reverse link
In radio communications, the link from a mobile user to a fixed base station. If the link includes a communications relay satellite, the reverse link will consist of both an uplink (mobile station to satellite) and a downlink (satellite to base station).
reverse link: mobile-to-base radio path
A reverse link is the radio transmission path running from a mobile transmitter (such as a handheld radio, cellular phone, or airborne unit) back to a fixed receiving station or network hub. It exists in contrast to the forward link, which carries data and voice from the base station outward to the mobile unit. In a ground-based system, the reverse link is a single hop; in a satellite system, it becomes two separate segments that must be coordinated as one logical channel.
In terrestrial mobile radio networks, the reverse link operates on a dedicated frequency or frequency band assigned to uplink traffic. The mobile transmitter typically uses lower power than the base station, ranging from a few hundred milliwatts in cellular phones to several watts in field radios. The base station must be sensitive enough to detect these weaker signals at distance, usually employing directional antennas and low-noise receivers positioned for optimal coverage of the service area.
Satellite and hybrid systems
When a communications satellite relays traffic, the reverse link divides into two stages: an uplink from the mobile station to the satellite (typically in the S-band, Ku-band, or Ka-band), and then a downlink from the satellite to the ground base station (often on a different frequency). The satellite must have sufficient sensitivity and processing capability to receive the uplink signal, often amplifying and frequency-converting it before retransmitting on the downlink. Timing, power control, and frequency coordination between these two segments directly affect link quality and network reliability.
Reverse link performance is constrained by several factors. Path loss increases with distance and frequency; atmospheric absorption and rain fade affect satellite uplinks severely. The mobile transmitter's power budget is tight, especially for battery-powered devices, so modulation efficiency matters. Interference from other mobile units sharing the same frequency or band can degrade the signal-to-noise ratio at the base receiver. Doppler shift, significant for airborne or satellite-borne mobile units, can push signals outside the receiver's passband if not corrected.
The term reverse originated in full-duplex radio systems where forward and reverse were simply the two directions of a conversation. The nomenclature persists in modern cellular, maritime, and aeronautical networks even though both paths are typically active simultaneously rather than alternating. Understanding reverse link limitations is essential when designing coverage, setting power classes for handsets, and planning frequency allocations in congested spectrum bands.