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What do Received Signal Level (RXLEV) and Received Signal Quality (RXQUAL) indicate in GSM?

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In GSM (Global System for Mobile Communications) networks, Received Signal Level (RXLEV) and Received Signal Quality (RXQUAL) are two key parameters used to measure and assess the quality of the radio signals received by a mobile device (Mobile Station, MS) from the base station (Base Transceiver Station, BTS). These parameters are crucial for determining the overall quality of the communication link between the mobile device and the network. Here's a technical explanation of what RXLEV and RXQUAL indicate in GSM:

  1. Received Signal Level (RXLEV):
    • Definition: RXLEV is a measurement of the power level or signal strength of the radio signal received by the mobile device from the base station. It is expressed in decibels (dBm) and provides an indication of the signal's strength at the MS.
    • Measurement: The RXLEV measurement is derived from the received power level at the mobile device's receiver, typically at the antenna. It is an absolute measurement that quantifies the power of the signal. The value is negative, with more negative values indicating weaker signals, and less negative values indicating stronger signals. For example, a signal with an RXLEV of -80 dBm is stronger than a signal with an RXLEV of -90 dBm.
    • Use: RXLEV is used for cell selection, handover decisions, and power control. It helps the MS determine which cell or BTS to connect to based on signal strength. A stronger RXLEV value indicates a higher signal strength and better connectivity.
    • Thresholds: Different networks may have specific RXLEV thresholds for cell selection and handovers. These thresholds help mobile devices decide when to switch between cells or maintain the current connection.
  2. Received Signal Quality (RXQUAL):
    • Definition: RXQUAL is a measurement of the quality of the received radio signal at the MS. It indicates how free the signal is from errors, interference, and noise. RXQUAL is expressed as a value between 0 and 7, with higher values indicating better signal quality.
    • Measurement: RXQUAL is calculated based on the bit error rate (BER) of the received signal. It measures how well the received bits match the transmitted bits. A lower RXQUAL value indicates a higher BER and poorer signal quality, while a higher RXQUAL value signifies a lower BER and better signal quality.
    • Use: RXQUAL is used to assess the link quality between the MS and the BTS. It helps the network make decisions regarding the modulation and coding schemes to use for data transmission. Higher RXQUAL values are preferred, as they indicate less error-prone communication.
    • Thresholds: Networks often have thresholds for RXQUAL values that trigger adjustments in modulation and coding schemes. For example, if RXQUAL degrades, the network may reduce the data rate to maintain a reliable connection.
    • Adaptation: Networks can dynamically adapt modulation and coding schemes to maintain a balance between data rate and reliability. In the presence of poor signal quality, the network may choose more robust modulation and coding schemes to ensure data integrity.

In summary, in GSM networks, RXLEV represents the received signal level or signal strength, while RXQUAL measures the quality of the received signal. RXLEV helps the MS make decisions about cell selection and handovers based on signal strength, while RXQUAL is used to assess the quality of the link and determine the appropriate modulation and coding schemes for data transmission. Both parameters are essential for optimizing communication reliability and performance in GSM networks.