Sibel Tombaz | Ericsson - Academia.edu (original) (raw)

Papers by Sibel Tombaz

The concept of fixed wireless access (FWA) makes it possible to double the impact of a 5G deploym... more The concept of fixed wireless access (FWA) makes it possible to double the impact of a 5G deployment by addressing the two prominent 5G use cases – mobile broadband and fixed broadband – simultaneously. The 5G beams that serve mobile users outdoors during the daytime can be redirected to an FWA terminal when people return home in the evening, thereby strengthening the case for 5G deployment and its outlook as an affordable and sustainable technology. The benefits of FWA include rapid service rollout, lower rollout costs and lower opex compared with fiber-to-home and other wireline solutions. The ability to deliver mobile and fixed broadband via the same technology and the same infrastructure will enable service providers to achieve true network convergence.

—Each mobile network architecture able to meet the traffic requirements of future 5G services com... more —Each mobile network architecture able to meet the traffic requirements of future 5G services comes with its own set of benefits vs. requirements for the radio and the transport segments. This paper focuses on the energy performance of four mobile network architectures, each one with different splitting options for the baseband processing functions. The radio segment under exam is based on a new radio access technology referred to as 5G-NX, while the transport segment is based on wavelength division multiplexing (WDM). The energy consumption of each mobile network architecture is weighted against (i) the benefits for the radio segment as a function of the level of centralization of the baseband processing resources and (ii) the required transport capacity and consequently the power consumption levels needed to accommodate the backhaul, midhaul, and/or fronthaul traffic generated at each base station. Our results show that a fully centralized radio access network (C-RAN) with centralization of all the baseband functions is not a practical approach for 5G mobile networks, while a partially centralized C-RAN architecture in which the physical layer baseband processing is performed at the base station site represents a promising solution.

Mobile networks are the largest contributor to the carbon footprint of the telecom sector and the... more Mobile networks are the largest contributor
to the carbon footprint of the telecom sector and
their contribution is expected to rapidly increase in
the future due to the foreseen traffic growth. Therefore,
there is an increasing urgency in the definition
of green mobile network deployment strategies. This
paper proposes a four-step design and power assessment
methodology for mobile networks, taking into
consideration both radio and transport segments. A
number of mobile network deployment architectures
for urban residential areas based on different radio
(i.e., macro base station, distributed indoor radio,
femto cell) and transport (i.e., microwave, copper,
optical fiber) technologies are proposed and evaluated
to identify the most energy efficient solution. The
results show that with low traffic the conventional
macro base station deployment with microwave based
backhaul is the best option. However, with higher traf-
fic values heterogeneous networks with macro base
stations and indoor small cells are more energy effi-
cient. The best small cell solution highly depends on
the transport network architecture. In particular, our
results show that a femto cell based deployment with
optical fiber backhaul is the most energy efficient,
even if a distributed indoor radio architecture (DRA)
deployment with fiber fronthaul is also a competitive
approach.

Asia Communications and Photonics Conference 2013, 2013

Journal

As the energy bill for mobile operators rises with the continuing traffic growth, energy efficien... more As the energy bill for mobile operators rises with the continuing traffic growth, energy efficiency problems attract an increasing
attention in the telecommunication industry. However, the investment for the implementation of any energy-saving solution could be so costly that it may not achieve the total cost reduction. Therefore, the economic viability of the proposed solutions is of substantial importance for the operators in the process of investment decisions. In this paper, we present a methodology for assessing the economic viability of energy-saving solutions. We conduct two case studies using the proposed methodology, and analyze the cost-benefit tradeoff for: i) hardware upgrade enabling dynamic sleep mode operation at the base stations (BSs), ii) energy efficient network deployment minimizing the network energy consumption. Simulation results show that the hardware upgrade can save up to 60 percent of energy consumption particularly when the high data rate requirement forces low network resource utilization. Consequently, the solution is shown to be increasingly cost effective as the unit energy cost increases. Network deployment optimized for energy efficiency is shown to bring about further energy savings, but it demands denser deployment of BSs. Thus, it is not deemed as economically viable considering today’s cost values.

