The error vector magnitude (EVM) is a ratio used to measure radio signal performance by calculating the difference between the measured signal strength and the ideal strength. It is often expressed as a Receive Constellation Error (RCE) and can be used to identify signal degradation and its source. EVM is measured using specialized software and can include a ratio of average powers in multicarrier radios. The magnitude of the error vector is typically measured for digital radio transmitters and receivers, and various mathematical calculations related to signal characteristics are often performed.
Radio signals are often analyzed by plotting something called an error vector. This is typically the difference between the measured signal strength and one of ideal strength, called a reference. Generally used to plot both signals, a graph called the IQ plane includes a vertical axis labeled Q and a horizontal axis labeled I; each letter corresponds to a component of the signal. An error vector, the numerical difference between both signals, can have a power mean called the error vector magnitude (EVM).
Often used to measure the performance of radio electronics, EVM is typically expressed as a ratio. The power of the error vector, together with a mathematical average of the reference power, is typically used to calculate the magnitude of the error vector. This is often called a Receive Constellation Error (RCE). Signal quality is often represented by the graphical placement of constellation points, but imperfections can occur for various reasons. The EVM usually measures the distance of these points from their intended locations.
The magnitude of the error vector is usually measured for digital radio transmitters and receivers. The equipment used to measure it can process a signal similar to how a radio component called a demodulator does. Calculations are then performed by the measurement system. These measurements are often used to identify what type of signal degradation is occurring; sometimes the source of the signal problem can also be identified.
A ratio of average power to peak power in a single carrier system, Error Vector Magnitude can also include a ratio of two average powers in multicarrier radios, where signal interaction can be a little more complex. The modulation error ratio in multicarrier systems generally represents the ratio of the average signal power to the average significance of an error. Under certain circumstances, it is related to EVM.
Specialized software can be used to measure the magnitude of the error vector. Many software programs are capable of determining signal integrity and may include pass/fail indicators to show if measurements meet particular criteria. Various other mathematical calculations related to signal characteristics are also often performed. On a computer graph, symbols and letters can be generated to indicate things like the location of the signal being measured and where the reference signal should be. Physical angles can be used to calculate the magnitude of the error, but this doesn’t always find the nature of the problem, even with the help of a computer.
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