna heights LdB F  B log d  E  G F 46.3  33.9 log f  13.82 log hb f >1500MHz 3 Metropolitan centers G  Medium sized city and suburban areas 0 EE 552/452 Spring 2007  Walfisch and Bertoni Model  Path loss Lb  Lo  Lrts  Lmsd (1) (2) (3) (1) Free space path loss : Lo 32.45  20 log10 d  20 log10 f (2) Roof-top-to-street diffraction and scatter loss term : Lrts  16.9  10 log10 w  10 log10 f  20 log10 (hroof  hm )  L  L   10  0.354 for 0   35o L  2.5  0.075(  35) for 35   55o L  4.0  0.114(  55) for 55   90o (3) Multiscreen diffraction loss : EE 552/452 Spring 2007  Walfisch and Bertoni’s model EE 552/452 Spring 2007  Wideband PCS Microcell Model  A 2-ray ground reflection model is a good estimate for path loss in LOS microcells, Low antenna heights  A simple log-distance path loss model holds well for obstructed microcells, Urban clutter  df represents the distance at which the first Fresnel zone just becomes obstructed by the ground 1 4 df  16ht2hr2  2 (ht2  hr2 )  16 10n1 log(d ) PL (d0 ) for 1  d  df PL (d )   10n2 log(d / df ) 10n1 log(df ) PL (d0 ) for d  df EE 552/452 Spring 2007 Measured data from San Francisco EE 552/452 Spring 2007  Indoor Propagation Models  The distances covered are much smaller  The variability of the environment is much greater  Key variables: layout of the building, construction materials, building type, where the antenna mounted, …etc.  In general, indoor channels may be classified either as LOS or OBS with varying degree of clutter  The losses between floors of a building are determined by the external dimensions and materials of the building, as well as the type of construction used to create the floors and the external surroundings.  Floor attenuation factor (FAF) EE 552/452 Spring 2007  Partition losses EE 552/452 Spring 2007  Partition losses EE 552/452 Spring 2007  Partition losses between floors EE 552/452 Spring 2007  Partition losses between floors EE 552/452 Spring 2007  Log-distance Path Loss Model  The exponent n depends on the surroundings and building type – X is the variable in dB having a standard deviation . PL (d )  PL (d0 ) 10n log(d / d0 ) X  EE 552/452 Spring 2007 Ericsson Multiple Breakpoint Model EE 552/452 Spring 2007  Attenuation Factor Model  FAF represents a floor attenuation factor for a specified number of building floors.  PAF represents the partition attenuation factor for a specific obstruction encountered by a ray drawn between the transmitter and receiver in 3-D   is the attenuation constant for the channel with units of dB per meter. PL (d )  PL (d0 ) 10nSF log(d / d0 ) FAF   PAF PL (d )  PL (d0 ) 10nMF log(d / d0 )   PAF PL (d )  PL (d0 ) 10log(d / d0 ) d  FAF   PAF EE 552/452 Spring 2007  Measured indoor path loss EE 552/452 Spring 2007  Measured indoor path loss EE 552/452 Spring 2007  Measured indoor path loss EE 552/452 Spring 2007  Devasirvatham’s model EE 552/452 Spring 2007  Signal Penetration into Buildings  RF penetration has been found to be a function of frequency as well as height within the building. Signal strength received inside a building increases with height, and penetration loss decreases with increasing frequency.  Walker’s work shows that building penetration loss decrease at a rate of 1.9 dB per floor from the ground level up to the 15 th floor and then began increasing above the 15th floor. The increase in penetration loss at higher floors was attributed to shadowing effects of adjacent buildings.  Some devices to conduct the signals into the buildings EE 552/452 Spring 2007 Ray Tracing and Site Specific Modeling  Site specific propagation model and graphical information system. Ray tracing. Deterministic model.  Data base for buildings, trees, etc.  SitePlanner EE 552/452 Spring 2007  Homework  4.9  4.15  4.16  4.19  4.25  4.34  Due 2/22/07 EE 552/452 Spring 2007  Questions? EE 552/452 Spring 2007