Configuring Payload Transmission Mode

Popoto Modems support a family of payload transmission modes designed to operate across a wide range of underwater acoustic channel conditions. All coherent modes share the same occupied bandwidth and symbol rate and use a common 1/2-rate convolutional Forward Error Correction, FEC, code.

Select a mode based on the available signal-to-noise ratio, range, multipath, platform motion, and interoperability requirements.

For payload rates of 2560 bps and below, BPSK is recommended for new applications because it generally provides greater robustness than QPSK. Use QPSK_5120bps for high-rate, short-range operation and FH_80bps when maximum low-SNR robustness is required.

Robustness is controlled through repetition coding. Lower bitrates correspond to higher redundancy and increased tolerance to low-SNR, multipath, or Doppler-degraded environments.

An additional uncoded QPSK mode is provided for advanced users who want to apply external error-correction schemes. A frequency-hopped FSK mode provides extreme robustness in the lowest-SNR environments.

This section covers:

• Configurable parameters for tuning the PSK receiver equalizer
• PayloadMode enumeration, including supported values and mode families
• Coding structure for coherent, uncoded QPSK, and FH-FSK modes
• Recommended modulation use based on operating conditions
• Measured SNR waterfall thresholds observed in representative coastal environments