Advanced OFDM Techniques for Emerging Wireless Communication Networks

Prof. Luc Vandendorpe
Digital Communications Group, Communications and Remote Sensing Laboratory, Université Catholique de Louvain

12 hours, 4 credits

September 9 - September 10, 2010

Dipartimento di Ingegneria dell'Informazione: Elettronica, Informatica, Telecomunicazioni, via Caruso, meeting room, ground floor

Contacts: Prof. Filippo Giannetti

Abstract

In order to answer the expectations for higher bit rates, wireless communications systems use wider bandwidths which tend to make the channel more and more frequency selective. A nice technique which emerged to counteract or exploit this frequency selectivity is Orthogonal Frequency Division Multiplexing (OFDM). OFDM is currently the basic modulation format in recent standards and their evolutions, like WIMAX or 3GPP LTE.

The goal of this series of lessons is to review the basics of OFDM and discuss the degrees of freedom it offers in terms of rate or diversity, and compare OFDM with single carrier (SC) transmission. For point to point communications, it will also be discussed how OFDM together with coding in the frequency domain can benefit from the turbo principle for the design of the detector and the channel estimator. This will be extended to MIMO OFDM. Recently there is also an increased interest for relaying techniques (distributed MIMO). The optimization of OFDM transmission enhanced by one or several relays will be discussed.

OFDM not only can be used as a modulation technique but it can also be used as an access technique, leading to OFD multiplexing in the downlink and OFD multiple access (OFDMA) in the uplink. After the description of the concept, it will be shown how the frequencies and the power can be optimally allocated among users, for scenarios without and with relaying.

Finally, a multicell scenario with high frequency reuse will be considered. Two approaches to mitigate co-channel interference will be discussed: resource (power and frequency) allocation and interference precancellation.

Syllabus

Introduction - basics of OFDM (Analog OFDM and discrete time version)

Diversity and rate (including waterfilling): comparison single carrier/multicarrier
MIMO OFDM: the SF-BICM-OFDM and turbo detection/estimation (MAP and MMSE)
P2P OFDM with relaying: various protocols and 2 or more DF relays: rate optimization
OFDM MAC (2 users) with relay
OFDMA: downlink and uplink optimized for sum rate
Multicell scenarii:
cochannel interference minimization by means of resource allocation
co-channel interference estimation and precancellation