Distributed beam forming with phase-only control for green cognitive radio networks

Abstract

Cognitive radio (CR) is an intelligent radio system and is able to share the spectrum with licensed users (LU). By adopting adaptive beam forming techniques, CR can reuse the spectrum with LU via directing main beams towards CR users while displaying nulls towards LU. In this article, we present a new distributed beam forming (DB) technique, and study the performance of its application to decentralized CR networks. The presented DB method only controls the phase of the transmitted signal of each CR node in the CR network, and therefore, it is called phase-only DB (PODB) method. It can be implemented at each node independently with only prior knowledge of its own location, and directions of distant CR (DCR) users and LU. The average beam pattern and the average gains for an arbitrary number of CR nodes of PODB method are discussed, showing that CR nodes can constructively transmit signals to DCR users with less interferences to LU via employing the PODB method to form and direct main beams towards directions of DCR users while nulls towards directions of LU. PODB proves to be a green DB method by prolonging the lifetime of the CR network due to effective battery power consumptions at CR nodes. The cumulative distributed function of the beam pattern for a large number of CR nodes is derived and analysed to demonstrate that the PODB method increases the possibility that the transmitted power of the whole CR network at the directions of LU is lower than a certain threshold, which guarantees that CR network causes less disturbing effect to LU.Keywords: distributed beam forming, collaborative beam forming, cognitive radio networks, phase-only distributed beam forming, null-steering distributed beam forming, green cognitive radio networks

Distributed beamforming in relay networks for energy harvesting multi-group multicast systems

“…The major drawback of this approach is the uneven battery utilization of the relays, resulting a node running out of energy independent of the others. In this case, a new beamformer weight vector should be designed for the remaining relays [10]. Instead, we restrict the relays to consume the same amount of power, hence leading to phase-only beamformer.…”

“…However, phase-only distributed beamforming where all relays use the same power is presented as a greener approach in [10]. It is proved that the lifetime of the relay network increases with phase-only design which prevents the uneven battery utilization.…”

“…It is proved that the lifetime of the relay network increases with phase-only design which prevents the uneven battery utilization. Motivated by [10], we introduce phase-only distributed beamforming for multi-group multicasting scenario as a second problem. The resulting problem can easily be solved using exact penalty function and an extended version of FPP-SCA.…”

Relay-assisted beamforming for multicast systems with energy harvesting capability

“…SADECE-FAZ SINIRLAMALI HÜZMȨ SEKİLLENDİRME Bir önceki bölümde, rölelerin güçlerini istenildigişekilde ayarlayabildikleri varsayımı yapıldı. Bu bölümde, herhangi bir rölenin gücünün digerlerinden bagımsız bitmesini önlemek ve bu sayede röle agının yaşam süresini uzatmak için sadecefaz sınırlamalı hüzmeşekillendirme ele alınmaktadır [9]. Bu senaryoda, röleler aynı gücü kullanmaya zorlanmaktadır.…”

“…Sonrasında [8]'de önerilen karesel programlama algoritması FPP-SCA, bu probleme uyarlanmakta ve problem verimli birşekilde çözülmektedir.İncelenen bu problemde, röle katsayılarının genliklerinin istenilenşekilde seçilebilecegi varsayılmıştır. Düzensiz batarya kullanımını engelleyen bir yaklaşım olarak [9]'da sadece-faz sınırlamalı hüzmeşekillendirme sunulmaktadır. Bu bildiride, geliştirilen yöntem sadece-faz sınırlamalı hüzmeşekillendirme için de kurgulanmıştır.…”