Perform sensing and transmission in parallel in cognitive radio systems: Spectrum and energy efficiency

Radio spectrum is a precious and limited resource for wireless communication networks. The proposed “Always Transmit (AT)” strategy in cognitive radio is a precious solution to overcome the inefficient spectrum allocation policy, since secondary user (SU) exploits spectrum sensing phase (first part of a time slot) for data transmission. This leads to a new challenge: “how SU can perform sensing simultaneously with data transmission in the same primary band?” In order to overcome this new problem, in this paper we propose two spectrum sensing detectors: we adapt the classical blind detector “energy detection” to the proposed scheme and we propose “own-waveform-based sensing” as an alternative innovative solution to detect collision/no collision between SU and primary user (PU) signals if PU is active/absent. In addition, since the transmit power and the interference power can be limited either by an instantaneous or an average constraint, we show, how SU can manage its power allocation policy under the proposed “AT” strategy in order to improve the short/long term of quality of service (QoS) of secondary system while the requirement of the short/long term of QoS for primary system is guaranteed. The closed form of outage probabilities are derived over Nakagami-m fading channels. Numerical results show that the proposed scheme “AT” outperforms other traditional/classical cognitive radio access strategies, guarantees 20.86% as a maximum degradation limit, and reduces the outage probability of the secondary system (a) by a factor of 492.83% versus interweave mode, (b) by a factor of 21.41% versus underlay mode and (c) by a factor of 398.89% versus mixed mode.