IEEE Globecom 2015

This paper presents the energy performance of a new radio access technology (RAT) component in 5G... more This paper presents the energy performance of a new radio access technology (RAT) component in 5G, here denoted as 5G-NX. The 5G-NX RAT encompasses massive beamforming and an ultra-lean design as two of its key technology components. The user throughput, resource utilization of the cells and daily average area power consumption are evaluated by means of system level simulations in an Asian city scenario, and the results are compared with a traditional LTE deployment using the same network layout. The simulation results indicate that the new 5G-NX system provides much better energy performance compared to LTE and this is primarily due to the ultra-lean design and the high beamforming gain that provides both longer and more efficient component sleep in the network. At expected traffic levels beyond 2020, 5G-NX is shown to decrease the network energy consumption by more than 50% while providing around 10 times more capacity.

IEEE PIMRC 2015

To meet future demands on user experience and traffic volumes, mobile networks need to evolve tow... more To meet future demands on user experience and traffic volumes, mobile networks need to evolve towards providing higher capacities and data rates. In this paper we investigate the feasibility of incorporating higher frequency bands (15 GHz) and beamforming to support this evolution. We see that using user-specific beamforming, the challenging propagation conditions at higher frequencies are mitigated and outdoor-in coverage is often possible. In places where 15 GHz coverage is not satisfactory, swift fallback to a lower frequency band is essential. This is seamlessly provided by carrier aggregation with a 2.6 GHz band. Together these components provide a ten-fold increase in capacity over a reference system operating only at 2.6 GHz.

IEEE Wireless Communications Letter, Aug 1, 2014

The energy efficiency of wireless access networks has attracted significant interest, due to esca... more The energy efficiency of wireless access networks has attracted significant interest, due to escalating energy cost and environmental concerns. How energy efficiency should be measured is, however, still disputed in the literature. In this letter, we discuss the impact of performance metrics and energy consumption models in network dimensioning. We argue that using a popular metric, the number of bits/Joule, may give misleading results, unless the capacity and coverage requirements of the system are carefully defined. We also claim that the energy consumption in the backhaul and the idle power of the base stations have to be taken into account. To support our claims, we demonstrate in a simple example how misleading results can be obtained by using flawed performance metrics.

Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand f... more Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand for new services and ubiqutious connectivity, will further increase the energy consumption. This situation imposes a big challenge for mobile operators not only due to soaring cost of energy, but also increasing concern for global warming and sustainable development.

This thesis focuses on the energy efficiency issue at the system level and studies how to incorporate energy-awareness into the design of future wireless access networks. The main contributions have been given in the areas of energy efficiency assessment, architectural and operational solutions, and total cost of investment analysis.

The precise evaluation of energy efficiency is the first essential step to determine optimized solutions where metrics and models constitute the two key elements.
We show that maximizing energy efficiency is not always equivalent to minimizing energy consumption which is one of the main reasons behind the presented contradictory and disputable conclusions in the literature. Further we indicate that in order to avoid the debatable directions, energy efficient network design problems should be formulated with well defined coverage and capacity requirements. Moreover, we propose novel backhaul power consumption models considering various technology and architectural options relevant for urban and rural environments and show that backhaul will potentially become a bottleneck in future ultra-high capacity wireless access networks.

Second, we focus on clean-slate network deployment solutions satisfying different quality of service requirements in a more energy efficient manner. We identify that the ratio between idle- and transmit power dependent power consumption of a base station as well as the network capacity requirement are the two key parameters that affect the energy-optimum design.
While results show that macro cellular systems are the most energy efficient solution for moderate average traffic density, Hetnet solutions prevail homogeneous deployment due to their ability to increase the capacity with a relatively lower energy consumption and thus enable significant energy savings in medium and high capacity demand regions.
%Considering the fact that orders of magnitude of more mobile data traffic will be generated at indoors in the near future, \emph{blasting the signals over the walls} is neither energy efficient nor feasible to satisfy the growing capacity demand.
Moreover, we investigate the energy saving potential of short-term energy aware management approach, i.e., cell DTX, taking advantage of low resource utilization in the current networks arising from strict QoS requirements. With the help of developed novel quantitative method, we show that Cell DTX brings striking reduction in energy consumption and further savings are achievable if the networks are designed taking into account the fact that network deployment and operation are closely related.

