12 Sep
2020
12 Sep
'20
4:23 a.m.
Hi Harald,
Indeed, it's been awhile since I've looked at that code!
Correct. The mapping itself is arbitrary. Consecutive numbering was
one simple approach.
I'll also add that one of the most difficult aspects of the
multi-carrier implementation had little to do with software. B210 was
the target device when the code was developed; the on board AD9361
RFIC was never recommended by ADI for multi-carrier operation. The DC
and aliasing effects were quite visible when using shifted carriers in
addition to the reduction in dynamic range. Conformance tests for
spectrum mask were challenging.
-Tom
On Fri, Sep 11, 2020 at 12:50:02PM +0200, Harald Welte
wrote:
Yes, among the physical channels there will be one centered at
baseband and one aliased across the Nyquist boundary - the latter is
unusable. Wider bandwidth / higher channel count was possible though
limited by practicality (configuration was difficult) and RF effects
(see below).
But why does the code ever only use up to three
of them?
tnt has meanwhile solved that mystery (due to the inherent property of
a polyphase filter bank) And why is
there a specific re-ordering, see radioInterfaceMulti.cpp in
getLogicalChan() ?
We suspect it is to have a monotonically increasing frequency from logical
transceivers 0, 1, 2.