Çok Antenli Bilişsel Radyolarda GLRD Tabanlı Spektrum Algılama

Öz

Bilindiği gibi, çok antenli Bilişsel Radyo sistemleri için özdeğer tabanlı spektrum algılama yöntemleri algılanacak sinyale ilişkin önceden hiçbir bilgi gerektirmemesi nedeni ile oldukça tercih edilen bir yöntemdir. Bunun yanısıra özdeğer tabanlı algılama yöntemleri genellikle gürültü belirsizliği faktöründen en az etkilenen yöntemlerdir. Özdeğer tabanlı algılama yöntemlerinde algılama performansı, test istatistiğinin doğru hesaplanmasına ve eşik değerine bağlıdır. Bu çalışmada genelleştirilmiş en çok olabilirlik tabanlı algılama(Generalized Likelihood Ratio Detection- GLRD) yöntemlerinde farklı eşik değerlerinin performans değerlendirilmesi amaçlanmıştır. Eşik değeri hesaplanırken, Wishart matrisleri için farklı olasılık dağılım fonksiyonları kullanılarak yanlış algılama olasılığı (Pfa) ve eşik değeri teorik olarak verilmiştir. Benzetim çalışmaları, MIMO-OFDM sistemleri için gürültü belirsizliği altında gerçekleştirilmiştir. Ayrıca benzetim çalışması sonuçlarında en yaygın spektrum algılama yöntemlerinden olan enerji algılamaya da yer verilmektedir. Yapılan benzetim çalışmaları farklı gürültü seviyeleri için verilmektedir. Alınan sonuçlara göre iyileştirilmiş GLRD yönteminin başarılı sonuçlar verdiği gözlenmiştir.

Anahtar Kelimeler

• Bilişsel Radyo,GLRD Eşik Değeri,MIMO-OFDM Sistemleri,Tracy-Widom Dağılımı,Spektrum verimliliği

Multiple Antenna Spectrum Sensing Based on GLR Detector in Cognitive Radios

Abstract

As it is known, eigenvalue-based spectrum detection methods are very preferred method for multi-antenna Cognitive Radio systems since they do not require any prior knowledge of the signal to be detected. In addition, eigenvalue based detection methods are generally the least affected by the noise uncertainty factor. In eigenvalue-based detection methods, detection performance depends on the correct calculation of the test statistics and the threshold value. In this study, it is aimed to evaluate the performance of different threshold values in generalized Likelihood Ratio Detection (GLRD) methods. While calculating the threshold value, misperception probability (Pfa) and threshold value are given theoretically using different probability distribution functions for Wishart matrices. Simulation studies were carried out under noise uncertainty for MIMO-OFDM systems. In addition, energy detection, which is one of the most common spectrum sensing methods, is included in the results of the simulation study. Simulation studies are given for different noise levels. According to the results, it is observed that the improved GLRD method gives successful results.

Keywords

• Cognitive Radio,GLRD Threshold Value,MIMO-OFDM Systems,Tracy-Widom Distribution,Spectrum efficiency

Kaynakça

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