Nikos Dimitriou

Downlink OFDMA Resource Allocation Under Partial Channel State Information

The problem of resource allocation (RA) in a downlink OFDMA system is examined under the realistic assumption of imperfect channel state information (CSI) at the base station. In this case, there is a nonzero outage probability that the assigned rate at a particular subcarrier/user pair will not be supported by the true channel realization, which may lead to a significant waste of the systems available resources. It is therefore necessary to obtain RA algorithms that take into account the effect of imperfect CSI. By exploiting the statistical description of the imperfect CSI, various algorithms are proposed that tradeoff complexity versus performance, aiming at maximizing the systems successfully transmitted rate.

Satellite radio interface and radio resource management strategy for the delivery of multicast/broadcast services via an integrated satellite-terrestrial system

A variety of hybrid systems combining third-generation mobile communication networks with broadcast systems have been proposed for the delivery of multimedia broadcast multicast services (MBMS) to mobile users. The article discusses one of these alternatives, which involves the use of a geostationary satellite component for MBMS delivery. In particular, it proposes a radio access scheme for the satellite component of the system that features maximum commonalities with the standardized T-UMTS WCDMA-based interface. The ultimate advantages of this approach are more efficient delivery of MBMS as far as the mobile network operator is concerned. The required adaptations at the interface layers are described, and the radio resource management strategy that fulfills the particular requirements of the satellite system is presented.

On the use of radio environment maps for interference management in heterogeneous networks

This article addresses the use of REMs to support interference management optimization in heterogeneous networks composed of cells of different sizes and including both cellular and non-cellular (e.g. WiFi) technologies. After presenting a general architecture for including REM databases in different network entities, the article analyzes the achievable benefits in relation to specific interference management techniques, including a discussion on practical considerations such as information exchange requirements, REM ownership, and security aspects. Finally, several research directions derived from the proposed framework are identified.

S-UMTS access network for broadcast and multicast service delivery: the SATIN approach

This paper proposes a complete satellite access network solution for multimedia broadcast multicast service (MBMS) delivery based on T-UMTS standards. First, the benefits of MBMS delivery via satellite (SAT-MBMS) for both S/T-UMTS network operators are shown with market and business analysis. A new integrated S/T-UMTS architecture for MBMS delivery is proposed featuring an intermediate module repeater (IMR) for coverage of urban areas. The architectural options of IMR and terminals are discussed considering the relevant cost and complexity. The IMR propagation channel conditions are investigated and a new propagation channel model is proposed. The potential of advanced coding schemes such as the layered coding technique to tackle the channel variations in broadcast/multicast environment is outlined. The functional and protocol architecture are defined along with the interface between the satellite access network and the UMTS core network. Required modifications on the terrestrial access scheme sub-layers to support MBMS data are investigated and the relevant logical, transport and physical channels are selected. Based on the channel selection and the point-to-multipoint service nature, we define a generic radio resource management (RRM) strategy that takes into account both QoS and GoS requirements. The efficiency of the proposed solutions is evaluated in the presented simulation results, advocating the feasibility of the overall approach. Copyright

Femtocell downlink power control based on Radio Environment Maps

The paper investigates the use of Radio Environment Maps (REMs) as a tool for Interference Management (IM) in two-tier cellular networks comprising macro- and femto-cells. The REMs are databases that provide, through different instances distributed over network elements, a variety of network- and user-related context information for improving IM and Radio Resource Management (RRM) procedures. In this context, the focus in this paper is to present the benefit of using REM information on practical power control schemes for the Femtocell downlink transmission in co-channel two-tier deployment.

Flexible radio: a framework for optimized multimodal operation via dynamic signal design

The increasing need for multimodal terminals that adjust their configuration on the fly in order to meet the required quality of service (QoS), under various channel/system scenarios, creates the need for flexible architectures that are capable of performing such actions. The paper focuses on the concept of flexible/reconfigurable radio systems and especially on the elements of flexibility residing in the PHYsical layer (PHY). It introduces the various ways in which a reconfigurable transceiver can be used to provide multistandard capabilities, channel adaptivity, and user/service personalization. It describes specific tools developed within two IST projects aiming at such flexible transceiver architectures. Finally, a specific example of a mode-selection algorithmic architecture is presented which incorporates all the proposed tools and, therefore, illustrates a baseband flexibility mechanism.

