Offset Quadrature Amplitude Modulation Based Orthogonal Frequency Division Multiplexing Research Articles

Time Domain IRCI-Free Pulse Compression for OQAM-OFDM Radar System

In this article, a novel majorization-minimization (MM)-based time domain pulse compression method (MM-based TDPCM) is proposed for offset quadrature amplitude modulation-based orthogonal frequency division multiplexing (OQAM-OFDM) radar system. We first propose a TDPCM by constructing a general linear model from the time domain with the estimated weights of the OQAM-OFDM signal and solving the model with a whitening operation to complete the pulse compression. The proposed TDPCM greatly reduces the required number of subcarriers for the given range cells and achieves inter range cell interference (IRCI)-free pulse compression. Furthermore, the MM-based TDPCM is proposed to maximize the signal-to-noise ratio (SNR) of the TDPCM. By theoretically analyzing the SNR performance of the TDPCM, we develop an optimization model to design the transmitted weights of the OQAM-OFDM signal. Then, the MM algorithm is proposed to solve the optimization model, realizing the maximum SNR output. Finally, numerical simulation results verify the superior performance of the proposed MM-based TDPCM.

Waveform designs for joint radar-communication systems with OQAM-OFDM

In this paper, we develop a joint radar-communication system with offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OQAM-OFDM), which is capable of realizing the radar and communication functions simultaneously. We first introduce a unified received signal model for the radar and communication systems by taking the multipath effect into account. Then, we propose a method to achieve information demodulation and radar pulse compression at the same time. By analyzing the signal-to-noise ratio (SNR) for the radar operations and the communication individually, we solve an optimization model to maximize the radar SNR and the communication SNR by designing the transmitted sequence of the OQAM-OFDM. Since the optimization problem is NP-hard, we present a joint method involving both the cyclic algorithm and the alternating direction method of multipliers algorithm (CA-ADMM) to obtain a solution. Finally, numerical results verify superior performance of the proposed scheme.

IRCI-free OQAM-OFDM radar pulse compression

In this paper, a pulse compression method is proposed with the offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OQAM-OFDM) signal. By establishing the received OQAM-OFDM signal as a linear model form and without inserting any cyclic prefix (CP), we propose a concise and easily implemented pulse compression method. The proposed method realizes the inter-range-cell interference (IRCI) free pulse compression perfectly, which improves the power efficiency, and the scope of observation will not be restrained by the number of subcarriers. Besides, the signal-to-noise ratio (SNR) after the pulse compression is derived. It is proved that the SNR gain for the proposed pulse compression method can reach the same as that of the method using the matched filter. Finally, numerical simulation results are provided and discussed.

OQAM-OFDM Radar Approximated IRCI-Free Pulse Compression

This paper proposes a pulse compression method by using the offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OQAM-OFDM) signal without inserting any cyclic prefix (CP). A modified interference approximation-based pulse compression method (MIA-based PCM) is proposed, by exploiting the demodulated real weights of the OQAM-OFDM signal, the inter-symbol and inter-subcarrier interferences to enhance the performance. The MIA-based PCM achieves approximated inter-range-cell interference (IRCI)-free pulse compression and perfect Doppler estimation, which has both the benefits of power efficiency and good Doppler tolerance. Finally, numerical simulation results are provided and discussed.

A prototype filter design based on channel estimation for OQAM/OFDM systems

A prototype filter design for offset quadrature amplitude–modulation based orthogonal frequency division multiplexing (OQAM/OFDM) systems is proposed in this study. The influence of channel estimation is considered, with the object to minimize stop-band energy. An efficient preamble structure is proposed to improve the channel estimation and save the frequency spectral efficiency. The reciprocal of the signal-to-interference-plus-noise ratio (RSINR) is derived to measure the influence of the prototype for channel estimation. After that, the problem of prototype filter design is formulated as an optimization problem with constraints on the RSINR. To accelerate the convergence and obtain a global optimal solution, the box-based branch and bound algorithm is utilized to solve the optimization problem. Simulation results demonstrate the validity and efficiency of the prototype filter designed in this study.

