Phy Channel Modeling Isotropic Radiation An isotropic antenna

Phy Channel Modeling

Isotropic Radiation Ø An isotropic antenna is an antenna that transmits equally in all directions d Ø Law of Conservation of Energy: “Energy can neither be created nor destroyed …” © Tallal Elshabrawy From “Wireless Communications” Edfors, Molisch, Tufvesson

Power Reception by an Isotropic Antenna Power Received by Antenna Ae=ARx Effective Area of Antenna Power Received by Isotropic Antenna From “Wireless Communications” Edfors, Molisch, Tufvesson LP Free-space Path-loss between two isotropic antennas © Tallal Elshabrawy 3

© Tallal Elshabrawy

Directional Radiation l A Directional Antenna: l Transmit gain Gt is a measure of how well an antenna emits radiated energy in a certain direction relative to an isotropic antenna. l Receive gain Gr is a measure of how well the antenna collects radiated energy in a given area relative to an isotropic antenna. Maximum transmit or receive antenna Gain Maximum (Peak) Antenna Gain Main Lobe 3 d. B Beam Width Side Lobes Antenna Pattern for Parabolic (dish-shaped) antenna © Tallal Elshabrawy 5

The Friis Equation l l The received power falls off as the square of the T-R separation distance The received power decays with distance at a rate of 20 d. B/decade Valid for Line of Sight (LOS) satellite communications The Friis free-space model is only valid for values of d in the far field. The far field is defined as the region beyond the far field distance df D is the largest linear dimension of the transmitting antenna aperture © Tallal Elshabrawy Note: df must also satisfy df>>D, df>>λ 6

PR(d) in the Far Field l The Friis equation is not valid at d=0 l PR(d) could be related to a power level PR(d 0) that is measured at a close in distance d 0 that is greater than df © Tallal Elshabrawy 7

In Wireless, Everything is Relative l © Tallal Elshabrawy

Path-Loss Models l l l The most general case of signal reception might consist of a direct path, reflected paths, diffracted paths, and scattered paths (which makes mathematical analysis cumbersome) Path-Loss models are empirical models that are based on fitting curves or analytical expressions that recreate a set of measured data Note: l © Tallal Elshabrawy A given empirical model might only be valid within the environment where the measurements used to estimate such model have been taken 9

Log-Distance Path-Loss Model Theoretical and Measurement-based Propagation suggest that the average received signal power decreases logarithmically with distance PL (d): Average path-loss for an arbitrary separation n : Path-loss exponent © Tallal Elshabrawy 10

Path-Loss Exponent for Different Environments Environment Free-Space Urban area cellular radio Shadowed urban cellular radio Path-Loss Exponent n 2 2. 7 to 3. 5 3 to 5 In building line-of-sight 1. 6 to 1. 8 Obstructed in building 4 to 6 Obstructed in factories 2 to 3 © Tallal Elshabrawy 11

Log-normal Shadowing l Distance between two nodes alone cannot fully explain the signal strength level at the receiver l Shadowing has been introduced as a means to model the variation of signal propagation behavior between two different signal paths assuming the same propagation distance PL (d): Path-loss model for an arbitrary separation d Xσ : Shadowing parameter (zero mean Gaussian distributed random variable in d. B with standard deviation σ also in d. B) © Tallal Elshabrawy 12

Received Power in Path-Loss Models d d 4 3 d d Position Index 1 © Tallal Elshabrawy 2 1 2 3 4 13

Received Power in Path-Loss Models d d 4 3 d d Position Index 1 © Tallal Elshabrawy 2 1 2 3 4 14

Reception Quality d d 4 3 d d Position Index 1 © Tallal Elshabrawy 2 1 2 3 4 γ: Desired received power threshold 15

Indoor Propagation Models l The indoor radio channel differs from the traditional mobile radio channel in the following aspects l Much smaller distances l Much greater variability of the environment for a much smaller range of T-R separation distances l Difficult to ensure far-field radiation l Propagation within buildings is strongly influenced by specific features such as l l l Building layout Construction materials Building type Open/Closed doors Locations of antennas © Tallal Elshabrawy 16

Example of Reflection in Indoor Models All Ray Paths for Lo. S, Single and Double Reflections between Tx 1 and RX Tx 1 Rx © Tallal Elshabrawy Tx 2 17

Log-Distance Pathloss Model l The lognormal shadowing model has been shown to be applicable in indoor environments © Tallal Elshabrawy 18

Attenuation Factor Model l This was described by Seidel S. Y. It is an in-building propagation model that includes l Effect of building type l Variations caused by obstacles l l l n. SF represents the path-loss exponent for the same floor measurements FAF represents the floor attenuation factor PAF represents the partition attenuation factor for a specific obstruction encountered by a ray drawn between the transmitter and receiver © Tallal Elshabrawy 19

Attenuation Factor Model l FAF may be replaced by an exponent that accounts for the effects of multiple floor separation l n. MF represents the path-loss exponent based on measurements through multiple floors © Tallal Elshabrawy 20

Partition Losses (Same Floor) “Wireless Communications: Principles and Practice 2 nd Edition”, T. S. Rappaport, Prentice Hall, 2001 © Tallal Elshabrawy 21

Partition Losses between Floors “Wireless Communications: Principles and Practice 2 nd Edition”, T. S. Rappaport, Prentice Hall, 2001 © Tallal Elshabrawy 22

THAT’S ALL I GOT TO SAY ABOUT THAT © Tallal Elshabrawy 23