Performance analysis of spatial OFDM for pixelated optical wireless systems

Abstract

Pixelated optical wireless systems can transmit at high speed by encoding data in transmitted images using spatial orthogonal frequency division multiplexing (spatial OFDM) but are susceptible to a number of limiting factors including defocus, linear fractional misalignment (LFM) and vignetting. This paper investigates the effects of these impairments on the performance of both forms of spatial OFDM: spatial DC-biased optical OFDM (SDCO-OFDM) and spatial asymmetrically clipped optical OFDM (SACO-OFDM). The novelty of this paper is in the theoretical analysis of the effect of defocus on a spatial OFDM based pixelated system. The theoretical results for defocus are found to be in agreement with the simulation results reported in the literature. Furthermore, the joint effects of defocus, LFM and vignetting are mathematically described. Analytical and simulation results show that these three factors are largely independent of each other. Simulation results indicate that these impairments and their associated mitigation techniques influence the optimum choice of DC bias for SDCO-OFDM. Finally, it is shown that for the case of the joint impairments and for a given data rate, the bit error rate performance of SDCO-OFDM with the optimum bias is slightly better than that of SACO-OFDM. ], which is an extension of the concept of conventional OFDM [18][19][20] to the 2-D spatial domain. For spatial OFDM, data are encoded in the spatial-frequency domain, the frequency representation of the 2-D image space, using a number of orthogonal 2-D subcarriers. Each of the encoded spatial frames is converted to a pixelated image before transmission. Spatial OFDM has several advantages for pixelated communication. Compared with systems that encode data directly in the spatial domain, a spatial OFDM scheme is less affected by a number of distortions occurring in the spatial domain [7,8,21,22]. Moreover, the formation of the data-carrying transmitted images can be well-designed. This means that, by using spatial OFDM algorithms at the transmitter side, the images can be generated in a way that makes them much robust to distortions. The receiver can then decode the

Impact of spatial sampling frequency offset and motion blur on optical wireless systems using spatial OFDM

“…Next, cyclic extensions in the form of a cyclic prefix (CP) and a cyclic postfix (CPo) [29] are added to both the rows and the columns of s, the corresponding matrix form of s l 1 ;l 2 . The term s which represents a spatial OFDM frame in the electrical domain is then applied to the input of the intensity modulator.…”

“…However, the technology of spatial OFDM based pixelated systems is still in its infancy and has to overcome several challenges including power constraints, spatial distortions [18,[27][28][29] and temporal distortions [16,30]. Limiting factors such as ambient light [14], spatial perspective distortions [14], spatial rotational error [19] and temporal synchronization problems [16] have been studied in the literature.…”

“…Limiting factors such as ambient light [14], spatial perspective distortions [14], spatial rotational error [19] and temporal synchronization problems [16] have been studied in the literature. In recent years, the author of this paper has analysed the effects of spatial distortions such as defocus blur [28,29], vignetting [18] and fractional misalignment error [27]. The results reported in the above-mentioned previous studies are based on the assumption that the numbers of pixels in the transmitted images and the corresponding received images are the same.…”

Edge-Based and Prediction-Based Transformations for Lossless Image Compression

“…In addition to the storage, data are often required to be transmitted over the Internet at the highest possible speed. Due to the constraint in storage facility and limitation in transmission bandwidth, compression of data is vital [1][2][3][4][5][6][7][8].…”

“…In such systems, a sequence of image frames is transmitted by liquid crystal display (LCD) or light emitting diodes (LED) arrays. A smart-phone with camera or an array of photodiode with imaging lens can be used as optical receivers [6][7][8]. Such systems have the potential to have huge data rates as there are millions of pixels on the transmitter screens.…”