Showing papers on "SC-FDE published in 2010"

Single Carrier Modulation With Nonlinear Frequency Domain Equalization: An Idea Whose Time Has Come—Again

Abstract: In recent years single carrier modulation (SCM) has again become an interesting and complementary alternative to multicarrier modulations such as orthogonal frequency division multiplexing (OFDM). This has been largely due to the use of nonlinear equalizer structures implemented in part in the frequency domain by means of fast Fourier transforms, bringing the complexity close to that of OFDM. Here a nonlinear equalizer is formed with a linear filter to remove part of intersymbol interference, followed by a canceler of remaining interference by using previous detected data. Moreover, the capacity of SCM is similar to that of OFDM in highly dispersive channels only if a nonlinear equalizer is adopted at the receiver. Indeed, the study of efficient nonlinear frequency domain equalization techniques has further pushed the adoption of SCM in various standards. This tutorial paper aims at providing an overview of nonlinear equalization methods as a key ingredient in receivers of SCM for wideband transmission. We review both hybrid (with filters implemented both in time and frequency domain) and all-frequency-domain iterative structures. Application of nonlinear frequency domain equalizers to a multiple input multiple output scenario is also investigated, with a comparison of two architectures for interference reduction. We also present methods for channel estimation and alternatives for pilot insertion. The impact on SCM transmission of impairments such as phase noise, frequency offset and saturation due to high power amplifiers is also assessed. The comparison among the considered frequency domain equalization techniques is based both on complexity and performance, in terms of bit error rate or throughput.

Unique word prefix in SC/FDE and OFDM: A comparison

Abstract: The concept of using unique word (UW) prefixes instead of cyclic prefixes (CPs) is already well investigated for single carrier systems with frequency domain equalization (SC/FDE). In OFDM (orthogonal frequency division multiplexing), where the data symbols are specified in frequency domain, the introduction of UWs — which are specified in time domain — is not that straight forward. In this paper we show how unique words can also be introduced in OFDM symbols. In OFDM our proposed method introduces correlations between subcarrier symbols. This allows to apply a highly efficient LMMSE (linear minimum mean square error) receiver. Throughout this paper we discuss the similarities and differences of UW-SC/FDE and UW-OFDM transmitter/receiver processing, and we present simulation results in indoor multipath environments.

Joint turbo equalisation and carrier synchronisation for SC-FDE schemes

Abstract: In this paper we consider the use of single carrier (SC) modulations combined with frequency-domain equalisation (FDE) in future broadband wireless systems. We propose iterative receiver structures with joint equalisation and carrier synchronisation. The proposed receivers can be regarded as modified frequency-domain turbo equalisers where we perform a decision-directed frequency offset estimation within each iteration of the turbo equaliser. Our performance results show that the proposed receiver structure has good bit error rate (BER), even with moderate frequency offsets and in severely time-dispersive channels. Moreover, our receiver has a relatively low implementation complexity, due to its fast Fourier transform (FFT)-based frequency-domain implementation. Copyright © 2010 John Wiley & Sons, Ltd.

An efficient CP compensation for SC-FDE with insufficient CP symbols

Abstract: In this letter, we propose a method to mitigate interferences for single carrier frequency domain equalization (SC-FDE) with insufficient cyclic prefix (CP) symbols. The resultant channel matrices are not circulant due to some missing symbols. Unlike OFDM, however, the reconstruction of missing symbols using the estimated symbols is not effective. We propose that these missing symbols may be filled with the symbols in the following received block when the channel is static over the consecutive blocks. Since this method does not require estimation of symbols, the precision of detection can be enhanced. The improvement in the performance of this method is still limited since interferences are not completely removed. An iterative interference cancellation method is used to remove the residual interferences. The performance of proposed method is verified by simulations.

