41 research outputs found
Dynamic Spectrum Reservation for CR Networks in the Presence of Channel Failures: Channel Allocation and Reliability Analysis
(c) 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this[EN] Providing channel access opportunities for new service requests and guaranteeing continuous connections for ongoing flows until service completion are two challenges for service provisioning in wireless networks. Channel failures, which are typically caused by hardware and software failures or/and by intrinsic instability in radio transmissions, can easily result in network performance degradation. In cognitive radio networks (CRNs), secondary transmissions are inherently vulnerable to connection breaks due to licensed users' arrivals as well as channel failures. To explore the advantages of channel reservation on performance improvement in error-prone channels, we propose and analyze a dynamic channel reservation (DCR) algorithm and a dynamic spectrum access (DSA) scheme with three access privilege variations. The key idea of the DCR algorithm is to reserve a dynamically adjustable number of channels for the interrupted services to maintain service retainability for ongoing users or to enhance channel availability for new users. Furthermore, the DCR algorithm is embedded in the DSA scheme enabling spectrum access of primary and secondary users with different access privileges based on access flexibility for licensed shared access. The performance of such a CRN in the presence of homogeneous and heterogeneous channel failures is investigated considering different channel failure and repair rates.The work of V. Pla was supported by the Spanish Ministry of Economy, Industry and Competitiveness under Grant TIN2013-47272-C2-1-R.Balapuwaduge, IAM.; Li, F.; Pla, V. (2018). Dynamic Spectrum Reservation for CR Networks in the Presence of Channel Failures: Channel Allocation and Reliability Analysis. IEEE Transactions on Wireless Communications. 17(2):882-898. https://doi.org/10.1109/TWC.2017.2772240S88289817
Priority-based initial access for URLLC traffic in massive IoT networks: Schemes and performance analysis
At a density of one million devices per square kilometer, the10’s of billions of devices, objects, and machines
that form a massive Internet of things (mIoT) require ubiquitous connectivity. Among a massive number of
IoT devices, a portion of them require ultra-reliable low latency communication (URLLC) provided via fifth
generation (5G) networks, bringing many new challenges due to the stringent service requirements. Albeit a surge
of research efforts on URLLC and mIoT, access mechanisms which include both URLLC and massive machine
type communications (mMTC) have not yet been investigated in-depth. In this paper, we propose three novel
schemes to facilitate priority-based initial access for mIoT/mMTC devices that require URLLC services while also
considering the requirements of other mIoT/mMTC devices. Based on a long term evolution-advanced (LTEA) or 5G new radio frame structure, the proposed schemes enable device grouping based on device vicinity
or/and their URLLC requirements and allocate dedicated preambles for grouped devices supported by flexible
slot allocation for random access. These schemes are able not only to increase the reliability and minimize the
delay of URLLC devices but also to improve the performance of all involved mIoT devices. Furthermore, we
evaluate the performance of the proposed schemes through mathematical analysis as well as simulations and
compare the results with the performance of both the legacy LTE-A based initial access scheme and a grant-free
transmission scheme.acceptedVersio
System Times and Channel Availability for Secondary Transmissions in CRNs: A Dependability Theory based Analysis
[EN] Reliability is of fundamental importance for the performance of secondary networks in cognitive radio networks (CRNs). To date, most studies have focused on predicting reliability parameters based on prior statistics of traffic patterns from user behavior. In this paper, we define a few reliability metrics for channel access in multichannel CRNs that are analogous to the concepts of reliability and availability in classical dependability theory. Continuous-time Markov chains are employed to model channel available and unavailable time intervals based on channel occupancy status. The impact on user access opportunities based on channel availability is investigated by analyzing the steady-state channel availability and several system times such as mean channel available time and mean time to first channel unavailability. Moreover, the complementary cumulative distribution function for channel availability is derived by applying the uniformization method, and it is evaluated as a measure of guaranteed availability for channel access by secondary users. The precision and the correctness of the derived analytical models are validated through discrete-event-based simulations. We believe that the reliability metric definitions and the analytical models proposed in this paper have their significance for reliability and availability analysis in CRNs.The work of V. Pla was supported by the Ministry of Economy and Competitiveness of Spain under Grant TIN2013-47272-C2-1-R. The review of this paper was coordinated by Dr. B. Canberk.Balapuwaduge, IAM.; Li, FY.; Pla, V. (2017). System Times and Channel Availability for Secondary Transmissions in CRNs: A Dependability Theory based Analysis. IEEE Transactions on Vehicular Technology. 66(3):2771-2788. https://doi.org/10.1109/TVT.2016.2585200S2771278866
Performance evaluation of channel aggregation strategies in cognitive radio networks with queues
With the growing usage of wireless communication devices, demand for the spectrum access is rapidly increasing.
