ABSTRACT
This research work presents the development of an improved ergodic capacity of underlay Cognitive Radio (CR) with imperfect Channel State Information(CSI). An underlay CR network under a Peak Interference Power (PIP) constraint imposed by a Primary User (PU) was considered .A closed former godic capacity expression of the Secondary User (SU)under PIP constraint was derived in order to determine the ergodic capacity under different fading types using Nakagami-m distributions.The m-parameter of the Nakagami-m fading channel measures the ratio of the Line-of-Sight (LoS) signal power to that of the multipath component. The improved ergodic capacity expression developed was validated with the existing ergodic capacity expression at m=1. The results showed that the ergodic capacity of the SU could be extended to different fading types in the CR path by adjusting the m-parameter. The impact of channel estimation errors, 2 ? and channel correlation coefficient, ? on the SUergodic capacity was studied under different fading types to provide an insight on the capacity behavior of CR network. The results obtained at different values of m parameters showed the ergodic capacity degraded as a result of increasing 2 ? and it increases with increasing ? .It was observed that at m=1/2,1,2 and 3, a significant capacity gains of 21.65%, 19.71%, 17.43%, and 15.82% were achieved, when 3% interference outage ? ? out P was considered for all the m values from ? 2 ?1 to 2 ? ? 0 . However, a capacity gains of 23.59%, 22.31%, 21.02%, and 20.26% were also achieved respectively at 1% out P . It was also found that at m=1/2,1,2 and 3, a spectral efficiency in (bits/S/Hz) of 0.5007, 0.2888,0.2660, and 0.2596 were achieved when 3% out P was considered from ? ? 0 to ? ?1, while a spectral efficiency of 0.2548, 0.1771, 0.1211, 0.0931 were also achieved at 1% P for the respective m values.