tailieunhanh - Báo cáo hóa học: "Research Article Achieving Maximum Possible Speed on Constrained Block Transmission Systems"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Achieving Maximum Possible Speed on Constrained Block Transmission Systems | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2007 Article ID 35689 11 pages doi 2007 35689 Research Article Achieving Maximum Possible Speed on Constrained Block Transmission Systems Obianuju Ndili and Tokunbo Ogunfunmi Department of Electrical Engineering Santa Clara University Santa Clara CA 95053 USA Received 20 May 2005 Revised 7 April 2006 Accepted 30 April 2006 Recommended by Vincent Poor We develop a theoretical framework for achieving the maximum possible speed on constrained digital channels with a finite alphabet. A common inaccuracy that is made when computing the capacity of digital channels is to assume that the inputs and outputs of the channel are analog Gaussian random variables and then based upon that assumption invoke the Shannon capacity bound for an additive white Gaussian noise AWGN channel. In a channel utilizing a finite set of inputs and outputs clearly the inputs are not Gaussian distributed and Shannon bound is not exact. We study the capacity of a block transmission AWGN channel with quantized inputs and outputs given the simultaneous constraints that the channel is frequency selective there exists an average power constraint P at the transmitter and the inputs of the channel are quantized. The channel is assumed known at the transmitter. We obtain the capacity of the channel numerically using a constrained Blahut-Arimoto algorithm which incorporates an average power constraint P at the transmitter. Our simulations show that under certain conditions the capacity approaches very closely the Shannon bound. We also show the maximizing input distributions. The theoretical framework developed in this paper is applied to a practical example the downlink channel of a dial-up PCM modem connection where the inputs to the channel are quantized and the outputs are real. We test how accurate is the bound kbps for this channel. Our results show that this bound can be improved upon. Copyright 2007