14,692 research outputs found
On the Statistics of Cognitive Radio Capacity in Shadowing and Fast Fading Environments (Journal Version)
In this paper we consider the capacity of the cognitive radio channel in
different fading environments under a low interference regime. First we derive
the probability that the low interference regime holds under shadow fading as
well as Rayleigh and Rician fast fading conditions. We demonstrate that this is
the dominant case, especially in practical cognitive radio deployment
scenarios. The capacity of the cognitive radio channel depends critically on a
power loss parameter, , which governs how much transmit power the
cognitive radio dedicates to relaying the primary message. We derive a simple,
accurate approximation to in Rayleigh and Rician fading environments
which gives considerable insight into system capacity. We also investigate the
effects of system parameters and propagation environment on and the
cognitive radio capacity. In all cases, the use of the approximation is shown
to be extremely accurate.Comment: Submitted to the IEEE Transactions on Wireless Commun. The conference
version of this paper appears in Proc. IEEE CrownCom, 200
Adaptive Modulation in Multi-user Cognitive Radio Networks over Fading Channels
In this paper, the performance of adaptive modulation in multi-user cognitive
radio networks over fading channels is analyzed. Multi-user diversity is
considered for opportunistic user selection among multiple secondary users. The
analysis is obtained for Nakagami- fading channels. Both adaptive continuous
rate and adaptive discrete rate schemes are analysed in opportunistic spectrum
access and spectrum sharing. Numerical results are obtained and depicted to
quantify the effects of multi-user fading environments on adaptive modulation
operating in cognitive radio networks
Multi-User Diversity with Optimal Power Allocation in Spectrum Sharing under Average Interference Power Constraint
In this paper, we investigate the performance of multi-user diversity (MUD)
with optimal power allocation (OPA) in spectrum sharing (SS) under average
interference power (AIP) constraint. In particular, OPA through average
transmit power constraint in conjunction with the AIP constraint is assumed to
maximize the ergodic secondary capacity. The solution of this problem requires
the calculation of two Lagrange multipliers instead of one as obtained for the
peak interference power (PIP) constraint and calculated using the well known
water-filling algorithm. To this end, an algorithm based on bisection method is
devised in order to calculate both Lagrange multipliers iteratively. Moreover,
Rayleigh and Nakagami- fading channels with one and multiple primary users
are considered to derive the required end-to-end SNR analysis. Numerical
results are depicted to corroborate our performance analysis and compare it
with the PIP case highlighting hence, the impact of the AIP constraint compared
to the PIP constraint application
Generalized Area Spectral Efficiency: An Effective Performance Metric for Green Wireless Communications
Area spectral efficiency (ASE) was introduced as a metric to quantify the
spectral utilization efficiency of cellular systems. Unlike other performance
metrics, ASE takes into account the spatial property of cellular systems. In
this paper, we generalize the concept of ASE to study arbitrary wireless
transmissions. Specifically, we introduce the notion of affected area to
characterize the spatial property of arbitrary wireless transmissions. Based on
the definition of affected area, we define the performance metric, generalized
area spectral efficiency (GASE), to quantify the spatial spectral utilization
efficiency as well as the greenness of wireless transmissions. After
illustrating its evaluation for point-to-point transmission, we analyze the
GASE performance of several different transmission scenarios, including
dual-hop relay transmission, three-node cooperative relay transmission and
underlay cognitive radio transmission. We derive closed-form expressions for
the GASE metric of each transmission scenario under Rayleigh fading environment
whenever possible. Through mathematical analysis and numerical examples, we
show that the GASE metric provides a new perspective on the design and
optimization of wireless transmissions, especially on the transmitting power
selection. We also show that introducing relay nodes can greatly improve the
spatial utilization efficiency of wireless systems. We illustrate that the GASE
metric can help optimize the deployment of underlay cognitive radio systems.Comment: 11 pages, 8 figures, accepted by TCo
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