Using Unclaimed Sub-Carriers in Opportunistic OFDMA Systems

• Published in: IEEE Vehicular Technology Conference pp. 1 - 5
• Main Authors: Svedman, P., Cimini, L.J., Ottersten, B.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.09.2006
• Subjects: Delay; Downlink; Feedback; Feeds; Frequency conversion; OFDM; Power engineering and energy; Power engineering computing; System performance; Throughput
• ISBN: 9781424400621; 1424400627
• ISSN: 1090-3038
• DOI: 10.1109/VTCF.2006.371

In this paper, we consider the unclaimed sub-carriers that no user feeds back in an opportunistic OFDMA system with a per sub-carrier power constraint. Unclaimed sub- carriers appear in OFDMA systems with reduced feedback, where the users concentrate the feedback on the sub-carriers with good channel quality. Here we propose and evaluate two ways to use these sub-carriers to improve the system performance. One approach is to transmit pilots symbols on the unclaimed sub- carriers. A second approach is to schedule users based on their feedback about adjacent sub-carriers. Simulation results show that for low to moderate channel RMS delay spread, it is more advantageous to transmit data on unclaimed sub-carriers, even at a low rate, than to use them for additional pilot symbols. For high delay spreads however, transmitting pilots on the unclaimed sub-carriers gives higher system throughput.