Iterative Frequency Domain Equalization and Carrier Synchronization for Multi-Resolution Constellations

Abstract: Broadband broadcast and multicast wireless systems usually employ OFDM modulations (Orthogonal Frequency Division Multiplexing) combined with non-uniform hierarchical constellations. However, these schemes are very prone to nonlinear distortion effects and have high carrier synchronization requirements. SC-FDE (Single-Carrier with Frequency-Domain Equalization) is an attractive alternative for OFDM, especially when an efficient power amplification is intended. In this paper we consider the use of SC-FDE schemes combined with non-uniform hierarchical constellations in broadband broadcast and multicast wireless systems. We study the impact of residual CFO (Carrier Frequency Offset) on the performance of multi-resolution schemes and we propose iterative frequency domain receivers with joint detection and carrier synchronization to cope with residual CFO estimation errors (a coarse CFO estimation and compensation is assumed before the equalization procedure). Our results show that while a very high carrier synchronization accuracy is required for the least protected bits, the most protected bits are relatively robust to the CFO. By employing the proposed receiver we increase significantly the robustness to residual CFO estimation errors.

Asymptotically optimal low-complexity SC-FDE in data-like co-channel interference

Abstract: In this paper, the design of a low-complexity linear equalizer is considered for single-carrier (SC) block transmission in the presence of inter-symbol interference (ISI) and data-like co-channel interference (CCI). Unlike the linear minimum mean-squared error (LMMSE) frequency-domain equalizer (FDE) designed to suppress ISI only, the LMMSE FDE suffers from high computational complexity due to the CCI component in the signal correlation matrix. Motivated by the fact that the double Fourier transform of the autocorrelation function of a wide-sense cyclostationary process consists of impulse fences with equal spacing, a low-complexity FDE is proposed that approximates the frequency-domain correlation matrix of the CCI plus noise by a block matrix with diagonal blocks. It is shown that the proposed FDE is asymptotically optimal in the sense that the average mean-squared error (MSE) converges to that of the LMMSE FDE as the block length tends to infinity. It is also shown that the proposed FDE is more numerically stable than the LMMSE FDE when the receive filter is matched to the transmit filter and its output is over-sampled to better capture the cyclostationarity of the CCI. Discussions and numerical results include SC block transmission systems with unique word instead of cyclic prefix, and systems with multiple receive antennas.

Radio Interface for High Data Rate Wireless Sensor Networks

Abstract: This paper gives an overview of radio interfaces devoted for high data rate Wireless Sensor Networks. Four aerospace applications of WSN are presented to underline the importance of achieving high data rate. Then, two modulation schemes by which High Data Rate can be achieved are compared : Multi carrier approaches, represented by the popular Orthogonal Frequency Division Multiplexing (OFDM) and Single carrier methods, represented by Single Carrier Frequency division Equalization and its application for multiple access Single Carrier Frequency division multiple Access (SC-FDMA). SC-FDMA, with a very low Peak Average Power Ratio (PAPR), is as strong alternative to the OFDM scheme for highly power constraint application. The Chosen radio interface will be, finally, tested by a model based design approach based on Simulink and FPGA realization. SC-FDMA, with a very low Peak Average Power Ratio (PAPR), is as strong alternative to the OFDM scheme for highly power constraint application. The Chosen radio interface will be, finally, tested by a model based design approach based on Simulink and FPGA realization.

Performance of Packet Combining ARQ Error Control in a TDMA SC-FDE System

Abstract: This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) with low-complexity soft combining ARQ schemes (Automatic Repeat reQuest). With our technique, packets associated to different transmission attempts are combined in a soft way, allowing improved performances. Its low complexity makes it particularly interesting for the uplink of wireless systems. This paper proposes an accurate analytical model for a TDMA (Time Division Multiple Access) scheme where packet combining ARQ is applied. It evaluates the uplink non-saturated packet delay and goodput for a generic message arrival process. Our analytical results are validated using physical and MAC layer simulations.

