GSM Voice Group Call Service - VGCS

Voice group call service (VGCS) is the process of transmitting a single voice conversation on a channel or group of channels so it can be simultaneously received by a predefined group of service subscribers. VGS allows the simultaneous reception of speech conversation of a predefined group of mobile radios and/or a dispatch console. Each mobile radio that has group call capability is called a group call member.

To help facilitate communication between multiple mobile devices and to integrate radio communication with other communication systems (such as a computer system,) a dispatch console may be used. A dispatch console is a device or system that allows a person or group of people to access communication systems and services. The person who operates a dispatch console is a dispatcher.

Dispatch consoles can be connected to a group call system wire (such as by an ISDN line) or via a radio base unit. When connected by wire, a dispatch console can be located at any location within or outside a radio coverage area. Specific users (such as a dispatcher) can be assigned priorities to allow them to override the communication of other users.

Group call service is also known as push to talk (PTT) service. PTT is a process of initiating transmission through the use of a push-to-talk button. VGCS operates in half duplex (one-way at a time) communication mode. The push to talk process involves the talker pressing a talk button (usually part of a handheld microphone) that must be pushed before the user can transmit. If the system is available for PTT service (other users in the group are not talking), the talker will be alerted (possibly with an acknowledgement tone) and the talker can transmit their voice by holding the talk button. If the system is not available, the user will not be able to transmit/talk.

Each group call member is uniquely identified by their own MSISDN and a group identification number (group ID). Each mobile radio or dispatcher can have access to more than one group code. Calls to a group may be limited to a specific geographic area (specific number of cell sites).

The list of members in a dispatch group, along with their identification, assigned priorities, and capabilities is stored in a group call register (GCR).

Figure 1.x shows how voice group call service may operate in a GSM system. In this diagram, a single voice message is transmitted on GSM radio channels in a pre-defined geographic area. Several mobile radios are operating within the radio coverage limits (group 5 in this example) of the cells broadcasting the group message. In this example, a user is communicating to a group. Each user in this group (including the dispatcher) listens and decodes the message for group 5. Other handsets in the area are not able to receive and decode the group 5 message.

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Introduction to GSM, 2nd Edition This book explains the basic components, technologies used, and operation of GSM systems. This book starts with the system components and basic services that the GSM system can provide. You will learn that the key types of GSM devices include single mode and dual mode mobile telephones, wireless PCMCIA cards, embedded radio modules, and external radio modems. You will then discover the different types of available services such as multiple types of voice services, data services, group call, and messaging services. $19.99 Printed, $16.99 eBook

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