ECE 5221 Personal Communication Systems

1. ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 5: Example of a macroscopic propagation model (Lee model) Spring 2011

2. Outline • Lee model equation • Propagation prediction over terrain database • Nominal cell radius calculation • 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 • Some popular macroscopic propagation models • Lee model • Hata-Okumura • COST 231 • Longley-Rice • Walfish-Ikagami, etc. Page 3

4. Lee model • Developed by W.C.Y Lee in 1970s • Statistical, empirical model • Popular due to is simplicity and relatively good accuracy • Valid for frequencies 800-2000MHz • Straight forward extension of log distance path loss model • Expected model accuracy: 6-9dB standard deviation of the prediction error • Model introduces reference conditions • Prediction conducted in two steps • Step 1. Predict the propagation path losses for standard conditions • Step 2. Correct the prediction for all differences between actual and standard conditions • Parameters of the environment are specified for standard conditions • Two parameters of the environment are given • Slope of the path loss in dB/dec (m) • Reference distance intercept in dBm (or reference distance path loss in dB) Illustration of Lee model reference conditions

5. Lee model – RSL form Form 1: RSL form Parameter explanations: RLS0 – reference distance intercept (dBm) m – slope (dB/dec) PT – transmit power (dBm) hte – effective antenna height of the transmitter hr – height of the receiver GT – transmit antenna gain Gm– mobile antenna gain d – distance between transmitter and receiver Correction coefficients have default values C= 15dB F = 10dB Frequency correction: • slope stays the same • intercept adjusted as

6. Lee model – path loss form Form 2: PL form Parameter explanations: PL0 – reference distance path loss (dB) m – slope (dB/dec) hte – effective antenna height of the transmitter hr – height of the receiver GT – transmit antenna gain Gm– mobile antenna gain d – distance between transmitter and receiver Correction coefficients have default values C= 15dB F = 10dB Frequency correction: • slope stays the same • PL0adjusted as

7. Effective antenna height – slope method • Lee model uses slope method for effective antenna height calculation • Slope of the local terrain of the receiver – extended • Effective antenna height – determined by intersection of the slope and the vertical through TX antenna • Two cases • Up-sloping terrain – effective height greater than actual height • Down sloping terrain – effective height smaller then effective height • Effective antenna height is a local parameter, i.e. it is different for every point within coverage region Note: calculation of effective height requires knowledge of terrain elevations with the coverage area

8. Diffraction losses • Diffraction losses – additional losses due to terrain blockage • Terrain obstacle – replaced by knife edge • Two steps for additional loss calculation • Step 1. Calculate Fresnel-Kirchoff parameter • Step 2. Estimate losses using diffraction formulas Illustration of KED calculations

9. Propagation over terrain Terrain data • Terrain database – fundamental input into propagation modeling • Accuracy of terrain database – bin size • Typical bin size 30-100m • Using terrain -> radio profile is generated • Through radio profile 3D propagation problem becomes 2D problem • Radio profile is used by propagation model to estimate path loss • Path loss is calculated between the transmitter and every bin within surrounding region Example of radio profile

10. Example 1 Consider a transmitter located in suburban environment. The effective height of the transmitter is 45m, its power is 20W and the gain of the transmit antenna is 8dB. Calculate the path loss and RSL at the mobile located at distance of 5miles. The gain of the mobile antenna is 0dB and its height is 1.5m. The frequency of operation is 850MHz. Use Lee model. Answers: RSL = -85.2dBm PL = 136.2dB

11. Example 2 Consider a system deployed in urban environment. Assume that the operating frequency is 1900Mhz and that the minimum RSL at the receiver is -95dBm. The base station has ERP of 50dBm and effective height of 40m. The mobile height is 1.5m and its antenna gain is 0dB. The error of propagation modeling is characterized by standard deviation of 8dB. • Determine the contour for 90% are reliability. • Using Lee model estimate distance to contour calculated in part a) • Repeat a) and b) for reliability of 95% • Estimate increase of the cell site count that corresponds to the increase of reliability requirement. Answers: a) RSLp=-89.96dBm b) d = 3 miles c) RSLp = -86.6dBm, d = 2.43 mile d) 95% reliability requires 50% more cells