Peak-to-average power ratio of SC-FDMA systems with localized subcarrier mapping

Abstract: Single carrier frequency division multiple access (SC-FDMA), which combines the single carrier frequency domain equalization (SC-FDE) and frequency division multiple access (FDMA) techniques is a promising broadband wireless access scheme However, previous research has shown that the peak-to-average power ratio (PAPR) of SC-FDMA is high especially in the case of localized subcarrier mapping In this paper, we simulate and analyze the PAPR for SC-FDMA with two subcarrier mapping schemes known as Localized FDMA (LFDMA) and Interleaved FDMA (IFDMA) respectively, and evaluate the PAPR performance of users assigned on different subcarriers in LFDMA To reduce the PAPR, we propose an efficient clipping-based PAPR reduction algorithm Simulation results show that with a small degradation in the system bit error rate (BER) performance the proposed scheme can achieve around 2dB PAPR reduction for LFDMA

On the Design of Linear Receivers for SC-FDE Schemes Employing OQPSK Modulation

Abstract: This paper considers the design of linear frequency-domain receivers with oversampling for OQPSK (Offset Quaternary Phase Shift Keying) signals. Based on a receiver structure able to eliminate the residual interference between in-phase (I) and quadrature (Q) components at the sampling instants, a method that minimizes the overall residual ISI (Inter-Symbol Interference) plus IQI (I-Q interference) is proposed. Therefore, this receiver significantly outperforms previous frequency-domain OQPSK receivers.

Delay Optimization on a p-Persistent MAC Protocol for a Multi-Packet Detection in SC-FDE System

Abstract: This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Frequency- Domain Equalization). We consider iterative frequency-domain receivers that jointly perform equalization, multi-packet separation and channel decoding operations, for up to Qmax mobile terminals transmitting in one slot. In this paper we propose an accurate analytical model for a p-persistent random access MAC protocol, designed to handle a total number of mobile terminals J above Qmax. It evaluates the uplink non-saturated packet delay and calculates the optimal configuration for the packet transmission probability associated to each mobile terminal that minimizes the delay. Our analytical results are validated using physical and MAC layer simulations.

A simple pilot position detection technique for channel estimation of SC-FDE

Abstract: This letter investigates the frequency domain pilot multiplexing technique (FDPMT) for channel estimation of single-carrier frequency domain equalization (SC-FDE) and proposes a simple pilot position detection technique to blindly estimate the pilot positions in the frequency domain by using the noise subspace. Simulation results show that the proposed technique is robust to multipath fading channels with exponential power delay profile.

Joint detection and channel estimation for block transmission schemes

Abstract: SC-FDE (Single-Carrier with Frequency-Domain Equalization) block transmission technique can have excellent performance in severely time-dispersive channels provided that accurate channel estimates are available at the receiver. In this paper we consider joint detection and channel estimation for SC-FDE schemes where a coarse channel estimate is obtained with the help of a training sequence and we employ iterative receivers where for each iteration the data estimates are used to improve the channel estimates. However, since the frequency-domain data blocks can have large envelope fluctuations, a decision-directed channel estimation might have significant noise enhancement effects. To overcome this problem, we combine channel estimates based on the training sequence with decision-directed channel estimates. Our performance results show that these techniques allow good performances without requiring high-power pilots or training blocks.

On the Design of Turbo Equalizers for SC-FDE Schemes with Different Error Protections

Abstract: In this paper we consider SC-FDE schemes (Single-Carrier with Frequency-Domain Equalization) employing multi-resolution hierarchical constellations and we consider the design of turbo receivers, implemented in the frequency-domain, for systems where we have different error protections. We present a versatile method to design the receiver that is suitable to any constellation.

On the design of iterative FDE receivers for OQAM modulations

Abstract: This paper considers receiver designs for SC-FDE schemes (Single-Carrier with Frequency-Domain Equalization) employing M-ary OQAM signals (Offset Quadrature Amplitude Modulation). It is shown that the interference between the in-phase (I) and quadrature (Q) components at the sampling points can lead to severe performance degradation. Therefore, receivers without residual I-Q interference (IQI), as well as receivers with IQI cancellation were developed. Our performance results show that the new receivers are suitable to M-ary OQAM schemes.

