Isotropic Orthogonal Transform Algorithm Research Articles

Laser Sharing Uplink Polarization Division Multiplexing FBMC Passive Optical Network

In this paper, we proposed and experimentally demonstrated a laser sharing filter bank multicarrier passive optical network (FBMC-PON) uplink architecture, to provide high spectrum efficiency frequency division multiple access (FDMA) to the optical network terminals (ONTs) with aggregated uplink data rate of up to 100 Gb/s/λ for each optical network unit (ONU), in a fiber to the frontage (FTTF) scenario utilizing existing copper infrastructure. Intensity modulation (IM) and heterodyne detection are implemented, combined with polarization division multiplexing (PDM) to double the system capacity. The uplink performance of FBMC-PON is emulated with two asynchronous ONT bands in transmission over 20 km single mode fiber (SMF). FBMC with prototype filters (PFs) PHYDYAS, extended Gaussian filter (EGF) and isotropic orthogonal transform algorithm (IOTA) is discussed in comparison with orthogonal frequency division multiplexing (OFDM) in terms of frequency guard band and multiple access interference (MAI). The laser from an external cavity laser (ECL) is split and shared among ONTs. The experimental results show that FBMC can achieve significant improved receiver sensitivity compared to OFDM in the asynchronous uplink. FBMC with PHYDYAS can avoid MAI with frequency guard interval of one time the subcarrier spacing. With optical receiving power (ROP) of −23 dBm, to support 2, 4 and 8 ONTs, the required optical power of the narrow linewidth laser is respectively 10, 16 and 22 dBm with bit error rate (BER) at the hard decision forward error correction (HD-FEC) threshold.

FDSS-Based DFT-s-OFDM for 6G Wireless Sensing.

Integrated sensing and communications (ISAC) is emerging as a key technology of 6G. Owing to the low peak-to-average power ratio (PAPR) property, discrete Fourier transform spread orthogonal frequency-division multiplexing (DFT-s-OFDM) is helpful to improve the sensing range and suitable for high-frequency transmission. However, compared to orthogonal frequency-division multiplexing (OFDM), the sensing accuracy of DFT-s-OFDM is relatively poor. In this paper, frequency-domain spectral shaping (FDSS) is adopted to enhance the performances of DFT-s-OFDM including sensing accuracy and PAPR by adjusting the correlation of signals. Specifically, we first establish a signal model for the ISAC system, followed by the description of performance indicators. Then, we analyze the influence of amplitude fluctuation of frequency domain signals on sensing performance, which shows the design idea of FDSS-enhanced DFT-s-OFDM. Further, a FDSS-enhanced DFT-s-OFDM framework is introduced for ISAC, where two types of FDSS filters including a pre-equalization filter and an isotropic orthogonal transform algorithm (IOTA) filter are designed. The simulation results show that the proposed scheme can obtain about 4 dB performance gain in terms of sensing accuracy over DFT-s-OFDM. In addition, FDSS-enhanced DFT-s-OFDM can significantly reduce PAPR and improve the power amplifier efficiency.

Enhancing PAPR and Throughput for DFT-s-OFDM System Using FTN and IOTA Filtering.

High frequency wireless communication aims to provide ultra high-speed transmissions for various application scenarios. The waveform design for high frequency communication is challenging due to the requirements for high spectrum efficiency, as well as good hardware compatibility. With high flexibility and low peak-to-average power ratio (PAPR), discrete Fourier transformation spreading-based orthogonal frequency division multiplexing (DFT-s-OFDM) can be a promising candidate waveform. To further enhance the spectral efficiency, we integrate faster-than-Nyquist (FTN) signaling in DFT-s-OFDM, and find that the PAPR performance can also be improved. While FTN can introduce increased inter-symbol interference (ISI), in this paper, we deploy an isotropic orthogonal transform algorithm (IOTA) filter for FTN-enhanced DFT-s-OFDM, where the compact time-frequency structure of the IOTA filter can significantly reduce the ISI. Simulation results show that the proposed waveform is capable of achieving good performance in PAPR, bit error rate (BER) and throughput, simultaneously, with dB gain in PAPR and 50% gain in throughput.

UF0MC-IOTA Based Cognitive Radio Transceiver

Express evolution in smart wireless communication address the issue of spectrum scarcity. Implementation of cognitive radio (CR) is one of the promising technologies for the effective utilization of spectrum. Sensing is the critical component of cognitive radio. Moreover, encouraged by the element of sensing is critical for consistently defining spectral opportunity and succeeding opportunity in spectrum access for the fifth generation (5G) wireless networks. Universal filtered multicarrier—Isotropic Orthogonal Transform Algorithm (UFMC-IOTA) is the excellent 5G waveform candidates. This article focuses on the performance of UFMC-IOTA based CR transceiver sensing challenges, downlink capacity of cognitive radio network (CRN). Simulation results also demonstrate that the proposed transceiver outperforms the capability of sensing than the conventional sensing methodologies in CRN. It also increases the detection probability of CRN at very low SNR level.

An Intrinsic Interference Mitigation Scheme for FBMC-QAM Systems

Quadrature amplitude modulation-based filter-bank multicarrier system (FBMC-QAM) is a promising new radio access technology for the upcoming 5G standalone standard (5G-NR SA). By way of highly localized prototype filters, FBMC-QAM system is able to achieve low out-of-band (OOB) radiation and high spectral efficiency without the cyclic prefix (CP), at the price of non-orthogonality between adjacent subcarriers, intrinsic interferences, and bit error rate (BER) degradation. As an attempt to mitigate these impairments, a precoding scheme is proposed in this paper, which aims to maximize signal-to-leakage-and-noise ratio (SLNR) while allowing pulse-shaping filters with superb spectral characteristics to be leveraged. To justify the efficacy, performance analysis is conducted for prototype filters such as square-root raised cosine (SRRC), isotropic orthogonal transform algorithm (IOTA), and Mirrabasi-Martin (same as suggested in the PHY-DYAS project) for both additive white Gaussian noise (AWGN) and time-dispersive channels. The computer simulation shows that SLNR-based FBMC-QAM system incurs low complexity overhead and is able to enhance BER performance effectively.

