Florida Institute of technologies ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 4: Estimation of coverage reliability Spring 2011

Florida Institute of technologies Page 2  Macroscopic propagation modeling  Edge reliability  Area reliability  Reudnik curves and fade margin calculations  Examples Outline Important note: Slides present summary of the results. Detailed derivations are given in notes.

Florida Institute of technologies Macroscopic propagation modeling  More input descriptors – more accurate models  As the models become more accurate, the standard deviation of the unexplained portion of path loss becomes smaller  The unexplained portion still retains log normal character Page 3 Log distance path loss model More general models  Macroscopic models predict median path loss at some distance d  As one measures the actual path loss, its value will always be different than predicted  The difference is a log normal random variable with zero mean and variance that depends on environment

Florida Institute of technologies Expected accuracy of propagation model  Macroscopic propagation models – limited accuracy  Accuracy depends: oInput data accuracy oType of the environment oComputational time oModel limitations  The accuracy is quantified through standard deviation of prediction error  For a well tuned model, standard deviation of prediction error is 6-8dB  Note: the error is relatively large  GOAL: coverage design using imperfect tools Page 4 Comparison of measurements and predictions Distribution of prediction error

Florida Institute of technologies Edge reliability  RSL T – Coverage threshold that needs to be met by the network. The threshold determined from coverage objectives  RSL T – contour provides 50% reliability (i.e. if one walks around the contour the threshold is met only 50% of locations)  RSL P – contour that provides required reliability for meeting the threshold RSL T  RSL P =RSL T +  where  is the value that needs to be determined based on required edge reliability  Mathematically: Page 5 Goal: determine RSL P contour that meets edge reliability requirements

Florida Institute of technologies Edge reliability - example Assume that one needs to perform design for RSL T = -90dBm. The area is characterized with standard deviation of  =8dB. What contour RSL P provides 70% edge reliability. Answer: RSL P = -85.2dBm,  =4.8dB Page 6  Edge reliability(%) Following the same approach one obtains the table

Florida Institute of technologies Concept of area reliability  Coverage is an areal phenomenon  Design needs to guarantee specified area reliability  One needs to find RSL P contour such that Where R a is the area reliability. Typical values for area reliability are 90-95% Page 7 Illustration of cell coverage area Note: there is tradeoff between coverage reliability and cell count

Florida Institute of technologies Calculation of area reliability (result) Page 8 Area reliability Where  Notes: oEquation – to complicated for day to day use oGives the answer oNeed for easier way to calculate Based on log- distance path model

Florida Institute of technologies Reudnik curves Page 9 Area reliability calculations – complicated Edge reliability calculations – easy Reudnik curves relate area and edge reliabilities Edge reliability Area reliability Properties of environments

Florida Institute of technologies Area reliability - examples Example 1: Consider environment with  / n = 3. Determine reliability over the area bounded with a contour having edge reliability of 70% Answer: 85% Example 2: Consider the following design task Design threshold: -95dBm Area reliability: 90% Path loss exponent: 3.84 Standard deviation of the modeling accuracy: 8dB Determine: a)Edge reliability requirementAnswer: 75% b)Required prediction contourAnswer: -89.4dBm Page 10

Florida Institute of technologies Fade margin – calculations (direct method)  Fade margin – difference between RSL P and RSL T  Can be calculated directly from area reliability requirement,  and n  Process: oCalculate  / n oDetermine z-score (table lookup) oFade margin is calculated as z-score x  Page 11

Florida Institute of technologies Example  Calculate the fade margin for the following scenario oArea reliability requirement: 95% oModel uncertainty: 8dB oSlope: 35dB/dec Answers:  / n = 2.29 z-score: 1.10 FM = 1.10 x 8 = 8.8 dB Page 12