14 research outputs found
Scaling Laws of Cognitive Networks
We consider a cognitive network consisting of n random pairs of cognitive
transmitters and receivers communicating simultaneously in the presence of
multiple primary users. Of interest is how the maximum throughput achieved by
the cognitive users scales with n. Furthermore, how far these users must be
from a primary user to guarantee a given primary outage. Two scenarios are
considered for the network scaling law: (i) when each cognitive transmitter
uses constant power to communicate with a cognitive receiver at a bounded
distance away, and (ii) when each cognitive transmitter scales its power
according to the distance to a considered primary user, allowing the cognitive
transmitter-receiver distances to grow. Using single-hop transmission, suitable
for cognitive devices of opportunistic nature, we show that, in both scenarios,
with path loss larger than 2, the cognitive network throughput scales linearly
with the number of cognitive users. We then explore the radius of a primary
exclusive region void of cognitive transmitters. We obtain bounds on this
radius for a given primary outage constraint. These bounds can help in the
design of a primary network with exclusive regions, outside of which cognitive
users may transmit freely. Our results show that opportunistic secondary
spectrum access using single-hop transmission is promising.Comment: significantly revised and extended, 30 pages, 13 figures, submitted
to IEEE Journal of Special Topics in Signal Processin
AN INVESTIGATION OF SECURITY CHALLENGES IN COGNITIVE RADIO NETWORKS
The recent advances in wireless communication have led to the problem of growing spectrum scarcity. The available wireless spectrum has become scarcer due to increasing spectrum demand for new wireless applications. The large portion of the allocated spectrum is sporadically used leading to underutilization of significant amount of spectrum. To improve the spectrum efficiency, the idea of cognitive radio technology was introduced. This concept of cognitive radio provides a promising solution for the spectrum scarcity issues in wireless networks. Meanwhile, the security issues of cognitive radio have received more attentions recently since the inherent properties of CR networks would pose new challenges to wireless communications. In this MS thesis, general concepts of security threats to the cognitive radio networks are briefly reviewed. Performances for primary user emulation attacks are studied from Neyman-Pearson criterion point of view. A novel system model with different configurations of the primary users has been proposed and studied. Our experimental results demonstrate the statistical characteristics of the probability of false alarm and miss detection in the proposed system. I will make performance comparison with others’ research in the future.
Adviser: Yaoqing Yan
AN INVESTIGATION OF SECURITY CHALLENGES IN COGNITIVE RADIO NETWORKS
The recent advances in wireless communication have led to the problem of growing spectrum scarcity. The available wireless spectrum has become scarcer due to increasing spectrum demand for new wireless applications. The large portion of the allocated spectrum is sporadically used leading to underutilization of significant amount of spectrum. To improve the spectrum efficiency, the idea of cognitive radio technology was introduced. This concept of cognitive radio provides a promising solution for the spectrum scarcity issues in wireless networks. Meanwhile, the security issues of cognitive radio have received more attentions recently since the inherent properties of CR networks would pose new challenges to wireless communications. In this MS thesis, general concepts of security threats to the cognitive radio networks are briefly reviewed. Performances for primary user emulation attacks are studied from Neyman-Pearson criterion point of view. A novel system model with different configurations of the primary users has been proposed and studied. Our experimental results demonstrate the statistical characteristics of the probability of false alarm and miss detection in the proposed system. I will make performance comparison with others’ research in the future.
Adviser: Yaoqing Yan
Cognitive Networks Achieve Throughput Scaling of a Homogeneous Network
We study two distinct, but overlapping, networks that operate at the same
time, space, and frequency. The first network consists of randomly
distributed \emph{primary users}, which form either an ad hoc network, or an
infrastructure-supported ad hoc network with additional base stations. The
second network consists of randomly distributed, ad hoc secondary users or
cognitive users. The primary users have priority access to the spectrum and do
not need to change their communication protocol in the presence of secondary
users. The secondary users, however, need to adjust their protocol based on
knowledge about the locations of the primary nodes to bring little loss to the
primary network's throughput. By introducing preservation regions around
primary receivers and avoidance regions around primary base stations, we
propose two modified multihop routing protocols for the cognitive users. Base
on percolation theory, we show that when the secondary network is denser than
the primary network, both networks can simultaneously achieve the same
throughput scaling law as a stand-alone network. Furthermore, the primary
network throughput is subject to only a vanishingly fractional loss.
