This report provides a review and assessment of satellite technologies for providing broadband data communications using Very Small Aperture Terminal (VSAT) network systems. In this context, "broadband" means that the application requires a data transfer rate greater than 100 kbps and should allow broadcast, multi- and uni-cast, and interactive bi-directional services to fixed locations worldwide. The applications considered are: Internet access over satellite, digital content distribution, wide area network (WAN) connectivity, video teleconferencing, distance learning, and telephony. The systems examined include digital video broadcasting (DVB) with IP (Internet Protocol) encapsulation, and bi-directional VSAT star networks. Detailed comparisons of various transmission parameters are provided to help evaluate currently available satellite and ground equipment capabilities. The report also gives the overview of the LINKSTAR technology, a new two-way broadband satellite communications system for (IP) connectivity over satellite. LinkStar is the highest performance star based VSAT system for service providers. LinkStar's edge is in its dynamic bandwidth allocation that makes it more efficient and faster than other TDMA systems. Terminals can transmit data to the network hub at speeds up to 1.15 Mbps with data downloads of upto 60 Mbps, satisfying bandwidth intensive applications using IP data. VSAT stands for "Very Small Aperture Terminal" and refers to receive/transmit terminals installed at dispersed sites connecting to a central hub via satellite using small diameter antenna dishes (0.6 to 3.8 meter). VSAT technology represents a cost effective solution for users seeking an independent communications network connecting a large number of geographically dispersed sites. VSAT networks offer value-added satellite-based services capable of supporting the Internet, data, LAN, voice/fax communications, and can provide powerful, dependable private and public network communications solutions.
[...] VSAT Direct is a communication network that provides on-demand data, voice and fax to remote locations via satellite with a flexible multi- channel communications for public, corporate and government applications. The available bandwidth ranging from 9.6 kbps up to 2048 kbps duplex. Its point-to-point or mesh architecture is useful for providing inter- connectivity amongst relatively high volume VSATs utilization. It supports connection on demand between any pairs or terminals in the system. With a mesh network, each VSAT can communicate with directly other VSATs on the network. [...]
[...] LINKSTAR Introduction LinkStar is a new two-way broadband satellite communications system for Internet Protocol connectivity over satellite. LinkStar consists of one or more central stations (the hub), many remote VSATs (Very Small Aperture satellite communication Terminals), and appropriate management and control subsystems. The remote VSAT called the Return Channel Satellite Terminal (RCST) is a small, low cost terminal designed for multimedia broadband connectivity in networks with a large number of sites. Because of the low cost of the remote terminal, LinkStar is an ideal solution for large enterprises and service providers,e.g., VPNs(Virtual Private Network) and ISPs(Internet Service Provider) that need broadband IP connectivity for multimedia applications over a large geographic area. [...]
[...] The most common method of modulation for satellite communications is digital phase modulation, called Phase Shift Keying (PSK). PSK shows good bit error rate(BER) characteristics and makes multi-phase modulation available. Two state or biphase PSK is called BPSK and four state or quadriphase is termed QPSK. 8PSK or Octal- phase keying and 16QAM (Quadrature Amplitude Modulation) are now becoming common in commercial satellite links. Phase Shift Keying (PSK) is the method of transfer of an electrical impulse which represents a data bit, onto a Modulated IF carrier. [...]
[...] Demand Assigned Multiple Access (DAMA) A DAMA system is a single hop satellite transmission network which allows direct connection between any two nodes in the network among many users sharing a limited pool of satellite transponder space. DAMA supports full mesh, point-to-point or point-to-multipoint communications, i.e., any user can connect directly to any other user anywhere within the network. The result is economical and flexible bandwidth sharing with any mix of voice, fax, video and data traffic. DAMA optimizes the use of satellite capacity by automatically allocating satellite resources to each active node upon demand. [...]
[...] A BER of less than 1 in 100,000 bits is generally desired for an average satellite communications channel (also referred to as a BER of 10-5). For some types of data, an even smaller BER is desired (10-7). Eb/No (Bit Energy-to-Noise Density ratio) - The BER is directly dependent on the Eb/No. Since the noise density present on the channel is difficult to control, this basically means that BER can be reduced through using a higher powered signal, or by controlling other parameters to increase the energy transmitted per bit. [...]
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