Single Carrier Frequency Division Multiple Access Systems Research Articles

Low Complexity Turbo Receiver for LTE Uplink with Transmitter IQ Imbalance

In this paper, we investigate two improved turbo receivers for the Long Term Evolution (LTE) uplink in the presence of transmitter (Tx) in-phase and quadrature-phase imbalance (IQI) with parameters known at eNodeB. For multiuser multiple-input multiple-output (MU-MIMO) single-carrier frequency division multiple access (SC-FDMA) systems, we derive a optimal joint linear minimum mean square error (MMSE) turbo multiuser detector (MUD) based on the mirror symmetry clusters. For the single use SC-FDMA system with Tx IQI, we derive an optimal widely linear MMSE (WLMMSE) turbo equalizer. Both receivers are implemented in the discrete frequency domain and only slightly increase the computational complexity compared to the conventional turbo receivers. Monte Carlo simulations show that the proposed receivers significantly outperform the conventional turbo receivers. The simulation results are then confirmed by the extrinsic information transfer (EXIT) chart analysis.

SOCP Approach for Reducing PAPR System SCFDMA in Uplink via Tone Reservation

The 3rd generation partnership project (3GPP) long term evolution (LTE) standard uses single carrier frequency division multiple access (SC-FDMA) scheme for the uplink transmissions and orthogonal frequency division multiplexing access (OFDMA) in downlink. In this paper, we point on the Peak-to-Average Power Ratio (PAPR) reduction for the uplink SC-FDMA system. Firstly, the conventional Tone Reservation (TR) is investigated. Then, the approach SOCP (Second Order Cone Programming) is applied for the complex baseband signals of SC-FDMA system with different subcarrier mapping. For the method TR, these subcarriers are located on unused subcarriers of SC-FDMA and we use a raised-cosine pulse. Besides, we prove that the IFDMA can be reduced the PAPR more than the localized FDMA (LFDMA) and distributed FDMA (DFDMA). Finally, this method does not degrade the bit-error-rate (BER) and the data bit rate and no side information (SI) transmission is obligatory.

SC-FDMA 수신기를 위한 잡음 백색화 판정궤환 등화기

이 논문에서는 SC-FDMA 수신기를 위한 잡음 백색화 판정궤환 등화기를 제안하였다. SC-FDMA 방식은 다중경로의 영향을 제거할 수 있는 OFDMA 방식의 장점을 유지하면서 OFDMA의 단점인 높은 PAPR 문제를 해결할 수 있는 장점을 가지고 있다. 또 SCFDMA 방식은 기본적으로 단일 반송파 전송방식이지만, 주파수 영역에서 채널 등화기를 구현함으로써 OFDMA 수신기와 마찬가지로 등화기의 복잡도를 크게 감소시킬 수 있다. 뿐만 아니라 시간 영역 신호가 디지털 변조된 복소심볼이므로 시간 영역에서 추가적으로 비선형 등화인 판정궤환 등화를 함으로써 주파수 영역의 선형 등화에 의해 잔류해 있는 심볼간 간섭을 더 제거할 수 있다. 한편 지금까지 제시된 SC-FDMA용 판정궤환 등화기는 판정기에 입력되는 신호에 포함된 잡음이 백색화되어 있지 않기 때문에 최적판정을 수행하고 있지 않다. 이 논문에서는 이러한 문제를 해결하기 위해 선형 잡음 백색화 필터를 판정기 앞에 연결하여 판정궤환 등화기의 성능을 더 향상 시킬 수 있는 방법을 제시한다. 또 컴퓨터 모의실험을 통해 기존의 등화기와 제안된 등화기의 비트 오율 성능을 비교한다. In this paper, we propose a noise whitening decision feedback equalizer for single carrier frequency division multiple access (SC-FDMA) receivers. SC-FDMA has the same advantage as that of orthogonal frequency division multiple access (OFDMA) in which the multipath effect can be removed easily, and also solves the problem of high peak to average power ratio (PAPR) which is the main drawback of OFDMA. Although SC-FDMA is a single carrier transmission scheme, a simple frequency domain linear equalizer (FD-LE) can be implemented as in OFDMA, which can dramatically reduce the equalizer complexity. Moreover, some residual intersymbol interference in the output of the FD-LE can be further removed by an additional nonlinear decision feedback equalizer (DFE) in time domain, because the time domain signal is a digitally modulated symbol. In the conventional DFE, however, the noise is not white at the input of the decision device and correspondingly the decision is not optimum. In this paper, we propose an improved DFE scheme for SC-FDMA systems where a linear noise whitening filter is inserted before the decision device of the conventional DFE scheme. Through computer simulations, we compare the bit error rate performance of the proposed DFE scheme with the conventional equalizers.

