The signal is orthogonal in the frequency domain, and each subcarrier does not interfere with the others. The peak of each subcarrier occurs at zero crossings of the others. Figure 5 shows a single OFDM carrier (the left plot) and multiple subcarriers (the right plot). That process provides better spectral efficiency than traditional digital modulation schemes, such as QAM and PSK, and robustness against channel linear distortion. OFDM uses many closely spaced orthogonal subcarrier signals to transmit data in parallel.

The technique has been adopted for many broadband wireless communication standards, such as 4G/5G, Wi-Fi, digital video broadcast for terrestrial and satellite communication systems. The orthogonal frequency-division multiplexing (OFDM) is a digital multi-carrier technique that possesses many unique advantages over single-carrier approaches. A designer can also reach a balance between lower peak-to-average power ratio (PAPR) and better resistance to distortion. There are several variable parameters for APSK modulation such as the number of rings, number of symbols on a ring, and spacing between rings. Constellation diagrams for APSK schemes and corresponding QAM formats Also, the higher output power creates more noise to the signal.įigure 4. Thus, nonlinear amplifiers require a modulation scheme tolerant to distortion. For example, the I/Q constellation outer points have higher output power levels, and the compression is because of the saturated output power in the RF power amplifier. Operating at compression levels causes AM/AM and AM/PM distortion, as shown in Figure 1. In satellite transmission, RF power amplifiers often operate at their compression levels to maximize conversion efficiency. The most fundamental digital modulation schemes are amplitude-shift keying (ASK), phase-shift keying (PSK), frequency-shift keying (FSK), and quadrature amplitude modulation (QAM). In digital modulation systems, a vector signal can be in changing the carrier signal’s magnitude, phase, or some combination of those. The Requirements of Satellite Communications This post discusses the modulation techniques for modern satellite communications. The modulation techniques for satellite communications require not only faster data rates but also minimizing the impacts of the channel impairments. However, satellite channel impairments such as large path losses, delays, and Doppler shifts pose severe challenges to the realization of a satellite network. With strong demand for faster data throughput, satellite communications use high-order modulation schemes to improve their spectral efficiency.

Comparison of ask fsk psk qpsk