Orthogonal Multiband CAP Modulation Based on Offset-QAM and Advanced Filter Design in Spectral Efficient MMW RoF Systems

In this study, to the first time, we demonstrate an offset-QAM carrier-less amplitude and phase modulation (OQAM-CAP) technique for spectral efficient multi-user radio-over-fiber systems. In comparison with traditional QAM-based CAP modulation schemes, the digital filter for each channel in OQAM-CAP can be adaptively redesigned to obtain either higher spectral efficiency or lower computational complexity. Two kinds of digital filters, namely, square-root raised-cosine (SRRC) filters and isotropic orthogonal transform algorithm (IOTA)-based filters, are studied and applied to shape the frequency window of each channel in CAP systems. We compared the performances among SRRC-OQAM CAP, IOTA-OQAM CAP, and traditional SRRC-QAM CAP. It is experimentally demonstrated that SRRC-OQAM-CAP can achieve higher spectral efficiency, IOTA-OQAM-CAP can obtain higher computational efficiency, and SRRC-QAM-CAP can be used in uplink transmission with lower interchannel interference. Bidirectional experiments are conducted with around 2-GHz nine aggregated channels on 60-GHz optical millimeter wave. Less than 7% error vector magnitudes are realized over 15-km standard single-mode fiber and 1.5-m wireless channel.

Interference tables: a useful model for interference analysis in asynchronous multicarrier transmission

In this paper, we investigate the impact of timing asynchronism on the performance of multicarrier techniques in a spectrum coexistence context. Two multicarrier schemes are considered: cyclic prefix-based orthogonal frequency division multiplexing (CP-OFDM) with a rectangular pulse shape and filter bank-based multicarrier (FBMC) with physical layer for dynamic spectrum access and cognitive radio (PHYDYAS) and isotropic orthogonal transform algorithm (IOTA) waveforms. First, we present the general concept of the so-called power spectral density (PSD)-based interference tables which are commonly used for multicarrier interference characterization in spectrum sharing context. After highlighting the limits of this approach, we propose a new family of interference tables called ‘instantaneous interference tables’. The proposed tables give the interference power caused by a given interfering subcarrier on a victim one, not only as a function of the spectral distance separating both subcarriers but also with respect to the timing misalignment between the subcarrier holders. In contrast to the PSD-based interference tables, the accuracy of the proposed tables has been validated through different simulation results. Furthermore, due to the better frequency localization of both PHYDYAS and IOTA waveforms, FBMC technique is demonstrated to be more robust to timing asynchronism compared to OFDM one. Such a result makes FBMC a potential candidate for the physical layer of future cognitive radio systems.

Design of isotropic orthogonal transform algorithm-based multicarrier systems with blind channel estimation

Orthogonal frequency division multiplexing (OFDM) technique has gained increasing popularity in both wired and wireless communication systems. However, in the conventional OFDM systems the insertion of a cyclic prefix (CP) and the transmission of periodic training sequences for purpose of channel estimation decrease the system's spectral efficiency. As an alternative to OFDM, isotropic orthogonal transform algorithm (IOTA)-based multicarrier system adopts a proper pulse shaping with good time and frequency localisation properties to avoid interference and maintain orthogonality in real field among sub-carriers without the use of CP. In this study, the authors propose linearly precoded IOTA-based multicarrier systems to achieve blind channel estimation by utilising the structure of auto-correlation and cross-correlation matrices introduced by precoding. The results show that the proposed IOTA-based multicarrier systems achieve better power and spectral efficiency compared with the conventional OFDM systems.

A Novel Channel Estimation Scheme for OFDM/OQAM-IOTA System

An OFDM/offset QAM (OQAM)-IOTA system uses the isotropic orthogonal transform algorithm (IOTA) function, which has good localization properties in the time and frequency domains. This is employed instead of the guard interval used in a conventional OFDM/QAM system in order to be robust for multi-path channels. However, the conventional channel estimation scheme is not valid for an OFDM/OQAM-IOTA system due to the intrinsic intersymbol interference of the IOTA function. In this paper, a condition is derived to reduce the intrinsic interference of the IOTA function. This condition is obtained with the proposed pilot structure used for perfect channel estimation. We also derive the preamble structure appropriate for practical channel estimation of the OFDM/OQAM-IOTA system. Simulation results show that the OFDM/OQAM-IOTA system with the proposed preamble structure performs better than the conventional OFDM system, and it has the additional advantage of an increased data transmission rate which corresponds to the guard interval retrieval.

Derivation of Extended Gaussian Functions Based on the Zak Transform

Siohan and Roche introduced recently a new family of modulated filter banks, which was derived from a set of continuous-time orthogonal functions named extended Gaussian functions (EGFs). At first, these EGFs were obtained using the isotropic orthogonal transform algorithm (IOTA), i.e., a two-step orthogonalization procedure of the Gaussian function. As shown recently, using the Zak transform, the IOTA method yields the tight window function canonically associated with the Gaussian. In this letter, it is shown that the Zak transform can also be useful in recovering the series expansion of the EGFs. Practical guidelines are also provided in order to get accurate approximations of the orthogonal EGFs.