Equalization and Carrier Frequency Offsets Compensation for the SC-FDMA System

Recently, the Single-Carrier Frequency Division Multiple Access (SC-FDMA) system has attracted the attention as an efficient alternative to the Orthogonal Division Multiple Access (OFDMA) system in the uplink communications. In this system, the Carrier Frequency Offsets (CFOs) disrupt the orthogonality between subcarriers, and give rise to Inter-Carrier Interference (ICI), and Multiple Access Interference (MAI) among users. In this paper, the impact of the CFOs on the performance of the Discrete Fourier Transform SC-FDMA (DFT-SC-FDMA) and the Discrete Cosine Transform SC-FDMA (DCT-SC-FDMA) systems is investigated. Based on the Minimum Mean Square Error (MMSE) criterion, a new low-complexity joint equalization and CFOs compensation scheme is proposed. It is refered to as the MMSE scheme. The MMSE weights of the proposed scheme are derived taking into account the MAI and the noise. Furthermore, a hybrid scheme comprising the proposed MMSE scheme and a Parallel Interference Cancellation (PIC) stage is also suggested and investigated to further enhance the performance of interleaved subcarriers mapping systems. From the obtained simulation results, it is clear that CFOs disrupt the orthogonality between the subcarriers in SC-FDMA systems and degrade the Bit Error Rate (BER) performance. The proposed compensation schemes are able to enhance the system performance, even in the presence of the estimation errors.

Low PAPR space frequency block coding for multiuser MIMO SC-FDMA systems: specific issues for users with different spectral allocations

Single-carrier space frequency block coding (SC-SFBC) is an innovative mapping scheme suitable for implementing transmit diversity in single-carrier frequency division multiple access (SC-FDMA) systems. The main advantage of SC-SFBC is that it preserves the low envelope variations of SC-FDMA, which is particularly interesting for the uplink of wireless communications systems. In this article, we apply the SC-SFBC concept in a multiuser multiple-input multiple-output (MU-MIMO) scenario. We introduce a novel algorithm allowing the optimization of the parameters of SC-SFBC to enable low-complexity decoding at the receiver side and to maximize the overall spectral occupancy in MU-MIMO SC-FDMA systems, and we show the good performance of the proposed MU scheme.

Peak-to-Average Power Ratio Reduction for Single Carrier- Frequency Division Multiple Access using Repeated Clipping and Filtering

A single carrier frequency division multiple access (SC-FDMA), is a technique that has a similar performance and essentially the same overall complexity as those of orthogonal frequency division multiple access (OFDMA). The main advantage of SC-FDMA over OFDMA is its lower peak-to-average power ratio (PAPR). In this paper, an enhancement of aSC-FDMA by decreasing the PAPR is addressed. An efficient repeated clipping and filtering (RCF) algorithm is applied to a SC-FDMA system, which results in a significant PAPR reduction. System performance remains the same after applying the RCF algorithm. Simulations show the proposed scheme provides a bit error as that of the conventional system. That is, due to the selection of the optimum clipping ratio (CR). For more accurate validation, simulations of the conventional system and the proposed system have been performed using different types of channels. The proposed scheme provides a PAPR reduction by a gain of approximately 4 dB with a slight increase of complexity.

