PESQ Score: Evaluating Speech Quality in GSM Networks

The Perceptual Evaluation of Speech Quality (PESQ) score is an important parameter used to objectively assess the quality of voice calls in GSM and other communication networks. Developed by ITU-T, PESQ measures how closely the transmitted audio matches the original audio. In GSM networks, PESQ is crucial for evaluating and improving voice call quality.

The following sections provide an overview of PESQ and its relevance to GSM technology.

Definition of PESQ (Perceptual Evaluation of Speech Quality)

• PESQ provides a quantitative score for speech quality by comparing the original (reference) audio signal with the transmitted (degraded) audio signal received after going through the network.

• PESQ accounts for different types of audio impairments such as background noise, distortion, clipping, delay, and packet loss.

• It provides a Mean Opinion Score (MOS) on a scale from 1 to 4.5, where:

  • 1 indicates very poor quality.
  • 4.5 indicates excellent quality, close to the original.

How PESQ Works in GSM Networks

• Comparison-based Evaluation: PESQ works by taking a sample of the original audio (as transmitted from the mobile device or network) and comparing it to the audio that is actually received after transmission through the GSM network.

• Modeling Human Perception: PESQ uses psychoacoustic models to simulate human perception, evaluating how impairments in the received signal impact the listener’s perceived quality.

• Algorithmic Calculation: PESQ analyzes distortions in frequency, time, and amplitude and assigns a numerical score based on how noticeable and disruptive these distortions are likely to be to human listeners.

Importance of PESQ in GSM Networks

• Objective Measure of Call Quality: PESQ provides a reliable, objective measure for voice quality, eliminating the need for subjective human listening tests.

• Network Optimization: Network engineers use PESQ scores to identify and troubleshoot areas with poor speech quality, enabling them to optimize handovers, reduce interference, and ensure stable connections.

• User Satisfaction: High PESQ scores are directly related to better user experiences, as clear and intelligible voice quality is crucial for user satisfaction.

• Compliance with Quality Standards: GSM network operators aim to maintain PESQ scores above a certain threshold (often above 3) to comply with quality standards and regulatory requirements.

Factors Affecting PESQ Scores in GSM

• Signal Interference: Interference from other signals can distort audio quality, reducing the PESQ score.

• Network Congestion: High congestion can lead to packet loss and delays, impacting voice quality and PESQ scores.

• Codec Limitations: GSM uses codecs to compress voice signals; while efficient, these codecs may degrade audio fidelity, especially under poor network conditions.

• Error Correction Mechanisms: In GSM, the use of error correction can help improve PESQ scores by compensating for packet loss or transmission errors.

• Background Noise and Environmental Conditions: High background noise, either in the user’s environment or due to network conditions, can lower PESQ scores.

PESQ Score Range and Quality Interpretation

• 1.0 - 1.9: Poor – Severe quality degradation, difficult to understand.

• 2.0 - 2.9: Fair – Noticeable quality issues, but speech is still intelligible.

• 3.0 - 3.9: Good – Acceptable quality with minor imperfections.

• 4.0 - 4.5: Excellent – High-quality audio, nearly identical to the original sound.

GSM networks typically aim for PESQ scores of 3 or higher, indicating good to excellent voice quality for a satisfactory user experience.

Application of PESQ in GSM Testing and Optimization

• Routine Network Testing: PESQ is used in regular testing and monitoring to assess network quality across different regions and optimize areas with low scores.

• During Network Upgrades: Operators use PESQ before and after upgrades (such as adding capacity or optimizing handovers) to measure improvements in voice quality.

• Troubleshooting: Low PESQ scores in specific cells may point to issues like interference, signal fading, or faulty equipment that needs addressing.

• Service Level Agreements (SLAs): PESQ is often part of SLAs to ensure a certain level of quality for corporate clients or high-value customers.

Summary

The PESQ score is a crucial tool for evaluating voice quality in GSM networks. By objectively measuring speech quality, PESQ helps network operators maintain high-quality voice services, troubleshoot performance issues, and enhance user satisfaction. In GSM, PESQ scores provide a reliable benchmark to ensure users experience clear, uninterrupted calls even in challenging network environments.