ERGODIC CAPACITY ANALYSIS OF THE RELAY ASSISTED DOWNLINK NOMA SYSTEMS IN COGNITIVE RADIO NETWORKS

Öz

this study, the ergodic capacity analysis of the relay assisted downlink non-orthogonal multiple access (NOMA) systems in cognitive radio networks is investigated. Mathematical inferences in the proposed system model are obtained by deriving the closed-form equations of the exact and approximate ergodic capacities for the far and near users in the secondary network by considering exponentially distributed channels. In case of successive interference cancellation is implemented in both relay, far and near users, the ergodic sum capacity performances are analyzed with 〖10〗^6 repeated Monte Carlo simulations, considering the distance between nodes, power allocation coefficient, transmission power, and path loss coefficient parameters. The numerical results show that the ergodic total capacity increases with the increase in power allocation assigned to the near user. It has also been observed that moving the primary network transmitter away from the relay improves the system performance. The exact calculation of the ergodic total capacity performance for the near user is only possible in the high signal-to-noise ratio (SNR) region to coincide with the approximately calculated ergodic total capacity performance. This situation is evaluated as the effect of the downlink NOMA system designed as a secondary network using the same frequency band as the primary network acting as a co-channel interference.

Anahtar Kelimeler

• Downlink NOMA
• Cognitive Radio
• Ergodic Capacity
• Relay Networks

RÖLE YARDIMLI AŞAĞI YÖNLÜ NOMA SİSTEMLERİNİN BİLİŞSEL RADYO AĞLARDAKİ ERGODİK KAPASİTE ANALİZİ

Öz

Bu çalışmada, röle yardımlı aşağı yönlü dikgen olmayan çoklu erişim (NOMA) sistemlerinin bilişsel radyo ağlardaki ergodik kapasite analizi incelenmektedir. Önerilen sistem modelindeki matematiksel çıkarımlar, ikincil ağdaki yakın ve uzak kullanıcılar için tam ve yaklaşık ergodik kapasite kapalı form denklemlerinin üstel dağılımlı kanal göz önüne alınarak türetilmesiyle elde edilmektedir. Hem rölede, hem de yakın ve uzak kullanıcılarda ardışık girişim iptali gerçekleşmesi durumunda, toplam ergodik kapasite performansı düğümler arası mesafe, güç paylaşım katsayısı, iletim gücü ve yol kaybı üssü parametreleri dikkate alınarak, 〖10〗^6 tekrarlı Monte Carlo benzetimleriyle analiz edilmektedir. Elde edilen nümerik sonuçlar, yakın kullanıcıya atanan güç tahsisinin artması ile ergodik toplam kapasitenin arttığını göstermektedir. Birincil ağ vericisinin röleden uzaklaşmasının sistem performansını iyileştirdiği de gözlenmiştir. Yakın kullanıcı için tam olarak hesaplanan ergodik toplam kapasite başarımının, yaklaşık olarak hesaplanan ergodik toplam kapasite performansı ile örtüşmesi, ancak yüksek işaret gürültü oranı (SNR) bölgesinde mümkün olmaktadır. Bu durum, ikincil ağ olarak kurgulanan aşağı yönlü NOMA sisteminin, ortak kanal girişimi olarak etki gösteren birincil ağ ile aynı frekans bandını kullanmasının etkisi olarak değerlendirilmiştir.

Anahtar Kelimeler

• Aşağı Yönlü NOMA
• Bilişsel Radyo
• Ergodik Kapasite
• Röle Ağlar

Kaynakça

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