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Single-carrier FDMA
Single-carrier FDMA
Single-carrier FDMA
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Single-carrier FDMA (SC-FDMA) is a frequency-division multiple access scheme. Originally known as Carrier Interferometry, it is also called linearly precoded OFDMA (LP-OFDMA). Like other multiple access schemes (TDMA, FDMA, CDMA, OFDMA), it deals with the assignment of multiple users to a shared communication resource. SC-FDMA can be interpreted as a linearly precoded OFDMA scheme, in the sense that it has an additional DFT processing step preceding the conventional OFDMA processing.

SC-FDMA has drawn great attention as an attractive alternative to OFDMA, especially in the uplink communications where lower peak-to-average power ratio (PAPR) greatly benefits the mobile terminal in terms of transmit power efficiency and reduced cost of the power amplifier. This is where SC-FDMA gets its name from: it's an OFDM signal that mimics the characteristics of a single-carrier QAM signal.[1] It has been adopted as the uplink multiple access scheme in 3GPP Long Term Evolution (LTE), or Evolved UTRA (E-UTRA).[2][3][4]

The performance of SC-FDMA in relation to OFDMA has been the subject of various studies.[5][6][7] Although the performance gap is small, SC-FDMA's advantage of low PAPR makes it desirable for uplink wireless transmission in mobile communication systems, where transmitter power efficiency is of paramount importance.

Transmitter and receiver structure

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The transmission processing of SC-FDMA is very similar to that of OFDMA. For each user, the sequence of bits transmitted is mapped to a complex constellation of symbols (BPSK, QPSK, or M-QAM). Then different transmitters (users) are assigned different Fourier coefficients. This assignment is carried out in the mapping and demapping blocks. The receiver side includes one demapping block, one IDFT block, and one detection block for each user signal to be received. Just like in OFDM, guard intervals (called cyclic prefixes) with cyclic repetition are introduced between blocks of symbols in view to efficiently eliminate inter-symbol interference from time spreading (caused by multi-path propagation) among the blocks.

In SC-FDMA, multiple access among users is made possible by assigning different users different sets of non-overlapping Fourier coefficients (sub-carriers). This is achieved at the transmitter by inserting (prior to IDFT) silent Fourier coefficients (at positions assigned to other users), and removing them on the receiver side after the DFT.

Localized and distributed mapping

The distinguishing feature of SC-FDMA is that it leads to a single-carrier transmit signal, in contrast to OFDMA which is a multi-carrier transmission scheme. Subcarrier mapping can be classified into two types: localized mapping and distributed mapping. In localized mapping, the DFT outputs are mapped to a subset of consecutive subcarriers, thereby confining them to only a fraction of the system bandwidth. In distributed mapping, the DFT outputs of the input data are assigned to subcarriers over the entire bandwidth non-continuously, resulting in zero amplitude for the remaining subcarriers. A special case of distributed SC-FDMA is called interleaved SC-FDMA (IFDMA), where the occupied subcarriers are equally spaced over the entire bandwidth.[8]

Owing to its inherent single carrier structure, a prominent advantage of SC-FDMA over OFDM and OFDMA is that its transmit signal has a lower peak-to-average power ratio (PAPR), resulting in relaxed design parameters in the transmit path of a subscriber unit. Intuitively, the reason lies in the fact that where OFDM transmit symbols directly modulate multiple sub-carriers, SC-FDMA transmit symbols are first processed by an N-point DFT block.[9]

In OFDM, as well as SC-FDMA, equalization is achieved on the receiver side, after the DFT calculation, by multiplying each Fourier coefficient by a complex number. Thus, frequency-selective fading and phase distortion can be easily counteracted. The advantage is that frequency domain equalization using FFTs requires less computation than conventional time-domain equalization, which require multi-tap FIR or IIR-filters. Less computations result in less compounded round-off error, which can be viewed as numerical noise.