Therefore, an efficient spectrum management and spectrum access techniques are necessary and critical.
However, studies on spectrum usage have revealed that most of the allotted spectrum is not used efficiently due
to the static frequency allocation methods. With the evolution of cognitive radio, spectrum access techniques
shift from static spectrum allocation to dynamic allocation with enhanced features such as spectrum sensing and
spectrum adaptation.
In the first part of this thesis, we study several spectrum access techniques in cognitive radio networks, which
have been developed with spectrum adaptation. The performance of cognitive radio systems are evaluated in
terms of capacity, blocking probability and forced termination probability of the secondary network. Due to the
strict priority over primary users, the performance of the secondary network is restricted. One of the successful
solutions to further improve the system performance by increasing the capacity and decreasing the blocking
and forced termination probabilities is the integration of a queuing model. Most of already designed queuing
models for cognitive radio systems have been designed with certain limitations of performance. Therefore in
this thesis, a bunch of techniques of performance improvement have been taken into account when designing the
queuing model. The features: channel aggregation, spectrum handover, channel sharing, priority based queuing
and heterogeneous traffic are considered together in order to model the queuing system as much as more realistic
way which can further enhance the overall system performance.
In the second part of this thesis, we propose a queuing system referred to as Priority based Multiple Queue
System (PMQS) which is designed with two queues separately for the real time and non-real time secondary
user services. Channel access opportunities are distributed between two queues such a way that the real time
services have the higher priority than elastic services. Two queuing approaches are introduced based on the
queuing ability of the interrupted non-real time services. Continuous time Markov chain models are developed
to evaluate the system performance in terms of capacity, blocking and forced termination probabilities of the
secondary network. In addition, we explore the cost analysis of the proposed queuing model in terms of mean
queuing delay. Other than that, spectrum utilization of the cognitive radio system is also evaluated. In order to
minimize the associated queuing delay, a maximum value for the number of waiting lines inside a queue is set
instead of an infinite queue size . Analytical results reveal that integration of the proposed queuing model could
increase the capacity of the secondary network while decreasing the blocking probability. And also one of the
proposed queuing methods can further decrease the forced termination rate of non-real time traffic. Associated
queuing delay is controlled by proper selection of maximum queue sizes. For these reasons, it can be concluded
that the proposed queuing model can be used to improve the system performance of multi-channel cognitive
radio networks
Channel Access and Reliability Performance in Cognitive Radio Networks:Modeling and Performance Analysis
Doktorgradsavhandling ved Institutt for Informasjons- og kommunikasjonsteknologi, Universitetet i AgderAccording to the facts and figures published by the international telecommunication
union (ITU) regarding information and communication technology (ICT)
industry, it is estimated that over 3.2 billion people have access to the Internet in
2015 [1]. Since 2000, this number has been octupled. Meanwhile, by the end of
2015, there were more than 7 billion mobile cellular subscriptions in the world, corresponding
to a penetration rate of 97%. As the most dynamic segment in ICT,
mobile communication is providing Internet services and consequently the mobile broadband penetration rate has reached 47% globally. Accordingly, capacity,
throughput, reliability, service quality and resource availability of wireless services
become essential factors for future mobile and wireless communications. Essentially,
all these wireless technologies, standards, services and allocation policies
rely on one common natural resource, i.e., radio spectrum.
Radio spectrum spans over the electromagnetic frequencies between 3 kHz and
300 GHz. Existing radio spectrum access techniques are based on the fixed allocation
of radio resources. These methods with fixed assigned bandwidth for exclusive
usage of licensed users are often not efficient since most of the spectrum
bands are under-utilized, either/both in the space domain or/and in the time domain.
