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ECE 5221 Personal Communication Systems - PowerPoint PPT Presentation

ECE 5221 Personal Communication Systems. Prepared by: Dr . Ivica Kostanic Lecture 4: Estimation of coverage reliability. Spring 2011. Outline . Macroscopic propagation modeling Edge reliability Area reliability Reudnik curves and fade margin calculations Examples.

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Presentation Transcript

Prepared by:

Dr. Ivica Kostanic

Lecture 4: Estimation of coverage reliability

Spring 2011

• 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.

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

• 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

• 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

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.

Following the same approach one obtains the table

• 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

Area reliability

• Notes:

• Equation – to complicated for day to day use

• Need for easier way to calculate

Based on log-distance path model

Where

Reudnik curves

Edge reliability

Area reliability calculations – complicated

Edge reliability calculations – easy

Reudnik curves relate area and edge reliabilities

Area reliability

Properties of environments

Example 1: Consider environment with s/n = 3. Determine reliability over the area bounded with a contour having edge reliability of 70%

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

• 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

• Calculate the fade margin for the following scenario

• Area reliability requirement: 95%

• Model uncertainty: 8dB

• Slope: 35dB/dec