Impact of the power amplifier on the performance of the single carrier frequency division multiple access system

Single-carrier frequency division multiple access (SC-FDMA) is a promising alternative to orthogonal frequency division multiple access (OFDMA) for uplink wireless communications in frequency-selective fading environments. In this paper, we investigate the impact of the power amplifier (PA) on the performance of the SC-FDMA system. The suitable saturation level thresholds of the PA that can be utilized in the SC-FDMA system are studied and determined through simulations for different modulation formats. Simulation results show that the saturation level of the PA has a significant effect on the bit error rate (BER) performance of the SC-FDMA system, especially with high order modulation formats.

Distributed Space-Time/Frequency Coding Schemes for Single-Carrier Frequency Division Multiple Access Systems

The single carrier-frequency division multiple access (SC-FDMA) system is a new system that was adopted in the standardization of the upcoming 3GPP long-term evolution (LTE). Designing diversity-achieving schemes for the SC-FDMA system is a challenging task. The codes adopted should not affect the peak-to-average power ratio (PAPR) among other constraints. In this paper, we consider the design of cooperative diversity schemes for SC-FDMA systems in the uplink direction. Specifically, two relay-assisted distributed space-time/frequency codes are proposed. The proposed distributed space-frequency code (SFC) achieves full spatial diversity in the uplink fast-fading channels, where a diversity of order three can be achieved. The proposed code keeps a low PAPR, which is a good feature of the system. A minimum mean square error (MMSE) decoder is used at the receiver of the destination node. Moreover, we propose a bandwidth-efficient distributed space-time code (STC) for slow-fading relay channels. A decode-and-forward (DF) protocol is used at the relay node, and the possibility of erroneous decoding is taken into account. Simulation results demonstrate the performance improvement of the proposed schemes.

Uplink single-carrier frequency division multiple access system with joint equalisation and carrier frequency offsets compensation

Similar to the orthogonal frequency division multiple access (OFDMA) system, the single-carrier frequency division multiple access (SC-FDMA) system also suffers from frequency mismatches between the transmitter and the receiver. As a result, in this system, the carrier frequency offsets (CFOs) disrupt the orthogonality between subcarriers and give rise to inter-carrier interference (ICI) and multiple access interference (MAI) among users. The authors present a new minimum mean square error (MMSE) equaliser, which jointly performs equalisation and carrier frequency offsets (CFOs) compensation. The mathematical expression of this equaliser has been derived taking into account the MAI and the channel noise. A low complexity implementation of the proposed equalisation scheme using a banded matrix approximation is presented here. From the obtained simulation results, the proposed equalisation scheme is able to enhance the performance of the SC-FDMA system, even in the presence of estimation errors.

Optimal Orthogonal Precoding for Power Leakage Suppression in DFT-Based Systems

A solution to the power leakage minimization problem in discrete Fourier transform (DFT) based communication systems is presented. In a conventional DFT based system, modulated subcarriers exhibit high sidelobe levels, which leads to significant out-of-band power leakage. Existing techniques found in the literature either do not achieve sufficient sidelobe suppression or suffer from significant spectral efficiency loss. Precoding can be seen as a general linear processing method for power leakage reduction, however, how to design the optimal linear precoder is still an open problem. In this paper, the power leakage suppression is first treated as a matrix Frobenius norm minimization problem, and then the optimal orthogonal precoding matrix design for the power leakage suppression is proposed based on singular value decomposition (SVD). By further exploiting the extra degrees of freedom in the precoding matrix, two kinds of optimized precoding matrices, one with multi-carrier property and the other with single-carrier property, are developed to take the advantages of orthogonal frequency division multiplexing (OFDM) and single carrier frequency division multiple access (SC-FDMA), respectively. Simulation results show that both the multi-carrier and the single-carrier precoding schemes achieve significant power leakage suppression, and have similar peak-to-average power ratio (PAPR) and bit-error-rate (BER) to those of OFDM and SC-FDMA systems, respectively.

