System parameter selection for asymmetric underlay CDMA networks with interference-minimizing code asssignment

We propose a framework for designing an underlay secondary CDMA network. The objective is to select the secondary system´s bit rate and spreading factor that improve the secondary network throughput given a required bit error rate and an allowable transmit power level acceptable to the primary network. The selection scheme is applied to both the case of random code assignment and an interference-minimizing code assignment (IMCA) scheme. Our simulations reveal that the parameter selection for the system with interference-minimizing code assignment scheme leads to higher system throughput over that achieved with random code assignment. We also show that the IMCA scheme, unlike random code assignment, suffers negligible interference from adjacent bands in asynchronous channels.