Title: An efficient spectrum shaping method for OFDM-based cognitive radio system

Authors: Parmila Devi; Manoranjan Rai Bharti

Addresses: Department of Electronics and Communication Engineering (ECE), NIT Hamirpur, Hamirpur, Himachal Pradesh, India ' Department of Electronics and Communication Engineering (ECE), NIT Hamirpur, Hamirpur, Himachal Pradesh, India

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) is widely used for transmitting digital data over wireless communication channels but suffers from high-side lobes causing energy leakage into adjacent frequency bands. This leakage can lead to interference between licensed and unlicensed OFDM-CR users. To minimise this interference, it is important to reduce the signal energy outside the OFDM frequency band. This can be achieved by shaping the spectrum of the OFDM signal. Therefore, in this paper, we have proposed a spectrum-shaping method for OFDM-based single-user and multi-user CR systems by using an orthogonal pre-coder in conjunction with raised cosine windowing to effectively reduce out-of-band radiation. The analytical and simulation results show that this method significantly decreases interference to licensed users while maintaining BER performance, though it slightly degrades the PAPR, which can be improved with a suitable reduction technique. Monte Carlo simulations validate the accuracy of our derived analytical expressions.

Keywords: cognitive radio; OFDM; spectrum shaping; pre-coding; sidelobe suppression; raised cosine windowing; PAPR.

DOI: 10.1504/IJWMC.2025.147618

International Journal of Wireless and Mobile Computing, 2025 Vol.29 No.1, pp.83 - 92

Received: 06 Dec 2023
Accepted: 22 Jul 2024
Published online: 24 Jul 2025 *

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