attenuation

What is attenuation?

Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. Sometimes called loss, attenuation is a natural consequence of signal transmission over long distances.

In conventional and fiber optic cables, attenuation is specified in terms of the number of decibels (dB) per foot, 1,000 feet, kilometer or mile. The less attenuation per unit distance, the more efficient a cable is.

When it is necessary to transmit signals over long distances via cable, repeaters can be inserted along the length of the cable. Repeaters boost the signal strength to overcome attenuation. This greatly increases the maximum attainable range of communication.

Attenuation in networking

Attenuation in computer networking is the loss of communication signal strength that is measured in decibels. As the rate of attenuation increases, the transmission, such as a phone call or an email a user tries to send, becomes more distorted.

Attenuation occurs on computer networks because of the following factors:

• Range. Both wired and wireless transmissions gradually dissipate in strength over longer distances.
• Interference. Radio interference or physical obstructions, such as walls, dampen communication signals on wireless networks.
• Wire size. Thinner wires suffer from more attenuation than thicker wires on wired networks.

Line attenuation on a digital subscriber line (DSL) network measures signal loss between a DSL provider's access point and a home, for example. Attenuation is critical on DSL networks because if the line attenuation values are too large, the data rates a household can obtain might be restricted. Values for line attenuation on a DSL connection are typically between 5 dB and 50 dB -- the lower the values, the better.

Wi-Fi supports what's called dynamic rate scaling, which enhances the distance at which wireless devices can connect to each other in exchange for lower network performance at longer distances. Depending on the transmission quality of the line, dynamic rate scaling automatically regulates the connection's maximum data rate up or down in fixed increments.

Attenuation in other contexts

The word attenuation is also used in contexts other than computer networking. For instance, sound mixers and audiophiles might use attenuation techniques to manage sound levels when they blend different audio recordings.

Attenuation is also frequently used in the radiology field to discuss the characteristics of an anatomical structure represented in an X-ray.

In brewing, attenuation refers to the process of converting sugars into alcohol and carbon dioxide by fermentation. The greater the attenuation, the more sugar has been converted into alcohol. If a beer is more attenuated, then it is drier and more alcoholic than a beer that is less attenuated.

The importance of attenuation

Attenuation is important in telecommunications and ultrasound applications because it's critical to determining signal strength as a function of distance. Minimizing the loss of attenuation is important in microwave, wireless and cellular applications because an optical data link depends on modulated light reaching the receiver with enough power to be correctly demodulated. This power is reduced through attenuation, resulting in a loss of the light signal that's being transmitted.

How to measure attenuation

The extent of attenuation is usually expressed in units called decibels (dBs).

If P_s is the signal power at the transmitting end (source) of a communications circuit, and P_d is the signal power at the receiving end (destination), then P_s > P_d. The power attenuation A_p in decibels is given by the formula:

A_p = 10 log₁₀(P_s/P_d)

Attenuation can also be expressed in terms of voltage. If A_v is the voltage attenuation in decibels, V_s is the source signal voltage, and V_d is the destination signal voltage, then the following is true:

A_v = 20 log₁₀(V_s/V_d)

How to increase signal strength to prevent attenuation

Amplification is a technique that can be used to increase signal strength to prevent attenuation.

Signal amplification electrically increases the strength of a line signal by one of several technical methods. Typically, on computer networks, amplification includes logic for noise reduction to prevent the underlying message data from becoming corrupted in the process.

A network repeater device integrates a signal amplifier into its circuitry, acting as an intermediary between two message endpoints. The repeater performs the following tasks:

• receives data from the original sender (or another upstream repeater);
• processes it through the amplifier; and
• transmits the stronger signal forward to its ultimate destination.

In addition to repeaters, directional antennas and other antenna upgrades also work well to boost signals.

Editor's note: This definition was updated to improve the reader experience.