1 research outputs found
On the Spectrum Sensing, Beam Selection and Power Allocation in Cognitive Radio Networks Using Reconfigurable Antennas
In this paper, we consider a cognitive radio (CR) system consisting of a
primary user (PU) and a pair of secondary user transmitter (SUtx) and secondary
user receiver (SUrx). The SUtx is equipped with a reconfigurable antenna (RA)
which divides the angular space into M sectors. The RA chooses one sector among
M sectors for its data transmission to SUrx. The SUtx first senses the channel
and monitors the activity of PU for a duration of T_{sen} seconds. We refer to
this period as channel sensing phase. Depending on the outcome of this phase,
SUtx stays in this phase or enters the next phase, which we refer to as
transmission phase. The transmission phase itself consists of two phases:
channel training phase followed by data transmission phase. During the former
phase, SUtx sends pilot symbols to enable channel training and estimation at
SUrx. The SUrx selects the best beam (sector) for data transmission and feeds
back the index of the selected beam as well as its corresponding channel gain.
We also derive the probability of determining the true beam and take into
account this probability in our system design. During the latter phase, SUtx
sends data symbols to SUrx over the selected beam with constant power {\Phi} if
the gain corresponding to the selected beam is bigger than the threshold
{\zeta}. We find the optimal channel sensing duration T_{sen}, the optimal
power level {\Phi} and a optimal threshold {\zeta}, such that the ergodic
capacity of CR system is maximized, subject to average interference and power
constraints. In addition, we derive closed form expressions for outage and
symbol error probabilities of our CR system