Digital modulation is widely used in satellite communication systems, and there are three basic methods: Amplitude Shift Keying (ASK), Phase Shift Keying (PSK) and Frequency Shift Keying (FSK).
Satellite communication has the following requirements for digital modulation :
Do not advocate the use of ASK technology (poor anti-interference, high bit error rate);
Choose a modulation technique that occupies as little radio frequency band as possible, can efficiently utilize limited frequency band resources, and has strong anti-fading and interference performance;
The side lobes of the modulated signal used should be small to reduce interference between adjacent channels.
Common modulation methods
In order to meet the above requirements, the modulation methods used in the satellite system are PSK, FSK and other modulation methods based on this.
From a power efficient point of view, commonly used
Quadrature Phase Shift Keying (QPSK)
Offset Quadrature Phase Shift Keying (OQPSK), pi/4-DQPSK
Minimum Shift Keying (MSK), Gaussian Filtered Minimum Shift Keying (GMSK)
From a spectrum efficient point of view, commonly used
Multilevel Phase Shift Keying (MPSK)
Multi-ary Quadrature Amplitude Modulation (MQAM)
Trellis Coded Modulation (TCM)
Multi-Carrier Modulation (MCM)—OFDM
signal processing technology
Digital Voice Interpolation (DSI), echo control and speech coding have become the three most basic signal processing technologies in satellite communications. Using digital voice interpolation (DSI) technology, the transmission efficiency can be more than doubled.
Using echo control techniques in satellite links with long delays can attenuate or cancel the effects of echoes
Using speech coding technology, it can transmit speech at a lower transmission rate (≤16 kb/s)
speech signal interpolation
echo control
speech coding
Spectral Band Vocoder for Parametric Coding
multiple access technology
FDMA features:
FDMA method
TDMA
TDMA features:
ALOHA way
