Using Unclaimed Sub-Carriers in Opportunistic OFDMA Systems

Abstract— In this paper, we consider the unclaimed subcarriers that no user feeds back in an opportunistic OFDMA system with a per sub-carrier power constraint. Unclaimed subcarriers 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 subcarriers. 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.

• Type: Conference
• Year: 2006
• Where: VTC
• Authors: Patrick Svedman, Leonard J. Cimini Jr., Björn E. Ottersten
• Keywords: Delay Spreads, Unclaimed Sub-carriers, Unclaimed Subcarriers, VTC 2006