Xavier Revés

Cross-layer scheduling strategy for UMTS downlink enhancement

This article describes the benefits of including cross-layer information in the scheduling mechanism of a UMTS downlink channel. In particular, the information obtained from the fast power control algorithm is used to properly schedule transmissions. A prioritization function that exploits the short-term channel variations is proposed. This strategy is shown to be a feasible approach to improve system performance in terms of capacity and delay. This enhancement is obtained as a benefit of intrinsic multi-user diversity. The proposal is applicable within the current UMTS radio resource management framework.

Software radios: unifying the reconfiguration process over heterogeneous platforms

Future radio transceivers supporting the software radio concept will provide increased features for radio access networks. However, the reconfiguration of radio equipment requires the existence of an architecture, a common framework, which allows the flexible management of software running on radio processors. Such a framework must take into account the heterogeneity of hardware devices and platforms for radio applications. Since the flexibility has a cost in terms of added overhead, a conceptually simple but efficient structure that allows powerful mechanisms to develop and deploy software radio applications is required. This paper describes our approach, the reasons that motivated it, and some implementation issues. The proposed framework is essentially based on four items: an abstraction layer which hides any platform-dependent issue, a simple time-driven software structure, a delimited interface format for software blocks which does not actually constrain communication, and a global time-reference mechanism to guarantee real-time behaviour.

Resource Modeling for a Joint Resource Management in Cognitive Radio

Cognitive radio characterizes an ambient aware and software-defined radio system that is capable to autonomously and intelligently adjust the system parameters. It has the potential to optimize the usage of all relevant resources for service- driven wireless communications. We identify four types of resources; these are the radio, the computing, and the radio and user application resources. This paper presents their modeling, including several models for each resource type. The modeling serves as the basis for a joint resource management in a cognitive radio system that may eventually trade-off one resource (type) against the other(s). Two approaches for such a management are presented: a distributed-cooperative and a centralized- integrated. We finally discuss the applicability and utility of the proposed models, and the potentials of a joint resource management in cognitive radio in terms of user satisfaction and revenues.

EVEREST testbed: QoS management evaluation in B3G networks

This paper describes the motivation, methodology and implementation approach of the testbed that has been developed in the framework of the EVEREST project. Such testbed is used for demonstrating some of the main concepts addressed within the project, concerning both: common radio resource management strategies and end-to-end QoS architectures and mechanisms for B3G systems based on the UMTS architecture. The complexity of the interaction between B3G systems and the user applications, while dealing with the QoS concept, pushes to develop this kind of emulation platforms, where algorithms and applications can/must be tested in realistic conditions, not achievable by means of off-line simulations

Software radio implementation of a DS-CDMA indoor subsystem based on FPGA devices

Software radio will have an important role in future terminal and base station definition. Although the ideal software radio architecture is highly restricted by technology, at present it is possible to build complex systems completely customised and reconfigurable using FPGA devices. They provide the designer with the possibility of modifying the hardware functional qualities without giving up high performance or using resources poorly. To check how important is this affirmation considering future wideband systems, a representative DS-CDMA subsystem has been built over an FPGA platform that allows fast reconfiguration of internal system blocks.

Computing Resource Management for SDR Platforms

Software defined radio (SDR) is an emerging technology that is based on the software implementation of the signal processing blocks found in a radio transceiver. The switch between radio access technologies may then be as easy as changing the software running on a future SDR terminal. SDR terminals refer to mobile equipment and base stations. These terminals will comprise general purpose processors, digital signal processors and/or reconfigurable logic devices. As a result, typical heterogeneous computing problems may appear in the SDR context. This article focuses on the mapping issue, discusses its relevance in software defined radio, and introduces an adequate mapping algorithm. The algorithm efficiently tackles the problem of mapping SDR function chains, i.e. signal processing blocks of a SDR transceiver, to heterogeneous processing platforms. We expose our approach, discuss its performance, present extensive simulation results and derive conclusions

FPGA's middleware for software defined radio applications

The division in several layers of the implementation of systems is a solution adopted to avoid complexity, provide flexibility and improve portability and code reusability through different hardware. Middleware (intermediate layer between two other layers) implementations are based on the use of increasingly high-level languages and application programming interfaces (API). The field programmable gate arrays (FPGA) world can also apply this approach to produce building blocks independent from hardware platforms and devices. This paper presents details of the implementation of a middleware, called platform and hardware abstraction layer (P-HAL) when applied to FPGA devices. It was specially designed for radio applications and allows designing specific functions independently of the hardware context where they are applied, thus providing flexibility to the so-called software radios employing FPGA devices.

Real-time emulation of RRM strategies for UMTS bearer services

This paper describes the implementation and the achieved capabilities of a real-time UMTS demonstrator developed within the framework of the IST ARROWS (advanced radio resource management on wireless services) project. Among the main goals of the ARROWS demonstrator are the evaluation of radio resource management (RRM) strategies in a UMTS network and the analysis of the impact that these strategies have on the end-to-end behaviour of multimedia applications with quality of service (QoS) requirements. The demonstrator platform is built over a network of personal computers and copes with the real-time restrictions imposed by the emulation of UMTS transport bearers. After providing a brief description of the developed HW/SW platform, the different approaches taken to emulate the main functions included in the test-bed are described, together with some of the achieved capabilities in terms of implemented RRM algorithms, supported scenarios, lower layer emulation and included services and applications with QoS requirements.

Integrated Resource Management in Cognitive Radio

The todays radio environment features a heterogeneous mix of radio access technologies. The technology that facilitates accessing different air interfaces at different times with the same radio equipment is known as software-defined radio (SDR). A cognitive radio system manages the operational modes of SDR equipment as a function of the radio environment. This paper introduces a novel approach to resource management in cognitive radio. We coin it integrated resource management (IRM) because it integrates the management of radio and computing resources. The corresponding system then features two cognitive cycles, the computing cycle and the radio cycle. We demonstrate the suitability of our proposal in a heterogeneous radio and computing scenario. In particular, simulation results show that two simple IRM algorithms can considerably reduce the number of lost user sessions due to inappropriate reconfiguration decisions. The paper concludes that such an integrated resource management, when embedded in a cognitive radio system, can intelligently distribute the radio and computing loads, while adapting to environmental changes.

Cooperative Resource Management in Cognitive Radio

Cognitive radio is generally understood as an intelligent wireless communication system aiming at the efficient utilization of radio resources. We argue for the extension of its scope to also address the management of computing resources, including processing and bandwidth capacities of SDR platforms, and present a cooperative resource management framework: The joint radio resource management (JRRM) and the computing resources management (CRM) entities interchange information to cooperatively decide if and what kind of terminal reconfiguration would be the most appropriate in each situation. Therefore, the cognitive radio system continuously observes the radio and the computing environments. We discuss a realistic case study and present a simple CRM algorithm. Simulation results show that such a cooperative resource management approach can achieve important improvements over the JRRM by itself. In particular, our proposal considerably reduces the number of lost user sessions due to inappropriate reconfiguration decisions and, thus, serves more wireless users.