A related concept is the combination of a single carrier transmission with the single-carrier frequency-domain-equalization (SC-FDE) scheme.[10] The single carrier transmission, unlike SC-FDMA and OFDM, employs no IDFT or DFT at the transmitter, but introduces the cyclic prefix to transform the linear channel convolution into a circular one. After removing the cyclic prefix at the receiver, a DFT is applied to arrive in the frequency domain, where a simple single-carrier frequency-domain-equalization (SC-FDE) scheme can be employed, followed by the IDFT operation.

Useful properties

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  1. Low PAPR (crest factor)
  2. Low sensitivity to carrier frequency offset
  3. Less sensitive to non-linear distortion and hence, it allows the use of low-cost power amplifiers
  4. Greater robustness against spectral nulls

See also

[edit]

References

[edit]
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Single-carrier FDMA

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Single-carrier (SC-FDMA) is a multiple access technique employed in wireless communication systems, particularly as the uplink transmission scheme in Long-Term Evolution (LTE) networks. It achieves multi-user by applying () precoding to modulation symbols before () modulation, thereby inheriting the low peak-to-average power ratio (PAPR) properties of single-carrier signals while enabling efficient spectrum sharing among users. This hybrid structure supports both localized (contiguous subcarrier allocation) and distributed (interleaved subcarrier allocation) mapping schemes, with the former preferred in LTE for its robustness to carrier frequency offsets. SC-FDMA was standardized by the 3rd Generation Partnership Project () in LTE Release 8, completed in 2008, as a response to the power efficiency demands of battery-limited , where traditional OFDMA's high PAPR leads to inefficient amplification and reduced coverage. Its development traces back to earlier single-carrier frequency-domain equalization (SC/FDE) concepts from the 1990s, which evolved to address multicarrier limitations in uplink scenarios. In LTE, SC-FDMA operates with subcarrier spacings of 15 kHz, resource blocks spanning 12 subcarriers over 0.5 ms slots, and supports modulation schemes like QPSK and 16-QAM alongside turbo coding for error correction. The transmitter in an SC-FDMA system processes blocks of N data symbols via an N-point DFT, maps the results to a of M (M > N) OFDM subcarriers, applies an M-point inverse DFT (IDFT), and inserts a cyclic prefix to combat inter-symbol interference. At the receiver, the cyclic prefix is removed, followed by DFT, one-tap frequency-domain equalization per subcarrier, demapping, and an N-point IDFT to recover the symbols. Key advantages include a PAPR reduction of approximately 1.5–2 dB relative to OFDMA, enabling higher power efficiency and extended battery life, though it may underperform OFDMA in high-modulation-order scenarios due to limited frequency diversity. Overall, SC-FDMA balances , robustness to channel impairments, and power constraints, making it a foundational element in modern cellular uplinks.

Introduction

Definition and Overview

Single-carrier frequency division multiple access (SC-FDMA) is a multiple access technique that combines the principles of single-carrier transmission with (FDMA), enabling multiple users to share a by allocating disjoint frequency sub-bands to each user, where each sub-band is modulated using a single-carrier signal. This hybrid approach maintains the low peak-to-average power ratio (PAPR) inherent to single-carrier systems while providing the and flexibility of FDMA for uplink communications in networks. Adopted in standards such as LTE for the uplink, SC-FDMA allows efficient power usage in mobile devices by avoiding the high PAPR challenges of multi-carrier alternatives like OFDMA. At its core, SC-FDMA operates by processing user data symbols in the time domain, which are then transformed into the frequency domain for allocation to specific subcarriers, ensuring that the transmitted signal resembles a single-carrier waveform shifted to the assigned frequency band rather than a multi-carrier superposition. This mechanism begins with grouping modulation symbols (e.g., from QPSK, 16QAM, or 64QAM) into blocks, applying a discrete Fourier transform (DFT) to convert them to the frequency domain, mapping the resulting frequency components to a subset of available subcarriers, and then performing an inverse DFT (IDFT) to generate the time-domain signal, followed by cyclic prefix addition for multipath mitigation. The receiver reverses this process with frequency-domain equalization to detect the symbols, preserving orthogonality among users through disjoint subcarrier assignments. A key distinction from traditional FDMA lies in the incorporation of DFT precoding (also known as DFT-spread), which spreads the data across subcarriers in a way that avoids the high PAPR typical of multi-carrier systems, resulting in a PAPR closer to that of the original single-carrier modulation—approximately 3 dB lower than equivalent OFDMA signals at low probability levels. This ensures that each user's signal maintains a continuous within its allocated sub-band, promoting better power amplifier efficiency without the peak power excursions of parallel subcarrier transmissions in pure FDMA variants adapted for multi-carrier use. Overall, the high-level signal flow—from time-domain symbol generation through frequency mapping and back to time-domain transmission—facilitates robust multiple access while prioritizing low-complexity, power-efficient operation.

