What are the benefits and drawbacks of using different modulation and coding schemes for SATCOM?

1 Analog modulation

Analog modulation is the simplest and oldest form of modulation, where the carrier wave is directly modulated by an analog signal, such as voice or video. The most common analog modulation schemes are amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). Analog modulation has the advantage of being easy to implement and compatible with legacy systems, but it also has several drawbacks for SATCOM. Analog modulation is susceptible to noise and interference, which degrade the quality of the signal. Analog modulation also requires a large bandwidth to transmit a given amount of information, which limits the number of channels and users that can share the same frequency band. Analog modulation is mostly used for broadcasting and low-data-rate applications, such as radio and TV.

2 Digital modulation

Digital modulation is the modern and dominant form of modulation, where the carrier wave is modulated by a discrete sequence of bits, representing digital data. The most common digital modulation schemes are amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK), and quadrature amplitude modulation (QAM). Digital modulation has the advantage of being more robust and efficient than analog modulation, as it can use error detection and correction techniques, and transmit more bits per symbol. Digital modulation also allows for higher data rates and more users per channel, by using multiple levels or dimensions of modulation. However, digital modulation also has some drawbacks for SATCOM. Digital modulation requires more complex and expensive hardware and software, and more power to maintain a given signal-to-noise ratio (SNR). Digital modulation also introduces quantization and synchronization errors, which affect the accuracy and timing of the signal. Digital modulation is used for most applications that require high-speed and reliable data transmission, such as internet, voice, and video.

3 Coding schemes

Coding schemes are methods of adding redundancy or error correction to the information bits, before or after modulation, to improve the reliability and efficiency of the transmission. Coding schemes can be classified into two main types: block codes and convolutional codes. Block codes divide the information bits into fixed-size blocks, and add extra bits to each block, based on a predefined algorithm. Convolutional codes process the information bits as a continuous stream, and add extra bits based on the previous bits, using a sliding window. Coding schemes have the benefit of reducing the bit error rate (BER) and increasing the SNR of the signal, by allowing the receiver to detect and correct errors caused by noise and interference. Coding schemes also enable the use of adaptive modulation and coding (AMC), where the modulation and coding parameters are adjusted according to the channel conditions, to optimize the throughput and quality of service. However, coding schemes also have some drawbacks for SATCOM. Coding schemes introduce a trade-off between bandwidth and power, as adding more redundancy increases the bandwidth requirement, but reduces the power requirement, and vice versa. Coding schemes also introduce a trade-off between latency and complexity, as adding more redundancy increases the delay and computation involved in encoding and decoding the signal. Coding schemes are used for most applications that require high reliability and efficiency, such as military, scientific, and commercial communications.

4 Here’s what else to consider

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