trx_toolkit/data_msg.py: remove obsolete documentation
We do have TRXC/TRXD documentation in osmo-gsm-manuals repository. These big comments are out of sync with what we have in the manuals, so let's better remove them to avoid maintaining docs in several places. Change-Id: I47786cf3039f712efadc85bc4e1c3ae89e79ff25 Related: OS#4006, SYS#4895
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@ -60,67 +60,7 @@ class Modulation(Enum):
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return None
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class DATAMSG(abc.ABC):
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""" TRXD (DATA) message codec (common part).
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The DATA messages are used to carry bursts in both directions
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between L1 and TRX. There exist two kinds of them:
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- L12TRX (L1 -> TRX) - to be transmitted bursts,
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- TRX2L1 (TRX -> L1) - received bursts.
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Both of them have quite similar structure, and start with
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the common fixed-size message header (no TLVs):
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+---------------+-----------------+------------+
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| common header | specific header | burst bits |
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+---------------+-----------------+------------+
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while the message specific headers and bit types are different.
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The common header is represented by this class, which is the
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parent of both DATAMSG_L12TRX and DATAMSG_TRX2L2 (see below),
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and has the following fields:
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+-----------------+----------------+-------------------+
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| VER (1/2 octet) | TN (1/2 octet) | FN (4 octets, BE) |
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+-----------------+----------------+-------------------+
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where:
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- VER is the header version indicator (1/2 octet MSB),
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- TN is TDMA time-slot number (1/2 octet LSB), and
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- FN is TDMA frame number (4 octets, big endian).
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== Header version indication
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It may be necessary to extend the message specific header
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with more information. Since this is not a TLV-based
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protocol, we need to include the header format version.
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+-----------------+------------------------+
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| 7 6 5 4 3 2 1 0 | bit numbers |
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+-----------------+------------------------+
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| X X X X . . . . | header version (0..15) |
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+-----------------+------------------------+
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| . . . . . X X X | TDMA TN (0..7) |
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+-----------------+------------------------+
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| . . . . X . . . | RESERVED (0) |
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+-----------------+------------------------+
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Instead of prepending an additional byte, it was decided to use
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4 MSB bits of the first octet, which used to be zero-initialized
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due to the value range of TDMA TN. Therefore, the legacy header
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format has implicit version 0x00.
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Otherwise Wireshark (or trx_sniff.py) would need to guess the
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header version, or alternatively follow the control channel
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looking for the version setting command.
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The reserved bit number 3 can be used in the future to extend
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the TDMA TN range to (0..15), in case anybody would need
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to transfer UMTS bursts.
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"""
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''' TRXD (DATA) message coding API (common part). '''
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# NOTE: up to 16 versions can be encoded
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CHDR_VERSION_MAX = 0b1111
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@ -289,26 +229,7 @@ class DATAMSG(abc.ABC):
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self.burst = None
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class DATAMSG_L12TRX(DATAMSG):
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""" L12TRX (L1 -> TRX) message codec.
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This message represents a Downlink burst on the BTS side,
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or an Uplink burst on the MS side, and has the following
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message specific fixed-size header preceding the burst bits:
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== Versions 0x00, 0x01
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+-----+--------------------+
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| PWR | hard-bits (1 or 0) |
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+-----+--------------------+
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where PWR (1 octet) is relative (to the full-scale amplitude)
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transmit power level in dB. The absolute value is set on
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the control interface.
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Each hard-bit (1 or 0) of the burst is represented using one
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byte (0x01 or 0x00 respectively).
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"""
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''' L12TRX (L1 -> TRX) message coding API. '''
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# Constants
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PWR_MIN = 0x00
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@ -435,95 +356,7 @@ class DATAMSG_L12TRX(DATAMSG):
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return msg
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class DATAMSG_TRX2L1(DATAMSG):
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""" TRX2L1 (TRX -> L1) message codec.
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This message represents an Uplink burst on the BTS side,
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or a Downlink burst on the MS side, and has the following
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message specific fixed-size header preceding the burst bits:
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== Version 0x00
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+------+-----+--------------------+
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| RSSI | ToA | soft-bits (254..0) |
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+------+-----+--------------------+
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== Version 0x01
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+------+-----+-----+-----+--------------------+
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| RSSI | ToA | MTS | C/I | soft-bits (254..0) |
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+------+-----+-----+-----+--------------------+
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where:
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- RSSI (1 octet) - Received Signal Strength Indication
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encoded without the negative sign.
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- ToA (2 octets) - Timing of Arrival in units of 1/256
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of symbol (big endian).
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- MTS (1 octet) - Modulation and Training Sequence info.
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- C/I (2 octets) - Carrier-to-Interference ratio (big endian).
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== Coding of MTS: Modulation and Training Sequence info
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3GPP TS 45.002 version 15.1.0 defines several modulation types,
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and a few sets of training sequences for each type. The most
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common are GMSK and 8-PSK (which is used in EDGE).
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+-----------------+---------------------------------------+
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| 7 6 5 4 3 2 1 0 | bit numbers (value range) |
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+-----------------+---------------------------------------+
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| X . . . . . . . | IDLE / nope frame indication (0 or 1) |
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+-----------------+---------------------------------------+
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| . X X X X . . . | Modulation, TS set number (see below) |
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+-----------------+---------------------------------------+
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| . . . . . X X X | Training Sequence Code (0..7) |
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+-----------------+---------------------------------------+
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The bit number 7 (MSB) is set to high when either nothing has been
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detected, or during IDLE frames, so we can deliver noise levels,
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and avoid clock gaps on the L1 side. Other bits are ignored,
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and should be set to low (0) in this case.
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== Coding of modulation and TS set number
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GMSK has 4 sets of training sequences (see tables 5.2.3a-d),
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while 8-PSK (see tables 5.2.3f-g) and the others have 2 sets.
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Access and Synchronization bursts also have several synch.
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sequences.
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+-----------------+---------------------------------------+
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| 7 6 5 4 3 2 1 0 | bit numbers (value range) |
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+-----------------+---------------------------------------+
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| . 0 0 X X . . . | GMSK, 4 TS sets (0..3) |
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+-----------------+---------------------------------------+
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| . 0 1 0 X . . . | 8-PSK, 2 TS sets (0..1) |
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+-----------------+---------------------------------------+
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| . 0 1 1 X . . . | AQPSK, 2 TS sets (0..1) |
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+-----------------+---------------------------------------+
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| . 1 0 0 X . . . | 16QAM, 2 TS sets (0..1) |
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+-----------------+---------------------------------------+
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| . 1 0 1 X . . . | 32QAM, 2 TS sets (0..1) |
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+-----------------+---------------------------------------+
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| . 1 1 1 X . . . | RESERVED (0) |
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+-----------------+---------------------------------------+
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== C/I: Carrier-to-Interference ratio
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The C/I value can be computed from the training sequence of each
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burst, where we can compare the "ideal" training sequence with
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the actual training sequence and then express that in centiBels.
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== Coding of the burst bits
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Unlike the transmitted bursts, the received bursts are designated
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using the soft-bits notation, so the receiver can indicate its
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assurance from 0 to -127 that a given bit is 1, and from 0 to +127
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that a given bit is 0. The Viterbi algorithm allows to approximate
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the original sequence of hard-bits (1 or 0) using these values.
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Each soft-bit (-127..127) of the burst is encoded as an unsigned
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value in range (0..255) respectively using the constant shift.
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"""
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''' TRX2L1 (TRX -> L1) message coding API. '''
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# rxlev2dbm(0..63) gives us [-110..-47], plus -10 dbm for noise
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RSSI_MIN = -120
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