# Link Budget Analysis

In the design of wireless communications links between two sites, issues of range, throughput, and received signal quality are of critical importance to the system engineer. Link budget analysis accounts for all gains and losses in the communication link. Some factors and design choices, such as propagation path length, signal polarization, and antenna feed cable, degrade signal quality, while others, such as the power amplifier and antenna size, can increase transmitted signal strength.

### Introduction

This example uses **linkBudgetAnalyzer** app to tabulate system parameters and compute gains and losses that impact system performance.

linkBudgetAnalyzer

### Settings

Separate tabs specify settings for **Uplink** and **Downlink**. The **Uplink** and **Downlink** tabs contain these collapsible input parameter sections:

**Link:**Contains link level parameters, such as frequency, bandwidth, required Eb/N0**Transmitter:**Contains transmitter specific parameters**Receiver:**Contains the receiver specific parameters**Propagation:**Contains parameters to specify various atmospheric elements that are used to compute losses in the signal propagation path

After specifying the uplink and downlink settings, select **Analyze** to update the gains and losses reported in the **Results** tab and the tabs with plots of free space path loss (FSPL) and G/T for uplink and downlink.

### Results

The **Results** tab contains **Uplink** and **Downlink** collapsible sections that provide the link budget results for uplink and downlink, respectively. The **Appendix** contains a list of functions used to compute the results.

**Distance**and**Elevation**are computed from the**Latitude**,**Longitude**and**Altitude**input parameters for the transmitter and receiver.**Tx Antenna gain**and**Rx Antenna gain**are functions of the corresponding**Antenna diameter**,**Antenna efficiency**, and**Frequency**input parameters.**Tx EIRP**is a function of the**Amplifier power**,**Amplifier backoff loss**,**Feeder loss**,**Radome loss**,**Other losses**, and**Tx Antenna gain**input parameters.**Tx EIRP**, which represents transmitted equivalent isotropically radiated power (EIRP), is the amount of power that would have to be radiated by an isotropic antenna to produce the equivalent power density observed from the actual antenna in a specified direction. Typically, EIRP is quoted for antenna boresight, which is defined as the axis of maximum radiation.The transmitted signal power is diminished by the geometric spreading of the wavefront. This loss is represented by

**Free space path loss**which is computed using the`fspl`

function,**Distance**, and**Frequency**.**Rain attenuation**is computed by the`rainpl`

function using**Distance**,**Frequency**,**Rain rate**,**Elevation**and**Polarization tilt**. The`rainpl`

function applies the International Telecommunication Union (ITU) rainfall attenuation model which applies only for frequencies at 1-1000 GHz. [1]The

`fogpl`

function computes**Fog/Cloud attenuation**using**Distance**,**Frequency**,**Fog/Cloud temperature**and**Fog/Cloud water density**. The`fogpl`

function applies the ITU cloud and fog attenuation model which is valid only for frequencies at 10-1000 GHz. [2]**Atmospheric gas attenuation**is a function of**Distance**,**Frequency**,**Temperature**,**Atmospheric pressure**and**Water vapor density**and is calculated using the <docid:comm_ref#bu6ghsw-1 gaspl> function which applies ITU atmospheric gas attenuation model that is valid for frequencies at 1-1000 GHz. [3]**Polarization loss**is derived from**Polarization mismatch**angle.**Total propagation losses**consists of all the above-mentioned losses.**Tx EIRP**is diminished by**Total propagation losses**and receiver**Radome loss**to provide**Received isotropic powe**r at the receiver.At the receiver, the antenna increases the

**Received isotropic power**by**Rx Antenna gain,**while**Feeder loss**and**Other losses**decrease the signal power.**Received signal power**shows the net result.**Rx G/T**provides information on the performance of the receiver and is computed from**Rx Antenna gain**and**System temperature**. The receiver performance improves as G/T increases.**C/N**represents SNR (Signal-to-Noise Ratio) and is a function of**Received signal power**,**System temperature**,**Bandwidth**and Boltzmann's constant.*

**C/No*** is computed from**C/N**and**Bandwidth**.**Received Eb/No**indicates energy per bit and is a function of**C/No**and**Bit rate**.**Margin**is computed from**Received Eb/No**,**Required Eb/No**, and**Implementation loss**. One goal when performing a link budget analysis is to have a satisfactory margin for the chosen data rate, bandwidth, EIRP and receiver figure of merit. Often some adjustment is needed to get the desired link margin.

### Visualization

For path loss and receiver performance plots, see the uplink and downlink FSPL and G/T tabs. Free space path loss constitutes the largest component of propagation losses. It is proportional to distance and frequency. Receiver figure of merit increases with antenna gain, which is proportional to antenna diameter. The specified **Frequency** and receiver **Antenna diameter** are shown by the red * marker in the plots.

### Appendix

Following functions are used to compute the various parameters and losses mentioned in this example:

### References

Radiocommunication Sector of International Telecommunication Union. Recommendation ITU-R P.838-3: Specific attenuation model for rain for use in prediction methods. 2005.

Radiocommunication Sector of International Telecommunication Union. Recommendation ITU-R P.840-6: Attenuation due to clouds and fog. 2013.

Radiocommunication Sector of International Telecommunication Union. Recommendation ITU-R P.676-10: Attenuation by atmospheric gases 2013.

## See Also

Satellite Link Budget Analyzer (Satellite Communications Toolbox)

## Related Topics

- Link Budget Analysis (Satellite Communications Toolbox)