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Research Areas


Optimization Theory Approaches to Scheduling of Wireless Transmissions

A. Ephremides, D. Yuan,  V. Angelakis, and Q. He


Scheduling is a mature, but unresolved, problem in wireless systems that share the same channel. It amounts to determining when each user transmits and at what rate. The answer depends on many parameters of the system, like channel characteristics, detector structure, transmission power, modulation, coding, etc but also on user demand. It is known that multiple users can transmit simultaneously and successfully if they adjust their transmission rates properly.


The version of the problem that we consider is based on the fact that to minimize latency and overall delay it suffices to minimize “service time”. Thus we focus on a version of the problem where the demand is expressed in terms of fixed “bit”-volumes that reside at the transmitter buffers and need to be transmitted in minimum time. This is also known as the “empty-the-network” problem. It is possible to formulate the problem as a linear program where the variables are the activation durations of the user sub-sets and the coefficients are the corresponding transmission rates. In addition to solution characterization, complexity and structural results, and efficient solution methods we are imbedding this work in a broader optimization context that combines multi-user information theory with optimization methodologies. Furthermore, we have developed practical algorithms and approximations that permit the application of our theoretical investigation to practical systems.



M2M networking for IoT-based Intelligent Environments

V. Angelakis, D. Yuan, and D. Gundlegård

The Internet of Things (IoT) comprises a large number of hardware and software objects such as sensors or smart phones with an array of communication technologies (LTE, RFID, 802.11, Zigbee) carrying out a variety of tasks over heterogeneous networks. This collective of interconnected smart objects is the cornerstone for the development of Intelligent Environments spanning from Green Buildings to Smart Cities, providing applications to individuals, companies, and authorities, that drive competitiveness, increase sustainability and improve the quality of life.

Our efforts within this context focus on the interconnection of large numbers of such heterogeneous smart objects, enabling the communication provision for applications spanning from Intelligent Transportation Systems to Intelligent Building Management. This is performed through the usage of cognitive radio inspired M2M communications, while we seek to identify and balance the trade-offs between the requirement for increased security, privacy, low energy consumption, and system performance. A parallel proof-of-concept activity is the development of Android-based ITS applications following the above design considerations.



Mobile Broadband Network Planning and Resource Management

V. Angelakis, L. Chen, and D. Yuan

Planning cellular networks deals with locating and configuring radio network elements to meet specified performance targets. One of the key factors that influence the above network performance indicators is interference. Our work in HSPA system modeling and optimization of antenna configuration has already shown a significant potential in reducing interference and increasing network performance in terms of downlink throughput and uplink connectivity. Ongoing research focuses on developing an HSPA system framework of models and optimization engines that take into account both the base station location and antenna configuration in order to maximize throughput and network coverage while minimizing costs.

Other than physical network planning, radio resource management is crucial for the interference management of OFDMA-based radio networks, such as HSPA, LTE and LTE-A. Users that lie in the edges of cells are the ones suffering the most in terms of throughput from inter-cell interference due to poor propagation conditions by the serving cell. To balance the cell-edge users throughput and overall throughput, frequency reuse schemes splitting the cell into center and edge zones have been proposed. Such schemes are facilitated in OFDM systems due to the allocation flexibility of the subcarriers. Our work is focused on designing a distributed and adaptive frequency reuse scheme based on the Fractional Frequency Reuse scheme, where cells are able to borrow and negotiate on the usage of the edge bands depending on local demand. Early results indicate that such solutions indeed limit the average throughput drop in the cell center observed in the FFR scheme, with at a predefined, bounded cost to the original scheme’s gain in edge throughput.




Real-Time Monitoring of Available Bandwidth

E. Bergfeldt and J. M. Karlsson

In recent years, there has been a rapid growth of interest in bandwidth estimation of communication networks. In the context of packet-switched data networks, such as the Internet, the term bandwidth commonly refers to the amount of information a network can deliver per time unit. Knowledge of bandwidth characteristics is of great significance in, e.g., end-to-end admission control, capacity planning, intelligent routing, audio/video streaming, and peer-to-peer applications.

We further develop and evaluate the BART (Bandwidth Available in Real-Time) method for real-time estimation of end-to-end available bandwidth of a network path. The available bandwidth corresponds to the minimum unused bandwidth capacity among all links between two nodes of a network. BART uses active probing and Kalman filtering to accomplish the estimation; probing implies injection of specific data packets, which are expected to be affected by the characteristics of the utilized network path. Experiments are being continuously performed in our laboratory networks as well as over the Internet.


Optimization Concepts for Capacity Analysis of Wireless Communications

L. Chen, V. Angelakis, and D. Yuan

Analysis of performance limit is a fundamental aspect in wireless communications, as well as in multi-hop ad hoc and meshes networks. The analysis is a foundation to the development of efficient radio resource allocation schemes. For wireless networks of general topology, numerically assessment the capacity limit involves of the solutions of mathematical optimization problems. There are many problem types, depending on the capacity definition, radio access technology, multiplexing scheme, etc. A key consideration is the signal-to-interference-and-noise ratio (SINR). Recent development of transmission technologies, such as cooperative relaying, adds new dimensions and increases the problem complexity.

