Orthogonal Frequency Division Multiplexing With Offset Quadrature Amplitude Modulation Research Articles

Novel Algorithm for Nonlinear Distortion Reduction Based on Clipping and Compressive Sensing in OFDM/OQAM System

Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation (OFDM/OQAM) signal has high peak-to-average power ratio (PAPR) problem. It not only affects the distortion in High Power Amplifier (HPA) but also results in bit error ratio (BER) degradation. In this paper an improved algorithm based on Clipping and Compressed Sensing (CS) is proposed. The transmitter uses clipping to reduce the PAPR and, the receiver uses an improved inverse model, to reduce the nonlinear distortion introduced by HPA and CS cancels the signal distortion introduced by clipping. Simulation results show that the proposed method not only significantly reduces the PAPR of OFDM/OQAM signals, but also effectively improves the BER performance of the system.

Joint Iterative filtering and companding parameter optimization for PAPR reduction of OFDM/OQAM signal

An efficient companding transform combined with iterative filtering is proposed to reduce the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) signals. The proposed method can jointly optimize PAPR and BER performance, and effectively eliminate out-of-band radiation caused by signal amplitude distortion in the iterative process. Moreover, by adaptively adjusting transform parameters in the iterative process, more design flexibility in companding and lower out-of-band radiation are given to satisfy various system requirements. The proposed method had a simple functional form and less computational complexity, the theoretical PAPR reduction gain and the impact of companding distortion were derived. Simulation results show that this scheme can substantially offer better overall performances in terms of PAPR reduction, BER performance and bandwidth efficiency.

BOMA and OFDM/OQAM modulation for a radio-over-fiber system with enhanced spectral efficiency.

A novel radio-over-fiber system with enhanced spectral efficiency is proposed by using a building-block-sparse-constellation-based orthogonal multiple access (BOMA) technique, and orthogonal frequency-division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) technique. With the help of BOMA, a user with good signal-to-noise ratio (SNR) can use the frequency band of a user with poor SNR to transmit extra information by sharing the same well-designed constellation. Moreover, the cycle prefix in OFDM is no longer required due to the properly designed prototype filters in OFDM/OQAM, contributing to maximum spectral efficiency (SE). To optimize transmission performance, four types of sparse constellations with different Euclidean distances between constellation points are designed. In our experiment, BOMA-OFDM/OQAM signals with a total net rate of 1.84Gb/s and average SE of 4.6bit/s/Hz are successfully transmitted over 25.2km standard single-mode fiber for two users with wireless distances of 0.8m and 0.3m, respectively. Experimental results show that SE is increased by 37.7% compared with the traditional orthogonal frequency-division multiple access technique.

Overlapped Segmental Active Constellation Extension for the PAPR Reduction of the OFDM-OQAM System

Orthogonal frequency division multiplexing with Offset Quadrature Amplitude Modulation (OFDM-OQAM) technique has drawn significant interests in recent years. However, most of the existing OFDM peak-to-average ratio (PAPR) reduction schemes cannot be used in the OFDM-OQAM system directly. In this paper, a modified scheme called overlapped segmental Active Constellation Extension (OS-ACE) is proposed to deal with the high PAPR problem specifically in the OFDM-OQAM system. For the proposed OS-ACE scheme, the input signals are divided into a number of overlapped segments and then the ACE operation is processed on each segment. Simulation results show that the modified scheme used in the OFDM-OQAM system can provide better performance than conventional ACE scheme directly used in the OFDM-OQAM system, and even outperforms conventional ACE scheme applied in the OFDM system.

OSTBC–MISO–OFDM/OQAM Systems with Time Reversal Technique

Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) is a multicarrier modulation scheme that can be considered as an alternative to the conventional OFDM with cyclic prefix (CP) for transmission over multipath fading channels. In this paper, we investigate the combination of the OFDM/OQAM with orthogonal space time blok coding (OSTBC) in multiple input single output (MISO) system with time reversal (TR) technique. TR can be viewed as a precoding scheme which can be combined with OFDM/OQAM and easily carried out in a MISO context. We present the simulation results of the performance of OFDM/OQAM system in SISO case compared with the conventional CP-OFDM system and the performance of the combination OSTBC---MISO---OFDM/OQAM with TR compared to Alamouti CP-OFDM. The performance is derived by computing the bit error rate as a function of the transmit signal-to-noise ratio.

