Subject: Mobile Computing

Difficulty: Medium

Marks: 4 Marks

A Broadcast Channel (BCH) is a downlink channel in a GSM system that is used by the base stations to provide signalling information to the mobile stations. The mobile station needs this information to find a network, synchronize with it and to connect to it. There are three types of broadcasting channels:

1.Frequency correction channel (FCCH)

2.Synchronization channel (SCH)

3.Broadcast control channel (BCCH)

1. FCCH - Frequency Correction Channel:The Frequency Correction Channel is a broadcast channelused by GSMbase stations. It provides a unique tone of 67.7 kHz for the Mobile Stations. This tone is used to synchronize the local clock of the mobile receiver with the base station. This is needed to correctly extract the data.

2. Synchronization channel (SCH): The Synchronization Channel (SCH) is a downlink broadcast channelof the base stations of a GSMnetwork. TheSCH provides information to the Mobile Stations needed to search for base stations, identify them and synchronize with them

3. Broadcast control channel (BCCH): The Broadcast Control Channel (BCCH) is a logical broadcast channelused by the base station in a GSMnetwork to send information about the identity of the network. This information is used by a mobile station to get access to the network. This information includes the Mobile Network Code (MNC), the Location Area Code (LAC) and a list of frequencies used by the neighboring cells (BA: BCCH Allocation List).