This paper proposes a novel generalized selec- tion combining (GSC)/maximal ratio combining(MRC) switching technique based on error detection in cooperative communica- tions with amplifiy-and-forward (AF) relays. In order to reduce the excessive burdern of MRC with all diversity paths at the destination node, the destination node decides if it performs GSC with order N( <K ) or MRC with order K +1 based on the error detection, where K is the number of relay nodes. Our ana- lytical and simulation results show that the proposed GSC/MRC switching outperforms the conventional MRC in terms of outage probability in AF based cooperative communications since the proposed scheme effectively reduces the spectral efficiency loss with the help of error detection codes. I. INTRODUCTION combined at a destination node since AF relays cannot decode the signal from a source and decide if they forward the signal to a destination node or not. Even though performance of diversity combining is generally proportional to the number of independent diversity paths, combining all the paths from relays might not be optimal in cooperative communications since more relays require more time-slotted orthogonal chan- nels which causes a spectral efficiency loss due to transmit duty cycle. In this context, this paper proposes a generalized selection combining (GSC)/maximal ratio combining (MRC) switching technique based on error detection at a destination node. The idea is motivated by (14) where the error detection was employed for diversity combining at RAKE receivers. When time-slotted orthogonal channels are adopted, the destination node first performs maximal ratio combining only with the earliest N branches (a S-D link and N − 1 R-D links), i.e., GSC with order N , and checks if any error occurs. If any error is not detected, the destination node broadcasts the success to relays to prevent remaining relays from transmitting the signals in their time slots/frames. Otherwise, the destination node waits until it gathers all the diversity paths from K relays and performs MRC with the signals from all the K relay nodes and the source node. Our outage probability analysis shows that the proposed GSC/MRC switching based on error detection improves the cooperative diversity performance in AF based cooperative relay communications since it can effectively reduce the spectral efficiency loss by virtue of error detection codes, despite a slight loss in spectral efficiency by sending the codes. The performance improvement in terms of outage probability becomes more significant as the number of relays K increases. Our analytical and simulation results indicate that a proper selection of N for the given error detection code can further improve diversity performance of AF based relay communications.
['Wan Choi', 'Jun-Pyo Hong', 'Dong In Kim', 'Byounghoon Kim']
An Error Detection Aided GSC/MRC Switching Scheme in AF based Cooperative Communications