Spectrum sensing is the key factor of cognitive radio for efficient utilization of the spectrum resources by identifying and making use of spectrum holes i.e., unused licensed frequency band. The performance of available spectrum sensing techniques may degrade substantially in low signal to noise ratio, multipath fading & shadowing environments. An attempt has been made to implement a transmitter and receiver section for efficient spectrum sensing in cognitive radio environment. A primary user detection algorithm using energy detector-based spectrum sensing technique is designed to analyze the effect of message length on the identification of primary user. Input message of variable length have been modulated using binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) before transmission. Additive white Gaussian noise (AWGN) is added as it possesses wide range of frequency over the channel. The energy of the received signal has been determined by applying Welch Periodogram based power spectral density approach. The performance of the developed algorithm has been evaluated by comparing selected threshold with the computed energy level of the received signal. The results reveal that that power spectral density (PSD) amplitude (received energy) obtained for QPSK modulated messages is found to be less as compared to using binary phase shift keying for similar message lengths. The primary users are identified along with unused spectrum frequencies (spectrum holes) to be utilized by secondary users. This may lead to development of applications to determine spectrum utilization and subsequently the spectrum holes in cognitive environment for varying signal loads.
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