Received Signal Level

Description

Received Signal Level (RXLEV) is a cornerstone radio measurement parameter defined in the GSM system and carried forward through 3GPP specifications. It quantifies the average power of the received radio signal, typically measured in dBm, over a specified measurement period. In the network architecture, RXLEV is measured by the Mobile Station (MS) on the downlink broadcast channels, such as the Broadcast Control Channel (BCCH) from serving and neighboring cells, and by the Base Transceiver Station (BTS) on the uplink from the MS. The measurement is performed on the radio frequency carrier, often using a power averaging filter to mitigate the effects of fast fading and provide a stable value representative of the path loss and large-scale shadowing.

The measurement procedure is tightly integrated into the GSM protocol stack, specifically within the Radio Resource (RR) management layer. The MS continuously measures and reports RXLEV values to the network. These raw measurements are mapped to an integer index (RXLEV 0-63) covering a defined power range (e.g., -110 dBm to -48 dBm in GSM). This indexed value is what is typically reported in measurement reports. The network's Base Station Controller (BSC) uses these reports, alongside other parameters like RXQUAL, to execute critical radio resource management functions.

RXLEV's role is pivotal for maintaining network connectivity and quality. It is the primary input for the cell selection (C1 criterion) and cell reselection algorithms when the MS is in idle mode. In dedicated mode, it is a key determinant for handover decisions; a handover may be triggered if the RXLEV from a neighboring cell exceeds that of the serving cell by a certain hysteresis margin. Furthermore, it is used for power control algorithms, where the BSC commands the MS or BTS to adjust its transmission power to maintain a sufficient RXLEV at the receiver while minimizing interference. Thus, RXLEV is a fundamental metric for coverage optimization, interference reduction, and overall network stability.

Purpose & Motivation

RXLEV was created as a fundamental building block for the automated control of a cellular network. Early mobile radio systems required manual tuning and offered limited mobility. The GSM digital system introduced the need for autonomous, network-controlled mobility (handover) and efficient resource use. RXLEV provides the essential, quantifiable metric for 'how strong the signal is,' which is the first-order determinant of whether a mobile can reliably communicate with a base station.

It solves the problem of enabling a mobile device to automatically select the best cell to camp on and, during a call, for the network to seamlessly transfer the connection to a stronger cell as the user moves. Before such standardized measurements, maintaining a call while mobile was highly challenging. RXLEV, combined with RXQUAL, allows the network to make informed decisions, balancing the goals of strong signal coverage (using RXLEV) and good signal integrity (using RXQUAL). Its creation was motivated by the need for a simple, robust, and universally implemented measurement that could drive algorithms for cell selection, handover, and power control, which are the core functions enabling widespread cellular mobility.

Key Features

• Measures average received RF carrier power in dBm
• Reported as an integer index (e.g., 0-63) over a standardized range
• Measured by both MS (downlink) and BTS (uplink)
• Primary input for cell selection and reselection (C1/C2 criteria)
• Key parameter for network-controlled handover decisions
• Used as an input for uplink and downlink power control algorithms

Evolution Across Releases

Defining Specifications