[Syd-Wireless] Re: [MLB-WIRELESS] The Age Technology article

[John Dalton]

Responding to Michael's email:

> OFDM is a more complex and newer modulation scheme
> than DSSS or FHSS, thus the speed.

Minor factual error here.  All these modulation schemes have
been around for many years.  The 802.11a (OFDM) standard actually
predates the 802.11b (DSSS) standard.  DSSS made it to market first.

The inceased speed of OFDM is not due to any technical superiority
over DSSS (assuming multiple DSSS users are overlaid using CDMA).
The speed difference is due to a design decision to trade robustness
for data rate (plus most DSSS impementations use low performance receivers).

OFDM and DSSS are practically equal in terms of theoretical performance.
In fact OFDM and DSSS are just special cases of a more general
technique called Code Division Multiple Access (CDMA).

In many ways, OFDM is actually simpler to implement than DSSS,
since the Fast Fourier Transform, used by OFDM, can be implemented
very efficiently.  The main reason 802.11b came to market first
was that the 2.5Ghz radios of 802.11b are easier to build than
the 5Ghz radios of 802.11a.

Answering one of Steven's questions:

> Is there any difference in bandwidth (ie channel width) of the 802.11b+
> equipment? or is the speed increase only due to the PBCC modulation?

Bandwidth is the same as 802.11b.  (note: As far as I know, 802.11b+ is
simply a marketing term as PBCC has not yet been written into the 802.11 standard).

Hope this is useful.

Regards
John

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