What is TCH/HS Traffic Channel using Half Rate Speech

TCH/HS: Doubling Call Capacity with Half Rate Speech in GSM Networks

Within the realm of GSM (Global System for Mobile Communications) networks, TCH/HS (Traffic Channel / Half Rate Speech) emerges as a resource-efficient solution for supporting additional voice calls. Here's a breakdown of the technical details:

Function:

• TCH/HS serves as a type of Traffic Channel (TCH) dedicated to voice calls in GSM networks.
• It utilizes a specific speech coding scheme called Half Rate Speech (HR) to achieve a significant reduction in the bit rate required for voice transmission compared to the standard TCH/F (Full Rate) channels.

Benefits of Half Rate Speech (HR):

• Increased Network Capacity: The primary advantage of TCH/HS lies in its ability to support two concurrent voice calls on a single physical channel.
  • This is achieved by reducing the bit rate for each call, essentially allowing two TCH/HS channels to operate within the same bandwidth allocation as a single TCH/F channel.
• Improved Network Efficiency: By utilizing lower bit rates, TCH/HS facilitates more efficient network resource utilization, enabling support for a higher number of calls in areas with limited network capacity.

Technical Considerations:

• The trade-off for increased capacity lies in the audio quality of TCH/HS calls.
• The HR codec operates at a bit rate of approximately 5.9 kbps, which is half compared to the 12.2 kbps of TCH/FS.
• This reduction in bit rate can lead to a slight decrease in voice quality, with potentially:
  • Narrower frequency range captured, resulting in less natural-sounding speech.
  • Increased susceptibility to background noise, potentially affecting intelligibility in noisy environments.

Network Management and Prioritization:

• Network operators might prioritize the use of TCH/HS channels in scenarios where maximizing call capacity is crucial, such as:
  • High call volumes during peak usage times.
  • Areas with limited cell coverage where network resources are scarce.
• Conversely, in situations where voice quality is paramount, network operators might prioritize TCH/F channels for calls requiring higher fidelity (e.g., conference calls).

Comparison with TCH/AFS:

• TCH/AFS (Adaptive Multi-Rate Full Rate Speech) also offers a degree of resource efficiency by dynamically adjusting the bit rate within the Full Rate range.
• However, TCH/HS provides a more significant reduction in bit rate, enabling support for two calls on a single channel, while potentially sacrificing some voice quality.

Applications of TCH/HS:

• TCH/HS channels are valuable in scenarios where network capacity is a concern, such as:
  • Densely populated urban areas with high call volumes.
  • Remote locations with limited cell infrastructure.
• Users prioritizing call availability over pristine audio quality might benefit from TCH/HS connections, especially in situations with limited network resources.

Evolution of Voice Coding:

• While TCH/HS served a crucial role in maximizing network capacity in GSM, newer cellular technologies like 3G, 4G, and 5G employ more advanced voice coding schemes.
• These advanced codecs offer:
  • Improved audio quality with efficient bit rates, potentially exceeding the quality of even TCH/F channels in GSM.
  • Techniques like VoLTE (Voice over LTE) that leverage internet protocol (IP) technology for voice calls, enabling even higher fidelity and advanced features.

In Conclusion:

TCH/HS stands as a testament to the resource management strategies employed in GSM networks. By utilizing Half Rate Speech, it doubles the network's call capacity within the same bandwidth allocation. However, a slight trade-off in audio quality exists. Understanding TCH/HS sheds light on the balance between network efficiency and voice quality in cellular communication systems, while also highlighting the continuous advancements in voice coding technologies seen in subsequent cellular generations.