- Single channel per carrier
Single channel per carrier (SCPC) refers to using a single signal at a given
frequency and bandwidth. Most often, this is used onbroadcast satellite s to indicate thatradio station s are not multiplexed assubcarrier s onto a singlevideo carrier, but instead independently share atransponder . It may also be used on othercommunications satellite s, or occasionally on non-satellite transmissions.In an SCPC system, satellite bandwidth is dedicated to a single source. This makes sense if it is being used for something like
satellite radio , which broadcasts continuously. Another very common application is voice, where a small amount of fixed bandwidth is required. However, it does not make sense forburst transmission s likesatellite internet access ortelemetry , since a customer would have to pay for the satellite bandwidth even when they were not using it.Where multiple access is concerned, SCPC is essentially
FDMA . Some applications use SCPC instead of TDMA, because they require guaranteed, unrestricted bandwidth. As satellite TDMA technology improves however, the applications for SCPC are becoming more limited.Advantages
* simple and
reliable technology
* low-cost equipment
* any bandwidth (up to a full transponder)
** usually 64 kbit/s to 2 Mbit/s
* easy to add additional receive sites (earth stations)Disadvantages
* inefficient use of satellite bandwidth for burst transmissions, typically encountered with packet data transmission
* usually requires on-site control
* When used in remote locations, the transmitting dish must be protected.
* A dish which is moved out of alignment can result in fines as high as $1,100 per minute (as of 2003) from the satellite operator.MCPC
With multiple channels per carrier (MCPC), several subcarriers are combined into a single bitstream before being modulated onto a carrier transmitted from a single location to one or more remote sites. This uses
time-division multiplexing (TDM). It is aretronym of sorts, as it was the only wayradio network s were transmitted ("piggyback ed" ontelevision network s) until SCPC.In
digital radio anddigital television , an ensemble or other multiplex or multichannel stations can be considered MCPC, though the term is generally only applied to satellites.The major disadvantage of MCPC is that all of the signals must be sent to a single place first, then combined for retransmission — a major reason for using SCPC instead.
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