Comparative study of efficient decision-feedback equalization schemes for MIMO systems

Decision-feedback (DF) equalization schemes, wellknown from multi-user detection, offer the opportunity of an additional performance gain compared to their corresponding linear equalizers by feeding back past decisions on already detected symbols, based on a fixed symbol detection order. For MIMO systems, an optimum symbol stream detection order has been found within the V-BLAST algorithm, which is determined adaptively during the detection process. The main focus of this paper is, to show the analogy of these two approaches, where the V-BLAST algorithm applied to frequency-selective channels just denotes an extension of the conventional DF system towards the optimum symbol stream detection order, but resulting in additional matrix inversions. Monte-Carlo simulations have shown, that using DF with a less demanding detection order approximately achieves the performance of a DF system with the optimum detection order. Finally, an extended DF receiver structure is presented, comprising as many DF blocks as concurrently transmitted symbol streams are to be detected. In order to obtain reasonable computational complexity, equalization is performed in the frequency domain for all presented detection schemes. 1