Finally, we develop a general framework for investigating the main cost elements and for evaluating the viability of energy efficient solutions.
We first reveal the strong positive impact of spectrum on both energy and infrastructure cost and further indicate that applying sustainable solutions might also bring total cost reduction, but the viability highly depends on unit cost values as well as the indirect cost benefits of energy efficiency.

Results obtained in this dissertation might provide guidelines for the network designers to achieve future high-capacity and sustainable wireless access networks.

IEEE Communications Letters, Apr 2014

Cell discontinuous transmission (DTX) is a new feature that enables sleep mode operations at bas... more Cell discontinuous transmission (DTX) is a new
feature that enables sleep mode operations at base station (BS)
side during the transmission time intervals (TTIs) when there
is no traffic. In this letter, we analyze the maximum achievable
energy saving of the cell DTX. We incorporate the cell DTX
with a clean-slate network deployment, and obtain optimal BS
density for lowest energy consumption satisfying a certain quality
of service (QoS) requirement considering daily traffic variation.
The numerical result indicates that the fast traffic adaptation
capability of cell DTX favors dense network deployment with
lightly loaded cells, which brings about considerable improvement
in energy saving.

IEEE ONDM'14, Mar 20, 2014

Providing wireless broadband access to rural and remote areas is becoming a big challenge for wir... more Providing wireless broadband access to rural and remote areas is becoming a big challenge for wireless operators, mostly because of the need for a cost-effective and low energy consuming mobile backhaul. However, to the best of our knowledge, energy consumption of different options for backhauling of future rural wireless broadband networks has not been studied yet. Therefore, in this paper we assess the energy consumption of future rural wireless broadband network deployments and backhaul technologies. In the wireless segment, two deployment strategies are considered, one with macro base station only, and one with small base stations. In the backhaul segment, two wireless, i.e., microwave and satellite, and one optical fiber based (i.e., long reach passive optical networks) solutions are considered. These options are compared in terms of their ability to satisfy coverage, capacity and QoS requirements of a number of rural users in the time span that goes from 2010 until 2021. From the presented results it is possible to conclude that wireless backhaul solutions can significantly increase the energy consumption of the access network. In contrast, the long reach PON based backhaul has much higher energy efficiency and in the long term might be a better choice for wireless operators

IEEE ICC'14, Jan 12, 2014

"Mobile operators are facing an exponential traffic growth due to the proliferation of portable d... more "Mobile operators are facing an exponential traffic growth due to the proliferation of portable devices that require a high-capacity connectivity. This, in turn, leads to a tremendous increase of the energy consumption of wireless access networks. A promising solution to this problem is the concept of heterogeneous networks, which is based on the dense deployment of low-cost and low power base stations, in addition to the traditional macro cells. However, in such a scenario the energy consumed by the backhaul, which aggregates the traffic from each base station towards the metro/core segment, becomes significant and may limit the advantages of heterogeneous network deployments. This paper aims at assessing the impact of backhaul on the energy consumption of wireless access networks, taking into consideration different data traffic requirements (i.e., from todays to 2020 traffic levels). Three backhaul architectures combining different technologies (i.e., copper, fiber, and microwave) are
considered. Results show that backhaul can amount to up to 50% of the power consumption of a wireless access network. On the other hand, hybrid backhaul architectures that combines fiber
and microwave performs relatively well in scenarios where the
wireless network is characterized by a high small-base-stations
penetration rate."

