Single Carrier Frequency Division Multiple Access Signal Research Articles

Effect of Nonlinear Detection Response Characteristics of Electric Field Probe on LTE Signal Measurement and Statistical Evaluation of Its Detection Response

To improve the calibration accuracy of an electric field (E-field) probe loaded with a diode detector for digital wireless communication signals with complex waveforms, the effect of the nonlinear characteristics of the E-field probe on the detection response of a long-term evolution (LTE) signal is investigated. In this article, we focused on single-carrier frequency division multiple access (SC-FDMA) and orthogonal frequency-division multiplexing access (OFDMA) signals used for LTE uplink and downlink, respectively. First, we investigated the effect of the nonlinear characteristics of the E-field probe on the detection response of continuous SC-FDMA and OFDMA signals simulating frequency division duplexing LTE. Then, intermittent SC-FDMA and OFDMA signals simulating time-division LTE were also investigated. Furthermore, we proposed a method of estimating the detection response of SC-FDMA and OFDMA signals using the probability density function of the envelope amplitude. When the envelope variation of the LTE signal is fully covered within the response time of the E-field probe, the estimated detection response agrees well with the measured result. In addition, the detection response of an intermittent LTE signal with a typical repetition period can be calculated with the proposed approximation formula by separately considering the probability density functions of the envelope amplitude for the burst and nonburst periods.

Non Linear Companding Transform to Mitigate PAPR in DCT Based SC-FDMA System

Discrete cosine transform (DCT) based single carrier frequency division multiple access (SC-FDMA) system outperforms discrete Fourier transform based SC-FDMA (DFT SC-FDMA) system in terms of bit error rate (BER) performance. However, the peak-to-average power ratio (PAPR) of the DCT SC-FDMA system is slightly higher than that of the DFT SC-FDMA system. In this paper, a companding transform is proposed by approximating the distribution of magnitudes of DCT SC-FDMA signal and thereby transforming it into a triangular distribution. Proposed companding transform effectively reduces PAPR by maintaining the average power of companded signal. By clipping the companded signal to a specific threshold, PAPR can be reduced further. Moreover, the proposed technique causes fewer spectrum side-lobes than µ law and absolute exponential companding techniques. Simulated results ensure that proposed companding followed by clipping offers better PAPR and BER performances than the absolute exponential companding technique.

On companding techniques to mitigate PAPR in SC-FDMA systems

Single Carrier Frequency Division Multiple Access (SC-FDMA) is being used successfully in the uplink communications of Long Term Evolution (LTE) standard. Owing to smaller envelope changes in SC-FDMA signal, it has a lower Peak to Average Power Ratio (PAPR) than Orthogonal Frequency Division Multiple Access (OFDMA) signal. But for higher order modulations, PAPR is still high and there is a requirement to mitigate PAPR in localised SC-FDMA systems. This paper discusses error function, exponential, rooting and logarithmic companding techniques that can be utilised to mitigate PAPR in SC-FDMA systems. Simulation results show that exponential companding technique provides better PAPR and Bit Error Rate (BER) performances at the cost of higher side lobes, and error function companding transform provides good PAPR and Power Spectral Density (PSD) performances at the cost of higher BER without increasing average signal power.

On companding techniques to mitigate PAPR in SC-FDMA systems

Single Carrier Frequency Division Multiple Access (SC-FDMA) is being used successfully in the uplink communications of Long Term Evolution (LTE) standard. Owing to smaller envelope changes in SC-FDMA signal, it has a lower Peak to Average Power Ratio (PAPR) than Orthogonal Frequency Division Multiple Access (OFDMA) signal. But for higher order modulations, PAPR is still high and there is a requirement to mitigate PAPR in localised SC-FDMA systems. This paper discusses error function, exponential, rooting and logarithmic companding techniques that can be utilised to mitigate PAPR in SC-FDMA systems. Simulation results show that exponential companding technique provides better PAPR and Bit Error Rate (BER) performances at the cost of higher side lobes, and error function companding transform provides good PAPR and Power Spectral Density (PSD) performances at the cost of higher BER without increasing average signal power.

