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Issue 8: Pacific Satellite Nusantara (PSN)

Connecting Indonesia: Serving the Unserved

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This paper is available in Bahasa Indonesia


The Satellite Technology

Communications satellites have been utilized quite extensively for some time in Indonesia. The common disadvantage of satellite communication is the relatively high cost of earth stations. This has hindered the use of conventional satellite communications as an affordable, widespread access network. The availability of low cost VSAT terminals over the past 10 years helped to a certain extent; it allowed corporate and government users to have high speed data and voice satellite networks at an economical cost. But the average household in the country still has to rely on terrestrial local loop access networks for basic telecommunications services that are still deemed not very economical to build outside urban areas. This and a lot of other factors impede teledensity growth in Indonesia.

The Asia Cellular Satellite System - Extending Reach to Rural Indonesia

The Asia Cellular Satellite System adopted the concept of a regional mobile satellite access network. It was designed to provide access to basic circuit-switched telecommunication services in Asia through the use of low cost, small handheld satellite terminals. It was not the first system of its kind when it was launched in 2000, but many of its characteristics are unique as we will elaborate further.

The ACeS System Architecture

The ACeS System network is comprised of 4 major components namely: the Garuda-1 Satellite, the small User Terminals (UT), earth station Gateways (GW) and a Network Control Center (NCC). Each of these are specifically tailored for the main purpose of the network. Like any other satellite system, ACeS also has a Spacecraft Control Facility (SCF) which is in this case co-located with the NCC. But to focus on the network, we will not go into the details of the SCF.

Describing in a glance the main functions of the components, to make an outgoing call the UT requests service directly via the Garuda-1 satellite to the GW, which in turn provides the necessary resources and forwards the call to the ultimate destination outside (or back inside) the network. The NCC plays a more supervisory role in the system such as static resource allocation among gateways, although it is also involved in some aspects of call setup. All communications between the 4 major components of the system is channeled via the Garuda-1 satellite through L-band and C-band links.

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Fig. 1: ACeS System Architecture

The concept of a regional (as opposed to global) system allowed the Indonesian providers to use a single geostationary satellite for the whole network. A drawback of such a configuration is the relatively higher transmission delay that can occur in some cases but ACeS has proven since the start of commercial operations of the system that the modest lag time is acceptable to the users.

Garuda-1 Satellite

The Garuda-1 satellite is a vital element of the system. The specific purpose of the network made the spacecraft design unconventional. The most distinguishing characteristics are the relatively high aggregate L-band Effective Isotropic Radiated Power (EIRP) and sensitivity (G/T) which is mostly attributed to the 12-meter L-band reflectors. This on-board satellite feature allows reliable two-way L-band communications to small, low-powered user terminals. This high gain characteristic of the L-band reflectors also narrows the beam-width, thus 140 separate spotbeams were needed to cover the whole footprint.

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Fig. 2: Garuda-1 Satellite and its Footprint Coverage

On-board the spacecraft is another unconventional element, a real-time TDMA processor. This feature allows the TDMA/FDMA ACeS network to route single hop calls directly between user terminals through the Garuda-1 Satellite, therefore minimizing the voice transmission delay. The spacecraft is designed to handle 10,000 simultaneous calls and cover almost all of Asia.

Gateways

The Gateway functions mainly as the interconnection point to the external networks. Its architecture to some extent resembles a terrestrial GSM cellular network architecture. Going from inner side outwards there is the Traffic Channel Equipment (BTS equivalent), a Gateway Station Controller (BSC equivalent) and a standard GSM Mobile Switching Center (MSC). Most protocols and functions used in the system are adopted from the GSM standard.

The Gateway is also responsible for generating billing data, providing secure subscriber authentication and subscriber provisioning. It also interacts with the NCC to allocate dynamic system resources on a per call-setup basis.

This similarity with the GSM networks allows one very important feature, that is inter-operator roaming capability with terrestrial GSM networks. This enables ACeS system users to roam among terrestrial GSM networks when going outside the satellite coverage areas or into buildings. Similarly, GSM subscribers can also take advantage of the ACeS system using the ACeS user terminals. Seamless switching between networks is made possible with the dual mode (ACeS-GSM) feature of the ACeS user terminals.

User Terminals

The high-power characteristics of the Garuda-1 Satellite allows the implementation of low-cost, handheld user terminals with the shape, transmit power and receive sensitivity comparable to terrestrial cellular user terminals. At the beginning of commercial operations, the R-190 terminal was available as a mobile satellite terminal for the ACeS network which is similar to a GSM phone. The major difference is the directional right-hand circular-polarized antenna which makes the R-190 user terminal a bit bulky. The R-190 features dual-mode ACeS and GSM network capability and 2.4 kbps data.

The nature of satellite communications also requires the Garuda-1 satellite to have a direct line-of-sight path with the user terminal, thus making the R-190 only suitable as outdoor mobile terminals.

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Fig. 3: R-190 (left) and FR-190 (right) user terminals

Another type of terminal was developed for fixed indoor use, the ACeS FR-190. With the main unit placed indoors connected to an outdoor antenna, the FR-190 also provides basic telephony and 2.4 kbps data.

Conclusion

With the availability of the R-190 and FR-190 terminals and the ACeS network, PSN is capable of deploying thousands of terminals throughout Indonesia in a relatively short time and at low cost as described in this article, including for Public Call Centers, for the USO and General Election projects and others, providing instant connectivity to rural Indonesia.

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