360 research outputs found
Listen-and-Talk: Protocol Design and Analysis for Full-duplex Cognitive Radio Networks
In traditional cognitive radio networks, secondary users (SUs) typically
access the spectrum of primary users (PUs) by a two-stage "listen-before-talk"
(LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before
transmitting in the second. However, there exist two major problems: 1)
transmission time reduction due to sensing, and 2) sensing accuracy impairment
due to data transmission. In this paper, we propose a "listen-and-talk" (LAT)
protocol with the help of full-duplex (FD) technique that allows SUs to
simultaneously sense and access the vacant spectrum. Spectrum utilization
performance is carefully analyzed, with the closed-form spectrum waste ratio
and collision ratio with the PU provided. Also, regarding the secondary
throughput, we report the existence of a tradeoff between the secondary
transmit power and throughput. Based on the power-throughput tradeoff, we
derive the analytical local optimal transmit power for SUs to achieve both high
throughput and satisfying sensing accuracy. Numerical results are given to
verify the proposed protocol and the theoretical results
Throughput analysis of full-duplex communication cognitive radio network
In this paper we deal with the throughput of full-duplex cognitive communication radio which exploits unused band of primary user (PU) network. Classical cognitive radio uses half-duplex communication spectrum sensing to perform spectrum sensing and data transmission at different time intervals. It’s well-established fact that in half-duplex communication cognitive radio spectrum sensing time increases at low SNR which gives rise to lesser data transmission time for secondary user (SU) and hence results in less throughput for SU. It’s useful idea to do spectrum sensing and data transmission at the same time with two different antennas co-located on the SU transceiver. This shall not only guarantee high probability of detection of PU but also increased data transmission which means more throughput for SU. However, simultaneous sensing and data transmission has inherent problem of self-interference. One of the possible solution is to use polarisation discrimination in which sensing and data transmission antennas must use different polarisation. This is feasible if there is prior information about the polarisation of the signals emitted by the PUs. It shall be of special interest to assess throughput using analytical expressions for probability of detection PD, probability of false alarm PFA at various values of SNR for time-slotted cognitive radio which uses half-duplex spectrum sensing and non-time-slotted cognitive radio which uses full-duplex communication cognitive radio
Full-Duplex Cognitive Radio: A New Design Paradigm for Enhancing Spectrum Usage
With the rapid growth of demand for ever-increasing data rate, spectrum
resources have become more and more scarce. As a promising technique to
increase the efficiency of the spectrum utilization, cognitive radio (CR)
technique has the great potential to meet such a requirement by allowing
un-licensed users to coexist in licensed bands. In conventional CR systems, the
spectrum sensing is performed at the beginning of each time slot before the
data transmission. This unfortunately results in two major problems: 1)
transmission time reduction due to sensing, and 2) sensing accuracy impairment
due to data transmission. To tackle these problems, in this paper we present a
new design paradigm for future CR by exploring the full-duplex (FD) techniques
to achieve the simultaneous spectrum sensing and data transmission. With FD
radios equipped at the secondary users (SUs), SUs can simultaneously sense and
access the vacant spectrum, and thus, significantly improve sensing
performances and meanwhile increase data transmission efficiency. The aim of
this article is to transform the promising conceptual framework into the
practical wireless network design by addressing a diverse set of challenges
such as protocol design and theoretical analysis. Several application scenarios
with FD enabled CR are elaborated, and key open research directions and novel
algorithms in these systems are discussed
Intelli MAC Layer Protocol for Cognitive Radio Networks
According to the FCC (Federal Communications Commission) [11], the utilization of the spectrum has been increasing rapidly over a wide range of frequency bands. There are various reasons that cause this dynamic growth. One reason is increase in network capacity. Another reason is increase in mobile services needed to carry over the spectrum. In order to overcome the shortage of spectrum due to increased usage, Cognitive Radio (CR) technology has been introduced. Cognitive Radios can utilize idle spectrum holes that are not occupied by the Primary Users (PUs) for performing temporary wireless communication tasks. PUs are licensed users which own and have access to certain spectrum bands. Challenging issues that need to be addressed by the CRs are spectrum sensing, spectrum sharing, spectrum management and spectrum mobility.
The main contribution of this thesis is to design a new MAC layer protocol in order to determine the behavior of Secondary Users (SUs) based on PUs transmission history while taking into account both PUs and SUs. SUs are non licensed users which transmit only on those spectrum bands that are unutilized by the PUs. SUs usually observe the activity of PUs on spectrum bands. This new protocol allows the CR nodes to sense, share and manage access of the nodes to the spectrum. This protocol prevents any damage caused by SUs to the PUs transmission. Also, the new MAC protocol will negotiate the spectrum by assisting the CRs to identify the underutilized spectrum based on channel conditions such as channel throughput, channel data rate, channel score, channel utilization and packet error rate (PER). The Intelli MAC layer protocol measures transmission time among PUs and reduces channel sensing time for SUs. For managing the entire network, this protocol uses the concept of Harmonious Channel (HC). This protocol uses multiple half duplex transceivers for carrying data communication among users
Performance analysis of spectrum sensing techniques for future wireless networks
In this thesis, spectrum sensing techniques are investigated for cognitive radio (CR) networks
in order to improve the sensing and transmission performance of secondary networks.
