Lóránt Farkas

Indoor base station location optimization using genetic algorithms

There is a growing interest in providing and improving radio coverage for mobile phones and wireless LANs inside buildings. The need of such coverage appears mainly in office buildings, shopping malls, train stations where many subscribers are placed. The cost of cellular systems and also the one of indoor wireless systems depend highly on the number of base stations required to achieve the desired coverage for a given level of field strength.

Predictive complex event processing: a conceptual framework for combining complex event processing and predictive analytics

Complex Event Processing deals with the detection of complex events based on rules and patterns defined by domain experts. Many complex events require real-time detection in order to have enough time for appropriate reactions. However, there are several events (e.g. credit card fraud) that should be prevented proactively before they occur, not just responded after they happened. In this paper, we briefly describe Complex Event Processing (CEP) and Predictive Analytics (PA). Afterwards, we focus on a major future direction of CEP, namely the inclusion of PA technologies into CEP tools and applications. Involving PA opens a wide range of possibilities in several application fields. However, we have observed that only few solutions apply PA techniques. In this paper, we define a conceptual framework which combines CEP and PA and which can be the basis of generic design pattern in the future. The conceptual framework is demonstrated in a proof--of--concept experiment. Finally we provide the results and lessons learned.

Peer-to-peer protocol evaluation in topologies resembling wireless networks. An experiment with Gnutella query engine

Peer-tepeer (P2P) protocols implemented in wireless networks and mixed scenarios would generate new applications and value added services. In order to analyze the performance of such protocols the specific topologies of current and future wireless networks should be taken into account. In our paper we analyze the performance of a Gnutella-type protocol query engine on random mesh (Random), semi-random mesh (Semi), connected stars (ConStan) and connected mesh (ConMesh) application layer network topologies. In addition we discuss and simulate for the considered topologies the effect of adaptive time-twlive (TTL) techniques. We take into account in our analysis the document replication phenomenon. Within this paper we limit ourselves to the simulation of static network topologies. The results of this study show that Semi and ConStan are the most useful topologies. Semi is the hest topology for heterogeneous devices, e.g. all of the nodes are mobile phones. ConStars is useful when the network consists of devices with dilferent capabilities, e.g. mobile phones and PC-s. If the node degrees are chosen appropriately the bandwidth needs can reasonably small making content sharing peer-twpeer applications feasible in pure wireless networks and mixed scenarios.

3G base station positioning using simulated annealing

During the planning of an UMTS radio network, there is a natural need for a base station positioning procedure. Good coverage at an acceptable level of network installation and maintaining costs, low interference and uniform interface load are the main requirements. In this paper we present an approach based on simulated annealing.

P2P applications on smart phones using cellular communications

In this paper we describe four P2P applications developed for smart phones, ranging from distributed computing to content sharing and search in closed and open user groups. Their common feature relies in the communication interface which has been cellular data transmission (SMS, HSCSD, respectively GPRS). Through our examples we highlight various aspects that application development on smart phones has to take into account, such as traffic efficiency, CPU load and social awareness. We discuss our main observations related to the experiments and highlight some promising directions for future mobile P2P applications. The discussed set of applications developed by us in the period between 2001-2005 cover the areas of distributed computing, large-scale content sharing in open communities, content sharing in closed groups, respectively keyword search in a social network of phones

Complex event processing synergies with predictive analytics

For Complex Event Processing (CEP), the synergy with Predictive Analytics (PA) is a promising research direction. In this paper we focus on the inclusion of PA technologies into CEP applications. Involving PA opens a wide range of possibilities in several application fields. However, we have observed that only a few CEP solutions apply PA techniques. We extended a CEP solution with predictive capabilities, defined the key aspects of the combination of these techniques, and summarized how CEP and PA could gain from the joint solution. Our approach is demonstrated in a proof-of-concept experiment and simulation results are provided.

Capacity regions of discrete asynchronous multiple access channels

Motivated by the importance of asynchronous multiple access channels we give an exact formalization. This formalization admits different distributions on delays. The two classical settings when the delay is uniformly distributed and when it is bounded are discussed as special cases of this model. Our method also allows for the analysis of a so far unexplored class of models, where the known distribution of the delay has a special form, leading to new interesting capacity regions.

Search engine for phonebook-based smart phone networks

Search engines generally lack the trust and personalization dimension. The outcomes of the search are not socially relevant: they often reflect only the content popularity based on lookup tables gathered by search robots. In order to obtain personalization and social relevance, in other words, to bring the search outcome closer to a common human perception of value and reliability, the search database itself could be personalized. One possible method to obtain personalization is through the social neighborhood of the searcher. An enabler for the personalization is the phonebook stored in mobile phones. The group of mobile phonebooks can create an infrastructure for a peer-to-peer search network with a social dimension. In order to demonstrate this concept our work introduces a novel search and recommender engine and application for phonebook-based smart phone networks. The concept has been implemented on the Symbian Series 60 platform over GSM using short message exchange. The efficiency of the search and recommendation system is also analyzed.

Random access and source-channel coding error exponents for Multiple Access Channels

A new universal coding/decoding scheme for random access with collision detection is given in case of two senders. The result is used to give achievable joint source-channel coding error exponents for multiple access channel and independent sources. In a modified model admitting zero rate communication between the senders, an improved exponent is derived, of form similar to Csiszárs joint source-channel exponent for the one-sender case.

Sharing the Experience with Mobile Video: A Student Community Trial

To understand the technical feasibility and user perception of mobile video, we conducted a two-week trial where a student community used mobile phone and web technologies to share the events of a campus festival. The questions we investigated included the capability of contemporary smart phones to capture and share the events via real time and stored video; the usage patterns that arise within mobile video community; and the social connections between shooters and viewers. Outcomes on the technical level indicate that challenges remain. The bandwidth of 3G cellular connections limits the quality of live videos and video transfer via public WLAN networks is unreliable causing lost connections. The best results today can be achieved by sending the captured videos from mobile phones to the server in the background and providing video-on-demand rather than live video service. The observed consumption patterns show that freshness of the videos is the least important selection factor while manual and automatic textual tagging is important. Seamless integration of video sharing to camera application would improve the user experience.