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Flexible relay wireless OFDM-based networks

Résultats exploitables

The first outcome in Fireworks has been to identify a common framework for inter-workpackage communication and a common ground for simulations. This has been achieved with the definition of the terminology, 5 target scenarios, 5 prototype scenarios, 5 traffic models, and 11 assessment criteria. Specifically, types of devices were clarified (Multihop BS, RS, SS, Enhanced Mesh AP) and the associated deployment and prototyping scenarios (Rural, City centre, Office, etc) with associated simulation parameters (e.g. typical cell sizes, devices powers, etc) were described. Using the scenario specifications, the system requirements of the various devices (e.g. standard compliance), the expected performance requirements and the regulatory constraints (bandwidth, mobility) are drawn. The defined requirements are based on a checklist provided by the EU IDABC program divided in the following Fireworks categories: system capability requirements (performance, cost, QoS…), system architecture requirements (functional requirements, node characteristics …) and operational characteristics requirements (system management at installation and maintenance, regulatory). From simulations, a business case analysis of the Fireworks relay-based system has been completed. Initially, the market and service assumptions for the business case have been established including the identification of the market segments (Broadband Wireless Access for Residential and SOHO, SMEs) along with their associated demographics (e.g. densities in urban, sub-urban and rural areas). A common set of assumptions case has been established on traffic (service penetration rate, activity factors, and generated traffic), device characteristics (transmit powers, number of antennas, topology, etc…) and, in particular, on the key technical features of the Fireworks system (OFDMA, multi-hop, cooperation, SDMA). They have been integrated to the financial and network simulation tools in order to complete the business case. A breakdown of CAPEX and OPEX has been completed. It was observed that relaying is cost-efficient only in coverage-limited scenarios where the CAPEX in rural deployments or during the early stages of urban deployments is reduced. From the first activity of the conceptual study of the project, an analysis of the impact of the relay position on the capacity and coverage of cellular multihop networks has been completed. The evaluation of cooperative relaying protocols in different propagation environments shows that large BS-RS capacity required to achieve significant throughput gain with cooperative relaying (e.g., LOS links, dedicated channel) while complex cooperative protocol seem to provide the best performance. The study of frequency- and time-domain forwarding in relaying systems served to identify the appropriate length of TDD guard time and the DL-UL, Tx-Rx synchronization issues. From the comparison, larger mutual capacity (in bps/Hz) is observed for FDD-based protocols. Additionally, the capacity increase due to SDMA in cellular WiMAX networks has been evaluated for the development of strategies to use SDMA in multihop deployments. Also, the impact of mobile subscriber stations in multihop deployment has been studied. Similarly, the impact of channel state knowledge at the relay station for cooperative amplify-and-forward protocols has been evaluated. Finally, a comparative study of different cooperative protocols, based on Decode-and-Forward, Amplify-and-Forward and Compress-and-Forward has been completed. Development, implementation and performance evaluation of a combined TD-/SDMA Medium Access Strategies to Support Relay-Enhanced Broadband Cells has been carried out. A mechanism for interference reduction by means of space-time sectorization and other approaches of cooperation across base stations and/or relay stations has been developed. Novel algorithms such as Integrated Sub-carrier, Bit and Power Allocation algorithm and an Integrated Radio Resource Allocation algorithm for OFDMA relaying systems have been studied and evaluated. Several radio resource allocation techniques based on capacity of cooperative relaying protocols for a multiuser setup have been investigated such as RRM techniques for D&F TDMA, RRM techniques for D&F TDMA/OFDMA and Spatial-reuse cooperative multiuser access (A&F). The multihop subframe concept with SDD operation of sub cells and several grouping strategies for a Hierarchical SDMA/TDMA scheduling process have been analysed. Also, the development and evaluation of concepts for: optimum positioning of fixed relays, RRM in OFDMA, AF with spatial reuse, and RRM for multihop AMC-OFDMA under PUSC/FUSC has been completed. Finally, handover algorithms in multihop developments have lead to the definition of means to optimize handover. In FIREWORKS, coexistence mechanisms for enabling an operation of IEEE 802.16 in spectrum shared with 802.11(a) have been developed following the development, implementation and evaluation of the Hot Zone concept for a hybrid MAN-LAN network. An analysis of the WiMAX/WiFi MAC overhead, range, and capacities has been completed. Also, a link level simulator for the evaluation of cooperative relaying has been produced. System level simulators for higher layer protocol optimization, MAC-PHY cross-layer issues and relaying functionality, and hybrid LAN MAN systems have been implemented while a MATLAB framework for mobility issues investigations in multihop deployments has been established.

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