Historical Development

The concept of (FDMA) originated in the first-generation () analog cellular systems of the late 1970s and 1980s, where the available spectrum was divided into discrete frequency channels to support multiple users simultaneously. The (AMPS), launched commercially in the United States in 1983, represented a landmark implementation of analog FDMA, utilizing 30 kHz channels for voice communications across a 824-849 MHz uplink and 869-894 MHz downlink band, with frequency reuse patterns to mitigate interference. This approach enabled the foundational infrastructure for but was limited by analog modulation's susceptibility to noise and . As cellular networks transitioned to digital technologies in the 1990s with second-generation () systems, single-carrier transmission techniques evolved alongside FDMA to incorporate error correction and digital encoding, though TDMA and CDMA became more prevalent for multiple access. Early digital single-carrier FDMA variants appeared in systems like the Japanese Personal Digital Cellular (PDC) standard, which used single-carrier π/4-DQPSK modulation with FDMA channel allocation starting in 1993, offering improved over analog predecessors. These developments laid groundwork for applications, emphasizing single-carrier's inherent low peak-to-average power ratio (PAPR) for efficient transmitter design. The modern form of single-carrier FDMA (SC-FDMA), also termed DFT-spread OFDMA, emerged in the early 2000s through research aimed at uplink efficiency in orthogonal frequency-division multiple access (OFDMA)-based systems. This hybrid scheme applies a discrete Fourier transform (DFT) precoding to single-carrier symbols before OFDMA mapping, enabling frequency-domain multiple access while retaining single-carrier benefits like reduced PAPR. A pivotal contribution came from Myung et al. in their 2006 analysis, which demonstrated SC-FDMA's superior throughput and lower PAPR (approximately 2-4 dB less than OFDMA) for uplink scenarios, making it suitable for power-limited user equipment. This innovation addressed the limitations of multi-carrier OFDM in mobile uplinks, where high PAPR strained battery life and amplifier efficiency. Standardization accelerated SC-FDMA's adoption, with the 3rd Generation Partnership Project () selecting it as the primary uplink waveform for Long Term Evolution (LTE) in Release 8, finalized in 2008, to support data rates up to 50 Mbps in 20 MHz bandwidth. The choice was driven by SC-FDMA's balance of performance and complexity, allowing frequency-selective scheduling similar to downlink OFDMA while minimizing uplink power consumption. Subsequent enhancements appeared in LTE-Advanced (Release 10, 2011), incorporating with SC-FDMA. In 5G New Radio (NR), standardized by in Release 15 (2018), DFT-s-OFDM—functionally equivalent to SC-FDMA—was retained as an optional uplink mode alongside CP-OFDM, particularly for coverage extension in low-power scenarios, with provisions for up to 256-point DFT sizes. This progression reflected ongoing priorities for energy-efficient mobile communications amid increasing data demands.

