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Previous removal of the energy detector requirement broke
the noise level calculation loop. The previous adaptive
approach was finicky - noticably at high gain levels. Since
we no longer use the energy threshold for primary burst gating,
we can return to a simpler world.
In the new approach, we compute a running average of energy
levels and track them with a noise vector. A timeslot that
passes the correlator threshold is a valid burst. These are
not used in the noise calculation. Everything else is
considered noise and used to compute the noise level with
respect to full scale input level, which for almost all
supported devices is 2^15.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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This patch applies oversampling, when selected with 4 sps,
to the downlink only, while running the receiver with
minimal sampling at 1 sps. These split sample rates allow
us to run a highly accurate downlink signal with minimal
distortion, while keeping receive path channel filtering
on the FPGA.
Without this patch, we oversample the receive path and
require a steep receive filter to get similar adjacent
channel suppression as the FPGA halfband / CIC filter
combination, which comes with a high computational cost.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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This patch primarily addresses observed repeated overrun
conditions in embedded environments - namely ARM.
The heartbeat of the transceiver is derived from the receive
sample stream, which drives the main GSM clock. Detach the
transmit thread from the receive loop to avoid interfering with
the receive I/O, which is sensitive to overrun conditions if
pull process is interrupted.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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Unsupported at 4 sps, and performance benefits remain
to be proven at 1 sps. Disable until further testing.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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Both RACH and normal bursts are detected with the same approach of
midamble correlation combined with peak-to-average ratio. The
difference is the midamble placements and lengths. Thus, there is
no reason to have independent implementations.
This patch creates a common call burstDetect(), while leaving the
correlation window indexing in the original calls.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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The adaptive energy threshold gating suffers a near-far problem
at certain gain levels. This is due to exponential threshold
raising, but linear decreases. A large signal level followed by
a period low signal level causes (comparatively) weak signals to
go undetected. Additionally, the algorithm performs differently
at multiple RF gain levels.
This patch switches solely to correlation based gating for burst
detection. The main computational load with this approach is
sub-sample width peak interpolation, which we disable for intial
detection and run after threshold passing.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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There is no temporal dependency on when the RACH sequence is generated,
so there is no need for transceiver to create it in response to a
command from GSM core. If we power on the transceiver, we will need
the RACH sequence, so just allocate it during initialization.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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There is no reason expose the pulse shaping filter outside of the
signal processing calls. The main transceiver object makes no use
of the filter and there's no reason to pass it around.
Initialize the pulse shape with the signal processing library, and
maintain an internal static member like many of the other library
variables. Similarly destroy the object when the library is closed.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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Because repeatedly typing mSamplesPerSymbol is giving me
carpal tunnel syndrome. Replace with the much shorter,
easier to type, and just as clear name of 'sps'.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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UHD device type was previously detected, but only categorized in
terms of bus type, USB or Ethernet, and sample rate capability.
With the number of supported device increasing, we can no longer
easily group devices since we need to handle more and more
device-specific peculiarities. Some of these factors are managed
internally by the UHD driver, but other factors (e.g. timing
offsets) are specific to a single device.
Start by maintaining an enumerated list of relevant device types
that we can use for applying device specific operations. Also
rename the USB/Ethernet grouping to transmit window type because
that's what it is.
enum uhd_dev_type {
USRP1,
USRP2,
B100,
NUM_USRP_TYPES,
};
Signed-off-by: Thomas Tsou <tom@tsou.cc>
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Submitted by: Ivan Kluchnikov <kluchnikovi@gmail.com>
Signed-off-by: Thomas Tsou <tom@tsou.cc>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@5690 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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Submitted-by: Andreas Eversberg <jolly@eversberg.eu>
Signed-off-by: Thomas Tsou <tom@tsou.cc>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@5677 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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Although currently unsupported in GSM core, enable TCH/H
support in Transceiver52M for testing and future availability.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@5169 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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The adaptive energy detection threshold does not scale relative
to signal level. In other words, the adjustment factor will be
the same whether the at 40% of signal level or 4%. If the receive
gain is reduced by a large amount, suppose 20 dB, the receiver
may take minutes to adjust to the new level.
When the receive gain is changed, reset the threshold back to
the initial level. This reduces issues of runtime gain adjustment
and prevents blocking bursts while the threhold level slowly
adjusts.
Signed-off-by: Thomas Tsou <tom@tsou.cc>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@4595 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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1)I did an experiment and compiled OpenBTS with clang yesterday, which
immediately highlighted two potential bugs in the Transceiver52 code.
I'm not sure they are indeed bugs and not the intended behavior, but
they look very much like that. The first one is below and the second
one is in the following mail.
GSM::Time() arguments are defined like #define USB_LATENCY_INTRVL
(10,0), which means that they are expanded into GSM::Time((10,0)).
This expression is a GSM::Time() with a single parameter where (10,0)
return value of the last argument, 0 in this case. I.e.
GSM::Time((10,0)) is equivalent to GSM::Time(0). I think this was not
the intention.
2) Printing \n after every complex number breaks output when you want to
print it in a single line, e.g. in many debug output.
I do not claim any copyright over this change, as it's very basic.
Looking forward to see it merged into mainline.
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@4515 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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Put a floor on the transmit latency of the B100 in order to suppress
underruns in typical conditions. Empirical data from a handful of
relatively recent machines shows that the B100 will underrun when
the transmit threshold is reduced to a time of 6 and a half frames,
so we set a minimum 7 frame threshold.
The overall benefit should be marginal and may increase the
possibility of bursts arriving stale (after the trasmit deadline),
but will reduce the number of alarming UHD related messages that
appear in the log file.
This patch is UHD and B100 specific - USRP1 is unaffected.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@3980 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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With the introduction of the B100, there is USB support
using UHD devices. The characteristics of the trasmit
side burst submissions are more reflective of the bus
type than the device or driver.
Use a fixed latency interval for network devices and the
adaptive underrun approach for USB devices - regardless
of driver or device type.
The GPMC based transport on the E100 appears unaffected
by either latency scheme, which defaults to network.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2677 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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Small name change to match setTime for a get/set pair.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2673 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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If no bursts were received over a long enough duration
then the threshold would roll into negative territory.
The energy detection is based on a comparison with the
squared threshold, so all handsets would become
effectively barred after a certain period of
inactivity.
In theory, this bug also exists in the mainline tree,
but there the daughterboard receive gain is fixed at
max, which always allows the ADC to generate sufficient
noise to trigger the energy dectector and keep the
system in a valid steady state.
To fix, simply add a negative value check like those
already in place for other locations.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2655 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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UHD will internally accept floats with a range of +/-1.0,
which corresponds to a 16-bit signed integer range of
apporximately +/- 32000. Set the default amplitude to .3,
which is a safe value agaist saturation elsewhere in the
transmit chain.
The non-UHD maximum amplitude is unchanged at 13500.
Remove digital gain control because it's unnecessary and
causes extra load on enbedded systems.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2654 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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The output of the modulator or resampler is scaled and
converted from floating point to fixed point. The scaling
factor is the leftover dB in RF attention (relative to max
transmit power), which is handled prior to the integer
conversion. This should work across all daughterboards and
non-UHD installations.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2650 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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Similar to the non-52 Mhz case,
589dd9091ef594ef6ef5804fbf6bfa70f3f02858
This drastically reduces underruns on the E100.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2648 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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Push the ability to set thread priority out to the 52M
Transceiver interface, because that's where the thread
control exists.
Signed-off-by: Thomas Tsou <ttsou@vt.edu>
git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2644 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@2307 19bc5d8c-e614-43d4-8b26-e1612bc8e597
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