IEEE GROWN'13 in conjunction with WiMob'13, Aug 1, 2013

In 2020, mobile access networks will experience significant challenges as compared to the situati... more In 2020, mobile access networks will experience significant challenges as compared to the situation of today. Traffic volumes are expected to increase 1000 times, and the number of connected devices will be 10-100 times higher than today in a networked society with unconstrained access to information and sharing of data available anywhere and anytime to anyone and anything. One of the big challenges is to provide this 1000-fold capacity increase to billions of devices in an affordable and sustainable way. Low energy consumption is the key to achieve this. This paper takes as starting point the situation of today, and tries to pinpoint important focus areas and potential solutions when designing an energy efficient 5G mobile network architecture. These include system architecture, where a logical separation of data and control planes is seen as a promising solution; network deployment, where (heterogeneous) ultra dense layouts will have a positive effect; radio transmission, where the introduction of massive antenna configurations is identified as an important enabler; and, finally, backhauling solutions that need to be more energy efficient than today.

IEEE PIMRC 2013, Jul 1, 2013

"Energy efficiency in mobile radio networks has recently gained great interest due to escalating ... more "Energy efficiency in mobile radio networks has recently gained great interest due to escalating energy cost and environmental concerns. Rapidly growing demand for capacity will require denser and denser networks which further increase the energy consumption. In this regard, the deployment of small cells under macro-cellular umbrella coverage appears a promising solution to cope with the explosive demand in an energy efficient manner. In this paper, we investigate the impact of joint macro-and femtocell deployment on energy efficiency of wireless access networks, based on varying area throughput requirements. We take into account the the co-channel interference, fraction of indoor users, femto base station density and backhaul power consumption. It is shown that utilizing indoor base stations provide significant energy savings compared to traditional macro only network in urban areas with medium and high user demand where the gain increases up to 75 percent as more data traffic.
is offloaded to femtocells"

Licentiate Thesis, Nov 1, 2012

Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand f... more Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand for capacity will further increase the energy consumption. Thus, improving energy efficiency has a great importance not only for environmental awareness but also to lower the operational cost of network operators. However, current networks which are optimized based
on non-energy related objectives introduce challenges towards green wireless access networks. In this thesis we investigate the solutions at the deployment level and handle energy efficiency assessment issues in wireless access networks.

The precise characterization of the power consumption of the whole network has a crucial importance in order to obtain consistent conclusions from any proposed solution at the network level. For this purpose, we propose a novel power consumption model considering the impact of backhaul for two established
technologies, i.e., fiber and microwave, which is often ignored in the literature. We show that there is a tradeoff between the power saved by using low power base stations and the excess power that has to be spent for backhauling their traffic which therefore needs to carefully be included into energy efficiency analysis. Furthermore, among the solutions that are analyzed, fiber-based backhaul solution is identified to outperform microwave regardless of the considered topology. The proposed model is then used to gain a general insight regarding the important design parameters and their possible impact on energy- and cost oriented network design. To this end, we present a high-level framework to see the main tradeoffs between energy, infrastructure cost, spectrum and show that future high-capacity systems are increasingly limited by infrastructure and energy costs where spectrum has a strong positive impact on both.

We then investigate different network deployment strategies to improve the energy efficiency where we focus on the impact of various base station types, cell size, power consumption parameters and the capacity demand. We propose a refined power consumption model where the parameters are determined in accordance with cell size. We show that network densification can only be justified when capacity expansion is anticipated and over-provisioning of the network is not plausible for greener network. The improvement through heterogeneous networks is indicated to be highly related to the traffic demand where up to 30\% improvement is feasible for high area throughput targets.

Furthermore, we consider the problem of energy efficiency assessment at the network level in order to allow operators to know their current status and quantify the potential energy savings of different solutions to establish future strategies. We propose elaborate metric forms that can characterize the efficiency and a methodology that indicate how to perform a reliable and accurate measurement considering the complexity of wireless networks. We show the weakness of the current metrics reporting the "effectiveness" and how these might indicate disputable improvement directions unless they are properly revised. This illustrates the need for a standardized network level energy efficiency evaluation methodology towards green wireless access.