An Efficient Receiver for Preamble Detection in LTE SC-FDMA Systems with an Antenna Array

In this letter, we propose an efficient low complexity receiver for the preamble detection in single-carrier frequency division multiple access (SC-FDMA) systems with an antenna array. The proposed low complexity receiver is derived using a digital mixer and a multistage decimation filter. The signals for each receive antenna are non-coherently combined. Simulations performed in various channel environments validate that the proposed receiver attains a high detection performance equivalent to the full frequency domain approach which provides the optimal performance, while being quite low in computational complexity.

Cooperative diversity schemes for uplink single-carrier FDMA systems

Single-carrier frequency division multiple access (SC-FDMA) is considered as a promising technique that is adopted in the uplink for the upcoming 3GPP long term evolution (LTE). This is because it keeps most of the advantages of OFDMA in addition to low peak to average power ratio (PAPR). Designing diversity achieving schemes for SC-FDMA is a challenging task. The code should not affect the PAPR among other constraints. In this paper, we propose cooperative diversity schemes for SC-FDMA systems. Specifically, distributed space-time/frequency codes are proposed. The proposed distributed space-frequency code (DSFC) takes into account the low PAPR which is the feature of the system. Both decode-and-forward (DAF) and amplify-and-forward (AAF) protocols are considered. Erroneous decoding at the relay node is taken into account. Moreover, we propose a bandwidth efficient distributed space-time code (DSTC) for slow fading relay channels with DAF. Analytical and simulation results indicate that the proposed schemes achieve full diversity at the expense of small performance loss compared to the proposed codes in the literature.

Carrier Frequency Offsets Problem in DCT-SC-FDMA System: Investigation and Compensation

The Single-Carrier Frequency Division Multiple Access (SC-FDMA) system is a well-known system, which has recently become a preferred choice for uplink channels. In this system, the Carrier Frequency Offsets (CFOs) disrupt the orthogonality between subcarriers and give rise to Intercarrier Interference (ICI), and Multiple Access Interference (MAI) among users. In this paper, the impact of the CFOs on the performance of the Discrete Cosine Transform (DCT) SC-FDMA (DCT-SC-FDMA) system is investigated. Then, a new low-complexity joint equalization and CFOs compensation scheme is proposed to cancel the interference in frequency domain. The Minimum Mean Square Error (MMSE) equalizer is utilized in the proposed scheme. A hybrid scheme comprising MMSE equalization, CFOs compensation, and Parallel Interference Cancellation (PIC) is also suggested and investigated for further enhancement of the performance of the DCT-SC-FDMA system with interleaved subcarriers assignment. For simplicity, this scheme will be referred to as the MMSE+PIC scheme. From the obtained simulation results, it is found that the proposed schemes are able to enhance the system performance, even in the presence of the estimation errors.

Frequency Domain Decision Feedback Equalization for Uplink SC-FDMA

Single carrier frequency division multiple access (SC-FDMA) is one well-known scheme, which has recently become a preferred choice for uplink channels. Due to the usage of single carrier, the performance of SC-FDMA systems degrades in deep frequency selective fading channels. In this paper, we propose a structure of equalizer based on frequency domain decision feedback which could be used for multi-user SC-FDMA systems. Specific parameters of the equalizer are analyzed as well. This algorithm is applicable to various carrier allocations in multi-user systems such as localized allocation, distributed allocation, and frequency-hopping (FH) allocation. To reduce the complexity, it is not necessary to derive the inversion of matrix, which is required in the traditional decision feedback equalizer for single carrier frequency domain equalization (SC-FDE-DFE). It is shown by the simulation results that perfect performance could be achieved under all kinds of situations for multi-user systems. This structure can be used in the broadcasting uplink channels with SC-FDMA scheme.

