SC (Single carrier)

Single Carrier (SC) refers to a modulation and transmission scheme used in communication systems to transmit data over a single channel or carrier frequency. It is an alternative to multi-carrier modulation schemes such as Orthogonal Frequency Division Multiplexing (OFDM). SC is designed to simplify the transmitter and receiver architecture, improve spectral efficiency, and provide better resistance to frequency selective fading channels.

In SC, the data stream is transmitted as a single continuous waveform, unlike OFDM where the data is divided into multiple subcarriers. The SC waveform typically consists of a stream of complex-valued symbols, where each symbol represents a group of bits. The symbol rate is determined based on the desired data rate and the characteristics of the channel.

The SC modulation process involves mapping the digital information to complex symbols, which are then converted into analog waveforms for transmission. The mapping can be achieved using various modulation techniques such as Phase Shift Keying (PSK), Quadrature Amplitude Modulation (QAM), or Amplitude and Phase Shift Keying (APSK). The choice of modulation scheme depends on factors such as the desired data rate, noise conditions, and available bandwidth.

One of the key advantages of SC is its simplicity. Unlike OFDM, which requires a complex Fast Fourier Transform (FFT) at the transmitter and receiver to convert between time and frequency domains, SC operates directly in the time domain. This reduces the complexity of the system and eliminates the need for a guard interval between symbols, which is necessary in OFDM to combat inter-symbol interference caused by multipath propagation.

The absence of guard intervals in SC makes it more efficient in terms of spectral efficiency. Since SC utilizes the entire available bandwidth for data transmission, it can achieve higher data rates for a given channel bandwidth compared to OFDM, where a portion of the bandwidth is dedicated to guard intervals.

Furthermore, SC can offer improved performance in frequency selective fading channels, where different frequencies experience different levels of attenuation and distortion. Due to its single-carrier nature, SC can mitigate the effect of frequency-selective fading by employing equalization techniques that compensate for the frequency-dependent channel response. This makes SC more robust in scenarios where the channel exhibits severe frequency-selective fading.

However, SC is more susceptible to frequency offset and phase noise compared to OFDM. Frequency offset occurs when the carrier frequency at the receiver deviates from the transmitter's carrier frequency, leading to inter-symbol interference. Phase noise refers to the random phase variations introduced by the transmitter and receiver components, which can degrade the demodulation process. These issues need to be carefully managed through techniques such as frequency synchronization and phase tracking.

In summary, Single Carrier (SC) is a modulation and transmission scheme that transmits data over a single carrier frequency. It offers simplicity, improved spectral efficiency, and better resistance to frequency selective fading channels. However, it is more vulnerable to frequency offset and phase noise compared to multi-carrier schemes like OFDM.