Lukasz Budzisz

Dynamic Resource Provisioning for Energy Efficiency in Wireless Access Networks: A Survey and an Outlook

Traditionally, energy efficiency aspects have been included in the wireless access network design space only in the context of power control aimed at interference mitigation and for the increase of the terminal battery lifetime. Energy consumption of network components has also, for a long time, not been considered an issue, neither in equipment design nor in network planning and management. However, in recent years, with the user demand increasing at nearly exponential pace and margins rapidly shrinking, concerns about energy efficiency have been raised, with the objective of reducing network operational costs (not to mention the environmental issues). Installing more energy-efficient hardware does not seem to fully solve the problem, since wireless access networks are almost invariably (over)provisioned with respect to the peak user demand. This means that efficient resource management schemes, which are capable of controlling how much of the network infrastructure is actually needed and which parts can be temporarily powered off to save energy, can be extremely effective and provide quite large cost reductions. Considering that most of the energy in wireless access networks is consumed in the radio part, dynamic provisioning of wireless access network resources is crucial to achieving energy-efficient operation. The consensus on this approach in the research community has been wide in the last few years, and a large number of solutions have been proposed. In this paper, we survey the most important proposals, considering the two most common wireless access technologies, namely, cellular and WLAN. The main features of the proposed solutions are analyzed and compared, with an outlook on their applicability in typical network scenarios that also include cooperation between both access technologies. Moreover, we provide an overview of the practical implementation aspects that must be addressed to achieve truly energy-efficient wireless access networks, including current standardization work, and trends in the development of energy-efficient hardware.

An Analytical Estimation of the Failover Time in SCTP Multihoming Scenarios

The motivation behind this paper is a need to have a more accurate estimation of the failover time in SCTP. The traditional one, commonly used in the literature, is based on the sum of the consecutive retransmission timeouts. This is not always appropriate, especially when using the SCTP multihoming feature as a basis for achieving transport layer mobility in wireless networking scenarios, where the transition time between available paths becomes a key aspect for the optimisation. Two new factors are introduced into the proposed estimation formula to reflect the influence of the network parameters and the behaviour of the most common protocol implementations. For the proposed model, we perform a best-worst case analysis, and then illustrate it with an example of a detailed estimation. Finally, we perform simulations comparing our proposal with the traditional estimation in a typical transport layer mobility scenario including long thin networks.

Assessment of the power saving potential in dense enterprise WLANs

Due to the requirements to provision a proper Quality of Service level in enterprise WLANs supporting both voice and data services the typical densities in the deployment of access points (APs) may exceed 4000 APs per square kilometer. While such density is necessary under heavy traffic conditions, it is obviously superfluous during the time of lower load- and dramatically excessive at night periods, with only marginal traffic intensity. We present a novel, aggressive approach for adjusting the AP density to the actual traffic conditions. In the limiting case of a very low traffic, we postulate keeping operational only a skeleton deployment, sufficient just to recognize that there is a station attempting an association. In this case additional APs can be powered up, in order to assure the requested connectivity, locally in this area. Using data from commercially available APs we estimate the potential of power saving in such an operation mode and relate it to the best approaches proposed so far.

On Concurrent Multipath Transfer in SCTP-Based Handover Scenarios

Handling mobility at the transport layer is a promising approach to achieve seamless handover in the context of heterogeneous wireless access networks. In particular, features such as multihoming and dynamic address reconfiguration provided by mobile SCTP (mSCTP) protocol are among the key enablers for handover support at the transport layer. This paper investigates the applicability of Concurrent Multipath Transfer (CMT) to distribute data among two end-to-end paths of an mSCTP association during the handover transition process. To that end, the principles of the mSCTP-CMT design are given, emphasizing the consequences of a sender-introduced reordering and its effect on congestion control. The proposed mSCTPCMT handover scheme is benchmarked with two other handover schemes, namely mSCTP and SCTP failover-based. Provided analysis indicates the possible application area of mSCTP-CMT, taking into account not only handover scenario parameters (dwelling time, available bandwidth ratio and round-trip time), but also an important design constraint: receiver buffer (rbuf) size. Rbuf size proves to be a major limiting factor shrinking significantly, yet not excluding mSCTP-CMTs application scope.

An all-IP heterogeneous wireless testbed for RAT selection and e2e QoS evaluation

In this paper, we present an all-IP heterogeneous wireless testbed for radio access technologies (RAT) selection and end-to-end (e2e) quality of service (QoS) evaluation. Presented testbed includes three different radio access networks (RANs): UTRAN, GERAN, and WLAN; and the core network (CN) based on DiffServ technology and multiprotocol label switching (MPLS). As an example two RAT selection algorithms implemented in the testbed, network-controlled cell-breathing (NCCB) and fittingness factor are described and analyzed in more details. The paper provides also simple case study that validates and compares both mentioned algorithms in a basic heterogeneous environment using the presented testbed.