Mobile communication networks alone consume 0.5 percent of the global energy today. Rapidly growi... more Mobile communication networks alone consume 0.5 percent of the global energy today. Rapidly growing demand for capacity will further increase the energy consumption. Thus, improving energy efficiency has recently gained great interest within the research community not only for environmental awareness but also to lower the operational cost of network operators. Base station deployment strategy is one of the key challenges to be addressed for fulfilling the future capacity demand in an energy efficient manner. In this paper, we investigate the relationship between energy efficiency and densification with regard to network capacity requirement. To this end, we
refine the base station power consumption model such that the parameters are determined by the maximum transmit power and develop a simple analytical framework to derive the optimum transmit power that maximizes energy efficiency for a certain capacity target. Our framework takes into account interference, noise and backhaul power consumption. Numerical results show that deployment of smaller cells significantly reduces the base
station transmit power, and thus shifts the key elements of energy consumption to idling and backhauling power. Network densification can only be justified when capacity expansion is anticipated.

Mobile communication networks account for 0.5% of the global energy consumption, a value that is ... more Mobile communication networks account for 0.5% of the global energy consumption, a value that is expected to double within the next five years. For this reason, means of reducing the energy consumption in cellular mobile radio networks has recently gained great interest within the research community. In mobile networks the backhaul contribution to the total power consumption is usually neglected because of its limited impact
compared to that of the radio base stations. However, meeting the almost exponential increase in mobile data traffic requires a large number of (mainly small) base stations. This means that backhaul networks will take a significant share of the cost and the energy consumption in future systems. Their actual contribution to the energy consumption will depend on the radio base station deployment scenario as well as on the technology and topology choices for the backhaul itself.
This paper presents an initial assessment of the power consumption of two established backhaul technologies, i.e., fiber and microwave. For the microwave case, three backhaul topologies are considered, i.e., tree, ring and star, while for the fiber case only one topology is analysed, i.e., a dedicated point-to-point star. The presented results, assuming off-the-shelf products and based on todays network capacity levels, confirm the importance of considering the backhaul when minimizing the total power consumption in heterogeneous network scenarios. They also show the impact of the basic technology and topology choices of the backhaul for minimizing total power consumption.

It is envisaged that diverse types of short-range wireless systems coexist in shared spectrum in ... more It is envisaged that diverse types of short-range wireless systems coexist in shared spectrum in a near future. For low-power systems, throughput and energy efficiency are two design objectives that often conflict with each other. In this paper, we investigate the tradeoff between the throughput and the energy efficiency for a data-hungry but battery-driven low power network which opportunistically shares radio spectrum in temporal domain. We provide a mathematical framework that determines the optimum frame lengths for the different objectives, and analyze the tradeoff. To this purpose, we propose an energy consumption model that reflects the characteristics of low-power transceivers including power consumption at the receiver side. Numerical results show that for the considered opportunistic system, the optimum frame length for energy efficiency results in significant loss in throughput, and vice versa. It is also observed this tradeoff highly depends on the parameters of primary traffic. This suggests that the transmission duration of the opportunistic network should be chosen depending on the prime system objective, which can be done by the framework.
proposed by this work.

Mobile communication networks alone today consume 0.5% of the global energy supply. Meeting the r... more Mobile communication networks alone today consume 0.5% of the global energy supply. Meeting the rapidly increasing demand for more capacity in wireless broadband access will further increase the energy consumption. Operators are now facing both investing in denser and denser networks as well as increased energy cost. Traditional design paradigms, based on assumptions of spectrum shortage and high cost base station sites, have produced current cellular systems based on 3G and 4G (LTE) standards. The latter ones are characterized by very high spectrum efficiency, but low energy efficiency. Deployment has favoured strategies with few, high power bases stations with complex antenna systems. The key method for indoor coverage has so far been to literally "blast signals through walls" - a solution that is neither energy efficient, nor very sound from a radiation perspective. As environmental aspects maybe perceived as important from a societal perspective, the cost remains the short to medium term concern for operators of future mobile broadband systems. What becomes evident now is that the so far mostly neglected energy cost will be a major concern. Future system deployment has to balance infrastructure deployment, spectrum and energy cost components.