Single-carrier transmission frequency-domain equalization based on a wiener filter

Abstract: Recently, frequency-domain equalization for single-carrier transmission (SC-FDE) has been given much attention. For example, the up-link in the 3.9 generation mobile phone long term evolution (LTE) system, an SC-FDMA method using SC-FDE and multiple access will be adopted. However in previous research, there are many papers describing the features and advantages of SC-FDE based on a comparison of SC-FDE and orthogonal frequency-division multiplexing (OFDM) systems. In this paper, we discuss single-carrier transmission equalization in the time-domain (SC-TDE) and SC-FDE in a unified way centered on the Wiener filter based on the minimum mean square error (MMSE) criterion. As a result, we could get useful information and pointers, especially for when we want to replace existing SC-TDE technology with SC-FDE technology.

Decision-directed channel estimation for SC-FDE in amplify-and-forward relaying networks

Abstract: In this letter, we propose a decision-directed channel estimation scheme for single-carrier frequency-domain equalization in amplify-and-forward (AF) relaying networks. For coherent combining of the received signals in AF-based cooperation, conventional channel estimation schemes have focused on estimation of source-destination and source-relay-destination channels. However, if the individual channels in the source-relay-destination link are not considered, the relaying gain is limited because the noise propagation from the relay to the destination affects the effective signal-to-noise ratio at the destination. The proposed scheme estimates the effective channel parameters for maximal-ratio combining, in the absence of channel-state information (CSI) from the relay. Simulation results show that the proposed scheme outperforms the conventional scheme and approaches the performance with perfect CSI.

Bit-interleaved coded multilevel modulation for single-carrier frequency-domain equalization

Abstract: This paper proposes a bit-interleaved coded multilevel modulation for single-carrier frequency-domain equalization (SC-FDE). In the proposed system, multiple layers are encoded and interleaved together, using one encoder and one interleaver, and then they are mapped by hierarchical symbol mapping. A corresponding receiver structure is presented, where multiple layers can be decoupled by iterative frequency-domain equalization with improved soft information. Simulation results show that the proposed system has better performance than conventional modulation schemes such as bit-interleaved coded modulation (BICM) and multilevel BICM (MLBICM).

On the impact of multipath propagation and diversity in performance of iterative block decision feedback equalizers

Abstract: SC modulation (Single-Carrier) with FDE (Frequency-Domain Equalization) combined with iterative (turbo) FDE schemes has excellent performance in severely time-dispersive channels, making it a promising candidate for future broadband wireless systems. In fact, it was observed that the performance can be close to the MFB (Matched Filter Bound). In this paper we consider a class of iterative FDE schemes and we study the impact of the number of multipath components and the diversity order on its performance. It is shown that for a high number of separable multipath components the asymptotic performance approaches the MFB, even without diversity. When we have diversity the performance approaches the MFB faster, even when we have just a small number of separable multipath components.

Polarization Division Multiplexing for SC-FDE Communications over Dispersive Optical Fibers

Abstract: High order linear modulations, combined with coherent detection and signal processing at the receiver, are nowadays considered to reach the new capacity targets for the communications over the optical fibers. In order to reduce the computational complexity of the algorithms at the receiver, it has recently been proposed to compensate for the chromatic dispersion (CD) and polarization mode dispersion (PMD) in the frequency domain. Orthogonal frequency-division multiplexing (OFDM) and single- carrier with frequency domain equalization (SC-FDE) are two alternative coding strategies to support frequency domain signal processing. Compared to OFDM, SC-FDE is particularly interesting because it potentially facilitates the implementation of the transmitter and it generates a lower peak-to-average power ratio (PAPR) waveform. The goal of the present paper is to demonstrate how the SC-FDE system can further support polarization division multiplexing (PDM) to double the communication capacity. The SC-FDE PDM system is derived analytically and its performance is assessed by numerical simulations. It is shown that a 72 Gbps bit rate can be obtained in a 10 GHz bandwidth.