Performance analysis of hybrid PAPR reduction technique for LTE uplink communications

Long Term Evolution standard implemented Single Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink communications due to its low peak to average power ratio (PAPR). But for higher order modulations, there is a need for further reduction of PAPR in SC-FDMA systems. There are numerous techniques to decrease PAPR, but clipping and companding techniques are very simple to implement without any side information. μ law companding provides good PAPR reduction but increases the average power of companded signal. In this paper, the distribution of SC-FDMA signal is approximated, and a companding technique is proposed to transform the approximated distribution into a uniform distribution, which reduces PAPR without increasing average power of the signal. For further improvement in PAPR, a hybrid technique is also proposed where the companded signal is clipped to a specific threshold value. Simulation results show that PAPR reduction achieved by the proposed companding technique is better than that of μ law companding with a slight degradation in bit error rate (BER) performance. The proposed companding technique with no decompanding operation has better BER performance when compared to that with approximated decompanding operation. The hybrid technique further reduces PAPR with similar BER performance as that of proposed companding technique by carefully choosing the clipping ratio.

Blind selective mapping for single-carrier frequency division multiple access system

Single-Carrier Frequency Division Multiple Access (SC-FDMA) signals have a Peak-to-Average Power Ratio (PAPR) problem. So, there is a need for PAPR reduction techniques to be implemented on these signals. The PAPR becomes larger as the modulation order increases. Recently, Conventional Selective Mapping (C-SLM) has been used to reduce the PAPR of SC-FDMA signals. Unfortunately, the standard C-SLM technique requires the transmission of Side Information (SI) to the receiver side. In this paper, a Blind Selective Mapping (B-SLM) technique is proposed to reduce the PAPR in the SC-FDMA system, where there is no change in the C-SLM algorithm at the transmitter and no necessity for SI transmission. Our simulation results show that the PAPR performance of the proposed B-SLM technique is approximately the same as that of the C-SLM technique. The proposed technique is applied to the SC-FDMA system for Single-Input Single-Output (SISO) and Multiple-Input Multiple-Output (MIMO) scenarios. The proposed B-SLM technique provides a reduction in bandwidth without a significant degradation in the Bit-Error Rate (BER) performance. Also, we present a comparison in the PAPR performance between the B-SLM and the other PAPR reduction techniques such as the Partial Transmit Sequence (PTS) and the C-SLM.

An accurate analysis of the nonlinear power amplifier effects on SC-FDMA signals

Single carrier-frequency division multiple access (SC-FDMA) is a multiple access technique in broadband wireless networks which has been adapted by 3GPP for uplink transmission in 4G mobile communications. In this paper, the nonlinear effect of practical power amplifier (PA) is studied on the power allocated SC-FDMA signals. The interference power on the estimated symbols of all users are derived by two approaches based on the polynomial model of nonlinear PA and allocated power of subcarriers. In the first approach, an accurate analysis is followed.An approximation of the accurate result is presented in the second approach to provide a closed form formula. A simulation study is conducted to verify the analytical outcomes. The simulation and the exact analytical results are significantly matched. Conversely, the approximate relations are extremely suitable for allocating power in system design due to their closed form nature where they provide acceptable accuracy for practical applications.

A New Trellis Shaping Design for Peak Power Reduction of SC-FDMA Signals With High-Order QAM

