Cell Broadcast Service (CBS)

Cell Broadcast Service (CBS)

Last updated: March 14, 2011

This section is only applicable to the lab applications.

You can test a mobile station's ability to receive Cell Broadcast messages using the Cell Broadcast Service capability in the test set.

Cell Broadcast Service (CBS) Overview

The Cell Broadcast Service in the test set allows you to send cell broadcast messages to the mobile station that are transmitted at a defined repetition interval (see Cell Broadcast Setup - General for more information). This allows the mobile station to receive the message even if entering the cell after the first transmission. The cell broadcast messages can be from one to fifteen pages in length, and are transmitted by the test set until the cell broadcast service is disabled or the state of the message(s) being transmitted is set to OFF.

The test set can enable up to three different messages to be transmitted each Repetition Period using the Cell Broadcast Service. The repetition period can potentially be set smaller than the time it takes to transmit all enabled messages, so priority is given to the messages in the following order (from high to low): message 1, message 2, then message 3. If there is not enough space to transmit the enabled messages, the test set either truncates the lowest priority messages or does not send them.

There are several message parameters that the test set allows you to set. It is important that you configure your mobile station to receive cell broadcast messages. This is done by enabling reception of messages in your mobile station and specifying the message parameters that it can receive, and set the parameters according to the type of cell broadcast message your mobile station is allow to receive. Cell broadcast messages are not acknowledged by the mobile station.

In addition to the pre-defined text strings, you can specify a custom text string and custom data to be sent in a cell broadcast message. See Cell Broadcast Messages -Content for more information on configuring the contents of the cell broadcast message.

WCDMA Cell Broadcast Messaging

The Cell Broadcast messages are transmitted by the Broadcast and Multicast Control (BMC) protocol layer over the CTCH (Common Traffic Channel) logical channel. The messages are sent using DRX (Discontinuous Reception) on the CTCH, and the CBS Schedule message states which fragments of CBS messages will be sent in specific frames. The MAC layer multiplexes the CTCH onto the FACH transport channel with the CCCH (Common Control Channel) logical channel. The FACH is then multiplexed onto the S-CCPCH (Secondary Common Control Physical Channel) with the PCH (Paging Channel) transport channel, which also uses DRX to transmit in particular frames. The test set gives priority to the PCH over the FACH. Thus, it is possible that CBS data might not be transmitted in the intended slot because the slot contains PCH data instead. If this occurs, the CBS data is sent in the subsequent slot, and the CBS data for the subsequent slot is discarded by the test set.

The BMC is responsible for the handling, scheduling and transmission of CBS messages. Its purpose is to allow the UE to selectively receive messages using Discontinuous Reception (DRX), by broadcasting a CBS Schedule Message in addition to the CBS message. The CBS schedule message contains information about subsequent CBS messages, including the timing of each transmission in the next schedule period. Each schedule period consists of transmission blocks called Common Traffic Channel Block Sets (CTCH-BS), and contains information about the subsequent scheduling period. The number of blocks in the scheduling period is limited by the 8-bit "Length of CBS Scheduling Period"; the value range being 1 to 256. Additionally, the CBS Schedule Message contains an 8-bit field "Offset to Begin CTCH-BS Index", ranging from 1 to 255, which points to the starting block of the next CBS Schedule period.

The CTCH is defined by 3GPP TS 25.301 as a point to multipoint unidirectional channel for the transfer of dedicated user information for all or a group of specified UEs. For CBS, the MAC layer multiplexes the CTCH onto the FACH with a fixed transport block size and TTI, where TTI is the transmission time interval that the FACH carries the CTCH. The TTI for the FACH is fixed at 10 ms in the test set, and can therefore transmit data 100 times a second. The actual TTI intervals in the FACH to be utilized by the CTCH are determined by the CTCH Allocation Period and the CBS Frame Offset parameter settings.

For example, in the figure below the CTCH Allocation period is 6, the CTCH Frame Offset is 2, and the number of radio frames in the TTI of the FACH that are used for the CTCH is 1.

