tailieunhanh - Vehicular Technologies Increasing Connectivity Part 4

Tham khảo tài liệu 'vehicular technologies increasing connectivity part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | From Linear Equalization to Lattice-Reduction-Aided Sphere-Detector as an Answer to the MIMO Detection Problematic in Spatial Multiplexing Systems 81 Fig. 10. Uncoded BER as a function of Eb No Complex Rayleigh 4 X 4 MIMO channel FSD algorithms with p 1 and ML detectors QPSK modulations at each layer. definition is extended and is considered as the solution that would be directly reached without neighborhood study. Another useful notation that has to be introduced is the sphere search around the center search Xc namely the signal in any equation of the form IIXc x 112 d where x is any possible hypothesis of the transmitted vector x which is consistent with the equation of an nj 1 sphere. Classically the SD formula is centred at the unconstrained ZF solution and the corresponding detector is denoted in the sequel as the naive SD. Consequently a fundamental optimization may be considered by introducing an efficient search center that results in an already close-to-optimal Babai point. In other words to obtain a solution that is already close to the ML solution. This way it is clear that the neighborhood study size can be decreased without affecting the outcome of the search process. In the case of the QRD-M algorithm since the neighborhood size is fixed it will induce a performance improvement for a given M or a reduction of M for a given target BER. The classical SD expression may be re-arranged leading to an exact formula that has been firstly proposed by Wong et al. aiming at optimizations for a VLSI implementation through an efficient Partial Euclidean distance PED expression and early pruned nodes . Wong . Tsui . Cheng and . Mow 2002 XZF DFD argmin Rezf 2 18 xeQnCT where ezF XZF x and Xzf HHH 1Hhr. Equation 18 clearly exhibits the point that the naive SD is unconstrained ZF-centred and implicitly corresponds to a ZF-QRD procedure with a neighborhood study at each layer. The main idea proposed by . Hochwald and S. ten Brink 2003 L. Wang L. Xu .