Performance of Uplink SCMA on Cognitive Femtocell System under Imperfect Spectrum Sensing

• Main Author: HAMDANI (NIM: 23215080), FADIL
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/27064
• Institution: Institut Teknologi Bandung

<p align="justify"> The needs for high capacity and massive connectivity for 5G system become main factors that stimulate the emergence of innovations to break the boundaries of limited availability of radio resources in cellular system. Sparse code multiple access (SCMA), cognitive radio, and femtocell are some of the innovations that become candidates to support 5G system. SCMA is a multiple access system which implements sparse spreading feature to minimize interferences inferred on every users due to resource element usage sharing. SCMA has the ability to maximize the system performances when working under overloading condition where the number of users <br /> <br /> served simultaneously by the system is higher than the number of available resource elements. Cognitive radio system has advantages which improve the spectral efficiency <br /> <br /> and with its spectrum sensing capabilities minimize interferences. Femtocell in Heterogeneous Network (HetNet) architecture has the ability to improve data rate <br /> <br /> performance in indoor environment. In this research, a system model to put together the concept of SCMA and cognitive radio on a femtocell in uplink communications is developed. The concept of cognitive radio is implemented by employing energy detection technique for spectrum sensing which is performed by an entity called spectrum agent, associated to the femtocell base station. The energy detection is performed to unknown deterministic signals on Rayleigh channels. The SCMA system is implemented to operate in the overloading condition over the Rayleigh channels. Performance evaluations of the uplink SCMA cognitive femtocell system are performed <br /> <br /> with SNR varying from 5 dB to 25 dB for complementary receiver operating characteristic (ROC), bit error rate (BER) performances on various probability of missed detection levels, and BER performances on various levels of decision threshold of energy detection based spectrum sensing. For comparison, a multicarrier code division <br /> <br /> multiple access (MC-CDMA) based system with binary phase shift keying (BPSK) modulation under 50% load with ideal spreading code (walsh-hadamard) is transmitted on orthogonal channels. The number of channels in the MC-CDMA based system equals that of the SCMA based system. The BER performances of the proposed uplink SCMA cognitive femtocell system without channel coding with overloading factor of 150% reach BER performances of the MC-CDMA based system at SNR of 19 dB. With SNR equal to and greater than 19 dB, the BER performances of the SCMA based system outperform the performances of the MC-CDMA based system. The proposed system is proven to support overloaded cognitive femtocell with performances comparable to the low <br /> <br /> load MC-CDMA based system with ideal spreading code, under the same number of resource elements. <p align="justify">