Block Diagram of SC-OFDM:
Data → Modulation → DFT → IFFT → Add CP → Transmit
Received Signal → Remove CP → FFT → Demodulation → Data
Key Features of SC-OFDM:
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Single Carrier Modulation:
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Unlike traditional OFDM, which uses multiple subcarriers to transmit data, SC-OFDM uses a single carrier for each block of data. This reduces the complexity and makes it more power-efficient in certain contexts.
In OFDM / OFDMA, the data bitstream is first converted from serial to parallel blocks, each block of symbols is modulated and directly assigned to distinct subcarriers, then those are passed through an IFFT (or IDFT) to produce a time-domain signal. After that, a cyclic prefix is appended before transmission.
In contrast, SC‑FDMA (a.k.a. DFT-spread OFDM or SC-OFDM in uplink context) includes an extra DFT precoding stage applied to the modulated symbol stream (without serial-to-parallel conversion). This spreads each data symbol across multiple frequencies. But uses single wideband carrier.
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Reduced PAPR:
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One of the advantages of SC-OFDM over standard OFDM is its lower peak-to-average power ratio (PAPR). This is crucial for power efficiency, especially in wireless communication where high PAPR can lead to more power consumption, higher interference, and reduced battery life in mobile devices.
- You can observe that for a typical OFDM signal, the sample amplitudes fluctuate more than those of SC‑OFDM. Thus, the peak‑to‑average power ratio (PAPR) of OFDM is high, which makes it less efficient in terms of signal‑transmission power and amplifier usage.
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Spectral Efficiency:
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SC-OFDM can offer improved spectral efficiency in certain conditions compared to OFDM due to its use of single-carrier transmission and frequency domain equalization.
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Applications:
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SC-OFDM is used in 5G New Radio (NR) for uplink transmission. In particular, it is useful for low-latency communication, where minimizing the power consumption of the uplink signal is crucial.
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It is also applied in systems with frequency-selective channels.
Advantages of SC-OFDM:
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Lower PAPR: This is a major advantage, especially in wireless communication systems where power consumption is a critical factor.
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Reduced Interference: By using a single carrier for transmission, SC-OFDM is less prone to out-of-band emissions and other forms of interference.
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Better for Uplink: In cellular systems like 5G, SC-OFDM is highly advantageous for uplink transmission, where power consumption and spectral efficiency are critical.
SC-OFDM in 5G:
SC-OFDM is used in 5G's uplink due to its lower PAPR and spectral efficiency. It enables faster data rates and more efficient power usage in devices like smartphones and IoT devices, especially when sending data in high-mobility environments.