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ECE 5221 Personal Communication Systems

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Presentation on theme: "ECE 5221 Personal Communication Systems"— Presentation transcript:

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 Continental Jupiter N/A Zurich Compri Citibank Woodfield Corp N/A Marriott NEC 600 Woodfield Average Std * 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 Urban 15 8 Suburban 10 6

5 Cellular system from link budget point of view
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 Omni-directional cell
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 Omni-directional cell Tri-sector 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 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: 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

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