Also known as: DMR burst, TDMA burst, DMR timeslot burst
A DMR burst is the fundamental transmission unit of DMR: the 264 bits (132 dibits) one TDMA timeslot sends in its 27.5 ms of a 30 ms frame.1 Every burst has the same skeleton — two 98-bit payload halves wrapped around a central 48-bit field — and that central field is what distinguishes a data/control burst (which puts a sync word or slot type there) from a voice burst (which puts embedded signalling there).2
Burst layout
GopherTrunk models the burst in internal/radio/dmr/burst.go as 132 dibits. For a
data/control burst the ETSI TS 102 361-1 §6.2 / §6.4.2 layout is:
| Dibits | Bits | Field |
|---|---|---|
| 0–48 | 98 | info[0] — first payload half |
| 49–53 | 10 | slot type, before sync |
| 54–77 | 48 | sync word or embedded signalling |
| 78–82 | 10 | slot type, after sync |
| 83–131 | 98 | info[1] — second payload half |
The two 98-bit info halves are read out and concatenated (Burst.PayloadBits) into the
196-bit BPTC(196,96) codeword that carries a
CSBK, voice link-control header, or data block. The two 10-bit slot-type
fields around the sync concatenate into a 20-bit slot-type
codeword (Burst.SlotTypeBitsAll). Splitting the payload in half and placing the sync and
slot type between the halves is deliberate: it puts the most reliably-recovered fields — the
sync landmark and the FEC-heavy slot type — at the burst’s centre, where a receiver that has
locked the sync is best synchronised, and it spreads the 196 payload bits symmetrically around
that anchor so a timing slip at either edge damages only one half.
Voice bursts differ
A voice burst carries no slot-type fields. Its split is 108 + 48 + 108 bits: three 72-bit AMBE+2 voice frames plus the central 48-bit field. The voice information reclaims the 20 bits the data burst spent on slot type, so the same 264-bit envelope holds more speech. In burst A of a voice superframe the central field is a voice sync word; in bursts B–F it holds embedded signalling instead — a 16-bit EMB framing a 32-bit fragment — which is why only burst A produces a sync match and the rest are located by TDMA cadence. A burst is thus self-describing only in part: the sync word and slot type identify a data burst outright, but a voice burst past the first is recognised by its position in the cadence, not by anything in the burst itself.
Relevance to SDR
Burst and its accessors are the seam between GopherTrunk’s dibit-level demodulator and its
protocol decoders. FirstHalf/SecondHalf, Sync, SlotTypeBefore/SlotTypeAfter, and the
PayloadBits/SlotTypeBitsAll bit-packers give every downstream layer — sync detection, slot
type, BPTC, embedded LC — a consistent view of the same 132 dibits. The same file also carries
the polarity machinery (RotateBurstDibits, CandidatePolarities) that lets a burst be
re-decoded at the flipped polarity a spectrum-inverted front end imprints, so the burst is the
natural place both the clean and inverted decode paths converge.
Sources
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Digital mobile radio — Wikipedia, on the DMR standard and its burst/timeslot structure. ↩
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Time-division multiple access — Wikipedia, on the two-slot TDMA framing DMR bursts occupy. ↩