Digital data transmission by satellite is widely used for broadcasting information by news and photo services, financial institutions, paging companies, advertising and many others. Digital data is usually transmitted to multiple receiving locations by satellite using a method called single channel per carrier (SCPC) whereby a single data channel, or multiple data channels (MCPC) that have been multiplexed together, are transmitted using a single satellite carrier. Digital data can be synchronous or asynchronous originating from a variety of sources including local area networks.
Digital SCPC carriers are normally transmitted using phase shift key (PSK) modulation. The two normal modes of PSK modulation are Bi-Phase Shift Key (BPSK) and Quadrature Phase Shift Key (QPSK). BPSK modulated carriers use twice the satellite bandwidth of the same data rate QPSK carrier, but at low data rates, such as 64 kbps, generally provide better service into smaller dish receive stations. BPSK modulation is also not as sensitive to LNB frequency drift and generally allows the use of less expensive non stabilized LNB's at lower data rates than QPSK modulation. QPSK modulation, since it occupies half the satellite bandwidth of BPSK, provides more efficient use of the satellite, and therefore yields more channel capacity per transponder and lower cost per channel. The higher quality satellite receivers available today, such as the International Communications Products, Inc. (ICP) DigiCeiver® products provide for operation with non stabilized LNB's, even in the BPSK mode (at data rates of 128 kbps and higher).
The ICP digital data system utilizes the latest digital technology to provide state-of-the-art broadcasting of data by satellite. The digital data system includes: packet multiplexer, TDM multiplexer, IP Gateway, modulator and Network Control System at the head-end location as well as ICP's unique programmable DigiCeiver® multi-function receivers containing the demodulators, demultiplexers at each of the receive locations.
The paragraphs below describe the equipment used in the digital data network as well as how this equipment is configured to provide the required services.
ICP's head end equipment is usually located at the uplink site. The equipment provides the multiplexing and modulation functions for the data. Synchronous or asynchronous data is introduced into the AD-3311 Packet Multiplexer or the DCR-960/970 multiplexer where it is combined into a single aggregate data stream. Data originating on a local area network can also be combined into the aggregate using ICP's IP-Gate unit.
The head-end equipment can be configured in a non-redundant or redundant configuration. The redundant configuration provides the highest availability possible. Redundancy is accomplished by providing automatic redundancy switching of the major functional blocks of the system, a well as providing full monitoring, troubleshooting and manual service restoral via patch panels.
The AD-3311 packet multiplexer provides for the multiplexing of the low speed services. This unit accepts up to 32 channels of low speed data (up to 38.4 kbps) and produces a packetized aggregate output stream at a data rate of either 56 kbps or 120 kbps. This output stream is then multiplexed into the TDM system aggregate stream with other information.
The input ports of the AD-3311 accept data via an RS-232 physical and electrical interface. Each channel may be configured independently in many variations. These include data rates from 300 baud up to 38.4 kb. Clocking may be internal or external. The data may be carried transparently in async form or synchronously using HDLC or BISYNC protocols. Any input port may be mapped to any output port in the system. Data may be further selected by the use of Product ID's (PID's) which are downloaded individually to each demultiplexer and each receive port in the system. The result of this unit is a very sophisticated and flexible unit serving a wide variety of applications and users.
The ICP DCM-960/970 TDM multiplexer combines up to 8/48 data sources into a single TDM aggregate stream. Each channel is programmable in data rate, in 64 kbps increments, up to a total aggregate rate of 2048 kbps. Channel 0 of the multiplexed data stream includes an 8 kbps channel used for network control and TDM synchronization. The remainder of channel 0 may be assigned for user data. The 8 kbps control channel is designated the network control (NCS) channel. In addition to synchronization, the NCS channel provides a carrier identification signal to all receivers to identify the correct signal in a multi-carrier satellite environment. It also includes a control stream, which allows the complete configuration and control of every receiver in its network from the head-end.
Connection to the NCS channel is provided via a Network Control (NCS) port. This port provides connection to the NCS computer. The ICP NCS software, running on the computer, provides access to the NCS channel to control the field population of receivers as well as providing configuration of the DCM-960/970. The NCS software is described in more detail below.
The channel input interfaces to the DCM-960/970 are provided via RS-422 electrical levels. The aggregate data output is also provided as an RS-422 signal. The NCS port utilizes an RS-232 electrical interface.
In addition to the NCS interface, the DCM-960/970 provides a summary fault relay output. It also has a relay isolated input which enables the data output drivers and clock output drivers to be separately enabled or disabled allowing redundant units to be physically paralleled and then remotely enabled or disabled for redundancy protection.
In pure SCPC configurations where no over the link control is needed, then the multiplexer and associated NCS may not be utilized.
The RC24OM Modulator is both data rate and frequency agile. It receives RS-449 (RS-422 levels) data from the DCM-960/970 TDM multiplexer and provides a 70 MHz IF output.
The modulator may be fully remote controlled via an RS-232 serial link. All configuration parameters may be controlled either from the front panel or through the remote port.
Audio Encoder - DAE-102
Although the topic of this technical description is for data networks, ICP's broadcast systems accommodate audio. At the head end our DAE-102 MPEG encoders provide MPEG Layer II encoding of 2 independent audio channels (or one stereo channel). The DAE-102 is capable of encoding audio channels at all the data rates and in all the modes provided for in Layer II. Note that channels are processed in pairs and each channel in the pair must be processed in the same mode. This means the channels are either stereo or monaural channels of the same bandwidth and bit rate. Many different bandwidth/bit rate configurations are possible.
