Space-time receivers for wireless communication systemsoffer the possibility to have both TIX-and RX-antennas.For a realistic simulation of such systems, a multiple input multiple output (MIMO) spatial channel model is required which reasonably characterizes the space-and time-variant effects of the mobile radio channel. This paper describes a space-time vector channel model with realistic fading simulation for different scenarios. Mutual correlation between the fading coefficients is considered. This allows an estimation of the diversity gain, that can be achieved with spacetime receivers in direrent scenarios.tors in the far-field. For each dominant reflector one significant multipath is assumed. This path consists of a large number of incoming waves which result from the structure of local scatterers in vinicity of the transmitter and receiver. Since the relative delays of these waves are small, they cannot be resolved by the receiver. In case of any movement in the scenario the superposition of the waves results in a space-time fading process. Independent fading is assumed for each significant multipath p with a specific time delay TP.After the introduction a MIMO-signal model in Section 2 including a discrete time matrix formulation, the MIMOchannel characteristics and their modeling are described in Section 3 in more detail. In Section 4 the results of the space-time fading models are compared with theoretical assumptions.

Multiuser dynamic orthogonal frequency division multiple access (OFDMA) can achieve high downlink capacities in future wireless networks by optimizing the subcarrier allocation for each user.When it comes to the integration into current wireless local area network (WLAN) standards, dynamic OFDMA raises several implementation issueswhich are neglected in theoretical papers. Putting this emerging approach into practice requires to treat these issues accordingly and to demonstrate the feasibility of the system design. In this paper, we propose a dynamic OFDMA integration for the physical layer of the widespread IEEE 802.11a standard. To test our implementation and demonstrate its practical relevance we use a pragmatic approach: We prototype multiuser dynamic OFDMA on a real-time software-defined radio testbed for WLANs. We discuss details of our implementation and provide measurements showing that it does not introduce significant overhead into the IEEE 802.11a system at high subcarrier allocation quality. We particularly focus on the problems of our integration as well as the concepts and limitations of the used testbed.

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