7 research outputs found
Interference and Deployment Issues for Cognitive Radio Systems in Shadowing Environments
In this paper we describe a model for calculating the aggregate interference
encountered by primary receivers in the presence of randomly placed cognitive
radios (CRs). We show that incorporating the impact of distance attenuation and
lognormal fading on each constituent interferer in the aggregate, leads to a
composite interference that cannot be satisfactorily modeled by a lognormal.
Using the interference statistics we determine a number of key parameters
needed for the deployment of CRs. Examples of these are the exclusion zone
radius, needed to protect the primary receiver under different types of fading
environments and acceptable interference levels, and the numbers of CRs that
can be deployed. We further show that if the CRs have apriori knowledge of the
radio environment map (REM), then a much larger number of CRs can be deployed
especially in a high density environment. Given REM information, we also look
at the CR numbers achieved by two different types of techniques to process the
scheduling information.Comment: to be presented at IEEE ICC 2009. This posting is the same as the
original one. Only author's list is updated that was unfortunately not
correctly mentioned in first versio
Performance Analysis of Arbitrarily-Shaped Underlay Cognitive Networks: Effects of Secondary User Activity Protocols
This paper analyzes the performance of the primary and secondary users (SUs)
in an arbitrarily-shaped underlay cognitive network. In order to meet the
interference threshold requirement for a primary receiver (PU-Rx) at an
arbitrary location, we consider different SU activity protocols which limit the
number of active SUs. We propose a framework, based on the moment generating
function (MGF) of the interference due to a random SU, to analytically compute
the outage probability in the primary network, as well as the average number of
active SUs in the secondary network. We also propose a cooperation-based SU
activity protocol in the underlay cognitive network which includes the existing
threshold-based protocol as a special case. We study the average number of
active SUs for the different SU activity protocols, subject to a given outage
probability constraint at the PU and we employ it as an analytical approach to
compare the effect of different SU activity protocols on the performance of the
primary and secondary networks.Comment: submitted to possible IEEE Transactions publicatio
Performance of Cognitive Radio Systems with Imperfect Radio Environment Map Information
In this paper we describe the effect of imperfections in the radio
environment map (REM) information on the performance of cognitive radio (CR)
systems. Via simulations we explore the relationship between the required
precision of the REM and various channel/system properties. For example, the
degree of spatial correlation in the shadow fading is a key factor as is the
interference constraint employed by the primary user. Based on the CR
interferers obtained from the simulations, we characterize the temporal
behavior of such systems by computing the level crossing rates (LCRs) of the
cumulative interference represented by these CRs. This evaluates the effect of
short term fluctuations above acceptable interference levels due to the fast
fading. We derive analytical formulae for the LCRs in Rayleigh and Rician fast
fading conditions. The analytical results are verified by Monte Carlo
simulations.Comment: presented at IEEE AusCTW 2009. Journal versions are under
preparation. This posting is the same as the original one. Only author's list
is updated that was unfortunately not correctly mentioned in the first
versio
A Cognitive Sensing Algorithm for Coexistence Scenario with LTE
Increasing demand for high data rate wireless communication motivates the wireless engineers to develop advanced technologies to address such needs. LTE and LTE-Advanced are examples of such wireless technologies, which support high data rate and a large number of users. However, higher data rate communication requires more frequency bandwidth.
Recent studies have shown that the inefficient utilization of frequency spectrum is one of the main reasons for the scarcity of frequency bandwidth. Cognitive Radio Network is introduced as a promising solution for this problem. It increases the utilization of bandwidth, by intelligently sensing the channel environment and dynamically providing access to the available resources (frequency bands) for a secondary user.
In this thesis, we developed an algorithm for dynamically detecting and anticipating the existence of underutilized resources in LTE system. The algorithm should be a real-time operation, i.e. the decision on availability of a detected resource should be made within a time much less than scheduling update period of LTE. This is the only way that rest of the unused resources becomes usable. For each specific channel assignment, the algorithm requires to start sensing as soon as possible.
Therefore, we develop the algorithm in three main steps. The first step is to blindly detect and identify the LTE-Downlink signal using cyclostationarity property of OFDM scheme. The second step is the acquisition of the LTE-Downlink sub-frame timing, which is basically performed by detecting the Primary Synchronization Signal.
The third step is to detect unused resources, for the duration of their transmission. This step is using a frequency domain energy detector. By performing the first and second steps, the sub-frame timing and scheduling update instances are known. So basically the algorithm does not require any previous knowledge of the LTE signal.
We evaluate the performance of the proposed algorithm with respect to the tolerable amount of interference at the primary user side. Using the proposed algorithm, in average up to 81 % of unused resources can be used by the secondary user
Stochastic Geometry for Modeling, Analysis and Design of Future Wireless Networks
This thesis focuses on the modeling, analysis and design of
future wireless networks with smart devices, i.e., devices with
intelligence and ability to communicate with one another
with/without the control of base stations (BSs). Using stochastic
geometry, we develop realistic yet tractable frameworks to model
and analyze the performance of such networks, while incorporating
the intelligence features of smart devices.
In the first half of the thesis, we develop stochastic geometry
tools to study arbitrarily shaped network regions. Current
techniques in the literature assume the network regions to be
infinite, while practical network regions tend to be arbitrary.
Two well-known networks are considered, where devices have the
ability to: (i) communicate with others without the control of
BSs (i.e., ad-hoc networks), and (ii) opportunistically access
spectrum (i.e., cognitive networks). First, we propose a general
algorithm to derive the distribution of the distance between the
reference node and a random node inside an arbitrarily shaped
ad-hoc network region, which helps to compute the outage
probability. We then study the impact of boundary effects and
show that the outage probability in infinite regions may not be a
meaningful bound for arbitrarily shaped regions. By extending the
developed techniques, we further analyze the performance of
underlay cognitive networks, where different secondary users
(SUs) activity protocols are employed to limit the interference
at a primary user. Leveraging the information exchange among SUs,
we propose a cooperation-based protocol. We show that, in the
short-term sensing scenario, this protocol improves the network's
performance compared to the existing threshold-based protocol.
In the second half of the thesis, we study two recently emerged
networks, where devices have the ability to: (i) communicate
directly with nearby devices under the control of BSs (i.e.,
device-to-device (D2D) communication), and (ii) harvest radio
frequency energy (i.e., energy harvesting networks). We first
analyze the intra-cell interference in a finite cellular region
underlaid with D2D communication, by incorporating a mode
selection scheme to reduce the interference. We derive the outage
probability at the BS and a D2D receiver, and propose a spectrum
reuse ratio metric to assess the overall D2D communication
performance. We demonstrate that, without impairing the
performance at the BS, if the path-loss exponent on cellular link
is slightly lower than that on D2D link, the spectrum reuse ratio
can have negligible decrease while the average number of
successful D2D transmissions increases with the increasing D2D
node density. This indicates that an increasing level of D2D
communication is beneficial in future networks. Then we study an
ad-hoc network with simultaneous wireless information and power
transfer in an infinite region, where transmitters are wirelessly
charged by power beacons. We formulate the total outage
probability in terms of the power and channel outage
probabilities. The former incorporates a power activation
threshold at transmitters, which is a key practical factor that
has been largely ignored in previous work. We show that, although
increasing power beacon's density or transmit power is not always
beneficial for channel outage probability, it improves the
overall network performance