Principles of Operation

Frequency Division Multiple Access Basics

(FDMA) is a multiple access technique that enables multiple users to share a by dividing the available bandwidth into non-overlapping bands, each assigned to a specific user for simultaneous transmission. This division allows users to transmit continuously without , ensuring orthogonal access through spectrally separated channels. To prevent interference between adjacent channels, small guard bands—unused gaps—are inserted between the allocated bands, which, while consuming some , are essential for maintaining in practical systems. In FDMA systems, is managed by the , which assigns sub-bands to users either in a fixed manner during call setup or dynamically based on traffic demand to optimize utilization. Fixed assignment provides and predictability but can lead to inefficiency for bursty data traffic, whereas dynamic assignment adapts allocations in real-time to accommodate varying user needs. The minimum channel separation required for , denoted as Δf\Delta f, is given by Δf=1/Ts\Delta f = 1/T_s, where TsT_s is the duration, ensuring that the bands do not overlap and thus avoiding inter-user interference. Interference management in FDMA relies on bandpass filters, such as raised-cosine filters, to shape the signal spectrum and confine energy within the assigned band, thereby minimizing . These filters, with their controlled factor, reduce spectral while preserving the , allowing tighter channel spacing without significant . In cellular networks, FDMA incorporates frequency reuse, where the same frequency bands are reassigned to non-adjacent cells sufficiently distant to limit , thereby increasing overall system capacity. A key prerequisite for effective multiple access in FDMA is the of user signals, achieved by ensuring non-overlapping spectra that prevent mutual interference across the shared medium. This spectral separation forms the foundation for reliable simultaneous access, distinguishing FDMA from time- or code-based methods.

Single-Carrier Modulation and

In single-carrier FDMA (SC-FDMA), the modulation process begins with mapping a sequence of input data bits to complex modulation symbols using (PSK) or (QAM) schemes, such as QPSK, 16-QAM, or 64-QAM, depending on channel conditions and required data rates. These time-domain symbols, denoted as XX for n=0n = 0 to N−1N-1, are then transformed into the via an NN-point (DFT) to enable multiple access. The DFT output YY spreads the symbols across NN points, given by : Y=∑n=0N−1Xe−j2πkn/N,k=0,1,…,N−1Y = \sum_{n=0}^{N-1} X e^{-j 2\pi k n / N}, \quad k = 0, 1, \dots, N-1 This step maintains the single-carrier characteristics while allowing allocation of specific subcarriers for FDMA. Following the DFT, subcarrier mapping assigns the NN frequency-domain symbols to a of MM available subcarriers (where M>NM > N), with zeros inserted in unused positions to fill the full bandwidth. Two primary mapping types are used: localized mapping, where the symbols occupy contiguous subcarriers for better selectivity, and distributed mapping, where symbols are spread non-contiguously across the bandwidth (e.g., interleaved or comb-like) to enhance diversity and robustness against channel fading. The choice between localized and distributed mapping impacts performance in multipath environments, with localized mapping preferred in standards like LTE for its robustness to carrier offsets. A key benefit of SC-FDMA's single-carrier nature is its low peak-to-average power ratio (PAPR), which arises because the time-domain signal after inverse DFT and cyclic prefix addition exhibits a relatively constant , unlike multi-carrier OFDM. PAPR is defined as: PAPR=10log⁡10(max⁡∣s(t)∣2E{∣s(t)∣2})\text{PAPR} = 10 \log_{10} \left( \frac{\max |s(t)|^2}{\mathbb{E}\{|s(t)|^2\}} \right) where s(t)s(t) is the transmitted signal, max⁡∣s(t)∣2\max |s(t)|^2 is the peak instantaneous power, and E{⋅}\mathbb{E}\{\cdot\} denotes the of the average power. This low PAPR (typically 2-4 dB lower than OFDM) reduces the requirements for power amplifiers, improving efficiency in mobile devices. At the receiver, demodulation reverses the process starting with an MM-point DFT on the received time-domain signal to obtain frequency-domain samples, followed by one-tap frequency-domain equalization on the frequency-domain samples, subcarrier demapping to extract the user's allocated YY, and an NN-point inverse DFT (IDFT) to recover the time-domain symbols XX before symbol detection and decoding. This frequency-domain equalization compensates for channel distortions and simplifies equalization compared to pure single-carrier systems.