Suppression of ICI and MAI in SC-FDMA communication system with carrier frequency offsets

Similar to other orthogonal frequency division multiplexing (OFDM)-based systems, carrier frequency offset (CFO) is a challenging problem in uplink communications of single carrier frequency division multiple access (SC-FDMA) system. It must be noticed that CFO, which is mainly due to oscillator instability and/or Doppler shift, would generate inter carrier interference (ICI) as well as multi-access interference (MAI) to disturb the received signals and seriously degrade system performance. Frequency synchronization in uplink communications is difficult because different users always experience different CFOs and one user's CFO correction would misalign other users. In this paper, we proposed a suppression method to overcome the multi CFOs problem. To implement this algorithm, block type pilots would be exploited, which is also utilized in LTE uplink standard. The proposed algorithm is based on the following two assumptions. Firstly the proposed algorithm is applied in this scenario, where different users start to communicate with the base station at different symbol periods, and secondly, during the pilot block and the following data blocks, the CFO of each user is quasi static, which is feasible since CFO is slow varying. Compared with other interference suppression methods, the proposed method could directly estimate the interference components from the inverse pilot matrix, thus it does not need to do the CFO estimation. Further more, since block type pilots is a common pilot pattern in wireless communication system, this algorithm can be easily extended to other communication system. Simulation results show that the proposed suppression algorithm can significantly improved system performance.

PAPR 감소와 효과적 채널 추정을 위한 SC-FDMA 통신 시스템의 파이럿 배치 방법

SC-FDMA(Single Carrier-Frequency Division Multiple Access) 통신 시스템에서 채널 추정을 위한 파일럿은 CAZAC 시퀀스를 이용하여 OFDM(Orthogonal Frequency Division Multiplexing) 신호의 높은 PAPR(Peak-to-Average Power Ratio)을 낮추는 방식을 사용한다. 그런데, 채널 추정을 위한 파일럿이 블록 타입으로 전송되므로, 수신단에서 파일럿 블록 사이의 여러 OFDM 심볼들은 시간 영역에서의 보간법을 시용하여 채널 추정하여야 하므로 매우 복잡하고 처리 시간이 길어질 수 있다. 또한 심한 fast fading 채널에서는 이러한 문제점이 더욱 커진다. 한편, 효과적인 고속 채널 추정을 위하여 OFDM 심벌 단위로, 주파수 영역에서 보간법을 수행하는 comb 타입의 파일럿을 사용하게 되면 OFDM 신호의 PAPR이 다시 높아지는 문제가 발생한다. 본 논문에서는 PAPR 감소와 효과적 채널 추정이 가능한 comb 타입의 파일럿을 배치 방법을 연구하였다. 이를 위하여 CAZAC 행렬 변환된 OFDM 신호에 comb 타입의 파일럿을 배치하고, 추가로 SLM 기법을 사용하였다. 그러나 기본적인 SLM(Selected Mapping) 기법은 위상 회전에 관한 부가 정보 전송이 필요하기 때문에 대역폭의 손실을 가져온다는 단점이 있다. 따라서, 본 연구에서는 파일럿은 SLM 위상 시퀀스와 곱해지지 않으며, SLM 위상 회전 시퀀스에 따라 서로 다른 파일럿을 신호에 삽입하여, 부가 정보를 사용하지 않고 대역폭의 손실이 없는 개선형 SLM 기법을 연구하였다. 시뮬레이션 결과, 4개의 위상 회전 시퀀스를 갖는 SLM을 사용하였을 때, 파일럿 삽입으로 인해 높아진 신호의 PAPR을 원래 수준과 비슷한 성능으로 감소되는 것을 알 수 있다. PAPR of the pilot symbols can be reduced down by the CAZAC sequence in the SC-FDMA communication system. However, it is very complicated and takes quite a long time to compute the interpolation between the OFDM information symbols for the channel estimation because the pilot data are trasmitted in the block type. Furthermore, situation will be much more serious in the severe fading channel. Actually the pilot insertion of the comb type is much efficient and convenient for the channel estimation since the calculation of the interpolation can be made in the frequency domain symbol by symbol. But, the PAPR will be regrown when the pilot data are inserted with the information data in the comb type. So, in this paper, we like to study the PAPR reduction and comb type pilot assignment for the efficient channel estimation. Unlike the conventional SLM(selected mapping) method requiring the side information, our improved SLM method is to use the phase rotation sequence into information data without rotating phase of pilot. We use different pilot data according to the different phase rotation sequence. From the simulation result, it can be confirmed that when SLM method of 4 phase rotation sequence is used, PAPR is almost same to the block type method without pilot.

