A proper design and analysis of future wideband wireless communication systems require an accurate radio channel model. This model is claimed to characterize both the spatial and temporal channel characteristics. This paper investigates the spatio-temporal channel modeling based on a ray-tracing approach. The temporal channels are characterized by a delay profile. The statistical median and fading-fluctuation range of delay profiles are predicted from ray tracing by incorporating the random phase approach. A high level of agreement between predicted results and measured ones is observed in the verification. The spatio-temporal channel impulse response (CIR) predicted from ray tracing is also transformed to have limited band-width and limited beam-width characteristics. The applicability of this transformation is also verified by the comparison with measurement. These verifications prepare the ground for the use of ray-tracing approaches to evaluate system performance in real environments.

The paper describes a low complexity tree-structure based user scheduling algorithm in an up-link transmission of MLD-based multi-user multiple-input multiple-output (MIMO) wireless systems. An M-branch selection algorithm, which selects M most-possible best branches at each step, is proposed to maximize the whole system sum-rate capacity. To achieve the maximum capacity in multi-user MIMO systems, antennas configuration and user selection are preformed simultaneously. Then according to the selected number of antennas for each user, different transmission schemes are also adopted. Both the theoretical analysis and simulation results show that the proposed algorithms obtain near optimal performance with far low complexity than the full search procedure.