Transmitter ON period

Description

The Transmitter ON period is a core concept in 3GPP radio transmission specifications that defines the time window during which a transmitter is allowed to emit data and reference symbols at its nominal power level. It is the counterpart to the Transmitter OFF period and is bounded by the Transmitter transient period, which represents the transition between ON and OFF states. During the ON period, the transmitter must meet stringent requirements for output power, modulation quality, and spectral emissions, ensuring that the transmitted signal is both effective and compliant with regulatory limits.

Architecturally, the ON period applies to the base station (BS) in LTE and NR, and it encompasses the transmission of downlink physical channels and signals. In LTE, the ON period includes data subframes and the Downlink Pilot Time Slot (DwPTS) in TDD configurations. In 5G NR, the ON period covers orthogonal frequency-division multiplexing (OFDM) symbols carrying data, control, and reference signals. The ON period is defined per transmitter antenna connector or per radiated interface, depending on the conformance test setup. The transmitter must remain within specified power limits during the ON period, and any deviation outside the transient period is considered a violation of the power versus time mask.

The ON period is critical for several reasons. First, it ensures that the base station transmits at the correct power level, which is essential for link adaptation, coverage, and interference management. Second, it defines the time during which the transmitter's spectral emissions must comply with the operating band unwanted emissions (OBUE) and ACLR requirements. Third, during the ON period, the transmitter must maintain the required error vector magnitude (EVM) and frequency error, ensuring that the signal can be correctly demodulated by user equipment (UE).

In TDD systems, the ON period is aligned with the downlink slots or subframes, and it must not overlap with the guard period or uplink slots, where the transmitter must be OFF. The exact switching time between ON and OFF is governed by the transient period, which is not considered part of the ON period for emission compliance. This separation allows transmitters to ramp up and down without violating the ON power requirements.

Key components of the ON period include the definition of the ON power level (e.g., rated output power, maximum output power), the measurement bandwidth, and the reference symbols used for power measurement. The ON period is also used in conformance testing to verify that the transmitter meets the required power dynamic range and that it can switch between ON and OFF states without causing excessive emissions. For IAB nodes, the ON period applies to both the IAB-DU and IAB-MT transmitters, which may operate in time-division multiplexing (TDM) mode, requiring careful scheduling to avoid self-interference.

The role of the ON period in the network is to enable efficient and reliable downlink transmission. Without a clear definition of when the transmitter is ON, it would be difficult to assess compliance with emission limits or to coordinate transmissions across cells. The ON period also facilitates dynamic power control and beamforming, as the transmitter must maintain the desired power and phase characteristics during the ON period. In summary, the Transmitter ON period is the active transmission window that ensures the base station can deliver data and reference symbols with the required quality and spectral purity.

Purpose & Motivation

The Transmitter ON period was established to formally define the time window during which a transmitter is permitted to emit radio frequency energy at its operational power level. Before its standardization, there was no consistent definition of when a transmitter was considered 'on' or 'off', leading to ambiguity in testing and potential interference. The ON period provides a clear benchmark for conformance testing, ensuring that transmitters meet power and emission requirements only during intended transmission intervals. This is particularly important in TDD systems, where the transmitter must switch off during uplink slots to avoid blocking reception.

In the context of LTE and NR, the ON period also supports the definition of the power versus time mask, which specifies the allowed power levels during ON, OFF, and transient periods. This mask is essential for regulatory compliance and for coexistence with other systems in the same or adjacent bands. The ON period enables operators to plan network coverage and capacity with confidence, knowing that base stations will transmit at the expected power levels during active periods.

As networks evolve towards more dynamic and flexible spectrum usage, the ON period concept remains relevant for new technologies such as IAB and full-duplex. It provides a fundamental building block for scheduling and interference management, ensuring that transmissions occur only when intended and at the correct power.