Low-Earth-Orbit Satellite (LEO)

                      Low Earth Orbit Satellite (LEO) is satellite communication technologies. One technology is called the Iridium. It is a mobile satellite system. Iridium was a concept of launching 66 satellites but it was originally 77 satellites when it was proposed on FCC. Iridium is owned by the Motorola. The application was submitted to FCC in the year 1990. Its original concept was to use 7 polar orbits with 11 satellites in each. The coverage of this is around the world. This concept uses line of sight coverage from point to point virtually any other point on the globe. This uses a spot beam from the radio communications services on board each of the satellites. This technology of the spot beam concept introduced the high frequency reuse capacities that had not been achieved before. The satellite that was used was small compared to the others that had been used. Its electronic circuits inside were very sophisticated.

                        The initial features available on LEO networks are Radio Determination Service (RDSS), Voice communications (VC), Paging (P), Facsimile (Fax) and Data Communications (DC). The RDSS is used at the location of vehicle fleets, aircraft, marine vehicles, etc.  Voice communication is used on dial up digital voice communications anywhere in the world. Paging is used as a one way paging service. It includes alphanumeric display for up to two lines, but will expand to short messaging services (SMS) at 160 characters. Fax is used as a two way facsimile service. Data communication is used in two way transmission of data.

Here is a figure of an arrangement concept of LEO:

                        In this particular arrangement, the satellites are located at the height of 400+ nautical miles above the earth, in a polar orbit. In the polar orbit, the satellite moves around the earth’s poles and passes over any specific point along its path very quickly. The satellites have a speed of 7,400 meters per second in different orbits. Gateway feeder links uses the spectrum in the Ka band. Iridium used approximately 16.5 MHz of bandwidth in the L band. 

Advantages to LEO satellite telemetry:

·         Global applications in developing a remote environmental monitoring communication system.

·         Two-way communications.

·         Easy to setup and low maintenance cost.

·         Low profile, non-directional whip helix antenna.

·         Easy access to data.

·         No FCC or other governmental agency requirements for data transmission.

·         Coverage in very remote areas.

·         Data is proprietary.

·         Stevens is able to quickly detect any problems with transmission of data.

·         Systems verifies that data has been transmitted which minimizes risk of missing data.

·         Event notification on line, by pager, etc.

·         Lower power transceivers compared to GEO transmitter system.

·         LEO transceivers hardware system is lower in cost than a GEO transmitter system.

Disadvantage to LEO satellite telemetry:  

·         Monthly service fee which could be expensive with frequent transmission of data.

·         Power outage at GCC would shut down the communication server, which could delay transmission of data to end user until power is restores. However, no data is lost.

·         LEO satellites have much shorter life span(five to eight years) than GEO satellites.

Sources:

Broadband Telecommunications Handbook by Regis Bates

http://www.stevenswater.com/telemetry_com/leo_info.aspx