Sign in Subscribe

SACCH Slow Associated Control Channel

Last updated on 


The Slow Associated Control Channel (SACCH) is a channel used in cellular telecommunications systems, specifically in Global System for Mobile Communications (GSM) networks. SACCH is responsible for carrying control information between the mobile device (MS - Mobile Station) and the base station (BTS - Base Transceiver Station). It operates at a lower rate compared to other control channels, hence the name "Slow" Associated Control Channel.

The SACCH serves various purposes in a GSM network, including:

  1. Link Quality Measurement: The SACCH carries information about the received signal quality and strength from the MS to the BTS. The measurements performed by the MS include the received signal strength (RSSI) and the bit error rate (BER). These measurements help the network determine the quality of the communication link and make decisions regarding handovers (i.e., switching the connection to a different cell or base station).
  2. Timing Advance: The SACCH is also responsible for transmitting timing advance information from the MS to the BTS. Timing advance is used to compensate for propagation delays in the radio path between the MS and the BTS. By adjusting the timing advance value, the network can ensure that the transmission from the MS arrives at the BTS at the correct time, reducing interference and improving overall system performance.
  3. Power Control: Another important function of the SACCH is power control. The SACCH carries power control commands from the BTS to the MS, instructing it to increase or decrease its transmit power. Power control helps optimize the power usage in the network and maintain a balance between the MS and BTS to ensure reliable communication with minimal interference.
  4. Cell Selection and Reselection: The SACCH also provides information about neighboring cells to the MS. This information includes measurements of signal strength and quality from neighboring cells, which enable the MS to evaluate and select the best cell for handover or reselection. The MS can use this information to determine whether it should switch to a different cell with a stronger signal or better quality.

The SACCH operates on a separate frequency from the Traffic Channel (TCH) used for voice or data transmission. It is a dedicated control channel that uses a lower data rate to carry the necessary control information. The SACCH frames are typically transmitted in between the voice or data frames on the TCH. The specific structure and timing of SACCH frames depend on the particular GSM system configuration and the network operator.

Overall, the SACCH plays a critical role in maintaining the performance and reliability of a GSM network. By providing control information, link quality measurements, timing advance, power control, and cell selection data, it helps optimize the communication between mobile devices and base stations, ensuring efficient and seamless connectivity.