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Björklund, Patrik
Publications (8 of 8) Show all publications
Björklund, P., Värbrand, P. & Yuan, D. (2006). A Dynamic Programming Method for Optimal Scheduling in High Speed Downlink Packet Access. In: The 3rd International Conference on Mobile Technologies,Applications and Systems Mobility 2006,2006.
Open this publication in new window or tab >>A Dynamic Programming Method for Optimal Scheduling in High Speed Downlink Packet Access
2006 (English)In: The 3rd International Conference on Mobile Technologies,Applications and Systems Mobility 2006,2006, 2006Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-42185 (URN)61236 (Local ID)61236 (Archive number)61236 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2012-06-25
Björklund, P. (2006). Applications of Resource Optimization in Wireless Networks. (Doctoral dissertation). : Institutionen för teknik och naturvetenskap
Open this publication in new window or tab >>Applications of Resource Optimization in Wireless Networks
2006 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

The demand for wireless communications is increasing every year, but the available resources are not increasing at the same rate. It is very important that the radio resources are used in an efficient way allowing the networks to support as many users as possible. The three types of networks studied in this thesis are frequency hopping GSM networks, ad hoc multi-hop networks and WCDMA networks.

One type of network with a promising future is ad hoc multi-hop networks. The users in this kind of networks communicate with each other without base stations. Instead the signal can be sent directly between two users, or relayed over one or several other users before the final destination is reached. Resources are shared by letting the users transmit in time slots. The problem studied is to minimize the number of time slots used, when the users broadcast. Two different optimization models are developed for assigning time slots to the users. A reduction of the number of time slots means a shorter delay for a user to transmit next time.

The rapid growth of the number of subscribers in cellular networks requires efficient cell planning methods. The trend of smaller cell sizes in urban areas for higher capacity raise the need for more efficient spectrum usage. Since the infrastructure of a second generation cellular system, such as GSM, already exists, and the available bandwidth of an operator is limited, frequency planning methods are of utmost importance. Because of the limited bandwidth in a GSM network, the frequencies must be reused. When planning a GSM network the frequencies can not be reused too tightly due to interference. The frequency planning problem in a GSM network is a very complex task. In this thesis an optimization model for frequency assignment in a frequency hopping GSM network is developed. The problem is to assign frequencies to the cells in the network, while keeping the interference to a minimum. Different meta heuristic methods such as tabu search and simulated annealing are used to solve the problem. The results show that the interference levels can be reduced to allow a capacity increase.

The demand for sending more information over the wireless communication systems requires more bandwidth. Voice communication was handled well by the second generation cellular systems. The third generation of mobile telecommunication systems will handle data transmissions in a greater extent. The last type of network considered in the thesis is a WCDMA cellular network. The aim is to schedule the transmission of packet data from the base station to the users. Scheduling models that maximize the utility are developed for both the downlink shared channel and the high speed downlink shared channel.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap, 2006. p. 124
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1029
Keywords
Optimization, telecommunication, scheduling, gsm, wcdma, ad-hoc, frequency planning
National Category
Telecommunications
Identifiers
urn:nbn:se:liu:diva-7234 (URN)91-85523-41-0 (ISBN)
Public defence
2006-09-01, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 13:15 (English)
Opponent
Supervisors
Available from: 2006-08-30 Created: 2006-08-30
Björklund, P., Värbrand, P. & Yuan, D. (2005). Optimized planning of frequency hopping in cellular networks. Computers & Operations Research, 32(1), 169-186
Open this publication in new window or tab >>Optimized planning of frequency hopping in cellular networks
2005 (English)In: Computers & Operations Research, ISSN 0305-0548, E-ISSN 1873-765X, Vol. 32, no 1, p. 169-186Article in journal (Refereed) Published
Abstract [en]

We consider a generalization of the classical frequency assignment problem. The generalization arises when frequency hopping is used in a cellular network. The planning problem concerns assigning lists of frequencies to blocks of transceivers, such that the total interference is minimized. This problem is considerably more difficult than the classical frequency assignment problem, because of the large number of possible frequency lists. We provide the technical background that motivates our study, and present a mathematical model which includes the classical frequency assignment problem as a special case. We describe a simulated annealing algorithm. The algorithm explores the solution space by solving an integer program in each iteration. We report computational results for real-life and synthesized networks. © 2003 Elsevier Ltd. All rights reserved.