In reality, it is observed that many spectrum bands are largely un-occupied
in many places [2], [3]. For instance, the spectrum bands which are exclusively allocated
for TV broadcasting services in USA remain un-occupied from midnight to
early morning according to the real-life measurement performed in [4]. In addition
to the wastage of radio resources, spectrum under-utilization constraints spectrum
availability for other intended users. Furthermore, legacy fixed spectrum allocation
techniques are not capable of adapting to the changes and interactions in the system,
leading to degraded network performance.
Unlike in the static spectrum allocation, a fraction of the radio spectrum is
allocated for open access as license-free bands, e.g., the industrial, scientific and
medical (ISM) bands (902-928, 2400-2483.5, 5725-5850 MHz). In 1985, the federal
communications commission (FCC) permitted to use the ISM bands for private
and unlicensed occupancy, however, under certain restrictions on transmission
power [5]. Consequently, standards like IEEE 802.11 for wireless local area networks
(WLANs) and IEEE 802.15 for wireless personal area networks (WPAN)
have grown rapidly with open access spectrum policies in the 2.4 GHz and 5 GHz
ISM bands. With the co-existence of both similar and dissimilar radio technologies,
802.11 networks face challenges for providing satisfactory quality of service (QoS).
This and the above mentioned spectrum under-utilization issues motivate the spectrum
regulatory bodies to rethink about more flexible spectrum access for licenseexempt
users or more efficient radio spectrum management. Cognitive radio (CR) is
probably the most promising technology for achieving efficient spectrum utilization
in future wireless networks
On the Performance of Channel Assembling and Fragmentation in Cognitive Radio Networks
[EN] Flexible channel allocation may be applied to multi-channel cognitive radio networks (CRNs) through either channel assembling (CA) or channel fragmentation (CF). While CA allows one secondary user (SU) occupy multiple channels when primary users (PUs) are absent, CF provides finer granularity for channel occupancy by allocating a portion of one channel to an SU flow. In this paper, we investigate the impact of CF together with CA for SU flows by proposing a channel access strategy which activates both CF and CA and correspondingly evaluating its performance. In addition, we also consider a novel scenario where CA is enabled for PU flows. The performance evaluation is conducted based on continuous time Markov chain (CTMC) modeling and simulations. Through mathematical analyses and simulation results, we demonstrate that higher system capacity can be achieved indeed by jointly employing both CA and CF, in comparison with the CA-only strategies. However, this benefit is obtained only under certain conditions which are pointed out in this paper. Furthermore, the theoretical capacity upper bound for SU flows with both CF and CA enabled is derived when PU activities are relatively static compared with SU flows.This work was supported by the EU Seventh Framework Programme FP7-PEOPLE-IRSES under Grant agreement 247083, project acronym S2EuNet. The work of L. Jiao was supported by the Research Council of Norway through the ECO-boat MOL project under Grant 210426. The work of V. Pla was supported in part by the Ministry of Economy and Competitiveness of Spain under Grant TIN2010-21378-C02-02. The associate editor coordinating the review of this paper and approving it for publication was H. Wymeersch.Jiao, L.; Balapuwaduge, IAM.; Li, FY.; Pla, V. (2014). On the Performance of Channel Assembling and Fragmentation in Cognitive Radio Networks. IEEE Transactions on Wireless Communications. 13(10):5661-5675. https://doi.org/10.1109/TWC.2014.2322057S56615675131
Priority Enabled Grant-Free Access With Dynamic Slot Allocation for Heterogeneous mMTC Traffic in 5G NR Networks
Although grant-based mechanisms have been a predominant approach for wireless access for years, the additional latency required for initial handshake message exchange and the extra control overhead for packet transmissions have stimulated the emergence of grant-free (GF) transmission. GF access provides a promising mechanism for carrying low and moderate traffic with small data and fits especially well for massive machine type communications (mMTC) applications. Despite a surge of interest in GF access, how to handle heterogeneous mMTC traffic based on GF mechanisms has not been investigated in depth. In this paper, we propose a priority enabled GF access scheme which performs dynamic slot allocation in each 5G new radio subframe to devices with different priority levels on a subframe-by-subframe basis. While high priority traffic has access privilege for slot occupancy, the remaining slots in the same subframe will be allocated to low priority traffic. To evaluate the performance of the proposed scheme, we develop a two-dimensional Markov chain model which integrates these two types of traffic via a pseudo-aggregated process. Furthermore, the model is validated through simulations and the performance of the scheme is evaluated both analytically and by simulations and compared with two other GF access schemes.publishedVersio
