* Posts by dbateman

3 posts • joined 29 Dec 2009

Ten free apps to install on every new PC

dbateman

Only one app needed on Windows

the one you can download from

http://goodbye-windows.com

D.

Dell bars Win 7 refunds from Linux lovers

dbateman

Dumping -> Product Tying

This is not dumping, which is selling a product below its market value to kill the competition, you can be sure that Microsoft is making a profit from this sale. This is product tying

http://en.wikipedia.org/wiki/Product_tying

which is tying the sale of one product that the customer wants to the sale of another unwanted and unrelated product. Yes its generally illegal in most countries, but the key here is proving that Windows 7 is an unrelated product to the PC its installed on..

D.

Tiny TV could make billions for FCC

dbateman

Read a book on OFDM please

The ability of DVB-T to "mesh" or rather create a single-frequency network (SFN) is based on the guard interval of the OFDM (or COFDM in DVB-T parlance) and not QAM that is used to modulate the individual carriers of the OFDM signal. The guard-interval of an OFDM signal is what is used to protect the received signal from multiple propagation paths from the transmitter to the receiver and in most OFDM systems is a cyclic prefix or a copy of part of the original signal from the start to the end of the OFDM block. In the DVB-T systems the cyclic prefix can be between 1/32 and 1/4 of an OFDM block. The longer the guard interval the better multi-path rejection of the system. The rejection is the same interval as the cyclic prefix itself.

A synchronized OFDM system means that multiple transmissions just look like multi-path and so an SFN is implicitly allowed in any OFDM system. An 8k carrier DVB-T frame with a 1/4 cyclic prefix has a guard interval of 250 microseconds... Multiple that by the speed of light and you'll see that the multi-path rejection is 75km between the propagation path lengths of the signals.. You'll probably want your transmitters closer than that in a real SFN, but 50km transmitter spacing with an 8k carriers 1/4 cyclic prefix is possible

Pity that the US system doesn't use OFDM.

D.

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