The idea behind the baseband frequency hopping is quite simple: we
have several RF carriers (transceivers) transmitting and receiving
on fixed frequencies (just like in a regular multi-trx setup), and
an additional burst routing layer between the schedulear and the
transceiver interface (TRXD over UDP).
Speaking in terms of the proposed implementation:
- on Downlink, dlfh_route_br() calculates the ARFCN corresponding
to the current TDMA frame number according to the hopping sequence
parametets, and picks the transceiver with matching ARFCN;
- on Uplink, ulfh_route_bi() iterates over the transceiver list of
of the BTS, calculating hopping ARFCNs for equivalent timeslots,
and picks the one with ARFCN matching the received burst.
In order to avoid frequent transceiver lookups on the Downlink path,
dlfh_route_br() maintains a "cache" in the timeslot state structure.
Unfortunately, this "cache" seems to be useless on the Uplink path,
so ulfh_route_bi() always needs to lookup the matching transceiver
for each burst received over the TRXD interface.
It may also happen that the scheduler will be unable to route an
Uplink or Downlink burst, e.g. due to inconsistent / incorrect
hopping sequence parameters received from the BSC, or in case
if a transceiver gets RF-locked by the BTS operator.
Such events are logged as "FATAL" and aditionally signalled by the
following osmo-bts-trx specific rate counters:
- trx_sched:dl_fh_no_carrier (Downlink), and
- trx_sched:ul_fh_no_carrier (Uplink).
Change-Id: I68f4ae09fd0789ad0d8f1c1e17e17dfc4de8e462
Related: SYS#4868, OS#4546
This change simplifies access to generic logical channel state
(struct gsm_lchan) from osmo-bts-trx specific state (struct
l1sched_chan_state), so there is no need to look it up using
get_lchan_by_chan_nr() on receipt of each Uplink burst.
Change-Id: Ic4378020f980845b962f71b9e4b7faea738bc174
This change is similar to what we did for Uplink bursts:
- group all Downlink burst parameters into a single structure,
- allocate it once and pass a pointer to lchan handlers,
- pass a pointer to trx_if_send_burst().
Given that the structure is allocated and (zero-)initialized in
trx_sched_fn(), we can get rid of some memset() calls in lchan
handlers and thus improve the overall performance a bit.
Change-Id: If3014e69746559963569b77561dbf7b163c68ffa
Currently we do not detect any of the DTX frames (SID_FIRST, SID_UPDATE
etc.) Detecting and tagging those frames as is_sub is important for
measurement processing. Also the RTP marker bit must be set on each
ONSET frame.
- Add detection of DTX frames
- Tag DTX frames as is_sub and set frame type to AMR_SID
- Set RTP marker bit when ONSET frames are received
Change-Id: I5afe730fff2fa3199a5913b0de4f5c7b23a39f31
Depends: libosmocore I2bbdb39ea20461ca08b2e6f1a33532cb55cd5195
Related: OS#2978
Let's drop it instead of having code duplication from common code in a
lower layer, and maintain only the one in l1sap for all BTS models.
As a result, osmo-bts-trx loses feature BTS_FEAT_MS_PWR_CTRL_DSP and
will only be able to use "ms-power-control osmo" in VTY, which will be
enabled by default (meaning: change of behavior, now MS Power Control is
enabled by default in osmo-bts-trx and can only by disabled by BSC).
Old bts-trx specific VTY command "(no) osmotrx ms-power-loop" is marked
as deprecated but still working for more usual case (1 TRX configured)
to avoid breaking backward compatibility.
TA low level loop is still kept in loops.c and will be moved to l1sap at
some point too.
Related: OS#1851
Change-Id: I0d8b0c981d9ead91d93999df6e45fb06e426aeb9
Before this patch, if due to whatever reason the TRX started fine (RSP
POWERON 0) and sockets were created but no CLOCK IND was ever received
by the BTS, it wouldn't notice since the timerfd timeouts
(bts_shutdown("no clock")) are only checked after the first CLOCK IND is
sent by the TRX.
As a result, the BTS would be kept on forever saying everything is fine
but it would be sending no DL burst at all to the TRX (tested with a
modfied osmo-trx dropping clock indication).
