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Advanced Trends in Wireless Communications Part 6

Tham khảo tài liệu 'advanced trends in wireless communications part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Block Transmission Systems in Wireless Communications 165 corresponding to a single group of m signal elements will normally be a sequence of n g non-zero sample values. The sequence of these n g values in the absence of noise is n v L biV-i ị 1 i 1 2 . n g 13 Taking a practical example to clarify the convolution here if m 2 and g 1 so n 3 and n g 4 . The output of the channel will be the 1X 4 vector V whose elements are V lb.y b2y-1 b3y-2 by b2.y o b3y-1 by b2 1 b3y0 b2 2 b3y1 14 Applying the limitations on the channel impulse response V may be written as V by b20 b30 by b2yo b30 b10 b2y1 b3yo b10 b20 b3y1 15 So this result is multiplication of B by a 3 X 4 matrix C that depends on 0 0 In vector form it may be written as yo 0 yo 0 yo V BC 16 17 where V is the 1 X n g received signal and C is the n x n g channel with ith row is g 1 n-i Ci 0 . 0 y0 y1 . ys 0 . 0 18 Assume now that successive groups of signal-elements are transmitted and one of these groups is that just considered. The first transmitted impulse of the group occurs at time T seconds. Fig. 5 shows the n g received samples which are the components of V. C 0 ISI from previous group g No ISI from other groups m ISI from next group g Fig. 5. Sequence of n g samples for one received block Due to the Inter Block Interference IBI the first elements of the block g components of V are affected in part on the preceding received group of m signal-elements. Also the last g components of V are dependent in part on the following received group of m elements. Thus 166 Advanced Trends in Wireless Communications there is Intersymbol Interference ISI from adjacent received groups of elements in both the first and the last g components of V. However the central m components of V depend only on the corresponding transmitted group of m elements and can therefore be used for the detection of these elements without ISI from adjacent groups. Returning back to the same example of m 2 and g 1 the central m components of V are .