This is a prime example of what happens when ...
... marketards attempt to do engineering.
Honestly, the mind boggles.
The world’s tallest free-standing broadcasting tower has a slight problem – it can’t broadcast very well. The ¥65 billion (£503m) Tokyo Skytree was opened to an awe-struck public in May this year. Standing at an impressive 634 metres (the Eiffel Tower tops out at 324 metres), the idea was that in January 2013 it would take …
Nope. It's quite feasible in the digital world to run multiple transmitters on the same frequency. It's rather cleverly known as a Single Frequency Network (SFN) and is actually one aspect of DAB that works quite well. With the completion of UK switchover for TV and the migration of TV from 800Mhz, SFN's are now being engineered into TV as well.
In analogue two transmitters on the same channel would cause mutual interference and black-spots, but because each "bit" of a digital transmission is like a discrete transmission at a very distinct time, other bits from other Tx's on the same frequency appear like short term echos. You just have to make sure the time interval between successive bits does not clash with the time delay from distant transmissions.
eg. if you have a 8000 carrier digital system, carrying 8mb/s, each carrier is carrying 1000 bits per second, ie. 1ms apart. As long as distant transmitters on the same frequency are recieved with less than 1ms delay (ie. about 300km max spacing) the system works. The caveats are that frequencies must be exactly synchronised, and the same datastream must be broadcast by all transmitters and again must be in sync. Normally that requires the use of some form of GPS sync reference, though of course any form of precise timing could be used.
"In analogue two transmitters on the same channel would cause mutual interference and black-spots, but because each "bit" of a digital transmission is like a discrete transmission at a very distinct time,"
Digital transmissions still use an analogue carrier which can still suffer from destructive interference with another carrier. But because digital signals generally use higher frequencies than analogue broadcasts these blackspots tend to be quite small.
Since each transmission signal spans (almost) the 8MHz bandwidth, comprised of (almost) 8k carriers for TV SFNs, 'ghosting'/reflections/echoes or other distant trasmitters effectively become notches in the received frequency spectrum domain, only severely affecting a handful of the 8k carriers - which the data redundancy and error-correction flywheels over. The symbol rate is of the order 1ms (off the top of my head; this closely related to the period of the frequency-intervals between the carriers so that the Fourier transform is nicely orthogonal) so as long as echoes/reflections/distant transmissions are delayed by rather less than 1ms (the safety "guard interval" probably being about 1/4 to 1/8th ms), then intersymbol interference won't be a problem and all will be hunky-dory.
Baht 'at? That's Ilkla Moor.
This Californian has been there & done that. In sleet. Was pretty narsty. Damn near caught me deeath o` cowd. But the pint & kiss at the end was tasty ... Howzat?
Recommended, once, or several times[1]. Live a little :-)
[1] I wasn't courting Mary Jane ... I was courting Katie G. ;-)