DVB Standards & C/N Reference
Every MODCOD, Its Threshold, and What the Numbers Actually Mean

1. Scope and sources

Every figure on this page was read from the published standard, not from a secondary table. The two documents that matter are ETSI EN 302 307-1 V1.4.1 (2014-11) for DVB-S2 and ETSI EN 302 307-2 V1.4.1 (2024-08) for DVB-S2X. Both were downloaded from the ETSI portal and parsed directly; the version numbers were confirmed against the ETSI directory rather than assumed.

Terrestrial and cable C/N thresholds also depend far more on channel model than satellite ones do. A satellite link is close to AWGN; a terrestrial one is a multipath channel where the required C/N for the same modulation and code rate can differ by several decibels between a fixed-roof and a portable-indoor reception model. A single number per mode is meaningful for satellite in a way it is not for terrestrial.

2. Es/N0, Eb/N0 and C/N — the distinction that costs money

These three are used interchangeably in conversation and are not interchangeable in arithmetic. Confusing them is the most common way a link budget comes out wrong by two or three decibels, which at Ku band is the difference between two antenna sizes.

The conversion between the first two is given in the note under Table 13 itself:

where η_tot is the spectral efficiency in bits per symbol. The sign matters and catches people out. For a high-efficiency mode η > 1, so Eb/N0 is lower than Es/N0. For a strong low-rate code η < 1 and Eb/N0 is higher. Worked from the table's own numbers:

QPSK 1/4 is the instructive row: a negative Es/N0 of −2,35 dB and a positive Eb/N0 of +0,75 dB describe the same link. The carrier really can sit below the noise floor and still be decoded, because each information bit is spread across more than two symbols. Anyone who says "you cannot receive a signal below the noise floor" is thinking in Eb/N0 while reading an Es/N0 number.

For C/N, the relationship to Es/N0 depends on the bandwidth you measure in. Measured in a bandwidth equal to the symbol rate, C/N and Es/N0 are numerically the same. Measured in the occupied bandwidth — symbol rate times one plus roll-off — C/N is lower by 10·log₁₀(1 + α):

3. What "works" means — the QEF definition

Every threshold on this page is the point at which the system reaches Quasi-Error-Free operation. That phrase has a precise definition in EN 302 307-1, and it is not "no errors":

Two consequences that matter operationally. First, the target is tied to a 5 Mbit/s service — a higher-bitrate service passes more packets per hour, so the same PER produces more error events. Second, QEF is a threshold with a cliff below it: LDPC coding means performance does not degrade gracefully. A link half a decibel above threshold is perfect; half a decibel below it fails almost completely. There is very little of the gradual picture degradation that analogue and even DVB-S exhibited.

4. Why these are "ideal" figures, and what to add

This is the caveat that most reproductions of these tables drop, and it is the difference between a table and a link budget. EN 302 307-1 states the conditions under which its numbers were obtained:

The standard is explicit about the conclusion: "For calculating link budgets, specific satellite channel impairments should be taken into account." In other words the table gives you a floor, and the implementation margin plus channel impairments plus rain fade allowance sit on top of it. Treating an ideal Es/N0 as a design threshold produces a link that works in clear sky and fails on the first weather event.

5. DVB-S2 — the complete Table 13

All 28 modes, transcribed from EN 302 307-1 V1.4.1 Table 13. Es/N0 at QEF, PER = 10⁻⁷, AWGN, FECFRAME length 64 800, no pilots. Decimal commas are as printed in the standard.

6. DVB-S2X — the extended modes

From EN 302 307-2 V1.4.1 Table 20a. Es/N0 at QEF, FER = 10⁻⁵, normal FECFRAMEs, 50 iterations. The second figure is the informative non-linear hard-limiter channel result — the same mode through a saturated transponder, at optimised input back-off and 10 % roll-off.

Three things to read out of this table:

• The -L suffix means linear. Those MODCODs use constellations optimised for a linear channel. Compare 16APSK 3/5 and 16APSK 3/5-L: identical spectral efficiency, but the linear variant needs 0,39 dB less on a linear channel and 0,56 dB more through a hard limiter. The choice depends on whether your transponder runs near saturation.
• The non-linear penalty grows with constellation order. QPSK 2/9 loses 0,4 dB through the hard limiter; 16APSK 1/2-L loses 2,4 dB; 256APSK 3/4 loses 4,45 dB. Amplitude-modulated constellations suffer when the amplifier compresses, which is why high-order APSK belongs on a lightly-loaded transponder or a linearised chain.
• The finer code-rate granularity is the practical gain. S2 jumps from 8PSK 2/3 (6,62 dB) to 8PSK 3/4 (7,91 dB) — a 1,3 dB gap you must either waste or fall through. S2X fills it with 8PSK 23/36, 25/36 and 13/18 at 6,12, 7,02 and 7,49 dB. On a link that varies with weather, that granularity converts directly into available hours.

7. Very Low SNR modes

S2X adds modes for links that DVB-S2 simply cannot close, using π/2 BPSK and very low code rates. From Tables 20b and 20c of EN 302 307-2 V1.4.1, at FER = 10⁻⁵:

The medium and short XFECFRAME tables use 75 decoding iterations rather than 50 for the BPSK modes — more decoder work traded for threshold. At −9,9 dB the carrier is nearly ten decibels below the noise, which is what makes very small terminals, deep rain fade operation and emergency links feasible at all.

8. From symbol rate to bitrate and bandwidth

Two relationships turn a MODCOD into the numbers you actually need. Both come straight from the table's own definitions.

Worked examples, computed from the table values above:

The first row is a real transponder configuration referenced elsewhere on this site — 35 300 ksym/s, FEC 2/3, DVB-S2 8PSK — which works out to roughly 70 Mb/s of usable transport stream in about 42 MHz, needing at least 6,62 dB before any margin. The last row is the same arithmetic at the other extreme: a narrow 5 Msym/s carrier delivering 2,45 Mb/s but closing at −2,35 dB.

The bitrate figure is the transport stream rate, which is what you compare against the numbers tsbitrate reports. If a measured stream rate does not match the arithmetic above, either the symbol rate, the code rate, or the pilot setting is not what you were told.

9. The standards family

Every version below was confirmed against the ETSI portal while preparing this sheet. Where a standard is old, that is because it is stable, not because it is superseded — DVB-S from 1997 still carries services today.

9.1 DVB-T2 structural parameters

From EN 302 755 V1.4.1. These are specified values, unlike the C/N thresholds:

10. Margin — what to add to a table figure

The tables give an ideal threshold. A design threshold is that plus everything the simulation excluded. The components are well known even though their magnitudes are installation-specific, and the honest position is to measure them rather than assume a rule of thumb.

For a service where continuity matters more than efficiency, there is a structural alternative to buying margin in decibels: receive the same transponder at more than one site and fail over between them. That trades RF margin for geographic diversity, which addresses rain fade — a local phenomenon — in a way that no amount of coding gain at a single site can. The TSDuck cookbook covers the mechanics with tsswitch, and the tuner sheet covers how the sources differ.

11. Standards and sources

• ETSI Standards portal — EN 302 307-1, EN 302 307-2, EN 302 755 and the rest of the family
• DVB Project — specification index and status
• MPEG Transport Stream Explained — the container these carriers deliver
• The TSDuck Cookbook — measuring the bitrate this page predicts
• Locked vs Unlocked SAT>IP Virtual Tuners
• SATLINE.TV Virtual SAT>IP Servers

12. About the author