Non-orthogonal CDMA forward link offers flexibility without compromising capacity

We proposed the use of non-orthogonal CDMA forward link in future micro-cellular multi-media CDMA systems. It allows the use of mobile-transparent hand-off, a hand-off method which does not require sending a control signal to a mobile for its initiation. This reduces the hand-off related signaling overhead, therefore makes non-orthogonal forward links well suited to micro-cellular systems where there will be frequent hand-offs. Comparing with orthogonal forward links, it also allow much more flexibility in data rates and channel coding rates, hence readily accommodate high bit rate or VBR services. In addition, the possibility of using low-rate error control codes in non-orthogonal links provides a way to compensate for the loss in capacity due to non-orthogonality. Simulation results show that when the flexibility in error control coding is exploited, orthogonal and non-orthogonal forward links have comparable capacities in Rayleigh fading channels. In static channels (or very slowly fading Rician channels), orthogonal forward links have higher capacities, but the capacities of non-orthogonal forward links are not much worse than those of orthogonal forward links when the path loss exponent is small.