Specifically, the detailed exploration comprises of three areas, including single-node spectrum
sensing based on eigenvalue-based detection, cooperative spectrum sensing under random
secondary networks and full-duplex (FD) spectrum sensing and sharing techniques.
In the first technical chapter of this thesis, eigenvalue-based spectrum sensing techniques,
including maximum eigenvalue detection (MED), maximum minimum eigenvalue (MME)
detection, energy with minimum eigenvalue (EME) detection and the generalized likelihood
ratio test (GLRT) eigenvalue detector, are investigated in terms of total error rates and achievable
throughput. Firstly, in order to consider the benefits of primary users (PUs) and secondary
users (SUs) simultaneously, the optimal decision thresholds are investigated to minimize
the total error rate, i.e. the summation of missed detection and false alarm rate. Secondly,
the sensing-throughput trade-off is studied based on the GLRT detector and the optimal
sensing time is obtained for maximizing the achievable throughput of secondary communications
when the target probability of detection is achieved.
In the second technical chapter, the centralized GLRT-based cooperative sensing technique
is evaluated by utilizing a homogeneous Poisson point process (PPP). Firstly, since collaborating
all the available SUs does not always achieve the best sensing performance under a
random secondary network, the optimal number of cooperating SUs is investigated to minimize
the total error rate of the final decision. Secondly, the achievable ergodic capacity and
throughput of SUs are studied and the technique of determining an appropriate number of
cooperating SUs is proposed to optimize the secondary transmission performance based on a
target total error rate requirement.
In the last technical chapter, FD spectrum sensing (FDSS) and sensing-based spectrum sharing
(FD-SBSS) are investigated. There exists a threshold pair, not a single threshold, due to
the self-interference caused by the simultaneous sensing and transmission. Firstly, by utilizing
the derived expressions of false alarm and detection rates, the optimal decision threshold
pair is obtained to minimize total error rate for the FDSS scheme. Secondly, in order to further
improve the secondary transmission performance, the FD-SBSS scheme is proposed and
the collision and spectrum waste probabilities are studied. Furthermore, different antenna
partitioning methods are proposed to maximize the achievable throughput of SUs under both
FDSS and FD-SBSS schemes
Maximum Throughput of a Secondary User Cooperating with an Energy-Aware Primary User
This paper proposes a cooperation protocol between a secondary user (SU) and
a primary user (PU) which dedicates a free frequency subband for the SU if
cooperation results in energy saving. Time is slotted and users are equipped
with buffers. Under the proposed protocol, the PU releases portion of its
bandwidth for secondary transmission. Moreover, it assigns a portion of the
time slot duration for the SU to relay primary packets and achieve a higher
successful packet reception probability at the primary receiver. We assume that
the PU has three states: idle, forward, and retransmission states. At each of
these states, the SU accesses the channel with adaptive transmission
parameters. The PU cooperates with the SU if and only if the achievable average
number of transmitted primary packets per joule is higher than the number of
transmitted packets per joule when it operates alone. The numerical results
show the beneficial gains of the proposed cooperative cognitive protocol.Comment: Accepted WiOpt 201
Wideband Autonomous Cognitive Radios: Spectrum Awareness and PHY/MAC Decision Making
The cognitive radios (CRs) have opened up new ways of better utilizing the scarce wireless spectrum resources. The CRs have been made feasible by recent advances in software-defined radios (SDRs), smart antennas, reconfigurable radio frequency (RF) front-ends, and full-duplex RF front-end architectures, to name a few. Generally, a CR is considered as a dynamically reconfigurable radio capable of adapting its operating parameters to the surrounding environment. Recent developments in spectrum policy and regulatory domains also allow more flexible and efficient utilization of wider RF spectrum range in the future. In line with the future directions of CRs, a new vision of a future autonomous CR device, called Radiobots, was previously proposed. The goals of the proposed Radiobot surpass the dynamic spectrum access (DSA) to achieve wideband operability and the main features of cognition. In order to ensure the practicality and robust operation of the Radiobot structure, the research focus of this dissertation includes the following aspects: 1) robust spectrum sensing and operability in a centralized CR network setup; 2) robust multivariate non-parametric quickest detection for dynamic spectrum usage tracking in an alien RF environment; 3) joint physical layer and medium access control layer (PHY/MAC) decision-making for wideband bandwidth aggregation (simultaneous operation over multiple modes/networks); and 4) autonomous spectrum sensing scheduling solutions in an alien ultra wideband RF environment. The major contribution of this dissertation is to investigate the feasibility of the autonomous CR operation in heterogeneous RF environments, and to provide novel solutions to the fundamental and crucial problems/challenges, including spectrum sensing, spectrum awareness, wideband operability, and autonomous PHY/MAC protocols, thus bringing the autonomous Radiobot one step closer to reality
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