My thoughts on Adaptive's White Paper? In nutshell, its a marketing piece and should be read, as any "white paper" from a manufacturer, with that thought firmly in the forefront of one's mind - flashing in neon if you can arrange it.
That said, I'm not trying to pick on Adaptive: I agree with their position on time division duplex (TDD). I like their use of ATM. In my opinion, combining TDD with ATM will result in the most efficient utilization of the available spectrum, regardless of RF air interface/modulation - if one is mixing traffic with varying QoS requirements over a common wireless link.
As for their position on TDMA versus OFDM or VOFDM or COFDM or WOFDM ( pick your flavor) - well they left out one very critical parameter which affects the comparison of their implementation versus other alternatives - frequency.
...Empirical data gathered from a study of urban and suburban areas, along with data from live customer installations, all provide strong support for the assertion that AB-Access has achieved effective coverage of LOS, near-LOS and first wall penetration scenarios....
No mention there....
Then this...
...Variants of OFDM have an advantage in mobile scenarios. Dynamic equalization works by "training" itself on the multipath environment and setting up the appropriate adjustments. If the system location remains fixed, the multipath environment remains relatively consistent and this technique is very effective. In a mobile scenario, the interference scenario is constantly changing. In this case, OFDM variants excel....
We continuously evaluate OFDM variants for inclusion in the AB-Access solution but remain convinced that adaptive equalization is a much more cost effective solution for fixed applications.....
There's a little game of hide the pea here.
The allure of VOFDM, as stated by Cisco et all, is its claimed ability to capture sufficient RF energy for an acceptable link in situations which were formerly unuseable, i.e., paths that were not line-of-sight ("LOS") or even near-line-of-sight ("near-LOS") (Comment: I wish someone, someday would quantify near-LOS; weasel terminology, which everyone uses.)
Well by not mentioning frequency, the paper unfairly diminishes Cisco/Clarity's claimed technology.
Heretofore, a system designer attempting to engineer a reliable radio link was faced with this basic problem: above 2 GHz LOS becomes increasingly necessary. By the time one reaches 10 GHz it is (has been - perhaps?) mandatory. For example, a two-way link at 2 GHz may work fine even if a moderately leafed tree is in between the transmitting and receive antennas. Take that exact same path, operated above 10 GHz, it probably doesn't work.
Adaptive fails to mention frequency, which is critical to a fair comparison, and then goes off in to the discussion of mobile - which is not a problem that VOFDM is - at present - claiming to address.
That's why I say hide the pea - a little hand waving, a little misdirection, and one has lost the point.
Again, I'm not trying to pick on Adaptive. They're in business - as is all their competitors - to sell hardware. If they don't blow their horn, no one will for them.
It's just the start of another religious war - TDMA, OFDM (and its various flavors) CDMA, HDR, etc, etc. I've got a file cabinet full of "white papers" and I think I would be safe in saying that each and every one of them has a few "whoppers."
ww
p.s. If I haven't been clear let me reiterate: Fair comparisons must specify the frequency to be used (2) specify the architecture - mobile or fixed and (3) specify the user application. Even if they are specified, there's a ton of places a manufacturer, any manufacturer, ALL manufacturers, can fudge the analysis.
Caveat Emptor |
