In this paper, we present a novel space-time signal subspace-based subband approach to space-time adaptive processing (STAP) that has been shown to be an effective method to suppress both the intersymbol interference (ISI) and the cochannel interference (CCI) in mobile communications. We first study the performance of STAP and make clear the conditions of perfect processing (i.e., perfect equalization of the desired user signal and perfect suppression of CCI signals). Based on the polyphase representation and the subspace analysis of the signal channels, we propose a space-time signal subspace-based subband approach to STAP, namely, the subband STAP, which highly improves the convergence rate without loss of the steady-state performance. Simulation results show its effectiveness under the procedure of signal subspace estimation and detection.

Subband arrays have been proposed as useful means to realize joint spatio-temporal domain equalization in digital mobile communications. They are used to mitigate channel impairment problems caused by the inter-symbol interference (ISI) and co-channel interference (CCI). In this paper, we propose the normalized subband array and locally orthogonalizing subband array techniques for channel equalization. The least square mean (LMS) algorithm is used for adaptation. The convergenceperformanceoftheproposedtechniques is analyzed and compared with that of conventional space-time adaptive processing (STAP) techniques. It is shown that subband decompositions provide great flexibility in implementing spatio-temporal equalizations. Both analytical and numerical simulation results demonstrate that the proposed subband array techniques substantially improve the convergence performance without significant additional computations. 1.

It is known that the output performance of a conventional adaptive antenna system is greatly influenced by its antenna array configuration. Such a conclusion holds true to space-time adaptive processing (STAP) systems of mobile communications, where receiving signals consist of the superimposed multipath rays with delay spread and angle spread. It is considered that the associated system performance measures, e.g., the minimum mean square error (MMSE) of STAP systems, could not be used to the design of the employed antenna array configuration due to involving a few nuisance parameters that make the design much more complicated or impossible. In this paper, we first derive an upper bound of the residual error power of STAP systems under the minimum mean square error (MMSE) criterion. Then, we establish a relationship between the bound and the space-time channel auto- and cross-correlation functions. According to the relationship, a criterion function that jointly maximizes the main beam and minimizes the sidelobe of the generalized space-time channel correlation waveform is obtained for the design of the array configuration under a given statistical signal environment. Numerical simulation results show the effectiveness of the proposed design method.

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