Ongoing incremental improvements in electronics and signal processing are bringing down the power consumption in base station. However, these improvements are not enough to match the orders-of-magnitude increase in energy consumption cause by demands for more capacity. It is clear that solutions to this problem have to be found at the architectural level, not just by increasing the efficiency of individual components. In this paper we propose a framework for a total cost analysis and survey some recent, more radical, "clean slate" approaches exploiting combinations of new spectrum opportunities, energy efficient PHY-layers and novel deployment and backhauling strategies that target minimizing overall system cost. The latter involve network deployment tightly tailored to traffic requirements, using low power micro base stations tailored specifically to decrease the power consumption compared to today’s high power macro base stations schemes.

To illustrate our findings, a power consumption model for mobile broadband access networks taking into account backhaul is presented and main trade-offs between infrastructure, energy and spectrum cost are analyzed. We will demonstrate optimal deployment strategies in some simple scenarios where a certain capacity has to be provided in a dense, interference limited scenario.

Energy efficiency in cellular mobile radio networks has recently gained great interest in the res... more Energy efficiency in cellular mobile radio networks has recently gained great interest in the research community. The development of more energy efficient hardware and software components aside, effect of different deployment strategies on energy efficiency are also studied in the literature.
The latter mainly consist of optimizing the number and the location of different types of base stations in order to minimize the total power consumption. Usually, in the literature, the total network power consumption is restricted to the sum of the power consumption of all base stations. However, the choice of a specific deployment also affects the exact implementation of the backhaul network, and consequently its power consumption, which should therefore be taken into account when devising energy efficient deployment.
In this paper, we propose a new power consumption model for a mobile radio network considering backhaul. We then handle a case study and perform a comparison of the power consumption of three different heterogeneous network deployments, and show how backhaul has a non-negligible impact on total power consumption, which differs for different deployments. An energy efficiency analysis is also carried out for different area throughput targets.

Asia Communications and Photonics Conference 2013, 2013

Journal

IEEE Globecom 2015

IEEE PIMRC 2015

IEEE Wireless Communications Letter, Aug 1, 2014

Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand f... more Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand for new services and ubiqutious connectivity, will further increase the energy consumption. This situation imposes a big challenge for mobile operators not only due to soaring cost of energy, but also increasing concern for global warming and sustainable development.

Results obtained in this dissertation might provide guidelines for the network designers to achieve future high-capacity and sustainable wireless access networks.

IEEE Communications Letters, Apr 2014

IEEE ONDM'14, Mar 20, 2014

IEEE ICC'14, Jan 12, 2014

IEEE GROWN'13 in conjunction with WiMob'13, Aug 1, 2013

IEEE PIMRC 2013, Jul 1, 2013

Licentiate Thesis, Nov 1, 2012

Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand f... more Wireless access networks today consume 0.5 percent of the global energy. Rapidly growing demand for capacity will further increase the energy consumption. Thus, improving energy efficiency has a great importance not only for environmental awareness but also to lower the operational cost of network operators. However, current networks which are optimized based
on non-energy related objectives introduce challenges towards green wireless access networks. In this thesis we investigate the solutions at the deployment level and handle energy efficiency assessment issues in wireless access networks.

”More than 50 billion devices will be connected in 2020” claims Ericsson. Considering the fact th... more ”More than 50 billion devices will be connected in 2020” claims Ericsson. Considering the fact that billions of users are already online, next step is to connect the ”things”. Meeting this demand will require ultra-dense network deployments, which as a result, increase the energy consumption. We believe that incremental improvements in equipment won’t be enough to overcome exponential increase of energy consumption. We need a paradigm shift in the way we design the networks and a new clean-slate approach shift the future network design from always on to always available.