With this patch, new APIs are added to indicate the scheduler_trx code
the timeframes where clock ind are expected (between RSP POWERON 0 and
RSP POWEROFF 0); if TRX sends clock indications out of that timeframe,
BTs lower layers will drop them (controlled by "powered" bool).
Hence, the scheduler_trx can now place a timeout (reusing same timerfd
because its new use is exclusive in time with its other previous use)
when it is told that CLOCK IND should start appearing, and if none
arrives in considerable time, then the BTS can be shut down to notify
the rest of the network.
Related: OS#4215
Change-Id: Iba5dbe867aff10e70ec73dbf1f7aeeecb15c0a4d
C/I (Carrier-to-Interference ratio) is a value in cB (centiBels),
computed from the training sequence of each received burst,
by comparing the "ideal" training sequence with the actual one.
So far, there was no way to expose more measurements from OsmoTRX,
excluding both RSSI and ToA. Since the new version of TRXD header,
we can receive C/I indications and send the averaged (per 4 bursts)
values to OsmoPCU (as a part of PCUIF_DATA.ind).
Please note that we also need to attach C/I measurements
to the following L1SAP primitives:
- PRIM_PH_RACH.ind,
- PRIM_PH_DATA.ind,
- PRIM_TCH.ind,
but this will be done in the follow up changes.
Change-Id: Ia58043bd2381a4d34d604522e02899ae64ee0d26
Fixes: OS#1855
The new version adds the following fields to the TRX2L1 message,
keeping the L12TRX message unchanged:
+------+-----+-----+-----+--------------------+
| RSSI | ToA | MTS | C/I | soft-bits (254..0) |
+------+-----+-----+-----+--------------------+
- MTS (1 octet) - Modulation and Training Sequence info, and
- C/I (2 octets) - Carrier-to-Interference ratio (big endian).
== Coding of MTS: Modulation and Training Sequence info
3GPP TS 45.002 version 15.1.0 defines several modulation types,
and a few sets of training sequences for each type. The most
common are GMSK and 8-PSK (which is used in EDGE).
+-----------------+---------------------------------------+
| 7 6 5 4 3 2 1 0 | bit numbers (value range) |
+-----------------+---------------------------------------+
| . . . . . X X X | Training Sequence Code (0..7) |
+-----------------+---------------------------------------+
| . X X X X . . . | Modulation, TS set number (see below) |
+-----------------+---------------------------------------+
| X . . . . . . . | IDLE / nope frame indication (0 or 1) |
+-----------------+---------------------------------------+
The bit number 7 (MSB) is set to high when either nothing has been
detected, or during IDLE frames, so we can deliver noise levels,
and avoid clock gaps on the L1 side. Other bits are ignored,
and should be set to low (0) in this case.
== Coding of modulation and TS set number
GMSK has 4 sets of training sequences (see tables 5.2.3a-d),
while 8-PSK (see tables 5.2.3f-g) and the others have 2 sets.
Access and Synchronization bursts also have several synch.
sequences.
+-----------------+---------------------------------------+
| 7 6 5 4 3 2 1 0 | bit numbers (value range) |
+-----------------+---------------------------------------+
| . 0 0 X X . . . | GMSK, 4 TS sets (0..3) |
+-----------------+---------------------------------------+
| . 0 1 0 X . . . | 8-PSK, 2 TS sets (0..1) |
+-----------------+---------------------------------------+
| . 0 1 1 X . . . | AQPSK, 2 TS sets (0..1) |
+-----------------+---------------------------------------+
| . 1 0 0 X . . . | 16QAM, 2 TS sets (0..1) |
+-----------------+---------------------------------------+
| . 1 0 1 X . . . | 32QAM, 2 TS sets (0..1) |
+-----------------+---------------------------------------+
| . 1 1 1 X . . . | RESERVED (0) |
+-----------------+---------------------------------------+
== C/I: Carrier-to-Interference ratio
The C/I value is computed from the training sequence of each burst,
where we can compare the "ideal" training sequence with the actual
training sequence, and then express that difference in centiBels.
