JPL's Wireless Communication Reference Website

Chapter: Cellular Telephone Networks.

Link Budget

 Cellular system planning is either coverage of capacity driven. Initially, an operator attempts to cover the service area as good as possible with only a limited number of base stations. His main concern is that the signal-to-noise ratio is sufficient at each location. The link budget is a kind of "balance sheet" to select the system parameters Interference is not yet limiting the system performance.

In a later phase when more subscribers are using the system, the operator typically attempts to improve capacity by adding more base stations. The grid of base stations becomes denser and signal-to-noise ratio is no longer limiting the performance. Because of dense reuse, co-channel and adjacent channel interference become more of concern.

GSM link budget calculator

This page allows you to calculate the link budget for a the uplink in a GSM (or GSM-like) network. Pathloss is computed using the Egli model, or if you enter a type of terrain, using Hata's model.

Default system parameters used in the spreadsheet below are similar to the GSM specs, We choose a handheld user indoor with a cell radius of 1 km. Typically, GSM only covers handheld indoor subscribers that are quite close to the base station.

Input parameters:
Carrier Frequency: MHz
MS tx power: watt
MS tx ant gain: dB
MS tx ant height: meter
Cell size: meter
Shadow margin: dB
Rayleigh margin: dB
Indoor loss: dB
Environment  
Interference degradation margin: dB
BS rx ant height: meter
BS rx ant gain: dB
BS rx ant cable loss: dB
BS rx sensitivity: dBm

Run calculation:

Results:
Planning Margin dBm
The shadow and Rayleigh fade margins usually are chosen in a semi-empirical way. Mathematical methods to find the outage probability are often omitted in "back of the envelope" link budget calculations.

The effect of interference is taken into account by simply assuming that the interference power level is a few (specifiable) dBs above the receiver noise floor. In networks dense reuse, this becomes an oversimplification.

Indoor penetration

Radio signals are heavily attenuated when travelling through a wall. For GSM, the inhouse field strength typically is about 10 dB below levels measured outside.
GSM subscribers tend to use their handsets in their car, without connecting an external antenna. This gives a substantial attenuation, and resulting reduction of the link budget. The figure compares the antenna coverage of a rooftop antenna with that of a handset inside the car.

Source credit: Procom, Denmark.

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JPL's Wireless Communication Reference Website © 1997.

Disclaimer: executable software is provided without any guarantee whatsoever. We are not responsible for any errors made by this spreadsheet. See License.