TABLE 102.3 Typical VSAT Systems Features Feature Interactive Point-to-point Broadcast Topology Star Point-to-point, mesh Point-to-multipoint Communication Between hub and VsAT to vsat Hub to vsat VSATS,Ⅴ SAT tO vsat through hub Frequency Ku-, C-band Ku-, C-band Ku-, C-band VSAT antenna 0.9-2.4m 0.5-24m Hub to remote access TDM, SCPC SCPC SCPC, spread hub ALOHA, reservation SCPC 9.6-2048 9.6-2048 data rate(Kbps BPSK, QPSK BPSK, QPSK BPSK, QPSK, FM2 DPSK FEC Rate 1/2 Rate 1/2 ate 1/2 convolutional or b convolutional nal or block Protocols SDLC, Bisync, sync,X25, TCP/IP Burroughs and others HDLC format was accounted for by the retail, automotive, and financial industries. VSATs are making private networks a viable alternative for many companies, for applications such as point-of-sale, reservation systems, remote monitoring and control, branch office administration, financial transactions, etc. A VSAT is a small earth station suitable for installation at a customers premises. A VSAT typically consists of antenna less than 2.4 m,an outdoor unit to receive and transmit signals, and an indoor unit containing the satellite and terrestrial interface units Rana et al., 1990 VSAT networks fall into three general categories: broadcast networks, point-to-point networks, and inter- active networks. In a broadcast network, a centralized hub station broadcasts data, audio, and/or video to a group of receive-only VSATs. Low-cost receive-only VSATs can receive news, weather services, and financial information. Music distribution and video broadcast via broadcast networks is widely used. Point-to-poir networks provide direct communication between two locations without the requirement of a large hub for data, voice, and image transmission. Variations of these networks include point-to-multipoint dedicated circuits or demand-assigned mesh topologies. Interactive networks are used for two-way communications services between a central hub station and a large number of vSATs in a star topology. Table 102.3 is a summary of the salient features of VSAT networks. VSATs are available for both C-and Ku-band frequency. Most VSAT systems BPSK modulation with Rate 1/2 FEC. For interactive networks the inbound channel is shared on contention basis to conserve space segment. More advanced systems use concatenated codes to improve performance. Recently, hybrid VSATs have been introduced to use terrestrial networks on the return channel. An example is the Hughs Direct PC which uses a high speed satellite receive channel, and a low speed terrestrial return channel. A critical element of VSAT networks is the network availability. The VSAT system availability is affected by three major components: effects of rain attenuation, equipment availability, and software availability. The effects of rain attenuation for Ku-band networks are significant. While link availability is usually specified at 99.5% link performance can be optimized to nearly any desired value through the use of energy dispersion techniques or large antenna sizes. The network hardware must be highly reliable Hub hardware should provide for optional redundancy and the ability to achieve better than 99.9% availability. The use of hub diversity and uplink power control can also be used to improve the network availability. The vSaT hardware availability is less catastrophic; the loss of one vsat does not constitute network failure but may require a service call to rectify the problem. Hence, it is common to use nonredundant but highly reliable VSAT units. Software availability needs to be improved since software failures dominate the overall availability of interactive networks in existing VSAT products. Interactive networks have been by far the most popular for data communication and audio/video overlays The remaining portion of this section is devoted to these networks. An interactive VSAT system consists of e 2000 by CRC Press LLC© 2000 by CRC Press LLC was accounted for by the retail, automotive, and financial industries. VSATs are making private networks a viable alternative for many companies, for applications such as point-of-sale, reservation systems, remote monitoring and control, branch office administration, financial transactions, etc.A VSAT is a small earth station suitable for installation at a customer’s premises. A VSAT typically consists of antenna less than 2.4 m, an outdoor unit to receive and transmit signals, and an indoor unit containing the satellite and terrestrial interface units [Rana et al., 1990]. VSAT networks fall into three general categories: broadcast networks, point-to-point networks, and inter￾active networks. In a broadcast network, a centralized hub station broadcasts data, audio, and/or video to a group of receive-only VSATs. Low-cost receive-only VSATs can receive news, weather services, and financial information. Music distribution and video broadcast via broadcast networks is widely used. Point-to-point networks provide direct communication between two locations without the requirement of a large hub for data, voice, and image transmission.Variations of these networks include point-to-multipoint dedicated circuits or demand-assigned mesh topologies. Interactive networks are used for two-way communications services between a central hub station and a large number of VSATs in a star topology. Table 102.3 is a summary of the salient features of VSAT networks. VSATs are available for both C- and Ku-band frequency. Most VSAT systems use BPSK modulation with Rate 1/2 FEC. For interactive networks, the inbound channel is shared on contention basis to conserve space segment. More advanced systems use concatenated codes to improve performance. Recently, hybrid VSATs have been introduced to use terrestrial networks on the return channel. An example is the Hugh’s Direct PC which uses a high speed satellite receive channel, and a low speed terrestrial return channel. A critical element of VSAT networks is the network availability. The VSAT system availability is affected by three major components: effects of rain attenuation, equipment availability, and software availability. The effects of rain attenuation for Ku-band networks are significant. While link availability is usually specified at 99.5%, link performance can be optimized to nearly any desired value through the use of energy dispersion techniques or large antenna sizes. The network hardware must be highly reliable. Hub hardware should provide for optional redundancy and the ability to achieve better than 99.9% availability. The use of hub diversity and uplink power control can also be used to improve the network availability. The VSAT hardware availability is less catastrophic; the loss of one VSAT does not constitute network failure but may require a service call to rectify the problem. Hence, it is common to use nonredundant but highly reliable VSAT units. Software availability needs to be improved since software failures dominate the overall availability of interactive networks in existing VSAT products. Interactive networks have been by far the most popular for data communication and audio/video overlays. The remaining portion of this section is devoted to these networks. An interactive VSAT system consists of a TABLE 102.3 Typical VSAT Systems Features Feature Interactive Point-to-point Broadcast Topology Star Point-to-point, mesh Point-to-multipoint Communication Between hub and VSAT to VSAT Hub to VSATs VSATs, VSAT to VSAT through hub Frequency Ku-, C-band Ku-, C-band Ku-, C-band Hub antenna 3–11 m — 3–11m VSAT antenna 0.9–2.4 m 1.8, 2.4 m 0.5–2.4 m Hub to remote access TDM, SCPC, SCPC SCPC, spread spread spectrum spectrum, FM2 Remote to hub access ALOHA, reservation SCPC — stream, CDMA Outbound data rate (Kbps) 56–512 9.6–2048 9.6–2048 Inbound data rate (Kbps) 9.6–256 9.6–2048 — Modulation BPSK, QPSK, BPSK, QPSK BPSK, QPSK, FM2 DPSK FEC Rate 1/2, Rate 1/2, Rate 1/2, convolutional or block convolutional convolutional or block Protocols SDLC, Bisync, Clear channel Clear channel, Async, X.25, TCP/IP synchronous, Burroughs and others HDLC format