Reduction of Feedback Overload by Exploiting Adaptive Channel in OFDMA Systems by Using Fixed Packet Size and Difference of Transmission Rate in Adaptive Modulation

Satoru IIJIMA  Takamasa HASEGAWA  Rui ZHOU  Iwao SASASE  

B - Abstracts of IEICE TRANSACTIONS on Communications (Japanese Edition)   Vol.J91-B   No.7   pp.746-755
Publication Date: 2008/07/01
Online ISSN: 1881-0209
Print ISSN: 1344-4697
Type of Manuscript: PAPER
OFDMA,  CQI,  adaptive modulation,  Doppler frequency,  

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In channel adaptive OFDMA systems, it is important to feed back channel information in a fast, accurate and efficient way to improve the system performance, such as throughput and bit error rate (BER). However, a base station requires a large amount of feedback information of channel qualtiy indicator (CQI). In order to reduce the overload of CQI feedback, we propose a feedback scheme which only selects the users scheduled in the next time slot to feedback the channel information according to user mobility. We use adaptive modulation to apply bit rate adaptation depending on user channel condition, where the scheduling time is fixed. By fixing the packet size, scheduling time and feedback period can be variable according to user transmission rate as different time slots. We demonstrate by computer simulation that the proposed scheme can reduce the overload of user feedback with the minimum suppression of the throughput degradation.