About the practicality of using partially overlapping channels in IEEE 802.11 b/g networks

IEEE 802.11 WLANs are currently one of the most popular wireless technologies, but their immediate success results in dense deployments and high demand of user traffic. This in turn leads to decrease in throughput and poor spectrum utilization. Especially in the 2.4 GHz ISM band, where the spectrum is a very scarce resource, all available WLAN channels should be exploited in the best possible way to achieve higher utilization. One way to reach this goal is the usage of partially overlapping channels (POC). Most of the previous work related to POC is based on two major studies addressing 802.11 b, but none of them evaluates the POC behavior in the 802.11 g networks. Moreover, most of the previous results are based on simulations. The main contribution of this work is an experimental evaluation of POC in 802.11g networks. In this paper we confirm quantitatively that 802.11b reacts as expected from the previous studies, while 802.11 g reacts entirely different to the presence of adjacent channel interference. That leads to the conclusion that the usage of POC for 802.11g is not recommended.

A beyond 3G real-time testbed for an All-IP heterogeneous network

This paper describes a real-time testbed emulating an all-IP B3G (Beyond 3rd Generation) network that includes UTRAN, GERAN, and WLAN emulation and the corresponding common core network based on DiffServ (Differentiated Services) technology and MPLS (Multiprotocol Label Switching). In such a complex scenario, considering real user applications and end-to-end (e2e) QoS, it is convenient to develop emulation platforms, where algorithms and applications can be tested in realistic conditions, not achievable by means of non-real-time simulations. Presented testbed will be used to evaluate three main objectives: to test the e2e QoS experienced by a user in a heterogeneous mobile environment with IP connectivity, to test and validate specific algorithms and mechanisms, and to evaluate real implementations of some subsystems.

Design Principles and Performance Evaluation of mSCTP-CMT for Transport-Layer Based Handover

Handling mobility at the transport layer is a promis- ing approach to achieve seamless handover in the context of het- erogeneous wireless access networks. In particular, features such as multihoming and dynamic address reconfiguration provided by mobile SCTP (mSCTP) protocol are among the key enablers for handover support at the transport layer. This paper investigates the applicability of Concurrent Multipath Transfer (CMT) to dis- tribute data among two end-to-end paths of a mSCTP association during handover transition process. To that end, the principles of the mSCTP-CMT design are given, emphasizing the consequences of such a sender-introduced reordering and its congestion control implications in a handover scenario. The proposed mSCTP-CMT handover scheme is benchmarked with a pure mSCTP handover scheme. Provided analysis indicates the possible application area of mSCTP-CMT, taking into account not only handover scenario parameters (dwelling time, available bandwidth ratio and round-trip time), but also the most important constraint of such a design: receiver buffer (rbuf) size. Rbuf size proves to be the major limiting factor shrinking significantly possible mSCTP-CMT application scope, yet not excluding definitively the proposed idea.

Evaluation of Perceived QoS with Multimedia Applications in a Heterogeneous Wireless Network

This paper presents a study addressed to evaluate the variation in perceived QoS experienced by a user running multimedia applications in a heterogeneous wireless network. To perform this evaluation, a real-time testbed emulating an all-IP B3G network that includes UMTS Terrestrial Radio Access Network (UTRAN), GSM/EDGE Radio Access Network (GERAN), and Wireless Local Area Network (WLAN); and the corresponding common core network (CN) based on DiffServ technology and Multiprotocol Label Switching (MPLS) has been used. Results for videostreaming and video conference applications when running under interruptions due to a vertical handover (VHO) are included in this paper, pointing out the variations in behaviour of different applications.

SCTP Multihoming Performance in Dynamically Changing Channels with the Influence of Link-Layer Retransmissions

Transport layer mobility is becoming a serious candidate for implementing seamless handover in a heterogeneous radio access network scenario. In this context, the stream control transmission protocol (SCTP) is in the core of most relevant transport layer mobility schemes being currently studied. Most of these proposals inherit multihoming and congestion control rules specified in the standard SCTP. However, standard SCTPs design was not targeted to cope with the variable nature of wireless channels. In this paper we analyse the performance of the SCTP failover mechanism when used as a handover solution in multihoming scenarios. In particular, the performance of the protocol is assessed under different radio channel variation patterns and different degrees of link level reliability. Obtained results are claimed to be a reference point for further investigation related to new proposals for handover schemes handled at the transport layer.