Hi Leolaohoo,
Thanks for the reply, I've been doing a bit of digging could you comment on the below please an exert from :
http://www.ja.net/documents/publications/factsheets/063-overlapping-channel-problem.pdf
In the UK, the area of the wireless spectrum set aside for the use of 802.11b/g wireless networking
devices is the ISM (Industrial, Scientific and Medical) band between 2.400 GHz and 2.497 GHz. In
the UK this is subdivided into 13 channels of 25 MHz. In the US, only the first 11 of these channels
are available – a fact with implications for UK deployments (see ‘WAG’s Advice’ below).
However, this description can give a misleading picture. Radio signals are not tightly confined to
a single point in the spectrum but are distributed symmetrically around a ‘mid’ frequency. This will
be familiar from the experience of tuning a radio, where the signal gradually gets stronger as you
turn the dial before hitting the peak frequency and then slowly dies away again. In fact, the width of
spectrum across which the signal is distributed is related to the bandwidth (in the networking sense)
of the data being transmitted and the symbol rate used to encode it (this relationship is discussed
in Nyquist/Shannon sampling theory). 802.11b, with a bandwidth of 11Mbit/s and a binary symbol
system, requires 22MHz per channel (802.11g achieves its greater data rate in the same channel
width by increasing the bits carried per symbol). So, a better picture of the channels in the 2.4
GHz spectrum is given by the following (the four differently shaded, solid curves indicate signals
associated with the four non-overlapping channels: 1, 5, 9 and 13):
Also why would Cisco publish :
Wireless LAN Design Guide for High Density Client Environments in Higher Education
Jim Florwick
Jim Whiteaker
Alan Cuellar Amrod
Jake Woodhams
Design Guide
November, 2011
Note:
Before considering a four-channel plan in 2.4 GHz, see
Channel Deployment Issues for 2.4-GHz 802.11WLANs
If the WLAN is located in a regulatory domain where the bandwidth to deploy four channels is
available (e.g., availability of channel 13 and 14) unless the WLAN is sufficiently isolated from every other network
it is likely that someone will deploy using the standard 1, 6, 11 model and drastically increase the interference to
the WLAN.
