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Energy Saving for Cognitive Multicast OFDM Systems: A TimeFrequency TwoDimensional Method
Wenjun XU Shengyu LI Zhihui LIU Jiaru LIN
Publication
IEICE TRANSACTIONS on Communications
Vol.E98B
No.6
pp.974983 Publication Date: 2015/06/01 Online ISSN: 17451345
DOI: 10.1587/transcom.E98.B.974 Type of Manuscript: PAPER Category: Energy in Electronics Communications Keyword: energy saving, cognitive radio, timefrequency, multicast, OFDM,
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Summary:
This paper studies the energysaving problem in cognitive multicast orthogonal frequencydivision multiplexing (OFDM) systems, for which a timefrequency twodimensional model is established to enable the system energy conservation through joint temporal and spectral adaptations. The formulated twodimensional problem, minimizing the total power consumption whilst guaranteeing the minimalrate requirement for each multicast session and constraining the maximal perceived interference in each timeslot for the active primary user, is categorized as mixed integer nonconvex programming, whose optimal solution is intractable in general. However, based on the timesharing property, an asymptotically optimal algorithm is proposed by jointly iterating spectrum element (SE) assignment and power allocation. Moreover, a suboptimal algorithm, which carries out SE assignment and power allocation sequentially, is presented as well to reduce the computation complexity. Simulation results show the proposed joint algorithm can achieve the nearoptimal solution, and the proposed sequential algorithm approximates to the joint one very well with a gap of less than 3%. Compared with the existing slotbyslot energysaving algorithms, the total power consumption is considerably decreased due to the combined exploitation of time and frequency dimensions.

