Nikos Passas

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Pilot Assisted Clipping Avoidance for OFDM

Orthogonal Frequency Division Multiplexing (OFDM) has become a popular technique for high bit rat... more Orthogonal Frequency Division Multiplexing (OFDM) has become a popular technique for high bit rate transmission over wireless fading channels. However, an OFDM signal exhibits large peak-to-average power ratio and therefore it is sensitive to nonlinear distortion caused by the high power ampli ers. In this paper a technique called pilot assisted clipping avoidance (PACA) is proposed, which exploits the existence of transmitted pilots to limit the e ects of clipping. The performance of the proposed method is assessed for AWGN channels using simulations for a HIPERLAN/2 OFDM system and it is compared with the Decision-Aided Reconstruction (DAR) [1] technique. Key-Words:OFDM, PAR, Clipping Avoidance

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Performance Analysis of NB-IoT Random Access Channel

Internet of Things, Infrastructures and Mobile Applications

A Comprehensive Study on LPWANs With a Focus on the Potential of LoRa/LoRaWAN Systems

This publication offers a comprehensive survey on the topic of Low-Power Wide Area Networks (LPWA... more This publication offers a comprehensive survey on the topic of Low-Power Wide Area Networks (LPWANs). We discuss the scope of LPWAN connectivity and present numerous well-established technologies that can offer such a service. From this presentation, LoRa/LoRaWAN systems emerge as one of the dominant solutions, and hence we offer details about end-to-end LoRa/LoRaWAN-enabled networking. As an area being in its infancy, LPWANs in general and LoRa/LoRaWAN in specific undergo extensive research. We shed light in key contributions, whereas we also provide our findings regarding the main research focus and needs. Simulation studies appear to be a popular choice among researchers, whereas real system implementations are constantly emerging thanks to low deployment and operational cost. For the former, we offer a comparative overview of existing simulators, whereas for the latter we discuss key considerations about the server-side part of a deployed system, which is usually supported by cl...

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The Need for QoE-driven Interference Management in Femtocell-Overlaid Cellular Networks

Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2014

Under the current requirements for mobile, ubiquitous and highly reliable communications, interne... more Under the current requirements for mobile, ubiquitous and highly reliable communications, internet and mobile communication technologies have converged to an all-Internet Protocol (IP) packet network. This technological evolution is followed by a major change in the cellular networks' architecture, where the traditional wide-range cells (macrocells) coexist with indoor smallsized cells (femtocells). A key challenge for the evolved heterogeneous cellular networks is the mitigation of the generated interferences. In the literature, this problem has been thoroughly studied from the Quality of Service (QoS) point of view, while a study from the user's satisfaction perspective, described under the term "Quality of Experience (QoE)", has not received enough attention yet. In this paper, we study the QoE performance of VoIP calls in a femto-overlaid Long Term Evolution-Advanced (LTE-A) network and we examine how QoE can drive a power controlled interference management scheme.

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Next Generation Cognitive Cellular Networks, LTE, WiMAX and Wireless Broadband Access

Lecture Notes in Electrical Engineering, 2012

This chapter provides a brief but comprehensive overview of the cognitive radio characteristics t... more This chapter provides a brief but comprehensive overview of the cognitive radio characteristics that are met in Next generation networks (NGN) such as LTE and WiMAX networks. As the main problem that is going to be addressed by the cognitive radios (CR) is the spectrum underutilization, increasing spectrum utilization solutions that allow CR users to access unutilized spectrum portions of these networks are included. Also, the current literature identifies CR and context-awareness as a key enabler for employing femtocell in LTE systems and, thus, technical challenges of this effort is presented. Additionally, a lot of attention is paid on introducing the recent standardization efforts on cognitive radio-based networks. Finally, the future spectrum access challenges under the claim of ubiquitous, reliable and always available wireless services are discussed.

QoS Sensitive Traffic Scheduling in Broadband Wireless Mesh Networks

WAND Design Requirements

ABSTRACT

Efficient Multicast Transmission in WiMAX Mesh Networks

Enabling D2D communications in LTE networks

2013 IEEE 24th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2013

Device-to-Device (D2D) communications provide the means to users of cellular networks for spatial... more Device-to-Device (D2D) communications provide the means to users of cellular networks for spatially reusing licensed spectrum by establishing direct connections. Considering the benefits for operators and consumers, a plethora of resource and interference management approaches in the literature deal with parallel cellular and D2D transmissions. However, this feature is not yet supported by modern cellular systems, such as the Long Term Evolution (LTE). The current paper targets at filling this gap by enabling D2D transmissions in LTE networks. Standardized LTE capabilities are utilized to provide a comprehensive framework on which existing or future resource and interference management schemes for D2D communications may be applied. The proposed framework is assessed under a moderate scenario where the cellular resource management policy is not affected. Results show that multiple D2D connections can be established in parallel to cellular uplink transmissions, while a satisfactory percentage of the cell region is available for spatial spectrum reuse.

