On contrary to the title, that is pressing you to skip this article RIGHT AWAY, you might well give a second thought to actually go through the context that has been described further, simple enough to be understood, even by a layman. For the love of science, I hope this article serves as a wonderful experience to your learning process.
The advent of satellite-fiber network dates back to 1965 when Intelsat launched the first commercial satellite. They proudly paraphrase this as ” Nasa put a man on the moon, and the world watched it happen via Intelsat”. It can be regarded as a breakthrough in the field of modern satellite-fiber communication system. Although optical fibers only came into extensive use since the early 90’s, the need for a cheaper and efficient system became prevalent, as neither satellite nor copper cables could suffice the need for the growing bandwidth. Cost of service being the other instigator.
Satellite-Fiber hybrid network is a seamless integration of satellite and fiber network that offers enhanced data rate, dynamism, robustness, flexibility and many more features that can’t be achieved by either of the network individually. A satellite-fiber network works in coordination with each other, such that, information sent through one of the network can be easily transferred to other for convenience. The transmission of information may take multiple interplay between them before being broadcasted. Information received over fibers may be transferred to satellite through antennas and then back to fibers, and vice-versa.
Satellite communication is a highly expensive form of communication system that offers much less bandwidth compared to Fiber networks. However in regard to reliability, security, mobility and availability of service, satellite communication holds its eminence aloft. Therefore, satellite communication is extensively used in military and scientific purpose. Fibers, on the other hand, offer higher bandwidth and transmission rate at a much, much cheaper rate compared to satellites. Data being transmitted in the form of light, invulnerability to external noise and interference is another advantage that fiber edges over satellite. However, one must have to endure network-complexity and the constant maintenance issue entailed by fibers.
Optical Fiber Network:
An optical fiber is a transmission medium that enables information to be sent through it in the form of light. It is made up of silica or polymer. Polymer fibers are generally used because of the durability and flexibility. An optical fiber is composed of three layers –
- Buffer Coating
The core is the inner-most part of the fiber. It is the very medium through which information is transmitted. The diameter of the core varies on the nature of fiber. It ranges from 8 micro meter to 100 micro meters (or more). The core material is made up of silica or polymer. The refractive index of the core and cladding determines the angle of incidence at which the light signal must strike the fiber core.
Cladding is a protective layer that encloses the core to maximize fiber strength and microbend resistance. It also prevents the light signal from straying away from the core. The material used for cladding should always have a refractive index lower than that of the core in order to attain total internal reflection. Also, the absorption coefficient of the cladding material must be low to prevent diffraction. The buffer coating offers enhanced durability to the fiber. It, along with the cladding, protects the core from physical and environmental damage.
On the basis of their working methodology, optical fibers can be broadly classified into two types:
- Single-mode fiber.
- Multi-mode fiber.
The classification is merely based on the nature of transmission of light inside the fiber. In the single-mode fiber, a highly directed light wave is sent through the fiber, perpendicular to the fiber surface to prevent the light from dissipating. Hence, the light travels along a straight path. The source is usually a laser device or an ultra-high frequency LED. Single-mode fibers are used in cases where high transmission rate and low interference is expected.
As the name suggests, multiple signals i.e. a beam of light is sent through the core in case of multi-mode fibers. Consequently, multi-mode fibers offer higher bandwidth. Thus is used in general purposes. However, multi-mode fibers are affected by ISI (Inter Symbol Interference) and Diffraction that deteriorates the system due to noise, signal overlapping and transmission delay. Graded index multi-mode fiber is a solution and a better form of multi-mode fibers.
A satellite is a geo-stationary object that revolves around the earth in a fixed orbit. It constantly exchanges information with the ground station in the form of RF signal. Satellite communication was primarily used for telecommunications and scientific purpose because of their expensive rate of service. Gradually they became more commercialized as the need for exchange of information in geographically remote couldn’t be accomplished by cable networks. The cost required to install a satellite in outer space and the need for a highly powerful transmission system in order to send information over such a long distance, imposes expensive service rate for satellite communications. A satellite communication system comprises of two terminals:
- Earth terminal (also known as ground station or earth station).
- Satellite terminal.
The earth terminal acts as a hub for data exchange between the satellite and the other communication channels. An antenna, maintained at line-of-sight with the satellite, is used to interact with the satellite. The signal received by the antenna is sent to the processing unit that processes and records information constantly. If the information needs to be sent over optical fiber, it is first converted into respective form and then transmitted. This forms a satellite-fiber network.
The link between the earth station and the satellite is called an uplink. An uplink is a channel that serves as a medium when an earth station transmits data to the satellite. Similarly the link between the satellite and the earth station is called a downlink. A downlink is a channel that serves as a medium when a satellite sends data to the earth station.
Satellite is effective in delivering point-to-multipoint coverage i.e. broadcasting, while fiber is more efficient to route point-to-point traffic. A satellite-fiber network is used in conjunction with each other to deliver information. However due to the difference in the nature of transmission one must always take in consideration – the data conversion process.
Information is sent in the form of RF signal in case of satellite. While in fiber communication, data is transmitted in the form of light. Hence, it must be converted to respective form before transmission. Also it must be noted that fibers offer much higher bandwidth compared to satellite. Therefore, the amount of information sent through fiber cannot be handled by satellite simultaneously. Hence, proper data scaling must be done before transmission i.e. before forwarding the data from fiber to satellite, it must be converted to a lower rate and vice-versa, expecting transmission delay.