OQAM-OFDM for Wireless Communications in Future Internet of Things: A Survey on Key Technologies and Challenges

In this survey paper, we focus on the offset quadrature amplitude modulation-based orthogonal frequency division multiplexing (OQAM-OFDM)-based wireless communications in future Internet of Things (IoT). First, we present the OQAM-OFDM-based wireless communication system model for IoT and show its superiority compared with OFDM. Then, we give a survey and analyze key technologies including the prototype filter design, peak to average power ratio reduction, tail reduction, channel estimation, and multiple-input multiple-output combination in OQAM-OFDM-based wireless communication systems for IoT. Extensive simulations are conducted to verify the spectral superiority of OQAM-OFDM and compare the corresponding performances of OQAM-OFDM with OFDM in the above key technology areas.

Experimental demonstration of the OQAM-OFDM-based wavelength stacked passive optical networks

We demonstrate a wavelength stacked passive optical network (PON) with offset quadrature amplitude modulation based orthogonal frequency division multiplexing (OQAM-OFDM), which can provide 100-km single mode fiber (SMF) transmission without any inline repeater amplifier for both downlink and uplink. By experiment, we verify the feasibility of this proposed PON system for bi-directional long distance transmission especially for asynchronous upstream. Experimental result shows that, negligible power penalty is achieved even with 100-km SMF transmission, and ~3.6-dB sensitivity improvement is obtained when compared to OFDM-based asynchronous system. Besides, the performance in terms of side-lode suppression and peak to average power ratio (PAPR) are also contrastively analyzed between OFDM and OQAM-OFDM-based PON system.

Block-wise Alamouti schemes for OQAM-OFDM systems with complex orthogonality

Offset quadrature amplitude modulation-based orthogonal frequency division multiplexing (OFDM) systems cannot be directly combined with the Alamouti code because of the intrinsic imaginary interference. In this paper, we propose a block-wise space-frequency block coding (SFBC) scheme and a block-wise space-time block coding (STBC) scheme for offset quadrature amplitude modulation-based OFDM systems, which achieve bit error rate performances that are close to OFDM systems. The proposed schemes satisfy the orthogonality condition of the Alamouti code in the complex field with guard band/intervals. To improve the spectral efficiency of the block-wise SFBC scheme, we also consider the case without the guard band. It is observed that only the two innermost subcarriers do not satisfy the complex orthogonality condition when the guard band is removed. Then, a simple equalization scheme is proposed to independently equalize the two innermost subcarriers. Simulation results show that the block-wise SFBC scheme works well under channels with mild-to-moderate frequency selectivity, and the block-wise (STBC ) scheme suffers less than 1 dB loss under severe frequency selective channels at the bit error rate of 10 − 3, when only a simple one tap zero-forcing equalizer is employed. Copyright © 2016 John Wiley & Sons, Ltd.

A Novel Multi-Block Tone Reservation Scheme for PAPR Reduction in OQAM-OFDM Systems

Due to the overlapping structure of the offset quadrature amplitude modulation-based orthogonal frequency-division multiplexing (OQAM-OFDM) signals, the peak-to-average power ratio (PAPR) in OQAM-OFDM systems cannot be efficiently reduced by existing PAPR reduction methods, which independently consider the PAPR reduction in each data block. In this paper, a novel multiblock tone reservation (MB-TR ) scheme is proposed for the PAPR reduction in OQAM-OFDM systems. The key idea of the MB-TR scheme is to exploit the overlapping structure of the OQAM-OFDM signals and jointly consider the adjacent data blocks to obtain the clipping noise. To effectively eliminate the peaks of the OQAM-OFDM signals, the MB-TR scheme generates the peak-canceling signal by employing the weighted least square algorithm to fit the waveform of the peak-canceling signal to the waveform of clipping noise. Simulation results and analysis show that the MB-TR scheme could offer better PAPR reduction with lower computational complexity than the clipping control tone reservation scheme directly employed in OQAM-OFDM systems.

PAPR Reduction of OQAM-OFDM Signals Using Segmental PTS Scheme With Low Complexity

In this paper, a novel segmental partial transmit sequence (S-PTS) scheme is proposed for the peak-to-average power ratio (PAPR) reduction in offset quadrature amplitude modulation based orthogonal frequency-division multiplexing (OQAM-OFDM) systems. The key idea of the S-PTS scheme is to divide the overlapped OQAM-OFDM signals into a number of segments, and then some disjoint subblocks are divided and multiplied with different phase rotation factors in each segment. Compared with the conventional PTS scheme directly employed in OQAM-OFDM sytems, the S-PTS scheme could offer better PAPR reduction with lower computational complexity.