Abstract
In OFDM-based cognitive radio networks, minimizing the interference caused to the primary user (PU) by the substantial amount of out-of-band (OOB) emission is a great challenge. In this paper, we propose a dynamic interference control method using the additive signal side lobe reduction technique and genetic algorithm (GA) in CR-OFDM systems. Additive signal side lobe reduction technique is based on adding a complex array to modulated data symbols in the constellation plane for side lobe reduction in OFDM system. In the proposed method, GA generates optimum additive signal which can effectively reduce the OOB signal interference to the primary system. The GA also strives to keep the interference below a predefined tolerable limit and at the same time it maximizes secondary user's transmission opportunity. The results show that the side lobes of the OFDM-based secondary user signal can be reduced by up to 38 dB and the PU interference tolerable limit can be satisfied at the cost of a minor addition in bit error rate (BER). The results further show that the proposed method delivers better performance as compared to non-GA additive signal method in terms of side lobe reduction as well as BER.
Highlights
The inefficient usage of existing spectrum can be improved through opportunistic access to the licensed bands by secondary users (SUs) without interfering or keeping the interference under a tolerable level to the existing primary users (PUs)
The main contributions of this paper are as follows: (i) We develop a dynamic interference control model using genetic algorithm (GA) to efficiently reduce the interference at f∗, in which f∗ is the closest boundary frequency of the primary system sensed to the secondary system
A technique that can dynamically control interference to PUs caused by Orthogonal frequency-division multiplexing (OFDM)-based SUs is proposed
Summary
The inefficient usage of existing spectrum can be improved through opportunistic access to the licensed bands by secondary users (SUs) without interfering or keeping the interference under a tolerable level to the existing primary users (PUs). OFDM is a good option for realizing a transmission system which does not require a continuous transmission band It is suitable for spectrum sharing in CRNs [4]. We propose a dynamic interference control technique for OFDM-based CR system. We used genetic algorithms (GA) to find an optimal additive sequence for major side lobe suppression. The GA converges for an optimal additive sequence to be added with the symbols transmitted by the OFDM-based SU, with constraints like keeping the SU OOB transmission under PU tolerable limit and low BER. (iii) With the precise side lobe reduction control, we can avoid any harmful interference to the primary users and reduce the possible BER loss due to the deviations in the constellation.
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