== Limitations
- The only supported modulation types are GMSK and 8-PSK.
Messages with other modulation types will be rejected.
- IDLE / NOPE indications are not (yet) handled.
- The logical channel handlers do not (yet) handle optional
fields, such as TSC and C/I. This will be implemented
in the follow-up changes.
Change-Id: If61c71d20d590bf07bfd019afb33000a0b6135bd
Related: OS#4006
It may be necessary to extend the message specific header with
more information. Since this is not a TLV-based protocol, we
need to include the header format version.
+-----------------+---------------------------+
| 7 6 5 4 3 2 1 0 | bit numbers (value range) |
+-----------------+---------------------------+
| X X X X . . . . | header version (0..15) |
+-----------------+---------------------------+
| . . . . . X X X | TDMA TN (0..7) |
+-----------------+---------------------------+
| . . . . X . . . | RESERVED (0) |
+-----------------+---------------------------+
Instead of prepending an additional byte, it was decided to use
4 MSB bits of the first octet, which used to be zero-initialized
due to the value range of TDMA TN (0..7). Therefore the current
header format has implicit version 0.
Otherwise Wireshark (or trx_sniff.py) would have to guess the
header version, or alternatively follow the control channel
looking for the version setting command.
This change introduces a new structure 'trx_ul_burst_ind', which
represents an Uplink burst and the corresponding meta info. The
purpose of this structure is to avoid overloading the existing
functions, such as trx_sched_ul_burst(), with more and more
arguments every time we bump the version.
On receipt of a TRXD message, trx_data_read_cb() now parses
the header version, and calls the corresponding dissector
functions, e.g. trx_data_handle_(hdr|burst)_v0().
Change-Id: I171c18229ca3e5cab70de0064a31e47c78602c0c
Related: OS#4006
Let's avoid fancy alignment in the description of logical channels
for the benefits of having better readability, the ability to add
more comments and fields without making it look ugly.
Get rid of value-string array 'trx_chan_type_names', since each
logical channel has its name defined in 'trx_chan_desc'.
Get rid of field 'chan' of 'trx_lchan_desc' structure since it's
not used anywhere, and not actually needed because the position
of each lchan description is defined by its TRXC_* type.
Replace both 'pdch' and 'auto_active' fields with more generic
bitmask field called 'flags', and define the following flags:
- TRX_CHAN_FLAG_AUTO_ACTIVE,
- TRX_CHAN_FLAG_PDCH.
Use RSL channel mode #defines from libosmogsm instead of having
hard-coded numbers. This increases readability.
As a bonus, let's add a human readable description to each lchan
definition, so it can be printed in the VTY some day.
Change-Id: I9d5d49ec569f133d37b8164b22607d4700474315
Backported from: I2fc61e1cdca4690a34e2861b9ee3b7c64ea64843
I7ab4958801b3422973b67ff0452b90afa8a3f501
This change modifies the logic of TDMA frame loss tracking. To
be more precise, the tracking logic was moved from per timeslot
level to per logical channel level, what makes OsmoBTS more
accurate in its measurements.
But before getting into details, it's important to clarify some
things about the Uplink burst processing in transceiver (OsmoTRX).
If an Uplink burst is detected, OsmoTRX demodulates it and sends
to OsmoBTS. If nothing is detected on a particular timeslot,
OsmoTRX will do nothing. In other words, it will not
notify OsmoBTS about this.
Meanwhile, there are usually a few logical channels mapped to a
single TDMA timeslot. Let's use SDCCH8 channel configuration as
an example (simplified layout):
/* SDCCH/8 (ss=0), subscriber A (active) */
{ TRXC_SDCCH8_0, bid=0 },
{ TRXC_SDCCH8_0, bid=1 },
{ TRXC_SDCCH8_0, bid=2 },
{ TRXC_SDCCH8_0, bid=3 }, // <-- last_fn=X
/* SDCCH/8 (ss=1), subscriber B (inactive) */
{ TRXC_SDCCH8_1, bid=0 },
{ TRXC_SDCCH8_1, bid=1 },
{ TRXC_SDCCH8_1, bid=2 },
{ TRXC_SDCCH8_1, bid=3 },
/* SDCCH/8 (ss=2), subscriber C (active) */
{ TRXC_SDCCH8_2, bid=0 }, // <-- current_fn=X+5
{ TRXC_SDCCH8_2, bid=1 },
{ TRXC_SDCCH8_2, bid=2 },
{ TRXC_SDCCH8_2, bid=3 },
SDCCH8 has 8 sub-slots, so up to 8 subscribers can use a single
timeslot. Let's imagine there are three subscribers: A, B, and C.
