Development of OFDM based Secondary Link: Some Experimental Results on USRP N210 Platform

Abstract

Some experimental results of the concept development and practical implementation of an Orthogonal Frequency Division Multiplexing (OFDM) based secondary cognitive link are presented in this paper. The secondary link is realized using Universal Software Radio Peripheral (USRP) N210 platforms. For communication with USRP, we use MATLAB toolbox. Several algorithms are used to overcome transmission problems. Time-synchronization is achieved using a method based on auto-correlation of two sliding windows. Frequency offset estimation is performed using a phase offset between samples in a signal header, comprised of a sinusoid. A channel is estimated using predefined symbols inserted at the beginning of every frame, which enables channel equalization. Also, the cognitive feature of spectrum sensing and changing transmission parameters is implemented. A least-mean-square adaptive filter is introduced to offer time-synchronization error estimation as well as an alternative option for channel equalization.

Keywords

• Cognitive radio
• OFDM
• secondary link
• spectrum sensing
• USRP platform