ORBCOMM General Operation

ORBCOMM is a very simple to operate system from the point of view of the final user or the solutions integrator. The system’s operation is described in this section in broad outline, without going into technical details.

General Description

From a general point of view, the system operates as shown in the diagram:

When an ORBCOMM (SC) satellite communicator has a message to send, it checks whether the ORBCOMM satellite signal is being received indicating that the satellite is in contact with a GES (Ground Earth Station).  If so a Gateway Connection exists and a communication slot is requested, the message is transmitted from the communicator to the satellite, and the satellite then retransmits it to the GES.  From the GES the message is sent to the GCC (Gateway Control Center) by means of a dedicated link, and from the GCC it is transmitted to the Final User via conventional public networks, generally the Internet.  For particular situations there are various other options for data transmission including - as the diagram shows - X.25, X.400, RTC, frame relay or copper / fiber / satellite dedicated links.

In the opposite direction, when the Final User wishes to send a message to an ORBCOMM communicator, the message is transmitted to the GCC via the pertinent earth network (Internet, X.25, RTC, Frame Relay, etc.) The GCC directs the message to the GES antenna locked to the satellite maintaining the destination ORBCOMM satellite communicator. The GES is permanently following various ORBCOMM satellites and therefore, when the message is received, it analyzes the direction of its destination and asks the satellite whether the communicator’s presence can be detected on the portion of the earth’s surface over which it has visibility.  If the communicator is visible from the satellite, this is communicated to the GES, which then transmits the message to the satellite for retransmission to the ORBCOMM Communicator.

Modes of Operation

There are two methods within this general mode of operation, called Standard or Gateway Method and Globalgram Method, depending on whether the satellite has or does not have simultaneous visibility of the Communicator and the GES.

Gateway (Standard) Mode

In this “normal” mode the satellite has simultaneous visibility of the ORBCOMM Communicator and the GES. The satellite serves as a communications link between the  two and communications pass in a metter of milliseconds. With this mode of functioning, report and message latency is a function of the distance of the SC from the GES. Within the continental US communications are generally under three minutes.

Globalgram Mode

In those cases when the satellite does not have simultaneous visibility of the ORBCOMM Communicator and the GES, it is necessary to utilize a Store & Forward method of communication called Globalgram mode.  With this method, the message is stored in the satellite, which continues its orbit until it encounters the GES on which to discharge the message. With this method of operation the delays are longer, between a few minutes and the approximately 100 minutes of a full orbit.

Graph of the Gateway and Globalgram methods, for different waiting periods.

The above graph shows the satellite’s availability (its latency) for several areas, South America, the United States and Europe amongst other zones, which fall within the Gateway method zone, with the estimated coverage of the zones outlined. The blank areas come under the “store and forward” method with a longer delay in traffic transmission and reception.

Communications are sent and received by SC’s (satellite communicators,) learn out about the models available.