Quality of experience-centric management in LTE-A mobile networks: The Device-to-Device communication paradigm

2014 Sixth International Workshop on Quality of Multimedia Experience (QoMEX), 2014

Device-to-Device (D2D) communications are planned to become an indispensable part of future mobil... more Device-to-Device (D2D) communications are planned to become an indispensable part of future mobile networks. A lot of attention has been paid to this new communication paradigm, due to the important benefits it brings for both cellular operators and end-users. Standardization efforts towards enabling D2D connections have started in Release 12 of the Long Term Evolution-Advanced standard and are expected to continue in next releases. Under this perspective, and realizing that the main asset of D2D is the enhancement of the user experience, we propose a Quality of Experience driven framework for the management of this new type of communications. Simulation results show that this framework is able to capture and enhance the overall experience of mobile users, and, thus, allow for proportionate financial benefits for operators.

Advanced mobility management for reduced interference and energy consumption in the two-tier LTE-Advanced network

Computer Networks, 2015

Femtocell deployment will play a key role for the wide adoption of LTE-Advanced, as it brings the... more Femtocell deployment will play a key role for the wide adoption of LTE-Advanced, as it brings the access network closer to the end user in a cost-effective manner. This disruptive communication paradigm, however, necessitates the employment of advanced interference and mobility management to cope with the comparably denser yet unplanned network layout. This paper describes an advanced mobility management approach for the two-tier LTE-Advanced network, aiming to resourcefully utilize the femtocell superior characteristics in an energy-efficient and interference-aware manner. The key features of the proposed approach are a) the exchange and utilization of standard signal quality measurements during the handover decision phase, to accurately estimate the mean user equipment (UE) transmit power on a per candidate cell basis, and b) the use of a novel handover decision algorithm that jointly considers the impact of interference, power consumption, and user mobility. A comprehensive analysis of the required network signaling is provided, while extensive simulation results demonstrate that compared to existing approaches, the proposed approach attains improved performance at the cost of moderate increase of network signaling.

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A MAC protocol for Wireless ATM

ABSTRACT

A Multimedia Traffic Scheduler for IEEE 802.16 Point-To-Multipoint Networks

2008 IEEE International Conference on Communications, 2008

In this paper, we describe and evaluate an advanced traffic scheduler for IEEE 802.16 point-to-mu... more In this paper, we describe and evaluate an advanced traffic scheduler for IEEE 802.16 point-to-multipoint networks, referred to as &quot;Colored Frame Registry Tree Scheduler&quot; (C- FRTS). The main characteristics of this scheduler are i) the use of a tree structure to prepare the creation of time frame maps and reduce processing requirements at the beginning of each frame, and ii)

Support of IP QoS over wireless LANs

2004 IEEE 59th Vehicular Technology Conference. VTC 2004-Spring (IEEE Cat. No.04CH37514), 2004

This paper addresses the potential issues that emerge when using WLANs as access systems to an IP... more This paper addresses the potential issues that emerge when using WLANs as access systems to an IP core and focuses on defining a consistent mechanism that supports IP QoS and resource reservation over an IEEE 802.11e WLAN. The proposed approach assumes that RSVP is used for negotiating IP QoS parameters and reserving end-to-end resources. For interworking between IP QoS and WLAN QoS we propose a mapping between RSVP and 802.11e QoS parameters. In addition, we present how RSVP signaling is integrated with 802.11e signaling for WLAN resource reservation. Finally, we introduce a new scheduling approach for the 802.11e HC that can provide enhanced features.