The MPEG encoders may be remotely controlled via a serial RS-232 link. The configuration of the encoder may be fully controlled through this port. The encoders may, of course, be manually controlled via their front panels. A summary fault relay output signal is also provided.
The MPEG encoded audio signals are multiplexed into the aggregate data stream at the DCR-960/970 multiplexer. Complete details on implementing a audio network can be from in our Digital Audio Network Technical Description.
Network Control System (NCS)
In MCPC audio/data systems, in addition to the audio and data channels there is an 8 kbps network control (NCS) channel multiplexed into each carrier which allows complete control of each audio receiver from its associated multiplexer. In SCPC audio systems where only a single data channel is broadcast, and if no control over the link is required, then the multiplexer and NCS may not be utilized.
The DCM-960/970 and the downlink receivers are controlled via the NCS computer. The NCS computer is an high quality PC computer running a windows based ICP NCS software package. The NCS software provides an easy to use operator interface to allow configuration of the system as well as ongoing performance monitoring. The features of the NCS software are summarized below:
The Model DCR-972 and DCR-974 DigiCeiver® are multi-function SCPC/MCPC programmable data/audio/IP Multicasting receiver intended for use in satellite-based broadcast systems. Its many applications include worldwide news services, radio program distribution to network affiliates, nationwide advertising distribution, financial and banking services, paging broadcasts, music distribution, corporate data base updates, and software distribution. In the DCR-972, audio decoding is provided by the four-channel DAP-104 daughter board which is "plugged" directly into the receiver motherboard. The DCR-974 utilizes a SAP-104 Eight channel board which also provides a store and forward function. Additional data ports are provided by the DDP-104, four-port data demultiplexer expansion card. See the detailed specifications under Products on our Web Site.
The DAP-104 utilizes a programmable single chip audio decoder to recover each channel pair (or stereo channel) from the aggregate data stream. High quality digital to analog converters (DAC's) then provide the analog audio output. The analog output is then buffered by an integrated balanced audio driver providing the required audio output levels as well as a high degree of longitudinal balance and low distortion. An AES/EBU digital output signal is also provided from the decoder. Each DAP-104 card holds two audio decoders, which can provide two stereo or 4 monaural channels (or 2 monaural and one stereo channel).
The DDP-104 is a four port data demultiplexer expansion card for use with the DCR-972 DigiCeiver®. The basic DCR-972 provides one data output and one optional data port. It also has two expansion slots for additional data or audio capability. Up to two of DDP-104 expansion cards can be added for a total of ten data outputs from a single DCR-972.
The DDP-104 allows a user to rapidly and cost effectively change and/or grow a network. The DDP-104 card is plug compatible with the two expansion slots in the DCR-972. Once installed, final operating configuration parameters are downloaded either over-the-network or through the receiver remote control port by the Network Control System (NCS). Data outputs may be authorized or de-authorized at any time via in-band commands from the NCS.
Each of the four DDP-104 ports can be configured either Time Division Multiplexed (TDM) or packet multiplexed data. In the TDM mode, a DDP-104 port will extract a transparent synchronous data channel from the TDM aggregate stream. Data rates for each port are selected by combining aggregate time-time slots in 64 kbps increments, limited by the aggregate maximum. The DDP-104 is compatible with all ICP TDM multiplexers.
A DDP-104 port can also be configured in packet mode to provide either synchronous or asynchronous data outputs. When operating in packet mode, the DDP-104 includes Product ID's. Product ID's allow individual receiver ports to be programmed from the NCS for selected services while restricting all others.
The SAP-104 expansion card, for use with the DCR-974 receiver, is designed to provide for the real-time reception of high quality MPEG encoded audio. The card also provides a store and forward feature that allows audio and HTML data files to be stored in the receiver and later played back on command. Typical applications include delayed play back across time zones, off set play back, spot storage and distribution, commercial regionalization, localization of network feed and delivery verification of spots to affiliates.
The SAP-104 card supports the standard ISO/MPEG 2 audio format. Standard data rates and sample rates are supported as well as the standard modes including mono, dual mono, stereo, and joint stereo. Standard MPEG file formats are supported for the store and forward functions.
The SAP-104 card is used in place of the DAP-104 audio card when a store and forward function is also required. It decodes up to four audio streams, each available as an analog or AES/EBU output. Real time audio or IP multicast files can be stored in the receiver for delayed play back. Files are stored on an integrated hard disk drive or optional non-volatile memory cartridge. Maximum storage capacity is dependent on data rate and disk size. Our standard hard drive can store 30 or more hours of audio at 128 Kbps. Higher capacity disk drives are available for even more of storage capacity. The recorded files may be triggered to play by local command or through our network automation system. File management is provided to maintain the local inventory of audio spots or programs.
An external computer running web browser software accomplishes local control of the play function. In addition to real-time audio operation and stored audio reproduction, the SAP-104 supports the store and forward of HTML data files. This can provide for the distribution of text and graphics, including news reports, weather maps, play schedules, etc.
Figure 1: Typical Data/Audio/IP Multicast Network
Figure 1 shows a simplified configuration for a broadcast network with high and low speed data, MPEG2 Audio, and IP multicast information. The head-end is shown in a non- redundant configuration and is also available in a fully automatic switchover, redundant configuration.