Single-carrier frequency-division multiple-access (SC-FDMA) has been adopted as the uplink radio access scheme of the fourth-generation mobile wireless communication system because of its signal with lower peak-to-average power ratio (PAPR) compared to multicarrier based signals. However, when it is combined with high-order quadrature amplitude modulation (QAM) for higher bandwidth efficiency, the SC-FDMA signal also exhibits relatively high PAPR, and thus, the resulting efficiency of power amplifier (PA) will be considerably reduced. Since PA is a dominant source of power consumption at the transmitter, further reduction of PAPR should be necessary in view of future green cellular systems. In this paper, we propose a new trellis shaping (TS) design for peak power reduction of SC-FDMA signals. We first observe that the direct application of the TS developed for peak power reduction of conventional single-carrier signals tends to incur high peaks at the edges of each SC-FDMA signal due to their circularly periodic structure. We tackle this problem by introducing a novel modification of TS such that the symbols at one edge can be controlled by those located at the other edge. It is shown that the SC-FDMA signal with the proposed TS is able to significantly improve the PA efficiency. We demonstrate its effectiveness by investigating system level performances, such as the achievable PA efficiency and resulting power spectral density, as well as its symbol error rate (SER) over additive white Gaussian noise channels with frequency-selective Rayleigh fading in the presence of PA nonlinearity.

Phase Noise Pre‐correction Scheme for SC‐FDMA Signals in LTE‐Uplink

This paper proposes a novel carrier Phase noise (PN) pre-correction scheme with an adaptive PN prediction algorithm for Single-carrier Frequency-division multiple-access (SC-FDMA) systems to alleviate degradation due to the PN. Our proposed PN prediction algorithm is a modified polynomial fitting algorithm which is based on receding horizon principle. The parameters of the prediction model are optimized by using the algorithm on PN samples of the local oscillator signal in a training window. By using the optimized prediction model parameters and the latest PN samples, we can predict future PN samples. Then these predicted PN samples are put into our proposed PN pre-correction scheme and the SC-FDMA symbols at the transmitter are pre-compensated. Due to the absence of the radio frequency delay device, the proposed scheme has a low hardware complexity. Simulation results show that our proposed scheme can greatly reduce the effect of the PN on the transmitted SC-FDMA signal.

Logarithmic Companding Technique to Improve Performance of SC-FDMA Systems

Objectives: This paper proposes logarithmic companding technique to improve PAPR and BER performance of conventional Single Carrier Frequency Division Multiple Access (SC-FDMA) system. Methods/Analysis: The lower signal envelope fluctuations in SC-FDMA signal results in low peak to average power ratio, in contrast to that of OFDMA. But still, there is a need to minimize PAPR in SC-FDMA systems. Although there are many techniques to minimize PAPR in SC-FDMA systems they are highly complex or need side information to be transmitted. This paper proposes a companding technique based on a logarithmic function which provides better PAPR reduction when compared to μ law companding. Findings: Simulation results demonstrate that proposed method provides better PAPR and BER performance when compared to conventional SC- FDMA system and μ law companding.

Improving the peak-to-average power ratio of single-carrier frequency division multiple access systems by using an improved constellation extension scheme with error correction

Single-carrier frequency division multiple access (SC-FDMA) is currently a widely used transmission technology that has been designated as the uplink transmission technology for the 4G mobile communications standard. SC-FDMA also has a lower peak-to-average power ratio (PAPR) compared with orthogonal frequency division multiple access (OFDMA), where OFDMA is the downlink transmission technology in the 4G standard. However, the PAPR of SC-FDMA increases with the M value in an M-ary modulation scheme, causing a decrease in the efficiency of high-power amplifiers at the transmission end. This study proposes a technique for minimizing the PAPR in SC-FDMA systems by dividing a 16-QAM product code (PC) into two subblocks, one of which is dedicated to encoding transmission data for enhanced error correction, and the other is for generating PAPR-reduction signals. Moreover, this study employed the constellation extension scheme to generate PAPR reduction signals because it can prevent additional data loss caused by the generated PAPR reduction signals. Simulation results show that the proposed technique not only reduces PAPR in SC-FDMA system, but its transmission signals also outperform conventional SC-FDMA signals in error correction because of the incorporated PCs.

