actually LTE doesnt quite work that way
LTE used OFDM on uplink and downlink.
The entire operator's LTE spectrum is divided up into 15kHz subchannels
which are generated/decoded in the usual OFDM FFT manner.
User payload is transmitted using 'resource blocks' (RB), which I think
are 12 carriers wide, or 12 * 15 = 180kHz minimum (I think). These 12
carriers that make up a RB are contiguous in the uplink spectrum.
Users are allocated on uplink a sequence of time slots (TS) and RB
sequences. The denser the sequences, the more uplink bandwidth. A user
may be allocated multiple simultaneous RBs per TS.
The downlink may be configured different ways, but generally one full
download ensemble.
The uplink OFDM user terminals also have two options of spectral purity-
poor and clean essentially, which permits lower PA power consumptino at
the expense of adjacent channel skirt blowout whch may be acceptable in
some low usage, sparse utilization conditions , the base station decides.
On 6/12/2017 8:49 AM, Adrian Musceac wrote:
OK Cool - OFDMA is new to me - I'll read up on it.
Hi David,
Consider this: with carrier per user instead of timeslot per user, you
don't have the distance limitation that TDMA introduces. Also, the
code is slightly more simple as it doesn't require tx burst timestamps
and hardware to support it. I've spent a week digging into the GSM
implementation of the osmo-trx software, and it's not straightforward
to do with a Gnuradio flowgraph. Reception is easy but transmission is
harder, and if you aim to maximize capacity you have very little time
to fit into a slot. Also, with OFDMA the PAPR issue is offset by
narrower receive bandwidth, unlike TDMA where you take the SNR hit for
all channels at the same time. I think it's worth looking into, I may
even have a demo by the end of the year if the holidays are
uneventful.
There are carefully tested Octave and C 4FSK modems that meet
theoretical performance in codec2-dev that you can use as a reference.
With open source, implementation complexity isn't a huge issue - someone
only has to build it once. mFSK isn't that much harder than 2FSK, and
certainly easier than a PSK modem.
I'd argue that 2FSK with convolutional encoding is way easier to
implement than 4FSK with same. But that's just my experience with
Gnuradio and may reflect my laziness. I'd say there are few people
writing code on this sort of stuff in the open, but I've seen open
source code for Yaesu's C4FM and the demodulation is much more complex
than generally believed. Meanwhile people tend to disregard open
source projects as inferior, so getting traction won't happen soon.
Best regards,
Adrian
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Freetel-codec2 mailing list
Freetel-codec2@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/freetel-codec2
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Freetel-codec2 mailing list
Freetel-codec2@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/freetel-codec2