Performance comparison of cooperative OFDM and SC-FDE relay networks in a frequency-selective fading channel

Abstract: Cooperative networking schemes provide spatial diversity gain (named cooperative diversity gain) using the antennas of spatially distributed users. Consistent research has been focusing on cooperative networks using orthogonal frequency division multiplexing (OFDM) and single carrier with frequency domain-equalization (SC-FDE). Coherent detection and frequency-domain equalization (FDE) require accurate channel estimation. In this paper, we present a performance comparison of cooperative OFDM relay network and cooperative SC-FDE relay network with pilot-assisted channel estimation. We consider a joint diversity combining and FDE in order to obtain a larger frequency diversity gain. When channel coding is used, cooperative OFDM relay network performs similarly to cooperative SC-FDE relay network in a frequency-selective fading channel.

Adaptive Detector for SC-FDE in Multiuser DS-UWB Systems Based on Structured Channel Estimation with Conjugate Gradient Algorithm

Abstract: In this work, we propose a conjugate gradient (CG) based structured channel estimation (SCE) scheme for single-carrier frequency domain equalization (SC-FDE) in multiuser direct-sequence ultra-wideband (DS-UWB) systems. The minimum mean square error (MMSE) linear detection strategy is used and a cyclic prefix is employed. We perform the adaptive channel estimation in the frequency domain and implement the despreading in the time domain after the FDE. In this scheme, the linear MMSE detection requires the knowledge of the number of users and the noise variance. For this purpose, we propose algorithms for estimating these parameters. A CG adaptive algorithm is then developed for the SCE scheme. With lower complexity than the recursive least squares (RLS) algorithm and better performance than the Least mean squares (LMS) algorithm, the SCE-CG achieves a better tradeoff between the complexity and the performance.

On maximum achievable information rates of single-carrier and multi-carrier systems over the ultra wideband channels

Abstract: In terms of information theory, in this paper, the maximum achievable information rates of modulation systems are investigated over ultra wideband (UWB) multi-path channels where channel state is only known at the receiver. The capacity and mutual information of multi-carrier and single-carrier systems with digital modulation are compared using different UWB channel parameters. Assuming the inputs are i.i.d. equiprobable, the mutual information of SC systems is evaluated with frequency domain equalization (FDE) and with an a posteriori probability (APP) detector, respectively. The capacity of multi-carrier systems is evaluated with orthogonal frequency-division multiplexing (OFDM). Numerical results show the mutual information of SC APP system is better than that of OFDM system over UWB channels, though SC FDE alone causes capacity loss of SC system due to residual ISI of linear MMSE processing. Therefore, a hybrid nonlinear or iterative SC system to eliminate the residual ISI is indispensable.

A sub-block orthogonal single carrier frequency domain equalization system in fast Rayleigh fading channel

Abstract: In this paper, we analyze the frequency domain linear equalization (FDLE) of single carrier block transmission (SCBT) systems under fast fading channel. First, we propose a new approximating model in which the channel is assumed to be static in sub-blocks vary each other. Based on this model, we derive a new 2-orthogonal-sub-blocked frequency domain equalization method. Then, we derive the conditions of the channel under which the equalization method can be applied to the 2-orthogonal-sub-blocked systems. Simulation demonstrates that the proposed method can improve the anti-Doppler ability of SC-FDLE and at the same time keep its high efficiency and low complexity.