Energy vs. Cyclostationarity-based Detection of Random Arrival and Departure of LTE SC-FDMA Signals for Cognitive Radio Systems

Abstract In cognitive radio systems, the random nature of primary users’ activities heavily influences the performance of spectrum sensing techniques. Considering both of the primary user random arrival and departure in one model is essential for mitigating the performance degradation in spectrum sensing. In this paper, we apply the probability based weighting energy detector (ED) to overcome the effect of random arrival and departure of primary user (PU), on a single carrier-frequency division multiple access (SC-FDMA) signal used in LTE uplink physical channel. Then compare the performance of weighted ED to the second order Cyclostationarity detector with/without the random arrival and departure of primary user signal during the secondary user’s sensing period. The simulation shows that the weighting ED approaches the performance of Cyclostationarity detector in the normal case, where there are no random activities of primary user signals during the secondary user’s sensing period, with less computational complexity. Moreover, the weighted ED outperforms the Cyclostationarity detector in the case of random arrival and departure of PU.

Reducing PAPR of SC-FDMA Signals through Simple Amplitude Predistortion

A novel peak-to-average power ratio (PAPR) reduction method is proposed for single-carrier frequency-division multiple access (SC-FDMA) signals. The proposed method deliberately distorts the amplitude values of a few of the complex modulated symbols that cause peaks beyond a predetermined threshold in the samples of the output signal. The method then marks the location indices of the distorted symbols by using a pilot block at the transmitter without transmitting side information. At the receiver, the method is then able to recover the distorted amplitude values through the marked location indices. Computer simulation results show that when compared to conventional SC-FDMA signals, the proposed scheme can effectively reduce the PAPR of SC-FDMA signals with asymptotically consistent bit error rate (BER) performance.

The digital predistortion of the SC-FDMA signals in LTE uplink system

ABSTRACTThe single-carrier frequency-division multiple access (SC-FDMA) is used in the uplink of the long-term evolution (LTE) and LTE-advanced systems because of the lower peak-to-average-power ratio (PAPR) compared with the widely used orthogonal frequency-division multiplexing (OFDM) scheme. However, the non-linearity caused by the characteristic of the radio frequency (RF) power amplifiers (PAs) is still a critical problem, and there are few researches about the linearisation for the SC-FDMA signals. The digital predistorter is widely applied by employing digital baseband distortion ahead of the amplifier to compensate for the non-linearity effects and provide efficiency enhancements for high PAs in the different communication systems. This letter presents an efficient and flexible inverse autoregressive moving-average (ARMA) model-based digital predistorter to linearise the PA distortion with memory in the LTE uplink system. The proposed digital predistortion (DPD) algorithm is for the first time applied to SC-FDMA signals and verified with a series of experimental measurements. The spectrum regrowth of SC-FDMA signals is improved by up to 12 dB from both simulation and measurement. The proposed predistorter has been shown to solve the distortion problem caused by the memory effect effectively in RF PA.

PAPR Reduction of SC-FDMA Signals Using Optimized Additive Pre-distortion

One challenge of employing high-order modulations in single carrier frequency division multiple access (SC-FDMA) systems is the resultant high peak-to-average power ratio (PAPR). We propose a novel PAPR reduction scheme by jointly considering the PAPR reduction and the incurred bit error rate (BER) degradation for SC-FDMA systems with high-order modulations. In the proposed scheme, an additive pre-distortion vector is introduced to modify the few modulated symbols causing the peak of the SC-FDMA signal. This pre-distortion vector is optimized to minimize the in-band distortion under the expected PAPR constraint. Simulation results demonstrate that our proposed scheme can achieve the desired PAPR reduction with negligible BER performance degradation.

Performance Improvement of IFDMA and LFDMA using NCT Technique

Orthogonal Frequency Division Multiplexing (OFDM) is a well-known modulation technique for transmission of large amount of digital data with high data rate in both wired and wireless communication systems. High peak-to-average power ratio (PAPR) is the main problem of OFDM system which can be improved by using single carrier frequency division multiple access (SC-FDMA) technique. A new scheme using LFDMA and IFDMA technique is proposed for further reducing the peak-to-average power ratio (PAPR). It transforms the SC-FDMA signal by properly choosing the transform parameters for achieving a favorable tradeoff between PAPR reduction and bit error rate (BER) performances. The simulation results show better performance of the proposed scheme than the existing technique. In this paper, we have improved the PAPR performance of single carrier frequency division multiplexing (SC-FDMA) using LFDMA and IFDMA with and without pulse shaping.

