Estimation of Coverage Reliability in Personal Communication Systems

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

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

3. Macroscopic propagation modeling Log distance path loss model • 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 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

4. Expected accuracy of propagation model • Macroscopic propagation models – limited accuracy • Accuracy depends: • Input data accuracy • Type of the environment • Computational time • Model 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 Comparison of measurements and predictions Distribution of prediction error

5. Edge reliability • RSLT – Coverage threshold that needs to be met by the network. The threshold determined from coverage objectives • RSLT – contour provides 50% reliability (i.e. if one walks around the contour the threshold is met only 50% of locations) • RSLP – contour that provides required reliability for meeting the threshold RSLT • RSLP=RSLT + D, where D is the value that needs to be determined based on required edge reliability • Mathematically: Goal: determine RSLP contour that meets edge reliability requirements

6. Edge reliability - example Assume that one needs to perform design for RSLT = -90dBm. The area is characterized with standard deviation of s=8dB. What contour RSLP provides 70% edge reliability. Answer: RSLP = -85.2dBm, D=4.8dB Following the same approach one obtains the table

7. Concept of area reliability • Coverage is an areal phenomenon • Design needs to guarantee specified area reliability • One needs to find RSLP contour such that Where Rais the area reliability. Typical values for area reliability are 90-95% Note: there is tradeoff between coverage reliability and cell count Illustration of cell coverage area

8. Calculation of area reliability (result) Area reliability • Notes: • Equation – to complicated for day to day use • Gives the answer • Need for easier way to calculate Based on log-distance path model Where

9. Reudnik curves Edge reliability Area reliability calculations – complicated Edge reliability calculations – easy Reudnik curves relate area and edge reliabilities Area reliability Properties of environments

10. Area reliability - examples Example 1: Consider environment with s/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: • Edge reliability requirement Answer: 75% • Required prediction contour Answer: -89.4dBm

11. Fade margin – calculations (direct method) • Fade margin – difference between RSLP and RSLT • Can be calculated directly from area reliability requirement, s and n • Process: • Calculate s/n • Determinez-score (table lookup) • Fade margin is calculated as z-score x s

12. Example • Calculate the fade margin for the following scenario • Area reliability requirement: 95% • Model uncertainty: 8dB • Slope: 35dB/dec Answers: s/n = 2.29 z-score: 1.10 FM = 1.10 x 8 = 8.8 dB