This paper gives an overview of channel characterization and modelling for two new wireless technologies: MIMO (multiple input multiple output) and UWB (ultra wide-band). MIMO exploits both the spatial and the temporal domain of the channel, while UWB systems exploit an extremely large frequency band. Both technologies promise high data rates, precise localization and a more efficient use of the available spectrum then today's systems. As the propagation channel is the principal contributor to many of the problems and limitations that beset mobile communications, successful design and implementation of MIMO and UWB require accurate channel models. Characteristic channel properties like path-loss, delay spread, angular spread, and distribution functions of the fast fading are discussed. Channel models should reproduce the stochastic properties of these parameters. The focus of this paper is to give a review on existing MIMO as well as UWB channel models and to specify their strengths and limitations.

This paper presents recent developments in ionospheric propagation research considering two specific issues: (1) the increase of the bit rate in HF ionospheric communication, using a SIMO technic and (2) the effect of equatorial ionospheric scintillations using the GNSS. For the first issue it is shown that a SIMO HF receiving system comprising several antennas (i.e. 4 antennas), greatly improve the bit error rate in digital transmissions. Examples of images transmitted via the ionospheric channel are presented for different error conditions. For the second issue the difficulty of performing radiolocation in the equatorial region is discussed. The physical mechanisms at the origin of the development of equatorial irregularities are presented and recent measurements of Total Electron Content (TEC) and scintillations parameters (S4 and ċĦ), performed in Vietnam, show the loss of lock of phase loop of the GPS receiver during strong scintillation events.