System Components

Transmitter Architecture

The transmitter architecture of single-carrier frequency division multiple access (SC-FDMA) processes modulated data through a series of transformations to generate a time-domain signal suitable for uplink transmission. The signal processing chain begins with data mapping, where binary data is modulated using schemes such as (QAM) or (PSK) to produce complex symbols. These symbols are then converted from serial to parallel format, forming blocks of N symbols for efficient frequency-domain processing. The block of time-domain symbols then undergoes an N-point (DFT), converting them into the . The DFT size N is typically chosen to match the number of assigned subcarriers, ensuring a one-to-one mapping without redundancy. The resulting N frequency-domain outputs are then allocated to specific subcarriers within a larger set of M subcarriers (where M > N), a process managed by a scheduler that assigns resource blocks based on channel conditions and user requirements. Subcarrier allocation can employ localized mapping for contiguous blocks or distributed mapping for interleaved placement, with the former often preferred in standards like LTE for its robustness to carrier frequency offsets. The allocated subcarriers undergo an M-point inverse fast Fourier transform (IFFT) to produce a time-domain signal, effectively precoding the data in a manner that resembles single-carrier modulation. The IFFT output is given by s=1M∑k=0M−1Y ej2πkn/M,n=0,1,…,M−1,s = \frac{1}{M} \sum_{k=0}^{M-1} Y \, e^{j 2 \pi k n / M}, \quad n = 0, 1, \dots, M-1, where YY represents the frequency-domain values after subcarrier mapping. A cyclic prefix (CP) is subsequently inserted by appending a copy of the last portion of the IFFT output to the beginning of the block, mitigating inter-symbol interference in multipath channels. The signal is then passed through pulse shaping, typically a raised-cosine filter, to limit bandwidth and reduce spectral sidelobes before digital-to-analog conversion and RF upconversion. The low peak-to-average power ratio (PAPR) inherent in SC-FDMA, due to its single-carrier-like time-domain waveform, enables more efficient operation of the power amplifier with reduced backoff, minimizing and improving energy efficiency compared to multi-carrier alternatives. This characteristic is particularly advantageous in uplink scenarios, where transmitter design must accommodate constraints such as limited battery life and computational resources, influencing choices like DFT size and modulation order to balance performance and power consumption.

Receiver Architecture

The receiver architecture for single-carrier frequency-division multiple access (SC-FDMA) systems is designed to recover the transmitted data from multiple users in the presence of multipath fading and interference, leveraging frequency-domain processing for efficiency. The process begins with cyclic prefix (CP) removal to eliminate inter-symbol interference introduced by the channel, followed by an M-point (FFT) that converts the time-domain received signal into the . Subcarrier deallocation then extracts only the subcarriers assigned to a specific user by zeroing out those allocated to others, enabling per-user processing. This is succeeded by frequency-domain equalization to compensate for channel distortions, an N-point inverse (IDFT) to return the signal to the , parallel-to-serial conversion to reconstruct the sequence, and finally demapping to recover the original bit stream from the constellation points. Equalization in the is crucial for handling multipath in SC-FDMA receivers, with the (MMSE) technique being widely adopted due to its balance of performance and complexity. The MMSE equalizer applies a one-tap filter per subcarrier, computed as Heq=H∗∣H∣2+SNR−1,H_{\text{eq}} = \frac{H^*}{|H|^2 + \text{SNR}^{-1}}, where HH is the channel frequency response at subcarrier kk, H∗H^* is its , and SNR−1\text{SNR}^{-1} accounts for . This formulation minimizes the between the equalized and transmitted symbols, providing robustness against frequency-selective without excessive computational overhead. Prior to FFT processing, synchronization is essential to correct timing offsets and carrier frequency errors, which can otherwise degrade orthogonality among subcarriers and users. Timing synchronization aligns the FFT window to the symbol boundaries using pilots or preambles, while frequency offset correction employs algorithms like those based on cyclic prefix correlations to estimate and compensate for Doppler-induced shifts. In multi-user scenarios at the base station, detection separates signals from different users by exploiting their disjoint sub-band allocations, allowing independent equalization and demapping for each after subcarrier deallocation. This approach maintains low inter-user interference when sub-bands are sufficiently separated, supporting scalable uplink access in standards like LTE.

