A New Code Family for QS-CDMA Visible Light Communication Systems

Abstract

Visible light communication (VLC) is a promising technology for wireless communication networks. Optical code division multiple access (OCDMA) is a strong candidate for VLC-based applications. The predominant source of bit error in OCDMA is the multiple access interference (MAI). To eliminate MAI in synchronous OCDMA, zero cross correlation (ZCC) codes have been proposed. However, synchronization problems and multipath propagation introduce relative non-zero time delays. Therefore, the zero correlation zone (ZCZ) concept was introduced. In this paper, we propose a new method for generating ZCC codes. The proposed construction can accommodate any number of users with flexible Hamming weight. The numerical results obtained show that the proposed codes significantly reduce MAI, compared to ZCC, as well as ZCZ codes.

New Construction of OVSF-OZCZ Codes in Multi-Rate Quasi-Synchronous CDMA VLC Systems for IoT Applications

“…where I denotes the average photocurrent of PD, the first item and the second item describe the shot noise and thermal noise respectively. When adopting Gaussian approximation in this system, the following (16) gives the average signal-to-noise ratio (SNR) for l-th desired user in N active users system when the probability of data bit for each user is 1/ 2 [23], [26].…”

“…Besides, precise synchronization among users is difficult to be achieved in IoT network due to non-perfect clock or multi-path transmission [22]. That is, quasisynchronous CDMA (QS-CDMA) should be considered for the IoT network based on VLC technology [23]. Optical zero correlation zone (OZCZ) codes with ideal correlation properties in the zero correlation zone have been designed for QS-CDMA-VLC system, which can effectively tolerate the inevitable time delay and eliminate multiple access interference (MAI) and phase-induced intensity noise (PIIN) [24]- [26].…”

Complex Signal Mapping for Improving Spectral Efficiency of Li-Fi Systems

“…Instead of applying Hermitian symmetry and signal clipping, a simple idea has been presented in [7] to ensure real-valued OFDM signals by mapping the complex time domain (output of IFFT) into a real value, with the same symbols prior to QAM modulation in the frequency domain. The work in [8] presented a new coding scheme by employing zero cross correlation (ZCC) codes to achieve the same goal and to eliminate multiple access interference, but this required large set sizes and, hence, more bandwidth. Motivated by this and in order to fully utilize the available bandwidth, this paper proposes a new approach based on complex signal mapping (CSM) with the pairing function method to Figure 1 represents the proposed CSM-OFDM-based Li-Fi transceiver.…”