Keywords
Frequency assignment, Frequency hopping, Simulated annealing, Telecommunications
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-45540 (URN)10.1016/S0305-0548(03)00210-7 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Björklund, P., Värbrand, P. & Yuan, D. (2004). A Column Generation Method for Spatial TDMA Scheduling in Ad Hoc Networks. Ad hoc networks, 2(Issue 4), 405-418
Open this publication in new window or tab >>A Column Generation Method for Spatial TDMA Scheduling in Ad Hoc Networks
2004 (English)In: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 2, no Issue 4, p. 405-418Article in journal (Refereed) Published
Abstract [en]

An ad hoc network can be set up by a number of units without the need of any permanent infrastructure. Two units establish a communication link if the channel quality is sufficiently high. As not all pairs of units can establish direct links, traffic between two units may have to be relayed through other units. This is known as the multi-hop functionality. In military command and control systems, ad hoc networks are also referred to as multi-hop radio networks. Spatial TDMA (STDMA) is a scheme for access control in ad hoc networks. STDMA improves TDMA by allowing simultaneous transmission of multiple units. In this paper, we study the optimization problem of STDMA scheduling, where the objective is to find minimum-length schedules. Previous work for this problem has focused on heuristics, whose performance is difficult to analyze when optimal solutions are not known. We develop novel mathematical programming formulations for this problem, and present a column generation solution method. Our numerical experiments show that the method generates a very tight bound to the optimal schedule length, and thereby enables optimal or near-optimal solutions. The column generation method can be used to provide benchmarks when evaluating STDMA scheduling algorithms. In particular, we use the bound obtained in the column generation method to evaluate a simple greedy algorithm that is suitable for distributed implementations.

Keywords
Ad hoc networks; STDMA; Scheduling; Column generation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32514 (URN)10.1016/j.adhoc.2003.09.002 (DOI)18422 (Local ID)18422 (Archive number)18422 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Björklund, P., Värbrand, P. & Yuan, D. (2004). A dynamic programming technique for downlink bandwidth allocation in WCDMA networks. In: Vehicle Technology Conference,2004. New York, NY, USA: IEEE
Open this publication in new window or tab >>A dynamic programming technique for downlink bandwidth allocation in WCDMA networks
2004 (English)In: Vehicle Technology Conference,2004, New York, NY, USA: IEEE , 2004Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
New York, NY, USA: IEEE, 2004
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-22604 (URN)1881 (Local ID)1881 (Archive number)1881 (OAI)
Note
ISBN: 0-7803-8256-0Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2012-06-25
Björklund, P., Värbrand, P. & Yuan, D. (2003). A Simulated Annealing Algorithm for Frequency Assignment in Frequency Hopping GSM Networks. In: International Conference on Computer, Communication and Control Technolgies CCCT 03,2003 (pp. 155). Orlando: IIIS
Open this publication in new window or tab >>A Simulated Annealing Algorithm for Frequency Assignment in Frequency Hopping GSM Networks
2003 (English)In: International Conference on Computer, Communication and Control Technolgies CCCT 03,2003, Orlando: IIIS , 2003, p. 155-Conference paper, Published paper (Refereed)
Abstract [en]

We consider the frequency assignment problem in frequency hopping GSM networks, where the task is to construct and assign lists of frequencies to blocks of transceivers, such that the total interference is minimized. We present a mathematical model and describe a simulated annealing algorithm. The algorithm explores the solution space by solving an integer program in each iteration. Computational experiments for real-life and synthesized networks show that considerable interference reduction can be achieved using the algorithm.

