In order to point out both the necessity and the validity of space diversity techniques usage, from the point of view of multipath fading and cochannel interference (CCI) influence mitigation, let us consider in this chapter performances of single-channel receiver over multipath fading channel in the presence of CCI. Performance evaluations that follow will consider multichannel reception, along with the presentation of appropriate expressions for evaluating the standard performance measures of these realistic systems over the CCI, such as outage probability (OP) and symbol error probability (SEP) of the various modulation/detection schemes defined in the literature. Most of the results in this chapter are originally reported by the contributing authors in the literature [1–5], and the reader who is interested in more details of the derivations is referred to the references.