artificially limit handset capabilities, a remnant of proprietary practices). In a complementary fashion, because of the SIM and the worldwide standardization of GSM systems, one can take the same handset, with the same Subscriber Identity Module, and make calls through distinct GSM local systems around the world. So, we see another success story for secure cores, this time due to the need for worldwide roaming on the part of the cellular telephone user. Today, the overwhelming majority of cellular phones in the world, more than two billion of them actually, contain a SIM, and other phones are converting to the SIM mechanism to provide international and national roaming capabilities.

The third success story can be found in the distribution of direct broadcast television, a system based on satellites placed in geosynchronous orbits that are used to distribute television broadcast signals over a wide area. The raison d’être for the use of a secure core in such systems is the need to limit access to the broadcast signal to those who have properly subscribed to the service; that is, to limit access to those who have paid for it.

Direct broadcast television makes use of a concept popularized by science fiction author Arthur Clarke. This is the use of satellites placed in a geosynchronous orbit. This orbit is a well defined path, located directly above the equator of the earth, for satellites to orbit the earth in exactly one day. By making the satellite move from west to east, the satellite revolves around the earth exactly in time with the earth’s rotation on its axis. The result is that a satellite in geosynchronous orbit hangs in the sky at a fixed spot directly above the equator. By selecting a satellite location that can be seen from within a specific area, for example by all the area comprising North America, an operational communication system can be implemented with relatively inexpensive equipment. The operational frugality derives from the ease of keeping the earth station antenna pointed at the satellite.

For a satellite in an orbit other than a geosynchronous orbit, an earth station on the ground must track the satellite as it moves through its orbital path if the earth station is to be able to exchange radio signals with the satellite; and, tracking stations are expensive, even for earth stations that use small, one meter diameter antennae. For a satellite in a geosynchronous orbit, however, the satellite sits at a fixed point in the sky. So, one simply has to point the antenna at that point in the sky and the earth station and the satellite can exchange radio transmissions. Now, if a large earth station transmits a strong signal up to a satellite, and the satellite receives that signal and then re-broadcasts it back toward the earth at a slightly different frequency, then any earth station antenna pointed at that location in the sky can receive the signal. Thus, a single television station can now be received by any earth station within the footprint of the transmission antenna on board the satellite. This allows the distribution of a television station across continent sized areas; much larger reception areas than can be achieved with normal transmission towers on the tops of buildings or mountains. From a business planning perspective, this architecture does leave a bit of a problem. If the satellite carries only a single channel, the distribution model is very inefficient relative to cable television distribution. So, another wrinkle is necessary.

The added wrinkle is a channel accessing scheme that allows many discrete sets of information to be carried within a single channel; essentially making a single radio frequency channel carry many simultaneous television channels. To realize this wrinkle requires that a digital data stream be transmitted from a single, large uplink earth station to a satellite which then re-broadcasts this stream back to the earth to be received by small earth station antennas at the home of each subscriber. Now, with a digitized stream carrying many channels, it is technically feasible to encrypt the stream and to lease the decryption mechanism to each subscriber. In this way, a

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