Place, publisher, year, edition, pages
Orlando: IIIS, 2003
Keywords
telekommunikation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32508 (URN)18416 (Local ID)18416 (Archive number)18416 (OAI)
Available from: 2009-10-09 Created: 2009-10-09
Björklund, P., Värbrand, P. & Yuan, D. (2003). Resource Optimization of Spatial TDMA in Ad Hoc Radio networks : A Column Generation Approach. In: IEEE INFOCOM 2003,2003 (pp. 818). San Francisco: IEEE
Open this publication in new window or tab >>Resource Optimization of Spatial TDMA in Ad Hoc Radio networks : A Column Generation Approach
2003 (English)In: IEEE INFOCOM 2003,2003, San Francisco: IEEE , 2003, p. 818-Conference paper, Published paper (Refereed)
Abstract [en]

Wireless communications using ad hoc networks are receiving an increasing interest. The most attractive feature of ad hoc networks is the flexibility. The network is set up by a number of units in an ad hoc manner, without the need of any fixed infrastructure. Communication links are established between two units if the signal strength is sufficiently high. As not all pairs of nodes can establish direct links, the traffic between two units may have to be relayed through other units. This is known as the multihop functionality. Design of ad hoc networks is a challenging task. In this paper we study the problem of resource allocation with spatial TDMA (STDMA) as the access control scheme. Previous work for this problem has mainly focused on heuristics, whose performance is difficult to analyze when optimal solutions are not known. We develop, for both node-oriented and link-oriented allocation strategies, mathematical programming formulations for resource optimization. We further present a column generation approach, which, in our numerical experiments, constantly yields optimal or near-optimal solutions. Our results provide important benchmarks when evaluating heuristic on-line algorithms for resource optimization using STDMA.

Place, publisher, year, edition, pages
San Francisco: IEEE, 2003
Keywords
Ad hoc, telecommunication
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32510 (URN)18418 (Local ID)18418 (Archive number)18418 (OAI)
Available from: 2009-10-09 Created: 2009-10-09
Björklund, P. (2002). Two Resource Optimization Applications in Wireless Networks. (Licentiate dissertation). Linköping: Linköpings universitet
Open this publication in new window or tab >>Two Resource Optimization Applications in Wireless Networks
2002 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

The demand for wireless applications is increasing every year. In a couple of years, much of the traffic in the networks is packet switched data. The radio resources are not increasing at the same rate as the demand for wireless communication. It is very important that the radio resources are used in an efficient manner allowing the networks to support as many users as possible. Resource allocation in wireless networks is about using the radio resources in an efficient way. The two types of networks studied in this thesis are frequency hopping GSM networks and ad hoc multi-hop networks.

The rapid growth of the number of subscribers in cellular networks requires efficient cell planning methods. The trend of smaller cell sizes in urban areas for higher capacity raise the need for more efficient spectrum usage. Since the infrastructure of a second generation cellular system, such as GSM, already exists, and the available bandwidth of an operator is limited, frequency planning methods are of utmost importance. Because of the limited bandwidth in a GSM network, the frequencies must be reused. When planning a GSM network the frequencies can not be reused too tightly due to interferences between co-channel and adjacent-channel frequencies. The frequency planning problem in a GSM network is a very complex task. In this thesis an optimization model for frequency assignment in a frequency hopping GSM network is developed. The problem is to assign frequencies to the cells in the network, while keeping the interference to a minimum. Different meta heuristic methods such as tabu search and simulated annealing are used to solve the problem.

Another type of network with a promising future are ad hoc multi-hop networks. The users in this kind of networks communicate with each other without base stations. Instead the signal can be sent directly between two users, or relayed over one or several other users before the final destination is reached. Resources are shared by letting the users transmit in time slots. The problem studied is to minimize the number of time slots used, when the users broadcast. Two different optimization models are developed for assigning time slots to the users. The models are solved by different techniques.

In the two different types of networks investigated, frequency hopping GSM networks and ad hoc multi-hop networks, resource allocation achieves better performance. In the former network, the interference levels can be reduced to allow a capacity increase. In the latter the number of time slots can be reduced to decrease the delay for a user.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2002. p. 96
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 943
Keywords
telekommunikation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32506 (URN)18414 (Local ID)91-7373-333-4 (ISBN)18414 (Archive number)18414 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-12
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