Single Carrier System With Frequency Domain Equalization Research Articles

Efficient Fast-Convolution Based Hybrid Carrier System

The weighted-type fractional Fourier transform (WFRFT)-based hybrid carrier (HC) system has been proposed to bridge the gap between orthogonal frequency division multiplexing (OFDM) system and single-carrier system with frequency domain equalization (SC-FDE). In this paper, we propose a novel HC system based on efficient fast-convolution (FC) without a cyclic prefix to meet the requirements of complex scenarios towards future communications. The proposed system can achieve flexible optimization of system performance, such as minimizing out-of-band emission (OOBE), peak to average power ratio (PAPR) and bit error rate (BER). This efficient FC based hybrid carrier (FCHC) system is among the most competitive waveforms. The closed-form BER expressions are derived and analyzed over additive white Gaussian noise (AWGN) and frequency-selective fading channels. A modified equalizer over frequency-selective channels is also provided to resist the inter-block interference (IBI). Moreover, the banded minimum mean-square error (MMSE) equalization based on FC can be embedded in the proposed system over doubly-selective channels, and then the interference caused by fading channels can be further suppressed through the combination of FC and HC. The simulation results demonstrate the superiority of the proposed system over the conventional HC system in terms of OOBE, PAPR and BER. The significant flexibility and combined performance advantages make the proposed system a potential scheme for future communications.

PAM-SCFDE for Optical Wireless Communications

Multipath dispersion is a serious challenge in visible light communication (VLC) systems as these systems are used for indoor applications where there can be many reflections of the transmitted signal from the ceiling, walls, equipment, etc. These reflected signals cause intersymbol interference in the receiver and can degrade the performance of the system considerably. Orthogonal frequency-division multiplexing (OFDM) for optical wireless communications was introduced to mitigate multipath dispersion and has been well investigated in the literature. Recently, single-carrier systems with frequency-domain equalization (SCFDE) have been proposed as alternatives to OFDM. In this paper, we present pulse amplitude modulated SCFDE (PAM-SCFDE) to mitigate multipath dispersion in VLC systems. We also compare the proposed PAM-SCFDE with existing OFDM and SCFDE techniques for optical wireless communications in terms of analytical and simulated bit-error-rate (BER) performance, power-spectral efficiency, peak-to-average power ratio (PAPR), and overall system complexity. The proposed PAM-SCFDE requires lower per bit signal-to-noise ratio to achieve a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> or smaller for modulation sizes common in practice, both with and without considering the effects of light-emitting diode transmitters, such as nonlinearity, forward current restriction, and bandwidth limitation. Furthermore, it exhibits better power efficiency for data rates less than 3 bit/s/Hz, lower PAPR and system complexity compared to other systems.

8$\,\times\,$40-Gb/s Optical Coherent Pol-Mux Single Carrier System With Frequency Domain Equalization and Training Sequences

Owing to its low transmitter complexity and low sensitivity to nonlinear impairments, phase noise, and frequency offset, the single carrier system with frequency domain equalization (SC-FDE) is of interest for high-bit-rate optical transmission. In this letter, we experimentally demonstrate a 8×40-Gb/s optical coherent polarization-multiplexed SC-FDE over 2080-km fiber transmission using novel training sequences. The sequences are designed based on Chu and Golay complementary sequences to have binary levels and are fully compatible with the commercial quadrature phase-shift keying (QPSK) systems. The use of these training sequences helps achieve accurate channel estimation and equalization in full-system demonstration.

A Differential MIMO SC-FDE Transceiver Design over Multipath Fast Fading Channels

In this paper, we propose a new differential MIMO single-carrier system with frequency-domain equalization (SC-FDE) aided by the insertion of cyclic prefix. This block transmission system not only inherits all the merits of the SISO SC-FDE system, but is also equipped with a differential space-time block coding (DSTBC) such as to combat the fast-changing frequency selective fading channels without the needs to estimate and then compensate the channel effects. Hence, for practical applications, it has the additional merits of decoding simplicity and robustness against high mobility transmission environments. Computer simulations show that the proposed system can provide diversity benefit as the non-differential system does, while greatly reducing the receiver complexity.

Turbo aided Cyclic Prefix reconstruction for coded Single-Carrier systems with Frequency-Domain Equalization (SC-FDE)

In this paper, a Turbo aided Cyclic Prefix (CP) reconstruction scheme, termed Turbo-CPR, is proposed for Single-Carrier systems with Frequency-Domain Equalization (SC-FDE) that employ insufficient CP in the transmitter. In Turbo-CPR, the decoder output is incorporated in the process of equalization, i.e. Turbo equalizer is employed. It is shown in the simulation results that Turbo-CPR not only recovers the performance loss due to insufficiency of CP, but also provides extra gains over the lower bound of performance for conventional CP reconstruction schemes.

Iterative Cyclic Prefix Reconstruction for Precoded SC-FDE

A cyclic prefix reconstruction scheme is proposed for precoded single-carrier systems with frequency-domain equalization (SC-FDE) that employ insufficient length of cyclic prefix. For SC-FDE, cyclic prefix is employed to facilitate frequency-domain equalization at the receiver. Since inserting cyclic prefix incurs a loss in bandwidth-utilization efficiency, it is desirable to limit the length of cyclic prefix for SC-FDE. This paper designs the energy spreading transform (EST), a precoder that enables iterative reconstruction of missing cyclic prefix. The performance of the proposed scheme is shown to be close to that of SC-FDE with enough length of cyclic prefix.

Efficient cyclic prefix reconstruction using decision feedback filter for coded single-carrier systems with frequency-domain equalization (SC-FDE)

In this paper, an efficient Cyclic Prefix (CP) reconstruction scheme is proposed for Single-Carrier systems with Frequency-Domain Equalization (SC-FDE) that employ insufficient length of CP at the transmitter. By utilizing a decision feedback filter to cancel the residual InterSymbol Interference (ISI) in the equalized signal, the proposed scheme can effectively lower the low bound of performance for the CP reconstruction schemes and can greatly improve the Bit Error Rate (BER) performance of SC-FDE systems. In addition, the existing methods and the proposed scheme are also optimized. It is shown in the simulation results that, when the Signal-to-Noise Ratio (SNR) exceeds a certain threshold, the proposed scheme can achieve the low bound of performance for the existing methods. Moreover, by increasing the number of iteration or through optimization, the low bound can be outperformed.

A comparison of an OFDM system and a single carrier system using frequency domain equalization

AbstractIn this work we compare an OFDM (Orthogonal Frequency Division Multiplexing) system and a SC/FDE (Single Carrier System with Frequency Domain Equalization) system in terms of their BER performance, channel estimation techniques, bandwidth‐efficiency and other design parameters. In both systems an estimation of the channel transfer function is needed for equalization purposes. Different frequency domain based channel estimation techniques for both systems are presented and compared. BER‐simulations have been performed for channel‐coded data in typical indoor multipath environments. The parameters of both systems are adapted to the Hiperlan/2 and IEEE 802.1 la standards. It will be pointed out that OFDM shows slight advantages when taking the BER performance into account, while the SC/FDE system exhibits advantages in terms of signal processing complexity. Finally a combination of OFDM and SC/FDE is described that exhibits significant advantages.