SIMO Haberleşme Kanallarında Enerji Tabanlı İşbirlikli Spektrum Algılama

Öz

Son yıllarda haberleşme sistemlerinde yaşanan hızlı gelişim süreci, kablosuz haberleşme uygulamalarının sayısını oldukça artırmış durumdadır. Kablosuz haberleşme sistemlerinde gerçekleşen bu gelişim, beraberinde spektrumda daha fazla band genişliği ihtiyacını da gerektirmektedir. Band genişliği talebinin artışı ise spektrum kıtlığı problemini gün yüzüne çıkarmıştır. Spektrum kıtlığı problemini aşmak için en geçerli yol, sabit frekans tahsisi yerine fırsatçı spektrum kullanımına geçilmesidir. Spektrumu fırsatçı kullanarak dinamik spektrum atama yöntemlerini uygulamak ise Bilişsel Radyo sistemlerinin temel amacıdır. Bilişsel Radyo bulunduğu spektrum ortamını algılayarak boş spektrum bölgelerini belirleyerek bu bölgeleri ikincil kullanıcıların erişimine açmaktadır. Ikincil kullanıcı spektrum kullanımı için belirli bir ücret ödemeyen veya bir spektrum bölgesini yasal olarak kullanma hakkına sahip olmayan kişidir. Aynı şekilde lisanslı kulanıcı ise belirli bir spektrum bölgesini yasal olarak kullanma hakkına sahip kişi olarak tanımlanmaktadır. Bu tanımlar doğrultusunda yapılan bu çalışmada Bilişsel Radyo sistemleri için spektrum algılama yöntemlerinden biri olan, Enerji Tabanlı Spektrum Algılama için, adaptif bir spektrum algılama yöntemi önerilmiştir. Ayrıca önerilen yöntemde gürültü seviyesinin tahmini için farklı bir kestirim yöntemi önerilmektedir. Bilindiği üzere enerji tabanlı algılama yöntemlerinin en büyük dezavantajı gürültü belirsizliği faktörünün algılama performansı üzerinde oluşturduğu olumsuz etkidir. Bu olumsuz etkiyi azaltmak için önerilen yöntemde ortamda bulunan gürültü, Marhenko Pastur teoremi ile tahmin edilerek, eşik değeri adaptif şekilde değiştirilmektedir. Önerilen yöntemin Rayleigh sönümlemeli tek giriş- çok çıkışlı sistemlerde benzetim çalışmaları yapılmıştır. Benzetim çalışmaları işbirlikli ve işbirliksiz algılama yöntemleri için farklı gürültü seviyeleri için incelenmiştir. Ayrıca benzetim sonuçlarında algılama teorisi çalışmaları için sıklıkla kullanılan ROC eğrilerine de yer verilmektedir. Böylece önerilen algılama yönteminde geleneksel enerji algılama yöntemine göre olumlu sonuçlar gözlemlenmiştir.

Anahtar Kelimeler

• Bilişsel Radyo,Enerji Algılama,Marchenko Pastur Teoremi,İşbirlikli Algılama,Spektrum Verimliliği

Energy-Based Cooperative Spectrum Sensing In SIMO Communication Channels

Abstract

The rapid development process in communication systems in recent years has increased the number of wireless communication applications considerably. This development in wireless communication systems requires the need for more bandwidth in the spectrum. The increase in bandwidth demand brought up the problem of spectrum shortage. The most valid way to overcome the problem of spectrum shortage is to switch to the use of opportunistic spectrum instead of fixed frequency allocation. Using spectrum opportunistically is the main purpose of Cognitive Radio systems. Cognitive Radio detects the spectrum environment in which it is located and determines the empty spectrum regions and makes these regions accessible to secondary users. The secondary user is the person who does not pay a specific fee for the use of the spectrum or does not have the legal right to use a spectrum region. Similarly, the licensed user is defined as the person who has the legal right to use a certain spectrum region. An adaptive spectrum sensing method for Energy Based Spectrum Sensing, which is one of the spectrum sensing methods for Cognitive Radio systems, is proposed in this study conducted in line with these definitions. In addition, a different estimation method is proposed for the estimation of the noise level in the proposed method. As it is known, the biggest disadvantage of energy based sensing methods is the negative effect of noise uncertainty factor on sensing performance. In the proposed method to reduce this negative effect, the noise in the environment is estimated by Marhenko Pastur theorem and the threshold value is adaptively changed. Simulation studies of single-multi-output systems with Rayleigh damping are proposed. Simulation studies have been studied for different noise levels for cooperative and non-cooperative detection methods. Also included in the simulation results are ROC curves that are frequently used for detection theory studies. Thus, positive results were observed in the proposed perception method compared to traditional energy perception method

Keywords

• Cognitive Radio,Energy Based Sensing,Marchenko Pastur Theorem,Cooperative Detection,Spectrum Efficiency

Kaynakça

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