Average transmit power

Description

Average transmit power is a measurement definition that specifies the average output power of a transmitter over a given time interval, including periods when no transmission occurs. Unlike average power, which is measured through a specific filter and excludes guard periods, average transmit power is a more general concept that captures the mean power over any interval, regardless of whether the transmitter is actively transmitting. This definition is used in specifications such as 25.101 (UE radio transmission and reception), 25.102 (UTRA repeater conformance testing), and 25.141 (Base station conformance testing).

The inclusion of periods with no transmission is significant because it accounts for the duty cycle of the transmitter. In many radio access technologies, transmitters are not continuously active; they may have periods of inactivity due to discontinuous transmission (DTX) or time-division duplexing (TDD). By including these periods, the average transmit power reflects the true mean power over time, which is important for thermal considerations, power consumption, and regulatory compliance.

The measurement interval can be specified according to the test requirements. For example, in some tests, the interval might be a frame or a superframe, while in others it might be a specific number of timeslots. The flexibility allows the measurement to be tailored to the specific characteristics of the transmitter and the test objectives. The average transmit power is typically measured using a power meter or a spectrum analyzer with appropriate averaging settings.

This parameter is closely related to other power metrics such as maximum output power and minimum output power, which define the extremes of transmitter operation. Average transmit power provides a central tendency that is useful for assessing long-term performance and efficiency. It is also used in link budget calculations and interference analysis, where the average power determines the typical impact on other users.

In summary, average transmit power is a versatile measurement that characterizes the mean output power of a transmitter over a specified interval, including idle periods. It is essential for conformance testing, power control, and system design in 3GPP networks.

Purpose & Motivation

Average transmit power was defined to provide a standardized way to measure the mean output power of a transmitter over time, including periods when the transmitter is not actively transmitting. This is important because many 3GPP systems employ discontinuous transmission or time-division duplexing, where the transmitter is silent for a portion of the time. Measuring only during active transmission would overestimate the average power and could lead to incorrect conclusions about thermal load, battery life, and interference.

The definition addresses the need for a metric that reflects the true average power consumption and emission over time. Regulatory bodies often specify limits on average power to ensure that devices do not exceed electromagnetic exposure limits or cause excessive interference. By including idle periods, the measurement aligns with these regulatory requirements.

Furthermore, average transmit power is used in equipment specifications to ensure that transmitters from different vendors meet the same performance criteria. It allows fair comparison and interoperability testing. The concept is simple yet powerful, providing a foundation for more specific power measurements like average power (filtered) and peak power.

Overall, average transmit power solves the problem of characterizing transmitter output in a way that accounts for real-world operating conditions, including idle periods, and supports regulatory, design, and testing needs.