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

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TCH/AHS (Traffic Channel using Adaptive Multi-Rate Half Rate Speech) is a channel type used in mobile communication systems, particularly in 2G GSM (Global System for Mobile Communications) networks. It is designed to optimize the utilization of network resources while maintaining acceptable speech quality during voice calls.

Here are some key aspects to understand in detail regarding TCH/AHS:

  1. Traffic Channels: In mobile communication networks, voice and data traffic are carried over dedicated channels known as traffic channels. Traffic channels are allocated to users for the duration of their voice calls or data sessions. These channels provide a dedicated path for transmitting and receiving voice or data packets between the mobile device and the base station.
  2. Adaptive Multi-Rate (AMR): AMR is a speech coding standard used for compressing and decompressing speech signals in mobile communication networks. It offers a range of coding rates to adapt to different network conditions and provide optimal speech quality. The AMR codec dynamically adjusts the coding rate based on the estimated channel quality to ensure efficient use of network resources.
  3. Half Rate Speech: Half Rate speech coding is a specific mode within the AMR codec that reduces the bandwidth required for voice calls. In this mode, the speech signal is compressed using a lower bit rate, allowing two voice calls to share the same bandwidth that would typically be required for a single full-rate speech call. Half Rate speech coding sacrifices some speech quality to achieve higher spectral efficiency and conserve network resources.
  4. TCH/AHS Channel Type: TCH/AHS is a specific type of traffic channel that supports Adaptive Multi-Rate Half Rate Speech coding. It allows multiple voice calls to be multiplexed and carried over a single TCH/AHS channel, effectively doubling the capacity compared to full-rate speech channels. TCH/AHS channels provide a balance between speech quality and resource utilization.
  5. Dynamic Channel Allocation: TCH/AHS channels are dynamically allocated to users based on the availability of network resources and the number of active voice calls. When a user initiates a voice call, the network assigns a TCH/AHS channel if one is available. If all TCH/AHS channels are occupied, the network may allocate a full-rate speech channel instead.
  6. Speech Quality and Bandwidth Efficiency: TCH/AHS channels provide a trade-off between speech quality and bandwidth efficiency. Half Rate speech coding reduces the amount of data required for voice transmission, allowing more calls to be supported within the available bandwidth. However, the lower bit rate can result in a slight degradation in speech quality compared to full-rate speech channels.
  7. Network Capacity Optimization: TCH/AHS channels play a crucial role in optimizing network capacity in GSM networks. By using the Adaptive Multi-Rate Half Rate Speech coding, TCH/AHS channels maximize the number of simultaneous voice calls that can be supported, which is particularly beneficial during periods of high voice traffic demand.
  8. Compatibility and Interoperability: TCH/AHS channels are standardized within the GSM specifications, ensuring compatibility and interoperability across different GSM network implementations and mobile devices. This allows seamless voice call connectivity and continuity when moving between different network operators or roaming on foreign networks.

In summary, TCH/AHS (Traffic Channel using Adaptive Multi-Rate Half Rate Speech) is a channel type used in GSM mobile networks to optimize voice call capacity and network resource utilization. By employing the Adaptive Multi-Rate Half Rate Speech coding, TCH/AHS channels allow multiple voice calls to share the same bandwidth, offering a balance between speech quality and network efficiency. TCH/AHS channels play a significant role in optimizing network capacity during periods of high voice traffic demand.