| Abstrakt: |
The cognitive radio wireless sensor network (CRWSN) suffers from a limited frequency spectrum and signal detection in which the sensing method cannot differentiate between signals from a primary user (PU) and a secondary user (SU). Channel capacity limit is an additional issue in CRWSN. These challenges prevent the realization of CRWSN especially in the presence of channel impairments and power constraints. Overcoming these challenges is the main objective of this article. Explicit analytical models are suggested for treatment purposes of these issues. Initially, the detection of PU becomes a challenge if user experiences fading effects in which users cannot distinguish between idle band and deep fading. Signal detection models of PU are suggested for tackling the sensing issues in CRWSN over imperfect Rician fading in CRWSN system. Several models for average probability of detection (PD) and probability of missed detection (PMD) of PU over imperfect Rician fading are built for handling the sensing insufficiency. The scarcity of the available spectrum and lacks of signal detection lead to shortage in channel capacity. Overcoming the channel capacity limit with special emphasis of average/peak interference/transmission power limits and channel degradations is addressed. Full analyses of three different capacities are proposed. These are SU capacity under imperfect chi square channel fading, capacity of truncated channel inversion with fixed rate (TIFR) strategy over Nakagami-m fading channel and ergodic capacity over Nakagami-m fading. The SU's ergodic capacity is implemented under equal power allocation (EPA) and optimal power allocation (OPA) strategies. Analytical frameworks for these capacities are developed for improvement of bandwidth of CRWSN in imperfect channel information. Because of allocating most transmitting power to the optimum antenna, the capacity with OPA is much better than of EPA. A comparison between capacity with TIFR and ergodic policies is presented. It is declared that cutoff of suspended transmission has no impact on the capacity with TIFR transmission. Hence, a plateau response above 3 dB is realized. Capacity values are insignificant for Nakagami-m fading above 10 dB. Ergodic capacity is shrinking after average fading value of 0.56 dB. Accordingly, an improvement of ergodic capacity is realized in comparison to capacity with TIFR transmission under imperfect fading environment. As a final conclusion, the optimal ergodic channel capacity with OPA policy reduces the consumed energy and increases the lifetime of the CRWSN. Therefore, the CRWSN can be implemented in hazardous and nuclear applications for longer times. [ABSTRACT FROM AUTHOR] |
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