What is satellite throughput?
Throughput is the net rate at which useful data is successfully transferred through a satellite communication system — what the user actually receives, as opposed to the raw channel capacity. While a Ka-band HTS carrier might have a raw symbol rate of 1 Gbps, actual user throughput is lower due to modulation overhead, forward error correction (FEC) redundancy, protocol headers, and TCP efficiency limitations imposed by satellite latency.
Factors limiting throughput
FEC overhead: DVB-S2X with QPSK 1/2 (used in heavy rain) spends half the channel capacity on error correction — net throughput is 50% of raw rate. With 32APSK 9/10 in clear sky, FEC overhead is only 11%. TCP window size: Standard TCP limits the amount of unacknowledged data in flight, which becomes the binding constraint over high-latency GEO links. Without Performance Enhancing Proxies (PEP), a GEO link with 600 ms RTT might deliver only 5–10% of available bandwidth to a standard TCP connection. Contention: In shared VSAT networks, multiple users share available return link capacity — each user's allocated throughput depends on total network load. Committed Information Rate (CIR) guarantees are specified to protect minimum throughput for enterprise customers.
Measurement standards
Throughput testing uses standardised tools (iperf3, speedtest.net, Netflix FAST) that measure TCP and UDP performance separately. For satellite SLA compliance, operators measure sustained throughput over 30-second intervals at specified times of day and averaging periods. SpeedTest data from 2025 shows Starlink achieving median download throughput of 150–220 Mbps globally, compared to 25–75 Mbps for GEO Ka-band broadband services.