Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học Journal of Biology đề tài: Research Article How Much Feedback Is Required for TDD Multi-Antenna Broadcast Channels with User Selection? Umer Salim and Dirk Slock | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2010 Article ID 278952 14 pages doi 2010 278952 Research Article How Much Feedback Is Required for TDD Multi-Antenna Broadcast Channels with User Selection Umer Salim and Dirk Slock Mobile Communications Department EURECOM BP 193 F-06904 Sophia Antipolis Cedex France Correspondence should be addressed to Umer Salim Received 7 October 2009 Revised 4 February 2010 Accepted 5 May 2010 Academic Editor Ana Perez-Neira Copyright 2010 U. Salim and D. Slock. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited. The enormous gains in a multi-antenna transmitter broadcast channel require the Channel State Information at the Transmitter CSIT . Although the fundamental question How much feedback is required for a broadcast channel has been treated in the literature to some extent a more comprehensive treatment is certainly desirable. We study the time-division duplex broadcast channel with initial assumption of channel state information CSI neither at the base station BS nor at the users side. We provide two transmission strategies through which the BS and the users get necessary CSI. We derive novel lower and upper bounds for the sum rate reflecting the rate loss compared to a perfect CSIT system. Corresponding approximate sum rate expressions are also developed for both schemes. These expressions fully capture the benefits of the CSIT feedback allowing multi-user diversity gain and better inter-user interference cancellation and the cost of exchange of information required. These expressions can be optimized for any set of system parameters to unveil the trade-off between the cost and the gains associated to feedback. Thus they allow to characterize the optimal amount of feedback which maximizes the sum .
