802.11b and channels

Hi

I was looking at the 802.11b channel listings, there are 14 channel,
FCC for us allows 1-11, Europe 1-13 , Japan channel 14.

Each DSSS channel is 22 Mhz wide

Channel Center Frequency (GHz)
1 2.412
2 2.417
3 2.422
4 2.427
5 2.432
6 2.437
7 2.442
8 2.447
9 2.452
10 2.457
11 2.462
12 2.467
13 2.472
14 2.484

and we all know that 1,6, 11 is where they do not overlap, however in
some places I have read that the channel is 30Mhz wide, I presume this
is due to some taking into account of the longer tail in the spread
spectrum...is this correct?, if so and 22Mhz is taken as the spread,
and what signal level is a zero signal assumed, i.e the spread will
have a "infinite tail" but signal must drop to x% at 11Mhz either side
of the peak hence its assumed that 22Mhz is okay.

My other question is that each peak a a 5Mhz sep, why is this ?

tks

Iqbal

For 802.11b, the channel width is 22 Mhz. If fc is channel center frequency,
the transmit spectral mask requires that, beyond fc+11 or fc-11, the
transmitted signal drop to below -30 dBr relative to the sinx/x value at fc.
Beyond fc+22 or fc-22, it must drop to below -50 dBr relative to peak
sinx/x. See the 802.11b standard, figure 145 (page 53).

25 Mhz between channel centers should be sufficient to eliminate
interference between networks.

You should think of the channels as 25-Mhz-wide, so there are a total of 14
overlapping channels, with centers spaced 5 Mhz apart. Alternatively, you
can think of it as 14 non-overlapping 5-Mhz-wide channels, in which case
802.11 "bonds" 5 of them together to make a network. It really doesn't
matter, the result is the same. Transmission on any channel produces some
energy in all the channels, so in reality they all over overlap to some
extent.

"Iqbal" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> Hi
>
> I was looking at the 802.11b channel listings, there are 14 channel,
> FCC for us allows 1-11, Europe 1-13 , Japan channel 14.
>
> Each DSSS channel is 22 Mhz wide
>
> Channel Center Frequency (GHz)
> 1 2.412
> 2 2.417
> 3 2.422
> 4 2.427
> 5 2.432
> 6 2.437
> 7 2.442
> 8 2.447
> 9 2.452
> 10 2.457
> 11 2.462
> 12 2.467
> 13 2.472
> 14 2.484
>
> and we all know that 1,6, 11 is where they do not overlap, however in
> some places I have read that the channel is 30Mhz wide, I presume this
> is due to some taking into account of the longer tail in the spread
> spectrum...is this correct?, if so and 22Mhz is taken as the spread,
> and what signal level is a zero signal assumed, i.e the spread will
> have a "infinite tail" but signal must drop to x% at 11Mhz either side
> of the peak hence its assumed that 22Mhz is okay.
>
> My other question is that each peak a a 5Mhz sep, why is this ?
>
> tks
>
> Iqbal

Thanks Gary, any ideas as to why 5Mhz between the peaks, is that a
standard somewhere, or is it because of dsss etc etc

Iqbal


(E-Mail Removed) (Iqbal) wrote in message news:<(E-Mail Removed). com>...
> Hi
>
> I was looking at the 802.11b channel listings, there are 14 channel,
> FCC for us allows 1-11, Europe 1-13 , Japan channel 14.
>
> Each DSSS channel is 22 Mhz wide
>
> Channel Center Frequency (GHz)
> 1 2.412
> 2 2.417
> 3 2.422
> 4 2.427
> 5 2.432
> 6 2.437
> 7 2.442
> 8 2.447
> 9 2.452
> 10 2.457
> 11 2.462
> 12 2.467
> 13 2.472
> 14 2.484
>
> and we all know that 1,6, 11 is where they do not overlap, however in
> some places I have read that the channel is 30Mhz wide, I presume this
> is due to some taking into account of the longer tail in the spread
> spectrum...is this correct?, if so and 22Mhz is taken as the spread,
> and what signal level is a zero signal assumed, i.e the spread will
> have a "infinite tail" but signal must drop to x% at 11Mhz either side
> of the peak hence its assumed that 22Mhz is okay.
>
> My other question is that each peak a a 5Mhz sep, why is this ?
>
> tks
>
> Iqbal