Performance and Properties

Key Advantages

Single-carrier frequency division multiple access (SC-FDMA) exhibits a notably low peak-to-average power ratio (PAPR), typically 3-4 dB lower than that of (OFDMA), due to its single-carrier structure that spreads the signal energy more evenly across the . This reduced PAPR enables higher power efficiency in uplink transmissions, allowing mobile devices to operate power amplifiers closer to their saturation point without excessive backoff, thereby minimizing energy consumption and improving overall system coverage. The scheme's robustness to multipath fading stems from its use of frequency-domain equalization (FDE) at the receiver, which effectively mitigates inter-symbol interference (ISI) in time-dispersive channels. By inserting a cyclic prefix and performing equalization in the frequency domain, SC-FDMA converts linear channel convolution into circular convolution, simplifying ISI compensation and achieving performance gains of up to 8 dB over uncoded OFDM in frequency-selective Rayleigh fading scenarios. This approach ensures reliable signal recovery even in environments with significant multipath propagation, such as urban wireless settings. In terms of bandwidth efficiency, SC-FDMA's localized subcarrier mapping assigns contiguous blocks of subcarriers to users, reducing the need for guard bands compared to traditional FDMA and thereby lowering overhead while maintaining high spectral utilization akin to OFDMA. This mapping strategy supports flexible without substantial wastage, enabling efficient multi-user access in bandwidth-constrained systems. SC-FDMA's low PAPR also enhances suitability for battery-powered mobile devices by reducing nonlinear in power amplifiers, which allows for more linear operation and extends device battery life during prolonged uplink activity. The resulting power savings are particularly beneficial in standards like LTE, where uplink constraints demand energy-efficient modulation.

Limitations and Challenges

One significant limitation of single-carrier frequency division multiple access (SC-FDMA) is its sensitivity to carrier frequency offsets (CFOs), particularly in mobile environments where Doppler effects induce frequency shifts that degrade the orthogonality among users' subcarriers. These offsets, arising from oscillator mismatches or high-speed mobility, lead to inter-user interference and require precise CFO estimation and compensation algorithms at the receiver to maintain performance. In uplink scenarios with multiple mobile users, such Doppler-induced CFOs can significantly impair bit error rate (BER), necessitating robust synchronization techniques that add to system overhead. Another challenge lies in the complexity of equalization, where SC-FDMA demands more intricate frequency-domain processing compared to the straightforward single-tap equalization in (OFDM). Specifically, (MMSE) equalization in SC-FDMA involves handling the precoded single-carrier structure across allocated subcarrier blocks, resulting in higher computational load at the , especially for multi-user scenarios. This increased processing demand can limit scalability in resource-constrained environments, as the equalizer must mitigate both inter-symbol interference and multi-user interference more comprehensively than OFDM's simpler per-subcarrier approach. SC-FDMA also exhibits limited flexibility in due to its preferred use of contiguous (localized) subcarrier blocks per user, although distributed mapping is also supported, making it less adaptive to varying traffic loads compared to (CDMA) schemes that allow dynamic power and code sharing across the full bandwidth. This fixed block allocation constrains scheduling efficiency in scenarios with fluctuating user demands, potentially leading to underutilized spectrum when loads vary rapidly. In terms of , SC-FDMA achieves slightly lower rates than OFDM in high (SNR) conditions, primarily due to the constraints of its single-carrier , which limits the exploitation of frequency-selective gains. For instance, at elevated SNRs, the average of SC-FDMA remains below that of OFDM for equivalent channel conditions, as the linear does not fully optimize multi-path diversity in the same manner.

