Optical N-parallel codes-shift-keying using generalized modified prime sequence codes and Hadamard codes

For optical wireless communications with intensity-modulation and direct-detection (IM/DD), the N parallel code shift keying (N-CSK) systems using a pseudo-noise (PN) codes are considered. Since N-CSK has the several PN codes, the data transmission rate and the bit error rate (BER) performance can improve by increasing the number of PN codes. However, the conventional optical PN codes are not suitable for optical N-CSK with IM/DD because the ratio of the number of PN codes and the PN-code length, M/L, is smaller than 1/√L. Therefore, one of serious problems encountered with optical wireless N-CSK with IM/DD is to design the optical PN code. In this paper, a PN code, which combines the generalized modified prime sequence code (GMPSC) with Hadamard code, is proposed. Moreover, a new N-CSK using the proposed PN code is shown. The proposed PN code can achieve M/L = 1. Therefore, it is expected that the proposed system can achieve high data transmission rate compared with the conventional optical N-CSK systems. Moreover, the bit error rate performance is evaluated under the additive white Gaussian noise channel. It is found that the proposed optical N-CSK outperforms the conventional optical N-CSK system.