Specifically, for the ad hoc and the infrastructure-supported primary models,
the primary network achieves sum throughputs of order and
, respectively. For both primary network models, for any
, the secondary network can achieve sum throughput of order
with an arbitrarily small fraction of outage. Thus, almost all
secondary source-destination pairs can communicate at a rate of order
.Comment: 28 pages, 12 figures, submitted to IEEE Trans. on Information Theor
Power adaptation for cognitive radio systems under an average sinr loss constraint in the absence of path loss information
An upper bound is derived on the capacity of a cognitive radio system by considering the effects of path loss and log-normal shadowing simultaneously for a single-cell network. Assuming that the cognitive radio is informed only of the shadow fading between the secondary (cognitive) transmitter and primary receiver, the capacity is achieved via the water-filling power allocation strategy under an average primary signal to secondary interference plus noise ratio loss constraint. Contrary to the perfect channel state information requirement at the secondary system (SS), the transmit power control of the SS is accomplished in the absence of any path loss estimates. For this purpose, a method for estimating the instantaneous value of the shadow fading is also presented. A detailed analysis of the proposed power adaptation strategy is conducted through various numerical simulations. © 2013 Springer Science+Business Media New York
Distributed spectrum leasing via cooperation
“Cognitive radio” networks enable the coexistence of primary (licensed) and secondary (unlicensed) terminals. Conventional frameworks, namely commons and property-rights models, while being promising in certain aspects, appear to have significant drawbacks for implementation of large-scale distributed cognitive radio networks, due to the technological and theoretical limits on the ability of secondary activity to perform effective spectrum sensing and on the stringent constraints on protocols and architectures.
To address the problems highlighted above, the framework of distributed spectrum leasing via cross-layer cooperation (DiSC) has been recently proposed as a basic mechanism to guide the design of decentralized cognitive radio networks. According to this framework, each primary terminal can ”lease” a transmission opportunity to a local secondary terminal in exchange for cooperation (relaying) as long as secondary quality-of-service (QoS) requirements are satisfied.
The dissertation starts by investigating the performance bounds from an information-theoretical standpoint by focusing on the scenario of a single primary user and multiple secondary users with private messages. Achievable rate regions are derived for discrete memoryless and Gaussian models by considering Decode-and-Forward (DF), with both standard and parity-forwarding techniques, and Compress-and-Forward (CF), along with superposition coding at the secondary nodes. Then a framework is proposed that extends the analysis to multiple primary users and multiple secondary users by leveraging the concept of Generalized Nash Equilibrium. Accordingly, multiple primary users, each owning its own spectral resource, compete for the cooperation of the available secondary users under a shared constraint on all spectrum leasing decisions set by the secondary QoS requirements. A general formulation of the problem is given and solutions are proposed with different signaling requirements among the primary users.
The novel idea of interference forwarding as a mechanism to enable DiSC is proposed, whereby primary users lease part of their spectrum to the secondary users if the latter assist by forwarding information about the interference to enable interference mitigation at the primary receivers. Finally, an application of DiSC in multi-tier wireless networks such as femtocells overlaid by macrocells whereby the femtocell base station acts as a relay for the macrocell users is presented. The performance advantages of the proposed application are evaluated by studying the transmission reliability of macro and femto users for a quasi-static fading channel in terms of outage probability and diversity-multiplexing trade-off for uplink and, more briefly, for downlink
Primary user emulation attack mitigation in cognitive radio networks.
M. Sc. Eng. University of KwaZulu-Natal, Durban 2014.The rapid progress in the number of users and applications in wireless communication have led to the problem of growing spectrum scarcity in recent years. This imminent spectrum scarcity problem is in part due to a rapidly increasing demand for wireless services and in part due to the inefficient usage of currently licensed spectrum bands. Cognitive radio (CR) is a new technology that is proposed to improve spectrum efficiency by allowing unlicensed secondary users to access the licensed frequency bands without interfering with the licensed primary users. A malicious secondary user can decide to exploit this spectrum access etiquette by mimicking the spectral characteristics of a primary user, and gain priority access to a wireless channel over other secondary users. This scenario is referred to in literature as Primary User Emulation Attack (PUEA).
