ERENCE FREQ, X2 x3 LOOULATOR L DOUBLE DO ANTENNA IF=LBAN MODEM (a) Conventional VSAT b) VSAT using direct modulation FIGURE 102.8 Simplified VSAT block diagram Direct modulation of the RF carrier may lower the cost of the VSAT IF and RF electronics while consolidating modulation and upconversion functions. Direct modulation allows the design of a VSat with fewer parts, smaller size, and lower weight than with traditional outdoor units. Figure 102.8 is a block diagram showing a conventional VSAT and a VSAT using direct modulation. An L-band receive interface between the ODU and IDU is preferable in order to receive audio and video overlays The IDU is located near the user terminal equipment. Major IDU functions include outbound carri acquisition, tracking, demodulation, bit synchronization, burst modulation, and protocol processin controls the operation of the ODU, monitors VSAT health, and responds to hub commands. The processing system performs satellite channel access and protocol and customer interface processing functions. A video/audio port can be provided with an RF splitter at the idu to separate the received audio/video signal for the optional video/ audio receiver Network Management System The network management system(NMS)is a critical element of a VSAT network. Through the NMS, the user can have full control of his network, which is usually not possible in the case of terrestrial network facilities. The NMS generally provides a centralized management tool for hub and VSAT equipment configuration control assignment of inbound and outbound satellite channels, network monitor and control, switchover to back-up equipment, network statistics collection, downline loading of new software, and report generation. In the shared hub environment, the hub operator controls the allocation of resources among various users and controls the F transmission facility. The user must have the ability to manage his portion of the network transparent to other users. In the case of a dedicated hub, a single management entity can exert full control over the network, including rF transmission facilities The network management system standards community has defined five functional areas as requirements for network management systems. These areas are fault management, accounting management, configuration man- gement, performance management, and security management. The VSAT network management system should capable of interfacing with other network management systems by supporting a standard network management protocol. The protocol standard most widely accepted is the Simple Network Management Protocol (SNMP) Transmission System Most VSAT systems employ BPSK or QPSK modulation with rate R= 1/2, K=7 convolutional coding and soft-decision Viterbi decoding on both the inbound and outbound channels. Differential phase shift keying (DPSK)modulation may be used to reduce the demodulator complexity and cost. DPSK is relatively insensitive e 2000 by CRC Press LLC© 2000 by CRC Press LLC Direct modulation of the RF carrier may lower the cost of the VSAT IF and RF electronics while consolidating modulation and upconversion functions. Direct modulation allows the design of a VSAT with fewer parts, smaller size, and lower weight than with traditional outdoor units. Figure 102.8 is a block diagram showing a conventional VSAT and a VSAT using direct modulation. An L-band receive interface between the ODU and IDU is preferable in order to receive audio and video overlays. The IDU is located near the user terminal equipment. Major IDU functions include outbound carrier signal acquisition, tracking, demodulation, bit synchronization, burst modulation, and protocol processing. It also controls the operation of the ODU, monitors VSAT health, and responds to hub commands. The baseband processing system performs satellite channel access and protocol and customer interface processing functions. A video/audio port can be provided with an RF splitter at the IDU to separate the received audio/video signal for the optional video/ audio receiver. Network Management System The network management system (NMS) is a critical element of a VSAT network. Through the NMS, the user can have full control of his network, which is usually not possible in the case of terrestrial network facilities. The NMS generally provides a centralized management tool for hub and VSAT equipment configuration control, assignment of inbound and outbound satellite channels, network monitor and control, switchover to back-up equipment, network statistics collection, downline loading of new software, and report generation. In the shared hub environment, the hub operator controls the allocation of resources among various users and controls the RF transmission facility. The user must have the ability to manage his portion of the network transparent to other users. In the case of a dedicated hub, a single management entity can exert full control over the network, including RF transmission facilities. The network management system standards community has defined five functional areas as requirements for network management systems. These areas are fault management, accounting management, configuration man￾agement, performance management, and security management. The VSAT network management system should be capable of interfacing with other network management systems by supporting a standard network management protocol. The protocol standard most widely accepted is the Simple Network Management Protocol (SNMP). Transmission System Most VSAT systems employ BPSK or QPSK modulation with rate R = 1/2, K = 7 convolutional coding and soft-decision Viterbi decoding on both the inbound and outbound channels. Differential phase shift keying (DPSK) modulation may be used to reduce the demodulator complexity and cost. DPSK is relatively insensitive FIGURE 102.8 Simplified VSAT block diagram