Spatial Multiplexing OFDM/OQAM Systems With Time Reversal Technique

Orthogonal Frequency Division Multiplexing with Offset Quadrature Amplitude Modulation (OFDM/OQAM) is a multicarrier modulation scheme that can be considered as an alternative to the conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) for transmission over multipath fading channels. In this paper, we investigate the combination of the OFDM/OQAM with Multiple Input Multiple Output (MIMO) system with Time Reversal (TR) technique. TR can be viewed as a precoding scheme which can be combined with OFDM/OQAM and easily carried out in a MIMO context using spatial data multiplexing. We present the simulation results of the performance of OFDM/OQAM system in SISO case compared with the conventional CP-OFDM system and the performance of the combination MIMO-OFDM/OQAM with TR compared to MIMO-CP-OFDM. The performance is derived by computing the Bit Error Rate (BER) as a function of the transmit signal-to-noise ratio (SNR).

Design of Robust Pulses to Insufficient Synchronization for OFDM/OQAM Systems in Doubly Dispersive Channels

This paper presents a pulse shaping method robust to insufficient synchronization in orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) systems over doubly dispersive (DD) channels. The proposed pulse is designed as a linear combination of several well localized Hermite functions. The coefficients optimization problem is modeled as a nonconvex constrained fractional programming problem based on the signal-to-interference ratio (SIR) maximization criterion. An efficient iterative algorithm is applied to simplify the problem to a series of quadratically constrained quadratic program (QCQP) problems which can be solved by semidefinite relaxation (SDR) method. Simulation results show that the proposed pulse is superior to traditional pulses with respect to SIR performance over DD channels in the presence of carrier frequency offset (CFO) and timing offset (TO).

Optimal Pulses Robust to Insufficient Synchronization for OFDM/OQAM Systems

In this paper, a novel pulse shaping method is presented for Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) systems. Designed as a linear combination of normalized Hermite functions, the proposed pulse is optimized with respect to interference caused by insufficient synchronization such as carrier frequency offset (CFO) and timing offset (TO). The optimization problem, based on signal-to-interference ratio (SIR) maximization criterion, is carried out using an efficient iterative algorithm. Simulation results show that this optimal pulse outperforms traditional prototype pulses in the presence of insufficient synchronization.

Overlapped Segmental Clipping for the PAPR Reduction of the OFDM-OQAM system

Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM-OQAM) technique has drawn significant interests in recent years. However, most of the existing OFDM peak-to-average ratio (PAPR) reduction schemes cannot be used in the OFDM-OQAM system directly. In this paper, a modified scheme called overlapped segmental clipping (OS-clipping) is proposed to deal with the high PAPR problem specifically in the OFDM-OQAM system. For the proposed OS-clipping scheme, the input signals are divided into a number of overlapped segments and then the clipping operation is processed on each segment. Simulation results show that the modified scheme used in the OFDM-OQAM system can provide better performance than conventional clipping scheme directly used in the OFDM-OQAM system, and even outperforms conventional clipping scheme applied in the OFDM system.

Peak-to-Average Power Ratio Reduction for OFDM/OQAM Signals via Alternative-Signal Method

In this paper, we consider the peak-to-average power ratio (PAPR) reduction problem for orthogonal frequency-division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM). In particular, the OFDM/OQAM signal is generated by summing over M time-shifted OFDM/OQAM symbols, where successive symbols are interdependent with each other. The alternative-signal (AS) method, which directly leads to the independent AS (AS-I) and joint AS (AS-J) algorithms, is employed to reduce the PAPR of the OFDM/OQAM signal. The AS-I algorithm reduces the PAPR symbol by symbol with low complexity, whereas the AS-J algorithm applies optimal joint PAPR reduction among M OFDM/OQAM symbols with much higher complexity. To balance the performance and the computation complexity, we propose a sequential optimization procedure, which is denoted AS-S, which achieves a desired compromise between performance and complexity.