In GSM (Global System for Mobile Communications), logic channels play a crucial role in facilitating communication between mobile devices and the network. These logic channels serve different purposes, including voice transmission, control signaling, and data exchange. Here are the main logic channels in GSM:
1. Traffic Channels (TCH):
Traffic channels are used for carrying voice and user data. There are two types of traffic channels:
a. Full Rate (TCH/F):
- Provides speech and user data at a rate of 13 kbps.
b. Half Rate (TCH/H):
- Utilized for voice compression, offering speech and user data at a rate of 6.5 kbps.
2. Control Channels:
Control channels are responsible for signaling and control functions within the GSM network. They include:
a. Broadcast Control Channel (BCCH):
- Broadcasts essential information about the network, such as cell identity and frequency.
b. Common Control Channel (CCCH):
- Includes several channels for common control purposes:
- Paging Channel (PCH): Alerts a mobile device about an incoming call or message.
- Access Grant Channel (AGCH): Assigns a dedicated channel after successful access.
- Access Reject Channel (AGCH): Indicates that the network cannot grant access.
c. Dedicated Control Channel (DCCH):
- Carries signaling information related to dedicated channels established for voice or data communication.
d. Standalone Dedicated Control Channel (SDCCH):
- A dedicated control channel used for signaling during call setup, location updating, and short message service.
3. Synchronization Channel (SCH):
- Provides synchronization information to mobile devices to help them align their timing with the network.
4. Random Access Channel (RACH):
- Used by mobile devices to initiate communication with the network, especially during power-on or location area changes.
5. Slow Associated Control Channel (SACCH):
- Carries information related to the quality of the radio link and facilitates power control.
These logic channels work together to establish, control, and maintain communication between mobile devices and the GSM network, ensuring efficient and reliable operation.