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Understanding Bit Error Probability (BEP) in GSM/GPRS/EDGE

gsm gprs edge bit error radio link

In the GSM/EGPRS/EDGE standards, the Bit Error Probability (BEP) is a crucial parameter for assessing radio conditions and determining the appropriate coding scheme. BEP is calculated on a burst-by-burst basis.

What is BEP?

BEP essentially gauges the likelihood of bit errors within a transmitted data burst. This information is vital for adapting the communication strategy to maintain a reliable connection. The BEP is used to determine two important parameters: CV_BEP and MEAN_BEP.

Key Parameters Derived from BEP

Two significant parameters are derived from the raw BEP measurements:

  • CV_BEP (Coefficient of Variation of BEP): This parameter measures the quality and consistency of the radio link from one burst to the next. It effectively captures the impact of factors like frequency hopping and the interleaving process (whether there are gains or losses). A high CV_BEP might indicate inconsistent radio conditions.

  • MEAN_BEP (Mean BEP): This parameter serves as an indicator of the Carrier-to-Interference ratio (C/I) and the mobile’s velocity. A higher MEAN_BEP generally suggests a poorer C/I ratio or a faster-moving mobile, both of which can degrade signal quality. It is calculated by averaging the BEP calculated for all four bursts of a radio block.

BEP Types

There are several variations of BEP used in the GSM/GPRS/EDGE context:

  • Mean BEP: As explained above, it’s the average BEP over multiple bursts, reflecting overall link quality.
  • Actual BEP: This is the “true” bit error probability observed in the received data.
  • Reported BEP: The mobile station reports its BEP measurement back to the network. This reported value may be subject to some processing or mapping.
  • CV BEP: As explained above, it reflects the burst-to-burst variations.

Mapping Between BEP Values

  • Mapping between MEAN_BEP and Actual_BEP: A specific mapping or formula is used to relate the measured MEAN_BEP to the estimated actual BEP. This mapping is crucial for the network to accurately assess the radio conditions.

  • Mapping between Reported CV_BEP and Actual CV_BEP: Similarly, a mapping exists between the CV_BEP reported by the mobile and the actual CV_BEP. This allows the network to understand the level of variability in the radio link quality.