The research develops novel optimization concepts, models, and mathematical programming algorithms for capacity analysis problems in wireless networks. Solving these problems generate insights and understanding going beyond the state-of-the-art of performance analysis of wireless communications. 



Resource Optimization in Ad Hoc and Wireless Mesh Networks 

L. Chen and D. Yuan

Ad hoc and mesh are two wireless networking paradigms that have enriched the landscape of wireless communications. In many applications, these networks provide attractive alternatives or complements to cellular-based systems. In ad hoc network, wireless devices establish a self-configured infrastructure-less networking environment. The core architecture of mesh networks is formed by low-cost radio access points, a type of ad hoc units, among which some are connected to a backbone infrastructure.

Ad hoc and wireless mesh networking poses a plethora of research challenges in designing networking concepts and resource management schemes. Examples of research topics are routing, scheduling, spectrum allocation, and energy-efficient broadcast and topology control. The research within the MT group develops models, theoretical results, and algorithms to these problems to provide new solutions to performance engineering of ad hoc and mesh networks.


Developing energy-efficient wireless network design in 4G LTE in relation to Quality of Service (QoS)

S. Fowler and D. Yuan

Today, more and more users have come to depend on mobile devices, such as cellular phones. These mobile devices are powered by battery, which is fixed-power source.  The limited power source for the battery-powered wireless devices is a huge obstacle for further development of more sophisticated devises, such as so called smart-phones, which is strongly demanded by consumers.  Previous research has focused on increasing battery capacities.  However, the slow development in battery capacities cannot catch up with the speed of evolution in Internet technologies and mobile devises.  Instead, researchers recently started to work toward making every layer of network more energy efficient.  Such an effort includes developing energy- efficient computer network architecture(s) or Green Network(s).  Unfortunately, to date, they are effectively solutions targeted only for specific area of network architecture and have not been successfully applied for practical uses.  Therefore, there is an urgent need to develop an effective energy-efficient mobile network solution for the Fourth Generation Wireless Network (4G).

The central theme of this study is that effectively designed optimization techniques in the computer network such as the Quality of Service (QoS) framework will improve overall system performance and achieve energy-efficient operation.  Therefore, we will conduct research based on developing model for simulation of energy efficient network design in Long Term Evolution (LTE).  LTE is a 4G technology, where energy-efficiency issue is open field and have to be addressed urgently.  We will design a simulator specifically tailored for testing energy-efficient networks for LTE.  The outcomes will enable us to apply QoS framework technologies to evaluate performance improvement in terms of energy-efficient operation.


Generating Road Traffic Information from Cellular Networks

D. Gundlegård and J. M. Karlsson

Real-time information about average speeds on links in a road network constitutes a very important component of efficient traffic management. Using this information enables to detect congestions, calculate travel times, predict future traffic situations and hence have a good base for correct traffic management measures. These measures are in turn important in order to reduce the environmental footprint from road traffic and decrease travel times. Retrieval of this information through the signalling information already available in cellular system is an efficient and scalable way of obtaining data. This information is available in GSM, UMTS and other cellular systems.

The aim of our work is to assess the potential of new technologies and communication patterns for extracting more accurate and reliable traffic information.  To this end we also develop new algorithms and simulation models to distil cellular signalling data into useful traffic information.


LTE Tracking Area Management

S. Modarres Razavi and D. Yuan

Formation of tracking areas (known as location areas in GSM systems) is a key function in mobility management in cellular networks. Optimal layout of tracking areas has to balance the amount of paging and registration signaling traffic required to collect and solicit user location information. From a network management perspective, a key concept in Long Term Evolution (LTE) is automatic reconfiguration. For tracking area formation, implementing the concept requires the management system’s ability of adapting the configuration to changes and trends in user distribution and mobility patters over time.

The research delivers new schemes for adaptive tracking area re-configuration to effectively deal with the system dynamics in cellular networks. Works are carried out along two lines. The first is the development of algorithms that are capable of re-optimizing tracking area configuration, and at the same time keeping the service interruption due to re-configuration within an acceptable level. The second line of research targets exploiting tracking area lists to go beyond the performance achievable by the conventional tracking area concept.


The research delivers new schemes for adaptive tracking area re-configuration to effectively deal with the system dynamics in cellular networks. Works are carried out along two lines. The first is the development of algorithms that are capable of re-optimizing tracking area configuration, and at the same time keeping the service interruption due to re-configuration within an acceptable level. The second line of research targets exploiting tracking area lists to go beyond the performance achievable by the conventional tracking area concept. 



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The MT group gratefully acknowledges the support of the following organizations:



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Last updated: Wed Sep 11 16:52:10 CEST 2013