Modified prime-hop codes for optical CDMA systems

In the early stage of optical CDMA systems, the spreading codes, such as optical orthogonal codes (OOCs) and prime codes, are only coded in the time domain. However, the small code size becomes the major issue for one-dimensional codes. To deal with this limitation of one-dimensional codes, a new family of two-dimensional codes is proposed for optical CDMA systems. The new codes are modified from the well known prime-hop codes. Hence, the authors refer to the new codes as ´modified prime-hop codes´. The modified prime-hop codes preserve the same code correlation properties as the original prime-hop codes, i.e. the cross-correlating constraint is equal to one and the autocorrelation constraint is equal to zero, and can be generated with lower cost, lower complexity and lower power loss encoders/decoders. Meanwhile, the optical CDMA systems with the modified prime-hop codes perform better and can accommodate more users than those with the original prime-hop codes