Channel Assembling with Priority-based Queues in Cognitive Radio Networks: Strategies and Performance Evaluation
[EN] With the implementation of channel assembling (CA) techniques, higher data rate can be achieved for secondary users in multi-channel cognitive radio networks. Recent studies which are based on loss systems show that maximal capacity can be achieved using dynamic CA strategies. However the channel allocation schemes suffer from high blocking and forced termination when primary users become active. In this paper, we propose to introduce queues for secondary users so that those flows that would otherwise be blocked or forcibly terminated could be buffered and possibly served later. More specifically, in a multi-channel network with heterogeneous traffic, two queues are separately allocated to real-time and elastic users and channel access opportunities are distributed between these two queues in a way that real-time services receive higher priority. Two queuing schemes are introduced based on the delay tolerance of interrupted elastic services. Furthermore, continuous time Markov chain models are developed to evaluate the performance of the proposed CA strategy with queues, and the correctness as well as the preciseness of the derived theoretical models are verified through extensive simulations. Numerical results demonstrate that the integration of queues can further increase the capacity of the secondary network and spectrum utilization while decreasing blocking probability and forced termination probability. © 2002-2012 IEEE.The authors would like to acknowledge the support from the EU FP7-PEOPLE-IRSES program, project acronym S2EuNet (Grant no. 247083). The work of V. Pla was partly supported by the Ministerio de Ciencia e Innovacion of Spain under Grant TIN2010-21378-C02-02.Balapuwaduge, IAM.; Jiao, L.; Pla, V.; Li, FY. (2014). Channel Assembling with Priority-based Queues in Cognitive Radio Networks: Strategies and Performance Evaluation. IEEE Transactions on Wireless Communications. 13(2):630-645. https://doi.org/10.1109/TWC.2013.120713.121948S63064513
Preamble Transmission Prediction for mMTC Bursty Traffic : A Machine Learning based Approach
Author's accepted manuscript.© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.acceptedVersio
A dynamic channel access strategy for underlay cognitive radio networks: Markov modelling and performance evaluation
[EN] Unlike in overlay cognitive radio networks, secondary users in underlay cognitive radio networks can access licensed
spectrum even at the presence of a primary user, given that the interference caused by the secondary transmission is
lower than a pre-specified threshold. Based on this underlay access principle, we propose in this paper a dynamic channel
access strategy for multi-channel cognitive radio networks. Different from existing underlay access techniques, channel
assembling, spectrum adaptation and restricted channel occupancy are also considered in the proposed strategy in order
to achieve better performance in the secondary network. Accordingly, a partial channel occupancy mode, which allows
secondary users to access a portion of a channel when co-existing with a primary user, is introduced in this study. The size
of this portion is adjusted by selecting an appropriate value of a configurable parameter ¿ in the partial channel occupancy
mode. The system performance is evaluated for both primary and secondary networks, and a comparison analysis is carried
out to assess the cost against the gain. Numerical results demonstrate that the proposed underlay channel access strategy
outperforms the corresponding overlay strategy in terms of secondary network capacity, blocking probability and dropping
probability. The cost and gain analysis identifies appropriate traffic conditions under which the overall system performance
could be improved by employing the proposed underlay strategy.The work of V. Pla was supported in part by the Ministry of Economy and Competitiveness of Spain under Grant TIN2013-47272-C2-1-R.Jalali, E.; Balapuwaduge, IAM.; Li, FY.; Pla, V. (2017). A dynamic channel access strategy for underlay cognitive radio networks: Markov modelling and performance evaluation. Transactions on Emerging Telecommunications Technologies. 28(1):1-11. https://doi.org/10.1002/ett.2928S11128