Over-The-Air (OTA) Testing
What Is Over-The-Air (OTA) Testing in Telecom?
Over-the-air (OTA) testing evaluates the performance, reliability, and compliance of telecom infrastructure. In a digital twin workflow, this testing becomes part of an ongoing operational cycle. The digital twin is kept up to date by repeated, automated data capture, allowing teams to monitor site conditions, validate performance, and spot issues as they develop.
For a typical telecom site, technicians collect measurements from antennas, transmitters, receivers, and the general environment. This data is then used to validate that the telecom site is operating as intended and that any issues with coverage, interference, and synchronization are promptly addressed.
In addition to network optimization, OTA testing helps telcos ensure their sites are fully compliant with all relevant industry and regulatory standards. It also supports infrastructure upgrades, allowing engineers to evaluate and plan around the impact that new hardware and software may have on the sites. This makes it extremely valuable for any provider seeking to deploy technologies such as 5G.
What Does OTA Testing Measure?
OTA testing for a telecom site is a comprehensive process. Each major component has its own array of measurements, as detailed below.
OTA Antenna Testing
For OTA wireless antenna testing, technicians typically measure the following:
Beamforming Accuracy
Assesses how effectively an active antenna system (AAS) can create, direct, and maintain beams.
Directivity
The intensity of the antenna’s RF energy in its strongest direction compared to all other directions and is often depicted in a visual representation known as a beam pattern or radiation pattern.
Efficiency
How much power the antenna actually converts into RF energy, expressed as a ratio of radiated power to input power. It also measures how much power is lost during the process.
Front-to-Back Ratio
Determines how effectively an antenna suppresses unwanted RF energy in the opposite direction of its main beam to reduce interference.
Gain
The intensity of the antenna’s radio frequency (RF) energy in a specific direction compared to a theoretical perfect model known as an isotropic radiator.
Polarization
Determines whether the antenna transmits and/or receives radio waves in the intended vertical, horizontal, and/or circular direction.
Radiated Power
Measures output power for each beam and/or direction in a multi-antenna system.
OTA Transmitter Testing
Technicians combine the measurements below to evaluate a telecom transmitter’s performance.
Adjacent Channel Leakage Power Ratio
Quantifies potential interference on a channel by comparing signal strength against how much RF power is leaking into adjacent channels.
Effective Isotropic Radiated Power (EIRP)
Expresses the maximum radiated RF power in the direction of peak antenna gain, referenced to an isotropic radiator.
Error Vector Magnitude (EVM)
How much a modulated signal deviates from its optimal trajectory after transmission. The lower the EVM, the less distorted the signal.
Frequency Error
Expresses the difference between the transmitter’s assigned carrier frequency and its real-world output frequency.
Intermodulation Products
Unwanted signals caused by mixed frequencies that can interfere with operation.
Occupied Bandwidth
Shows how much frequency is taken up by the transmitter’s wireless signal.
Spurious Emissions
Any and all RF signals generated outside the transmitter’s assigned bands. These must comply with regulatory limits.
Time Alignment Error (TAE)
The nanosecond offset in signals sent from separate transmitter branches. Essential for multi-antenna and multiple input, multiple output (MIMO) systems.
Total Power Dynamic Range
The difference between the transmitter’s maximum and minimum total radiated power (TRP). This is usually expressed in decibels and measured under specific conditions.
Total Radiated Power (TRP)
The total amount of RF energy within a spherical area around the transmitter.
Transmitter Transient Period
How long it takes for a transmitter to both start up and shut down during time-slotted or burst transmission applications.
OTA Receiver Testing
When measuring receivers, technicians focus on eight key figures.
Bit Error Rate
How many bits or blocks the receiver encounters during wireless testing, expressed as a ratio against the total received.
Blocking
How effectively the receiver is able to perform in the presence of strong unwanted signals. This figure is closely related to desensitization.
Desensitization
The degree to which strong signals or mixed signals impact receiver performance. Also known as intermodulation susceptibility.
Isotropic Sensitivity
Expressed as two metrics. Effective Isotropic Sensitivity (EIS) is the minimum required signal strength for a receiver. Total isotropic sensitivity is an average of all EIS values.
Linearity
The accuracy by which the receiver processes signals of different strengths.
Noise Figure
A ratio that defines how much noise the receiver’s hardware generates.
Selectivity
How reliably the receiver can identify its target signal.
Throughput
The receiver’s rate of usable data when operating OTA with a wireless antenna.
Additional OTA Measurements
Technicians must also ensure a site operates within safety limits for radiation exposure, a figure known as radiation hazards. Electromagnetic compatibility (EMC) compliance is a closely related metric that tests compatibility with electronic devices. Finally, signal-to-noise helps the telco identify how much background noise exists on the site.
How Digital Twins Are Transforming OTA Testing
Traditional OTA testing typically requires painstaking manual data collection by technicians. This tends to be both costly and time-consuming, while also carrying no small degree of risk. Autonomous drone technology equipped with onboard sensors can automate nearly the entire testing process, dramatically reducing the overhead and time commitment of an OTA test.
Using autonomous drones for inspections allows tests to be performed more often and with greater accuracy, resulting in digital twins that ensure the continuous data collection provides a more accurate window into the telecom site’s condition and performance.