Contents 1 Introduction
At IEMN (Institut d'Electronique et de Microelectronique du Nord), one of the main projects in the field of telecommunication is about diffusing mobile objects (mobile phone, PAD, …): the purpose is to propose a complete indoor communication system at 60GHz where each object must be able to send information to another whatever its type. At this frequency, the signal is strongly attenuated: the attenuation coefficient peak value is around 15dB / km at 60GHz. This property is a real advantage for indoor propagation: it provides an important interference reduction and it leads to a low electro-magnetical pollution. However, in the case of mobile indoor communications, multi-path propagation causes severe transmission quality degra-dations. To reach really high data rate over fading channels, multicarrier modulation like OFDM is often required. However fading confront us with the problem of lost packets and the need for frequent retransmissions. To reduce bit error rate, many strategies have been proposed. We propose to compare two approaches of adaptive modulation. These bit loading algorithms propose to adapt the number of bits associated to each subcarrier according to the channel frequency response. The difference between these algorithms concerns some additive constraints: in the first algorithm a given symbol error rate is required whereas in the second one a data rate is required. Adaptive modulation improv-ment has been verified on simulated Rayleigh channels and tests have been realised on real data too.
