Shyamalie Thilakawardana

Spectrum Sharing for WINNER Radio Access Networks

This paper presents the concept of spectrum sharing in connection to beyond 3rd generation (B3G) systems. Inter-system spectrum sharing mechanisms are summarised and classified depending on their coordination capabilities and the relative priorities between the systems involved in the sharing. Novel radio resource management (RRM) functionalities for coordinating the sharing of the spectrum with legacy systems and other B3G radio access networks (RANs) are outlined to permit the efficient implementation of spectrum sharing. These B3G spectrum sharing RRM functionalities are proposed in the context of the European IST WINNER project. Capabilities to share spectrum with other radio access systems will significantly increase the efficiency of the WINNER system as well as the compatibility with legacy systems. The RRM architecture enables WINNER systems to benefit from the most important aspects of the envisioned spectrum sharing. Spectrum sharing provides the WINNER system with new spectrum access possibilities, facilitating flexible deployment, usage and a gradual evolution of the system in coexistence with legacy systems

Cross-Layer Design Approach for Multicast Scheduling over Satellite Networks

In this paper, we propose a cross-layer design approach using perfect prediction-based wireless channel conditions to improve the performance of a multicast packet scheduler over satellite network environments in the downlink transmission. The satellite channels are modeled in single and multi-environments with different values of Rician K factors and its corresponding elevation angle, mean and standard deviation values. From simulation results, the channel state information (CSI) of each user in the multicast group is considered and becomes the condition for the transmission of the multicast packet. We assume the users suffer slow-varying channels such that the CSI update is within the time interval for slot allocation. The result indicates that a positive performance improvement is gained by adopting a cross-layer-design approach in a fading environment. By obtaining the CSI before transmitting multicast flows, the approach reduces unnecessary transmission of background traffic and hence reduces unnecessary resource allocation and retransmission requests

Network-centric user assignment in the next generation mobile networks

This letter addresses the user assignment problem for multimedia streaming applications in heterogeneous multicast-enabled wireless networks using a network-centric strategy. The optimal problem is mathematically formulated and proven to be non-deterministic polynomial-time (NP)-hard. An efficient heuristic algorithm is then proposed to find sub-optimal solutions in practical systems. Simulation results demonstrate the improved performance of this heuristic in comparison to a conventional user-centric algorithm

Dynamic Spectrum Sharing Algorithm Between Two UMTS Operators in the UMTS Extension Band

This paper proposes a fast scale spectrum sharing algorithm to exploit instantaneous spectrum use during the peak hour between two Universal Mobile Telecommunication System (UMTS) operators. The algorithm is based on a joint call admission framework between the two UMTS operators. The process is both coordinated and cooperative. An intelligent network agent is used. A simulation platform has been developed in order to evaluate the performance of the algorithm. The performance of the fast-scale Dynamic Spectrum Allocation (DSA) algorithm is compared with Fixed Spectrum Allocation (FSA) when no spectrum sharing takes place. The impact of uniform and non-uniform traffic on the performance of the algorithm has been investigated. The non-uniform traffic case includes hotspot cells which have higher call volume. The results show a decrease in the spectrum sharing gain from 5% (Uniform traffic) to 2% (Non-Uniform traffic) due to these hotspot cells.

WINNER Spectrum Sharing with Fixed Satellite Services

The IST 6 framework WINNER project defines spectrum sharing techniques for future wireless communication systems. This paper addresses spectrum sharing capabilities between different radio technologies. More particularly, spectrum sharing between WINNER system and the Fixed Satellite Service (FSS) community is at stake. The goal is to efficiently share the spectrum without causing harmful interference towards the primary system (i.e., FSS). A power assignment mechanism for the coexistence is proposed where different power levels are assigned in the cellular network in the areas surrounding the FSS system. Simulation results for the coexistence between both systems is carried out where the spectrum used by the WINNER system is punctured for the transmission of the primary FSS system. Finally, the results show that spectrum utilization is significantly improved.

Efficient call admission control and scheduling technique for GPRS using genetic algorithms

In future wireless packet networks, it is anticipated that a wide variety of data applications, ranging from WWW browsing to Email, and real time services like packetized voice and videoconference will be supported with varying levels of QoS. Therefore there is a need for packet and service scheduling schemes that effectively provide QoS guarantees and also are simple to implement. This paper describes a novel dynamic admission control and scheduling technique based on genetic algorithms, focusing on static and dynamic parameters of service classes. A performance comparison of this technique on a GPRS system is evaluated against data services and also a traffic mix comprising voice and data.