The block size of the FACH is fixed in the test set so that 20 octets of data are available for each CTCH interval. Some of this space is used up for RLC headers. The formula to determine the number of blocks needed to carry a message of size X octets is: Number of Blocks = (X+20)/19 . The repetition period and allocation period both affect the bandwidth of CBS messages. If there is space to transmit only a portion of a message, the test set will truncate the message where possible and lower priority messages are not sent.

Cell Broadcast Message Setup

All three of the messages available for use in the test set's Cell Broadcast Service can be configured independently. The content of each message can include either one of two predefined text messages, a custom text message or a custom binary/UCS2 message.

There are several configurable parameters for each cell broadcast message. The serial number is made up of three of these parameters: Geographical Scope, Message Code, and Update Number as shown in the diagram below. Refer to 3GPP TS 23.041 version 9.6.0 section for more information about cell broadcast message parameters.

Serial Number
Octet 1 Octet 2


6 5 4 3 2 1 0


6 5 4 3 2 1 0
GS Message Code Update Number

Additionally, each message is classified by topic and allocated a message identifier, data coding scheme, and message content. The following list contains all the configurable cell broadcast message parameters offered by the test set.

Cell Broadcast Setup - General

The settings for the parameters explained in this section apply to all cell broadcast messages.

Cell Broadcast Messages -Content

Several Cell Broadcast Service (CBS) message options are available which allow you to choose or create messages to be sent. You can set the Content parameter to Text1 , Text2 , Custom Text, or Custom Data . See the sections below for more information about these settings.

Predefined Cell Broadcast Text Messages

User Defined Text Message (Custom Text)

User Defined Text Message (Custom Data)

Predefined Cell Broadcast Text Messages

There are two predefined cell broadcast text messages. The ASCII text strings of these messages are as follows:

  • Predefined text message 1 ( Text1 )

    The quick brown fox jumps over the lazy dog

  • Predefined text message 2 ( Text2 )

    This instrument provides functional testing of cell broadcast SMS by sending up to three broadcast messages to the device under test. Two fixed text messages and user defined text or binary/UCS2 messages are available for selection. The second fixed message spans multiple pages.

User Defined Text Message (Custom Text)

You can set the cell broadcast message to send a customized text message by setting the Content parameter to Custom Text . You can define the text for the custom text cell broadcast message using the following GPIB command:

CALL:SMService:CBRoadcast:MESSage[<n>]:CTEXt .

A custom text message can be defined only via the remote user interface and HTTP. The maximum length for the cell broadcast user defined messages is 1395 characters.

The default the custom text message is:

" Enter your text here"

Text messages sent from the test set to the mobile station are encoded using the ETSI Default Alphabet character set. The ETSI Default Alphabet encoding shares the majority of its character codes with those used by the ASCII character set. Between the two character sets, all alphanumeric characters and most punctuation characters have identical codes.

For the custom user defined text message, the test set accepts a 7-bit ASCII string. This string is then encoded using the ETSI Default Alphabet before it is transmitted. The ASCII code for each character in this string is mapped to the ETSI Default Alphabet character with the same code. Characters present in the user defined text message whose ASCII and ETSI Default Alphabet codes are not identical will be received and displayed by the mobile station as the ETSI Default Alphabet character with the original ASCII character's code. This behavior is only noticeable with certain user defined text messages as all of the predefined text messages use only alphanumeric and basic punctuation characters.


User Defined Text Message (Custom Data)

You can set the cell broadcast message to send a customized data message by setting the Content parameter to Custom Data . You can define the binary data/UCS2 for the custom data cell broadcast message using the following GPIB command:

CALL:SMService:CBRoadcast:MESSage[<n>]:CDATa .

A custom data message can be defined only via the remote user interface. The maximum length for the cell broadcast user defined messages is 2460 hexadecimal characters.

The default custom data message is an empty string.

Related Topics

HTTP Interface for Cell Broadcast Service - Introduction

Short Message Service (SMS)

Point-to-Point SMS

How to use the Short Message Service Features

Cell Broadcast Service (CBS) Troubleshooting