SC-OFDM Single Carrier -OFDM

Single Carrier Orthogonal Frequency Division Multiplexing (SC-OFDM) is a modulation scheme used in digital communication systems to transmit data over wireless or wired channels. It is derived from the more commonly used Orthogonal Frequency Division Multiplexing (OFDM) modulation technique. SC-OFDM offers several advantages over traditional OFDM, including reduced complexity and improved spectral efficiency.

To understand SC-OFDM, let's first review the basic concepts of OFDM. OFDM divides the available frequency spectrum into multiple subcarriers, each carrying a lower-rate data stream. These subcarriers are orthogonal to each other, meaning they do not interfere with each other. This orthogonality allows multiple subcarriers to be transmitted simultaneously, thereby increasing the overall data rate.

In OFDM, the subcarriers are typically orthogonalized using the Inverse Fast Fourier Transform (IFFT) at the transmitter and Fast Fourier Transform (FFT) at the receiver. This process converts the data symbols into the time domain, where they are transmitted as a series of overlapping time-domain signals. At the receiver, the FFT operation converts the received time-domain signals back into the frequency domain, allowing the individual subcarriers to be extracted and demodulated.

Now, let's delve into SC-OFDM and its key differences from OFDM:

1. Single Carrier Transmission: In SC-OFDM, unlike traditional OFDM, the data symbols are transmitted using a single carrier waveform instead of multiple carriers. This means that instead of using multiple subcarriers, a single wideband subcarrier is used to carry the entire data stream. By transmitting the data on a single carrier, SC-OFDM simplifies the implementation and reduces the complexity of the receiver.
2. Filtering and Equalization: SC-OFDM employs filtering and equalization techniques to combat the frequency selectivity of the channel. Since a single carrier is used, the channel's frequency response may introduce severe distortion due to multipath fading and interference. To mitigate these effects, SC-OFDM employs a filter at the transmitter to shape the transmitted waveform, and an equalizer at the receiver to compensate for the channel distortion.
3. Cyclic Prefix: Similar to OFDM, SC-OFDM utilizes a cyclic prefix to combat the inter-symbol interference (ISI) caused by multipath propagation. The cyclic prefix is a copy of the end portion of the OFDM symbol that is appended to the beginning. It provides a guard interval, allowing the receiver to remove the ISI and recover the transmitted symbols.
4. Spectral Efficiency: SC-OFDM offers improved spectral efficiency compared to OFDM in certain scenarios. Since SC-OFDM transmits on a single carrier, it eliminates the need for guard bands between adjacent subcarriers, reducing the spectral overhead. This allows more efficient utilization of the available frequency spectrum and potentially higher data rates.
5. Peak-to-Average Power Ratio (PAPR): One of the challenges in OFDM systems is the high PAPR, which occurs when multiple subcarriers add constructively and result in high peak power levels. SC-OFDM mitigates this issue as it only uses a single carrier, leading to a lower PAPR and simplifying power amplification requirements.

In summary, SC-OFDM is a modulation scheme that utilizes a single carrier waveform to transmit data, unlike traditional OFDM systems that employ multiple subcarriers. It reduces complexity, improves spectral efficiency, and addresses challenges such as inter-symbol interference and PAPR associated with OFDM. SC-OFDM finds applications in various communication systems, including wireless broadband, digital audio/video broadcasting, and 4G/5G cellular networks.