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 OFDMA-Based Medium Access Control for Next-Generation WLANs | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2009 Article ID512865 9 pages doi 2009 512865 Research Article OFDMA-Based Medium Access Control for Next-Generation WLANs H. M. Alnuweiri 1 Y. Pourmohammadi Fallah 2 P. Nasiopoulos EURASIP Member 3 and S. Khan3 1 Department of Electrical and Computer Engineering Texas A M University at Qatar P. O. Box 23874 Doha Qatar 2 Institute of Transportation Systems EECS CEE University of California Berkeley 604 Davis Hall Berkeley CA 94720-1710 USA 3 Department of Electrical and Computer Engineering The University of British Columbia 5500-2332 Main Mall Vancouver BC Canada V6T1Z4 Correspondence should be addressed to H. M. Alnuweiri Received 4 August 2008 Revised 6 December 2008 Accepted 18 January 2009 Recommended by Yan Zhang Existing medium access control MAC schemes for wireless local area networks WLANs have been shown to lack scalability in crowded networks and can suffer from widely varying delays rendering them unsuited to delay sensitive applications such as voice and video communications. These deficiencies are mainly due to the use of random multiple access techniques in the MAC layer. The design of these techniques is highly linked to the choice of the underlying physical PHY layer technology. The advent of new PHY schemes that are based on orthogonal frequency division multiple access OFDMA provides new opportunities for devising more efficient MAC protocols. We propose a new adaptive MAC design based on OFDMA technology. The design uses OFDMA to reduce collision during transmission request phases and makes channel access more predictable. To improve throughput we combine the OFDMA access with a carrier sense multiple access CSMA scheme. Data transmission opportunities are assigned through an access point that can schedule traffic streams in both time and frequency subchannels domains. We demonstrate the effectiveness of the .
