APPLYING DISTRIBUTED ORTHOGONAL SPACE TIME BLOCK CODING IN COOPERATIVE COMMUNICATION NETWORKS
In this research, we investigate cooperative spectrum sensing using distributed orthogonal space time block coding (DOSTBC). Multiple antennas are introduced at the transmitter and the receiver to achieve higher cooperative diversity in the cooperative wireless (CW) networks. The received signals from the primary users (PUs) at the cooperative relays (CRs) are encoded and retransmitted to the cooperative controller (CC), where further decisions are made depending on the information sent from the CRs. The cooperative relaying protocol employed here in CRs is based on decoding forward (DF) technique. The proposed Alamouti scheme in orthogonal space time block code (OSTBC) has been found to enhance detection performance in CW networks. The analyses over independent Rayleigh fading channels are performed by the energy detector. In CW networks the secondary users (SUs) use the available frequency band as the PUs is absent. The SU discontinue using the licensed band and head off as soon as the PU is present. The SUs is more responsive and intelligent in detecting the spectrum holes. The principal aim of the CW network is to use the available holes without causing any interference to the PUs. The CRs are preferably placed close to the PU to detect transmitted signal, with decoding capability the information collected are decoded by CRs using Maximum Likelihood (ML) decoding technique. The CRs then re-encode the decoded data and retransmit it to the receiver. The energy detector accumulates information from various users, compares it using threshold value (T_f) predefined and the final decision made. The probabilities of detection and false alarm are observed using DOSTBC on PU and SU in cooperative communication via DF protocol. The system performance is investigated with single and multiple relays; with and without direct path between the PUs and SUs. Selection Combining (SC) and Maximum Ratio Combining (MRC) schemes are applied in energy detector and the outcomes are evaluated with and without direct link between PU and SU. The proposed cooperative spectrum sensing using DF protocol at CRs with Alamouti space time block code (STBC) is processed and results are validated by computer simulation.
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