Polar OFDM Research Articles

Optical polar based MIMO‐OFDM with fully generalised index‐spatial LED modulation

A novel efficient visible light communication (VLC) modulation technique teams as polar fully generalised index-spatial (PFGIS) modulation light emitting diode (LED) for the multi-input multi-output (MIMO) optical polar based OFDM (MIMO-POFDM) system is proposed here. The PFGIS is a spectrally efficient (SE) modulation scheme which introduces an elegant solution to tackle the OFDM signal shaping problem, moreover, the PFGIS improves the optical MIMO-OFDM system SE. In the PFGIS, the Cartesian complex OFDM signal is transformed to polar OFDM (POFDM). Then, the indices of the active LEDs are exploited to convey the POFDM signal components. While, the spatial position of the LEDs are exploited as a spatial modulation (SM). In the SM, the LEDs indices used for data transmission are changed from the case of two LEDs are selected to case where all/multiple LEDs are selected. Subsequently, the proposed system achievable data rate is linearly increased with the LEDs number. The PFGIS gives higher SE even with a lower LEDs number compared with the recently OFDM optical LED index modulation techniques. Simulation results confirm the efficiency of the proposed PFGIS in improving both the achievable data rate and the bit error rate compared with the up-to-date LED index modulation OFDM schemes.

Full-subcarriers Polar-OFDM for optical spectrum-efficient transmission exploiting Polarization Multiplexing

Abstract The exponential growth of the demand for broadband services has imposed great challenges on the design of spectrum-efficient optical transmission system in Passive Optical Network (PON). Recently, an innovative Orthogonal Frequency Division Multiplexing (OFDM) scheme, called Polar-OFDM (P-OFDM), has emerged as a promising solution to boost the spectral efficiency of optical transmission in PON. However, the traditional P-OFDM does not yet perform best in spectral efficiency as it only uses half of the total subcarriers. In this paper, we verify a promising complementation between Polarization Multiplexing (POLMUX) and P-OFDM aiming at higher spectral efficiency. We then propose the full-subcarriers P-OFDM by loading data on the even-indexed subcarriers of X polarization and the odd-indexed subcarriers of Y polarization, respectively. Thus, all of the subcarriers will be utilized for effective data transmission, which can double the spectral efficiency. More importantly, because the subcarriers are interlaced on different polarizations, the cross-polarization interference can be significantly mitigated, which enables the independent channel estimation and equalization at the receiver to recover the data carried on each polarization. Our evaluation results demonstrate that the proposed system realizes the double spectral efficiency of the traditional P-OFDM with reasonable Bit Error Rate (BER) performance loss.

A Simple OFDM Scheme for VLC Systems Based on u-Law Mapping

A simple orthogonal frequency division multiplexing (OFDM) scheme termed ${\mu }$ -OFDM is proposed for visible light communication (VLC). In this scheme, the peak-to-average power ratio (PAPR) reduction technique, ${\mu }$ -law companding, is first introduced in VLC systems to achieve the required signal format for VLC transmission. Due to the inherent characteristics of the companding operation, low PAPR signals are obtained in the scheme. Compared with most of the unipolar optical OFDM schemes, such as asymmetrically clipped optical OFDM scheme, ${\mu }$ -OFDM doubles the spectral efficiency. Furthermore, this scheme shows significant energy advantages over direct-current biased optical OFDM scheme and polar OFDM scheme. To the best of our knowledge, this is the first design of a unipolar optical OFDM scheme, which is able to achieve both high spectrum and energy efficiency under a constraint of the dynamic range of the light-emitting diodes.

Polar-Based OFDM and SC-FDE Links Toward Energy-Efficient Gbps Transmission Under IM-DD Optical System Constraints [Invited

Recent studies have investigated the use of orthogonal frequency division multiplexing (OFDM) and single carrier frequency-domain equalization (SC-FDE) for gigabyte per second (Gpbs) short-range optical wired and wireless access networks based on direct intensitymodulation with direct detection (IM-DD). OFDM systems have an inherent high peak-to-average power ratio (PAPR). SC-FDE systems have lower PAPR and thus outperform comparable OFDM systems in terms of bit-error performance under various practical considerations, mainly the limited dynamic range of operation at the transmitter. In RF-based OFDM and SC-FDE systems, the output signal is bipolar, complex, and cannot be transmitted in IM-DD systems. Therefore, several power efficient schemes, however spectrally inefficient, have been proposed to make positive OFDM and SC-FDE signals, e.g., asymmetrically clipped optical OFDM (ACO-OFDM) and repetition and clipping optical SCFDE (RCO-SCFDE). To increase the data rate, novel OFDM and SC-FDE signal formats, called polar OFDM (P-OFDM) and polar SC-FDE (P-SC-FDE), based on a polar representation of complex symbols, are proposed. The proposed format offers twice as much spectral efficiency as state-of-the art unipolar OFDM and SC-FDE formats. Moreover, using a power allocation approach on the time-domain positive samples, the PAPR is further reduced, and the numerical evaluation of the bit-error performance under optical source power and dynamic range constraints demonstrates superior results toward Gpbs transmission.