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From: lindah74uk on 26 Oct 2005 02:54
Hello all,

What kind of modulation scheme that will suit high speed transmission
(at least to 1 Gbps)?
And obvious choice will be those highly spectral efficient modulation
scheme like OFDM. However, if the linearity requirement and the
sensitivity to phase noise are very high, then OFDM could be out of
question especially for system that operate at very high frequency such
as 40-70GHz .

So what other modulation schemes that can give good trade off between
linearity requirement, sensitivity to phase noise, equalization
complexity, performance in such a high speed system?


Any comments will be highly appreciated.

Regards,
Lindah

From: allanherriman on 26 Oct 2005 04:04
lindah74uk(a)yahoo.co.uk wrote:
> Hello all,
>
> What kind of modulation scheme that will suit high speed transmission
> (at least to 1 Gbps)?
> And obvious choice will be those highly spectral efficient modulation
> scheme like OFDM. However, if the linearity requirement and the
> sensitivity to phase noise are very high, then OFDM could be out of
> question especially for system that operate at very high frequency such
> as 40-70GHz .
>
> So what other modulation schemes that can give good trade off between
> linearity requirement, sensitivity to phase noise, equalization
> complexity, performance in such a high speed system?

You missed one critical specification - the bandwidth of the channel.
With a millimetre wave carrier, the bandwidth might be quite large
(GHz), allowing inefficient yet robust and simple to implement
modulation schemes like BPSK.

Regards,
Allan

From: Eric Jacobsen on 26 Oct 2005 12:46
On 25 Oct 2005 23:54:06 -0700, lindah74uk(a)yahoo.co.uk wrote:

>What kind of modulation scheme that will suit high speed transmission
>(at least to 1 Gbps)?
>And obvious choice will be those highly spectral efficient modulation
>scheme like OFDM. However, if the linearity requirement and the
>sensitivity to phase noise are very high, then OFDM could be out of
>question especially for system that operate at very high frequency such
>as 40-70GHz .
>
>So what other modulation schemes that can give good trade off between
>linearity requirement, sensitivity to phase noise, equalization
>complexity, performance in such a high speed system?

What are the channel characteristics?

I often see OFDM touted as "spectrally efficient", but it's only
efficient if the channel is frequency selective. If the channel is
AWGN with a reasonable SNR then a high-order single carrier QAM system
may be better.

As you've already hinted the radio impairments matter as well. As
does the expected range, power usage, etc.


Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org
From: lindah74uk on 27 Oct 2005 07:53
> What are the channel characteristics?
>
> I often see OFDM touted as "spectrally efficient", but it's only
> efficient if the channel is frequency selective. If the channel is
> AWGN with a reasonable SNR then a high-order single carrier QAM system
> may be better.
>
> As you've already hinted the radio impairments matter as well. As
> does the expected range, power usage, etc.
>
>
> Eric Jacobsen
> Minister of Algorithms, Intel Corp.
> My opinions may not be Intel's opinions.
> http://www.ericjacobsen.org

Hi Eric,

The channel is freqeuncy selective as shown by many measurements. As
pointed out by Allan that we have a huge bandwidth, then a less
efficeint could be used. So the question is which modulation will give
the best trade-off among the the constraints mentioned above.

I guess it might not be so easy to answer unless simulation is
performed in a realistic channel and circuit models. But I would be
interested to hear some opinions and discussions from the experts in
this newgroup about the suitability of type of modulation subject to
the aforementioned problems.

Comments are very much welcome.

Regards,
Lindah

From: Snowball on 27 Oct 2005 07:43
"Eric Jacobsen" <eric.jacobsen(a)ieee.org> wrote in message
news:ogcvl1lvfbfviikp7vkfkqnrbnm9l3uo64(a)4ax.com...
> On 25 Oct 2005 23:54:06 -0700, lindah74uk(a)yahoo.co.uk wrote:
>
> I often see OFDM touted as "spectrally efficient", but it's only
> efficient if the channel is frequency selective. If the channel is
> AWGN with a reasonable SNR then a high-order single carrier QAM system
> may be better.

Correct me if I am wrong, but isn't it the case that the symbol rate for QAM
can be only as high as the carrier frequency? This limits the channel
bandwidth you can cover, and hence the total data-rate you can achieve. For
example, assume you have a flat fading channel that can pass frequencies
from DC to 1MHz. If you place the QAM carrier at 500kHz, your symbol rate
would have to be 500Ksymbols/s max. With OFDM you can fill up (almost) the
entire 1MHz with carriers, hence reaching an aggregate symbol rate close to
1Msymbol/s. Is this correct...?


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