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DIGITAL RADIO GUIDE SATELLITE TRANSMISSION - WORLDSPACE
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Broadcasters using the service are able to uplink their programmes from either
centralised hubs or via individual feeder links located in any of the uplink footprints of the
3 satellites. Whilst this ease of access for broadcasters is a plus feature, the low power
single channel uplink with its large footprint could be vulnerable to jamming. There have
not been any occurrences of jamming to either satellite in more than four years of
continuous operation, and procedures are in place to handle such attempts.
Figure 5.2. WorldSpace Up-link Coverage
AmeriSpace AfriSpace AsiaSpace
Broadcasters using the WorldSpace system have the choice of using a low power uplink
local to the studio (PFLS), or routing their service(s) to a remote, high power uplink
(TFLS) site. This arrangement is possible by the use of Frequency Division Multiplex
Access (FDMA) for the uplink.
When received at the satellite, the signals from a PFLS are ”assembled” by the on-board
processors to form a broadcast multiplex. The arrangement will allow each of the three
spot beams to downlink its own multiplex on the processed transponder. In short, the on-
board processing simplifies the uplinking procedures.
The downlink for each beam uses Time Division Multiplex Access (TDMA) and the
baseband processing on-board the satellite carries out the FDM to TDM conversion.
For its transmission system, WorldSpace uses a system it has developed itself (early in
1998, WorldSpace made details of the system available to the ITU-R and the system is
now designated ITU-R System Ds). The WorldSpace decision to use time division
multiplexing (TDM) provides a greater link margin (the extent to which the clear sky
carrier to noise ratio exceeds the threshold for reception level) than would be available
with a COFDM system such as Eureka 147 (T-DAB). A greater link margin can be used
to serve a larger coverage area, but cannot overcome the problem of blockage, which is
a fundamental problem for all satellite systems.