Applications and Comparisons

Use in Wireless Standards

Single-carrier frequency division multiple access (SC-FDMA), also known as DFT-spread OFDM, serves as the mandatory uplink transmission scheme in the 3GPP Long Term Evolution (LTE) standard under Release 8, finalized in 2008. This adoption leverages SC-FDMA's lower peak-to-average power ratio (PAPR) compared to (OFDMA), enabling more efficient power amplification in with limited battery resources. The LTE uplink employs a fixed 15 kHz subcarrier spacing and supports scalable channel bandwidths from 1.4 MHz to 20 MHz, allowing flexible resource allocation across multiple users while maintaining compatibility with downlink OFDMA. In the subsequent 5G New Radio (NR) framework, defined in 3GPP Release 15 and completed in 2018, SC-FDMA becomes an optional waveform for uplink communications, particularly beneficial for low-mobility and coverage-limited scenarios where power efficiency is paramount. It coexists alongside the default cyclic prefix OFDM (CP-OFDM) to offer deployment flexibility, such as in enhanced machine-type communications or scenarios requiring extended battery life. This optional status allows network operators to select SC-FDMA for specific use cases without mandating hardware changes from LTE infrastructure. Beyond cellular networks, SC-FDMA has been explored in communications for power-constrained environments, such as geostationary systems in Ku- and Ka-bands, where its reduced PAPR supports efficient transmission from battery-limited terminals. Evaluations demonstrate its robustness against channel impairments like nonlinear amplification and Doppler effects, making it suitable for mobile uplinks. In broadband wireless standards, IEEE 802.16m ( 2.0) considered SC-FDMA as an uplink enhancement to complement OFDMA, with proposals emphasizing its PAPR advantages for improved coverage and efficiency in mobile scenarios, though OFDMA remained the baseline. In 2025, agreed to retain DFT-s-OFDM (equivalent to SC-FDMA) for the uplink to ensure with , particularly for low-power IoT devices requiring extended coverage and energy efficiency. This approach facilitates seamless integration of legacy IoT ecosystems into future networks, prioritizing continuity in and design.

Comparison with Multi-Carrier Methods

Single-carrier FDMA (SC-FDMA) differs from multi-carrier methods like orthogonal frequency-division multiplexing (OFDM) primarily in its signal structure, which employs discrete Fourier transform (DFT) precoding to generate a single-carrier-like waveform in the time domain. This results in a lower peak-to-average power ratio (PAPR) for SC-FDMA, typically offering a 2 dB gain over OFDM, making it more suitable for uplink transmissions where power efficiency is critical for battery-constrained mobile devices. In contrast, OFDM exhibits higher PAPR due to the superposition of multiple subcarriers, necessitating greater power backoff and reducing amplifier efficiency. Despite the PAPR advantage, SC-FDMA and OFDM achieve similar spectral efficiency, with OFDM slightly outperforming by about 0.5 dB in certain scenarios due to its flexible subcarrier allocation. OFDM is preferred for downlink channels because it enables simpler one-tap equalization per subcarrier, effectively converting frequency-selective fading into multiple flat-fading channels. SC-FDMA, while requiring more complex frequency-domain equalization to handle inter-symbol interference, maintains comparable performance through DFT spreading that provides inherent frequency diversity. Compared to multi-carrier FDMA (MC-FDMA), which aligns closely with OFDM-based multiple access, SC-FDMA serves as a variant that mitigates peakiness through its precoded structure, reducing the need for extensive PAPR mitigation techniques. MC-FDMA inherits the high PAPR of multi-carrier modulation, leading to inefficiencies in power amplification, whereas SC-FDMA's lower envelope fluctuations support higher transmit power without . Key trade-offs between SC-FDMA and multi-carrier methods include performance in frequency-selective fading environments and processing demands. SC-FDMA performs well for mobile users in such channels, as its low PAPR allows for efficient power utilization and robust single-carrier-like equalization, minimizing sensitivity to nonlinearities. Multi-carrier approaches like OFDM excel in parallel processing, facilitating advanced techniques such as multiple-input multiple-output () and easier implementation of multi-user diversity through subcarrier scheduling. In practical deployments, hybrid scenarios leverage the strengths of both, as seen in Long-Term Evolution (LTE) standards where SC-FDMA is used for the uplink to prioritize power efficiency and OFDM for the downlink to maximize throughput and simplicity. This asymmetric design balances the constraints of user equipment with the capabilities of base stations.

