7,297 research outputs found
Aggregate Interference Modeling in Cognitive Radio Networks with Power and Contention Control
In this paper, we present an interference model for cognitive radio (CR)
networks employing power control, contention control or hybrid power/contention
control schemes. For the first case, a power control scheme is proposed to
govern the transmission power of a CR node. For the second one, a contention
control scheme at the media access control (MAC) layer, based on carrier sense
multiple access with collision avoidance (CSMA/CA), is proposed to coordinate
the operation of CR nodes with transmission requests. The probability density
functions of the interference received at a primary receiver from a CR network
are first derived numerically for these two cases. For the hybrid case, where
power and contention controls are jointly adopted by a CR node to govern its
transmission, the interference is analyzed and compared with that of the first
two schemes by simulations. Then, the interference distributions under the
first two control schemes are fitted by log-normal distributions with greatly
reduced complexity. Moreover, the effect of a hidden primary receiver on the
interference experienced at the receiver is investigated. It is demonstrated
that both power and contention controls are effective approaches to alleviate
the interference caused by CR networks. Some in-depth analysis of the impact of
key parameters on the interference of CR networks is given via numerical
studies as well.Comment: 24 pages, 8 figures, submitted to IEEE Trans. Communications in July
201
Communication in a Poisson Field of Interferers -- Part I: Interference Distribution and Error Probability
We present a mathematical model for communication subject to both network
interference and noise. We introduce a framework where the interferers are
scattered according to a spatial Poisson process, and are operating
asynchronously in a wireless environment subject to path loss, shadowing, and
multipath fading. We consider both cases of slow and fast-varying interferer
positions. The paper is comprised of two separate parts. In Part I, we
determine the distribution of the aggregate network interference at the output
of a linear receiver. We characterize the error performance of the link, in
terms of average and outage probabilities. The proposed model is valid for any
linear modulation scheme (e.g., M-ary phase shift keying or M-ary quadrature
amplitude modulation), and captures all the essential physical parameters that
affect network interference. Our work generalizes the conventional analysis of
communication in the presence of additive white Gaussian noise and fast fading,
allowing the traditional results to be extended to include the effect of
network interference. In Part II of the paper, we derive the capacity of the
link when subject to network interference and noise, and characterize the
spectrum of the aggregate interference.Comment: To appear in IEEE Transactions on Wireless Communication
Spectrum Sensing Performance in Cognitive Radio Networks with Multiple Primary Users
Radio Spectrum sensing has been a topic of strong research in the last years due to its importance to Cognitive Radio (CR) systems. However, in Cognitive Radio Networks (CRNs) with multiple Primary Users (PUs), the Secondary Users (SUs) can often detect PUs that are located outside the sensing range, due to the level of the aggregated interference caused by that PUs. This effect, known as Spatial False Alarm (SFA), degrades the performance of CRNs, because it decreases the SUs’ medium access
probability. This work characterizes the SFA effect in a CRN, identifying possible actions to attenuate it. Adopting Energy-based sensing (EBS) in each SU, this work starts to characterize the interference caused by multiple PUs located outside a desired sensing region. The interference formulation is then used to write the probabilities of detection and false alarm, and closed form expressions are presented and validated through simulation. The first remark to be made is that the SFA can be neglected, depending on the path loss factor and the number of samples collected by the energy detector to decide the spectrum’s occupancy state. However, it is shown that by increasing the number of samples needed to increase the
sensing accuracy, the SUs may degrade their throughput, namely if SUs are equipped with a single radio that is sequentially used for sensing and transmission. Assuming this scenario, this paper ends by providing a bound for the maximum throughput achieved in a CRN with multiple active PUs and for a given level of PUs’ detection inside the SUs’ sensing region. The results presented in the paper show the impact of path loss and EBS parameterization on SUs’ throughput and are particularly useful to guide the design and parametrization of multi-hop CRNs, including future ad hoc cognitive radio networks considering multiple PUs
Interference modelling and management for cognitive radio networks
Radio spectrum is becoming increasingly scarce as more and more devices go wireless.
Meanwhile, studies indicate that the assigned spectrum is not fully utilised.
Cognitive radio (CR) technology is envisioned to be a promising solution to address
the imbalance between spectrum scarcity and spectrum underutilisation. It improves
the spectrum utilisation by reusing the unused or underutilised spectrum owned by
incumbent systems (primary systems). With the introduction of CR networks, two
types of interference originating from CR networks are introduced. They are the interference
from CR to primary networks (CR-primary interference) and the interference
among spectrum-sharing CR nodes (CR-CR interference). The interference should be
well controlled and managed in order not to jeopardise the operation of the primary
network and to improve the performance of CR systems. This thesis investigates the
interference in CR networks by modelling and mitigating the CR-primary interference
and analysing the CR-CR interference channels.
Firstly, the CR-primary interference is modelled for multiple CR nodes sharing the
spectrum with the primary system. The probability density functions of CR-primary
interference are derived for CR networks adopting different interference management
schemes. The relationship between CR operating parameters and the resulting CRprimary
interference is investigated. It sheds light on the deployment of CR networks
to better protect the primary system.
Secondly, various interference mitigation techniques that are applicable to CR networks
are reviewed. Two novel precoding schemes for CR multiple-input multipleoutput
(MIMO) systems are proposed to mitigate the CR-primary interference and
maximise the CR throughput. To further reduce the CR-primary interference, we also
approach interference mitigation from a cross-layer perspective by jointly considering
channel allocation in the media access control layer and precoding in the physical
layer of CR MIMO systems.
Finally, we analyse the underlying interference channels among spectrum-sharing CR
users when they interfere with each other. The Pareto rate region for multi-user MIMO
interference systems is characterised. Various rate region convexification schemes are
examined to convexify the rate region. Then, game theory is applied to the interference
system to coordinate the operation of each CR user. Nash bargaining over MIMO
interference systems is characterised as well.
The research presented in this thesis reveals the impact of CR operation on the resulting
CR-primary network, how to mitigate the CR-primary interference and how
to coordinate the spectrum-sharing CR users. It forms the fundamental basis for interference
management in CR systems and consequently gives insights into the design
and deployment of CR networks
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