Osmocom GSM/GPRS/EGPRS transceiver, originally forked from OpenBTS transceiver. For building SDR based GSM BTS with osmo-bts-trx.
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README

This is the interface to the transcevier.

Each TRX Manager UDP socket interface represents a single ARFCN.
Each of these per-ARFCN interfaces is a pair of UDP sockets, one for control and one for data.
Give a base port B (5700), the master clock interface is at port P=B.
The TRX-side control interface for C(N) is on port P=B+2N+1 and the data interface is on an odd numbered port P=B+2N+2.
The corresponding core-side interface for every socket is at P+100.
For any given build, the number of ARFCN interfaces can be fixed.



Indications on the Master Clock Interface

The master clock interface is output only (from the radio).
Messages are "indications".

CLOCK gives the current value of the transceiver clock to be used by the core.
This message is sent whenever a trasmission packet arrives that is too late or too early. The clock value is NOT the current transceiver time. It is a time setting the the core should use to give better packet arrival times.
IND CLOCK <totalFrames>



Commands on the Per-ARFCN Control Interface

The per-ARFCN control interface uses a command-reponse protocol.
Commands are NULL-terminated ASCII strings, one per UDP socket.
Each command has a corresponding response.
Every command is of the form:

CMD <cmdtype> [params]

The <cmdtype> is the actual command.
Parameters are optional depending on the commands type.
Every response is of the form:

RSP <cmdtype> <status> [result]

The <status> is 0 for success and a non-zero error code for failure.
Successful responses may include results, depending on the command type.


Power Control

POWEROFF shuts off transmitter power and stops the demodulator.
CMD POWEROFF
RSP POWEROFF <status>

POWERON starts the transmitter and starts the demodulator. Initial power level is very low.
This command fails if the transmitter and receiver are not yet tuned.
This command fails if the transmit or receive frequency creates a conflict with another ARFCN that is already runnng.
If the transceiver is already on, it response with success to this command.
CMD POWERON
RSP POWERON <status>

SETPOWER sets output power in dB wrt full scale.
This command fails if the transmitter and receiver are not running.
CMD SETPOWER <dB>
RSP SETPOWER <status> <dB>

ADJPOWER adjusts power by the given dB step. Response returns resulting power level wrt full scale.
This command fails if the transmitter and receiver are not running.
CMD ADJPOWER <dBStep>
RSP ADJPOWER <status> <dBLevel>


Tuning Control

RXTUNE tunes the receiver to a given frequency in kHz.
This command fails if the receiver is already running.
(To re-tune you stop the radio, re-tune, and restart.)
This command fails if the transmit or receive frequency creates a conflict with another ARFCN that is already runnng.
CMD RXTUNE <kHz>
RSP RXTUNE <status> <kHz>

TXTUNE tunes the transmitter to a given frequency in kHz.
This command fails if the transmitter is already running.
(To re-tune you stop the radio, re-tune, and restart.)
This command fails if the transmit or receive frequency creates a conflict with another ARFCN that is already runnng.
CMD TXTUNE <kHz>
RSP TXTUNE <status> <kHz>


Timeslot Control

SETSLOT sets the format of the uplink timeslots in the ARFCN.
The <timeslot> indicates the timeslot of interest.
The <chantype> indicates the type of channel that occupies the timeslot.
A chantype of zero indicates the timeslot is off.
CMD SETSLOT <timeslot> <chantype>
RSP SETSLOT <status> <timeslot> <chantype>


Messages on the per-ARFCN Data Interface

Messages on the data interface carry one radio burst per UDP message.


Received Data Burst

1 byte timeslot index
4 bytes GSM frame number, big endian
1 byte RSSI in -dBm
2 bytes correlator timing offset in 1/256 symbol steps, 2's-comp, big endian
148 bytes soft symbol estimates, 0 -> definite "0", 255 -> definite "1"


Transmit Data Burst

1 byte timeslot index
4 bytes GSM frame number, big endian
1 byte transmit level wrt ARFCN max, -dB (attenuation)
148 bytes output symbol values, 0 & 1