What is TCH/AHS Traffic Channel using Adaptive Multi-Rate Half Rate Speech

TCH/AHS: Optimizing Network Resources for Voice Calls in GSM

Within the realm of GSM (Global System for Mobile Communications) networks, TCH/AHS (Traffic Channel / Adaptive Multi-Rate Half Rate Speech) emerges as a technique specifically designed to optimize network resource utilization for voice calls. Here's a breakdown of the technical details:

Function:

• TCH/AHS is a type of Traffic Channel (TCH) used for voice communication in GSM networks.
• It leverages Adaptive Multi-Rate (AMR) technology, similar to TCH/AFS, but operates at a lower bit rate, specifically focusing on the Half Rate (HR) capabilities of AMR.

Focus on Efficiency:

• The primary goal of TCH/AHS is to provide acceptable voice quality while utilizing less network bandwidth compared to TCH/F (Full Rate) channels or even TCH/AFS (Full Rate AMR).
• This approach is particularly beneficial in scenarios with:
  • Limited network resources: When network congestion occurs, TCH/AHS allows for more calls to be supported on the available bandwidth.
  • Weaker signal conditions: In areas with poor signal strength, TCH/AHS can maintain call functionality with a lower bit rate, potentially improving call reliability.

AMR Half Rate (HR) Modes:

• TCH/AHS typically utilizes the Half Rate (HR) modes of the AMR codec:
  • AMR 5.9 kbps: Delivers a good balance between speech quality and network efficiency.
  • AMR 4.75 kbps: Offers a lower bit rate for extreme network limitations, but with a potential decrease in voice quality.

Dynamic Rate Adaptation:

• While TCH/AHS primarily focuses on HR modes, it might still employ a degree of dynamic rate adaptation within the HR range.
• The network can adjust the specific HR mode (e.g., 5.9 kbps or 4.75 kbps) based on real-time channel conditions to optimize resource utilization while maintaining acceptable speech intelligibility.

Benefits of TCH/AHS:

• Improved Network Capacity: By utilizing lower bit rates, TCH/AHS allows more calls to be accommodated on the network, increasing overall capacity.
• Robustness in Challenging Conditions: TCH/AHS offers better call functionality compared to full-rate channels in scenarios with limited resources or poor signal strength.
• Cost-Effectiveness: Network operators can benefit from efficient resource utilization by supporting more calls with the available infrastructure.

Limitations:

• Reduced Voice Quality: Compared to full-rate codecs, TCH/AHS might experience a slight decrease in speech quality, especially at the lower bit rate (4.75 kbps).
• Not All Situations Favorable: TCH/AHS is most advantageous in resource-constrained scenarios. In good network conditions, full-rate channels might offer superior voice quality.

Applications of TCH/AHS:

• TCH/AHS is particularly valuable in situations where network resources are limited, such as:
  • High call volumes during peak times
  • Areas with limited cell coverage
  • Users with limited data plans who prioritize call functionality over audio fidelity

Evolution of Voice Coding:

• While TCH/AHS plays a significant role in GSM, newer cellular technologies like 3G, 4G, and 5G employ more advanced voice coding schemes that offer even higher efficiency and improved audio quality at lower bit rates compared to AMR.

In Conclusion:

TCH/AHS serves as a vital technology in optimizing network resources for voice calls within GSM networks. By utilizing Adaptive Multi-Rate Half Rate Speech (AMR HR), it facilitates efficient call support even in challenging network conditions. Understanding TCH/AHS sheds light on the technical considerations and trade-offs involved in balancing network capacity with voice call quality in cellular communication systems.