Cell Broadcast Service (CBS)

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 9.4.1.2 for more information about cell broadcast message parameters.

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.

• State - allows you to configure which messages are sent using CBS. The message state must be ON for each message you want to send. The State for Message 1 is set to ON by default.

  The GPIB command for this parameter is CALL:SMService:CBRoadcast:MESSage[<n>]:STATe .

• Geographical Scope (GS)

  This parameter indicates the geographical area over which the message code is unique and the mode that should be used by the mobile station when displaying the cell broadcast message.

  The following list contains the settings available for the Geographical Scope parameter.

  • Cell Wide / Immediate (CIMMediate) - Similar messages received in any other cell is regarded as new. The immediate display setting indicates that the cell broadcast message is displayed on the mobile station at all times. This setting corresponds to a GSCOPE request URL equal to 0.
  • PLMN Wide / Normal (PNORmal)- The message code and/or update number must change in the next cell for the cell broadcast message to be considered new. The cell broadcast message is displayed on the mobile station only when the user wants to see it.This setting corresponds to a GSCOPE request URL equal to 1.
  • Service Area Wide/Normal (SNORmal) - The cell broadcast messages with the same message code and update number are considered new only if the next cell is in a different location area than the current cell. The normal display mode displays the message only when the user wants to see it.This setting corresponds to a GSCOPE request URL equal to 2.
  • Cell Wide / Normal (CNORmal) - Similar messages received in any other cell is regarded as new. The normal display mode displays the message when the user wants to see it. This setting corresponds to a GSCOPE request URL equal to 3.

  The GPIB command for this parameter is CALL:SMService:CBRoadcast:MESSage[<n>]:GSCope .

• Message Code

  The Message Code distinguishes messages from the same source and that are different types or themes. For more information on this parameter, refer to 3GPP TS 23.041 version 9.6.0 section 9.4.1.2.1.

  The GPIB command for this parameter is CALL:SMService:CBRoadcast:MESSage[<n>]:CODE .

• Update Number

  This parameter is used to identify a particular version of a message. This is useful for reporting a dynamic situation, where a message may be reporting one event (such as road works or road construction ahead), but the details change periodically (the length of the tail-back or traffic jam caused, for example). A mobile station which remains in one cell for a length of time receives messages with the same message code but increments the update numbers as updated versions of the same message are received. A mobile station that has just entered a cell receives only the most recent version of the message, followed by any subsequent versions. The update number wraps from 15 to 0.

  The GPIB command for this parameter is CALL:SMService:CBRoadcast:MESSage[<n>]:UPDate .

• Message Identifier

  The parameter is a header number identifying the message topic (such as 'Weather Report' or 'Traffic Information').

  Several categories of message topics are identified in 3GPP TS 23.041 version 9.6.0 section 9.4.1.2.2. The main topics are location services (LCS), the earthquake and tsunami warning system (ETWS), and the commercial mobile alert system (CMAS). Many message identifier values are reserved for future use but will likely be specified in future releases of 3GPP TS 23.041.

  Message identifier values in the decimal range 1000 to 1003 are used for LCS.

  ETWS and CMAS are part of the public warning system (PWS) required for use in the United States. Message identifier values in the decimal range 4352 to 4356 are used for ETWS. CMAS defines three classes of warning notification: presidential, imminent threat and child abduction emergency (e.g. Amber Alert). Message identifier values within the decimal range 4370 to 4399 are used for CMAS. The exact meaning of each message identifier value is specified in 3GPP TS 23.041 version 9.6.0 section 9.4.1.2.2.

  The test set allows entry of any message identifier value within the full decimal range specified by 3GPP TS 23.041: 0 to 65535.

  The GPIB command for this parameter is CALL:SMService:CBRoadcast:MESSage[<n>]:IDENtifier .

• Data Coding Scheme Specification

  This parameter indicates the method used to set the data coding scheme. The methods available are Language (see Data Coding Scheme Language ) and Value (see Data Coding Scheme Value ).

  The GPIB command to specify the which method is used is CALL:SMService:CBRoadcast:MESSage[<n>]:DCSCheme[:SPECify] .

• Data Coding Scheme Language

  This parameter sets the data coding scheme value associated with the indicated language. The data coding scheme indicates the intended handling of messages, the alphabet and coding of the message content, and the associated language of the text. Changing this parameter does not translate the text of a message or change the message contents; it is used to configure the message's data coding scheme value.

  Although this method is only appropriate for configuring text messages, no error message is displayed if you set a data coding scheme value when the message content is set to data.

  Refer to 3GPP TS 23.038 version 9.1.1 section 5 for details about setting the CBS Data Coding Scheme.

  The GPIB command to specify the how the mobile station interprets the content of received text messages by specifying a language is CALL:SMService:CBRoadcast:MESSage[<n>]:DCSCheme:LANGuage .

• Data Coding Scheme Value

  This parameter sets the 8-bit data coding scheme value that indicates the intended handling of messages, the alphabet and coding of the message content, and the associated language of the text. Changing this parameter does not translate the text of a message, it is used to automatically configure the message's data coding scheme.

  Refer to 3GPP TS 23.038 version 9.1.1 section 5 for details about setting the CBS Data Coding Scheme.

  The GPIB command to specify the how the mobile station interprets the content of received text messages by specifying the data coding scheme value is CALL:SMService:CBRoadcast:MESSage[<n>]:DCSCheme:VALue .

• Content associates the message with the actual data to be sent by the test set. See Cell Broadcast Messages -Content for more specific information on the cell broadcast messages that can be sent from the test set.

  The GPIB command for this parameter is CALL:SMService:CBRoadcast:MESSage[<n>]:CONTent .

Cell Broadcast Setup - General

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

• Repetition Period

  The repetition period determines how often the cell broadcast messages are transmitted. The repetition period is applied to all cell broadcast messages. The test set checks the value of the repetition period every time a schedule is built. If the value has changed from its previous value, then the next message repetition time is recalculated based on the new repetition period setting.

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)