UEM (unwanted emissions mask)

The Unwanted Emissions Mask (UEM) is a regulatory requirement and technical specification used in the field of telecommunications, particularly for wireless communication systems. It defines the allowable levels of unwanted radiofrequency emissions that a transmitter can produce outside of its designated frequency band. The UEM is an essential tool for ensuring that wireless devices and transmitters do not cause interference with other communication systems operating in adjacent frequency bands.

Importance of Unwanted Emissions Mask (UEM):

Wireless communication systems, such as cellular networks, Wi-Fi, Bluetooth, and other radio technologies, operate on specific frequency bands allocated by telecommunication regulatory authorities. These frequency bands are usually separated by guard bands to prevent interference between neighboring systems. However, no communication system can be perfectly isolated, and some level of unwanted emissions is inevitable. The UEM defines the maximum permissible levels of these unwanted emissions to maintain spectrum efficiency and prevent harmful interference to nearby services.

Key Concepts of Unwanted Emissions Mask (UEM):

1. Emission Mask Definition: The UEM specifies the shape and level of the emission mask, which is a graphical representation of the maximum allowed power levels of unwanted emissions across the frequency range outside the transmitter's designated channel. The mask typically consists of upper and lower limits, and emissions must stay within these limits.
2. Measurement Bandwidth: The UEM is defined over a specific measurement bandwidth, which is the range of frequencies considered for evaluating unwanted emissions. The measurement bandwidth is typically wider than the transmitter's operational bandwidth to account for potential out-of-band emissions.
3. Mask Margin: To provide additional protection against interference, the UEM often includes a margin below the maximum allowable emission levels. The mask margin ensures that even under adverse conditions (e.g., temperature variations), the emissions do not exceed the specified limits.
4. Regulatory Compliance: Telecommunication regulatory authorities, such as the Federal Communications Commission (FCC) in the United States or the European Telecommunications Standards Institute (ETSI) in Europe, define the UEM requirements to ensure that wireless devices and systems meet the established standards for spectral purity.

Example of Unwanted Emissions Mask (UEM):

An example of a UEM for a wireless communication system operating in a frequency band from f1 to f2 might specify that the power level of unwanted emissions outside the operational band must not exceed certain limits. For instance, the UEM could define that the unwanted emissions must be lower than -40 dBm (decibels relative to 1 milliwatt) at frequencies beyond f1-Δf and f2+Δf, where Δf is the guard band width.

Enforcement and Compliance:

Manufacturers of wireless communication devices and transmitters must ensure that their products comply with the UEM requirements set forth by the relevant regulatory bodies. Compliance testing involves measuring the unwanted emissions of the device and comparing them to the UEM limits. Devices that meet the UEM standards are granted certification and can be legally sold and used in the specific frequency bands.

Conclusion:

The Unwanted Emissions Mask (UEM) is a critical tool for regulating and ensuring the proper use of wireless spectrum. By defining the allowable levels of unwanted emissions, the UEM helps prevent interference between neighboring communication systems, enabling efficient and reliable wireless communication services for various applications and industries.