Link budget

Overview

A link budget adds up the gains and losses along a communication link to check that the signal arriving at the receiver is strong enough, above the noise, to be received at the required error rate, with some margin left over. The same idea is used for radio links, optical links and wired serial links, though each field has its own terms and contributions.

How it works

For a radio link, the budget starts from the transmitter's output power, adds the gain of the transmit and receive antennas, and subtracts the losses in cables, matching networks and the path between the antennas, including any allowance for fading, rain or obstacles. The result is the power at the receiver, which is compared with the receiver's sensitivity: the weakest signal it can receive at the required error rate, set by its noise figure, bandwidth and the signal to noise ratio the modulation needs. The difference is the link margin.

For an optical link the same accounting uses launched optical power, fibre attenuation, connector and splice losses and dispersion penalties. For a wired serial link it is usually called a channel budget, and counts loss, reflections, crosstalk and jitter between the transmitter and receiver pins.

Each part of the budget is turned into a specification for the block that owns it, so that the antenna, the front end, the package and the board can each be designed to their share.

Examples

• A short-range radio whose budget shows a small margin at the required range once the antenna loss inside the enclosure is counted.
• A cellular front end where the budget sets the noise figure the low-noise amplifier must reach.
• A millimetre-wave module where package and antenna losses take up much of the budget.
• A fibre link checked against the receiver sensitivity after connector losses are added.

Why it matters

The link budget connects a system requirement, such as range or data rate, to specifications for each chip and component in the path. A shortfall found late usually means a redesign of the front end, the antenna or the package. RF system engineers, RF designers, antenna engineers and optical engineers work with it.

In the RF lifecycle it is set during specification, checked by simulation through design and post-layout, and confirmed by conducted or over-the-air measurements on silicon.

It matters most to: Antenna-in-Package Engineer, Optical Module Hardware Engineer

Common confusions

Not the same as a channel budget for a wired serial link

A channel budget is the wired form of the same accounting, counting loss, reflections, crosstalk and jitter between pins. A radio link budget counts transmit power, antenna gains, path loss and receiver sensitivity.

Not the same as link margin

The link margin is the result of the budget: how much stronger the received signal is than the minimum the receiver needs.

Sources

1. Telecommunications Link Design Handbook (810-005) (opens in a new tab), NASA Jet Propulsion Laboratory, Deep Space Network, 2026-11-10
2. Recommendation ITU-R P.525: Calculation of free-space attenuation (opens in a new tab), International Telecommunication Union (ITU-R), 2026-11-10
3. Analysis and verification of communication link budgets for small satellites (IAC-13) (opens in a new tab), Delft University of Technology, 2026-11-10

Related terms

• Channel budget
• Optical link budget

Where it appears on the Hub

Used on 25 pages of the Hub. In each group, the pages that mention it most come first.