Performance Analysis of Multi-Branch Switched Diversity Schemes for Spectrum Sharing Systems

Under the scenario of an underlay cognitive radio network, we compare our proposed joint switched transmit diversity and adaptive modulation schemes, namely the switching efficient scheme (SES) and the bandwidth efficient scheme (BES). The proposed schemes use the scan and wait (SWC) combining technique where a transmission occurs only when a branch with an acceptable performance is found, otherwise data is buffered. In our schemes, the modulation constellation size and the used transmit branch are determined to either minimize the average number of switched branches or to achieve the highest spectral efficiency, given the fading channel conditions, the required error rate performance, and a peak interference constraint to the primary receiver. Selected numerical examples show that the BES scheme increases the capacity of the secondary link when compared to the SES scheme. This spectral efficiency comes at the expense of an increased average number of switched branches. We have also extended the SES and BES schemes to a multiuser scheduling and our final poster will include the results regarding these extensions.