What Is a Radio Link?

A radio link is a point-to-point wireless communication path that carries information between two fixed or mobile endpoints using radio frequency signals. It forms one of the fundamental building blocks of telecommunications infrastructure, providing connectivity across distances where physical cabling is impractical or cost-prohibitive. Radio links operate across a broad range of frequency bands, from microwave and millimeter wave channels used in backbone networks to sub-gigahertz frequencies used in rural and mobile deployments.

The concept of the radio link traces its lineage to the early twentieth century development of fixed wireless telegraphy, and it has since evolved into a precise engineering discipline governed by international standards. Modern radio links are characterized by specified quality-of-service parameters, including link availability, bit error rate, and latency, all of which are determined by the allocated spectrum, antenna gain, transmit power, and the propagation environment between the two endpoints.

Link Budget and Signal Propagation

A radio link budget is the accounting of all gains and losses in a transmission system, from the transmitter through the medium to the receiver. Engineers calculate free-space path loss, atmospheric absorption, antenna gains, and fade margins to determine whether a link will meet its availability target, typically expressed as a percentage of annual uptime. For microwave links operating above 10 GHz, rain fade becomes a dominant impairment, requiring additional link margin or adaptive modulation to maintain the required service level. The ETSI standards for fixed radio links define the performance criteria and testing methodologies that apply to licensed point-to-point and point-to-multipoint systems across Europe and beyond.

Modulation and Capacity

Radio links achieve high spectral efficiency through advanced modulation schemes such as quadrature amplitude modulation (QAM), with commercial microwave systems commonly using 256-QAM or higher to transmit multiple bits per symbol. Adaptive modulation allows the link to trade off capacity for reliability as propagation conditions change, stepping down to a more robust modulation order during periods of heavy rain or interference. Frequency division duplex (FDD) and time division duplex (TDD) are both used, depending on spectrum allocation and operator preference. The capacity of a radio link scales with bandwidth and modulation order, with modern backhaul links supporting multi-gigabit-per-second throughputs across line-of-sight paths of 10 to 80 kilometers.

Backhaul and Access Applications

Radio links serve two broad roles in telecommunications: backhaul and access. In backhaul applications, they connect base stations, remote cell sites, and aggregation points to the core network where fiber is unavailable or too expensive to deploy. In access applications, they provide last-mile connectivity to homes and enterprises. The role of radio links in mobile network backhaul has grown substantially with the deployment of dense small-cell networks for 4G and 5G, where a cellular network's radio access architecture often depends on hundreds of microwave and millimeter wave hops to aggregate traffic from distributed sites. Research into E-band (71 to 86 GHz) and D-band (130 to 174 GHz) links has extended the capacity of fixed wireless connections into the range needed to support 5G small-cell backhaul, as explored in work published through the IEEE Communications Society.

Applications

Radio link technology has applications in a range of fields, including:

• Mobile network backhaul for 4G and 5G base stations
• Broadcast contribution links for live video distribution
• Emergency and public safety communications
• Utility and energy sector supervisory control networks
• Military and defense point-to-point secure communications