Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học Journal of Biology đề tài: Research Article Spectrally Efficient OFDMA Lattice Structure via Toroidal Waveforms on the Time-Frequency Plane | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2010 Article ID 684097 8 pages doi 2010 684097 Research Article Spectrally Efficient OFDMA Lattice Structure via Toroidal Waveforms on the Time-Frequency Plane Sultan Aldirmaz Ahmet Serbes and Lutfiye Durak-Ata EURASIP Member Department of Electronics and Communications Engineering Yildiz Technical University Yildiz Besiktas 34349 Istanbul Turkey Correspondence should be addressed to Sultan Aldirmaz sultanaldirmaz@ Received 2 January 2010 Accepted 29 June 2010 Academic Editor L. F. Chaparro Copyright 2010 Sultan Aldirmaz et al. 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. We investigate the performance of frequency division multiplexed FDM signals where multiple orthogonal Hermite-Gaussian carriers are used to increase the bandwidth efficiency. Multiple Hermite-Gaussian functions are modulated by a data set as a multicarrier modulation scheme in a single time-frequency region constituting toroidal waveform in a rectangular OFDMA system. The proposed work outperforms in the sense of bandwidth efficiency compared to the transmission scheme where only single Gaussian pulses are used as the transmission base. We investigate theoretical and simulation results of the proposed methods. 1. Introduction As the demand for mobility and high performance in multimedia services increase efficient spectrum usage becomes a critical issue in wireless communications. Orthogonal frequency division multiplexing OFDM is a multicarrier modulation that has been employed by a number of current and future wireless standards including a g ad long term evolution LTE downlink and next generation networks. OFDM has been a popular method because of its robustness in frequency selective fading characteristics of .
