Bills would boost unlicensed Wi-Fi

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Frequencies and channels: Don't forget the internally approved frequency ranges:

TV operates on 4 frequency bands from fixed stations. Applications for mobile stations MUST be fitted so that any frequency drift caused by Doppler effect for speed up to 300km/h in each band does not cause pollution of surrounding channels. Protection of frequencies already requires a 0.25MHz min separation for fixed stations in low band I, and 0.5 MHz in band III, and 0.75 Mhz in bands IV and V.

The FCC proposed to use the highest band for mobile WiFi. This would extend the frequency gap to 1MHz. Given that these bands (in US only) are divided in channels of only 6MHz, this severealy limits the usable bandwidth per channel to 5MHz.
In Europeand its overseas (including in the Antillas), the VHF band I (42-72 MHz and 80-88 MHz, between the AM and FM bands) is divided in a few channels of 7MHz (leaving 6MHz of bandwidth, not enough for numeric TV multiplexes, but still used for encrypted analog TV broadcasts in PAL or SECAM + NICAM stereo), and the other UHF TV bands are divided in channels of 8MHz (leaving 7MHz of bandwidth, fully usable for MPEG2 or MPEG4 broadcasts) :

* band III (174-230 MHz, channels E5 to E12): used in UK for numeric TV broadcast, but prefered in continental Europe for numeric radio (in DAB or DTV-T standards), when analog TV will be stopped.

* band IV (470-582 MHz, channels 21 to 34):
currently used by numeric TV multiplexes in simulcasts with analog TV channels: protection of frequencies requires a 0.33 MHz interval guard for protection in portable or mobile reception, meaning nearly a 0.67MHz gap between channels; in UK, each numeric channel is multiplexed in 2000 sub-channels, in continental Europe, the 8000 sub-channels splitting scheem is used most often with 64QAM modulation and 2/3 FEC error correction ratio (either system givesplaces for 6 TV programs per multiplex).

* band V (470-582 MHz, channels 35 to 69): The channel protection requires a 0.67MHz interval gap, i.e. 1MHz of separation. Note that the highest channels between 61 and 69 are often partically allocated to long distance military operations, often over more than 300km (3 channels per country, protected on borders)

All these channels, combined, only allow operating 6 national networks, plus a partial 7th one. With numeric TV, it's alreadyextremely difficult to find 3 channels for numeric multiplexes in every country (there are LOTS of problems on borders, and in some areacovered by the signals of several countries, it will be impossible to support even just one numeric multiplex, without first shuttingdown a analog TV channel to leave space for a single multiplex (but as each multiplex can support 6 PV programs, the existing 6 analog TV channels would be shut off simultaneously, offering 36 numeric programs on the same frequencies, including the existing 5 or 6 free programs).

I think that the situation in US is more complex, just because the channels are more narrow (only 6MHz) than else where (this explains the poorer image quality and colors of NTSC in US, compared to PAL and SECAM elsewhere). I don't know the details of the NTSC standard in Japan and if it also uses a6MHz bandwidth per channel.

Now the world if moving to 8MHz channels (in UHF bands IV and V), or 7 MHz channels (in UHF band III) for numeric TV broadcast, which means a much simpler management of services supported by each multiplex (including additional numeric radios, classic TV, HDTV, or multilanguage programs).

Only old band I (between AM and FM)will no longer be used by TV (it becomes the natural candidate for extension of radio to DAB, with a already overcrowded FM band, and explains why numeric radio will probably not use band III in Europe, although there are pressures to use it, it should be usedonly within mixed radio/TV multiplexes in DVB standard and not in DAB standard).

Is US also going to support 8MHz channels for its multiplexes? The abandon or band IV is going to a direction opposed to other countries that have largely promoted the existing UHF band III and IV as the best support for numeric TV (currently in simulcast with analog TV). If US chooses band III (channels 5 to 12) and IV (channels 21 to 34) for numeric TV, it will once again promote a US-only solution, with highercosts for customers with devices working only in US.

Note that Canada, almost all of Asia and South America is already using the European scheme, and asaconsequence, the prices of devices is extremely low, and is continuing to fall dramatically (for now decoders mostly use the MPEG2 image encoder for free TV, but MPEG4 encoders are already widely used on cable and DSL TV distribution, and on pay-TV over numeric TV broadcasts, meaning that MPEG4 will be the final encoding for all multiplexes in a medium term, most decoders being upgradable to MPEG4 onve the pay-TV scrambling systems are standardized and made interoperable).; Posted by: PhilippeV Posted on: 02/22/06 You are currently: a Guest | Members login | Terms of Use