Satellite Data Rate Calculator
Calculate throughput based on bandwidth, modulation, and coding.
Typical Transponder: 36 MHz or 72 MHz
0.35 (DVB-S Legacy)
0.25 (DVB-S2 Typical)
0.20 (DVB-S2 Tight)
0.15 (DVB-S2X)
0.05 (DVB-S2X Aggressive)
Guard band overhead
BPSK (1 bit/symbol)
QPSK (2 bits/symbol)
8PSK (3 bits/symbol)
16APSK (4 bits/symbol)
32APSK (5 bits/symbol)
64APSK (6 bits/symbol)
256APSK (8 bits/symbol)
Spectral efficiency
1/4 (High Protection)
1/3
1/2
3/5
2/3
3/4 (Standard)
4/5
5/6
8/9
9/10 (Low Protection)
Ratio of data vs. total bits
Single Pol (SISO)
Dual Pol (Cross-Pol/MIMO)
Frequency reuse factor
Calculated Symbol Rate:
– Msps
Gross Data Rate (Air Rate):
– Mbps
Net Information Rate (IP Rate):
– Mbps
Understanding Satellite Link Budgets and Data Rates
Calculating the data rate of a satellite link involves understanding the relationship between the allocated spectrum (Bandwidth) and the efficiency with which data is packed into that spectrum (Spectral Efficiency). Unlike terrestrial fiber connections, satellite throughput is heavily defined by physics constraints, specifically the Shannon-Hartley theorem and DVB-S2/S2X standards.
Key Factors in Calculation
- Allocated Bandwidth (MHz): This is the slice of the frequency spectrum leased from the satellite operator (e.g., 36 MHz on a Ku-band transponder).
- Roll-off Factor (α): Satellite filters are not perfect squares. The roll-off factor determines the "guard band" required to prevent interference between adjacent carriers. A lower roll-off (e.g., 0.20 or 0.05 in DVB-S2X) allows for a higher symbol rate within the same bandwidth.
- Symbol Rate (Msps): This is the actual number of transmission events per second. It is calculated as
Bandwidth / (1 + Roll-off). - Modulation Scheme: Determines how many bits are represented by one symbol. For example, QPSK represents 2 bits per symbol, while 16APSK represents 4 bits. Higher modulation requires a stronger signal (higher C/N).
- FEC (Forward Error Correction): To overcome atmospheric attenuation (rain fade) and noise, redundant bits are added to the data stream. A 3/4 FEC rate means that for every 4 bits sent, 3 are data and 1 is for error correction.
How to Interpret the Results
Gross Data Rate is the total raw bit rate moving over the air interface. However, this is not your usable internet speed.
Net Information Rate is the actual usable throughput for IP traffic. This calculator derives the Net Rate by multiplying the Symbol Rate by the Modulation Order and the FEC rate. Note that additional Layer 2/3 overhead (MPE/GSE encapsulation) may slightly reduce the final speed experienced by the end-user.