Comparison between MIMO techniques in UMTS-HSDPA system

An analytical model for the evaluation of UMTS-HSDPA capacity is proposed and used to carry out a comparison between several MIMO systems. HSDPA is an evolution of the UMTS standard over-the-air interface to achieve higher aggregate bit rates through the introduction of advanced radio technologies including MIMO (space time coding and BLAST) techniques. An algorithm to select the number of HS-DSCH codes and the modulation and coding scheme in this framework is proposed. The model is used to compare MIMO systems, a typically difficult task, and provide insight on expected performance and capacity. Results, supported by simulation, indicate that the use of adaptive MIMO increases system capacity, especially when the loss of orthogonality of CDMA codes is low (for example when a multiuser detector is used). The adaptive space time coding seems to perform better when the code´s orthogonality loss is high. The adaptive BLAST, on the contrary, achieves better performance with the decrease of orthogonality loss.