References

  1. https://www.eurasip.org/Proceedings/Eusipco/Eusipco2007/Papers/d3l-a01.pdf
  2. https://arxiv.org/pdf/1404.2115
  3. https://www.mitsubishielectric-rce.eu/wp-content/uploads/2020/02/Ciochina_EW2010.pdf
  4. https://www.tmit.bme.hu/sites/default/files/LTE_SCFDMA.pdf
  5. https://sites.pitt.edu/~dtipper/2720/2720_Slides5.pdf
  6. https://www.sciencedirect.com/topics/physics-and-astronomy/frequency-division-multiple-access
  7. http://www.arib.or.jp/english/html/overview/doc/5-STD-27_L-1p3-E.pdf
  8. https://ieeexplore.ieee.org/document/4099344
  9. https://www.researchgate.net/publication/310434956_Generalized_DFT-Spread-OFDM_as_5G_Waveform
  10. https://ieeexplore.ieee.org/book/8040245
  11. https://www.sciencedirect.com/topics/engineering/frequency-division-multiple-access
  12. https://atlantarf.com/uploads/1/4/3/4/143448818/multiple_access_-_fdma_-_tdma_-_cdma.pdf
  13. https://www.sciencedirect.com/topics/computer-science/raised-cosine-filter
  14. https://www.sciencedirect.com/topics/computer-science/frequency-division-multiple-access
  15. https://www.electronics-notes.com/articles/connectivity/4g-lte-long-term-evolution/ofdm-ofdma-scfdma-modulation.php
  16. https://hal.science/hal-00856746v1/document
  17. https://www.mitsubishielectric-rce.eu/wp-content/uploads/2020/02/Ciochina_IEEETWCom09.pdf
  18. https://ieeexplore.ieee.org/document/4349760/
  19. https://ieeexplore.ieee.org/document/7099187
  20. https://www.utdallas.edu/~aldhahir/fde_final.pdf
  21. https://discovery.ucl.ac.uk/1529403/1/Grammenos%252C%2520Darwazeh%2520-%25202010%2520-%2520SC-FDMA%2520and%2520OFDMA%2520The%2520two%2520competing%2520technologies%2520for%2520LTE.pdf
  22. https://ieeexplore.ieee.org/document/8998652/
  23. https://ieeexplore.ieee.org/document/5425747
  24. https://ietresearch.onlinelibrary.wiley.com/doi/10.1049/tje2.12042
  25. https://asp-eurasipjournals.springeropen.com/articles/10.1186/s13634-016-0333-3
  26. https://en.lntwww.de/Mobile_Communications/The_Application_of_OFDMA_and_SC-FDMA_in_LTE
  27. https://orbit.dtu.dk/files/5549279/eq_comparative_analysis.pdf
  28. https://ieeexplore.ieee.org/document/4526118
  29. https://ieeexplore.ieee.org/document/6221230
  30. https://ieeexplore.ieee.org/document/6906483
  31. https://jwcn-eurasipjournals.springeropen.com/articles/10.1155/2009/957159
  32. https://dsp.stackexchange.com/questions/37834/sc-fdma-disadvantages
  33. https://www.etsi.org/deliver/etsi_ts/136200_136299/136213/08.03.00_60/ts_136213v080300p.pdf
  34. https://www.3g4g.co.uk/Lte/LTE_SCFDMA_WP_0804_Agilent.pdf
  35. https://www.etsi.org/deliver/etsi_ts/138200_138299/138211/15.03.00_60/ts_138211v150300p.pdf
  36. https://www.itu.int/en/ITU-D/Regional-Presence/AsiaPacific/SiteAssets/Pages/Events/2019/ITUPITA2018/ITU-ASP-CoE-Training-on-/5G%2520networks%2520and%25203GPP%2520Release%252015_vf.pdf
  37. https://www.etsi.org/deliver/etsi_tr/103200_103299/103297/01.01.01_60/tr_103297v010101p.pdf
  38. https://www.ieee802.org/16/tgm/contrib/S80216m-08_100r1.pdf
  39. https://the-mobile-network.com/2025/08/6g-meeting-settles-on-same-old-air-interface/
  40. https://www.ericsson.com/en/blog/2024/5/future-6g-radio-access-network-design-choices
  41. https://vbn.aau.dk/ws/files/19119920/IEEEmagazine.pdf
  42. https://discovery.ucl.ac.uk/id/eprint/1529403/1/Grammenos%2C%20Darwazeh%20-%202010%20-%20SC-FDMA%20and%20OFDMA%20The%20two%20competing%20technologies%20for%20LTE.pdf
  43. https://www.nxp.com/docs/en/white-paper/3GPPEVOLUTIONWP.pdf
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