Florida Institute of technologies

ECE 5221 Personal Communication Systems

Prepared by:

Dr. Ivica Kostanic

Lecture 6: Link budgets and nominal cell planning

Spring 2011

Florida Institute of technologies

Page 2

Vehicle penetration losses

Building penetration losses

Aggregate fade margin

Link budget evaluation

Examples

Outline

Important note: Slides present summary of the results. Detailed derivations are given in notes.

Florida Institute of technologies

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

o Type of vehicle

o Vehicle orientation

o Environment

Vehicle losses are variable

Typically modeled as normal variable in log domain

For nominal cell planning

o Mean vehicle loss; 6-8dB

o Standard deviation: 3dB

Page 3Histogram of vehicle losses

Florida Institute of technologies

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

Page 4

Some building penetration data from some published sources*:

Building Frequency: 900MHz 1900MHz ---------------------------------------------------------------------------------------Ameritech 18.3 13.8Continental 13.3 12.2Jupiter 11.7 N/AZurich 11.9 10.8Compri 6.7 7.9Citibank 8.3 10.6Woodfield Corp. 12.4 N/AMarriott 13 15.7NEC 8.1 6.1600 Woodfield 3.9 3.6----------------------------------------------------------------------------------------

Average 10.8 10.2Std. 5.8 5.6

* Garry C. Hess, Handbook of radio-mobile system coverage, Artech House, Inc, 1998

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

Example building penetration measurements

Florida Institute of technologies

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

o 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

o On the street

o In vehicle

o In building

Page 5

Cellular system from link budget point of view

Florida Institute of technologies

Elements of link budget – Rx Sensitivity

Rx sensitivity – minimum RSL required for an RF connection of sufficient quality

Calculated as:

Page 6

NSFkTB log10RxSens

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.

dBm10212710200104log10RxSens 318

Note: typically BS receivers have better sensitivity than the MS.

Florida Institute of technologies

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

Page 7

Cables on a cell tower

Coaxial cables Note: on the RX link cable losses

are sometimes compensated through tower mounted amplifiers

Florida Institute of technologies

Antennas

Two configurations of antenna systems

o Omnidirectional

o Sectored (usually 3 sectors/site)

Nominally – 3 antennas/cell

o Middle – transmit

o Edge – receive A,B

o 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

o Gain (6-15dB)

o Horizontal radiation pattern

o Vertical radiation pattern

Page 8

Omni-directional cell

Tri-sector cell

Florida Institute of technologies

Penetration and body losses

Penetration losses

o Vehicular losses

o 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

Page 9

22 PLT

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:

a) Composite standard deviation: 10dB

b) Z-score: 0.7436

c) Fade margin: 7.44dB

Florida Institute of technologies

Simple link budget example

Environment

o Path loss exponent: 3.84

o Model uncertainty: 8dB

o Penetration losses Mean: 15dB

Std: 6dB

o Reliability: 90%

Base station

o Transmit power: 20W

o Cable losses: 3dB

o Antenna gain: 9dB

o Bandwidth: 200KHz

o Noise figure: 5dB

o Required S/N: 12dB

o Diversity gain: 3dB

Mobile

o Transmit power: 2W

o Antenna gain: 0dB

o Bandwidth: 200KHz

o Noise figure: 8dB

o Required S/N: 12dB

o Body losses: 3dB

Page 10

1. Rx sensitivity at the base

dBm10412510200104log10RxSensBS 318

2. Rx sensitivity at the mobile

dBm10112810200104log10RxSensBS 318

Florida Institute of technologies

Page 11

Simple link budget example (cont.)

3. FM calculations

dB1068 22 T 6.284.3/10 nT 7436.0%90,6.2scoreZ

dB4.7FM4. Link budget spreadsheet

Note: Max allowable path loss is greater for forward link