Carrier power

Description

Carrier power is defined in 3GPP specifications as the power at the antenna connector in the channel bandwidth of the carrier, averaged over at least one subframe for NR or E-UTRA, at least one slot for UTRA, and the useful part of the burst for GSM/EDGE. This definition provides a standardized method for measuring the average power of a carrier, which is essential for evaluating transmitter performance, ensuring regulatory compliance, and optimizing network coverage and capacity. The carrier power is a key parameter in radio transmission and reception, as it directly affects the signal-to-noise ratio (SNR) and the overall quality of service experienced by users.

The measurement of carrier power involves integrating the power over the channel bandwidth of the carrier and averaging it over a defined time period. For NR and E-UTRA, the averaging period is at least one subframe (1 ms for LTE, and variable for NR depending on numerology), which ensures that the measurement captures the average power over a typical scheduling interval. For UTRA, the averaging is over at least one slot (0.667 ms), and for GSM/EDGE, it is over the useful part of the burst (excluding guard periods). These technology-specific averaging periods account for the different frame structures and transmission characteristics of each RAT.

The carrier power is typically measured using a power meter or a spectrum analyzer with appropriate settings. The antenna connector is the reference point, meaning that the measurement excludes any antenna gain or cable losses. This allows the transmitter's output power to be evaluated independently of the antenna system. In practice, the carrier power is often expressed in dBm and is compared against the maximum output power and minimum output power requirements specified for the base station or UE. It is also used to calculate other parameters such as power spectral density (PSD) and adjacent channel power ratio (ACPR).

In the context of carrier aggregation, the carrier power may refer to the power of an individual component carrier or the aggregate power of multiple carriers. The 3GPP specifications define requirements for both cases, ensuring that the total power remains within regulatory limits and that inter-modulation products do not cause excessive interference. The carrier power is also a critical input for link budget calculations, which determine the coverage and capacity of a cell. By accurately measuring and controlling carrier power, operators can optimize network performance and ensure a consistent user experience.

The definition of carrier power has evolved over releases to include new technologies. Initially defined for E-UTRA, UTRA, and GSM/EDGE, it was later updated to include NR in Release 15. This reflects the ongoing development of 3GPP standards and the need to maintain a common metric across all radio access technologies. The carrier power remains a fundamental concept in the physical layer, underpinning many aspects of radio resource management and performance evaluation.

Purpose & Motivation

The definition of carrier power exists to provide a standardized and technology-agnostic method for measuring the average power of a carrier in cellular networks. It solves the problem of inconsistent power measurements across different radio access technologies by specifying the exact measurement conditions, including the reference point (antenna connector), the bandwidth (channel bandwidth of the carrier), and the averaging period (subframe, slot, or burst). This ensures that power measurements are repeatable and comparable, which is essential for conformance testing, regulatory compliance, and network planning.

Historically, as cellular technologies evolved, each RAT had its own way of defining and measuring power. For example, GSM used burst power, while UMTS used code domain power. The 3GPP definition of carrier power harmonized these approaches by providing a common framework that can be applied to all technologies. This was particularly important for multi-RAT networks and for equipment that supports multiple technologies. The inclusion of NR in Release 15 extended the definition to 5G, ensuring that the same principles apply to the latest generation of cellular systems.

Without a precise definition, power measurements could vary significantly depending on the measurement equipment and settings, leading to disputes and non-compliance. The carrier power definition eliminates this ambiguity by specifying the averaging period and the reference point. It also enables the calculation of other important metrics, such as power spectral density and total radiated power (when combined with antenna gain). For regulators, the carrier power is a key parameter for ensuring that transmissions do not exceed licensed power limits and do not cause harmful interference to other services.