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GSM

What is GSM physical channels?

What is GSM physical channels?

GSM (Global System for Mobile Communications) is a widely used digital cellular network technology that uses various physical channels to facilitate communication between mobile devices and the network infrastructure. These physical channels are an essential part of GSM’s air interface and play distinct roles in voice and data transmission. Let’s delve into the details of GSM’s physical channels:

1. Physical Broadcast Channel (PBCH):

The Physical Broadcast Channel (PBCH) is used to broadcast essential system information to all mobile devices within the cell. Key characteristics of PBCH include:

  • Constant Broadcasting: PBCH continually broadcasts information about the cell, allowing newly arrived or powered-on mobile devices to quickly access necessary network details.
  • Synchronization: It helps mobile devices synchronize with the network’s timing and frequency parameters.
  • Cell Identification: PBCH contains information about the cell’s identity, which helps mobile devices identify and select the appropriate cell.

2. Common Control Channels:

  • Frequency Correction Channel (FCCH): The FCCH is used to provide frequency correction information to mobile devices. It helps them adjust their receivers to the correct frequency of the cell.
  • Synchronization Channel (SCH): The SCH carries synchronization information, enabling mobile devices to align their timing with that of the network.
  • Broadcast Control Channel (BCCH): The BCCH is used to broadcast general control information, cell-specific details, and system information to mobile devices within the cell. It is essential for mobile devices to access information about the network’s configuration and available services.

3. Traffic Channels:

GSM uses several traffic channels for voice and data communication:

  • Full Rate (TCH/F): This channel provides a full-rate voice service, delivering speech in its original quality. It is commonly used for voice calls.
  • Half Rate (TCH/H): The half-rate channel is used to conserve bandwidth by reducing the data rate while maintaining acceptable voice quality. It is often employed during periods of high network congestion.
  • Enhanced Full Rate (EFR): EFR is an extended version of the full-rate channel that further enhances voice quality.
  • Adaptive Multi-Rate (AMR): AMR is a more recent voice codec that offers variable rates, adapting to the quality of the radio link. It provides both good voice quality and efficient bandwidth utilization.

4. Control Channels:

  • Stand-alone Dedicated Control Channel (SDCCH): SDCCH is used for signaling and control purposes, such as call setup, location updates, and SMS delivery. It provides dedicated resources for control signaling between the mobile device and the network.
  • Slow Associated Control Channel (SACCH): SACCH operates in parallel with traffic channels (TCH) and carries control information related to the ongoing call, including power level adjustments and handover commands.
  • Fast Associated Control Channel (FACCH): FACCH is used for transmitting time-critical control information during a voice call. For example, if there is a need to hand over the call to a different cell, the control information is sent via FACCH to minimize interruption.

5. Random Access Channel (RACH):

The Random Access Channel (RACH) is used by mobile devices to initiate contact with the network for various purposes, such as call setup, SMS transmission, or location updates. When a mobile device wants to transmit data to the network, it sends a request on the RACH, and the network responds accordingly.

6. Dedicated Control Channels (DCCH):

Dedicated Control Channels (DCCH) are used for dedicated signaling and control associated with a specific mobile device and its active call. Examples include the Stand-alone Dedicated Control Channel (SDCCH) and FACCH.

7. Slow and Fast Associated Control Channels (SACCH and FACCH):

SACCH and FACCH are used to convey control and signaling information during an ongoing call. SACCH operates at a slower rate and is used for less time-critical information, while FACCH operates at a faster rate and is used for urgent control messages.

In summary, GSM uses a combination of physical channels to facilitate voice and data communication. These channels serve various purposes, from broadcasting essential information to establishing and maintaining connections between mobile devices and the network. Each channel plays a vital role in ensuring the reliable and efficient operation of the GSM cellular network.

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