Though quite a lot of research efforts have been focused on the detection and defense strategy of PUEA in cognitive radio networks, less attention have been given to combating and mitigating PUEA in a cooperative spectrum sensing environment. This dissertation seeks to contribute to research in the field of cognitive radio networks through an investigation into the impacts of Primary User Emulation Attacks (PUEA) on cognitive radio networks, the problem of trust amongst users in the networks and also mitigating the activities of PUEA in the network.
An analytical and system model for PUEA in cognitive radio networks is presented and its impacts are also studied using Neyman-Pearson Composite Hypothesis Test. The intention is to evict malicious users from the network and maximize spectrum utilization efficiency. To achieve this, techniques to verify that the source of spectrum occupancy information is from a genuine user are proposed.
In a primary user emulation attack, malicious users tend to destruct the spectrum sensing process of a cognitive radio network by imitating the primary signal and deceive other secondary users from accessing vacant frequency bands. An energy detection cooperative spectrum sensing technique is proposed to mitigate this attack. This technique assists in the reduction of errors made by secondary users in detecting primary user signals in frequency bands considering the existence of PUEA in the network. The performance of our proposed method is compared to an existing energy detection spectrum sensing method that does not consider the existence of PUEA in the network. Simulated results show that the proposed method can effectively mitigate PUEA in a cognitive radio network
Throughput Analysis of Wireless Ad-Hoc Cognitive Radio Networks
In this dissertation we consider the throughput performance of cognitive radio
networks and derive the optimal sensing and access schemes for secondary users that
maximizes their sum-throughput while guaranteeing certain quality of service to primary
networks. First, we consider a cognitive radio network where secondary users
have access to N licensed primary frequency bands with their usage statistics and
are subject to certain inter-network interference constraint. In particular, to limit
the interference to the primary network, secondary users are equipped with spectrum
sensors and are capable of sensing and accessing a limited number of channels
at the same time. We consider both the error-free and erroneous spectrum sensing
scenarios, and establish the jointly optimal random sensing and access scheme, which
maximizes the secondary network expected sum throughput while honoring the primary
interference constraint. We show that under certain conditions the optimal
sensing and access scheme is independent of the primary frequency bandwidths and
usage statistics; otherwise, they follow water-filling-like strategies.
Next, we study the asymptotic performance of two multi-hop overlaid ad-hoc
networks that utilize the same temporal, spectral, and spatial resources based on
random access schemes. The primary network consists of Poisson distributed legacy
users with density λ^(p) and the secondary network consists of Poisson distributed
cognitive radio users with density λ^(s) = (λ^(p))^(β) that utilize the spectrum opportunistically.
Both networks employ ALOHA medium access protocols where the
secondary nodes are additionally equipped with range-limited perfect spectrum sensors
to monitor and protect primary transmissions. We study the problem in two
distinct regimes, namely β > 1 and 0 < β < 1. We show that in both cases, the
two networks can achieve their corresponding stand-alone throughput scaling even
without secondary spectrum sensing ; this implies the need for a more comprehensive
performance metric than just throughput scaling to evaluate the influence of
the overlaid interactions. We thus introduce a new criterion, termed the asymptotic
multiplexing gain, which captures the effect of inter-network interference . With this
metric, we clearly demonstrate that spectrum sensing can substantially improve the
overlaid cognitive networks performance when β > 1. On the contrary, spectrum
sensing turns out to be redundant when β < 1 and employing spectrum sensors
cannot improve the networks performance.
Finally, we present a methodology employing statistical analysis and stochastic
geometry to study geometric routing schemes in wireless ad-hoc networks. The techniques
developed in this section enable us to establish the asymptotic connectivity
and the convergence results for the mean and variance of the routing path lengths
generated by geometric routing schemes in random wireless networks