ECE 5221 Personal Communication Systems

1. ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 7: Example of link budgets and coverage planning Spring 2011

2. Outline • Balanced path • Nominal cell radius calculation • Typical link budget matrix • Example of a coverage design • Cross band coverage planning • Examples Important note: Slides present summary of the results. Detailed derivations are given in notes.

3. Balanced path • Forward and reverse link need to be balanced • Links are balanced if the maximum sustainable losses are the same • Base station has much more power than the mobile • Usually power from the base station needs to be reduced • Other ways to balance the link • Use different gain antennas for forward an reverse link • Use tower top mounted amplifiers • Use higher sensitivity receivers at the base station Example of unbalanced links. To achieve balance power on the forward link need to be reduced by 4dB

4. Nominal cell radius • Radius that corresponds to maximum sustainable path loss • Determined using link budget analysis and appropriate propagation model • Used for nominal budget estimation • Dependant on the required reliability • More reliable coverage results in smaller nominal radii • Typically design is done to 90% area reliability • Nominal call radius is a principal input into budgetary planning of the deployment • Practical experience – Nominal planning determines cell count within 10-15% margin Example. Link budget evaluation in suburban area determined maximum allowable path loss of 128dB. The operating frequency is 850MHz. Using Lee model determine the nominal cell radius. If the size of the suburban area is 400 square miles, determine the number of required cells. Assume 20% cell overlap. Answers: • Nominal radius: 3.12 miles • Area of the cell: 30.6 miles • Cell count: 17 cells

5. Link budget matrix – coverage design • In basic nominal design • four environments: dense urban, urban, suburban, rural • three design goals: in-building, in-vehicle, street level • RSLT – threshold is always the same • Each combination (environment, design goal) has its on RSLP threshold • Each RSLP value can be translated into corresponding nominal cell radius • Knowing nominal cell radii, for different environments one may estimate required cell count Nominal design flow

6. Clutter maps (land classification maps) • Maps with land use classification • Available from USGS or commercial companies • Usually 12 standard categories • Each category may have its own propagation parameters • Each category may have its own design goals • In a nominal design phase – use nominal propagation parameters • In later phases of the design – more sophisticated propagation modeling is used • Models obtained through propagation modeling studies • The models are obtained through measured versus predicted analysis • Typically 5-10 representative sites for each morphological type are surveyed Example of a land classification map for Chicago area

7. Example of coverage design Consider a system with following parameters: Environment: one mile intercept: 109dB, slope: 38.4dB, StDev: 8dB Rx Sensitivity: Bandwidth: 30KHz, noise figure: 8dB, S/N min: 17dB In-building coverage: area reliability: 90%, building losses: 15dB, StDev: 6dB In-vehicle coverage: area reliability: 90%, vehicle losses: 8dB, StDev: 3dB Street level coverage: area reliability: 90% MS parameters: antenna gain 0dB, body loss 3dB BS parameters: ERP 47dBm Determine: • Rx Sensitivity A: -104.2dBm • RSLp for in-building coverage A: -79dBm • RSLp for in-vehicle coverage A: -87.5 dBm • RSLp for street level A: -95dBm

8. Link budget evaluation Examine attached link budget

9. Coverage planning across multiple bands • Different frequencies – different propagation • Majority of networks operate in multiple frequency bands • Examples: • In US the networks may operate between: 850MHz and 1900MHz • In Europe the networks may operate between 900MHz, 1800MHz and 2100MHz • Additional challenge – balance the coverage between bands • Use higher antenna gain • Power down lower frequency sites • “one to one” collocation between the bands • Deploy mobiles with dual band capabilities • All technologies support multiband operation • Handoff and mobility management Frequency allocation for different countries may be found @ http://www.worldtimezone.com/gsm.html

10. Coverage maps • Provided on websites of every cellular provider • Three shades for three coverage criteria • Plots are usually generated for 90% reliability • One can easily see correspondence between signal level and population centers • Remember: objective is not to cover everything, but to cover more of relevant areas than the competition Example – ATT coverage map (2011)

11. Homework assignment Homework 2