In a conventional WCDMA system, each user is detected non-cooperatively where other users’ signals are treated as noise. This basic scheme has a low implementation complexity but a limited overall spectral efficiency due to multiple-access interference (MAI).
Higher spectral efficiency can be achieved by reducing the MAI. In contrast to conventional RAKE receivers, the Multi-user detection (MUD) receiver does not treat intra-cell user signals as noise, but tries to eliminate their interfering effect.
There are two main variants of The MUD receiver structures: interference cancellation (IC) and joint detection (JD). The first category involves a subtractive scheme where the receiver produces estimates of the interference and then subtracts them from the received signal. The second category (JD) involves linear transformation of the received signal using, depending on the algorithm, information regarding the signals' time offsets, codes, amplitudes and phases.
The major advantage of this scheme is its relatively low complexity compared to other MUD techniques. Interference cancellation receivers belong to the class of non-linear suboptimal MUD techniques and their complexity is a linear function of the number of users compared to polynomial or exponential complexity for other types of MUD receivers. In effect, IC enhances the interference limited uplink capacity of WCDMA cellular systems.