Power and Transmission Duration Control in Un-Slotted Cognitive Radio Networks
Marwa Ali, Ahmed Ahmedin, Ahmed Sultan, Mohammed Nafie
Signals and Telecommunication Journal, Vol. 3, No. 1, 2014.
DOI: 
Link: http://www.dline.info/stj/fulltext/v3n1/1.pdf
Abstract:
We consider an unslotted primary channel with alternating on/off activity and provide a solution to the problem of finding the optimal secondary transmission power and duration given the sensing outcome. The goal is to maximize a weighted sum of the primary and secondary throughput where the weight is determined by the degree of protection and the minimum rate required by the primary terminals. Two sensing schemes are considered: perfect sensing in which the actual state of the primary channel is revealed, and soft sensing in which the secondary transmission power and time are determined based on the sensing metric directly. We use an upper bound for the secondary throughput assuming that the secondary receiver tracks the instantaneous secondary channel state information. We justify the upper bound on informationtheoretic grounds and also provide a lower bound on secondary throughput. The weighted sum throughput objective function is non-convex and, hence, the optimal solution is obtained via exhaustive search. Our results show enhanced throughput by allowing the secondary to transmit even when the channel is found to be busy. The enhancement increases as the channel gain between the secondary transmitter and primary receiver decreases. For the examined system parameter values, the throughput gain from soft sensing depends on the â€œdistanceâ€ between the likelihood functions of the received primary signal at the secondary transmitter. Further investigation is needed to quantify the potential of soft sensing.