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Project: Cooperative and Antenna Diversity for Broadband Wireless Networks

Acronym: CADWIN
Main Objective:
Wireless services are of great economic and social value and will be one of the enablers of the so-called information society. It is envisioned that among the multiple networks/services that will be part of what is commonly termed as 4G, we will have a broadband component, where spectrum efficiency will be a premium. This means that the terminals/access points will need to explore in a “quasi-optimal” way all the dimensions provided by the space/time and frequency domains of the radio channels. Diversity is inherent and well known in the physical layer and either time, frequency, space has been used to combat the fading by trying to stabilize the channel. Diversity can also be achieved in the MAC or higher layer, which is termed network diversity, which can be divided in multiuser diversity (by scheduling or routing) and cooperative diversity (by cooperative transmission). While research concerning the classical forms of diversity has already taken a very practical flavour with proposals/technological evaluation and integration, the know-how to exploit the benefits brought by the cooperative dimension is still far behind and also the understanding of the impact it may have on wireless network planning. These provided the main impetus for this project proposal whose key objectives are:
Definition, evaluation and validation of techniques exploiting channels diversity and cooperation between users in order to enable the high bit rates targeted in the broadband component of future wireless systems; improve the power and spectrum efficiencies of the existing OFDM-based wireless systems and improving and/or extending coverage and fairness. Most of the research work in this area have assumed dedicated relays (fixed or nomadic), while the CADWIN project will also consider relaying functionalities at the MT. To reach these main goals, specific research objectives are:
•Design and evaluation of practical VMIMO or distributed coding algorithms. In a first phase we will start with space-time/frequency block codes designed for co-located antennas, which will be evaluated in a distributed environment. In a second phase, specific and optimized solutions will be proposed and investigated.
•Design and evaluation of practical distributed precoding algorithms considering different levels of the channel state information available at the transmitter (BS in the downlink), relay and destination (MT in the Downlink). Precoding algorithms to enable cooperation between base stations to provide intercell interference cancellation will also be considered.
•Design and evaluation of joint distributed precoding and space-frequency/time coding algorithms. In a first phase the concepts of distributed precoding and coding are considered separately, while in a second phase the researchers working on the two topics will consider the optimized joint precoding/coding schemes.
•Design and evaluation of channel estimation algorithms. In a first phase we will evaluate the classical channel estimation algorithms in cooperative communications scenario with emphasis on AF relaying protocol. In a second phase, will investigate and evaluate specific algorithms to deal with the issue of estimating non point-to-point channels, present in the envisioned scenarios.
•Design and optimization of medium access control protocols for centralized and decentralized systems with joint scheduling, relay node selection and dynamic link adaptation.
•Study and design of systems with imperfect network station information and evaluation of signalling resources for setting up cooperative relaying schemes.
•Development of a system level simulation tool for analysis of a hybrid cellular network incorporating cooperative diversity.
•Usage of the simulation tool to validate the algorithms developed and demonstrate at a system level the potential of cooperative diversity.
Reference: PTDC/EEA-TEL/099241/2008
Funding: FCT/PTDC
Start Date: 01-01-2010
End Date: 01-12-2012
Team: Adão Paulo Soares da Silva, Atilio Manuel da Silva Gameiro, Carlos Miguel Nogueira Gaspar Ribeiro
Groups: Mobile Networks – Av
Local Coordinator: Adão Paulo Soares da Silva

Associated Publications
  • 2Boock Chapters
  • A. Silva, R. Holakouei Holakouei, A. Gameiro, Multi-Cell Cooperation for Future Wireless Systems, Chapter in, Recent Advances in Wireless Communications and Networks, Jia-Chin Lin, In-Tech, 2011
  • D. Neves, C. Ribeiro, A. Silva, A. Gameiro, Channel and Parameters Acquisition in Cooperative OFDM Schemes, Chapter in, Chapter in Wireless Technologies, I-Tech Education and Publishing, In-Tech, 2011