György Miklós

Design aspects of network assisted device-to-device communications

Device-to-device (D2D) communications underlaying a cellular infrastructure has been proposed as a means of taking advantage of the physical proximity of communicating devices, increasing resource utilization, and improving cellular coverage. Relative to the traditional cellular methods, there is a need to design new peer discovery methods, physical layer procedures, and radio resource management algorithms that help realize the potential advantages of D2D communications. In this article we use the 3GPP Long Term Evolution system as a baseline for D2D design, review some of the key design challenges, and propose solution approaches that allow cellular devices and D2D pairs to share spectrum resources and thereby increase the spectrum and energy efficiency of traditional cellular networks. Simulation results illustrate the viability of the proposed design.

Performance aspects of Bluetooth scatternet formation

The emergence of Bluetooth as a default radio interface allows handheld electronic devices to be rapidly interconnected into ad hoc networks. Bluetooth allows large numbers of piconets to form a scatternet using designated nodes that participate in multiple piconets. We study the performance implications of forming scatternets from piconets. The contribution of our work is twofold. First, we establish a network model and define performance metrics for Bluetooth scatternets. Our model is derived from constraints specific to the Bluetooth technology, but is sufficiently abstract to relate to the more general field of ad hoc networking. Second, using a number of simulation studies, we relate scatternet parameters to performance metrics and discover correlations between scatternet formation rules and performance. These results reveal some important performance implications of scatternet design decisions and can serve as guidelines for future scatternet formation algorithms.

A pseudo random coordinated scheduling algorithm for Bluetooth scatternets

The emergence of Bluetooth as a default radio interface allows handheld devices to be rapidly interconnected into ad hoc networks. Bluetooth allows large numbers of piconets to form a scatternet using designated nodes that participate in multiple piconets. A unit that participates in multiple piconets can serve as a bridge and forwards traffic between neighbouring piconets. Since a Bluetooth unit can transmit or receive in only one piconet at a time, a bridging unit has to share its time among the different piconets. To schedule communication with bridging nodes one must take into account their availability in the different piconets, which represents a difficult, scatternet wide coordination problem and can be an important performance bottleneck in buillding scatternets. In this paper we propose the Pseudo-Random Coordinated Scatternet Scheduling (PCSS) algorithm to perform the scheduling of both intra- and inter-piconet communication. In this algorithm Bluetooth nodes assign meeting points with their peers such that the sequence of meeting points follows a pseudo random process that is different for each pair of nodes. The uniqueness of the pseudo random sequence guarantees that the meeting points with different peers the node will collide only occasionally. This removes the need for explicit information exchange between peer devices, which is a major advantage of the algorithm. The lack of explicit signaling between Bluetooth nodes makes it easy to deploy the PCSS algorithm in Bluetooth devices, while conformance to the current Bluetooth specification is also maintained. To assess the performance of the algorithm we define two reference case schedulers and perform simulations in a number of scenarios where we compare the performance of PCSS to the performance of the reference schedulers

Automatic repeat request (ARQ) mechanism in HIPERLAN/2

A WLAN standard, called HIPERLAN/2 (H/2), is currently defined in the ETSI/BRAN project. The standard can provide wireless access to several fixed networks with high data rate (up to 54 Mbps) in 5 GHz frequency range. To guarantee robustness in various types of radio channels a selective repeat ARQ with partial bitmap SRPB has been adopted as an error control mode. The SRPB ARQ mechanism was selected due to efficient retransmissions and low overhead of ARQ acknowledgements. The dynamic assignment ARQ acknowledgement opportunities integrated in SRPB can reduce the delay of acknowledgements and enhance the throughput. In this paper we describe the SRPB ARQ mechanism in H/2 and show the simulated performance.

Peakedness characterization in teletraffic

The bursty nature of traffic over many time scales is one of the most challenging characteristics of high speed networks. In this paper we deal with the generalized peakedness as a promising candidate measure of this poorly understood phenomenon. An extension of the framework of the theory of generalized peakedness in discrete time with the applications for the most important traffic models are developed and the results are demonstrated in the paper. A new model fitting technique is also given in this framework with examples. Finally, the engineering aspects of the measurement of peakedness and applications for various real traffic (MPEG video, aggregated ATM, Ethernet) are presented.

A novel scheme to interconnect multiple frequency hopping channels into an ad hoc network

Frequency hopping radios have very attractive features to be used as PAN links, but their use in ad hoc networking is problematic because of the difficulty to synchronize the channels and coordinate transmission attempts. We propose a novel mechanism to interconnect multiple frequency hopping channels into an ad hoc network based on an adapted version of CSMA/CA. The performance of the proposal is investigated using analytical and simulation tools. By using multiple channels, we achieve significant improvement in aggregate throughput despite the penalty of switching between channels. We show how this performance penalty can be decreased by grouping devices based on the traffic pattern.

Distributed Fair Bandwidth Allocation of a Wireless Base Station

We present a novel approach to wireless fair scheduling in a distributed architecture. Our scheme is based on a simple extension of wireline fair scheduling by compensation for lost capacity after the losses occur. In addition, the scheduler can give limited compensation for unused capacity. This provides an incentive for users of the location-dependent wireless channel to optimize their channel usage on their own. In this way the scheduler does not need to be aware of the state of the wireless channel for each user. We present a mechanism for user behaviour and illustrate our scheme by simulation results.

Mobile Network Evolution -- The Return of the Pipe

The mobile network evolution from second generation to third generation systems has opened possibilities for inclusion of new technologies both in the network infrastructure as well as on the radio access. Within this paper, we concentrate on the evolution of the network infrastructure towards a future mobile network that balances the demand for increased flexibility with the necessity of limiting system complexity. Based on existing architectures, to lower complexity such as layered architecture for the core network and mobile packet backbone, we describe one possible evolution path for the control layer. Our approach is a step towards a control space that includes packetpipe control functions for a multitude of packetpipes. Such control function needs to be supported in the heterogeneous networks of today and the future.