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In this paper is introduced the Orbcomm space segment as a wide area packet switched and global two-way data transfer network providing satellite communication, tracking, monitoring and logistics services between mobile, remote, semi fixed or fixed Subscriber Communication Units (SCU) in Mobile Satellite Service (MSS) and Gateway Earth Stations (GES) or Gateway Control Centres (GCC) accomplished via LEO satellites and Network Control Centres (NCC). Orbcomm Global, L.P., from Dulles, Virginia, USA equally owned by Teleglobe and the Orbital Sciences Corporation, provides global services via the world's first LEO satellite data and messaging communications system. The US Federal Communications Commission (FCC) granted Orbcomm system a commercial license in October 1994 and the Commercial service began in 1998. Orbital Sciences was the prime contractor for the design project of Orbcomm satellites. The Company owns and operates a network consisting in 36 Little LEO satellites and several GES deployed around the world, connecting small, low-power and commercially proven SCU terminals to private and public networks, including the Internet. Orbcomm delivers information to and from virtually anywhere in the world on a nearly realtime basis to the Terrestrial Telecommunication Network (TTN). The Orbcomm space segment has subscriber transmitters (Tx) that provide a continuous 4.8 Kb/s to 9.6 Kb/s stream of downlink packet data to the receivers (Rx), and vice versa.

This paper describes in particular Space Division Multiple Access (SDMA) applicable in Mobile Satellite Communications (MSC). In satellite communication systems, as a rule, especially in Mobile Satellite Communications (MSC) many users are active at the same time. The problem of simultaneous communications between many single or multipoint mobile satellite users, however, can be solved by using Multiple Access (MA) technique. Since the resources of the systems such as the transmitting power and the bandwidth are limited, it is advisable to use the channels with complete charge and to create a different MA to the channel. This generates a problem of summation and separation of signals in the transmission and reception parts, respectively. Deciding this problem consists in the development of orthogonal channels of transmission in order to divide signals from various users unambiguously on the reception part.

In this paper are introduced Low-Gain Omnidirectional Antennas for Mobile Satellite Communications (MSC) and Navigation. In many respects the Mobile Satellite Antenna (MSA) infrastructures currently available for MSC and Navigation. Medium and high gain MSA need to track the satellite, following both movements of mobiles and satellite orbital motions. Sometimes this is difficult and expensive to synchronize and have to be introduced in the understanding manner. On the other hand, the vehicular antenna with a low gain does not need to perform tracking but the capacity of the communications link is limited. In such a way, all MSA are classified into omnidirectional or not directional and directional or antennas with tracking system. The Inmarsat, Eutelsat, Cospas-Sarsat, Iridium, Globalstar, Orbcomm, and other Geostationary Earth Orbit (GEO) and Non-GEO current and forthcoming mobile satellite operators have conducted research on all network segments, including different types of MSA and their future development and improvements. The special types of MSA related to the kind of transportation system, such as maritime, land, aeronautical and transportable or portable mobile antenna types are classified. The common types of Low-Gain Omnidirectional Antennas and Medium-Gain Directional Antennas are introduced in the technical ways as of importance for MSC.

The paper introduces development and implementation of new Satellite Communications, Navigation and Surveillance (CNS) of GPS or GLONASS for enhancement of safety and emergency systems including transport security and control of aircraft freight, logistics and the security of the crew and passengers onboard aircraft and helicopters. These improvements include new solutions for better management and operation of airports and they are needed more than ever before, because of world aircraft fleet expansion. Namely, the world's commercial airways fleet is expected to double in the next 20 years. This will result in crowded routes leading to fuel wastage and delays, which could cost millions of dollars annually. The potential benefits will assist Air Traffic Control (ATC) to cope with increased traffic as well as improving safety and security and reducing the infrastructures needed on the ground. The establishment of Aeronautical CNS is also discussed as a part of Global Satellite Augmentation Systems (GSAS) of GPS and GLONASS systems integrated with existing and future Regional Satellite Augmentation Systems (RSAS) and Local Satellite Augmentation System (LSAS) in airports areas.

This paper describes in particular Code Division Multiple Access (CDMA) applicable in Mobile Satellite Communications (MSC) connecting Mobile Earth Stations (MES) via Land Earth Stations (LES). However, in satellite communication systems, as a rule, especially in MSC many users are active at the same time. The problem of simultaneous communications between many single or multipoint mobile satellite users, however, can be solved by using Multiple Access (MA) technique. Since the resources of the systems such as the transmitting power and the bandwidth are limited, it is advisable to use the channels with complete charge and to create a different MA to the channel, such as example of the described CDMA. This generates a problem of summation and separation of Radio Frequency (RF) signals in the transmission and reception parts, respectively. Deciding this problem consists in the development of orthogonal channels of transmission in order to divide signals from various users unambiguously on the reception part.

In this paper is introduced the Orbcomm system as a wide area packet switched and global two-way data transfer network providing satellite communication, tracking, monitoring and logistics services between mobile, remote, semi fixed or fixed Subscriber Communication Units (SCU) in Mobile Satellite Communications (MSC) and Gateway Earth Stations (GES) or Gateway Control Centres (GCC) accomplished via LEO satellites and Network Control Centres (NCC). Orbcomm Global, L.P., from Dulles, Virginia, USA equally owned by Teleglobe and the Orbital Sciences Corporation, provides global services via the world's first LEO satellite-based data and messaging communications system. The US Federal Communications Commission (FCC) granted Orbcomm a commercial license in October 1994 and the Commercial service began in 1998. Orbital Sciences was the prime contractor for the design project of Orbcomm satellites. The Company owns and operates a network consisting in 36 Little LEO satellites and several GES deployed around the world, connecting small, low-power and commercially proven SCU terminals to private and public networks, including the Internet. Orbcomm delivers information to and from virtually anywhere in the world on a nearly real-time basis to the Terrestrial Telecommunication Network (TTN). The Orbcomm ground segment and subscriber transmitters (Tx) that provide a continuous 4.8 to even 9.6 Kb/s stream of downlink packet data to the receivers (Rx), and vice versa.