BER performance of a new overloading scheme for cellular DS-CDMA on Rayleigh fading channel

Overloading is a technique to accommodate more users than the spreading factor N. This is a bandwidth efficient scheme to increase the number of users in a fixed bandwidth for mobile communication. One of the efficient schemes to overload a CDMA system is to use two sets of orthogonal signal waveforms (O/O). The first set is assigned to the N users and the second set is assigned to the additional M users. An iterative soft decision interference cancellation receiver (SDIC) scheme is used to cancel interference between the two sets of users. In this paper, the BER performance of a new overloading scheme using orthogonal Gold code sets (OG/OG) is evaluated with SDIC receiver on a Rayleigh fading channel. It is observed that this scheme provides the channel overloading of 40% at a BER of 0.0005, with an SNR degradation of about 1 dB as compared to single user performance on a Rayleigh fading channel. An improved overloading scheme is also proposed, which gives 100% channel overloading on Rayleigh fading channel with near single user performance.