Both A and C are active subscribers, i.e. they are continuously
transmitting UL bursts, while B is not using ss=1 anymore.
The original way of TDMA frame loss tracking was the following:
- when an UL burst is received, store it's frame number in
the timeslot state structure (last_fn);
- when the next UL burst is received on same timeslot, compute
how many frames elapsed since the last_fn;
- if elapsed = (current_fn - last_fn) is lower than 10, then
iterate from (last_fn + 1) until the current_fn and send
dummy zero-filled bursts to the higher layers;
- otherwise (elapsed > 10), process the current burst,
and do nothing :/
According to our example, subscriber A is sending 4 bursts, then
nobody is sending anything, and then subscriber C is sending
4 bursts. So, there is a 4 frames long gap between the both
transmissions, which is being substituted by dummy bursts. But,
as the logical channel on ss=1 is not active, they are dropped.
This is not that scary, but the current algorithm produces lots
of false-positives, and moreover is not able to track real frame
drops in longer periods (i.e. >10). So, tracking the frame loss
per individual logical channels makes much more sense.
Let's finally drop this hackish 'while (42) { ... }', and track
the amount of lost / received TDMA frames (bursts) individually
per logical channels. Let's also use the multiframe period as
the loss detection period, instead of hardcoded 10. And finally,
let's print more informative debug messages.
Also, it makes sense to use the amount of lost / received bursts
during the calculation of the measurement reports, instead of
sending dummy bursts, but let's do this separately.
Change-Id: I70d05b67a35ddcbdd1b6394dbd7198404a440e76
Related: OS#3428
This patch adds scheduler support for the channel combinations that
substitute SDCCH index 2 for a CBCH in either a SDCCH/8 or SDCCH/4.
Change-Id: Icc15603079a1709ec094f400a9bcf0008211890f
Closes: OS#1617
Each logical channel (e.g. SACCH, SDCCH, etc.) has a counter of
lost L2 frames. Let's use a bit better name for it, and correct
its description in the 'l1sched_chan_state' struct definition.
Change-Id: I92ef95f6b3f647170cfd434a970701406b0a7c82
There's no need to express TOA as a float:
* We receive it as signed 16bit integer in units 1/256 symbol periods
* We pass it to L1SAP as signed integer in 1/4 symbol periods
So turn it into an int16_t with 1/256 symbol period accuracy throughout
the code to avoid both float arithmetic as well as loosing any precision.
Change-Id: Idce4178e0b1f7e940ebc22b3e2f340fcd544d4ec
There are use cases for the multiframe scheduler tables outside the
context of the entire scheduler. Let's prepare for that.
Related: OS#2978
Change-Id: I6a501e66c47809ae3cdc55bef2cb6390ee0096b1
For proper measurement processing of RX{LEV,QUAL}-SUB, we will
need this information.
Related: OS#2978
Change-Id: I768fde62452a74dce471ebf946e56eb1e4de1abc
Existing interfaces are coded with the implicit expectation of using
a burst sequence length of 148, which is constant with GSM and GPRS.
That changes with EGPRS, where the burst length may be 444 due to
the use of 8-PSK instead of GMSK modulation.
Setup the interface to accept and return a length value with the
burst sequence. This allows 444 length bit vectors to/from the
EGPRS decoder/encoder. Length is explicitly used as a identifier for
8-PSK vs. GMSK modulated sequences.
Change-Id: I90b46b46b11b6ce280e7f8232d5a2fccec2d4f18
Signed-off-by: Tom Tsou <tom.tsou@ettus.com>
Pau Espin
Vadim Yanitskiy
Philipp Maier
Vadim Yanitskiy
Harald Welte