Inter-Operator Dynamic Spectrum Selection in UMTS

Dynamic and flexible spectrum management schemes can improve spectrum utilization efficiency and hence are promising approaches to satisfy the increasing demand for radio spectrum. This work investigates the possibility for competing network operators to partially cooperate without any operational information exchange and to exploit the instantaneous opportunities for sharing which appear within each network. Under the proposed two novel dynamic spectrum selection (DSS) protocols all handsets have a primitive cognitive ability in order to enable multi-operator functionalities for inter-operator DSS. The worst case scenario for voice traffic where two networks with the same radio access technology (RAT) having an entirely correlated average traffic distribution (same capacity demand) during the busy hour is investigated. It has been shown through a UMTS system level simulator that the suggested protocols can increase each operators throughput by up to 10% compared to the conventional fixed spectrum allocation (FSA) scheme, and hence better spectrum utilization can be accomplished. Also, the effects of queuing incoming and handover calls before blocking or dropping them on DSS gains have been investigated. The results suggest an increase of up to 25% in throughput against the FSA if the DSS protocol and the queuing scheme are implemented.

Performance of Multicast File Transfer Protocol (MFTP) over geostationary satellite systems with DAMA uplinks

Their inherent broadcasting capabilities over very large geographical areas make satellite systems one of the most effective vehicles for multicast service delivery. Recent advances in spotbeam antennas and high-power platforms further accentuate the suitability of satellite systems as multicasting tools. The focus of this article is reliable multicast service delivery via geostationary satellite systems. Starburst MFTP is a feedback-based multicast transport protocol that is distinct from other such protocols in that it defers the retransmission of lost data until the end of the transmission of the complete data product. In contrast to other multicast transport protocols, MFTP retransmission strategy does not interrupt the fresh data transmission with the retransmissions of older segments. Thanks to this feature, receivers enjoying favourable channel conditions do not suffer from unnecessarily extended transfer delays due to those receivers that experience bad channel conditions. Existing research studies on MFTPs performance over satellite systems assume fixed-capacity satellite uplink channels dedicated to individual clients on the return link. Such fixed-assignment uplink access mechanisms are considered to be too wasteful uses of uplink resources for the sporadic and thin feedback traffic generated by MFTP clients. Indeed, such mechanisms may prematurely limit the scalability of MFTP as the multicast client population size grows. In contrast, the reference satellite system considered in this article employs demand-assignment multiple access (DAMA) with contention-based request signalling on the uplink. DAMA MAC (Medium Access Control) protocols in satellite systems are well-known in the literature for their improved resource utilisation and scalability features. Moreover, DAMA forms the basis for the uplink access mechanisms in prominent satellite networks such as Inmarsats BGAN (Broadband Global Area Network), and return link specifications such as ETSI DVB-RCS, However, in comparison with fixed-assignment uplink access mechanisms, DAMA protocols may introduce unpredictable delays for MFTP feedback messages on the return link. Collisions among capacity requests on the contention channel, temporary lack of capacity on the reservation channel, and random transmission errors on the uplink are the potential causes of such delays, This article presents the results of a system-level simulation analysis of MFTP over a DAMA GEO satellite system with contention-based request channels. Inmarsats BGAN system was selected as the reference architecture for analyses. The simulator implements the full interaction between the MFTP server and MFTP clients overlaid on top of the Inmarsat BGAN uplink access mechanism. The analyses aim to evaluate and optimise MFTP performance in Inmarsat BGAN system in terms of transfer delay and system throughput as a function of available capacity, client population size, data product size, channel error characteristics, and MFTP protocol settings. Copyright @ 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Effect of service modeling on medium access control performance

Due to the tractability in analytical methods exponential burst distributions are more common in service modeling literature. However, previous traffic measurements findings argue heavy tailed distributions such as Pareto represents burst sizes in WWW browsing and Cauchy distributed burst sizes in e-mail sessions. The effect of long range dependence (LRD) introduced by these heavy tailed distributions results in self similarity in the aggregate traffic. The impact of self similarity is significant in the area of queue delay performance characteristics. This work addresses the issues of service modeling in medium access control (MAC) performance compared to traditional exponential session distributions against the above mentioned distributions in WWW browsing and e-mail sessions applied to an example GPRS MAC system. The results conclude high delay in Cauchy e-mail connection sizes and Pareto WWW burst sessions compared to exponential connections/bursts. Also, once looking in to the matter it can be seen that this delay is mainly due to the congestion caused by different types of bursts/connection distributions. Therefore the bursty traffic such as WWW browsing which demonstrates self similarity at the aggregate level influence the MAC protocol performance greater than in traditional traffic models.

The impact of queuing and call setup delays on UMTS spectrum sharing algorithm

This paper proposes spectrum sharing algorithms between two Universal Mobile Telecommunication System (UMTS) operators in order to improve underutilization of the spectrum. Furthermore, it investigates the call setup delays present in the proposed Fixed Spectrum Allocation (FSA) and Dynamic Spectrum Allocation (DSA) schemes, and the associated messages involved. The spectrum efficiency gains of the proposed algorithms are obtained by simulations. The impact of the queuing and call setup messages on the overall algorithm performance is also discussed. It is shown that due to the proposed techniques, spectrum sharing gain of about three percent (3%) is possible at an operating point of 98% satisfaction ratio, when the impact of the call setup messages is considered.