Single channel per carrier (SCPC) refers to using a single
signal at a given
frequency and
bandwidth. Most often, this is used on
broadcast satellites to indicate that
radio stations are not
multiplexed as
subcarrier
A subcarrier is a sideband of a radio frequency carrier wave, which is modulated to send additional information. Examples include the provision of colour in a black and white television system or the provision of stereo in a monophonic radio broa ...
s onto a single
video carrier
Carrier may refer to:
Entertainment
* ''Carrier'' (album), a 2013 album by The Dodos
* ''Carrier'' (board game), a South Pacific World War II board game
* ''Carrier'' (TV series), a ten-part documentary miniseries that aired on PBS in April 20 ...
, but instead independently share a
transponder. It may also be used on other
communications satellites, or occasionally on non-satellite
transmission
Transmission may refer to:
Medicine, science and technology
* Power transmission
** Electric power transmission
** Propulsion transmission, technology allowing controlled application of power
*** Automatic transmission
*** Manual transmission
*** ...
s.
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
Satellite radio is defined by the International Telecommunication Union (ITU)'s ITU Radio Regulations (RR) as a ''broadcasting-satellite service''. The satellite's signals are broadcast nationwide, across a much wider geographical area than ter ...
, which
broadcast
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting began ...
s continuously. Another very common application is voice, where a small amount of fixed bandwidth is required. However, it does not make sense for
burst transmissions like
satellite internet access or
telemetry, 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 50
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.
MCPC
With multiple channels per carrier (MCPC), several subcarriers are combined or multiplexed 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
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fracti ...
(TDM) as well as
frequency-division multiplexing. It is a
retronym of sorts, as it was the only way
radio networks were transmitted ("
piggyback
Piggyback, piggy-back, or piggybacking may mean:
Transport
* Piggyback (transportation), something that is riding on the back of something else
Art, entertainment, and media
* Splash cymbal piggybacking, mounting a cymbal on top of an already ...
ed" on
television networks) until SCPC.
In
digital radio
Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services.
Types
In digital broadcasting syst ...
and
digital 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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Broadcast engineering