A single-carrier modulation system based on the fractional fourier domain equalization in aeronautical channels

Abstract: The channel is time-frequency-selective due to considerable relative movement between airborne communication transceivers in aeronautical communications systems. The performances based on traditional orthogonal frequency division multiplexing (OFDM) and single carrier frequency domain equalization (SC-FDE) systems are degraded because of the timing variant characteristic under time-frequency-selective channels. To get better performance, researches have been done for the OFDM system based on the fractional Fourier transform through selecting the optimal fractional order. However, the application of the method is limited because of the request of feedback link. This paper proposes a signal carrier modulation systems with equalization based on the fractional Fourier transform (SC-FRFDE), in which the feed-back link is not necessary. After description of the channel characteristic, the channel estimator and equalizer are designed according to the least squares (LS) algorithm and zero forcing criterion. Moreover, the algorithm for selecting the optimal order of fractional Fourier transform is derived. Theoretical analysis and numerical simulation results show that the system can significantly improve the performance of SC-FDE system.

A simple simi-blind equalization algorithm for precoding single carrier system with frequency domain equalization

Abstract: A semi-blind equalization method is proposed for precoding single carrier system with frequency domain equalization(SC-FDE) The method is modified according to Bussgang algorithm and the implementation is easy because it does not need complex computation Simulations are used to demonstrate the proposed method

Are SC-FDE Systems Robust to CFO?

Abstract: This paper investigates the impact of carrier frequency offset (CFO) on Single Carrier wireless communication systems with Frequency Domain Equalization (SC-FDE). We show that CFO in SC-FDE systems causes irrecoverable channel estimation error, which leads to inter-symbol-interference (ISI). The impact of CFO on SC-FDE and OFDM is compared in the presence of CFO and channel estimation errors. Closed form expressions of signal to interference and noise ratio (SINR) are derived for both systems, and verified by simulation results. We find that when channel estimation errors are considered, SC-FDE is similarly or even more sensitive to CFO, compared to OFDM. In particular, in SC-FDE systems, CFO mainly deteriorates the system performance via degrading the channel estimation. Both analytical and simulation results highlight the importance of accurate CFO estimation in SC-FDE systems.

An adaptive SC-FDE transmission enhancing frequency diversity benefit

Abstract: This paper proposes an adaptive single-carrier modulation with frequency domain equalization (SC-FDE) scheme further enhancing frequency diversity benefit. We have so far proposed the periodic spectrum transmission realized by the even-numbered time domain samples, which further improves the bit error rate (BER) of SC-FDE in severe frequency selective fading channels. However, in frequency non-selective fading channels, the periodic spectrum transmission provides worse BER than the traditional non-periodic transmission. Therefore, the proposed adaptive transmission chooses the appropriate transmission mode by comparing the error vector magnitudes (EVM) of the periodic and non-periodic transmissions. Moreover, since the EVM is measured by the CAZAC-based pilot signals used for channel estimation, additional redundancy is not needed any more. Numerical results show that the proposed adaptive scheme always provides the best performance irrespective of the frequency selectivity in channels while its frequency selectivity gives some BER degradation in the periodic and non-periodic transmissions.

Enhanced phase tracking for unique word based SC-FDE on frequency selective channels

Abstract: This paper proposes a new residual carrier frequency offset (CFO) estimation technique for the unique word (UW) based single-carrier transmission with frequency domain equalizer (SC-FDE) on frequency selective channels. In extremely frequency selective channels, UW symbols for CFO estimation can also be corrupted by the inter-symbol interference (ISI). Since the UW can be included in the equalizer, we employ the FDE before the CFO estimation. Moreover, we utilize the repeated pattern of UW symbols to improve the estimation accuracy.

Pilot interval design for linear interpolated channel estimation in SC-FDE system

Abstract: This paper investigates the effects of pilot interval design on linear interpolated channel estimation in single carrier frequency domain equalization(SC-FDE) system. Based on the properties of noise accumulation and fading channel correlation, the optimal pilot interval design is proposed. Simulations are finished over the four-ray Rayleigh channel, and the results prove that the proposed method is finally practicable. The experiential value of the optimal pilot interval is given, and is provided reference for engineering design.