Integrated optical wireless positioning and multi-user communication based on petal-shift keying structured beams

Light-emitting diode (LED)-based Optical wireless communications is capable to provide ultracheap wireless communication for many applications, especially for the indoor applications, it can be used to provide flexible wireless communication system for data communication (to connect personal computers/laptops with printers, and digital imaging devices) or creating access points in the floors the LED-based optical wireless communication has many advantages over RF communications like lower system complexity, cheaper components, simple interfacing, and security. Besides these advantages, the LED optical wireless communications face many challenges for its implementation in indoor applications because of high interference from other light sources like florescent lamps, CFL’s, which not only emits the light at same spectrum but may also use the switching frequencies (including harmonics) similar modulation frequencies. However, many solutions have been already presented to overcome these challenges. This paper provides the simple and efficient spectrum spreading approach which not only reduces the effect of interference but also enables multiuser communication without using modulating carrier. The simulation results shows that the proposed technique provides much better results than the Manchester coded systems.

Multicarrier code division multiple access (MC-CDMA) is a transmission scheme that combines the robustness of orthogonal modulation with the flexibility of CDMA schemes. It can lower the symbol rate and is therefore suited to the bandwidth limited optical wireless indoor channel. In this paper, new work is presented for an optical wireless (OW) system that utilizes MC-CDMA to improve the bit error rate (BER) performance. Our results indicate that at a BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> a 7 dB SNR improvement is obtained by a 4 user MC-CDMA OW system compared to a single user OW OOK system. This improvement is obtained while enabling multi-user communication. The performance degrades gradually as the number of users increases due to the increase in multiple access interference (MAI). A consistent BER performance is achieved for all receiver positions in a line strip spot-diffusing transmitter system (LSMS) with an angle diversity receiver, whereas a fluctuating BER performance is obtained in a conventional diffuse optical wireless system (CDS).

Underwater wireless optical communication (UWOC) has been regarded as a promising technology for providing high-speed underwater data transmission. Traditional UWOC systems primarily focus on the accurate transmission of bit sequences, aiming to minimize bit error rates through sophisticated source and channel coding. However, this approach often leads to inefficiencies in challenging environments. Semantic communication emerges as a novel communication paradigm that shifts the objective from exact bit recovery to the faithful reconstruction of semantic information behind source data, enhancing robustness and efficiency. In this paper, we propose a semantic communication framework based on residual quantization variational autoencoder (RQ-VAE) with N-dimensional carrier-less amplitude phase (N-D CAP) modulation for image transmission. At the transmitter, the input images are encoded into latent feature vectors, which capture core semantic information. Then, the RQ technique is implemented to approximate these vectors by recursively finding the closest matching codeword in a learned codebook. Instead of directly transmitting the latent feature vectors, we only transmit a stack of multi-stage quantized codes, thereby substantially reducing the data volume. Integrating with N-D CAP, the quantized codes from different stages are in line with the multi-user communication concept of N-D CAP, enabling concurrent transmission over the same frequency band. And we demonstrate this scheme in a 450 nm laser-based UWOC system with a 5 m transmission distance. We adopt the traditional JPEG and LDPC standards as the baseline. Experimental results show that the proposed scheme outperforms the traditional scheme by improving PSNR by up to 4.68 dB at similar frame rates, or increasing frame rate by 329% at similar PSNR. A transmission rate of 4,394,531 image instances/patches per second at 64×64 was achieved. To the best of our knowledge, this is the highest reported rate for underwater image transmission.

Non-orthogonal multiple access (NOMA) has been studied as a promising multiple access technology for optical communication systems due to its superior spectral efficiency. However, the multi-user communication systems that employ NOMA with successive interference cancellation (SIC) suffer from error propagation (EP). Besides, the issue of non-ideal rise and fall time of the received signal can result in severe bit error rate (BER) degradation while decoding by the SIC technique. In this paper, we propose a straightforward two-stage program judgment filter (PJF) for signal reshaping and a SIC-free decoding method for NOMA. Based on the amplitude threshold (AT) decoding method, we demonstrate a real-time, two-user uplink underwater wireless optical communication (UWOC) system via field programmable gate arrays (FPGAs). With a power allocation ratio (PAR) of 2:1 (user 1: user 2), the established real-time NOMA-based UWOC system utilizing commercial light emitting diodes (LEDs) achieves a data rate of 30 Mbps for each user with BERs of 7.8 × 10-6 and 3 × 10-4 for user 1 and user 2, respectively. The results show that the AT-based NOMA can obtain a lower BER compared to the SIC-based NOMA, especially for user 2.