Joakim Kalvenes

Hierarchical cellular network design with channel allocation

Abstract The design of a cellular network is a complex process that encompasses the selection and configuration of cell sites and the supporting network infrastructure. This investigation presents a net revenue maximizing model that can assist network designers in the design and configuration of a cellular system. The integer programming model takes as given a set of candidate cell locations with corresponding costs, the amount of available bandwidth, the maximum demand for service in each geographical area, and the revenue potential in each customer area. Based on these data, the model determines the size and location of cells, and the specific channels to be allocated to each cell. To solve problem instances, a maximal clique cut procedure is developed in order to efficiently generate tight upper bounds. A lower bound is constructed by solving the discrete optimization model with some of the discrete variables fixed. Computational experiments on 72 problem instances demonstrate the computational viability of our new procedure.

Base Station Location and Service Assignments in W--CDMA Networks

Designing a wideband code division multiple access (W--CDMA) network is a complicated task requiring the selection of sites for radio towers, analysis of customer demand, and assurance of service quality in terms of signal-to-interference ratio requirements. This investigation presents a net-revenue maximization model that can help a network planner with the selection of tower sites and the calculation of service capacity. The integer programming model takes as input a set of candidate tower locations with corresponding costs, a number of customer locations with corresponding demand for traffic, and the revenue potential for each unit of capacity allocated to each demand point. Based on these data, the model can be used to determine the selection of radio towers and the service capacity of the resulting radio network. The basic model is a large integer program and requires a special algorithm for practical solution. Our algorithm uses a priority branching scheme, an optimization-gap tolerance between 1% and 10%, and two sets of global valid inequalities that tighten the upper bounds obtained from the linear programming relaxation. The algorithm has been implemented in software for the AMPL/CPLEX system and an empirical investigation has been conducted. Using over 300 problem instances with up to 40 towers and 250 service locations, various combinations of algorithm settings have been evaluated. Using the recommended setting results in a design tool that generally runs in under 20 minutes on a 667 MHz AlphaStation.

Design of Robust Business-to-Business Electronic Marketplaces with Guaranteed Privacy

Firms that set up electronic marketplaces to enhance their supply and/or distribution channels face challenges in attracting their competitors to participate. A major obstacle is the perception that the owner can unfairly exploit trading information for competitive advantage. In this paper, we propose a marketplace design that shifts the locus of control over trader privacy from the marketplace operator to each individual trader. We show how online transactions between trading partners can be conducted in total privacy, so that not even the marketplace owner/operator can exploit transaction information for strategic purposes. At the same time, our approach includes robust methods for transaction integrity and nonrepudiation, as well as posttransaction dispute resolution.

The impact of intersatellite communication links on LEOS performance

LEOS communication systems are rapidly moving from dream to reality. When operational, the LEOS systems can offer mobile and fixed‐site communications between any two points on the globe. Yet, many LEOS system design issues remain unresolved. Some of the planned systems, such as Iridium and Teledesic, rely on intersatellite communication to provide space based routing from origin to destination while others, like Globalstar, use ground based routing. This paper investigates the effect of satellite crosslink design on user‐to‐user delay and satellite power consumption. Delay is an important measure of quality of service and may have a significant impact on system revenues. The results indicate that the choice of crosslink architecture has a large effect on user‐to‐user delay. In a polar orbit LEOS system, there will be two seams from pole to pole 180° apart, where satellites in orbits on opposing sides of the seam move in opposite directions. It is demonstrated that the ability to maintain communication links across the seams is of relatively minor importance for user‐to‐user delay. Finally, the choice of crosslink pattern and crosslink antenna technology is shown to have no significant impact on satellite power consumption or on LEOS system capacity.

Research NoteInformation Technology, Contract Completeness, and Buyer-Supplier Relationships

The theory of incomplete contracts has been used to study the relationship between buyers and suppliers following the deployment of modern information technology to facilitate coordination between them. Previous research has sought to explain anecdotal evidence from some industries on the recent reduction in the number of suppliers selected to do business with buyers by appealing to relationship-specific costs that suppliers may incur. In contrast, this paper emphasizes that information technology enables greater completeness of buyer-supplier contracts through more economical monitoring of additional dimensions of supplier performance. The number of terms included in the contract is an imperfect substitute for the number of suppliers. Based on this idea, alternative conditions are identified under which increased use of information technology leads to a reduction in the number of suppliers without invoking relationship-specific costs. We find that a substantial increase in contract completeness due to reduced cost of information technology could increase the cost per supplier even though the cost of coordination and the cost per term monitored decrease. Such an increase in the cost per supplier leads to a reduction in the number of suppliers with whom the buyer chooses to do business. Similarly, we find that if coordination cost is reduced when more information technology is deployed so that the number of suppliers in the buyers pool increases substantially, the buyer might choose to make the supplier contracts less complete, instead relying on a more market-oriented approach to finding a supplier with good fit.

