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 Research Article Dynamic Subcarrier Allocation for Real-Time Trafﬁc over Multiuser OFDM Systems | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2009 Article ID 298451 9 pages doi 2009 298451 Research Article Dynamic Subcarrier Allocation for Real-Time Traffic over Multiuser OFDM Systems Fanglei Sun 1 Mingli You 1 and Victor O. K. Li2 1 Research and Innovation Center Alcatel-Lucent Shanghai Bell Co. Ltd Shanghai 201206 China 2 Department of Electrical and Electronic Engineering The University of Hong Kong Hong Kong Correspondence should be addressed to Fanglei Sun Received 24 January 2009 Accepted 14 April 2009 Recommended by Dmitri Moltchanov A dynamic resource allocation algorithm to satisfy the packet delay requirements for real-time services while maximizing the system capacity in multiuser orthogonal frequency division multiplexing OFDM systems is introduced. Our proposed crosslayer algorithm called Dynamic Subcarrier Allocation algorithm for Real-time Traffic DSA-RT consists of two interactive components. In the medium access control MAC layer the users expected transmission rates in terms of the number of subcarriers per symbol and their corresponding transmission priorities are evaluated. With the above MAC-layer information and the detected subcarriers channel gains in the physical PHY layer a modified Kuhn-Munkres algorithm is developed to minimize the system power for a certain subcarrier allocation then a PHY-layer resource allocation scheme is proposed to optimally allocate the subcarriers under the system signal-to-noise ratio SNR and power constraints. In a system where the number of mobile users changes dynamically our developed MAC-layer access control and removal schemes can guarantee the quality of service QoS of the existing users in the system and fully utilize the bandwidth resource. The numerical results show that DSA-RT significantly improves the system performance in terms of the bandwidth efficiency and delay performance for real-time services.