17 research outputs found
On the Capacity of a Class of MIMO Cognitive Radios
Cognitive radios have been studied recently as a means to utilize spectrum in
a more efficient manner. This paper focuses on the fundamental limits of
operation of a MIMO cognitive radio network with a single licensed user and a
single cognitive user. The channel setting is equivalent to an interference
channel with degraded message sets (with the cognitive user having access to
the licensed user's message). An achievable region and an outer bound is
derived for such a network setting. It is shown that under certain conditions,
the achievable region is optimal for a portion of the capacity region that
includes sum capacity.Comment: 13 pages, 8 figures, Accepted for publication in Journal of Selected
Topics in Signal Processing (JSTSP) - Special Issue on Dynamic Spectrum
Acces
State of the cognitive interference channel: a new unified inner bound
The capacity region of the interference channel in which one transmitter
non-causally knows the message of the other, termed the cognitive interference
channel, has remained open since its inception in 2005. A number of subtly
differing achievable rate regions and outer bounds have been derived, some of
which are tight under specific conditions. In this work we present a new
unified inner bound for the discrete memoryless cognitive interference channel.
We show explicitly how it encompasses all known discrete memoryless achievable
rate regions as special cases. The presented achievable region was recently
used in deriving the capacity region of the general deterministic cognitive
interference channel, and thus also the linear high-SNR deterministic
approximation of the Gaussian cognitive interference channel. The high-SNR
deterministic approximation was then used to obtain the capacity of the
Gaussian cognitive interference channel to within 1.87 bits.Comment: Presented at the 2010 International Zurich Seminar on Communications
- an 2nd updated version
Difference Antenna Selection and Power Allocation for Wireless Cognitive Systems
In this paper, we propose an antenna selection method in a wireless cognitive
radio (CR) system, namely difference selection, whereby a single transmit
antenna is selected at the secondary transmitter out of possible antennas
such that the weighted difference between the channel gains of the data link
and the interference link is maximized. We analyze mutual information and
outage probability of the secondary transmission in a CR system with difference
antenna selection, and propose a method of optimizing these performance metrics
of the secondary data link subject to practical constraints on the peak
secondary transmit power and the average interference power as seen by the
primary receiver. The optimization is performed over two parameters: the peak
secondary transmit power and the difference selection weight . We show that, difference selection using the optimized parameters
determined by the proposed method can be, in many cases of interest, superior
to a so called ratio selection method disclosed in the literature, although
ratio selection has been shown to be optimal, when impractically, the secondary
transmission power constraint is not applied. We address the effects that the
constraints have on mutual information and outage probability, and discuss the
practical implications of the results.Comment: 29 pages, 9 figures, to be submitted to IEEE Transactions on
Communication