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DFT-S-OFDM (DFT spread OFDM)

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Introduction

DFT-S-OFDM (Discrete Fourier Transform Spread Orthogonal Frequency Division Multiplexing) is a variant of OFDM (Orthogonal Frequency Division Multiplexing) that is used in wireless communication systems. The basic idea behind OFDM is to divide the available frequency spectrum into multiple subcarriers, each of which is orthogonal to the others. This allows multiple users to transmit data simultaneously over the same frequency band without interfering with each other.

However, the main disadvantage of traditional OFDM is its high peak-to-average power ratio (PAPR), which can lead to inefficient power amplification and reduced spectral efficiency. DFT-S-OFDM overcomes this issue by using a DFT (Discrete Fourier Transform) spreading technique that reduces the PAPR while maintaining the orthogonality of the subcarriers.

In this article, we will explore the basic principles of DFT-S-OFDM, its advantages over traditional OFDM, and its applications in wireless communication systems.

Principles of DFT-S-OFDM

DFT-S-OFDM uses a spreading technique that spreads the data symbols in the frequency domain using a DFT matrix. The basic idea is to convert the data symbols into the frequency domain using a DFT, and then spread the resulting frequency-domain symbols across multiple subcarriers.

The DFT matrix used in DFT-S-OFDM is an N x N matrix, where N is the number of subcarriers used in the OFDM system. Each row of the matrix corresponds to a particular subcarrier, and each column corresponds to a particular frequency component of the signal.

To spread the data symbols, the DFT matrix is first multiplied by the frequency-domain symbols. This results in a time-domain signal that is spread across multiple subcarriers. The resulting signal is then transmitted over the wireless channel using an OFDM system.

At the receiver, the signal is first demodulated using an OFDM demodulator to recover the frequency-domain symbols. The DFT matrix is then multiplied by the recovered symbols to undo the spreading process and recover the original data symbols.

Advantages of DFT-S-OFDM

DFT-S-OFDM has several advantages over traditional OFDM, including:

  1. Reduced PAPR: One of the main advantages of DFT-S-OFDM is its reduced PAPR compared to traditional OFDM. This is because the spreading process used in DFT-S-OFDM distributes the energy of the signal across multiple subcarriers, reducing the peak power of the signal. This makes it easier to amplify the signal efficiently, which can lead to improved spectral efficiency and reduced power consumption.
  2. Improved spectral efficiency: DFT-S-OFDM can also improve spectral efficiency compared to traditional OFDM. This is because the spreading process allows for a more efficient use of the available frequency spectrum. By spreading the data symbols across multiple subcarriers, DFT-S-OFDM can better utilize the available bandwidth, allowing for higher data rates and improved spectral efficiency.
  3. Low complexity: DFT-S-OFDM has a lower complexity compared to other PAPR reduction techniques, such as clipping and filtering. This is because the spreading process used in DFT-S-OFDM can be implemented efficiently using the fast Fourier transform (FFT) algorithm. This makes it easier to implement DFT-S-OFDM in practical wireless communication systems.

Applications of DFT-S-OFDM

DFT-S-OFDM has several applications in wireless communication systems, including:

  1. 5G wireless networks: DFT-S-OFDM is one of the key technologies used in 5G wireless networks. The reduced PAPR and improved spectral efficiency of DFT-S-OFDM make it well-suited for high-speed data transmission in 5G networks. DFT-S-OFDM is used in the 5G New Radio (NR) standard for both downlink and uplink transmission.
  2. Digital broadcasting: DFT-S-OFDM is also used in digital broadcasting systems, such as the Digital Audio Broadcasting (DAB) and Digital Video Broadcasting (DVB) standards. The reduced PAPR and improved spectral efficiency of DFT-S-OFDM make it well-suited for broadcasting applications, where a large number of users need to receive the same data simultaneously.
  3. Power line communication: DFT-S-OFDM is also used in power line communication (PLC) systems. PLC systems use the power lines in a building to transmit data, and DFT-S-OFDM is used to improve the reliability and efficiency of the communication over the power lines. The reduced PAPR and improved spectral efficiency of DFT-S-OFDM make it well-suited for PLC systems, which have limited bandwidth and high noise levels.

Conclusion

DFT-S-OFDM is a variant of OFDM that uses a spreading technique based on the DFT matrix to reduce the PAPR and improve the spectral efficiency of the signal. DFT-S-OFDM has several advantages over traditional OFDM, including reduced PAPR, improved spectral efficiency, and low complexity. DFT-S-OFDM has applications in 5G wireless networks, digital broadcasting, power line communication, and other wireless communication systems. As wireless communication systems continue to evolve, DFT-S-OFDM is likely to play an important role in improving the efficiency and reliability of these systems.