Smart femto-cell controller based distributed cognitive pilot channel

This paper presents an extension of the Cognitive Pilot Channel (CPC) concept to the case of a distributed version thereof (namely, DCPC), and demonstrates a potential instantiation of this concept in the design of Smart Femto-Cell Controllers (SFC-C) for handling the management of co-existing homogeneous or heterogeneous networks. Instead of covering the various networks by a single CPC, the novel idea consists in deploying the CPC transmission in a distributed way within each of the individual Smart Femto Cell (SFC) controlled Composite Networks (CNs), an example of which can be a heterogeneous home or business deployment including the collection of a Femto- Cell Base Station (FC-BS), a Wireless LAN (WLAN) Access Point (AP), a ZigBee network controller, a Bluetooth network controller, etc. A typical implementation of this concept leads to an integration of the DCPC transmitter into a SFC which consists of the FC-BS for provision of cellular access and the SFC-C for network management and DCPC provision. In this case, the SFC owner is able to manage the attached composite network by providing suitable context and policy information within the DCPC. The paper furthermore introduces intra-network and inter-network interference scenarios and explains how the DCPC concept allows the introduction of corresponding interference management mechanisms.

Dynamic radio resource and interference management for MIMO-OFDMA mobile broadband wireless access systems

A multi-user multi-cell Multiple-Input Multiple Output/Orthogonal Frequency Division Multiple Access (MIMO/OFDMA) system for next generation Broadband Wireless Access (BWA) networks is studied, in which the Base Station (BS) or evolved Node B (eNB) has only knowledge of the statistics of the channel. A combination of MIMO and OFDMA could increase the spectral efficiency in a high speed network. We investigate methods with scalable channel feedback and we analyze the trade off between the amount of Channel State Information (CSI) to the transmitter and the system performance. The proposed schemes with limited feedback are combined with other cell interference reduction strategies based on cooperation for improving the performance of a coordinated multi-cell system under very dynamic conditions like high velocity and fast fading. Simulation results demonstrate that substantial gain is obtained by the proposed schemes which take advantage of the statistical information of the highly dynamic channel.

Cooperative schemes for path establishment in mobile ad-hoc networks under shadow-fading

The performance of routing protocols for multi-hop path-establishment in Mobile Ad-hoc NETworks (MANET) is examined when the individual radio links undergo shadow fading of parameterized severity. Such propagation modeling is typical of ground-level networking along with node mobility. The metrics of main interest are the probability of having a reliable multi-hop path plus the temporal statistics of such availability under a Markovian model. Such availability is an indicator for the suitability of the network to carry delay-sensitive applications (push-to-talk voice, streaming video) in uninterrupted manner. It is shown that high levels of diversity are necessary in such adverse environments, as obtained either by multiple independent paths or via concurrent cooperative transmission. Analytical and simulation comparisons of typical routing options are presented on the above metrics, plus on the required nodal engagement for supporting such diversity.

Downlink Mobile OFDMA Resource Allocation with Minimum User Rate Requests

The problem of resource allocation (RA) in a downlink OFDMA system with minimum user rate requests is examined under the realistic scenario of partial (imperfect) channel state information (CSI) at the base station. The challenge in this setting is the non-zero probability of outage events which may lead to significant performance degradation if algorithms assuming perfect CSI are utilized. In this paper the statistical description of the partial CSI is incorporated for deriving an (optimal) RA algorithm as the solution of an appropriate constrained optimization problem. Simplifications of the algorithm are utilized for significant complexity reduction with the additional property of allowing the system to adapt on-the-fly to time-varying minimum user rate requests.