A new approach for fast handovers in mobile multimedia networks

2004 IEEE 59th Vehicular Technology Conference. VTC 2004-Spring (IEEE Cat. No.04CH37514), 2004

ABSTRACT This paper focuses on the performance evaluation of a novel scheme that exploits the int... more ABSTRACT This paper focuses on the performance evaluation of a novel scheme that exploits the inter access point protocol (IAPP), standardized by IEEE, in order to expedite the RSVP path reestablishment that takes place after a handover from one WLAN access point (AP) to another. The prime characteristic of this scheme is that a WLAN AP serves as a resource reservation protocol (RSVP) proxy that starts RSVP signaling on behalf of the mobile node much earlier compared with the standard RSVP operation in a WLAN. Therefore, a considerable handover latency reduction can be achieved, which can be as high as 30% under heavy traffic conditions. To evaluate the performance and the benefits of the proposed scheme, we display and discuss a series of simulation results.

Traffic scheduling for multimedia QoS over wireless LANs

IEEE International Conference on Communications, 2005. ICC 2005. 2005, 2005

In this paper we present a novel traffic scheduling algorithm for IEEE 802.11e, referred to as AR... more In this paper we present a novel traffic scheduling algorithm for IEEE 802.11e, referred to as ARROW (Adaptive Resource Reservation Over WLANs), able to handle multimedia traffic. The novel characteristic of ARROW is that it performs channel allocations based on the actual traffic (not estimated traffic) buffered in the various mobile stations. Additionally, a variation of ARROW is studied for improving the performance for constant bit rate traffic. The ARROW algorithm and its enhancement are evaluated against two other schedulers found in the literature, namely the Simple Scheduler and SETT-EDD. Results from a detailed simulation model show that much better channel utilization and considerably improved performance can be provided. A.

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Adaptable resource management in wireless IP links

2003 IEEE 58th Vehicular Technology Conference. VTC 2003-Fall (IEEE Cat. No.03CH37484), 2003

ABSTRACT Although the resource reservation protocol (RSVP) is considered efficient for fixed acce... more ABSTRACT Although the resource reservation protocol (RSVP) is considered efficient for fixed access networks, its performance is problematic over wireless links, due to the variable available bandwidth they provide, asking for adaptable resource management techniques. If, for example, the channel quality falls to a level that the available bandwidth cannot support all reservations of admitted flows, then none of them is operating properly. One solution to this problem is to reject one or more of the flows in order to maintain quality of service (QoS) to the rest. In this paper describes a flow rejection mechanism that is based on priorities and bandwidth requirements, and aims at minimizing the number of rejected flows. Simulation results have shown that, compared to a random rejection mechanism, the attained flow rejection probability is significantly reduced, especially for high priority flows, while, at the same time, the bandwidth utilization remains at the same level.

A graceful degradation method for congestion control in wireless personal communication networks

Proceedings of Vehicular Technology Conference - VTC, 1996

This paper presents an overload control method for the radio part of PCN to temporarily reduce th... more This paper presents an overload control method for the radio part of PCN to temporarily reduce the source rate requirements to a sustainable level, in order to avoid a sudden degradation in QoS. The control is activated when the aggregate rate crosses a predefined threshold that identifies congestion. To ensure fairness, the selection of the sources whose rate will be

Design of call control signaling in wireless ATM networks

Proceedings of ICC'97 - International Conference on Communications, 1997

In this paper, a multiservice, local-area, wireless access ATM system is explored from a signalin... more In this paper, a multiservice, local-area, wireless access ATM system is explored from a signaling protocol viewpoint. The signaling architecture considered here follows the signaling structure of Broadband ISDN (B-ISDN) User-Network Interface (UNI), thus offering the possibility for integration of the wireless ATM access system into fixed B-ISDN. It is shown that the use of the employed signaling structure substantially simplifies the call/bearer and handover control. The evaluation of the signaling protocol architecture yields results, which fall within acceptable ATM signaling performance measures. A comparison with alternate access signaling configurations is also carried out to quantify the relative gains.

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Flexible Resource Allocation in IEEE 802.16 Wireless Metropolitan Area Networks

2005 14th IEEE Workshop on Local & Metropolitan Area Networks, 2005

IEEE 802.16 is considered today as the most promising technology, to provide extension of wireles... more IEEE 802.16 is considered today as the most promising technology, to provide extension of wireless broadband communications into metropolitan environments. One of the main design challenges in 802.16 is the introduction of an efficient traffic scheduler that handles resource allocation in the wireless interface. This paper proposes such a scheduler, referred to as the "Frame Registry Tree Scheduler", that aims at providing differentiated treatment to data connections, based on their QoS characteristics. The scheduler uses a tree structure in order to prepare time frame creation and reduce processing needs at the beginning of each time frame. Simulation results show that the proposed scheduler can attain considerable improvement in terms of throughput and packet losses.

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