Performance enhancement of SC-FDMA systems using a companding technique

In this paper, a companding technique is proposed to effectively reduce the peak-to-average power ratio (PAPR) in single-carrier frequency division multiple access (SC-FDMA) systems. By companding the samples with large amplitudes, while enhancing those with small amplitudes, a significant reduction in the PAPR can be achieved. The performance of the proposed SC-FDMA with companding system is studied and compared with that of the standard SC-FDMA system. Simulation results show that the SC-FDMA with companding system has a lower PAPR when compared with the conventional SC-FDMA system, while the complexity of the system slightly increases. Results also reveal that the companding coefficient must be chosen carefully in order to limit the PAPR without introducing degradations into the bit error rate performance.

Inter-subcarrier interference compensation in the frequency-hopped single-carrier frequency division multiple access communication system

Single-carrier frequency division multiple access (SC-FDMA) system having very good characteristic on peak-to-average power ratio is promising in communication area. But the performance of SC-FDMA system is very sensitive to inter-subcarrier interference (ICI), and existing phase noise suppression algorithm has reduced just phase noise only. Therefore the authors propose effective method, phase noise and frequency offset suppression (PNFS) algorithm, using comb-type pilot. PNFS algorithm can suppress phase noise, carrier frequency offset and even Doppler effect simultaneously in frequency domain. Through PNFS algorithm, SC-FDMA system has robust characteristic against ICI of performance degradation. Moreover, in these days, most electronic communication systems are weak to jamming. So, frequency-hopped (FH) scheme, which is one kind of spread spectrum techniques as a means of making performance better to supplement a disadvantage of SC-FDMA system on jamming attack, is considered. The authors would like to analyse ICI and jamming in SC-FDMA system and employ FH technique in SC-FDMA system because existing studies have not considered the situation regarding ICI and jamming exist simultaneously in mobile channel. So, the authors analyse degradation factors in FH-SC-FDMA system about ICI and jamming signal categorised as partial band jamming and multi-tone jamming. Then, the proposed FH-SC-FDMA system using PNFS algorithm has strong performances about ICI and jamming.

Transceiver scheme for single-carrier frequency division multiple access implementing the wavelet transform and peak-to-average-power ratio reduction methods

Single-carrier frequency division multiple access (SC-FDMA) has been adopted as a possible air interface for future wireless networks. It combines most of the advantages of orthogonal frequency division multiple access (OFDMA) and the low peak-to-average-power ratio (PAPR) of single-carrier transmission. This study proposes a new transceiver scheme for SC-FDMA systems implementing the wavelet transform to decompose the transmitted signal into approximation and detail components. The approximation component can be clipped or companded whereas the detail component is left unchanged because of its sensitivity to noise. Wavelet filter banks at the transmitter and the receiver demonstrate the ability to reduce the distortion in the reconstructed signal while retaining all the significant features present in the signal. The performance of the proposed scheme is investigated with different PAPR reduction methods. Simulation results show that the proposed scheme with the hybrid clipping and companding method provides a significant performance enhancement when compared with the conventional SC-FDMA system, while the complexity of the system is slightly increased.

Analysis of CFO effects on and phase compensation method for SC-FDMA systems

Discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) based single carrier-frequency division multiple access (SC-FDMA) is accepted as the uplink transmission scheme by the 3GPP-long term evolution standardization organization. In this paper, the effects of carrier frequency offset (CFO) on DFT-S-OFDM system are analyzed for both single user and multiple user accessing scenarios. According to the analysis, the CFO results in the attenuation, linear phase rotation, inter-symbol interference (ISI) and inter-sub-carrier interference (ICI) on the demodulated symbols of each desired user, and the multi-user interference (MUI) among uplink users. The theoretical values of ISI, ICI, and signal to interference ratio (SIR) are presented for the DFT-S-OFDM system with full and partial bandwidth detection respectively. A phase compensation method is proposed to reduce the effect of linear phase rotation on the demodulated symbols. Finally, the analytical values are verified by the simulation results.