ECE 5221 Personal Communication Systems

1. ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 6: Link budgets and nominal cell planning Spring 2011

2. Outline • Vehicle penetration losses • Building penetration losses • Aggregate fade margin • Link budget evaluation • Examples Important note: Slides present summary of the results. Detailed derivations are given in notes.

3. Vehicle penetration losses • Many calls are made inside vehicles • Macroscopic propagation model predict “on the street level” • Vehicle introduces additional signal losses • These losses depend on • Type of vehicle • Vehicle orientation • Environment • Vehicle losses are variable • Typically modeled as normal variable in log domain • For nominal cell planning • Mean vehicle loss; 6-8dB • Standard deviation: 3dB Histogram of vehicle losses

4. Building penetration losses • Many calls are placed inside buildings • Buildings introduce additional losses • Losses depend on type of building, frequency of operation and environment • Treated as a random variable following normal distribution Some building penetration data from some published sources*: Building Frequency: 900MHz 1900MHz --------------------------------------------------------------------------------------- Ameritech 18.3 13.8 Continental 13.3 12.2 Jupiter 11.7 N/A Zurich 11.9 10.8 Compri 6.7 7.9 Citibank 8.3 10.6 Woodfield Corp. 12.4 N/A Marriott 13 15.7 NEC 8.1 6.1 600 Woodfield 3.9 3.6 ---------------------------------------------------------------------------------------- Average 10.8 10.2 Std. 5.8 5.6 * Garry C. Hess, Handbook of radio-mobile system coverage, Artech House, Inc, 1998 Example building penetration measurements Commonly assumed values used in design of RF systems (800/1900 MHz) ----------------------------------------------------------------------- Building type Average(dB) Std.(dB) Urban Core 20 10 Urban 15 8 Suburban 10 6

5. Link budget analysis • Used to determine maximum allowable path loss that balances two links • Important: Cellular communication is 2-way – two links need to balance • Usually – mobile power smaller and the link budget is determined by the uplink • Typical process: • Calculate uplink budget • Adjust BS power to have balanced links • In nominal cell planning link budget is used to determine expected cell radius • For nominal cell planning – three types of users • On the street • In vehicle • In building Cellular system from link budget point of view

6. Elements of link budget – Rx Sensitivity • Rx sensitivity – minimum RSL required for an RF connection of sufficient quality • Calculated as: Where: kT – PSD of thermal noise ~ 4e-18 mW/Hz B – bandwidth of the system expressed in Hz F – noise figure expressed in dB S/N – required signal to noise ratio in dB Components of RxSens Example. Consider technology with bandwidth of 200KHz, Rx noise figure of 7dB and min required S/N ratio of 12dB. Calculate the Rx sensitivity. Note: typically BS receivers have better sensitivity than the MS.

7. Cable losses • Cellular systems use coaxial cables • There is a coaxial cable that connects each o the antennas • Losses expressed in xdB/100feet • For a typical tower heights losses of the cables are on the order of 2-5dB • Standard 50ohm impedance • There may be other elements in Tx/Rx path introducing signal loss (duplexers, filters, jumper cables, splitters,…) • In link budget analyses – all of the “pluming” losses need to be taken into account Cables on a cell tower Coaxial cables Note: on the RX link cable losses are sometimes compensated through tower mounted amplifiers

8. Antennas • Two configurations of antenna systems • Omnidirectional • Sectored(usually 3 sectors/site) • Nominally – 3 antennas/cell • Middle – transmit • Edge – receive A,B • Two receive antennas provide diversity reception • When there is space constraint on tower, one of the antennas may duplex TX and RX • Antennas are characterized by • Gain (6-15dB) • Horizontal radiation pattern • Vertical radiation pattern Tri-sector cell Omni-directional cell

9. Penetration and body losses • Penetration losses • Vehicular losses • Building losses • Specified by mean and std • Mean added to the radio path losses • Independence between the path loss and penetration losses is assumed • Penetration losses contribute to the model uncertainty • Total uncertainty-composite standard deviation Example. Consider system in an environment with model uncertainty of 8dB and path loss exponent of 3.84. Calculate fade margin for in-building coverage assuming standard deviation of penetration losses of 6dB. The reliability requirement is 90% Answers: • Composite standard deviation: 10dB • Z-score:0.7436 • Fade margin: 7.44dB

10. Simple link budget example • Environment • Path loss exponent: 3.84 • Model uncertainty: 8dB • Penetration losses • Mean: 15dB • Std: 6dB • Reliability: 90% • Base station • Transmit power: 20W • Cable losses: 3dB • Antenna gain: 9dB • Bandwidth: 200KHz • Noise figure: 5dB • Required S/N: 12dB • Diversity gain: 3dB • Mobile • Transmit power: 2W • Antenna gain: 0dB • Bandwidth: 200KHz • Noise figure: 8dB • Required S/N: 12dB • Body losses: 3dB 1. Rx sensitivity at the base 2. Rx sensitivity at the mobile

11. Simple link budget example (cont.) 3. FM calculations 4. Link budget spreadsheet Note: Max allowable path loss is greater for forward link