SMS Cell Broadcast

SMS cell broadcast provides a mechanism to broadcast short messages from a radio network to the MSs in a cell area . The sources of SMSCB can come from broadcast applications, such as traffic reports and weather reports. The message is limited by the capacity of the broadcast channel that carries it. A single CB message can carry up to 88 bytes. The service broadcasts on a cell level because the SMS-CB uses a specially defined channel called CBCH. The presence of a CBCH is indicated by the system information messages broadcasted for an individual cell on the BCCH. The system information tells the MSs camped on a cell on which frequency and channel CB message are sent.

A CB message has a message header and a payload. The CB message header has an identifier, which identifies the source and subject of the SMSCB message. It also has a sequence number, which enables the MS to determine when a new message from a given source is available. SMS-CB messages are not acknowledged by the MS. Reception of SMS-CB messages by the MS is only possible in idle mode.The SMS cell broadcast service is designed to minimize the battery usage requirements for an MS. An MS can read the first part of a CB message and then decide whether or not to read the rest of the message.

In addition, the network may broadcast schedule messages, which provide information in advance about the CB messages that will be sent immediately afterward. The MS may use this scheduling information to restrict reception to those messages the customer is interested in receiving.The CB short messages are generated in the cell broadcast entity (CBE). The functionality of a CBE is not specified in the GSM standards. The CBE can be understood as a source of SMS-CB, such as a weather information center. It includes all aspects of formatting the CB messages as well as splitting a message into various segments, which will eventually be transmitted on one channel.

The CBC actually handles all the GSM related functions of SMS-CB. It may be getting input from multiple CBEs and could be connected to one or multiple BSCs. The CBC coordinates the formatting and organization of the messages it receives from the CBE into GSM form. It performs functions such as determining the rate at which certain messages must be delivered; setting the language; and determining area where a certain message is to be sent.The BSS takes care of the radio part of transmitting CB messages. The BSC performs functions such as storing the messages as long as they are to be transmitted; routing the messages to the appropriate BTSs; and scheduling of the CB messages according to the repetition rate. BTS puts the message on the CBCH at the time specified by the BSC.