The impact of satellite altitude on the performance of LEOS based communication systems

Low earth orbit satellite (LEOS) systems promise to provide global communication, including voice and data services from Iridium and high capacity broadband services from Teledesic. In design of LEOS systems, the choice of satellite altitude is an important consideration, which has a significant impact on system performance. Among the factors affected by satellite altitude choice are system capacity, user‐to‐user delay, power system design and communication services that can be offered. This paper analyzes the effects of satellite altitude on quality of service, frequency reusability and power system sizing. It is found that a choice of low altitude has a positive impact on system capacity and power system requirements. As a consequence, satellite mass and launch cost can be reduced for satellites in lower orbits due to the lower power requirements. In terms of user‐to‐user delay, the results are in favor of medium altitudes, while very high altitudes are not a good choice relative to these measures.

Traffic Estimation and Capacity Assignment in Multimedia Distribution Networks with Guaranteed Quality of Service

This paper considers the provisioning of transmission line bandwidth on a private network with given traffic routing for the purpose of distribution of video-on-demand service with guaranteed end-to-end quality of service. We present an architecture for video-on-demand service delivery and model the assignment of bandwidth in the distribution network as a constrained, nonlinear optimization problem. To solve this optimization problem, we develop three new auction algorithm-based solution procedures. The optimization problem assumes that there is a functional relationship between the maximum acceptable end-to-end delay and the bandwidth requirement for the links in the distribution network. Absent reliable video traffic data models for MPEG-2 format, we sample a large number of DVD-recorded movies to form a basis for randomly generated aggregate traffic streams. The aggregate traffic streams are used in a simulation experiment to measure the maximum transmission buffer occupancy for each given traffic stream for different transmission rates. Based on this simulation experiment, we derive an empirical transmission line provisioning function that guarantees delivery of all video frames without frame loss within a maximum frame delay tolerance. To illustrate the effectiveness of the proposed solution procedure for the bandwidth assignment problem, we solve to near optimality 570 small problem instances under three demand structures and 100 large problem instances with uniformly distributed demand.

W-CDMA network design

In this investigation, the W-CDMA network design problem is modelled as a discrete optimisation problem that maximises revenue net the cost of constructing base stations, Mobile Telephone Switching Offices (MTSOs) and the backbone network to connect base stations through MTSOs to the Public Switched Telephone Network (PSTN). The formulation results in a very large scale integer programming problem with up to 18,000 integer variables and 20,000 constraints. To solve this large scale integer programming problem, we develop a pair of models, one for the upper bound and one for the lower bound. The upper bound model relaxes integrality on some of the variables while the lower bound model uses a 5% optimality gap to achieve early termination. Additionally, we develop a heuristic procedure that can solve the largest problem instances very quickly with a small optimality gap. To demonstrate the efficiency of the proposed solution methods, problem instances were solved with five candidate MTSOs servicing some 11,000 simultaneous cellular phone sessions on a network with up to 160 base stations. In all instances, solutions guaranteed to be within 5% of optimality were obtained in less than an hour of CPU time.

Multi-dimensional credentialing using veiled certificates: Protecting privacy in the face of regulatory reporting requirements

Traditional certificates are designed to establish and document characteristics belonging to a specific individual, be it an identification number (i.e., social security number, drivers license number), a level of achievement (i.e., college degree, license to practice a profession), or membership status (i.e., company ID, trade union card). The digital certificate extends this concept into the electronic world, identifying and linking the certificate holder to a public encryption key that is subsequently used as a means of identification. Current identity certificates provide unique identification and tracking, however it is exactly these characteristics that have led to concerns over identity theft and privacy of personal information. The veiled certificate introduced in this paper addresses these issues by providing means of linking certificates from multiple certifying authorities while masking the users identity from non-authorized individuals and satisfying the regulatory need of unique, explicit identification. With the ability to be implemented within existing X.509 standards, veiled certification extends traditional digital certificates with features useful in combating identity theft and invasion of privacy.

Efficient Bandwidth in Multimedia Distribution Networks with Guaranteed Quality of Service

In spite of predictions to the contrary, video on demand service has yet to be-come a significant channel for distribution of audiovisual entertainment to consumers’ homes. The main reason for the delay in development in this market can be attributed to a lack of cost-efficient distribution channels for this type of transmissions. In this work, we examine the quality of service requirements for delivery of video on demand services and develop a new measure of bandwidth requirements for this type of network transmissions. A limited simulation experiment is performed with which we derive the overlay bandwidth requirements for a single movie stream viewed simultaneously by multiple consumers with randomly distributed starting times. We conclude that video on demand service can be offered at reasonable quality of service with relatively modest overlay network transmission capacity requirements.