Spectrum Sensing of Interleaved SC-FDMA Signals in Cognitive Radio Networks

This paper develops a spectrum sensing technique for interleaved single-carrier frequency-division multiple access (SC-FDMA) systems. By designing a metric that exploits cyclostationary features of interleaved SC-FDMA signals, we establish a framework for signal detection. Using Gaussian approximation for this metric, the parameters of the metric distributions under two hypotheses are derived, and both hypotheses are examined by the Neyman-Pearson test. We validate the accuracy of the Gaussian approximation by comparing theoretical and simulated metric histograms. The performance of the proposed method is presented for additive white Gaussian noise and multipath Rayleigh fading channels. We also investigate the effect of the block length, the number of users, the metric window length, and the presence of the pilot signals on the detection performance. Through comparative performance evaluation, we demonstrate the superiority of our proposed detection scheme over energy detection and the detection method based on autocorrelation of the cyclic prefix (CP). We obtain similar detection performance to that of the mentioned methods at about 8-13 dB lower signal-to-noise ratio (SNR). It is noteworthy that the complexity of our method is comparable to that of the energy detection and slightly higher than that of CP detection.

Second-Order Cyclostationarity-Based Detection of LTE SC-FDMA Signals for Cognitive Radio Systems

In this paper, we investigate the detection of long term evolution (LTE) single carrier-frequency division multiple access (SC-FDMA) signals, with application to cognitive radio systems. We explore the second-order cyclostationarity of the LTE SC-FDMA signals, and apply results obtained for the cyclic autocorrelation function to signal detection. The proposed detection algorithm provides a very good performance under various channel conditions, with a short observation time and at low signal-to-noise ratios, with reduced complexity. The validity of the proposed algorithm is verified using signals generated and acquired by laboratory instrumentation, and the experimental results show a good match with computer simulation results.

A Comparative Analysis of SC-FDMA and OFDMA over WiMAX Broadband Networks

WiMAX, is the modern technology for providing broadband wireless access over long distance communication here we are adopted orthogonal frequency division multiple access (OFDMA) and single carrier frequency division multiple access (SC-FDMA) scheme for the uplink transmissions, SCFDMA utilizes single carrier modulation and frequency domain equalization. In this paper, we are presenting a Raised Cosine and Root raised cosine scheme to reduce the peak-toaverage power ratio (PAPR) of SCFDMA signals. The current scheme can transform the original SC-FDMA signals into Raised Cosine and Root Raised Cosine like distributed. Moreover, the scheme use IFDMA for compress the large signals and repetition while DFDMA for allocating different subcarriers. Computer simulation results show that the proposed SC-FDMA scheme can offer better PAPR compare to OFDMA.

PAPR Reduction in Coded SC-FDMA Systems via Introducing Few Bit Errors

We propose a simple and flexible peak-to-average power ratio (PAPR) reduction scheme for coded single carrier frequency division multiple access (SC-FDMA) signals in the uplink of the Long Term Evolution (LTE). The proposed scheme is based on the introduction of few bit errors to modify the few complex modulated symbols of each data SC-FDMA symbol in a sub-frame, which cause peaks of the output signal samples to be larger than a predetermined threshold value. In addition, the effect on the bit error rate (BER) performance of the few deliberately corrupted bits can be greatly mitigated by using the channel decoding at the receiver. Computer simulations show that the proposed scheme can reduce the PAPR of SC-FDMA signals effectively with almost the same BER as the conventional SC-FDMA signals when the signal-to-noise ratio (SNR) is below 35 dB.